Prospective study of soft tissue contour changes following chin bone graft harvesting

Abstract

This study sought to evaluate changes in the soft tissue contour after chin bone graft harvesting. Thirty selected patients underwent chin bone graft harvesting and evaluations were made using lateral cephalograms preoperatively and postoperatively at 30 and 180 days. Fixed points and lines were established on cephalometric tracings and used to measure the selected vertical and sagittal parameters. Results showed statistically significant alterations to the vertical position values of the vermilion (V-VPV) which increased from 9.70 to 11.01 and the exposure of lower incisors (V-ELI) which increased from 1.85 to 3.5, showing an increase in their distance from the plane of reference and a lowering of their position, the clinical equivalent of a labial ptosis condition. None of the sagittal parameters analysed showed any statistically significant variation in the final evaluation. The study concluded that the alterations to patients’ soft tissue contours resulted mainly from failure to ensure precise reattachment of the mentalis muscles and identified the need for further investigation of that aspect.

The use of autogenous bone grafts harvested from the mandibular symphysis has been widely reported as a reliable procedure offering easy access and bone tissue of a suitable quality . The bone tissue’s ectomesenchymal and membranous origin ensures early vascularisation and the maintenance of its volume and viability . Most of the patients undergoing this type of grafting procedure experience some postoperational morbidity but it is transitory and considered to be acceptable .

The use of this donor area is indicated in cases of alveolar reconstruction involving extensions of up to four teeth, or sites involving one or two teeth that require gains in alveolar height and/or thickness and also in the correction of alveolar-palatine clefts .

Most studies on mandibular symphysis grafts focus on the bone graft itself rather than on procedures to take care of the soft tissues involved , studies are needed to assess the alterations to soft tissues after the bone graft material has been harvested from this donor area. Accordingly, this prospective, non-randomized study analyses the alterations occurring in the surrounding soft tissues after the removal of chin bone grafts.

Materials and methods

This prospective, non-randomized study included 30 patients (22 women; eight men), aged 21–65 years (average 45 years) who needed to undergo the harvesting of a chin bone graft to be used in alveolar ridge augmentation pre-maxilla, preparatory to subsequent rehabilitation with implants. Patients were excluded if they: had undergone chin surgery; had no first or second molar or lower central incisors; or did not agree to participate in the study. Two surgeons conducted the operations using standard surgical techniques.

The surgical procedure to harvest the graft involved a horizontal incision in the alveolar mucosa in the inter-canine region, 5 mm below the mucogingival line. Subsequently an incision was made through the mentalis muscles on each side and on down to the bone. After carefully raising the muco-periosteal flap at the lower border of the mandible and locating the mental foramina, the osteotomy was carried out using a N° 702 cross-cut fissure burr. The form of each graft block removed was determined by the reconstruction it was destined for, but in every case a distance of at least 5 mm was maintained from the roots of the canine teeth, the mental nerves and the base of the mandible. The final separation and removal of the graft block was achieved using chisels. In all patients a 30 × 10 mm corticocancellous block was removed. Closure was carried out in two stages. The internal sutures consisted of three stitches using 3-0 suture catgut (Point Suture, Fortaleza, Brazil) and were designed to achieve precise repositioning of the mentalis muscles. A continuous suture using the same kind of catgut was used for closure of the mucosa. A microporous tape was then placed over the site to minimize oedema and haematoma formation. The tape was removed 72 h later.

Evaluation

To assess any alterations occurring in the soft tissues in the region, lateral cephalograms were taken preoperatively and postoperatively after 30 and 180 days ( Figs 1–3 ). All of the radiographs were made using the same technique, and the same X-ray machine and the cephalometric tracings were made by the same researcher on 0.07 mm acetate sheet using a 0.5 mm lead pencil. The cephalometric tracings were all done by the same professional individual and three separate tracings were made for each lateral cephalogram, at each one of the periods when they were taken. The measurements considered for research purposes were the average of the measurements obtained from the tracings.

Fig. 1
Preoperative lateral cephalogram.

Fig. 2
Postoperative lateral cephalogram after 30 days.

Fig. 3
Postoperative lateral cephalogram after 180 days.

The analysis of the soft tissue contours was based on a set of points and lines proposed by C haushu et al. ( Fig. 4 ): 1, mandibular occlusal plane (MOPL), a horizontal plane tangent to the uppermost points of the lower first or second molar and the lower incisor; 2, soft tissue menton (Mes), the most inferior point of the soft tissue of the chin; 3, soft tissue pogonion (Pgs), the most anterior point on the soft tissue of the chin; 4, soft tissue supramentale (Sms), the point of greatest concavity in the midline of the lower lip between the vermilion inferius and the soft tissue pogonion; 5, vermilion inferius (Vei), a point on the mucocutaneous border of the lower lip; and 6, the stomion inferior (Stoi), the uppermost point on the vermilion of the lower lip.

Fig. 4
Reference points and lines.
Source : C haushu et al. , adapted by the authors.

The analysis of soft tissue positions in the vertical direction made use of the following parameters ( Fig. 5 ): lower lip length (V-LLL), the distance from Stoi (6) to Mes (2), perpendicular to the MOPL (1); exposure of the lower incisors (V-ELI), the distance from Stoi (6) to the MOPL (1); vertical position of the vermilion (V-VPV), the distance from Vei (5) to the MOPL (1); vertical position of the soft tissue supramentale (V-VPSms), the distance from Sms (4) and the MOPL (1); and vertical position of the soft tissue pogonion (V-VPPgs), the distance from Pgs (3) and the MOPL (1).

Fig. 5
Reference points and lines used to evaluate changes in the vertical profile.
Source : C haushu et al. , adapted by the authors.

The analysis of soft tissue positions in the sagittal plane made use of the following parameters ( Fig. 6 ): lower lip thickness (S-LLT), the distance from Vei (5) and the lower incisor, parallel to the MOPL; soft tissue thickness at supramentale (S-SmTs), the distance from Sms (4) to the hard tissue, parallel to MOPL; soft tissue thickness at pogonion (S-PgTs), the distance from Pgs (3) to the hard tissue, parallel to MOPL; depth of mentolabial sulcus (S-MLS), the distance from Sms (4) to Vei (5), perpendicular to the MOPL; mentolabial angle (S-MLA), the angle formed by the intersection of tangents through Vei (5) and Pgs (3) drawn from Sms (4).

Fig. 6
Reference points and lines used to evaluate changes in the sagittal profile.
Source : C haushu et al. , adapted by the authors.

Statistical analysis

Initially an exploratory analysis was made using PROC LAB from the SAS statistics programme. In the case of the S-MLA variable it proved necessary to transform the data to a logarithmic format to carry out a parametric analysis, then analysis of variance (ANOVA) for repeated measurements was done and the Tukey test. The V-ELI variable was subjected to the Friedman non-parametric test with the data expressed in means, maximums and minimums, because it does not meet the requirements for conducting a parametric analysis. In all cases, the level of significance was 5%.

Results

Changes in the vertical parameters studied are given in Tables 1 and 2 . Statistically significant differences were observed for the variable lower lip length (V-LLL), which increased from 49.46 to 50.3 between preoperative and postoperative measurements at 30 days. In the comparison between preoperative and postoperative measurements at 180 days there was a statistically significant change in the variables exposure of the lower incisors (V-ELI) and vertical position of the vermilion (V-VPV), which also increased from 1.85 to 3.5 and 9.70 to 11.01, respectively.

Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Prospective study of soft tissue contour changes following chin bone graft harvesting
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