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Evaluation of the accuracy of measuring the thickness of palatal tissue by different methods

The main donor graft has the palatal mucosa as the main donor area, widely used to increase the thickness of the alveolar ridge, to increase the dimensions of keratinized tissue around teeth and implants.1–6 Connective tissue grafts are also well recommended to improve the chance of covering gingival recession.7,8 The thickness of connective tissue is important in view of the fact that very thin or too thick grafts can lead to the failure of the procedure.9 Although knowing the palatal mucosa thickness would be important to improve the predictability of the result of various surgical procedures, this preoperative assessment of the donor area thickness is ignored due to the lack of reliable methods for this purpose.Applying conventional histology, studies were performed on cadavers to determine the thickness of the palatal mucosa10–12, we had a general idea of the best area for graft removal. However, each area and patient has variations in the amount available for removal. Invasive methods, such as the use of needles,2,13 endodontic files14 and periodontal probes15–19 have been described in the literature. These methods have a great disadvantage because they require the use of local anesthesia and are performed shortly before graft removal, not allowing an accurate pre-surgical planning of the procedure.The use of an ultrasound device is a non-invasive method, it has also been described in the literature, however, this method has a certain degree of complexity in obtaining results.11,14,20,21


Introduction
The main donor graft has the palatal mucosa as the main donor area, widely used to increase the thickness of the alveolar ridge, to increase the dimensions of keratinized tissue around teeth and implants. [1][2][3][4][5][6] Connective tissue grafts are also well recommended to improve the chance of covering gingival recession. 7,8 The thickness of connective tissue is important in view of the fact that very thin or too thick grafts can lead to the failure of the procedure. 9 Although knowing the palatal mucosa thickness would be important to improve the predictability of the result of various surgical procedures, this preoperative assessment of the donor area thickness is ignored due to the lack of reliable methods for this purpose.Applying conventional histology, studies were performed on cadavers to determine the thickness of the palatal mucosa 10-12 , we had a general idea of the best area for graft removal. However, each area and patient has variations in the amount available for removal. Invasive methods, such as the use of needles, 2,13 endodontic files 14 and periodontal probes [15][16][17][18][19] have been described in the literature. These methods have a great disadvantage because they require the use of local anesthesia and are performed shortly before graft removal, not allowing an accurate pre-surgical planning of the procedure.The use of an ultrasound device is a non-invasive method, it has also been described in the literature, however, this method has a certain degree of complexity in obtaining results. 11,14,20,21 To analyze the maxillofacial region, conical beam computed tomography (CBCT) has been widely used. 4,5,22 CBCT technology is an essential tool in dentistry, offering high quality images to aid diagnosis. It has long been described that CBCT is not recommended for evaluation of soft tissues, being considered a tool to exclusively evaluate hard tissues of the maxillofacial complex. 5 However, recently, information was obtained from evaluations that demonstrate that CBCT can be applied to visualize and measure soft tissues in the gingival region. 22 In a recent retrospective study, images obtained by computed tomography (CT) beam were analyzed, and the thickness of the different regions of the palatal masticatory mucosa was determined with these images. 23 However, the method has been described as unreliable using images to assess these measures.Due to the limited knowledge of the individual thickness and regional differences of the palatal mucosa, a method based on the CBCT technology has been developed to consistently visualize and effectively measure the dimensions of the palatal mucosa. 23 The aim of this study was to evaluate the accuracy of measuring the thickness of palatal tissue by different methods.

