Volumetric and Clinical Evaluation of Peri-implant Soft Tissue Augmentation in Different Sites After Laser-aided Pouch Roll Technique: a Prospective Study

Introduction Adequate soft tissue thickness at the vestibular aspect of dental implants are crucial for satisfactory implant engraftment and aesthetic outcome. To pursue this objective, numerous surgical procedures have been adopted to augment the peri-implant gingiva, including autologous soft tissue grafting, xenogeneic collagen matrix, acellular dermal matrix, and roll/pedicle flap techniques: however, the available data do not suffice to clearly indicate which technique yields the best results.

The pouch roll techniques, originally proposed by Abrams in 1980 and subsequently improved, are particularly effective because they maintain vascularity of the grafted flap, which greatly facilitates its survival. Most of these procedures use a scalpel to shape the flap and remove the keratinized epithelial layer, but this conventional pouch roll technique is hampered by the fact that flap thickness must be no less than 3 mm and it is very difficult to perform hand scalpel gingival de-epithelization of the without damaging the underlying connective tissue, thereby causing bleeding and predisposing to scarring in the long term. More recently, laser-aided epithelial photoablation has been proposed as a possible solution to these issues. In fact, diode laser operating at 810 nm wavelength (λ) has been successfully used for selective de-epithelialization for several periodontal therapy purposes, e.g. palatal grafts for gingival recession defects, gingival hyperpigmentation, intra/extra pocket decontamination in chronic periodontitis and placement to second-stage surgery for buried implant exposure. Laser photoablation offers several advantages, namely excellent hemostasis that results in a dry surgical field and better view of the operative field, tissue surface sterilization and shallow penetration limited to the gingival epithelium with minimal injury and inflammation of the underlying lamina propria. On this ground, the investigators successfully combined diode laser photoablation (λ 810 nm) to conventional roll flap technique for mild vestibular ridge deficiencies: in a preliminary, limited series of patients (n=3) this improved method resulted in fast healing, satisfactory clinical and aesthetic results, rapid prosthetic restoration and no need for local or systemic analgesics. The present study aims on one hand at expanding the case series to consolidate the preliminary findings, on the other hand at evaluating another key clinical outcome parameter of this laser-aided roll flap procedure, namely the actual, objective gingival soft tissue augmentation over time. To this purpose, the volume of the treated regions, acquired by a digital intra-oral scanning, was measured and analyzed by appropriate 3D software and compared before roll flap surgery and implant placement and upon 12-month follow-up. Post-operative discomfort and aesthetic satisfaction of the patients were also assessed.

Material and methods

Volumetric measurements and analysis - Volume changes of the vestibular gingiva before and after the laser-aided roll-flap augmentation were evaluated and compared on digital intra-oral scanning impressions taken with an intra-oral scanner (Dentsply Syrona, Rome, Italy) and 3D reconstruction software (Exocad, Darmstadt, Germany). To reduce possible deviations and ensure higher accuracy of 3D analysis, quadrant instead of full-arch scans were recorded. These were converted to standard tessellation language (STL) format. Pre and post-operative STL files were collected, aligned and superimposed by selecting 10 reproducible anatomical points as landmarks prior to be analyzed with an appropriate software (Rhyno3D, Washington DC, USA). This software allowed: i) to demarcate an exact 3D region of interest (ROI), ii) to superimpose the same ROI taken at 2 time points, i.e. before surgery (day 0) and at 12-month follow-up, while to measure the volume of the 2 corresponding ROI and to objectively assess their differences at the different time points. Each selected ROI corresponded to a single or multiple implant site. According to previous studies, ROI in the single implant sites was demarcated on the vestibular gingival aspect using the following criteria:

1. gingiva-to-implant margin (or coronal gingival ridge, if before implant placement) as horizontal coronal border;
2. muco-gingival junction as horizontal apical border;
3. two vertical lines, 2 mm aside the surgical flap incision and corresponding to the mid-point of the interdental papillas, as mesial and distal borders.