Influence of wound closure on the volume stability of particulate and non-particulate GBR materials: an in vitro cone-beam computed tomographic examination. Part II.

Objectives: to test whether GBR with an L-shaped soft-block bone substitute and particulate bone substitute differs from GBR with particulate bone substitute as regards the volume stability of the augmented region during flap closure. Materials and methods: twenty peri-implant box-shaped bone defects were created in 10 pig mandibles. Every bone defect was augmented with each of the following two GBR procedures in turn: control group - particulate xenograft applied buccally + collagen membrane + pins; test group - particulate xenograft applied buccally + L-shaped soft-block xenograft applied buccally and occlusally + collagen membrane + pins. Cone-beam computed tomography scans were obtained before and after wound closure. The horizontal thickness (HT) of the augmented region (bone substitute + membrane) was assessed at the implant shoulder (HT0 mm ) and at 1 mm to 5 mm apical to the implant shoulder (HT1 mm -HT5 mm ). In the test group, the vertical thickness (VT) and 45° thickness (45-T) of the augmented region were measured from the implant shoulder. The changes in HT during flap suturing were calculated as absolute (mm) and relative values (%). Repeated-measures ANOVAs were used for statistical analysis. Results: the reduction in HT0 mm was 20.5 ± 23.3% (SD) in the control group and 2.4 ± 9.2% (SD) in the test group (P = 0.014). There were no statistically significant differences in changes in HT1-5 mm between the groups (P > 0.05). In the test group, the reduction in VT amounted to 28.0 ± 11.9% (SD) and the reduction in 45-T amounted to 24.8 ± 10.2% (SD) (P < 0.001). Conclusion: the addition of an L-shaped soft-block bone substitute to a particulate xenograft, covered by a collagen membrane and fixed with pins, significantly improved the horizontal volume stability of the augmented region during wound closure