This study investigated mandibular displacement and masticatory muscle activity during clenching in lateral occlusal position in relation to the lateral occlusal pattern. Twenty healthy human subjects (mean = 26.5 years) volunteered for this study. Metallic occlusal overlays were fabricated for the lower working side canine to second molar and non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion (balancing contact). Three-dimensional displacements of the bilateral condyle and electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern was revealed to have statistically significant effects on both condylar displacement and EMG activity (P < 0.001 and P < 0.001, respectively). When compared to the simulated group function occlusion, the simulated canine protected occlusion and balancing contact caused statistically significant smaller superior displacements of the non-working side condyle, which suggests that they may result in reduced temporomandibular joint (TMJ) loading. Furthermore, the simulated canine protected occlusion was associated with the lowest EMG activity, which suggests that this occlusal pattern has the capacity to reduce the level of parafunctional activity.
This study investigated the influence of experimentally altered occlusal guidance on masticatory muscle activity. Twenty healthy human subjects (15 males and five females with an average age of 26.5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid on the second molar and the non-working side second molar to simulate a canine-protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern revealed to have statistically significant effects on EMG activity. As the most characteristic change, EMG activity in the anterior temporalis significantly increased in the simulated group function occlusion and the simulated bilateral balanced occlusion compared with the simulated cuspid protected occlusion. The increased teeth contacts to the posterior region altered the unilateral pattern of the anterior temporalis activity to the bilateral pattern, while that of masseter activity remained unchanged.
As cited in literatures, canine protected occlusion has a potential to reduce clenching induced temporomandibular joint loadings. However, these previous studies did not perform a control of the clenching level which differed with the depending occlusal conditions. This result may be due largely to an associated reduced jaw closing muscle activity. The present study has investigated clenching induced condylar displacements with controlled clenching level. Twenty healthy human subjects (15 males and five females with an average age of 26.5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid to the second molar and the non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyographic (EMG) activity from the bilateral masseter, anterior temporalis, and posterior temporalis was recorded. These signals were rectified, summarized, and presented to each subject using an oscilloscope screen. Using this visual feedback, subjects were asked to perform clenching tasks at a 50% level of maximal voluntary contraction exerted with simulated group function occlusion and three-dimensional condylar displacements were recorded. An experimental occlusal pattern that shows statistically significant affects on condylar displacements (anova: P<0.001) was found. When compared with the simulated canine protected occlusion, the simulated group function occlusion caused smaller working side condylar displacement and the simulated bilateral balanced occlusion caused significantly smaller non-working side and working side condylar displacements. These results suggest that the increased working side tooth contacts have a potential to reduce working side joint loadings, and a balancing side contact has a potential to reduce non-working side joint loadings, under the laboratory condition where the clenching level is controlled.
In this study, we confirmed that the principle of rigid support was indispensable for RPD design from the evaluation of a clinical education program. On the other hand, we found out that an objective assessment of the educational system or RPD is necessary to improve the RPD clinical educational program. AbstractPurpose: The aim of this study was to survey the undergraduate removable partial denture (RPD) clinical program and RPD's fabricated by students in 2006, and to identify the problems to be solved in the future. Methods:Sixty-nine students in their final semester at Tokyo Medical and Dental University (TMDU) recorded the following preoperative data: age, gender, chief complaint, and Kennedy and Eichner classifications. The students were requested to present their treated cases and were subjected to an oral examination by the professor to determine the treatment plan and prosthetic design of denture. Additionally, the students surveyed the chewing function score and visual analogue scale (VAS) regarding esthetics and stability of RPD, and the material used for RPD frameworks was summarized. Results: The patients included 35 men and 34women, and their chief complaints were mostly dissatisfaction with their current dentures. More than 80% of cases were classified as Kennedy I or II, and about one-fourth were classified as Eichner B4 or C1, in which the occlusal supports could not easily be reconstructed. Chewing function score significantly improved compared to preoperative state (P<0.05) and postoperative VAS was clinically acceptable. 89% of frameworks, were cast with Co-Cr alloy in one piece and a palatal strap or bar and a lingual bar were applied in 77% of treated RPDs. Conclusion:It is thought that our educational methods for delivery of RPDs are adequate. Since it is suggested by an objective assessment of them that they are unsatisfactory, we should deal with that problem without delay.
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