Effect of L-shaped, loosely packed versus non-trimmed, compactly packed non-fixed collagenated bone blocks on the stability of augmented sites in chronic peri-implant dehiscence defects: a pre-clinical in vivo experimental study

This pre-clinical study aimed to compare the efficacy of L-shaped, loosely packed soft block bone substitutes (BBS, LP group) with that of non-trimmed, compactly packed soft BBS (CP group), both covered with a non-fixed collagen membrane, on augmentation stability and new bone formation in chronic peri-implant dehiscence defects treated with guided bone regeneration (GBR). In 4 mongrel dogs, 4 standardized box-shaped buccal defects were surgically created in each jaw. Following a 4-week period of spontaneous healing, a total of 32 dental implants were placed, with 2 implants inserted into each defect. Each defect was randomly assigned to either the LP or CP group. Statistical comparisons between groups were conducted using the Mann-Whitney U test. Bland-Altman and Spearman correlation analyses were also performed to evaluate the relationship and agreement between micro-computed tomography (micro-CT) and histomorphometric measurements. Micro-CT and histomorphometric analyses revealed no significant differences in bone width at any apical level between the LP and CP groups. Both groups exhibited similar increases in bone width, although bone retention in the coronal region remained limited. Additionally, micro-CT tended to slightly overestimate bone width (mean difference, 0.31 mm), but showed a strong correlation with histomorphometric analysis (r=0.971, P<0.001), supporting the reliability of radiographic methods for bone assessment. Neither LP nor CP soft BBS effectively prevented morphological collapse in the coronal region of augmented sites when used without additional membrane fixation. These findings underscore the necessity of enhanced stabilization techniques to improve structural integrity and bone regeneration in GBR procedures.