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Main Contemporary Oral Medicine: A Comprehensive Approach to Clinical Practice
Contemporary Oral Medicine: A Comprehensive Approach to Clinical PracticeCamile S. Farah, Ramesh Balasubramaniam, Michael J. McCullough
This book, written by world authorities in the field, is a comprehensive, up-to-date guide to the specialty of Oral Medicine, which is concerned with the diagnosis, prevention, and predominantly non-surgical management of medically related disorders and conditions affecting the oral and maxillofacial region. The pathophysiology, clinical presentation, diagnostic evaluation, and treatment of all relevant diseases and disorders are described with the aid of a wealth of clinical cases and illustrations that enable the reader to appreciate the diversity and potential complexity of Oral Medicine. In addition to the wide-ranging coverage of oral conditions, separate sections are devoted to bone and cutaneous pathology and to orofacial pain and its management, in addition to dental sleep medicine. The clinician who treats Oral Medicine patients will find this book to be an excellent aid to optimal management grounded in a sound knowledge of basic science and the dental and medical aspects of each disorder. In addition, it will serve as an outstanding textbook for undergraduate and postgraduate students.
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© Springer Nature Switzerland AG 2019 Camile S. Farah, Ramesh Balasubramaniam and Michael J. McCullough (eds.)Contemporary Oral Medicinehttps://doi.org/10.1007/978-3-319-72303-7_31 Internal Derangements of the Temporomandibular Joint James J. R. Huddleston Slater1 and Reny de Leeuw2 (1)Groningen, The Netherlands (2)Division of Orofacial Pain, College of Dentistry, University of Kentucky, Lexington, KY, USA James J. R. Huddleston Slater Email: firstname.lastname@example.com Reny de Leeuw (Corresponding author) Email: email@example.com Abstract An internal derangement of the temporomandibular joint (TMJ) is anatomically described as a deviation in position or in form of the tissues within the capsule of the joint that interferes with smooth joint movement. Although often regarded as such, an internal derangement is not a diagnostic entity, but it is merely a description of symptoms and signs of a number of clinical problems that involve the joint. Among these clinical problems are disc condyle complex disorders, hypomobility disorders, adherences, hypermobility disorders, fractures, inflammatory disorders, crystal deposition diseases, hyperplasia, and hypoplasia. Clinical features include a snapping or tearing sensation during mouth opening, a sensation of significant instability in the TMJ, or a significant injuring force in the TMJ area. Some patients may have more serious complaints, such as the sudden inability to open the mouth, or the occasional locking of the joint on maximal mouth opening and some may experience significant pain or discomfort. Some patients with these conditions may not require treatment, while others may cause major disturbances for which pervasive interventions are necessary. Conservative treatment is advocated for the management of disc derangements, arthralgia, osteoarthritis, and adherences, although minimally invasive procedures such as lysis and lavage (arthrocentesis) can be considered for refractory cases. Keywords Temporomandibular jointTMJ mobility disordersTMJ inflammatory disordersTMJ fracturesTMJ internal derangementCrystal deposition disorders Introduction The temporomandibular articulation comprises two distinct temporomandibular joints (TMJ) connecting the base of the skull with the mandible. The TMJ is a complex joint both morphologically and functionally. The joint itself is made up of two incongruent parts: the mandibular condyle and the glenoid fossa of the temporal bone; referred to further here as condyle and fossa. The articular disc is formed of dense fibrous tissue and is positioned between the condyle and fossa. The disc divides the joint cavity in two compartments: an upper and a lower compartment (Fig. 1).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig1_HTML.jpg] Fig. 1The articular disc divides the joint cavity in two compartments; an upper and a lower compartment. E eminence, C condyle, D disc, L lower joint compartment, U upper joint compartment The central part of the disc is considerably thinner than the posterior and anterior parts. The disc compensates for the incongruence between the condyle and the eminence, as it fits like a cap over the condyle, thereby distributing compression forces over a broader articular surface (Fig. 2). The architecture of the TMJ enables it to make rotational and sliding movements. Most of the rotational movements occur in the lower compartment between the condyle and the disc, whereas most of the sliding movements occur in the upper compartment, between the disc and the fossa. The joint itself is encapsulated: a fibrous capsule is attached to the temporal bone along the limits of the fossa and the condyle. It consists of a loose arrangement of connective tissue that is reinforced laterally by the temporomandibular ligaments (Fig. 3).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig2_HTML.jpg] Fig. 2Histology of the TMJ. Blue dye represents cartilage, burgundy dye is bone. E eminence, C condyle, D disc, L lower joint compartment, U upper joint compartment. Staining: Heidenhain's AZAN trichrome stain [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig3_HTML.jpg] Fig. 3The encapsulated TMJ: a fibrous capsule is attached to the temporal bone along the limits of the fossa and the condyle. It consists of a loose arrangement of connective tissue that is reinforced laterally by the temporomandibular ligaments. C capsule, CP coronoid process, M mastoid, ZA zygomatic arch TMJ disorders are generally characterized by pain and impairment of joint function and joint sounds. Problems with TMJ functioning were recognized in the thirtieth century B.C. when the ancient Egyptians described a technique for the reduction of a mandibular dislocation. Later, in the fifth century B.C., Hippocrates also described such a technique (Schwartz 1966). During the following centuries, interest in TMJ problems remained, though mainly from an anatomical point of view. Clicking and locking of the TMJ were attributed to an anteriorly displaced articular disc by Annandale in 1887 (Annandale 1887). It was only a few decades ago that advances in imaging techniques, such as tomography, arthrography, computed tomography (CT), and later, magnetic resonance imaging (MRI), resulted in an improved visualization of the inner structures of the TMJ in living humans which resulted in better understanding of its functional disorders. Farrar (Farrar 1971) and McCarty (McCarty 1980) emphasized the role of disc interferences within this group of functional problems and used the term "internal derangements." "Internal derangement " is an orthopedic term, defined as "a localized mechanical fault interfering with smooth joint movement" (Adams and Hamblen 1990; Stegenga 1996). An internal derangement is anatomically described as a deviation in either the position or the form of the tissues within the capsule of the joint. Clinical features that are likely to indicate an internal derangement of the TMJ are a snapping or tearing sensation during movements of the mouth, a sensation of significant instability in the TMJ, or a significant injuring force in the TMJ area. These complaints may be accompanied by the inability to get the teeth into a full, comfortable, occlusion. Most patients, however, will only report clicking sounds that arise from the TMJ during mouth opening and/or closing. Some patients may have more serious complaints, such as the sudden inability to open the mouth, or the occasional locking of the joint on maximal mouth opening and may experience significant pain or discomfort. Although often regarded as such, an internal derangement is not a diagnostic entity. Rather, it is a description of symptoms and signs. In fact, internal derangements of the TMJ are symptoms of a number of clinical problems that involve the TMJ. Among these clinical problems are disc condyle complex disorders, hypomobility disorders, hypermobility disorders, fractures, inflammatory disorders, crystal deposition diseases, hyperplasia, and hypoplasia. Condyle disc complex disorders (Table 1) are characterized by a displacement of the disc in the closed jaw position that improves its structural relationship with the condyle during mouth opening, usually accompanied by a click (Fig. 4) (Farrar and McCarty 1982).Table 1Internal derangements Disc derangements Clicking in early mouth opening Clicking in later mouth opening Intermittent locking Permanent or so-called closed lock Hypomobility and adherences Temporary Permanent Adhesions Ankylosis Impedance of the coronoid process Hypermobility disorder s Subluxations Luxations Fractures of the condylar process Fractures of the mandibular caput (the head of the mandible) Fractures of the mandibular collum (the neck of the mandible) Inflammatory disorders Sterile (e.g., arthritis, traumatic arthritis, rheumatoid arthritis) Bacterial (e.g., infectious arthritis, abscess) Systemic disease (e.g., syphilis, tuberculosis, actinomyocosis) Crystal deposition diseases Gout (hyperuricemia, arthritides, sodium urate crystal deposition in and around joints, renal disease, and urolithiasis) Osteochondromatosis Condylar hyperplasia Condylar hypoplasia [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig4_HTML.jpg] Fig. 4In a condyle disc complex disorder, the disc usually is located anterior to the head of the condyle in the closed position (a) and improves its relationship with the condyle during mouth opening (b). C condyle, D articular disc, E eminence In joints with an internal derangement and hypomobility, often the capsule undergoes fibrosis resulting in the synovial surfaces being lined with fibrin. In extreme cases, often occurring after severe intra-articular trauma, this may lead to adherences/adhesions (Katsnelson et al. 2012; Al-Baghdadi et al. 2014). In hypermobile joints, there is an excessive range of motion of the condyle without overstretching of the structures (Garcia-Campayo et al. 2011). A fracture of the condylar structures may involve a fracture of the mandibular caput (head of mandible) and/or a fracture of the mandibular collum (neck of the mandible) (Afrooz et al. 2015). Inflammatory disorders involve inflammation or inflammatory symptoms of the intra-articular structures that can be sterile (e.g., arthritis, traumatic arteritis, rheumatoid arthritis) or bacterial (e.g., infectious arthritis, abscess) or more systemic disease (syphilis, tuberculosis, actinomyocosis) (Kalladka et al. 2014). Crystal deposition diseases are mostly found in knee joints, but a few reports describe crystal formation in the TMJ (Phelan et al. 2011). These disorders will be described in detail below. Epidemiology A number of, and surely not all, internal derangements of the TMJ have one particular feature: a snapping, clicking, popping, or tearing sound on joint movement (da Silva et al. 2016). Traditionally, epidemiological studies have mainly focused on the clinical symptoms of internal derangements, such as either the simple clicking sounds, or reciprocal clicking that occurs on opening and closing of the mouth. Little focus has been given on the underlying causes of the internal derangement that result in the clicking sounds, such as disc condyle complex disorders, hypermobility disorders, or deviation in form. As a result, many epidemiological studies describe the incidence and prevalence of clicking