The old reconstructions have to be replaced. But how? A challenging case treated by Dr. Sven Mühlemann, University of Zurich.

Objectives: Guided bone regeneration by means of membranes and bone substitutes is one of the most documented approaches for restoring deficient alveolar ridges. Despite routine use of the techniques, it is not known to what extent these approaches can restore the tissue volume lost after tooth extraction. The aim of this study was to analyse the volume loss occurring after extraction and how much lost volume can be recovered by three different bone augmentation procedures. Methods: To create the alveolar ridge defects, the teeth were sectioned in a buccal–lingual direction at the furcation level, and the mesial roots of M1 and P4 and distal roots of P3, P2 and P1 (monoradicular) were individually extracted. Three vertical grooves of about 6mm in height and 6mm in depth (as far as the lingual cortical bone) were prepared in order to eliminate the buccal bone plate. After 12 weeks, the dogs were randomly assigned to one of three regenerative procedures: graft-only (B) in which the defect was filled with a particulate bone substitute (Bio-Oss Collagen); membrane only (M) in which the defect was covered with a bioabsorbable collagen membrane (Bio-Gide); and combination group (T) in which the defect was filled with a particulate bone substitute (Bio-Oss Collagen) and membrane was added. Conventional polyvinyl impressions were taken before extraction and defect creation at one time point (T1), before regenerative surgery (T2) and after 3 months of healing (T3). The cast models were optically scanned to obtain stereolithography (STL) files. Linear and volumetric measurements included volumetric analysis, distance between surfaces, and tissue thickness at three levels below the alveolar ridge on the buccal side of the regenerated site(at 1, 3 and 5mm). Results: A total of 18 casts were obtained at T1, with 18 at T2 and 9 at T3. No impressions were taken at the time of sacrifice to avoid disturbing early healing. The box-shaped defects were effective in creating horizontal and vertical ridge deformities (comparison T1–T2). None of the three regenerative approaches resulted in complete reconstitution of the alveolar ridge to baseline dimensions (comparison T1–T3), although volume gain in groups B and T was significantly better than in groupM (comparison T2–T3). Conclusion: The three regenerative approaches failed to rebuild the post-extraction loss in tissue volume.

Objectives: To evaluate the 5-year clinical outcome of regenerative periodontal therapy (RPT) using minimally invasive surgery and a collagen-enriched bovine-derived xenograft (1), and to identify predictors for gains in clinical attachment level (CAL) and vertical radiographic bone (RB) (2). Methods: Subjects were 95 non-smoking patients, with up to 25% full-mouth plaque and bleeding presenting at least 6 months after initial periodontal therapy with more than one isolated interdental infrabony defect. They were treated consecutively by the same clinician with combined surgery and xenograft. Clinical and radiographic data were collected before surgery, and after 1 year and 5 years. Results: Eighty-four patients (39 men, 45 women, mean age 53 years) were available for follow-up after 1 year and demonstrated a mean probing depth (PD) of 7.8mm, a CAL of 10.0mm and a defect depth of 5.2mm before surgery. Thirteen patients dropped out between year 1 and year 5. At 5 years, mean PD reduction was 3.3mm (SD 2.2 ), CAL gain was 3.0mm (SD 2.1) and RB gain was 57% (SD 38). Of these, 45% showed ≥4.0mm CAL gain, and 24% were considered failures (≤ 1.0mm CAL gain), 48% showed considerable RB gain (≥75%).The only predictor for CAL gain included sites that were always plaque-free during aftercare (p= 0.003). Predictors for RB gain included patient compliance (p=0.001) and sites that were always plaque-free during aftercare (p=0.010). Conclusions: Regenerative periodontal therapy using minimally invasive surgery and a collagen-enriched bovine-derived xenograft demonstrated favourable clinical and radiographic outcomes after 5 years. Oral hygiene and patient compliance had a significant impact in the long term.