Assessment of thickness of palatal mucosal donor site and its association with age and gender.

AIM: The purpose of the study is to determine the thickness of the palatal mucosa by a direct clinical method, and the association of age and gender with the thickness of the palatal mucosa.
MATERIALS AND METHODS: Forty systemically and periodontally healthy Indian subjects participated in the study. The subjects were categorized according to age and gender. The thickness of the palatal mucosa was assessed by bone sounding. Acrylic stents provided 15 consistent locations for the measurement, defined according to the gingival margin and mid-palatal line.
RESULTS: The mean thickness of palatal mucosa was 2.48΁0.03 mm, ranging between 2.07 and 3.00 mm, among the participants. The younger age group had significantly thinner mucosa than the older age group. Females had thinner palatal mucosa than males, but not statistically significant.
CONCLUSION: The palatal area from the distal line angle of the canine to the mesial line angle of the palatal root of the first molar provides sufficient donor tissue for grafting procedures. Factors such as body weight and genetic factors need to be further investigated. As the dimension of the soft tissue graft is an important factor influencing the success of the treatment procedure the assessment of the dimension is relevant to clinical periodontics.

INTRODUCTION

The use of free palatal grafts finds a routine application in reconstructive periodontal procedures, such as, root coverage, ridge augmentation, natural GTR membrane and so on.[1-4] One of the contraindications of palatal graft harvesting relates to the palatal area that fails to provide adequate donor tissue, either as a result of palatal anatomic form[3] or insufficient thickness of the harvesting soft tissue.[5] As the dimension of the donor graft tissue plays an important role in the clinical outcome of periodontal plastic surgical procedures, it is important to determine the available dimension of the palatal donor tissue prior to harvesting, without violating the neurovascular bundles.[36-9]

MATERIALS AND METHODS

The protocols for the human subjects were approved by the Vinayaka Mission Dental College Review Committee and the study was conducted in accordance with the Helnisinki Declaration. Forty systemically healthy individuals in age group of 17-45 years of age were selected for the study after providing informed consent.

Patients were grouped as (20 patients in each group):

Group I: Younger age group between 17 and 29 years

Group II: Older age group between 30 and 45 years

The inclusion criteria were, healthy periodontal tissue with no loss of attachment and no probing depth >4 mm in the upper arch with / without the third molar, no prosthetic appliances, healthy mucosa, no drug intake, which could influence the volume of the mucosa, no alcohol abuse and smoking habits, no pregnancy or lactation, no fixed partial denture between the upper canine and the second molar and no tooth malposition, rotation, or spacing.

After explaining about the objectives of the study, the expected outcomes, and the degree of discomfort that might occur, the subjects gave their consent. In the first visit, an upper arch impression was taken using an alginate impression material. A study model and a clear acrylic stent were fabricated. Fifteen measurement points were defined and marked [Figure 1] on the study models as described by Wara-aswapati et al.[9]

Figure 1

Dental cast with the reference-points marked

The gingival margin is represented as line a. Three lines (b, c, and d) run parallel to line a. Line b run 3 mm from the gingival margin. Line c and d are located a quarter and half the distance between line b and line M, respectively. Line Ca, P1 , and P2 are positioned at the mid-palatal aspect of the canine (tip of the canine), first premolar (palatal cusp), and second premolar (palatal cusp), respectively. Lines M1 and M2 run through the mesiopalatal cusp of the first and second molars, respectively. Holes were created on the stent at the points where lines Ca, P1 , P2 , M1 , and M2 intersected with lines b, c, and d, at 90° to the surface of the stent. The prepared stent provided a consistent location for the assessment of mucosal thickness.

On the second visit, the palatal mucosa was anesthetized with a local anesthetic, which had a vasoconstrictor. Precautions were taken to prevent inadvertent volume increase of the mucosa, induced by the local anesthetic, by using minimal amount of anesthetic solution (0.1 ml) and by slowly injecting the solution. The thickness measurements were performed 20 minutes after the injection. With the stent placed properly on the upper arch, the 15 measurement points on the palate were marked with an indelible pencil according to the holes prepared on the stent. The anesthetized palatal masticatory mucosa was measured by ‘bone sounding’ after removing the stent, using a UNC - 15 periodontal probe with a rubber stopper [Figure 2]. The rubber stopper was placed in contact with the mucosal surface, for accurate measurement. The probe with the rubber stopper securely in place was then lined up against a 0.5 mm scale; sterile, stainless steel ruler, and the value was consistently rounded up to the nearest 0.5 mm. When the measurement point was on the rugae area, the base of the rugae, not the hill, was chosen as the measurement point. All measurements were done twice, at 10 minute intervals, by the same investigator. The average of the two measurements was used as the final measurement for the thickness at each location. Comparison of the mean mucosal thickness at the subject level, by age and gender, was done by multiple linear regression analysis. The Wilcoxon test was used to determine the difference in mucosal thickness between the age and genders at each measurement point.