sounds and largely ignore the diagnostic entities of the clinical symptoms and signs (Keeling et al. 1994; Gazit et al. 1984; Locker and Slade 1988). Studies that have assessed disc condyle complex disorders and hypermobility disorders have usually used clinical evaluation of joint sounds (Gazit et al. 1984). However, other techniques have also been used to assess the prevalence of internal derangements. Among these techniques are questionnaires (Locker and Slade 1988), magnetic resonance imaging (MRI) (Nebbe and Major 2000), and autopsy studies (Kondoh et al. 1998). In general, clicking sounds are frequently seen, with the reported prevalence ranging from 17.5% to 74.7% (Haiter-Neto et al. 2002; Nebbe and Major 2000). The most commonly reported internal derangements are disc condyle complex disorders (Vogl et al. 2016). Disc displacement has been described as partial or complete, and the direction of the displacement may be anterior, anteromedial, medial, anterolateral, lateral, and posterior, though the latter position is rare (Huddleston Slater et al. 2005; Okochi et al. 2008). The reported prevalence, and evaluation method utilized, is outlined in Table 2.Table 2Reported prevalence of internal derangements Study Diagnosis Population Evaluation method Prevalence N Gazit et al. 1984 Joint sounds Children 10–18 years of age Clinical examination 35.8% 369 Locker and Slade 1988 Joint sounds 18 years and over Questionnaire 48.8% 1002 Keeling et al. 1994 Joint sounds Children 6–12 years of age Clinical examination 10.0% 3428 Kondoh et al. 1998 Disc displacements Cadavers Autopsy 57% 30 Nebbe and Major 2000 Disc displacements Nonconsecutive adolescent sample MRI 61.8% (male), 74.7% (female) 194 Haiter-Neto et al. 2002 Disc displacements Symptom-free healthy subjects (mean age of 26.9 years) MRI 17.5% 40 Not surprisingly, there is little research on the incidence of other types of internal derangements without clicking sounds, such as hypomobility disorders, adhesions, fractures, inflammatory disorders, and crystal deposition diseases, simply because the lack of clinical symptoms did not warrant any investigation on the incidence. Etiology Disc Derangements Over the years, a variety of possible etiological factors have been proposed to explain the occurrence of disc derangements. Previously, it was thought that the superior head of the lateral pterygoid muscle pulled the disc anteriorly during mouth opening. In that perspective, disc displacement was regarded as the result of a spasm of that muscle. Research could not corroborate these ideas, because in autopsy specimens only a limited number of cases were found where the fibers were shown to insert directly in the disc (Savalle 1988; Bittar et al. 1994). The main function of the muscle seems to be merely reflected by its continuous holding action, which is enabled by its low-stimulation threshold and fatigue resistant fibers (Eriksson and Thornell 1983). It has, however, been observed that the incidence of clicks develops with an increasing age, especially during childhood and adolescence (Egermark-Eriksson et al. 1981; Dibbets and van der Weele 1992; Thilander et al. 2002). Unfortunately, the interpretation of these studies is hampered by firstly a lack of classification, as only the clinical symptom of "clicking" has been studied, secondly relatively large age increments were used, and finally orthodontic samples have been studied (Egermark-Eriksson et al. 1981; Dibbets and van der Weele 1992). Orthodontic samples are not representative for the study of condylar development, because in this patient population disc displacement is seen more in class II patients (Gökalp 2016). Conversely, in joints from adolescents, rather prominent progressive remodeling changes have been shown to occur (Krisjane et al. 2012). It was suggested that the development of disc derangements is related to various anatomical relations between components of the TMJ (Pullinger et al. 2002). Thus, a disc derangement in this younger age group could be related to progressive remodeling associated with growth. This is in agreement with observations that the condyle undergoes considerable change in shape during the period of transition from birth to adulthood (Petrovic 1972). In these individuals with the symptom of a clicking joint, the anterior disc position could indeed be within the range of normal anatomic variation. In line with this suggestion and the finding that the closing click often occurs just before the condyle re-enters the fossa (Farrar and McCarty 1982; Huddleston Slater et al. 2002), an anterior disc displacement may be the result of a space insufficiency within the joint, so that the condyle and disc cannot be jointly accommodated in the fossa. As a result, the disc becomes anteriorly displaced. In support of this notion is the fact that individuals with skeletal class II profiles and hyperdivergent growth patterns have been shown to have an increased frequency of TMJ disc displacement and degenerative disorders (Manfredini et al. 2016). Clicking due to anterior disc displacement in early or later mouth opening is often termed as anterior disc displacement with reduction (Figs. 5 and 6). A permanent or so-called closed lock of the TMJ movement is often termed as a nonreducing disc displacement (Figs. 5 and 7). Retrospective studies support the general idea that a disc displacement is likely to progress to osteoarthritis (Rasmussen 1981; Wilkes 1989). It has been postulated that individuals with disc displacements show a temporal progression that commences with clicking in early mouth opening (i.e., disc displacement with early reduction), to clicking in later mouth opening (i.e., disc displacement with late reduction) to intermittent locking (i.e. disc displacement with occasional reduction), and finally ending in a permanent or so-called closed lock of the TMJ movement (i.e., disc displacement without reduction) (Rasmussen 1981; Wilkes 1989). Since a permanent or so-called closed lock is an acute sign suggestive of an early osteoarthritis, these observations supported the idea that a disc displacement eventually progresses to osteoarthritis.[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig5_HTML.png] Fig. 5Anterior displacement of the articular disc, relative to the head of the condyle. (a) Disc relationship with the condyle in the closed mouth position. (b) Anterior disc displacement with reduction: On mouth opening, the displaced disc acts as a localized mechanical fault that interferes with smooth joint movement. This is the cause of the clinically observed clicking sound with joint movements as the disc "clicks" onto the head of the condyle. (c) Disc displacement without reduction: On mouth opening, the displaced disc once again acts as a localized mechanical fault that interferes with smooth joint movement. However, the disc fails to "click" onto the head of the condyle with mouth opening. Mouth opening is limited resulting in a closed lock condition (Original drawing by Dr Hala Al Janaby, Perth WA, Australia) [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig6_HTML.jpg] Fig. 6Anterior disc displacement (a) with reduction (b) on opening. D disc, C condyle, GF glenoid fossa, AE articular eminence. Dotted white lines indicate extent of the disc. (Images courtesy of Clinical Associate Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig7_HTML.jpg] Fig. 7Anterior disc displacement (a) without reduction (b) on opening. D disc, C condyle, GF glenoid fossa, AE articular eminence. Dotted white lines indicate extent of the disc. (Images courtesy of Clinical Associate Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Apart from the fact that it has been shown that the position of the click on mouth opening is poorly correlated with the actual position of the condyle (Huddleston Slater et al. 2002), longitudinal epidemiological studies do not support the concept of temporal progression outlined above (de Leeuw et al. 1994, 1995a). In one study, 293 subjects with clicking were followed for a period of 10 years and found only one subject who reported intermittent locking during this time (Magnusson et al. 1993). Additionally, this lack of progression of internal derangement from a clicking (or better: a reducing disc to a non-reducing disc condition) was confirmed in several studies (Greene and Laskin 1988; Könönen et al. 1996). Given a disc displacement with reduction may persist for decades, this implies that a progressive course does not seem to be a general rule. By contrast, it has often been described that a disc displacement may persist for decades (de Leeuw et al. 1994), and can even subside for some time, to reappear again later (Könönen et al. 1996). Trauma to the TMJ or mandible has also been thought to be a cause for disc displacements. Most often an acceleration-deceleration or an indirect trauma is appointed as cause for pathology (McKay and Christensen 1998; Brown 1997). An acceleration-deceleration injury is an injury resulting from a collision between a body part and another object or body part while both are in motion (Mosby's Medical Dictionary 2013). An indirect injury is an injury that is not the result of a direct blow (Oxford Dictionary of Sports Science & Medicine 2006). Trauma is further subdivided into macrotrauma and microtrauma (Speck et al. 1979). Macrotrauma is the direct result of a major traumatic event to the TMJ or mandible, resulting in overextension of the joint. It can also result from (open) joint surgery. Other examples of macrotrauma can be extreme and prolonged mouth opening during a dental procedure (e.g., extraction, root canal treatment) or during intubation prior to general anesthesia. Microtrauma are small repetitive injuries to the joint that repeatedly cause a soft tissue response, such as plastic deformation of the ligaments. Diurnal clenching is thought to be an example of microtrauma (Speck et al. 1979). In adolescence, diurnal clenching may be a risk factor for intermittent locking in individuals with disc displacements (Kalaykova et al. 2011). Diurnal clenching is thought to result in viscoelastic deformation of the disc that, during normal circumstances, are temporary and have no further consequences. However, if the burden on the system is severely upregulated, the delicate balance between synthesis and breakdown (i.e., between anabolic and catabolic activity) within the articular tissues may become disturbed such that morphologic changes within the joint permit adaptation of the shape of the joint components, which in turn lead to locking of the joint (Fujimura et al. 2005). The natural course of anterior disc displacement without reduction has been studied in 44 subjects who agreed to observation without treatment (Sato et al. 1997). The incidence of successful resolution of the condition without treatment was 68% at 18 months (Sato et al. 1997). This finding suggests that the signs and symptoms of anterior disc displacement without reduction tend to be alleviated during the natural course of the condition. To summarize, clinical evidence does not support progressive worsening of the disc displacement in most patients. It is not exactly clear which patients have the greatest risk of progressing to more advanced stages. Consequently, clinicians who justify aggressive treatment of asymptomatic TMJ clicking based on their belief in a high progression rate to a nonreducing state should instead exercise patience and clinical vigilance in their management of this condition. At present, considerable evidence has been obtained that disc displacement cannot be regarded as the sole predominant primary etiologic factor for TMJ disorders (de Leeuw et al. 1994, 1995a; Magnusson et al. 