Cone-beam computerized tomography as a novel noninvasive method to determine the palatal grafts thickness

Prabhati Gupta; Suhail M Jan; Roobal Behal

doi:10.4103/2321-3841.144672

ORIGINAL ARTICLE

Year : 2014 | Volume : 2 | Issue : 3 | Page : 72-76

Cone-beam computerized tomography as a novel noninvasive method to determine the palatal grafts thickness

Prabhati Gupta, Suhail M Jan, Roobal Behal
Department of Periodontics and Oral Implantology, Government Dental College, Srinagar, Jammu and Kashmir, India

Date of Web Publication

14-Nov-2014

Correspondence Address:
Prabhati Gupta
70-D/C Gandhinagar, Jammu - 180 004, Jammu and Kashmir
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/2321-3841.144672

Abstract

Aim: The aim of this study was to apply a novel noninvasive method to obtain high quality images by cone-beam computerized tomography (CBCT) that consistently allowed the determination of the dimensions of palatal masticatory mucosa, which is the main donor area for soft tissue and connective tissue grafts used in periodontics, implant dentistry, and oral surgery. Materials and Methods: A total of 20 patients requiring palatal surgery participated. Thickness of the palatal tissue was measured at various points radiographically. At the time of the CBCT scanning, the patients wore acrylic measurement stent guides with radio-opaque markers at the measurement points. Results: The average thickness of the palatal mucosa was 2.96 mm in the canine area, 3.55 mm at the first premolar, 3.92 mm at the second premolar and 3.20 mm at the first molar. Statistically significant differences were observed as the distance from the gingival margin increased and the tissue over the premolars was found to be thicker than the other teeth. Conclusion: Cone-beam computerized tomography can be used as a noninvasive method accurately and consistently to determine the soft tissue thickness of the palatal masticatory mucosa at different locations on the palate.

Keywords: Cone-beam computerized tomography, connective tissue grafts, donor area, palatal masticatory mucosa

How to cite this article:
Gupta P, Jan SM, Behal R. Cone-beam computerized tomography as a novel noninvasive method to determine the palatal grafts thickness . J Oral Maxillofac Radiol 2014;2:72-6

How to cite this URL:
Gupta P, Jan SM, Behal R. Cone-beam computerized tomography as a novel noninvasive method to determine the palatal grafts thickness . J Oral Maxillofac Radiol [serial online] 2014 [cited 2023 Mar 29];2:72-6. Available from: https://www.joomr.org/text.asp?2014/2/3/72/144672

Introduction

The palatal masticatory mucosa is the main donor area of soft tissue and connective tissue grafts used for increasing the dimensions of keratinized mucosa around teeth and implants, covering exposed roots and increasing localized alveolar ridge thickness. Connective tissue grafts are also well indicated to enhance the probability of complete root coverage when associated with coronally advanced flaps in certain types of gingival recessions. ^[1]

A critical aspect in the treatment planning of these cases is the determination of the thickness of the graft donor site, since the thickness of tissue grafted from the palate to the recipient site directly affects the surgical outcome. ^[2] Revascularization of the graft may be prevented if the donor tissue is too thick and graft shrinkage may occur if the tissue is too thin. To prevent these undesirable outcomes, methods have been developed to help the clinician determine the thickness of the palatal masticatory mucosa prior to harvesting the graft. One such method is the use of ultrasonic measuring devices that transmit ultrasonic pulses through the soft tissue and uses an echo of the pulse to calculate the thickness. ^[3] Another frequently used method is the bone-sounding technique, a direct method that involves anesthetizing the patient and subsequently penetrating the palatal masticatory mucosa with either a periodontal probe or needle to determine tissue thickness. While highly accurate, a drawback to this method is that it is commonly performed immediately prior to surgery as the patient must be anaesthetized. This may hinder appropriate treatment planning of the procedure as the clinician may find that there is not sufficient tissue thickness in the preanesthetized area. ^[1]

Cone-beam computerized tomography (CBCT), in particular, has been used since its development in the 1990s for imaging of the maxillofacial region. ^[4] Compared to conventional computerized tomographic (CT) systems, CBCTs produce a more focused beam, less radiation scatter, ^[5] and more rapid volumetric image acquisition, ^[6] along with being smaller in size and less expensive. In addition, CBCT has become popular for three-dimensional imaging in the dental field both because of its high spatial resolution and clear images on scans, and its relatively low radiation dose, which is similar to a full mouth series of periapical films ^[7] and well below that of classic CT. ^[8] A benefit of the use of CBCT scans in dental imaging that has gained much attention in the recent literature is its accuracy in reproducing linear dental measurements. ^[9]

It reported in 2008 that CBCT can be applied for visualizing and measuring soft tissues of the dentogingival unit. ^[10] In 2009, it was reported that CBCT can also be used for assessing and measuring palatal masticatory mucosa. ^[1] But there is limited knowledge of individual thickness and regional differences of the palatal mucosa. So, the aim of this study was to apply a novel noninvasive method to obtain high-quality images by CBCT that consistently allowed the determination of the dimensions of palatal masticatory mucosa.

