Influence of molar support loss on stress and strain in premolar periodontium: A patient-specific FEM study
Introduction
Conservative approaches for the management of patients with loss of molar support should focus on the long-term survivability of the remaining dentition. The effect of molar support loss on the migration of the remaining teeth,1, 2 possible interactions with temporomandibular disorders,3, 4 and chewing functions5, 6 has been assessed extensively. The results of these studies generally suggest that, following the loss of molar teeth, an initial, minor migration of the remaining teeth may lead to a new occlusal equilibrium.2, 4, 7 While, the influence of molar loss on the prognosis of the remaining dentition has not been sufficiently evaluated in relation to the biomechanical environment in the supporting periodontal structures. A prospective analysis of the dentition should involve changes in the masticatory function such as the load-bearing capability.
Stress and strain created in the periodontal structures have been used to predict the potential damage occurring under mechanical stress or loading, mostly by means of computational models with the finite element (FE) method.8, 9 Previous studies, however, utilized analytical models often constructed as representative morphology created from dimensions of one patient. Such models ignored interindividual variations, thus potentially compromising the generalization of the solutions.10, 11
We created patient-specific FE models based on occlusal contact records and morphological measurements of each patient to analyse the stress and strain distributions in the periodontal structures of the premolars. We aimed to test the hypothesis that loss of molar support causes increase in stress in the supporting tissues of the teeth. We also aimed to assess the influence of denture use on stress distribution.
Section snippets
Subjects
Subjects with loss of all molar teeth on the right side (n = 7; mean age 59.0 years, range 50–62 years; ML1 group) and on both sides of the mandibular arch (n = 7; mean age 61.0 years, range 51–69 years; ML2 group) were recruited from female patients visiting the clinic for post-prosthodontic maintenance and oral hygiene instructions but without complaints of any symptoms. As all subjects were female, gender effects could not be taken into account. Inclusion criteria were the retention of
Results
The results of the morphological measurements are summarized in Table 1. No significant differences in alveolar support, bone height and bone width were found among the groups for the same tooth (p > 0.05). Fig. 1B indicates the plots of the OLC for all subjects. The mean OLC was located posterior to the zero point in the CD group (−9.4 mm) and ML1 group (−6.7 mm for D− and −6.4 mm for D+), whereas the ML2 group exhibited more anterior OLC (+1.3 for D− and −2.6 for D+). The largest mean lateral
Discussion
The mean bite force registered on the second premolar tooth in the ML2 group was greater than that in the ML1 and CD groups (Fig. 3A). The high mean bite force in this group can be attributed to the larger anterior deviation of the mean occlusal load center (OLC) as compared with that of the other groups. The mean OLC was located at the centre of the first molar tooth in the CD and ML1 groups but moved to the second premolar region in the ML2 group (Fig. 1B). This may be due to changes in the
Conclusions
In this analytical study utilizing patient-specific FE models, we found higher maximum principal stress and strain in periodontal tissues of the second premolars in the bilateral molar loss group, in comparison with the unilateral molar loss and complete dentition groups. The stress could not be prevented by wearing a denture. Although a stable occlusal position or equilibrium has been reportedly confirmed in patients with loss of molar support, our results suggest that the periodontium of the
Acknowledgements
This study was supported by KAKENHI 20592307 (to N.W.) and High-Tech Research Project 2005–2009 grants from JSPS/MEXT.
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