1993; Westesson et al. 1989). Hypomobility and Adherences Adherences, due to a prolonged pressure of the joint structures (e.g., clenching the teeth), are usually temporary and can be eliminated by mobilization of the joint via external force to the joint structures to free its movements. However, if the adherence cannot be freed (e.g., permanent displaced disc), the immobilization may eventually become permanent (adhesion) (Lei et al. 2017). Damage to the synovial membrane may result in an inflammatory reaction that triggers the development of fibrotic connective tissue (Katsnelson et al. 2012). Further, fibrosis of the connective tissue that lines the synovial surfaces may result in adhesions (Al-Baghdadi et al. 2014). It is also known that open TMJ surgery is a risk factor for the development of hypomobility and adhesions (DeMerle et al. 2017; Rastogi et al. 2015). The relative risk, however, largely varies between studies and depends upon indication for the surgery and the surgeon (Cevidanes et al. 2010). Ankylosis is a fibrotic or bony connection between the articular surfaces that may lead to a persistent intra-articular hypomobility (DeMerle et al. 2017; Rastogi et al. 2015). Ankylosis usually occurs after intra-articular bleeding, for example after a severe trauma (Fig. 8). Ankylosis after a condylar fracture in juveniles may lead to growth disturbances of the lower face (retrognathia). Another form of hypomobility can be caused by impedance of the coronoid process (Fig. 9) (Mulder et al. 2012). During opening, the coronoid process passes antero-inferiorly between the zygomatic process and the posterior lateral surface of the maxilla. If the coronoid process is elongated, or if fibrosis has developed in this area, its movement may be inhibited and chronic hypomobility of the mandible can result (Kim et al. 2014; Tavassol et al. 2012; Zhong et al. 2009).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig8_HTML.jpg] Fig. 8Ankylosis of the left TMJ. Between the zygomatic arch and the condyle on the right side (nonankylotic side) a distinct dark line is visible. On the left side, the dark line is not visible, because the condyle is connected to the zygomatic arch or better said the fossa. Cone Beam CT image, coronal section. C condyle, ZA zygomatic arch [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig9_HTML.jpg] Fig. 9Coronal reconstruction (a) of the coronoid processes (arrows) from a multidetector CT scan with a 3-D reconstruction of the left TMJ and coronoid process (arrow) (b), illustrating bilateral coronoid hyperplasia. Hypomobility will result secondary to impingement between the laterally flared and elongated coronoid processes as they abut and impinge upon the zygomatic arches (za) limiting further mouth opening. (Images courtesy of Clinical Associate Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Hypermobility Disorders A common cause of (sub)luxation is iatrogenic and may occur during a lengthy surgical procedure or during the intubation process for the treatment of trauma or systemic diseases. Patients with certain anatomical features, such as those with a shallow or steep articular eminence or abnormal condylar shape, may also be more prone to luxations or subluxations (Liddell and Perez 2015). Luxations, or subluxations, can also occur spontaneously during yawning or singing in the absence of any pathologic condition. In a hypermobile joint, the ligaments are loose. The looseness of ligaments should be regarded as a variation of normal anatomy. As the condyle moves beyond the crest of the articular eminence, it appears to jump forward into a more-wide open position. The patient usually reports that the jaw "goes out" anytime he or she opens wide. Symptomatic TMJ hypermobility seems to be related with gender, as women tend to be more hypermobile than men (Seow et al. 1999; Larsson et al. 1993). TMJ hypermobility seems to be unrelated to either disc displacement or to intermittent closed locking (Kalaykova et al. 2011). Hypermobile joints are common and occur in about 10–25% of the population (Garcia-Campayo et al. 2011). It is usually not associated with any symptoms, but a minority develop other conditions caused by their unstable joints. The most common heritable connective tissue disorder is the Ehlers-Danlos syndrome (EDS). EDS is a clinically and genetically heterogeneous group of disorders, including an increasing number of variants which share the variable combination of dermal fragility, internal organ and vessel ruptures, and joint hypermobility (Table 3). Table 3Classification of Ehlers-Danlos syndrome (Castori 2012) Major forms Hypermobility/JHS • Vascular • Kyphoscoliotic • Arthrochalasia • Dermatosparaxis Rare/emerging forms • Cardiac-valvular • Periodontitis Fractures Since the introduction of various security measures in the last decades (helmets, air bags, cage constructions in car design), the number of facial fractures that arise from traffic accidents have steeply declined. By contrast, the number of fractures caused by violent crimes in relation to alcohol and illicit drugs has not declined, and in fact, for illicit drugs in particular this has increased (Afrooz et al. 2015). In addition, sports accidents are also causes of facial injuries (Afrooz et al. 2015; Yamamoto et al. 2015; Zhou et al. 2015; de Lucena et al. 2016; Farneze et al. 2016). Of all mandibular fractures, between 25% and 50% also involve fractures of the condylar process (Powers 2017; Kruger and Tennant 2016; Afrooz et al. 2015). Fractures of the condylar process can be subdivided into fractures of the mandibular caput (the head of the mandible) and fractures of the mandibular collum (the neck of the mandible). Fractures of the collum are most frequently seen and these fractures (Fig. 10) are caused by trauma to the corpus (body) of the mandible (Afrooz et al. 2015). Forces are distributed to the condylar process and damage occurs at the weakest point, which is the collum. This is generally beneficial because, if this does not occur, the mandibular caput could be displaced through the thin base of the skull. The potential for repair of these fractures without intervention is significant. The long-term implications of condylar and subcondylar fractures are generally good and seem not to have any increased likelihood for the development of arthritis or clicking (Hovinga et al. 1999; Zachariades et al. 2006; Laskin 2009; Lekven et al. 2011), unless undiagnosed and left untreated (Nagori et al. 2014).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig10_HTML.jpg] Fig. 10Condylar (left; black arrows), mandibular fracture (right; blue arrows) and coronoid process fracture (white arrow). C condyle, CP coronoid process (Image courtesy of Dr Larry Cunningham, University of Kentucky, Lexington, KY, USA) Inflammatory Disorders Most of the current understanding of articular cartilage maintenance and degradation is derived from large load-bearing synovial joints, in particular the knee joint. Both the knee joint and the TMJ are complex synovial joints with comparable mechanical features. Furthermore, the cartilage degenerative processes are believed to develop similarly. An important difference between these joints is the type of cartilage that forms the articular lining. In the knee joint, articular surfaces are covered with hyaline cartilage, whereas in the TMJ, this lining consists of fibrocartilage. Both the knee joints and TMJs share similar risk factors for osteoarthritis including age, gender, overloading, joint injuries, and genetics. The risk of osteoarthritis increases with age, probably because the quality of the tissues is reduced with aging. Epidemiologic studies indicate a female predisposition for osteoarthritis of the TMJ, and interestingly, women between the ages of 44–55 years are most likely to seek treatment, suggesting a role for estrogen in the disease process of the TMJ (Manfredini et al. 2010). The mandibular condylar cartilage differs from other articular cartilages as it undergoes endochrondral ossification. In long bones, estrogen is responsible for endochondral growth plate fusion in both males and females, and the role of estrogen receptors (ERs) has been characterized (Chen et al. 2014). For example, estrogen via ER alpha is responsible for growth plate fusion in both male and female mice. In contrast, ER beta is involved in growth inhibition in only young female mice (Nelson et al. 2013). The exact mechanism is yet to be elucidated. Also, repetitive microtraumatic overloading may damage the delicate structures beyond their healing capacity. Injuries, such as open joint surgery, may increase the risk of osteoarthritis (Fig. 11). There is little doubt that a genetic background is a significant determinant of an individual's susceptibility to disease. Osteoarthritis is covered in detail in another chapter of this book titled "Arthritic Conditions Affecting the Temporomandibular Joint" [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig11_HTML.jpg] Fig. 11Osteoarthritis of the TMJ. Sagittal (a) and coronal (b) view of right condyle with flattening, erosion, pseudocysts, and osteophyte (arrow). C condyle, EAC external auditory canal . Crystal Deposition Diseases Gout is the tra ditional term for a heterogenous group of diseases that among other structures may affect the TMJs. The diseases include hyperuricemia, arthritides, sodium urate crystal deposition in and around joints, renal disease, and urolithiasis. The crystallization of uric acid, often related to relatively high levels in the blood, is the underlying cause of gout. This can occur for a number of reasons, including diet, genetic predisposition, or underexcretion of urate, the salts of uric acid. Underexcretion of uric acid by the kidney is the primary cause of hyperuricemia in about 90% of cases. Calcium pyrophosphate deposition disease is characterized by the presence of crystal deposits in the affected joint. It is also called pseudogout (Fig. 12).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig12_HTML.jpg] Fig. 12Seventy-year-old female with chondrocalcinosis due to pseudogout (calcium pyrophosphate deposition) with advanced arthropathy: Axial (a), oblique sagittal (b), and coronal bone (c), and soft-tissue window (d) reconstructions from a multidetector CT scan; there is extensive chondrocalcinosis (white dotted arrows and oval in b). This calcification is situated both in the joint capsule as well as being intra-articular in location. A more discrete ossified body is present, posterior to the condyle (white arrow in b). All images show marked joint space narrowing, articular surface flattening, irregularity and peripheral osteophytosis consistent with osteoarthritis. The axial image (a) shows scalloped erosion of the articular surfaces corresponding to the foci of chondrocalcinosis (white dotted arrows) typical of pseudogout (Images courtesy of Clinical Associate Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Crystal deposition diseases are mostly found in knee joints, but a few reports describe crystal formation in the TMJ (Dijkgraaf et al. 1998). Osteochondromatosis (also known as synovial chondromatosis) is a rare disease that forms bony cartilaginous nodules by a cartilaginous metaplasia in the synovium or joint-lining tissue. The nodules move freely within the synovial fluid, which they require for nutrition and growth. Progressive enlargement and ossification occur with time. In severe cases, they may occupy the entire joint space or penetrate to adjacent tissues. Also, they can reestablish a blood supply and become replaced by bone. In most cases, the disease is unilocular and involves either the knee, the hip, or the elbow. Rarely does it involve the TMJ (Fig. 13) (Phelan et al. 2011). The etiology is unknown.