Material and method
A male individual aged 64 years was evaluated. The individual sought the Implantology Service of the Metropolitan University of Santos to install implants in the posterior maxilla. The individual was molded with Hydrogum irreversible hydrocolloid (Zhermack, BadiaPolesine (RO), Italy) to make an individual tray on an acetate plate (Figure 1), where on this plate 3 markings were made on the palate, at a distance of 5 mm from the cervical palate of the first molar, second premolar and first premolar teeth, these holes were filled with zinc phosphate.An ORTHOPHOS XG 3D Cone-Beam Computed Tomography -PAN / TELE / TOMO (Sirona Dental Systems GmbH, Bensheim, Germany) was performed for evaluation and possible implant installation, the individual used the acetate plate with the markings to perform the tomography, as well as the lip retractor so that the lips and cheek do not disturb the taking of the image following the technique of Barriviera et al. (2009).A mold was made for making a model in special stone type IV Durone (Dentsply), which was scanned by the InEos Blue device (Sirona Dental Systems GmbH, Bensheim, Germany).
The individual was also scanned directly in the mouth using Open Access J Sci. 2020;4(2):61-64.
the Trios scanner (3Shape, HolmensKanal 7. 1060 Copenhagen K Denmark). To measure the markings, three methods were used, directly in the tomographic image (Group 1) (Figure 2), in the superimposition of the computed tomography and the scanning of the plaster model (Group 2) ( Figure 3) and in the superimposition of the computed tomography and scanning in mouth (Group 3) (Figure 4).The Blue Sky Plan software (800 Liberty Drive Libertyville, IL 60045 United States) was used to overlay the images ( Figure 5). During the implant installation surgery, the measurement considered in this study as the gold standard was performed, at the time of anesthesia, using the needle with an endodontic stop and with an individualized acetate tray in position, the punctures were performed in the places marked at 5 mm of the cervicals of the determined teeth ( Figure 6). The needle with the obtained thickness was photographed and measured using the ImageJ64 image software (Wayne Rasband National Institute of Health, USA) (Figure 7).        Figure 8 demonstrates the evaluation of group 1 evaluation only CBCT Figure 9 demonstrates the evaluation of group 2 the overlapping of CBCT and the scanning of the plaster model and Figure 10 demonstrates the evaluation of group 3 the overlapping of CBCT and scanning of plaster mouth. In Table 1, group 1 was the one that presented values closer to the gold standard values.

Results
In Table 2, the first Premolar and first Molar regions were the regions that showed the smallest difference when compared to the gold standard.

Discussion
The thickness of the palatal mucosa is characterized by variations that correlate with the dental regions, 2,11 the second premolar region in this study presented the region with the largest thickness of the palatal mucosa when compared to the molar and first regions of pre- molar distance of 5 mm from the cervical of the teeth. Other studies characterize the region between premolars and canine as an area with better mucosa conditions, in addition to being thicker. [15][16][17][18][19] The palatal mucosa is the main donor area for use in various procedures when soft tissue is used, 1,3 there are several methods for assessing the amount of palatal mucosa invasively, using cannulas and probes, 2 the noninvasive method using techniques based on computed tomography cone beam (CBCT) is being used to obtain high quality images of the palatal mucosa, and can be very reliable to visualize and measure the thickness of the mucosa. 4,22,23 Other studies also confirm the results obtained in this study, the efficiency of the use of CBCT, allowing a clear visualization, making it possible to measure the dimensions and analyze the relationship between soft and bone tissue structures, assisting clinicians in planning preoperative. 21     Evaluating the best way to select the location of the donor area and even projecting the thickness and quantity to be collected, it is possible to evaluate it through ultrasonic evaluation, 20,21 but only mucosa. This study, on the other hand, proves the possibility of evaluating by means of cone beam computed tomography the alveolar bone set and the palatal mucosa structure. Several other studies have demonstrated this possibility. 4,22,23 In the treatment of cleft palate, the main threedimensional techniques for assessing the soft tissues used are CT, CBCT, magnetic resonance imaging, stereo photogrammetry and scanning the laser surface. These techniques are mainly used for soft tissue analysis, bone graft evaluation and changes in the craniofacial skeleton. 7 Scanning techniques in the mouth and digital dental molds have been transforming into a possibility of evidencing and determining digital palatal mucosa over time, the available evidence implies that 3D imaging methods can be used to assist in the assessment of mucosal soft tissue palatal. 7 In this study it was found that CBCT presented results with values closer to the gold standard than those with overlapping digital images.

Conclusion
According to this study and its limitations, the group 1 method (CBTC) was the one that came closest to the gold standard in the three measured points, when compared with the other methods. Therefore, the use of CBCT to assess the thickness of the palatal mucosa is the most indicated.