PubMed · 8354776
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J O Grippo. 1993. A noteworthy study.. https://doi.org/10.14219/jada.archive.1993.0158
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A linear programming model, operating in a three-dimensional coordinate system, was written to study the effect on unilateral maximum bite forces (MBFs) of small changes in the design of human jaws. Under some conditions the MBF was larger on a more anterior tooth than a more posterior tooth for a given bite direction. The MBF was increased (i) as the bite force was tilted forward, (ii) as the jaw was opened if its direction was kept perpendicular to the occlusal plane of the lower jaw, (iii) by placing teeth nearer the midline, (iv) by raising the height of the teeth for forward bite forces, and (v) by tilting forward the articular surface of the condyle (equivalent to creating an articular eminence). Increasing the distance between the condyles spread the load more evenly between the two joints. The articular eminence was the only design feature which seemed to be clearly related to increasing the MBF.
The accumulation of experimental and clinical evidence during the past decade has significantly contributed to the understanding of the role of occlusally generated tensile stress in the etiology of certain noncarious cervical lesions of teeth. More important, this knowledge has led to the understanding of the reasons why traditional restorative treatments of these stress-induced cervical lesions fail. The case of failure can be attributed to the occlusally generated stresses that are concentrated at the cervical region and result in debonding, leakage, retention failure, and, ultimately, restorative failure. With the new understanding, restorative approaches that combine chemical adhesion and restorative materials of appropriate elastic properties show promise of long-term success.
PURPOSE: This study examined the effects of positional screw size and placement configuration on osteotomy site stability in a sagittal split ramal osteotomy model. MATERIALS AND METHODS: A reproducible analog of a sagittal split ramus osteotomy was developed to facilitate equitable comparisons of fixation stability. The distal segment of each analog was advanced by 7 mm and fixed bilaterally with 2.0-mm or 2.4-mm cortical screws applied in either a linear or a triangular configuration. Reduced analogs were placed in a straining frame, and simulated masticatory loads wee applied alternatively to the mandibular first molars. Ensuring osteotomy site displacements were acquired and registered by displacement transducers attached to a computer-based data acquisition program. A coordinate transformation procedure was used to convert the component displacements captured by the individual transducers into a common "instability factor" to reflect fixation stability for each construct and loading condition. RESULTS: Between configurations, the magnitude of interfragmentary displacement was less when the screws were applied in a triangular than in a linear configuration (P < or = .0001). Within configurations, 2.4-mm cortical screws provided greater stability than 2.0-mm screws. The stability profiles of the 2.0-mm screws, applied in a linear configuration at the superior border, were very similar regardless of whether two or three screws were used. The loads at which the linear systems became unstable were significantly higher (P < or = .0001) than for the triangular systems. Despite the twofold or higher difference in the mean instability factor of the individual test constructs, the SDs for each construct were only one tenth to one fifth of the corresponding means. CONCLUSIONS: None of the internal screw systems were grossly unstable when used to stabilize ramal osteotomies. Other conditions, including quality and strength of investing bone, being equal, cortical screws placed in a triangular configuration provide greater stability than screws placed in a linear configuration. Osteotomy sites stabilized by 2.4-mm screws are more stable than those stabilized by 2.0-mm screws. It does not matter whether two or three screws are applied at the superior border in a linear configuration, provided that the outer screws are an inch apart. The model system has a very good measurement precision and has important implications in optimizing fixation device design and placement configuration.