[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig13_HTML.jpg] Fig. 13Synovial chondromatosis of the upper TMJ space. (a) CT – multiple faintly calcified bodies are present in the distended upper joint space (white dotted margin). (b) MRI – a fat saturation T2 sagittal sequence demonstrates marked distension of the upper joint space (white margin) by high signal synovial proliferation containing lower signal foci (white dotted arrows) representing chondroid or osseous bodies. (c) MRI – a post gadolinium T1 sagittal sequence demonstrates enhancement (hyperintense signal) of the synovial proliferation in the distended upper joint space (black dotted margin). The disc is shown as nonenhancing structure, apposed to the condylar head; it is of similar signal to the multiple small intra-articular bodies (black arrows). (d) Histopathology – multiple small ossified bodies (Images courtesy of Clinical Associate Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Hyperplasia Condylar hyperplasia is an increased development of one mandibular condyle. It is not known when condylar hyperplasia begins and how long it lasts. Statistically it affects more women in adolescence, although it does not discriminate by age or gender (Fig. 14).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig14_HTML.jpg] Fig. 14Condylar hyperplasia of the right condyle. Both the neck and the condyle on the right side are enlarged (black arrows). The unilateral growth resulted in an open bite on the ipsilateral side (white arrow). C condyle (Image courtesy of Dr Joseph van Sickels, University of Kentucky, Lexington, KY, USA) Hypoplasia Condylar hypoplasia (Fig. 15a) is an underdevelopment of the mandibular condyle, due to damage of the condylar growth or due to ankylosis of the joint at youth. Among possible causes are a trauma, irradiation, surgical intervention (e.g., gross tumor resection), juvenile idiopathic arthritis, or an infection of the joint. The level of deformation depends upon the age at which the condylar growth was interrupted. If the hypoplasia is inherited, the underdevelopment is observed at an early age (Fig. 15b). [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig15_HTML.jpg] Fig. 15Condylar hypoplasia and agenesis: (a) Right condylar hypoplasia and marked mandibular asymmetry. (b) Agenesis of the right condyle apart from a small separate ossified fragment. There is marked mandibular asymmetry (Images courtesy of Clinical Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Pathophysiology Disc Derangements During function of the TMJ, forces generated by the masticatory muscles are transferred to the inner structures of the temporal bone and as a result these structures become loaded. The articular disc compensates for the incongruity of the bony surfaces during its joint movements and a direct response of the loading of the tissues is the viscoelastic deformation of the disc. In normal circumstances, the deformations are temporary and have no further consequences. If necessary, the biological system reacts with remodeling of the joint to adapt to the increased loading. Since the ability of the disc to remodel is very limited (if present at all), remodeling is the result of resorption of the subchrondal bone by osteoclasts. If the outline of the tissues alters in such a way that the disc cannot slide smoothly during articulation, the disc may displace into an altered position to allow for movement of the condyle. Displacement of the disc can only happen by stretching of the firm retrodiscal ligaments that connect the disc with the condyle. This means that the disc does not displace spontaneously, but will only do so after advanced intra-articular remodeling. This remodeling is not always visible on panoramic or on CT imaging, but has been shown in a cadaver study (De Bont et al. 1986). Displaced discs may elicit responses, particularly in the disc and retrodiscal tissues (De Bont et al. 1986). These responses are a normal reaction of the body adapting to changing circumstances. Remodeling of the TMJ associated with normal adaptation to altered functional demands seems to be particularly prominent during late growth and early maturity, which is when the joint components undergo considerable changes in overall shape (Solberg et al. 1985). Discs can displace in an anterior, lateral, medial, and even posterior direction (Huddleston Slater et al. 2005). Anteromedial and anterolateral displacements are most frequently observed (Tasaki et al. 1996; Montagnani et al. 2005; Whyte et al. 2006; Ikeda and Ikeda 2016). Reduction of the disc is the repositioning of the disc from a displaced position into its original position on the condyle during mouth opening (Fig. 16). On opening of the mouth, the condyle pushes the disc forward until there is enough pressure that the condyle can "jump" past the posterior band of the disc and assumes its position under the intermediate zone of the disc. The elasticity of the tissues, together with the degree of deformation of the disc and the degree of the overstretching, determine whether "reduction" of the displacement can occur. Not all disc displacements have the capacity of a reduction; some discs have a semipermanent displacement and others are chronic displacements without any form of reduction (Fig. 17). When a disc is chronically displaced (i.e., without reduction), the anterior band undergoes atrophy or folds over the intermediate zone, while the posterior band becomes flattened and elongated in the superior joint space and enlarged inferiorly (de Leeuw et al. 1995b). Responses to disc displacement observed in the retrodiscal tissues include increased presence of dense connective tissue, decreased vascularity, and decreased innervation, suggesting that during altered disc position, the retrodiscal tissue may eventually adapt and function as a pseudodisc. Apparently, the TMJ has the capacity to adapt to changing functional demands. Degradation and loss of articular cartilage may lead to subsequent reduced smoothness of the articular surfaces and if surface irregularities have developed, joint noises (crepitation) may become present. It is highly unlikely that disc displacement is a prerequisite for osteoarthritis to occur. It is incorrect to assume (but nevertheless this view is still widely held) that a disc displacement would inevitably progress to degenerative joint disease.[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig16_HTML.png] Fig. 16Disc displacement with reduction. (1) The articular disc is anteriorly displaced relative to the head of the condyle when the mouth is fully closed. (2, 3) As the mouth begins to open, the condyle further displaces the articular disc anteriorly. (4) A click is noted as the disc reduces and assumes its original position on the condylar head. (5) The mouth is wide open and the articular disc remains in its original position relative to the condylar head. (6, 7, 8) The mouth begins to close, where occasionally another click might be noted as the disc slips anteriorly off the head of the condyle when the mouth is fully closed again (1) (Original drawing by Dr Hala Al Janaby, Perth WA, Australia) [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig17_HTML.png] Fig. 17Disc displacement without reduction. (1) The articular disc is anteriorly displaced relative to the head of the condyle when the mouth is fully closed. (2, 3, 4) As the mouth begins to open, the articular disc is unable to resume its original position on the condylar head. (5) Mouth opening is limited as the anteriorly displaced articular disc prevents the condyle from fully translating. (6, 7, 8) The anteriorly displaced disc remains as the mouth begins to close (Original drawing by Dr Hala Al Janaby, Perth WA, Australia) Hypomobility and Adherences Adherences occur when the TMJ is subject to prolonged static loading. They result in a temporary hypomobilty, and oftentimes can be released by the patient through manipulation of the jaw. The release is usually accompanied by a loud noise, upon which mobility is restored. Adhesions are the result of the development of fibrotic connective tissue between the articular surfaces after damage to the joint. The fibrotic connective tissue lines the original synovial surfaces and may result in adhesions. If the connective tissue can organize itself, for example in the case of a prolonged fixation of the joint (e.g., after intermaxillary fixation due to orthognathic surgery) it may lead to capsular fibrosis. In more extreme cases, especially after intra-articular bleeding, more advanced fibrosis may occur. Ankylosis is a fibrotic or bony connection between the articular surfaces, which may lead to a persistent intra-articular hypomobility. Clinically, the result is a permanently reduced mouth opening. Ankylosis after a condylar fracture in juveniles may lead to growth disturbances of the lower face (retrognathia). Hypermobility Disorders Hypermobility or subluxation should be regarded as a nonpathologic condition. As in a hypermobile joint, the ligaments are loose and the condyle can move beyond the crest of the articular eminence; it appears to jump forward into a more wide open position (Gutierrez et al. 2011). Complaints usually occur due to overextension of the muscles and the discomfort of temporarily not being able to close the mouth. In unilateral dislocation, the mandible deviates toward the healthy side, while in bilateral dislocation, the mandible slides forward in a gaping mouth opening. Fractures As the forces generated by trauma are transmitted to the articular surfaces in the TMJ, an inflammatory response occurs in the synovial lining. Proliferation of surface cells, increased vascularity, and fibrosis of the subsynovial tissues occur, and erythrocytes extravasate. A proliferative synovitis ensues. Despite the damage, the potential for repair is high. The subsynovial tissues have a rich vascularity and their regenerative abilities are excellent. It has been reported that, within weeks of a trauma, the injured synovial tissues are indistinguishable from normal tissues. The potential for repair after trauma is high but is incomparable to an inflammatory disorder, such as osteoarthritis (see below). The latter disorders heal slowly and usually coincide with far more symptoms than fractures. Arthralgia The auriculotemporal nerve innervates the TMJ. The nociceptors within the joint have a high threshold and only react to serious overloading of the capsule. In case of an inflammation of the joint, the threshold of the nociceptors is lowered and as a result, normal movements of the joint become painful. Inflammatory exudate (hydrops) in the joint build up some pressure in the joint and may elucidate a pain reaction on palpation of the joint or during its movements (Kothari et al. 2015). Pain in the joint may result in co-contraction of the masticatory muscles (muscular splinting), which in turn can become painful (Okeson 2013). Arthralgia of the TMJ can be due to inflammation of the synovial membrane (synovitis), or can be due to inflammation of the capsule (capsulitis), or a combination of latter causes (Kalladka et al. 2014). Osteoarthritis Osteoarthritis involves degeneration and inflammation and may be considered as a maladaptive response. It involves replacement of the original tissue structure by a tissue of inferior quality and on a cellular level, in addition to adaptive responses, necrosis is present. Normal tissue turnover involves synthesis and breakdown in a well-regulated balance, but a relative increase of breakdown, such as that caused by degenerative activity, leads to accumulation of degradative products. At first, an adaptive increase