Pre-augmentation Soft Tissue Expansion (STE): a Report of Four Pilot Cases

Objectives: This pilot study aimed at investigating the safety and feasibility of pre-augmentation soft tissue expansion (STE) as a potential approach in facilitating bone augmentation surgery, by enhancing soft tissue quantity and quality. Methods: Self-inflating osmotic soft tissue expanders of different sizes (expander final volume range: 240 - 1300 mm3) were implanted subperiosteally in four patients requiring vertical and/or horizontal bone augmentation, and left in situ for 20-60 days. Guided bone regeneration was carried out after STE completion & expander removal. In all cases, bone augmentation was performed using particulate autogenous bone, mixed with xenograft. In case of vertical bone augmentation, the bone graft was covered with titanium reinforced PTFE high-density membrane, while collagen membrane was used in horizontal bone augmentation. In patients that completed the study, dental implants were placed 6 months post-augmentation. CBCT scans were taken before placement of soft tissue expanders and 4-6 months following bone augmentation procedures. Vertical & horizontal bone gains were calculated on CBCT scans by subtracting bone height or width "before augmentation" from bone height or width "before placement of dental implants"at landmark sites. For volumetric analysis, optical scanning of pre-and post-expansion cast models fabricated was done through an optic scanner. Afterwards, superimposition of the optically scanned pre- and post-expansion models was done for each patient through two CAD software applications, to calculate the soft tissue volume increase. Results: Four patients (3 females, 1 male, mean age= 53.6 ±7.1 years) were included in this pilot investigation. Expanders were placed at 5 surgical sites (in one case, 2 expanders were placed in the same patient). During STE, healing was uneventful in 2 patients (3 surgical sites) while STE failed in 2 patients (2 surgical sites). One patient dropped out after failed STE; therefore, only 3 patients completed the scheduled treatment. Horizontal bone gain averaged 3 mm in 2 successfully expanded sites while one site had a vertical bone gain of 8 mm. All 3 patients received dental implants in the augmented areas (total= 7 implants). All implants were successfully osseointegrated. Regarding volumetric analysis (2 patients, 3 surgical sites), soft tissue volume increase (STVI) was 259.4 mm3for the 0.24 ml expander, 436.1 mm3for the 0.7 ml cylinder expander, and 755.9 mm3 for the 1.3 ml expander (mean STVI of the 3 successful sites= 483.8 ± 251.7 mm3). Thus, STVI corresponded only to the 0.24 ml expander, while this increase was almost half of the final expander volume for the 0.7 ml and 1.3 ml expanders, probably due to higher pressure distribution to the underlying bone surface with bigger final volume expanders. Nonetheless, the surplus amount of soft tissues through STE still allowed for tension-free primary flap closure without the need for deep periosteal and/or vertical releasing incisions during bone augmentation. Conclusions: Soft tissue expansion (STE) might be a beneficial pre-augmentation approach, especially in the vertical dimension. The ideal area for this specific application would be the posterior mandible with the presence of alveolar mucosa. However, the presented technique still requires improvement before being applied routinely in everyday dental practice. Schlagwörter: guided bone regeneration, soft tissue expanders, soft tissue expansion, soft tissue management