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Acute inflammation at a mandibular solitary horizontal incompletely impacted molar.

Acute inflammation is frequently seen in the elderly around incompletely impacted molars located apart from molars or premolars. To identify the factors causing acute inflammation in the solitary molars without second molars or without second and first molars, ages of patients and rates of acute inflammation in 75 horizontal incompletely impacted mandibular molars in contact or not in contact with molars in subjects 41 years old or older were studied using orthopantomographs. Acute inflammation was seen in nine third molars out of 48 third molars in contact with second molars (18.8%), whereas acute inflammation was seen in 11 molars out of 19 solitary molars without second molars or without first and second molars (57.9%) (p < 0.01). The mean age of 48 subjects with third molars in contact with the second molar was 50.42 ± 7.62 years, and the mean age of 19 subjects with isolated molars was 65.16 ± 10.41 years (p < 0.0001). These indicate that a solitary horizontal incompletely impacted molar leads more frequently to acute inflammation along with aging due to possible bone resorption resulting from teeth loss.


Introduction
Acute infl ammation around the horizontal impacted third molar is frequently seen in not only the third molar in contact with the second molar but also that not in contact with the second molar or that without the second molar in the elderly (Figure 1). A partially impacted tooth affects soft tissue infection, 1,2 and it is estimated that acute infl ammation is affected by local factors, especially the position and angulation of the mandibular third molar, 1,3,4 which results in complications. 5 The area surrounding the crown of a horizontal impacted molar, where periodontium is not present, may easily develop acute infl ammation as the name pericoronitis implies. Third molars may continue to have a negative impact on periodontal health well into middle-age and beyond in adults. 6 Accordingly, an understanding of the expression of acute infl ammation is important to prevent possible extension to severe complications in the elderly. However, there is a lack of information about isolated impacted molars because of the inability to distinguish the third molar in reports of molar loss.
A completely impacted third molar is not usually removed unless there are signs and symptoms around the region. However, the crown of the tooth could be exposed with bone resorption due to periodontitis or removal of adjacent tooth and, especially in aging, opportunities of infection around the exposed crown of a horizontal impacted third molar may increase complications and patient quality of life concerns. Recognition of the horizontal impacted third molar status is important for assessment of the quality of life in elderly. Subjects with an impacted third molar with or without a decayed second molar may benefi t from information on the increased risk for acute infl ammation. Nevertheless, little is known regarding the status of the horizontal incompletely impacted solitary molar.
Our study sought to find predictive ability of acute information in age and adjacent tooth loss occurring bone resorption. Differences between impacted third molars in contact with second molars and solitary incompletely impacted molars in the absence of second molars, or second and fi rst molars, were studied as a basis to identify the factors causing acute infl ammation in horizontal impacted molars, since horizontal impaction of fi rst or second molars is extremely rare, and a risk of infl ammation is known in patients with horizontal incompletely impacted third molars. 5 We report the rates of acute infl ammation around horizontal incompletely impacted molars isolated from the fi rst molar or premolar, the patient ages, and discuss the prognostic value of factors infl uencing acute infl ammation.

Methods
Orthopantomographs were examined from 47 teeth from 43 men and 28 teeth from 26 women who had horizontal incompletely impacted mandibular third molars in contact or not in contact with the second molars ( Figure 2) or molars isolated from the second or/and fi rst molars ( Figure 1) with or without acute infl ammation at the initial examination for diagnosis and treatment between April 1984 and March 1997 at Matsumoto Dental University Hospital, Oral and Maxillofacial Surgery Department (Table 1). Their chief complaints were exposure of tooth-like material, sense of discomfort, pain, or swelling. Acute infl ammation was diagnosed from redness, swelling, tenderness, and/or discharge of pus with spontaneous pain around the tooth, trismus, and dysphagia. Presence of a horizontal incompletely impacted molar was confi rmed with orthopantomographs taken with a Panoramax Auto 20 mA, 80-84 kVp (Asahi, Kyoto, Japan) and the fi lms were processed in an automatic developing machine (Konica SRX-501; Konica, Tokyo, Japan). Incompletely impacted third molars were horizontal to the second molar in angulation and were not fully covered with bone. Horizontal angulation was measured using horizontal lines drawn at various heights at which the occlusal plane of the second molar 7 or the fi rst molar when the second molar was lost, or the premolars when the second and fi rst molars were lost. The inclination of the occlusal plane of the third molar was read from the line on a compass. Teeth with inclinations of 70° or greater were selected as horizontal angulation following Shiller. 7 Measurements of radiograms were performed twice by the same experienced oral surgeon. The second time was performed after a period of months without seeing primary data. Mean values in measurements were calculated. Teeth with inclination of 69° or smaller on either measurement within two measurements were excluded from the study. Teeth were separated in three groups; a group of third molars in contact with the second molar in the presence of fi rst and second molars; a group of teeth not contact with the second molar; and a group of molars without second molars or without fi rst and second molars. Analysis was performed by comparing these groups. Patients with periapical lesions of the second and third molars, root fragments of these teeth, a radiographically true cyst or tumor in the molars, mesioangular impaction, a vertical impaction, or distoangular impaction and history of fracture were excluded from analysis. Horizontal incompletely impacted molar

