The mechanism for regulating the isometric contraction of masseter muscles is involved in determining the vertical dimension of occlusion

Myths surrounding vertical dimension of occlusion in restorative dentistry: A scoping review

OBJECTIVE

This scoping review aims to clarify the concept of vertical dimension of occlusion (VDO) in prosthetic dentistry, addressing prevalent myths, and controversies regarding its clinical management and impact on the stomatognathic system.

METHODS

This paper critically examines common beliefs about VDO alteration and its effects on temporomandibular disorders (TMD) through an extensive literature review and an international survey. The survey included 862 general dentists and prosthodontists and explored their approaches to altering VDO and their perceptions of the clinical implications. The literature review provided a thorough analysis of existing research on VDO modification techniques, the adaptability of the stomatognathic system, and the relationship between VDO changes and TMD.

RESULTS

The survey revealed insights into dentists' perspectives on VDO, showing that while many practitioners test a new VDO due to concerns about patient adaptation, a significant majority observed that patients typically adjust well to a new VDO regardless of the technique used. The survey highlighted differing beliefs about the need for a gradual process and trial phase for VDO alteration, as well as the stability of modified VDO. Literature review suggests the stability and adaptability of VDO changes due to muscle adaptability and indicates no direct causal or curative link between VDO changes and TMD. Traditional methods for determining VDO in complete dentures may not be suitable for worn dentition, underscoring the need for tailored approaches.

CONCLUSION

This paper suggests that the traditional belief in the need for a prolonged trial phase for VDO alterations may be reconsidered in light of evidence supporting the adaptability of the stomatognathic system. Moreover, it emphasizes the importance of distinguishing between methods suitable for complete dentures and those for managing cases of worn dentition. The purported link between VDO alterations and TMD is also found to lack scientific evidence, highlighting the need for individualized patient care based on current evidence and clinical judgment.

Electromyographic Diagnostic Ranges Defining Temporomandibular Disorders and Healthy Individuals' Results in Functional Clenching Index

Background: Temporomandibular disorders (TMDs) represent a significant public health issue, among which masticatory muscle pain is the most common. Current publications increasingly indicate surface electromyography (sEMG) as an effective diagnostic tool for muscle dysfunctions that may be employed in TMDs recognition. The objective of this study was to establish reference ranges for TMDs patients with masticatory muscle pain and healthy individuals in the electromyographic Functional Clenching Index (FCI) for the temporalis muscles (TAs) and masseter muscles (MMs). This research aimed to provide an additional diagnostic tool for TMDs patients. Methods: A total of 48 individuals (n = 30 women and n = 18 men) with the muscular painful form of TMDs were recruited alongside a numerically and gender-matched control group-healthy, pain-free controls. The Functional Clenching Indexwas calculated for both groups. Results: Data analysis revealed statistically significant differences with a very large effect size. Healthy individuals had higher FCI scores compared to those with TMDs. The healthy group exhibited higher threshold values compared to the TMDs group. Conclusions: For healthy individuals, the FCI ranges for TAs were between 58 and 145, while for MMs, between 72 and 210. Lower values may indicate muscle activation disorders and occur in patients with the painful, muscular form of TMDs. This is the first study to define reference ranges for electromyographic indices; therefore, caution is recommended, and the replication of this study on a larger and more culturally diverse sample is advised.

DO ORAL CARE AND REHABILITATION IMPROVE COGNITIVE FUNCTION? A SYSTEMATIC REVIEW OF CLINICAL STUDIES

OBJECTIVES

An increasing number of studies have identified an association between oral health status and cognitive function. However, the effect of oral interventions, including oral health care, dental treatment and oral motor exercises, on cognitive function remains unclear. This systematic review examined whether oral interventions contribute to the long-term improvement of cognitive status.

METHODS

Four databases were searched (MEDLINE, Web of Science, Cochrane Library, and ICHUSHI Web) to identify randomized and nonrandomized controlled trial studies and prospective cohort studies from inception until 1 September 2023, published in English or Japanese. The Cochrane risk of bias tool for randomized controlled trials and the risk of bias assessment tool for nonrandomized studies were used to assess bias risk.

RESULTS

A total of 20 articles were included in the qualitative analysis; 13 articles were published in English, and 7 were published in Japanese. The implemented interventions were oral care in 8 studies, dental treatment in 8 studies, and oral motor exercise in 4 studies. One study found a significant effect on attention following oral care intervention. Some dental treatments influenced cognitive function, although a clear positive effect was not determined. In 1 study, attention and working memory improved in the chewing exercise group.

CONCLUSIONS

Several studies verified the improvement effects of oral interventions, such as oral care, dental treatment, and oral motor exercise, on cognitive function or impairment. However, there was still a lack of conclusive evidence that such an intervention clearly improved cognitive function. To clarify the effects of oral interventions on cognitive function, it is necessary to examine participants, interventions, and outcome measures in detail.

Surface Electromyography in Dentistry-Past, Present and Future

Surface electromyography (sEMG) is a technique for measuring and analyzing the electrical signals of muscle activity using electrodes placed on the skin's surface. The aim of this paper was to outline the history of the development and use of surface electromyography in dentistry, to show where research and technical solutions relating to surface electromyography currently lie, and to make recommendations for further research. sEMG is a diagnostic technique that has found significant application in dentistry. The historical section discusses the evolution of sEMG methods and equipment, highlighting how technological advances have influenced the accuracy and applicability of this method in dentistry. The need for standardization of musculoskeletal testing methodology is highlighted and the needed increased technical capabilities of sEMG equipment and the ability to specify parameters (e.g., sampling rates, bandwidth). A higher sampling rate (the recommended may be 2000 Hz or higher in masticatory muscles) allows more accurate recording of changes in the signal, which is essential for accurate analysis of muscle function. Bandwidth is one of the key parameters in sEMG research. Bandwidth determines the range of frequencies effectively recorded by the sEMG system (the recommended frequency limits are usually between 20 Hz and 500 Hz in masticatory muscles). In addition, the increased technical capabilities of sEMG equipment and the ability to specify electromyographic parameters demonstrate the need for a detailed description of selected parameters in the methodological section. This is necessary to maintain the reproducibility of sEMG testing. More high-quality clinical trials are needed in the future.

Increased vertical dimension of occlusion for varying periods differentially impairs learning and memory in guinea pigs

There is an increasing number of studies showing that occlusal dysfunction impairs learning and memory. We previously demonstrated that the brain has a mechanism to calibrate between the activities of spindle afferents and periodontal-mechanoreceptor afferents for controlling the chewing movement, and the accurate calibration can be done only at the proper vertical dimension of occlusion (VDO). Then, the chewing at an inappropriate VDO may induce a severe mental stress due to a mal-calibration. However, it is not clear how the impairment of learning/memory progresses over the period of stress induced by occlusal dysfunction. We investigated by passive avoidance test how the behavior and learning/memory are altered in guinea pigs in which the VDO was raised by 2-3 mm over the period up to 8 weeks. We found that the guinea pigs reared under the raised occlusal-condition (ROC) for 1 week showed a very high sensitivity to electrical stimulation whereas this did not cause the memory consolidation in the 1st-day retention trial, suggesting that such hypersensitivity rather hampered the fear learning. In the guinea pigs reared under the ROC for 2 and 8 weeks, the learning ability was not largely affected and memory consolidation occurred similarly whereas the memory retention deteriorated more severely in the latter guinea pigs than in the former ones. In the guinea pigs reared under the ROC for 3 and 4 weeks, learning was severely impaired, and memory consolidation did not occur. These results suggest that the occlusal dysfunction for varying periods differentially impairs learning and memory.