The Effects of Frontal Trauma on 4 Interforaminal Dental Implants: A 3-Dimensional Finite Element Analysis Comparing Splinted and Unsplinted Implant Configurations.

PURPOSE: With increased implant-prosthodontic rehabilitation for mandibular edentulism together with the increased life expectancy and activity of the elderly population, a greater number of implant patients may be at risk of facial trauma. The aim of this 3-dimensional (3D) finite element analysis (FEA) was to evaluate the biomechanical effects of the edentulous mandible (EM) with and without implants exposed to frontal facial trauma including assessment of the fracture risk of different mandibular areas. MATERIALS AND METHODS: By use of a 3D FEA, our experimental study design comprised 3 different models (model A, EM; model B, EM with 4 unsplinted interforaminal implants; and model C, EM with 4 splinted interforaminal implants) exposed to application of symphyseal frontal trauma of 2 MPa. In 3 defined regions of interest (ROIs) (ROI 1, symphyseal area; ROI 2, mental foraminal area; and ROI 3, condylar neck), the effective stress was measured at predefined sites in the superficial cortical mandibular area. The stress values of all ROIs evaluated were compared within each model (intramodel) as well as between the 3 models (intermodel). RESULTS: For all models evaluated, a frontal traumatic load generated the highest stress levels in the condylar neck. However, for both models with implants (models B and C), the stress values were reduced significantly (P < .01) in the condylar neck region (ROI 3) but increased significantly (P < .001) in the mental foraminal area (ROI 2) compared with the EM model without implants. For the symphyseal area (ROI 1) evaluated, the unsplinted 4-implant model (model B) presented significantly (P < .001) higher stress values than the splinted implant model (model C) when frontal forces were applied. CONCLUSIONS: Regardless of splinting or lack of splinting of 4 interforaminal implants, force absorption or transmission may shift the predominant risk factor from the condylar neck to the corpus or foramen mandibulae. However, splinting of 4 interforaminal implants may be beneficial in reducing the risk of bone fracture by providing protection for anterior risk situations.

Changes in the facial soft-tissue profile after mandibular orthognathic surgery.

OBJECTIVES: To investigate the correlation between soft- and hard-tissue changes after mandibular orthognathic surgery, to generate precise prognostic values for the esthetic treatment outcome of the facial profile. MATERIAL AND METHODS: In this retrospective study, sagittal changes in the facial soft tissue profile in relation to surgical changes in hard structures after mandibular osteotomy were examined. The sample population included 144 reported adult patients aged 17-50 years who had received combined mandibular orthognathic surgery and orthodontic treatment at the Department of Orthodontics, Ludwig-Maximilians University of Munich, Germany. Both mandibular advancement and mandibular setback cases in monognathic and bignathic osteotomy procedures were included. All subjects had undergone rigid fixation. A cephalometric analysis of presurgical and postsurgical cephalograms was performed, and the correlations between hard-tissue and soft-tissue change ratios were evaluated using a bivariate linear regression analysis. RESULTS: The lower lip, represented by the landmark Labrale inferius (Li), followed the lower incisor (Ii) by 77%. The soft-tissue B-point (B') followed the B-point (B) by 97% and the soft-tissue Pogonion (Pg') followed the Pogonion (Pg) by 97% in a linear correlation. CONCLUSION: The scatterplots show a distinct linear correlation and no significant difference in the direction of the movement. A wider spread for the lower lip (Li/Ii) indicates a lower predictability of the expected lip position, whereas a narrow spread of the chin values (B'/B and the Pg'/Pg) reveals a very good predictability of the postoperative chin position. CLINICAL RELEVANCE: This study contributes valid data for the soft-tissue profile prediction in orthognathic surgery.