An in vitro study of the effect of bony buttressing on fixation strength of a fractured atrophic edentulous mandible model

Purpose: The purpose of this study was to measure the resistance to displac ement in an adult bovine rib mandible model as the vertical dimension of th e bone decreases, and to compare the fixation strength of titanium miniplat es and reconstruction plates. Materials and Methods: Five groups of 6 ribs each were tested based on the vertical dimension of the rib and method of fixation (group 1, 40 mm, minip late), (group 2, 30 mm, miniplate), (group, 3, 20 mm, miniplate), (group 4, 10 mm, miniplate), (group 5, 10 mm,, reconstruction plate). In the 4 group s stabilized with a miniplate, a 3-hole-per-segment, 2.0-mm titanium minipl ate and 6.0-mm monocortical titanium screws were used. In group 5, a 3-scre w-per-segment, 2.4-mm titanium reconstruction plate and 2.4-mm bicortical t itanium screws were used for fixation. A 2-dimensional beam model (Class II I lever) was established, and an Instron machine was used initially to deve lop a load-displacement curve to 100 N for each specimen. An osteotomy was then created, and the segments were reduced without preload. The ribs were then loaded to failure in the Instron machine. The load-displacement curve and failure load were recorded. Results: There was no significant difference (P less than or equal to .05) between any of the groups before the osteotomy. At 75 N, groups 1 and 2 wer e superior to group 5 in resistance to displacement Group 4 showed signific antly less (P less than or equal to.05) resistance to displacement than the other experimental miniplated subgroups. As loads increased, groups 1 and 2 continued to show increased resistance to displacement when compared with groups 3, 4, and 5. Loads to failure for groups 1 and 2 were comparable to group 5. Conclusions: Decreased resistance to displacement occurs with decreasing ve rtical dimension of the bovine rib. Lu fractures of the edentulous mandible , a miniplate is more likely to provide adequate fixation if the mandible i s 30 to 40 mm in height (nonatrophic). At higher loads, groups with greater vertical height (30 mm and 40 nun) provided resistance to displacement equ ivalent to the 10-mm. group repaired with a reconstruction plate. Therefore , fractures of the atrophic mandible may be better treated with more rigid techniques.