Background: Alveolar ridge preservation (ARP) is a surgical technique designed to prevent naturally occurring post-extraction bone resorption.. The purpose of this study was to investigate clinical and histological healing outcomes following ARP performed on molar and premolar sites by using freeze-dried bone allograft (FDBA) together with a collagen membrane. Maxillary and mandibular sextants were compared for clinical and histological parameters.
Methods: Inclusion criteria were single tooth extraction with intact mesial and distal adjacent teeth. Exclusion criteria were smokers, patients with ystemic health problems and acute infection. A stent was prepared from clear acrylic. Pre-operative clinical measurements included the amount of keratinized gingiva and clinical attachment level at tooth scheduled for extraction and at adjacent teeth were taken. The thickness of buccal and lingual plate, the length and diameter of the extracted tooth, buccal-lingual and mesial-distal defect size and, the distance from stent in place-occlusal plate to alveolar crest were measured. FDBA and collagen membrane were placed and flap was sutured. A re-entry surgery was performed following approximately 140 days healing period. Clinical measurements were repeated. A bone core was obtained and immediately frozen in liquid nitrogen. Frozen bone cores were analyzed with micro-CT scan for bone volume density and bone trabecular connectivity. Following micro-CT scan, cores were fixed in formalin, decalcified, embedded in paraffin and sectioned. Slides obtained from the mid-portion of the bone core were stained with trichrome and analyzed under light microscopy.
Results: Twenty-one patients were completed the study. Following ARP, ridge height loss change was negligible (a loss of 0.4±0.3 mm in maxilla and a gain of 1.3±0.3 mm in mandible). However, average ridge width loss was 2.4±0.8 mm and 2.5±0.5 mm in maxilla and in mandible, respectively. In maxilla, initial CAL at mesial surface of the extracted tooth had statistically significant effect on post-treatment interproximal bone height (r=0.747; p=0.021 and r=0.682; p=0.043 for mesial and distal interproximal sites, respectively). Also, maxillary root length of the extracted tooth was negatively correlated with post-treatment mid-buccal bone height (r=-0.752; p=0.019). Similarly, initial palatal bone thickness had statistically significant effect on post-treatment maxillary mesial-distal distance (r=0.797; p=0.01). Otherwise, approximately 1.2±0.7 mm narrowing in maxillary M-D distance was observed. In mandible, baseline CAL at mid-buccal site of extracted tooth was negatively correlated with post-treatment ridge height at the site (r=-0.562, p=0.046). Also, initial buccal and lingual bone thicknesses and root length of the extracted tooth had statistically significant effect on post-treatment mesial-distal distance (r=0.771; p=0.002, r=0.811; p=0.001 and r=-0.816; p=0.001, respectively). Micro CT scan results revealed no statistically significant differences in trabeculation between grafted maxilla and mandible (P>0.05). However, mineralization per unit volume was higher in newly forming bone than in residual bone graft in mandible (P=0.03) while this difference was not statistically significant in maxilla (P>0.05). Histometric analysis revealed similar distribution of residual biomaterial, new cellular bone and nonmatured tissue in maxilla and in mandible (P>0.05).
Conclusion: Within the limits of this study, it appears that in different anatomical locations different factors may determine the clinical treatment outcome following ARP.