Genetic Polymorphisms in ACTN3 Contribute to the Etiology of Bruxism in Children.

Objective: Bruxism is a condition defined as a masticatory muscle activity with an unexplored genetic background. The aim of this study was to evaluate the association between genetic polymorphisms in ACTN3 and bruxism. Study design: A total of 151 biological-unrelated children, aged 7-12 years were included in a case control ratio of 1:1.5. The data collection was performed during interview and clinical examination. Saliva samples were collected from all children and 3 genetic polymorphisms in the ACTN3 (rs678397, rs1671064 and rs1815739) were selected for genotyping using real time PCR. Pearson chisquare calculation was used to assess Hardy-Weinberg equilibrium and to evaluate the association between genotypes and alleles frequencies for each genetic polymorphism in the co-dominant and recessive models. An alpha of 5% was used. Results: The genetic polymorphisms rs678397, rs1671064 and rs1815739 were associated with bruxism in the co-dominate model and in the recessive model (p<0.05). Allele distribution was also associated with bruxism for the polymorphisms rs678397 and rs1671064 (p<0.05). Conclusion: The genetic polymorphisms rs678397, rs1671064 and rs1815739 in ACTN3 are associated with bruxism and can contribute to the etiology of this condition in children.

Impact of temporomandibular disorders on the stomatognathic system in children.

BACKGROUND: To evaluate the EMG activity and thickness of right masseter (RM), left masseter (LM), right temporal (RT) and left temporal (LT) muscles and bite force in children with temporomandibular disorders (TMD). MATERIAL AND METHODS: Forty five children (mean age 8.8 years; 22 boys and 23 girls) were examined on the basis of the RDC/TMD and the Faces Pain Scale-Revised (FPS-R) was used to determine the level of severity of the signs and symptoms of TMD, resulting in four groups: GI - without TMD (n=10); GII - with mild TMD (n=18), GIII: with moderate TMD (n=12) and GIV: with severe TMD (n=5). The data of electromyographic activity, maximum bite force and muscle thickness were tabulated and submitted to statistical analysis (ANOVA, P≤0.05). RESULTS: Children with TMD signs and symptoms had lower EMG activity than children of the control group. There was significant difference among the groups for the LT at rest (P=0.01), right (P=0.03) and left (P=0.05) laterality, and for the LM (P=0.01) and LT (P=0.03) muscles in maximum voluntary contraction. There were no statistically significant differences among the groups regarding muscle thickness. The bite force was lower in the TMD groups than children of the control group, with significant statistical difference for the right region (P=0.03). CONCLUSIONS: The severity of TMD signs and symptoms affected the EMG activity and the molar bite force in children. However, structural changes in the thickness of masticatory muscles are not perceptible in children with TMD signs and symptoms.

Prevalence of sleep bruxism in children: a systematic review of the literature.

The aim of the present investigation was to perform a systematic review of the literature dealing with the issue of sleep bruxism prevalence in children at the general population level. Quality assessment of the reviewed papers was performed to identify flaws in the external and internal validity. Cut-off criteria for an acceptable external validity were established to select studies for the discussion of prevalence data. A total of 22 publications were included in the review, most of which had methodological problems limiting their external validity. Prevalence data extraction was performed only on eight papers that were consistent as for the sampling strategy and showed only minor external validity problems, but they had some common internal validity flaws related with the definition of sleep bruxism measures. All the selected papers based sleep bruxism diagnosis on proxy reports by the parents, and no epidemiological data were available from studies adopting other diagnostic strategies (e.g. polysomnography or electromyography). The reported prevalence was highly variable between the studies (3·5-40·6%), with a commonly described decrease with age and no gender differences. A very high variability in sleep bruxism prevalence in children was found, due to the different age groups under investigation and the different frequencies of self-reported sleep bruxism. This prevented from supporting any reliable estimates of the prevalence of sleep bruxism in children.