Figure 2

UNC-I5 periodontal probe

RESULTS

The palatal masticatory mucosa was measured for thickness and ideal site for grafting procedures in 40 systemically healthy individuals. The measurements were compared between the younger and older age groups and between men and women.

Table 1 presents the mean scores of palatal thickness at the subject level. The mean thickness of palatal mucosa was 2.48±0.03 mm, ranging between 2.07 and 3.00 mm among the participants. The mean thickness of palatal mucosa for men was 2.54±0.04 mm, ranging between 2.23 and 3.00 mm, and for women 2.42±0.05 mm, ranging between 2.07 and 2.80 mm. The mean thickness of the palatal mucosa for younger age group (group I) was 2.40±0.04 mm, ranging between 2.07 and 2.80 mm and for the older age group (group II) 2.56±0.04 mm, ranging between 2.23 and 3.00 mm [Figure 3]. The younger age group had significantly thinner mucosa than the older age group. Females had thinner mucosa than males, but the difference was not statistically significant.

Table 1

Mean thickness of palatal masticatory mucosa by age group and gender at the subject level

Figure 3

Subject level mean thickness of masticatory mucosa for Groups I and II; and male and female

Analysis of the palatal masticatory mucosa at each measurement point [Table 2, Figure 4] indicated that the palatal mucosa was thinnest at the canine region, increased distally, and became thickest at the second molar area, and also in sites farther from the gingival margins. The exception was at the first molar region on line c (1.28±0.30), where the palatal mucosa was considerably thin compared to the premolar and molar regions on the same line. The mean thickness ranged between 1.93 mm at the canine region on line b and 5.63 mm at the second molar on line d. The thickness of the palatal mucosa increased as the distance from the gingival margin increased except on line c at the molar area. The older age group showed a thicker palatal mucosa [Table 3] than the younger subjects, particularly at the canine, premolar, and molar areas on line b, and on line d at the canine region (statistically significant P<0.05). The younger age group showed a thicker mucosa than the older age group at the second molar region on lines c and d. Men had a statistically significant (P<0.05) thicker mucosa [Table 4] in the canine, first premolar, and second molar areas on line c, and in the second molar area on line d. As an exception, the females had a thicker mucosa at lines b and d at the first molar.

Table 2

Mean thickness of palatal masticatory mucosa in millimeters by age group and gender at 15 individual points

Figure 4

Overall (Groups I and II) thickness of masticatory mucosa at 15 individual points

Table 3

Wilcoxon test for age group difference P value

Table 4

Wilcoxon test for gender difference P value

DISCUSSION

The study evaluated the thickness of palatal masticatory mucosa in Indian subjects of age between 17 to 49 years, using ′bone-sounding′ (transgingival probing technique). The mean thickness of the palatal mucosa ranged between 2.07 and 3.00 mm. The younger age group had significantly thinner mucosa than the the older age group. Females had thinner mucosa than males, but the difference was not statistically significant. The palatal area from the distal line angle of the canine to the mesial line angle of the palatal root of the first molar provided sufficient donor tissue.

The thickness of masticatory mucosa is evaluated by invasive and non-invasive methods. The invasive method uses sharp cannulas, measurement of histological sections, graduated periodontal probes, endodontic reamers or conventional histology on the cadaver jaws.[4-9] Non-invasive methods involve the use of ultrasonic devices.[10-14]

Wara-aswapathi et al.[9] and Studer et al.[8] assessed the thickness of the palatal mucosa by using transgingival probing, Vandana and Savitha,[14] by using an ultrasonic device, found thicker mucosa in men. However, the results were not statistically significant. Müller et al.,[10] utilizing ultrasonography and Stipetić et al .[7] using the transgingival probing technique also demonstrated significantly thick palatal masticatory mucosa in men.

It is possible that the thickness of the orthokeratinized epithelial layer of the hard palate mucosa increases with age, resulting in a thicker palatal mucosa in older subjects, observed in this study. With increasing age, the number of cellular elements decreases, but results in a more coarse and dense gingival tissue.[15]

In addition, the hard palate possesses a submucosal layer, which contains various amounts of adipose tissue and small mucous glands.[16] The structural changes in the epithelium and connective tissue, with age, is controversial.[1718] Vandana and Savitha[14] studied the thickness of the gingiva in association with age and found the gingiva to be thicker in the younger age group than in the older.

