ACTN3 genotype influences masseter muscle characteristics and self-reported bruxism

Inflammatory Markers and Sleep Architecture in Sleep Bruxism-A Case-Control Study

Background: Sleep bruxism (SB) is a common sleep-related movement behavior with a multifaceted etiology and a deficiently understood pathophysiology. A recent hypothesis suggests a link between SB and systemic inflammation. The scope of the study was to determine whether bruxers have altered sleep structure and different levels of inflammatory parameters compared to nonbruxers. Methods: A total of 83 adults underwent full-night polysomnography. The polysomnograms were evaluated using the American Academy of Sleep Medicine (AASM) guidelines. Then, the blood samples were obtained from the participants by venipuncture and the analyses were performed. The study group was divided based on bruxism episode index (BEI) into two groups: BEI ≤ 4 and BEI > 4. Results: In comparison with nonbruxers, the oxygen desaturation index (ODI) was significantly higher in severe bruxers (7.5 ± 11.08 vs. 3.33 ± 5.75, p < 0.005), as well as the arousal parameters (7.77 ± 4.68 vs. 4.03 ± 2.97, p < 0.001), and the mean oxygen desaturation (3.49 ± 0.69 vs. 3.01 ± 0.67, p < 0.05). Moreover, the differences in sleep architecture and deprivation of the deep sleep phase were observed, the non-REM sleep stage 3 was significantly shorter in severe bruxers (p < 0.03). Differences were also noted in non-REM sleep stage 1 and REM sleep phase. In the investigated group, there were no statistical differences in inflammatory cytokines levels between bruxers and nonbruxers. Conclusions: Sleep bruxism is associated with sleep structure alterations and may be associated with deep sleep phase deprivation. The inflammatory markers are not linearly correlated with the severity of sleep bruxism expressed as BEI.

Systematic Review on the Link between Sleep Bruxism and Systemic Chronic Inflammation

Sleep bruxism (SB) is a sleep-related behavior characterized as rhythmic (phasic) or non-rhythmic (tonic) masticatory muscle activity. SB is a common sleep behavior with a predominantly central origin. The aim of this systematic review was to evaluate the relationship between inflammatory status and SB according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 (PRISMA 2020). The research was registered at PROSPERO (CRD42023395985). We performed a systematic literature analysis using five different databases. Furthermore, the backward snowballing technique was applied to identify additional papers. Initially, 28 papers were screened from the database search, and 162 papers were revealed in the backward snowballing process. Eventually, five articles were included. Data concerning the inflammatory status of patients experiencing SB were investigated and summarized. Due to the heterogeneity of the compared studies, only a qualitative comparison and narrative summary were performed. The results suggest that SB could be associated with systemic inflammation. In fact, this systematic review revealed that there are no papers conclusively showing that the inflammatory status in bruxers is comparable to non-bruxers. However, each of the examined studies utilized different methods of assessing systemic inflammation, which makes the results dubious.

Ectomesenchymal Six1 controls mandibular skeleton formation

Craniofacial development requires intricate cooperation between multiple transcription factors and signaling pathways. Six1 is a critical transcription factor regulating craniofacial development. However, the exact function of Six1 during craniofacial development remains elusive. In this study, we investigated the role of Six1 in mandible development using a Six1 knockout mouse model (Six1 ^-/- ) and a cranial neural crest-specific, Six1 conditional knockout mouse model (Six1 ^f/f ; Wnt1-Cre). The Six1 ^-/- mice exhibited multiple craniofacial deformities, including severe microsomia, high-arched palate, and uvula deformity. Notably, the Six1 ^f/f ; Wnt1-Cre mice recapitulate the microsomia phenotype of Six1 ^-/- mice, thus demonstrating that the expression of Six1 in ectomesenchyme is critical for mandible development. We further showed that the knockout of Six1 led to abnormal expression of osteogenic genes within the mandible. Moreover, the knockdown of Six1 in C3H10 T1/2 cells reduced their osteogenic capacity in vitro. Using RNA-seq, we showed that both the loss of Six1 in the E18.5 mandible and Six1 knockdown in C3H10 T1/2 led to the dysregulation of genes involved in embryonic skeletal development. In particular, we showed that Six1 binds to the promoter of Bmp4, Fat4, Fgf18, and Fgfr2, and promotes their transcription. Collectively, our results suggest that Six1 plays a critical role in regulating mandibular skeleton formation during mouse embryogenesis.

Influence of genotype and perioral musculature on maxillary and mandibular development

OBJECTIVES

To determine whether there is an association between skeletal jaw position and perioral musculature, and if genotypes can predict skeletal growth.

MATERIALS AND METHODS

A prospective study on 42 patients over 1 year was performed. The study included 22 females and 20 males with and average age of 28.5 years. Lip strength was compared to radiographic cephalometric measurements. Allelic and genotypic frequencies from polymorphisms rs678397 and rs1815739 in ACTN3 and rs10850110 in MYO1H were compared to each variable. Chi-square and Fisher exact tests were used to determine if differences were statistically significant (alpha = 0.05).

RESULTS

The data showed significant differences between rs678397 genotype and allele frequencies and SNA angle (P = .01; P = .003, respectively); between rs1815739 allele frequency and SNA angle (P = .01); between rs678397 allele frequency and ANB angle (P = .049); between rs678397 genotype and allele frequencies and lip strength in females (P = .045; P = .02); and between rs678397 allele frequency and overall lip strength (P = .049), after mean strength values used as cut off being customized by sex.

CONCLUSIONS

Polymorphisms in ACTN3 are associated with weak lips and larger SNA and ANB angles.