Relative stability of deep‐ versus shallow‐side bone levels in angular proximal infrabony defects

The relative changes with lime, in the position of the coronal margin of the mesial and distal bone of proximal, angular infrabony defects, were investigated. Tracings of the radiographs of 51 mandibular posterior sites, treated by flap curettage, with a mean post‐surgical duration of 11.8 years, were measured using a digitizer pad. The group consisting of shallow‐side sites ( N = 51), exhibited no significant change in the bone height with time; however, there was a significant decrease in bone height in the deep‐side group ( N = 51). The mean area of proximal bone decreased significantly with time. The defects were divided into early ( N = 25) and advanced ( N = 26) angular groups, and then into deep‐ and shallow‐side subgroups. In the early defect group, there was a significant decrease in the mean bone height of the deep‐side subgroup. There were no differences in the changes of mean bone level of the remaining 3 subgroups with time. There was no correlation between changes in bone levels of adjacent mesial and distal sides of angular defects with time ( r = 0.27). There was no difference between the deep‐ and shallow‐side groups in the number of sites which gained, lost or evidenced no change in bone height. In the study population, the bone height of 73% of the deep‐side, and 84% of the shallow‐side sites was either unchanged or in a more coronal position. The findings indicate that: (1) progressive bone resorption appears to be localized at the deep‐side of the early angular defect; (2) bone heights of adjacent proximal deep and shallow sides of angular defects appear to be independent; (3) the deep side of a proximal angular delect does not pose a threat to the bone height of the adjacent shallow side; (4) bone loss in the majority of proximal angular defects can be arrested by treatment.