Statistical analysis
Rates of teeth with acute infl ammation and ages of patients were calculated and analyzed statistically using Fischer's t-test or x 2 analysis, and Student's t-test among these groups.

Results
We studied 47 teeth from men and 28 teeth from women. The mean age of men was 55.89 ± 11.06 years (range: 41-81 years), and that of women was 51.29 ± 9.76 years (range: 41-73 years). No signifi cant difference was seen between men and women. Eight teeth (fi ve teeth in men and three teeth in women) that were horizontal impacted third molars not in contact with the second molar in the presence of fi rst and second molars were excluded from the present study in order to compare the solitary molars with the third molars in contact with the second molars ( Table 1). The results revealed that the mean age of 42 men was 57.10 ± 10.98 years (range: 41-81 years) and that of 25 women was 50.40 ± 9.11 years (range: 41-73 years). Differences between men and women were signifi cant (p Ͻ 0.05). None of patients showed bilaterally acute infl ammation.
Rates of teeth with acute infl ammation in men and women were as follows: 17 teeth, including eight teeth with acute infl ammation in teeth in contact with second molars, and nine solitary teeth with loss of the second molar or the second and fi rst molars out of 42 teeth in men, in whom 'no contact with molar' was excluded, accounted for 40.5%. Three teeth including one tooth with acute infl ammation in teeth in contact with the second molars, and two teeth in loss of the second molar or the second and fi rst molars out of 25 teeth in women, in whom 'no contact with molar' was excluded, accounted for 12%. Differences between men and women were signifi cant (p Ͻ 0.05).
On the other hand, the mean age of 48 subjects (28 teeth from men and 20 teeth from women) with third molars in contact with second molars was 50.42 ± 7.62 years (range: 41-72 years), and 19 subjects (14 teeth from men and fi ve teeth from women) without second molars or second and fi rst molars was 65.16 ± 10.41 years (range: 50-81 years). Signifi cant differences were seen between them (p Ͻ 0.0001). Nine third molars showed acute infl ammation out of 48 third molars in contact with second molars in men and women (18.8%), whereas 11 molars showed acute infl ammation out of 19 molars with loss of the second molar or the second and fi rst molars in both men and women (57.9%). The difference between third molars in contact with second molars and molars without second molar or second and fi rst molars was signifi cant (p Ͻ 0.01). Moreover, the mean age of nine subjects with third molars in contact with second molars with acute infl ammation was 53.44 ± 9.26 years (range: 43-67 years), whereas the mean age of 11 solitary molars with acute infl ammation was 67.45 ± 11.65 years (range: 50-81 years). A signifi cant difference was seen between them (p Ͻ 0.01).

