Soft-tissue graft design for an average single-tooth defect in the posterior region

3HVBH ORAL COMMUNICATION CLINICAL INNOVATIONS

Background: Soft tissue augmentation is necessary to regain reduced or lost tissue in edentulous patients. Autologous soft tissue grafts are the gold standard despite drawbacks: limited tissue availability, invasive surgical procedure, and patient pain/discomfort. Moreover, different geometries of individual tooth defects require chair-side graft shaping prior application. To avoid complications at the donor site, xenogenic and allogenic matrices were developed. However, they also need shape adjustments.

Aim/Hypothesis: This study aimed to develop a standardized procedure for designing average grafts adapted to optimally fit the common single-tooth soft tissue defects in the posterior jaw region.

Materials and Methods: Casts from 33 patients with single tooth defects in the posterior region of the upper and lower jaws were collected and scanned. The grafts were designed with the 3Shape dental designer based on an incision line placed 1.5 mm away from adjacent teeth and extended 4 mm down to the vestibular side. A systematic procedure was developed using GOM inspect software to standardize the measurements across all grafts. The occlusal, mesial-distal and buccal-lingual planes were defined to section the graft, and each graft was represented as a mesh of 1 mm³ cubes. The thickness values of each cube were documented in a coordinate system chart with the corresponding mesial-distal and buccal-lingual orientations. Orange software was applied on each sample to generate a “bubble” graph depicting thickness, shape and dimension of the graft. The “complete” hierarchical clustering workflow was applied to group the grafts. For each group, median thickness was calculated to obtain an average shape.

Results: Based on shapes, the designed grafts were clustered into three groups. Two types of average graft shapes could be distinguished for the upper jaw defects. The first graft (n = 13) had a square shape with average dimensions of 10 mm in a lingual-buccal and 7–10 mm in a mesial-distal direction. The second graft shape (n = 11) was longer (11 mm lingual-buccal) and narrower (4–7 mm mesial-distal). The average graft shape for lower jaw defects (n = 9) was smaller and different compared to the upper jaw average graft shapes. The lingual-buccal dimension was 6–8 mm and mesial-distal in a range of 5–10 mm. Regarding the thickness, all three average graft shapes had the highest thickness in the middle portion, above the alveolar ridge region, with mean values around 2 mm. The graft thickness decreased gradually in the buccal and palatal/lingual directions towards the margin, where the lowest thickness at specific points was below 0.2 mm.

Conclusions and Clinical Implications: The study demonstrates the proof of concept approach to design average shape grafts for soft-tissue augmentation of single-tooth defects in the posterior jaw region. Application of prefabricated xenogenic and allogenic matrices in shapes adapted to the geometry of most common soft tissue defects will bring accuracy for required augmentation and reduce surgical time. Future work aims at confirming the obtained average shapes with more samples, and design average shapes for other defect types.

Keywords: Soft tissue augmentation, Digital design, Single-tooth defect, Novel graft shape.