in phagocytic activity of the synovial membrane starts, but when the levels of degenerative products exceed the clearing capacity of the synovial tissues, an inflammatory response is initiated. The inflammatory reaction reflects increased degenerative activity and is core of the disease process. Chondrocyte metabolism is very sensitive to its environment and cartilage breakdown may reflect decreased synthesis of new matrices, increased breakdown of existing matrices, or both. Although osteoarthritis is considered a degenerative process, primarily affecting the articular tissues and eventually leading to destruction of cartilage and the subchondral bone, the secondary inflammatory components account for many of its clinical symptoms, named arthralgia. It is known that the synovial fluid of affected joints is less viscous than that of healthy joints. This is due to a lower quality of the highly viscous hyaluronic acid that acts as a boundary lubricant for soft tissues. As a result, the synovial fluid has reduced protective lubricating ability. This reduced protection, together with the impaired joint mobility, is thought to trigger a sequence of events that hamper the transsynovial flow and subsequently the metabolic and rheological homeostasis of the joint. It has been suggested that free radicals could act as a potential mechanism for the initiation of the molecular events in osteoarthritis (Sheets et al. 2006). Normally, accumulation of free radicals is prevented by endogenous free radical–scavenging mechanisms, but the scavenging capacity is probably exceeded by an overwhelming production of free radicals. Free radicals may be produced by direct mechanical trauma as well as by several other mechanisms. It has been thought that an increased intra-articular pressure in joints might evoke a period of hypoxia. By alterations in the metabolism on reperfusion, cells may generate free radicals. This mechanism is termed hypoxia-reperfusion injury. Currently, there is however no evidence to corroborate the hypothesis that hypoxia-reperfusion occurs in patients with osteoarthritis in the TMJ (Vos et al. 2012). Nevertheless, damage evoked by the accumulation of free radicals in affected joint tissues can be expanded by the production of extracellular matrix degradation products, by activation of inflammatory cells to synthesize and secrete cytokines, and by the generation of proinflammatory molecules (e.g., prostaglandins, bradykinin, and histamine). The ensuing collagen breakdown causes disruption of the collagenous network. As a result, the tissue swells and softens (termed chondromalacia). The increase of breakdown products in the synovial fluid may result in an inflammatory response in the synovial membrane, which may produce an appearance of joint effusion on MRI (Fig. 18), probably representing tissue edema rather than increased fluid production. Joint "effusion" on the MRI is a sign of bone marrow edema and has been shown to be present in 80% of painful joints (Takahashi et al. 1999). Bone marrow edema is a significant pain generator and may be a primary contributor to disease (Eustace et al. 2001; Hofmann et al. 2004). Because of the above-mentioned changes of the articular surfaces, adaptive and compensatory changes (e.g., muscular responses, changes within the capsule, retrodiscal tissue and subchondral bone) or decompensation (e.g., erosions, perforations) occur. Over time, this may lead to (mechanical) changes of the associated tissues. Radiographic changes are the vast reminder of these processes. Interestingly, about 50–90% of symptom-free individuals have been shown to have radiographically visible changes probably due to osteoarthritis. This may reflect the tendency of clinical symptoms of osteoarthritis to subside with time, but radiographic changes may also be the result of remodeling that is associated with growth and recovery, or repair, which results in adaptation and normalization of function. It is essential to understand that osteoarthritis is a disorder that occurs in joints regardless of the position of the articular disc and is characterized by two basic pathologic mechanisms: degeneration and inflammation. It is highly unlikely that disc displacement is a prerequisite for osteoarthritis to occur. Often, however the term "internal derangement" has become a false diagnostic description in patients with symptoms such as pain, clicking, and restriction of mouth opening.[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig18_HTML.jpg] Fig. 18Fat-saturation T2 oblique sagittal MRI scans of the left TMJ in two patients with internal derangement and pain. (a) A moderate sized, hyperintense ("bright") effusion is present in the anterior recess of the upper joint space with a small effusion in anterior recess of the inferior joint space (white dotted arrows). Synovitis is also hyperintense (white arrows) but the signal is lower than that of joint fluid. The condyle is remodelled with focal subarticular reactive marrow change (white dotted oval). (b) There is a large, hyperintense effusion in the anterior recess of the upper joint space (white dotted arrow). Marked synovitis around the bilaminar zone (white arrows) and inferior joint space with extensive condylar erosion and resorption (white open arrow) in a young female adult with Idiopathic Condylar Resorption (ICR) (Images courtesy of Clinical Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Rheumatoid Arthritis Rheumatoid arthritis is a chronic inflammatory disease that primarily affects the periarticular structures such the capsule, tendons, and ligaments. It secondarily involves the articular cartilage and subchondral bone. Approximately 50–70% of patients with rheumatoid arthritis have involvement of the TMJ. It is bilateral in about half of the patients. Mandibular movement may be severely limited in the late stages of the disease, often through stiffening of the joint. Often an anterior open bite is seen, due to destruction of the joints. In young patients, under 16 years of age, a distinct form named juvenile rheumatoid arthritis, also called juvenile idiopathic or chronic arthritis, exists. In an estimated 45–75% of children with this disease, the TMJ is involved, with significant adverse effects on dental occlusion, oral health, and in particular facial growth (Twilt et al. 2004; Billiau et al. 2007; Weiss et al. 2008). Spondyloarthritides Ankylosing spondylitis is a rheumatic disease characterized by inflammatory stiffening of the spine and sacroiliac joints. The primary pathologic site is not the synovium, but rather the ligaments and the surrounding joint capsule. The disease is characterized by fibrosis and ossification rather than joint degeneration. The TMJ may be involved in the disease (Wenneberg 1983). Psoriatic arthritis is an inflammatory arthritis associated with psoriasis. Although most patients with psoriasis have a benign course, a subgroup has a more severe course, including arthritis. Pain, swelling, or stiffness in one or more joints is commonly present in psoriatic arthritis. Affected joints are generally red or warm. Most often the joints of the hands and wrists are affected, but in selected cases the TMJ can also be affected. Along with the above noted pain and inflammation, there is extreme exhaustion that does not subside with adequate rest (Lee et al. 2010). The exhaustion may last for days or weeks without abatement. Psoriatic arthritis may remain mild, or may progress to more destructive joint disease. Periods of active disease, or flares, will typically alternate with periods of remission. Because prolonged inflammation can lead to joint damage, early diagnosis and treatment to slow or prevent joint damage is recommended. Reiter syndrome or reactive arthritis can be defined as aseptic arthritis triggered by an infectious agent not present in the joint itself. It usually includes a combination of urethritis, arthritis, and conjunctivitis (Stavropoulos et al. 2015). The exact pathogenesis is unknown, but several infective agents and a specific genetic (HLA-B27) background are recognized. The TMJ can be involved in patients who suffer from Reiter Syndrome (Könönen et al. 1992). Crystal Deposition Diseases Gout is a disorder of purine metabolism, and occurs when its end product, uric acid, crystallizes, precipitates, and forms deposits (tophi) in joints, on tendons, and even in the surrounding tissues. Microscopic tophi may be walled off by a ring of proteins, which blocks interaction of the crystals with cells, and therefore avoids inflammation. Unprotected crystals may break out due to minor physical trauma to the joint, surgical stress, or rapid changes in uric acid levels and as a result trigger an inflammatory reaction. The triggers for precipitation of uric acid are not well understood (Larsen et al. 2015). While it may crystallize at normal levels, it is more likely to do so as levels increase (Zhu et al. 2017). Other factors believed to be important in triggering an acute episode of arthritis include cool temperatures, rapid changes in uric acid levels, acidosis, articular hydration, and extracellular matrix proteins, such as proteoglycans, collagens, and chondroitin sulfate (Schlee et al. 2017). Blood uric acid levels may be normal during an attack. Calcium pyrophosphate dihydrate (CPPD) crystals are predominantly found in articular cartilage and meniscus, but are also found in the membrane, joint capsule tendons, ligaments, and blood vessels. The pathogenesis of CPPD crystal formation is still unclear (Abhishek and Doherty 2016). CPPD crystal formation may result from the presence or exposure of nucleating factors or the absence of inhibitors for precipitating factors. Crystal nucleation may be predisposed by changes in the matrix, such as collagen fibril fragmentation and changed composition of glycosaminoglycans or proteoglycans (Abhishek and Doherty 2016). It is still unknown whether crystal deposition is a result of or a contributing factor to osteoarthritis, but based on the findings of intracellular CPPD crystals, it was suggested that an intracellular pathway of CPPD crystal formation could exist (Sheets et al. 2006). Hyperplasia The direct consequence of condylar hyperplasia is asymmetric facial deformity, by which the mandible displaces to the nonactive side. The occlusal plane is also displaced and an open bite occurs (Fig. 14). The result is an enlarged condylar head and elongated mandibular collum. Often the open bite is compensated for by eruption of the teeth. Sometimes, a unilateral cross-bite on the nonactive side occurs, which is the result of the rotational growth process (Olate et al. 2013; Portelli et al. 2015). Hypoplasia In most cases, condylar hypoplasia is unilateral and is often noticed as a facial asymmetry. Often, there is an unilateral impairment of the sliding motion of the joint. Further, the antogonal notch is more prominent. Bilateral hypoplasia is observed as a mandibular retrognathia, sometimes with a frontal open bite. Clinical–Pathologic Features Disc Derangements The clinical features of disc derangements depend on the mobility of the displaced disc, the lubrication of the joint, and the extent of displacement. A disc displacement with reduction (Fig. 16) is often characterized by reciprocal clicking, meaning that a clicking, popping, or snapping sound or sensation can be heard/felt on opening as well as on closing the mouth. In the closed mouth position, the disc is typically displaced in an anterior, anteromedial or anterolateral position. On opening the condyle pushes the disc forward until there is enough pressure that the condyle can "jump" past the posterior band of the disc and assume its position under the intermediate zone