Discussion
The present study showed a higher frequency of acute infl ammation in molars with loss of second molars or second and fi rst molars than third molars in contact with second molars in the elderly at the fi rst examination. The horizontal incompletely impacted molars were probably third molars because the space represents the width of the crown of lost teeth. These were shown to be characteristic in the elderly as the age of the population with loss of the second molars or second and fi rst molars was signifi cantly higher than that with third molars in contact with second molars, and the age of men was also signifi cantly higher than that of women, whereas pericoronitis is frequently seen between 16 and 30 years of age, 3 and more in females. 8 Our data shows that solitary horizontal incompletely impacted molar had an age-dependent increase in the risk of acute infl ammation. The plausible explanation is that causes of the high frequency of acute infl ammation in the elderly might be an easy eruption of the crown, 9 which has no periodontium, resulting from a natural bone resorption with increasing age or due to loss of the second and fi rst molars, increases the risk of acute infl ammation, probably through denser bone tissue than younger patients, and acute infl ammation might develop or be prolonged because of a higher tolerance for pain with cognitive impairment. This may support our previous report that noncontact with an adjacent tooth might be associated with purulent infl ammation in patients 45 years of age or older with completely impacted third molars. 10 Thus, among patients with a mandibular horizontal incompletely impacted third molar, those without adjacent tooth have a higher risk of acute infl ammation than those with adjacent tooth. This study shows that loss of adjacent tooth is predictor of acute infl ammation among the elderly with mandibular horizontal incompletely impacted third molar. This relationship may be dependent of aging. In fact, alveolar bone resorption takes place with increasing age, [11][12][13][14][15][16][17][18] resulting in low prevalence of completely impacted third molars in the edentulous jaw. 19 An incompletely impacted third molar might be removed because of possibility of acute infl ammation when the second molar was removed. Factors determining the alveolar bone resorption are gender 11,15,18,20 other than age, and bone resorption is signifi cant in women over 60 years old. 18 Time after extraction is also a factor, 12 and there is more alveolar ridge resorption after tooth loss in women than men. 20 Especially, earlier stages of edentulism 21 result in a high degree of mandibular residual ridge resorption in more than half the edentulous patients. 22 Such bone resorption has been usually measured with a panoramic radiograph. Recently, mandibular cortical width values were demonstrated to be stable in men over 60 years old. 18 These indicate that bone resorption after tooth removal should be inferred in not only vertical length but also horizontal width of alveolar bone to determine if a completely impacted third molar will be exposed with removal of the second molar.
Given the observation that rates of acute infl ammation in third molars was higher in men than women, although the mean age of men was signifi cantly higher than women, we should also consider whether gender differences affect local factors in molars with and without second or second and fi rst molars. This might be supported by the traditional attitude in the provinces that men are less likely to visit the dentist than women, as shown in the elderly in the north of England. 23 This seems to be a cultural difference, not only in England but also in Japan with implications in terms of health care provision, and suggests a cultural gender difference, as it is noted that women associate the impact of oral health with their feelings of attractiveness, 24 as shown by the observation that denture wearers were more likely to be female among an elderly institutionalized population. 25 On the other hand, although the occurrence of acute infl ammation has not been shown to be related to oral hygiene practices, 1 local factors such as food impaction in pockets around the crown or the inability to perform adequate cleaning due to the diffi culty of brushing solitary incompletely impacted molars located away from the fi rst molar or the premolars may result in insuffi cient tooth hygiene and a high prevalence of acute infl ammation. Points between different locations may be selectively controlled by local immunity associated with innate and adaptive immune responses to initiate a range of host defense mechanisms, since Muthukuru and colleagues 26 showed that gingiva is infi ltrated by large numbers of Toll-like receptor 2+ (TLR2[+]), and TLR4(+) cells increase in chronic periodontitis, and Erciyas and colleagues 27 showed that local immune response was poor in patients with chronic periodontitis. Further study is needed to assess whether the adjacent tooth protects the third molar by local immunity.
A study of the third molar in elderly has been restricted because of loss of teeth, and the third molar has been investigated in the presence of fi rst and second molars to ensure that it is the third molar. This does not always indicate problems in the elderly, and loss of these teeth based on tooth caries or periodontitis results in limited knowledge of the third molars. Although loss of the second molar or the second and fi rst molars should be interpreted with caution, fortunately, horizontal impaction allowed identifi cation of the third molar because impacted horizontally and solitary second or fi rst molars are extremely rare. This study was limited by small samples. Review of follow-up data is also needed in many cases.
In conclusion, patients may have quality of life deterioration when a horizontal incompletely impacted third molar is present under loss of the adjacent tooth since acute infl ammation in molars without second molars or second and fi rst molars increases along with aging and with possible bone resorption. These suggest an increased risk of acute infl ammation in patients who have had an adjacent tooth removed. Removal of the horizontal impacted third molar is recommended when the second molar is removed. This information could be useful for the diagnosis and treatment of not only solitary horizontal incompletely impacted molars but also horizontal incompletely impacted third molar in contact with decayed second molars.