Occlusal interference induces oxidative stress and increases the expression of UCP3 in the masseter muscle: A rat model

The Impact of Increase in the Vertical Dimension of Occlusion on Nociception in Rats - A Preliminary Report

Since the change in vertical dimension of occlusion (VDO) is extremely important in prosthetic dentistry, the aim of the study was to examine the effect of VDO increase on nociception parameters in rodent experimental model. The study was performed on seven experimental groups (6 animals per group) on male Wistaralbino rats: sham; 0.6/3, 0.9/3, and 1.2/3 groups where VDO was increased by 0.6, 0.9, and 1.2 mm (respectively), for three days; 0.6/20, 0.9/20, and 1.2/20 groups where VDO was increased by 0.6, 0.9, and 1.2 mm (respectively), for twenty days. The VDO raising protocols were performed as follows: on a day 1, following anaesthesia, a two-phase impression was taken with addition silicones; on a day 3, the cementing process for both maxillary incisors and inside crowns preparation was performed, and cementing zirconium crowns, manufactured using CAD-CAM technology, were applied. The behavioural testing (the tail flick and hot plate test) was performed on day 3 and 20. The results obtained in the tail flick test suggest that the raise in VDO in the early phase induced increased sensitivity to pain in a stepwise manner, while this hyperalgesic effect was diminished in a timedependent manner. The stepwise increase in VDO also resulted in significant decline in the pain tolerance with the higher VDO (0.9 and 1.2 mm) in the hot plate test that persisted after twenty days in 1.2/20 group. It seems that VDO elevation is sufficient to produce hyperalgesic effect in this experimental model, which may be attenuated in time-dependent manner.

Functional magnetic resonance imaging evaluation of masticatory muscle dysfunction in unilateral exodontia rabbits

Objective:

Occlusal alteration due to tooth loss may cause overload of masticatory muscle and promote muscle dysfunction. This study explored the feasibility of using functional magnetic resonance imaging (fMRI) to evaluate muscle dysfunction in an established unilateral exodontia animal model.

Methods:

six rabbits were extracted right maxillary molars. T2 mapping, T2* mapping and Iterative Decomposition of water and fat with Echo Asymmetry and Least Square Estimation (IDEAL-IQ) were performed one day before extraction and every 2 weeks (2th~12th week) after extraction. The T2 and T2* values and fat fraction (FF) of bilateral temporal muscle (TM), masseter muscle (MM) and medial pterygoid muscle (MPM) were measured and compared between the extraction side-and the contralateral side. Parameters of three monitoring time points (0th, sixth, 12th week) were also analyzed.

Results:

T2 values of MM on extraction side-were significantly higher than those of contralateral side-from fourth week to 12th week after extraction (p < 0.05). T2 values of MM and MPM on extraction side-and TM on contralateral side-were significantly higher in 12th week than those in 0th week (p < 0.05). And FF of bilateral MM was significantly higher in 12th week than those in 0th week (p < 0.05). T2* value showed no significant difference between extraction side-and contralateral side-and also at above three time points.

Conclusion:

T2 and T2* value and FF can be used as indicators of masticatory muscle dysfunction. fMRI is expected to be a non-invasive method for in vivo and real-time evaluation of masticatory muscle functional abnormality.

Vidarabine, an anti-herpes agent, prevents occlusal-disharmony-induced cardiac dysfunction in mice

We recently reported a positive relationship between occlusal disharmony and cardiovascular disease via activation of β-adrenergic signaling in mice. Furthermore, inhibition of type 5 adenylyl cyclase (AC5), a major cardiac subtype in adults, protects the heart against oxidative stress. Here, we examined the role of AC5 in the development of occlusal-disharmony-induced cardiovascular disease in bite-opening (BO) mice, prepared by cementing a suitable appliance onto the mandibular incisor. We first examined the effects of BO treatment on cardiac function in mice treated or not treated for 2 weeks with vidarabine, which we previously identified as an inhibitor of cardiac AC. Cardiac function was significantly decreased in the BO group compared to the control group, but vidarabine ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but vidarabine blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as increased activation of the Ca2+-calmodulin-dependent protein kinase II/receptor-interacting protein 3 signaling pathway. These data suggest that AC5 inhibition with vidarabine might be a new therapeutic approach for the treatment of cardiovascular disease associated with occlusal disharmony.

Development of a biomechanical model for dynamic occlusal stress analysis

The use of traditional finite element method (FEM) in occlusal stress analysis is limited due to the complexity of musculature simulation. The present purpose was to develop a displacement boundary condition (DBC)-FEM, which evaded the muscle factor, to predict the dynamic occlusal stress. The geometry of the DBC-FEM was developed based on the scanned plastic casts obtained from a volunteer. The electrognathographic and video recorded jaw positional messages were adopted to analyze the dynamic occlusal stress. The volunteer exhibited asymmetrical lateral movements, so that the occlusal stress was further analyzed by using the parameters obtained from the right-side eccentric movement, which was 6.9 mm long, in the stress task of the left-side eccentric movement, which was 4.1 mm long. Further, virtual occlusion modification was performed by using the carving tool software aiming to improve the occlusal morphology at the loading sites. T-Scan Occlusal System was used as a control of the in vivo detection for the location and strength of the occlusal contacts. Data obtained from the calculation using the present developed DBC-FEM indicated that the stress distribution on the dental surface changed dynamically with the occlusal contacts. Consistent with the T-Scan recordings, the right-side molars always showed contacts and higher levels of stress. Replacing the left-side eccentric movement trace by the right-side one enhanced the simulated stress on the right-side molars while modification of the right-side molars reduced the simulated stress. The present DBC-FEM offers a creative approach for pragmatic occlusion stress prediction.

Myogenous temporomandibular disorders and salivary markers of oxidative stress-A cross-sectional study

BACKGROUND

The clinical care of chronic pain requires personalised understanding of the mechanisms involved. Temporomandibular disorders (TMD) are the most common chronic orofacial pain conditions, and oxidative stress has been proposed to be implicated in their pathophysiology, especially in arthrogenous TMD. However, few studies have explored oxidative stress in myogenous TMD (TMDM).

OBJECTIVE

The aims of this study were to compare the salivary oxidative stress profiles between individuals with TMDM and healthy controls, and to explore associations of these markers with clinical characteristics.

METHODOLOGY

Saliva samples were collected from 39 individuals with TMDM and 37 age and sex-matched healthy volunteers. Psychological stress levels and clinical characteristics were assessed in all participants. The samples were analysed for total oxidant status (TOS), total antioxidative capacity (TAC) and superoxide dismutase activity (SODa). Comparisons between groups were performed using parametric and non-parametric tests depending on data distribution.

RESULTS

Psychological stress was higher in TMDM compared to controls (P < .001). TAC levels were significantly higher (P < .05) whereas TOS levels were significantly lower (P < .05) in TMDM compared to controls. There were no differences in SODa levels between groups and no correlations were found between clinical characteristics and oxidative stress markers.

CONCLUSION

Individuals with TMDM showed higher levels of antioxidative markers, but lower levels of oxidative markers. These results can be explained in part by chronicity and adaptation to the disease and other factors, such as psychological stress. Longitudinal studies must be conducted to clarify the role of oxidative stress in TMDM.