of the disc. The "jump" is heard or felt as a click, pop or snap. Before the disc reduces on opening, one may observe a deviation of the jaw to the ipsilateral side due to the disc obstructing smooth movement. On closing, the disc presumably slips back off the condylar head, giving rise to another joint sound (Huddleston Slater et al. 2002). This condition is frequently asymptomatic and pain free. A disc derangement with intermittent locking is characterized by an intermittent inability to fully open the mouth. In this condition, the condyle transiently cannot clear the posterior band of the disc, resulting in limited translational movement. Clinically, the mouth opening is limited, and, if unilateral, the jaw typically deflects to the ipsilateral side on opening and protrusion. This condition is also called acute closed lock. The clicking sound is absent during the period of acute locking. A person with this condition may be able to unlock his/her jaw and the jaw may resume with the features of a disc displacement with reduction. Sometimes the help of a clinician is needed to unlock the jaw. A disc derangement without reduction is characterized by a sudden closed lock as described above; however, in this case the disc is permanently displaced in anterior, anteromedial, or anterolateral position. The displaced disc interferes with the patient's ability to open the mouth fully, and as a result the mouth opening is limited and, if the condition occurs unilaterally, the jaw oftentimes deflects to the ipsilateral side on opening and protrusion (Fig. 17). If the disc is displaced anteriorly, anteromedially, or anterolaterally, movement of the jaw to the contralateral side may be limited due to the disc barricading the forward and medial movements of the condyle. This condition frequently prompts a patient to seek help, not only because of the inability to open the mouth but because this condition is often associated with pain. Posterior disc displacement without reduction is described as a painful inability to maximally occlude the teeth together. The displaced disc interferes with the ability of the condyle to seat in its normal position, causing the condyle to be seated downward and forward, and resulting in an ipsilateral posterior open bite. Posterior disc displacement with reduction is characterized by a click on closing. When the patient attempts to occlude, the disc assumes its normal position on the condyle. A snapping or clicking sound can be appreciated when the condyle passes the anterior band of the disc (Huddleston Slater et al. 2005). Hypomobility and Adherences Adherences cause a similar clinical picture to an anterior disc displacement without reduction. When the condition occurs unilaterally, the clinical picture shows limited mouth opening and deflection to the ipsilateral side on opening and protrusion. When this condition occurs bilaterally, the limited mouth opening will be the only clinical finding. Depending on where the adherence is located, the patient's mouth opening will be more or less limited. If the adherence occurs in the lower joint compartment, the rotation of the joint is compromised, but the translational capacity is intact. If the adherence occurs in the upper joint compartment, the translation of the joint is compromised but the rotational capacity remains intact. The latter condition will result in less mobility than the former condition. A patient with this condition will relate that the jaw sometimes gets locked and that s/he is able to move the jaw smoothly again after a loud snapping, popping, or cracking sound has occurred. This condition often occurs after a period of immobility or clenching. Patients with adherences will describe their condition as an occasional limitation of mouth opening relieved by a single loud sound, whereas a patient with a disc displacement with reduction will describe the condition with more consistent and frequent joint sounds, i.e., "every time I chew or open my mouth." Adhesions also cause a similar clinical picture to a disc displacement without reduction and adherences: limited mouth opening, and deflection on opening or protrusion to the ipsilateral side. The difference between this and the other two conditions is that in the case of adhesions the limitation occurs more gradually. Adhesions are more frequent in the advanced stages of internal derangement and osteoarthritis (Zhang et al. 2009; Millon-Cruz et al. 2015). Impedance of the coronoid process is characterized by a slowly progressive limitation of jaw movements. The condition is often bilateral, and the patient will report a slowly progressing limitation of jaw movements in all directions. When the condition occurs unilaterally, there is deflection to the ipsilateral side and limited movement to the contralateral side. This condition is typically pain free, but normal mouth functions, such as opening and eating, and dental procedures will become increasingly hampered. Computerized tomography with open mouth images show impact of the coronoid process against the zygomatic bone. Hypermobility Disorders Subluxation or luxation of the jaw is characterized by the inability of the patient to close the mouth after wide opening without a specific maneuver performed either by the patient or a clinician. Consequently, the patient will be unable to bring the teeth in occlusion. If the condition is unilateral, the jaw will deflect to the contralateral side. This condition is frequently associated with significant pain and distress. Pain may either result from strain of the joint which may result in inflammation, or from overextension of the muscles. Thus, pain may linger or persist after the luxation has been salvaged. On clinical examination, pain to palpation of the muscles and affected joint(s) may be noted. A preauricular depression may be noted in the presence of the open lock (Fig. 19). In case of bilateral joint dislocations, the patient may appear prognathic or show elongation of the lower third of the face. Radiographically, the condyle is positioned in front of the eminence and the fossa is empty (Guttierrez et al. 2011) (Fig. 20).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig19_HTML.jpg] Fig. 19Preauricular depression (arrow) in the presence of the open lock. The condyle is located anterior to the eminence creating a marked prominence (C). C condyle (Image courtesy of Dr Pratishtha Mishra, University of Kentucky, Lexington, KY, USA) [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig20_HTML.jpg] Fig. 20Hypermobility of the right TMJ. The right TMJ is located in front of the eminence, and the left TMJ remains in the fossa (arrows). C condyle (Image courtesy of Dr Jeffrey P. Okeson, University of Kentucky, Lexington, KY, USA) Fractures Fractures of the condylar head or neck may result in limited mouth opening, malocclusion, swelling, pain, deflection on opening and protrusion, and facial asymmetry. Both acute displaced and nondisplaced fractures may present with these features depending on the severity of the responsible insult. These characteristics may be temporary when left untreated in nondisplaced fractures, but some of these may remain in untreated displaced fractures. About 1–2% of condylar fractures result in ankylosis (Anyanechi 2015). Arthralgia and Osteoarthritis Arthralgia is characterized by report of pain felt in the preauricular area or in the ear on jaw movement and/or jaw function. If the condition is accompanied by significant inflammation, a malocclusion may be reported by the patient. Due to inflammation, effusion, or swelling of the intra-articular tissues, the patient may not be able to bring the teeth into occlusion on the ipsilateral side, clinically detectable as a posterior open bite. Attempting to bring the teeth in occlusion may result in increased pain. The patient may also report limited mouth opening due to pain. Palpation of the area or manipulation/compression of the affected side results in an increase of the familiar pain. The clinical characteristics of osteoarthritis are similar to those of arthralgia. However, depending on the extent of degenerative changes, the patient may report a malocclusion with the sense of a heavier occlusion on the ipsilateral side, or the inability to bring the molars in occlusion on the contralateral side. Manual manipulation of the mandible in an attempt to seat the condyle in its musculoskeletal supported position may unveil a discrepancy between this position and habitual occlusion. In case of bilateral degenerative changes, an anterior open bite may result (Fig. 21).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig21_HTML.jpg] Fig. 21Open bite due to bilateral (juvenile) osteoarthritis. Frontal (a) and lateral views (b and c). Note the physiological attrition of the cusps of the molars Crystal Deposit Diseases Gout and CPPD are characterized by acute pain, redness, and swelling due to intense inflammation in the joint. The clinical characteristics, therefore, are the same as those for arthralgia. Synovial (osteo)chondromatosis of the TMJ is characterized by progressive swelling and pain and may be accompanied by intermittent or long-lasting malocclusion and limitation of movement. The malocclusion and limitation can be intermittent due to free-floating osteocartilaginous bodies interfering with smooth movement of the joint. When more severe, the limitation and/or malocclusion may be more permanent. Joint noises are frequently present, but in some cases, the disease is asymptomatic. Hyperplasia Condylar hyperplasia is an uncommon idiopathic unilateral disorder of jaw growth consistent with exuberant or persistent activity of the condyle nucleus. Hyperplasia of the TMJ or of the mandible is characterized by a slowly increasing facial asymmetry with chin point deviation to the contralateral side, and may be accompanied by malocclusion. The condition is typically not associated with pain, and the patient's concern is usually the increasing facial asymmetry. On examination, facial asymmetry, chin point deviation, and canting of the occlusal plane are evident. This is best observed when the head is bend backward. On opening and protrusion, the jaw will deflect to the contralateral side. A cross-bite may also be observed (Olate et al. 2013). Radiographic imaging can be used to confirm the diagnosis and the extent of the excessive growth (Fig. 22). In addition, isotope bone scan with Single Photon Emission Computed Tomography (SPECT) imaging can be used to determine whether the process is still active (Fig. 23).