Influence of mini-screw diameter and loading conditions on static and dynamic assessments of bone-implant contact: An animal study.

Abstract

The goal was to compare static versus dynamic bone-implant interface histology of mini-screws and to evaluate its relation to diameter and load. Canine animal model. Custom-machined, titanium alloy (Ti6AI4V) mini-screws (n=70) of 1.60, 2.00, 3.00 and 3.75mm diameter were placed into edentulous sites in five skeletally mature beagle dogs. Using a split-mouth design, no load (NL) was applied to one side while a 2N load (L) was applied by calibrated coil springs on the other side. Intravenous bone labels were administered 21 and 7days prior to sacrifice. Dogs were euthanized 90days after screw placement. Bone sections were analysed under bright-field and epifluorescent light. The region of interest was defined as the bone within the threads of the screws. The following parameters were quantified: (a) Static-bone volume/tissue volume (BV/TV %) and bone-implant contact (BIC, %); (b) Dynamic-labelled bone/bone volume (LB/BV, %), and dynamic BIC (DBIC, %). BV/TV ranged from 71.2% to 85.0% of the screw surface. BIC ranged from 45.7% to 55.4% of the screw surface and was not affected by diameter (P=0.66). In contrast, the percentage of DBIC did not vary with the applied load (P=0.41); however, it correlated significantly with the diameter of the screw (P=0.001). The percentage of DBIC that is actively remodelling increases with increasing diameter of the screw. Dynamic histomorphometry is more sensitive to detecting changes in bone-implant contact when compared to static measurements.