ALVEOLAR SOCKET PRESERVATION TECHNIQUE: HISTOLOGICAL HEALING OF HARD AND SOFT TISSUES.

INTRODUCTION After tooth extraction, the use of grafting materials and absorbable membrane, alone or in association, were proposed for maintenance procedures of alveolar ridge volume. The preservation of bone volume in posterior maxillary area might be necessary to optimize the delayed implant placement without sinus augmentation procedure. In addition, importance of peri-implant soft tissue has been related to final aesthetic outcomes. The alveolar socket preservation technique may affect the healing of the overhanging mucosa. This research is composed by two studies (A and B). Aim of the study A was to evaluate histologically the integration and remodelling of porous bovine bone particles (PBBM) grafted in the extraction socket, and to compare the dimensional alterations of the alveolar ridge in the molar maxillary area after extraction with or without the graft of PBBM particles, at medium and advanced endpoints. Aim of the study B was to histologically compare soft tissue features of augmented alveolar sockets covered or not covered with collagen membrane. Methods Study A: This is a randomized double-blind controlled clinical trial. Sixteen patients who needed the extraction of one maxillary molar tooth were included in the study. After extraction seven sites were treated with PBBM particles (Bio-Oss Collagen) covered with collagen membrane (test), and nine sites were left untreated as control. At baseline, 3 and 6 months the alveolar ridge dimension changes were evaluated using an acrylic resin stent. At 3, 6 and 9 months one tissue sample was harvested in three selected patients and processed for histological analysis. At 9 months the authors also decided for implant placement with or without previous sinus floor augmentation. Study B. This is a randomized double-blind controlled split-mouth clinical trial. Twelve patients requiring extraction of 2 controlateral maxillary premolar teeth were included. Following extractions in each patient, one randomly selected site was augmented with graft material (Bio-Oss Collagen, Geistlich) (control group), the other site was augmented and covered with collagen membrane (Bio-Gide, Geistlich) (test group). Following 5 weeks (early endopint, n=7 patients) or 12 weeks (late endpoint, n=5 patients) samples of newly-formed soft tissue were harvested and processed for evaluation of micro vascular density (MVD) (immunohistochemistry with CD31), collagen content (AA%) and amount of inflammatory infiltrate (immunohistochemistry with CD3 for T-lymphocytes and CD20 for B-lymphocytes). Non-parametric statistical analyses were performed to compare data from test and control groups at early and late endpoint. Data from the same group were also compared between early and late endpoints. Pearson’s correlation was used to compare intra-patient data. RESULTS: Study A. Data on alveolar ridge volume changes did not show significant differences between test and control group. However in the control group sites that maintained the buccal bone showed a substantial loss of buccal bone compared to the test group. At 3 months histological evaluation grafting material was detected immersed in highly cellular connective tissue. At 6 and 9 months grafting material was mainly remodeled and remaining particles were in contact with newly formed lamellar bone. The odds ratio for receiving the sinus augmentation before implant placement resulted 2.25 times greater in control group than in test group (p=0.39). Study B. At 5 weeks after extraction, in both groups, epithelial and connective tissues appeared normally organized, without increased inflammatory infiltrate or cellular morphological alterations. Connective tissue of both groups presented remaining graft particles surrounded by mature collagen fibres. At 12 weeks a more mature structure of the epithelium and connective tissue was detected. No graft particles were observed. At 5 weeks the vascularization of tissue in samples sites treated with the graft+ resorbable membrane was significantly lower (MVD= 6.18) than in samples harvested from sites treated only with the filling material (MVD= 9.44) (Wilcoxon Matched Pair-Signed Rank, p<0.05). At this endpoint, data on Lymphocytes T and B, and collagen content showed no significant differences between test and control group. At 12 weeks no significant differences between test and control group were found for any of the considered parameter. Data on MVD and collagen content resulted increased at 12 weeks after surgery in both groups, however only data on collagen content in test group increased significantly. CONCLUSIONS: The alveolar ridge augmentation procedure increases the possibility to insert implants without sinus augmentation procedure. PBBM undergoes remodeling process, however particles included in newly formed bone still remain at 9 month. Soft tissue samples of the sites treated with PBBM particle and covered with collagen membrane showed an initial delayed healing process with a lower microvascular density and collagen content that sites treated with filling material alone. Subsequently sites treated with the membrane seem to gain the same maturation level than control sites, and were characterized by a strong augmentation of collagen fibers and microvascular density.