An in vitro comparison of an adjustable bone fixation system.

PURPOSE: The purpose of this study was to biomechanically compare an adjustable plating system and several variations with an inverted-L pattern of 3 bicortical screws to fix a bilateral sagittal split osteotomy. MATERIALS AND METHODS: Sixty polyurethane mandible replicas (Synbone, Laudquart, Switzerland) were used in this study. Ten uncut mandibular replicas served as control models. Fifty experimental synthetic mandibles had bilateral sagittal split osteotomies created with a 7-mm advancement. Fixation modalities included 3 bicortical screws in an inverted-L pattern, a 4-hole sagittal split plate with adjustable slider (slide 0), an adjustable plate with an additional bicortical screw (slide 1), an adjustable plate with 2 additional bicortical screws (slide 2), and an adjustable plate with 3 additional bicortical screws (slide 3). The alloplastic mandibles were secured in a custom fabricated jig and subjected to vertical loads at the incisal edge and torsional loading at the molar region by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. Mechanical deformation data within a 0- to 900-N range were recorded. Yield load, yield displacement, and stiffness were determined. Means and standard deviations were derived and compared for statistical significance using a Fisher's Protected Least Significant Differences Test with a confidence level of 95% (P < .05). Second-order best-fit polynomials were created for the experimental data curves. RESULTS: For incisal edge loading, the control was significantly greater for yield load than the experimental models. No significant difference was noted between slide 0, slide 1, and slide 2, but significant differences were seen with slide 3 and the inverted-L. There were no significant differences between slide 1, slide 2, slide 3, and inverted-L. For molar load, the control was significantly different than the experimental models. However, there was no significant difference between the experimental models. CONCLUSIONS: Mandibular advancements of 7 mm in a synthetic mandible fixed with a 4-hole sagittal split plate with adjustable slider alone is resistant to torsional forces and comparable to that seen with 3 bicortical screws placed in an inverted-L fashion. However, when loading at the incisal edge, additional bicortical screws are necessary to achieve the similar resistance to vertical load as that seen with 3 bicortical screws.

A biomechanical evaluation of bilateral sagittal ramus osteotomy fixation techniques.

OBJECTIVES: The purpose of this investigation was to evaluate and compare the biomechanical behavior of various rigid internal fixation plates designed to aid in the condylar positioning of bilateral sagittal ramus osteotomies, to positional screws in an inverted-L pattern, and a control. MATERIALS AND METHODS: Fifty polyurethane synthetic mandible replicas (Synbone, Laudquart, Switzerland) were used in this investigation. Five controls and 5 each of 4 different fixation modalities (3 bicortical positional screws in an inverted-L pattern, monocortical 4-hole straight plates, monocortical 6-hole curved plates, and monocortical adjustable 4-hole slide plates) were subjected to vertical loading at the incisal edge and torsional loading at the molar region by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. Mechanical deformation data within a 0 to 900 N range were recorded. Yield load, yield displacement, and stiffness were determined. Means and standard deviations were derived and compared for statistical significance using a Fisher's Protected Least Significant Differences Test with a confidence level of 95% (P < .05). Second-order polynomial best-fit curves were also created for each group to further evaluate mechanical behavior. RESULTS: For incisal edge loading, statistically significant differences were noted between the control group and all other groups for yield load and stiffness, and between the control group and straight, curved, and slide plates for yield displacement. Differences were also noted between the inverted-L and straight, strut, and slide plates for yield load; and inverted-L and straight, curved, and slide, as well as straight and slide for yield displacement. For molar loading, statistically significant differences were noted between the control group and all other groups for yield load and stiffness. Differences were noted between the slide and straight, curved, and control; as well as between the inverted-L and straight and strut plates for yield displacement. Lastly, differences were noted between the straight and curved plates, and the slide and straight, curved, and inverted-L for stiffness. CONCLUSION: In this in vitro study, differences were noted between the control and all experimental groups in their abilities to resist loads under all of the conditions tested. Differences were also noted among specific experimental groups. Yet when placed in the context of functional parameters, only the bicortical positional screws in an inverted-L pattern met the requirements for both molar loading and incisal edge loading.

The relationship between enophthalmos, linear displacement, and volume change in experimentally recreated orbital fractures.

PURPOSE: The purpose of this investigation was to establish the relationship between enophthalmos, linear displacement, and volume change for various patterns of experimentally recreated orbital fractures. MATERIALS AND METHODS: We fabricated an experimental apparatus that permitted uniform displacement of simulated orbital wall fractures. Measurements of linear displacement, volume change, and degree of simulated enophthalmos were taken for 1- and 2-walled displacements. Means and standard deviations were derived, and analysis of variance was used to compare means for statistically significant differences ( P < .05) between groups and among major categories. RESULTS: No statistically significant differences were found for any uniform displacement caused by 1-walled defects or for any given displacement caused by 2-walled defects The linear coefficient for displacement and enophthalmos or for displacement and volume change approached 1.0 for all groups (range, 0.9802 to 0.9999). However, statistically significant differences in mean enophthalmos and mean volume change at uniform displacements were found between 1- and 2-walled defects. CONCLUSIONS: Displacement of 1- and 2-walled orbital defects results in a direct and linear change in both orbital volume and enophthalmos, regardless of the location of the defect.

A biomechanical evaluation of mandibular condyle fracture plating techniques.

OBJECTIVES: The purpose of this investigation was to evaluate the biomechanical behavior of various rigid internal fixation techniques for mandibular condylar process fractures. MATERIALS AND METHODS: Synthetic mandible replicas (Synbone, Landquart, Switzerland) were used to evaluate a control, and four monocortical mandibular condyle plating techniques. Each group was subjected to linear loading in lateral to medial, medial to lateral and posterior to anterior directions by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. Yield load, yield displacement, and stiffness were measured. In addition, each group was subjected to torsional loading using an Instron 8521 (Instron). Yield torque, yield rotation, and stiffness were measured. Five samples were tested for each group and method of loading (n = 100). Means and standard deviations were derived and compared for statistical significance using a 1-way analysis variance (P <.05). Third-order polynomial best-fit curves were also created for each group to further evaluate and compare the mechanical behavior. RESULTS: Statistically significant differences were noted between fixation groups for the different mechanical measures evaluated under the different conditions of linear loading. Statistically significant differences were noted between groups for yield rotation during torsional loading. Although different in magnitude, similar patterns of mechanical behavior were observed in the third-order polynomial best-fit curves for lateral to medial loading, medial to lateral loading and torsional loading. For posterior to anterior loading, different patterns of mechanical behavior were noted between the experimental groups, but similar behavior was noted between the control and mini dynamic compression plate CONCLUSIONS: While differences were noted between each of the fixation systems in their abilities to resist loads under the conditions tested, the mini dynamic compression plate provided the most favorable mechanical behavior. Based on the presumed clinical parameters, we can suggest that none of the systems evaluated were ideal for the treatment of mandibular condyle fractures, but that the mini dynamic compression plate is the closest to an effective means for reconstruction.