Do position and soft tissue affect distraction vector? An in vitro investigation

Objectives: The purpose of this investigation was to provide an in vitro evaluation of the effects of soft tissue and position on vector during distraction. Materials and Methods: A polyurethane skull and mandible replica (Synbone, Landquart, Switzerland) was used in this study along with an internal distraction device (Synthes Maxillofacial, Paoli, PA). The first portion of the investigation evaluated the effects of distractor position (inferior body, midbody, and superior body) on distraction vector. The second portion of the investigation used polyethylene straps to simulate the suprahyoid muscles and muscles of mastication, and polysulfide to simulate periosteum and mucosa. A laser light source attached to the synthetic mandible was projected on a grid 7.1 m from the construct to measure deflection from the starting point. The distractor was advanced 8.0 mm for each trial. Five trials each for inferior, middle, and superior, with and without simulated soft tissues (N = 30) were performed. Vertical and horizontal deflection along with absolute distance were measured and recorded. Means and standard deviations were derived for groups, and compared for statistical significance (P <.05) with a 1-way analysis of variance for the effects of position with and without simulated soft tissue, and with a paired t-test for the effects of simulated soft tissue within groups of similar distractor position. Results: Statistically significant differences (P <.05) for distractors without simulated soft tissues were only noted for vertical deflection between the inferior and superior distractor groups. Statistically significant differences were noted for all measures, for all distractor positions with simulated soft tissues. Statistically significant differences were noted for all measures between similar distractor positions with and without simulated soft tissues. Distractors without simulated soft tissues were deflected lateral to the y-axis and above the x-axis. Distractors with simulated soft tissues were deflected lateral to the y-axis, but below the x-axis. For distractors with simulated soft tissues, the closer to the inferior border, the less the deflection from the x-axis. Conclusion: Position alone had minimal effects on distraction vector. Simulated soft tissues affected the vector of distraction. The combination of position and simulated soft tissues affected distraction vector. (C) 2002 American Association of Oral and Maxillofacial Surgeons.