Histological analysis of bone healing following alveolar preservation technique by deproteinised bovine bone covered by a xenogenic collagen matrix

Introduction: The aim of the present study was to histologically evaluate the new bone formation and the dimensional changes in tissues following two different healing protocols (16 weeks and 32 weeks) using deproteinized bovine bone mineral (DBBM) covered with a collagen matrix (CM) for alveolar ridge preservation in the aesthetic area frontal before implant placement. Materials and methods: Sixteen patients (mean age 48.2 years), requiring the extraction of a single monoradiculated tooth in the frontal area were recruited for the study. The surgical protocol was performed with great care to preserve the buccal plate and surrounding soft tissues. Each selected tooth was extracted using a minimally invasive technique. Subsequently, in each patient, the alveolus was filled with DBBM with 10% collagen (Bio-Oss® Collagen; Geistlich Pharma AG, Switzerland). A xenogenic reabsorbable CM (Mucograft®, Geistlich Pharma AG, Switzerland) was subsequently adapted to marginal soft tissues and positioned to cover the DBBM in order to promote primary tissue healing. A resorbable suture was placed on the wound to stabilize the CM and to allow a flap closure without tension. Following the tooth extraction, the vertical distance from the center of the buccal and palatal/lingual alveolar crest (AC) and the cemento-enamel junction (CEJ) of the adjacent teeth that was recorded using a periodontal probe. The buccal-palatal/lingual alveolar width and thickness was measured at the center of both buccal and lingual walls using a caliper. After the surgical procedure was completed, each patient was randomized for evaluation of short-term (16 weeks) or long-term (32 weeks) healing group protocol for subsequent implant placement. Moreover, after the elevation of the flap, a biopsy was obtained useful for histological analysis; therefore, a 4.0 mm diameter implant was placed into the surgical site. A Student t-test was performed for the analysis of dimensional ridge changes and in changes of the histological parameters between the two groups. A value of p<0.05 was set as statistically significant. Results: Regarding the dimensional alveolar ridge variations, no significant difference were found, between groups, in the thickness of the buccal plate (short term 1.09 ± 0.26 mm vs long term 1.15 ± 0 , 31 mm) and in the CEJ-AC buccal distance change (short term 2.38 ± 0.22 mm vs long term 2.49 ± 0.26 mm) and in the palatal/lingual CEJ-AC distance (short term 2, 41 ± 0.31 mm vs long term 2.37 ± 0.24 mm), respectively. Furthermore, there was no significant difference between groups in the buccolingual alveolar thickness (P = 0.12). However, the 32-week protocol resulted in a better new bone formation and fewer tissue dimensional changes (P = 0.01) compared to the 16-week protocol. The 16-week group presented a vital bone percentage of 35.58% compared to 47.76% of the 32-week group. Regarding the percentage of residual graft, there was no significant difference between groups (short-term= 34.23%, long-term= 25.43%). Conclusions: This study indicates that there was significantly greater new vital bone formation by a xenograft protocol for the alveolar socket preservation with DBBM plus CM at 32 weeks compared to 16 weeks before dental implant placement.