The optimal thickness of palatal mucosa required for various grafting procedures demonstrated by different studies are: 1.5-2.0 mm (Goldman et al.),[19] 0.9 mm (James and Macfall),[20] 2.0 mm (Miller),[21] 1.0-1.5 mm (Maynard),[22] and 0.8-1.3 mm (Soehren et al.).[5] A free palatal graft of 0.9 mm thickness proved to be functionally sufficient regardless of whether they healed on denuded alveolar bone or a periosteal bed.[20]

In younger and older subjects, from all the areas on lines b, c, and d, mesial to the second molar it is possible to harvest the epithelialized graft of thickness 1.5 mm, except from the first molar on line b and c. The palatal root of the first molar acts as an′anatomical barrier,′ limiting donor tissue volume.[8] In addition, it is not advisable to harvest soft tissue grafts beyond this structure, to avoid increasing a risk of accidental damage to the greater palatine artery or its branches.[3] It is also possible to harvest connective tissue grafts, excluding the epithelium. From areas on line c and d, at the canine and premolar areas, it is possible to harvest a graft of 2 mm thickness. The area of the palate from the distal line angle of the canine to the mesial line angle of the palatal root of the first molar provides sufficient donor tissue for grafting procedures[789] and also reduces the risk of violating the associated neurovascular structures.[3] If the palatal donor site is found to be inadequate for harvesting, graft tissues, options can be augmenting thee palatal connective tissue area, which can subsequently be used for connective tissue grafting.[23]

According to Coslet et al.[2] and Breault et al.,[24] return of the palatal rugae was observed several months postoperatively. Thus, the canine and premolar areas appeared to be the most appropriate donor site for grafting procedures.

The palatal neurovascular bundle, which is housed in a palatal groove and located approximately 7 to 17 mm from the cementoenamel junction (CEJ) of the upper premolars and molars (depending on the shape of the palatal vault), may have an effect on the measurement, if the probe penetrates into the neurovascular structures.[39] However, in the present study, there were no clinical indications that the neurovascular bundle had been penetrated (such as bleeding after probing, hematoma formation, or paresthesia). When the mucosal thickness at the canine and premolar areas was compared with that reported by Studer et al.[8] in Caucasians and Wara-aswapathi et al.[9] in Asian subjects, using the same measurement method, it was found that the thickness obtained from subjects in the present study was smaller. This may be partly due to ethnic differences. The measurements in the study conducted by Stipetić et al .[7] are concordant with the present study.

‘Bone-sounding’ or the transgingival probing technique using a periodontal probe and minimal local anesthesia, along with a prepared clear acrylic stent, to ensure consistent locations for the repeated measurements, was employed in this study to assess the thickness of the palatal mucosa. The transgingival probing method was cost effective and easy to perform.[6] In the hard palate area, a measurement error of 0.2 mm was reported when the mucosal thickness was assessed by ‘bone sounding’.[8]

In recent times, an ultrasonic device has been introduced to measure the thickness of most parts of the oral masticatory mucosa.[13] Eventhough it is an atraumatic method, at sites where mucosal thickness exceeds 2-2.5 mm, ultrasonic measurements are non-reliable.[25] It is difficult to access and ideally position the ultrasonic probe.[13] Ultrasonic devices need a lot of knowledge for interpretation, are relatively unavailable, and are expensive. Thus, simple bone sounding is the method of choice.[7] Müller et al. found a measurement error of 0.54 mm when the palatal mucosal thickness was examined using an ultrasonic device.[10] This was attributed to difficulties in locating the same measurement site, the varying thickness of the tissues, and the presence of palatal rugae. Hence, to overcome these problems conventional transgingival probing was utilized in the present study, to assess the thickness of masticatory mucosa. Terakura,[12] observed high correlation between transgingival probing and ultrasonic methods, and suggested reliable results with transgingival probing. Direct measurements with sharp cannulas showed higher thickness values than measurement with blunt periodontal probes or ultrasonographic measurements.[4] These higher thickness values might be due to the penetration of the sharp cannula into the periosteum or the porous palatal bone.

There are many factors that may influence the palatal submucosal thickness such as race, genetic factors, age, gender[89] dental arch, periodontal phenotype,[11] body weight[7] and so on. The amount of adipose tissue in the palatal submucosal layer may results in an increased thickness of the palatal mucosa. The effect of the body mass index (BMI) on palatal mucosal thickness was investigated and showed positive results.[47]

CONCLUSION

The mean thickness of the palatal mucosa ranged between 2.07 and 3.00 mm among the participants. Based on the comparison of the measurements of thickness of the palatal mucosa between genders and age groups, the older age group had a significantly thicker palatal masticatory mucosa than the younger age group; the difference in thickness between the genders was not significant. The canine-premolar area provided an adequate site for harvesting soft tissues grafts, without violating the neurovascular bundles.