Materials and Methods

Twenty systemically healthy subjects (10 males, 10 females), ages ranging from 19 to 53 years (mean age of 32 years) requiring palatal surgery were selected from the Department of Periodontics, Government Dental College and Hospital, Srinagar for the study. Informed written consent of subjects and ethical committee clearance was obtained prior to commencement of the study. Inclusion criteria for the selection of subjects for the study were the presence of all maxillary teeth, except third molars. Subject exclusion criteria were history of palatal surgery, history of presence of pathology in the area being investigated and pregnancy.

After the subject was deemed eligible, a maxillary impression was made with alginate impression material and poured in a Type III dental stone. Acrylic measurement guides (Clear Splint Biocryl, 0.5 mm thickness were then fabricated on the cast model and trimmed appropriately to include all teeth present in the arch. Using a standardized UNC-15 probe (Hu-Friedy), measurements were made at distances of 2 mm, 5 mm, and 8 mm from the mid-palatal point of the gingival margin for the canine, first and second premolars, and the first molar on both the sides. A hole was subsequently punctured through the acrylic stent at each measurement point [Figure 1]. Gutta-percha was used to fill each measurement site [Figure 2]. The purpose of the gutta-percha was to have a radio-opaque marker on the CBCT scan. This stent was subsequently used for all radiographic measurements.

Figure 1: Measurement stent on cast with holes punctured at the measurement sites

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Figure 2: Measurement stent on cast with gutta-percha as radio-opaque markers

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All subjects wore the CBCT stent during the CBCT scan. During CBCT scans, patients were seated and had their heads and chins stabilized. Each patient was asked to bite a wooden spatula placed across a mouth at the level of the maxillary and mandibular molars (first and second molars) to prevent the tongue from touching the soft and hard palates during image acquisition. Together with the wooden spatula, a plasic lip retractor was placed in the patient's mouth so that the cheeks did not touch the facial aspects of the teeth, thus also allowing the facial gingiva to be visible. A scan of the maxilla was taken using the CBCT unit (New Tom Giano, Qr S.R.L.,20-Verona Genoa, Liguria-37135, Italy) by a trained technician at 110 KVp and 15 mA for 36 s (voxel size: 0.25 mm; grayscale: 12 bis). The reconstructed images were generated using a computer software package (Keystone Easy Guide, Keystone Dental, Inc., Burlington, MA). Each gutta-percha point was visualized using a sagittal view and measurements of the soft tissue thickness were made at each point by one investigator and recorded. All measurements were made perpendicular to the palatal soft tissue. Twenty-four total radiographic measurements were taken on each scan (for canine, first and second premolars and first molar at the distances of 2 mm, 5 mm and 8 mm from gingival margin on both right and left sides of the maxilla). Data were analyzed with the help of means and standard deviations. For inter-group analysis, t-test was applied. ANOVA test was used for intra-group analysis. P < 0.05 was considered as statistically significant.

Results

[Figure 3] and [Figure 4] show the representative CBCT images of the measurements performed at the distance of 5 mm and 8 mm from the gingival margin in case of the first premolar. [Table 1] shows the mean thickness with standard deviations of the palatal mucosa (right and left sides) in different teeth, at different heights of the measurement in male and female subjects.

Table 1: Mean thickness with SD of the palatal mucosa in different teeth, at different heights of measurement in male and female subjects

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Figure 3: Representative cone-beam computerized tomography scan showing the radiographic measurement at 5 mm

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Figure 4: Representative cone-beam computerized tomography scan showing the radiographic measurement at 8 mm

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The thickness of the soft tissue, as estimated by the statistical analysis, was influenced by palatal location. Both the distance from the tooth and the tooth type were significantly related to the depth (P < 0.001). The tissue became thicker as the distance from the tooth increased [Table 1] and [Graph 1]. [Additional file 1] In all the teeth, the palatal mucosa was thicker at 8 mm when compared with those closer to the gingival margin (2 and 5 mm). Also, the tissue measured at the premolars was thicker than that measured at the molar or canine areas [Table 2]. No, statistically significant difference was found between male and female subjects. Also, the measurements were similar on both the sides (right and left sides). There was a tendency for thicker masticatory mucosa to be found in older subjects (above 40 years old) when compared to younger patients (below 40 years old).

Table 2: Mean thickness with SD of the palatal mucosa in different teeth

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Discussion

Successful surgery depends on several factors, such as a sufficient blood supply to the graft, minimal damage at the donor site and the patient comfort after the surgery. These factors require the anatomical knowledge of the palatal mucosa and the greater palatine artery, which supplies the palatal gingiva with blood for the determination of the optimal treatment plan and prognosis. Over the past two decades, the use of CBCT for imaging of the maxillofacial region has increased dramatically. ^[4] This study describes a noninvasive technique based on CBCT, which consistently produces images that allow the measurement of the dimensions of the palatal masticatory mucosa.