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig22_HTML.jpg] Fig. 22Mandibular hyperplasia of the right mandible and tilted occlusal plane. The dotted line indicates the difference in height between the left and right ramus, and the dashed line shows the tilted occlusal plane [image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig23_HTML.png] Fig. 23Twenty-one-year-old male with right condylar hyperplasia. An isotope bone scan with SPECT was performed to determine if there was persistent abnormal growth in the right condyle to aid timing of orthognathic surgery. The study demonstrates asymmetric and abnormal isotope uptake (metabolic activity) in the right condyle (black dotted arrow). Uptake in the condyles can be quantitated by comparison with uptake in the clivus (central skull base): a + b, or the L4 vertebral body: c (Images courtesy of Clinical Professor Andy Whyte, Perth Radiological Clinic, Perth WA, Australia) Hypoplasia Hypoplasia of the condyle or the mandible is also characterized by a slowly increasing facial asymmetry. Lack of mandibular and/or condylar growth will result in facial asymmetry, occlusal canting, malocclusion, and chin point deviation to the affected side (Fig. 15). On opening and protrusion, the jaw will deflect to the ipsilateral side. A cross-bite may also be observed. If the condition is bilateral, micrognathia will ensue. Radiographic imaging can be used to confirm the diagnosis and the extent of deficiency. Patient Management Disc Derangements Depending on the type of derangement, and the impact a disc derangement has on a person's quality of life, and the preference of the clinician, treatment can vary from reassurance and education to surgical interventions. Literature suggests that disc displacement with reduction may persist for many years without progression causing minimal to no discomfort to the patient (Greene and Laskin 1988; de Leeuw et al. 1994). It is also known that little to no degenerative changes occur when a disc displacement with reduction persists for many years (de Leeuw 1995a). Thus, common sense would indicate that the patient should be educated about the condition and its long-term prognosis, and that invasive or aggressive methods to restore the position of the disc should be avoided. If there is pain involved, then the clinician should focus on reducing and eliminating the pain. This can be achieved by controlling contributing and perpetuating factors such as unnecessary loading or relative overloading of the joint and using supportive non-pharmacological or pharmacological management strategies. The concepts of self-awareness of jaw use and overuse, and employing therapies such as soft diet and habit reversal techniques should be introduced to the patient and subsequently reinforced. Soft diet suggestions would include anything the patient can eat within pain free limits, i.e., anything that does not aggravate the pain. Habit reversal techniques include methods to increase awareness of adverse habits and to train the patient to check periodically for such habits especially during circumstances and activities which have been identified to likely trigger the adverse habit, and implement relaxation techniques aimed at keeping the teeth and lips slightly apart. Supportive pharmacological treatment can include short-term use of nonsteroidal anti-inflammatory medications or other mild analgesics, such as acetaminophen, or in acute and severe cases a short course of glucocorticoids. Nonpharmacological treatment can include moist heat and jaw relaxation exercises. When there is significant joint pain on awakening, a maxillary hard acrylic full coverage stabilization appliance may be indicated (Fig. 24).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig24_HTML.jpg] Fig. 24(a) Frontal view of a full coverage maxillary hard acrylic stabilization appliance. (b) Frontal view of a full coverage maxillary hard acrylic stabilization appliance in place When the patient is diagnosed with disc displacement with intermittent locking, especially with the locking occurring on awakening, an anterior repositioning appliance may be indicated (Fig. 25). This appliance will keep the disc on the condyle during the night and relieves pressure on the retrodiscal tissue allowing this tissue to heal. The purpose of the appliance is not to eliminate the clicking but rather to bring the patient back to pain free clicking. The appliance should be worn only at night in order to avoid occlusal changes. In case of an acute closed lock, the clinician should attempt to unlock the jaw. If the attempt is successful, but the patient's jaw locks immediately again upon closing, an anterior repositioning appliance should be fabricated to keep the jaw from locking. In this case, the patient is advised to wear the appliance full time for no longer than 5 days in order to avoid permanent occlusal changes. After that time, the patient should wean off the use during the day to use only at night, if there is still a need for night-time use.[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig25_HTML.jpg] Fig. 25(a) Frontal view of anterior repositioning appliance (b) Lateral view of anterior repositioning appliance (Images courtesy of Dr Jeffrey P. Okeson, University of Kentucky, Lexington, KY, USA) When a patient presents with a disc displacement without reduction, treatment should initially aim at reducing pain and discomfort, which can be done as described above for disc displacement with reduction, and then followed by jaw exercises aimed at increasing the mouth opening. Exercises can be performed by the patient by means of slowly stretching the jaw open by stacking tongue blades between the teeth, or by pushing with the thumb on the maxillary incisors and with a finger on the mandibular incisors. A passive motion device such as the Therabite (Fig. 26) can also be used. The exercises should be performed within pain-free limits to avoid inflammation. Jaw stretching manipulation can also be performed by physical therapists (see below). Studies have shown that with no (Sato et al. 1998; Sato et al. 2002) or minimal (Rasmussen 1981; de Leeuw et al. 1994) treatment, symptoms and signs of pain and limited jaw movements gradually improve. However, with treatment, signs and symptoms improve faster (Kai et al. 1998; Minakuchi et al. 2001; Murakami et al. 2002). A recent systematic review and meta-analysis on the effectiveness of manual therapy and therapeutic exercises for temporomandibular disorders (Armijo-Olivo et al. 2016) concluded that there was only a slight trend toward better pain reduction and increased mouth opening with exercises compared to education, splint therapy, or a control group. However, two recent reviews found that manual therapy (Martins et al. 2016) or manual therapy in combination with exercises (Armijo-Olivo et al. 2016) was superior to splint therapy, self-care, or pharmacological management with regard to reducing pain and increasing mouth opening. Manual therapy can involve joint mobilization, manipulation, or soft tissue treatment. A recent systematic review (Goiato et al. 2016) investigating the benefits of intraarticular injections of hyaluronic acid included two articles with a total of 118 patients with internal derangements. This review showed a significant reduction in pain in one of the studies at 1 week and 6 weeks for hyaluronic acid compared to saline and corticosteroid or tenoxicam injections, while the second included study found no significant effect of intraarticular injections of either hyaluronic acid or tenoxicam up to 3 months (Goiato et al. 2016).[image: ../images/337287_1_En_31_Chapter/337287_1_En_31_Fig26_HTML.jpg] Fig. 26Therabite® Clinical Practice Guidelines for Oral and Maxillofacial Surgery of the American Association of Oral and Maxillofacial Surgeons (Bouloux et al. 2017) state that surgical interventions for internal derangement should only be attempted after nonsurgical treatments have proven ineffective and pain or dysfunction is moderate to severe. They specifically state that surgery is not indicated for preventive reasons or for asymptomatic or minimally symptomatic cases. The surgical options that are available vary from arthrocentesis to full joint replacements. Arthrocentesis is a simplified arthroscopy surgery without the use of a camera and intra-articular instruments and is rapid, minimally invasive, and safe. Arthrocentesis can be performed under local anesthesia either with or without intravenous sedation. Typically, after disinfection and preparation of the surgical area, the area is anesthetized with an auriculotemporal nerve block. Then, a 19 gauge needle is introduced into the upper joint compartment and 1–2 ml of lactated Ringer's solution is introduced into the joint to distend the joint slightly after which in the case of restricted mouth opening, the mandible is manipulated in an attempt to improve joint mobility. Subsequently, a second 19-gauge needle is introduced into the upper joint compartment near the eminence. This needle serves as an outlet for the saline solution. Subsequently, 200–300 ml of lactated Ringer's solution is flushed through the joint over a period of about 15 minutes (Nitzan et al. 1991). Some surgeons prefer to end the procedure by leaving steroids in the joint, while others choose to use hyaluronic acid. At this time, there is no clear indication that one method is better than the other (Goiato et al. 2016). As with any invasive procedure, there is a risk of bleeding, bruising, infection, soreness at the injection site, transient paralysis of the facial nerve, transient malocclusion, and a chance that the procedure does not provide relief. A meta-analysis including three studies with patients diagnosed with disc displacement showed that arthrocentesis was highly successful for these patients (Reston and Turkelson 2003). Arthrocentesis is the least invasive type of surgical intervention with good outcomes in patients with closed lock. Even in the absence of correction of the disc-condyle relationship, the improvement of dysfunction and mouth opening can be achieved (Al-Belasy and Dolwick 2007). Surgical procedures, including discoplasty, disc repositioning techniques, and modified condylotomy (Hall et al. 2000), typically aim to improve the disc-condyle relationship. Discectomy, either with or without replacement, of the removed disc has also been used with varying degrees of success (Bjornland and Larheim 2003; Nyberg et al. 2004; Dimitroulis 2005; Holmlund et al. 2013). Discectomy procedures with alloplastic implants (silastic or proplast) have shown less favorable results than discectomy without replacement or nonsurgical treatment (Fricton et al. 2002). Patients who received discectomy with dermis graft replacements (Dimitroulis 2005) or no replacements (Bjornland and Larheim 2003; Miloro and Henriksen 2010; Holmlund et al. 2013) seemed to improve in mandibular function, however the studies cited did not use a comparison group. Replacements with ear cartilage or free fat have been performed as well. While ear cartilage has a tendency to fragment or proliferate, free-fat grafts, while quickly shrinking in volume after transplantation, may minimize intra-articular scar formation. While temporalis flaps have enjoyed popularity as interpositional grafts, no randomized controlled studies are available to demonstrate their effectiveness (Dimitroulis 2011). Adherences Adherences can be treated by arthrocentesis or arthroscopic lysis and lavage, and further prevented by avoiding continuous or prolonged loading of the joints. This can be accomplished by education regarding, and avoidance of contributing factors such as awake and sleep bruxism. In case of sleep bruxism, an interocclusal appliance (Nitzan et al. 1997) may be provided. While there is no consensus regarding the mechanism of action of interocclusal appliances, it is widely acknowledged that they redirect the force from sleep bruxism. Adhesions Adhesions typically cannot be managed in a conservative way. If a patient has a limited mouth opening as a result of adhesions and is otherwise asymptomatic, and the patient claims the limitation in mouth opening does not result in unacceptable reduction in quality of life, one could opt to observe for clinical progression rather than intervening. Otherwise, adhesions are treated with arthroscopic lysis and lavage to break down and remove the adhesions and smoothen the articular surfaces. These procedures result in increased mouth opening, improved jaw function, and reduced pain (Zhang et al. 2011a; Leibur et al. 2010). Adhesions are more common in joints with more advanced stages of internal derangement (Millon-Cruz et al. 2015). Hypermobility Disorders Mechanical hypermobility disorders are first and foremost treated by helping the patient understand the underlying mechanics so that the patient can learn to avoid the