Comparison of strengths of five internal fixation methods used after bilateral sagittal split ramus osteotomy: An in vitro study

Abstract

Background: Results on the strength and displacement of internal fixation methods for bilateral
sagittal split ramus osteotomy are controversial, and some designs have not been adequately studied.
Therefore, this study was conducted to compare techniques using bicortical or monocortical screws.
Materials and Methods: In this in vitro study, 35 sheep hemi‑mandibles were randomly
assigned to five groups of seven each: fixation using (1) a 13 × 2 screw, (2) two 13 × 2 screws
(arranged vertically), (3) three 13 × 2 screws, (4) 1 plate with 4 holes and four monocortical screws,
and (5) a Y‑shaped plate and five monocortical screws. Specimens underwent vertical forces until
failure. Breakage forces and displacements of groups were recorded and compared statistically.
Using one‑way analysis of variance (ANOVA) with a Tukey’s post hoc test and Kruskal–Wallis test.
Level of significance was predetermined as 0.05.
Results: Strengths of Groups 1–5 were, respectively, 14.43 ± 4.35, 28.00 ± 8.89, 28.29 ± 8.01,
29.43 ± 8.24, and 61.29 ± 12.38 N, respectively (P = 0.000, analysis of variance). The
corresponding displacement extents were 7.98 ± 0.04, 7.85 ± 0.26, 8.00 ± 0.00, 7.35 ± 1.73, and
6.79 ± 2.03 mm (P = 0.298, Kruskal–Wallis test).
Conclusion: Use of a single bicortical screw is the weakest method, while Y‑shaped plates might
provide the highest strength. Using two or three bicortical screws or 4‑hole plates might deliver
similar strengths.