In 2008, Song et al. demonstrated the possibility to measure the thickness of the palatal masticatory mucosa on images obtained by conventional CT. ^[11] Compared with conventional tomography, CBCT presents advantages such as lower radiation, better image quality, greater comfort for the patient and lower cost. Another important factor reported here is the possibility of evaluating both sides of the maxilla in the same image, providing the dentist with options to choose the side he/she thinks is the best donor area. ^[1]

The gingiva and the mucosa of the hard palate are two distinct soft tissues and together they represent the masticatory mucosa. ^[12] There is considerable intra-individual and inter-individual variation in the thickness of this mucosa. Thin (<0.05 mm) or intermediate (0.05-0.75 mm) thickness grafts are used for increasing the width of attached gingiva and thick (0.75-1.25 mm) or full thickness (>1.25 mm) grafts are used for ridge augmentations and root coverage procedures. ^[2] Grafts with thickness 1.25-2 mm are thick enough to sustain themselves over avascular root surfaces while thinning without splitting until the plasmatic diffusion can be effective. They have greater primary contraction owing to a large amount of elastic fibres but minimal secondary contraction because of thicker lamina propria.

The CBCT technique presented here is certainly an excellent tool to determine the location from where a soft tissue graft may be harvested, thus enabling more accurate treatment planning of procedures prior to the surgical appointment. The technique described in the present study reveals a high-quality image of the hard (teeth and bone), and soft (facial and palatal gingiva) tissues and allows measurements of the dimensions and relationships of these structures. A clear visualization of the palatal mucosa is evident in the images, and precise measurement of its thickness can be performed. Furthermore, because the aspect ratio of the images obtained by CBCT is 1:1 and these images can be saved and printed, repeated measurements can be performed either on a computer screen or on hard copies. ^[10],[11] It is important to mention here that this is a quantitative and not a qualitative method because the differences between the epithelium, fat and connective tissues cannot be seen on the images.

In the present study, measurements were made at the distances of 2 mm, 5 mm, and 8 mm from the mid-palatal point of the gingival margin for the canine, first and second premolars, and the first molar on both the sides. Free gingival grafting and subepithelial connective tissue grafting involves the use of a horizontal incision, perpendicular to the underlying bone surface which is made approximately 2-3 mm apical to the soft tissue gingival margin. According to a study conducted by Ramesh et al. in 2014, ^[13] the most appropriate donor site for carrying out grafting procedures is distal canine to mid-palatal aspect of first molar area with a minimum height of 5 mm to 8 mm in the premolar area in all cases. Keeping in view all these facts and observations, these points (2 mm, 5 mm and 8 mm) were selected for measurement of palatal mucosal thickness.

In this study, the mean thickness of the palatal mucosa varied according to different regions of the palate. At the level of the canines, the thickness was 2.96 mm; 3.55 mm at the first premolar region; 3.92 mm at the second premolar and 3.20 mm at the first molar region. These measurements were similar to those reported in previous studies using other methods to assess gingival thickness. ^{[1],[2],[3],[14]} The results of the other studies and this study on thickness of palatal mucosa are tabulated as follows:

In the present study, there was no statistically significant difference of palatal tissue thickness between males and females. This result was consistent with those of previous studies by Studer et al. 1997, ^[14] Wara-aswapati et al. ^[2] and Barriviera et al. 2009 ^[1] but inconsistent with those of other studies by Muller et al. 2000 ^[3] and Song et al. 2008. ^[11] Our results also show an increased thickness of the palatal mucosa at higher measurements; that is, the farther away from the gingival margin, the thicker the palatal mucosa was in all teeth of all patients. There was a tendency for a thicker palatal mucosa to be found in older patients when compared with younger ones, which is consistent with the findings reported by Song et al. ^[11]

Since the palatal mucosa is widely used as an autologous donor graft material, there is growing interest in the determination of the anatomical location of greater palatine neurovascular bundle which is the most important structure associated with the palatal mucosa. According to a study conducted by Cho et al., ^[15] the greater palatine artery is located 10.72 mm from the alveolar crest and 4.38 mm from the surface of the palatal mucosa in the palatal region between the first premolar and the first molar. Therefore, the free gingival graft and the connective tissue grafts at approximately 8 mm from the alveolar crest could be a suitable donor site during subepithelial connective tissue grafting that involves taking a dense wedge-shaped piece of connective tissue. ^[15] Thus, CBCT being a noninvasive reliable method that accurately and consistently provides the thickness of the palatal mucosa at different locations on the palate may prevent any damage to this greater palatine neurovascular bundle during the surgical procedure.

Conclusion

Cone-beam computerized tomography can be used as a noninvasive method to accurately and consistently determine the soft tissue thickness of the palatal masticatory mucosa at different locations on the palate. This reliable, simple and reproducible method could provide important benefits in planning dental procedures, especially in periodontics, implant dentistry and oral surgery. Further studies on the use of this technique for other applications for soft tissue visualization must be performed.

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