occurrence of (sub-)luxations and learn to self-manipulate the jaw through bimanual intraoral traction should additional subluxations occur. The technique can be applied with the patient sitting or in supine position. Some authors claim the supine position is better because it allows the clinician a better view of the dental arches and dynamic occlusion, is faster and less painful (Xu et al. 2016). Initiating a gag reflex as well as yawning have been described as self-reducing techniques as well (Liddell and Perez 2015). In patients with a history of habitual TMJ luxation, the mandible should be supported during an extraction or other lengthy oral surgery or dental procedures, and the patient should if possible avoid opening their mouth excessively. In case of persistent dislocation, the patient may be need to be sedated in order to unlock the jaw, and intermaxillary fixation is often needed to avoid relapse due to muscle memory. Recurrent luxations have been managed by injecting autologous blood or sclerosing agent s in the joint and surrounding tissues. The procedures will cause scarring, fibrosis, and/or adhesions which will reduce mobility. Risks of these procedures include the inability to predict the extent of scarring and fibrosis (Machon et al. 2009). Chewing efficiency is reported to improve and maximum mouth opening to decrease with treatment with autologous blood. Success rates range from 64% to 73% after one treatment (Machon et al. 2009; Coser et al. 2015). Treatment with dextrose prolotherapy does not appear to be more beneficial than placebo (Cömert Kiliç and Güngörmüş 2016). Treatment protocols such as number of injection sites and number of sessions vary. Surgical methods such as flattening the eminence, adding a barricade, or limiting the mobility by means of downfracturing the eminence or zygomatic arch, placement of miniplates, or sutures and mini anchors have also been proposed (Liddell and Perez 2015). A recent systematic review showed that there is no consensus with regard to the most effective treatment for recurrent joint luxation, but that eminectomy was resorted to whenever other surgeries failed or a relapse occurred, leading the authors to believe that eminectomy is still the standard of care (de Almeida et al. 2016). If the cause of the luxation is due to dystonia, dyskinesia, or spasm of the inferior lateral pterygoid muscle, injection with botulinum toxin may be indicated (Liddell and Perez 2015). This treatment may also be indicated to reduce the force of translation of the inferior lateral pterygoid muscle and is intended to decrease the risk of additional luxations (Liddell and Perez 2015). Likewise, weakening the elevator muscles may increase the ease and effectiveness of the traction maneuver because it reduces the amount of resistance provided by these muscles. The inferior lateral pterygoid muscle can be approached through an intraoral as well as extraoral approach. Both approaches should be carried out under electromyographic guidance. Typically, a dose of 25–50 units of onabotulinum toxin A is used for the masticatory muscles. Effects should be noticeable in about a week and usually last between 2 and 3 months (Clark 2003). If myospasm of the inferior lateral pterygoid is a repeat offender causing frequent and debilitating luxations, stripping of the lateral pterygoid may be indicated (Liddell and Perez 2015). Fractures Much debate exists about whether displaced condylar fractures should be treated with open or closed reduction. A recent study with 50 patients indicated that both methods yielded similar results with the exception of deflection on opening, which was present only in the group that received closed reduction of the fracture (Rastogi et al. 2015). A meta-analysis of 26 studies comparing surgical to nonsurgical treatment methods found that surgical approaches yielded better results with regard to malocclusion and deflection on opening and that nonsurgical approaches yielded better results with regard to infection. Surgical procedures also yielded better results with regard to lateral movements and protrusion, but no differences were found with regard to maximal mouth opening. In addition, no differences were found with regard to TMJ pain or noise (Chrcanovic 2015). Arthralgia and Osteoarthritis Management of arthralgia and osteoarthritis of the TMJ should aim at decreasing the loading to the joint as best as possible. This can be accomplished by controlling contributing and perpetuating factors such as unnecessary loading or relative overloading of the joint and using supportive non-pharmacological or pharmacological management. The concepts of self-awareness of jaw use and overuse, and employing therapies such as soft diet and habit reversal techniques should be introduced to the patient and subsequently reinforced. Soft diet suggestions would include anything the patient can eat within pain free limits, i.e., anything that does not aggravate the pain. Habit reversal techniques include methods to increase awareness of adverse habits and to train the patient to check periodically for such habits especially during circumstances and activities which have been identified to likely trigger the adverse habit, and implement relaxation techniques aimed at keeping the teeth and lips slightly apart instead. Supportive pharmacological treatment includes the short-term use of nonsteroidal anti-inflammatories or other mild analgesics or in acute and severe cases, a short course of glucocorticoids. Generally, there is limited support for the use of intra-articular corticosteroid injections or steroid for treatment of TMJ arthralgia (Stoustrup et al. 2013; Gencer et al. 2014). Concerns remain with regard to potential damage to the articular cartilage and particularly in children with regard to interference with mandibular growth (Stoustrup et al. 2013). Non-pharmacological treatment can include application of moist heat and jaw relaxation exercises. A systematic review examining the differences in outcome between lavage and nonsurgical treatment (Vos et al. 2013a) only slightly favored lavage for pain intensity but no differences were found between the modalities as far as mouth opening was concerned. Another systematic review (Goiato et al. 2016) investigating the efficacy of intraarticular injections of hyaluronic acid, including six studies with a total of 234 patients with arthritis or arthralgia, found no superiority of this product over injections with corticosteroids in these conditions. Crystal Deposit Diseases Treatment of acute gout and CPPD is aimed at symptom reduction and includes cold packs, rest, and use of anti-inflammatory medications such as nonsteroidal anti-inflammatory medications or glucocorticoids. For chronic conditions, low-dose nonsteroidal anti-inflammatories with gastroprotection or low-dose colchicine are indicated (Zhang et al. 2011b). For gout, diet and urate lowering medications such as allopurinol, febuxostat, or probenecid can be used, although evidence suggests that the beneficial effects of these medications takes about 1 year (Shekelle et al. 2016). Hyperplasia Some cases of TMJ hyperplasia are subtle. If the patient is not symptomatic and the quality of life is not affected or the patient is not bothered by facial asymmetry, and if there is no indication of active growth, no treatment is required. However, if active growth is suspected, further investigation is warranted. Scintigraphic (technetium-99 m) imaging (bone SPECT) can be used to determine whether the process is still active or not. Bone SPECT detects well focused (99 m) Tc-MDP uptake in the TMJ, and thus allows to achieve noninvasively the final diagnosis of primary condylar hyperplasia. The sensitivity of this procedure is claimed to be 88%, whereas the specificity is about 70% (Rushinek et al. 2016). Consensus on best timing and therapeutic approaches for condylar hyperplasia are yet to be reached, but if active growth is established, surgical correction should be postponed. Otherwise, the treatment of facial asymmetry consists of high condylectomy or orthodontic and orthognathic correction once it has been established that the growth has ceased (Mouallem et al. 2017). Hypoplasia Similar to mandibular or condylar hyperplasia, the condition can be asymptomatic and facial asymmetry can be subtle. If both are the case, the patient may opt not to be treated. Otherwise, mandibular hypoplasia can be treated with functional appliances in growing patients. Mandibular distraction osteogenesis and surgical reconstruction are other options. In mild cases, genioplasty can be an alternative option to improve the asymmetry. Most often the patient also requires orthodontic treatment in conjunction with orthognathic surgery (Arun et al. 2002). Conclusions and Future Directions Numerous conditions can interfere with the smooth movement of the TMJ as evidenced above. The symptoms of some conditions may be minimal without any impact on the patient's quality of life and may not require treatment while others may cause major disturbances for which pervasive interventions are necessary. Conservative treatment is still the mainstay for the management of disc derangements, arthralgia, osteoarthritis, and adherences although minimally invasive procedures such as lysis and lavage (arthrocentesis) are frequently used early on in the care of the patient. The TMJ has a remarkable capacity to adapt to changing functional demands. In most, but not all cases, internal derangements do not warrant treatment. In general, limited data is available for evidence-based effective treatments for internal derangements, and more research is needed in several areas using sound methodology and large populations. There is a growing interest in markers for cartilage degradation in synovial joints because of their potential diagnostic and prognostic value. Recently, it was found that the concentrations of carboxyterminal telopeptide type II (CTX-II) were unexpectedly high in patients with arthritis as compared to healthy controls. This suggests that this marker may in the future be useful to quantify cartilage degradation in the TMJ (Vos et al. 2013b). Conservative treatment for degenerative joint disorders is often time-consuming and has unpredictable success rates. Earlier indication of arthrocentesis may cease further degeneration of the articular tissues. Repeated intra-articular injections of hyaluronic acid (2–5 times) may replenish the cartilage with protective hyaluronic acid. A review showed a significant reduction in pain in one of the studies at 1 week and 6 weeks for hyaluronic acid compared to saline and corticosteroid or tenoxicam injections, while the other included study found no significant effect of intra-articular injections of either hyaluronic acid or tenoxicam up to 3 months (Goiato et al. 2016). While it should be noted that the position of the disc or even the presence of a disc does not seem to be a major factor in the prognosis of the patient's condition, future directions include tissue engineering efforts to create viable biological functional implants to replace damaged discs (Emans et al. 2005; Shu et al. 2015). Depending on the severity of the condition and the impact it has on the patient's life, condylar and mandibular hyperplasia and hypoplasia are treated with a combination of orthodontic therapy and maxillofacial surgery. New and exciting technologies for these conditions include the integration of 3-D surgical and orthodontic approaches to correct facial asymmetries due to condylar hyperplasia or hypoplasia (Janakiraman et al. 2015). 3-D technologies can also be used in the design of full joint replacements. 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