Correlation between occlusal contacts and masticatory muscle activity: A comparative study of cotton and wax normalization methods showing improved repeatability and comfort.

Objective: This study aimed to correlate occlusal marks on posterior teeth and cusp tips, recorded using an analog qualitative method, with digital evaluations of masseter and temporal muscle activity through electromyography indexes, comparing two normalization techniques (cotton and wax) using the standardized Percentage Overlap Coefficient of the Anterior Temporal muscle and Percentage Overlap Coefficient of the Masseter muscle indexes.

Design: This is a comparative cross-sectional observational study. Occlusal contact and electromyography records of the anterior temporal and masseter muscles were detected in 30 individuals with an average age of 34.9 years. During the electromyography examination, two repetitions of normalization were performed, each with maximum voluntary clenches of 5 seconds on cotton and on wax. The average electromyography amplitude was calculated from three repetitions for each material. According to the average obtained for each pair of muscles, the muscle activity index was calculated and correlated to the number of contacts, which were converted into percentages.

Results: Normalization with cotton showed a positive correlation between occlusal contacts and muscle activity (rs = 0.465, p = 0.010). The mean muscle activity index for cotton was 79.4 ± 13.9 for the masseter and 83.3 ± 9.2 for the temporal muscle, with no significant difference between the two muscles (p = 0.195). Normalization with wax showed better intra-subject repeatability with less than 5 % variation (masseter: 4.9 %, temporal: 4.2 %). There was no significant difference in muscle contraction between the different normalization materials (p = 0.902).

Conclusion: Both normalization methods demonstrated a variation of less than 10 %, with wax being considered more comfortable by the participants, indicating occlusal and muscular adaptation to the different methods. The results showed a positive correlation between posterior occlusal contacts and masticatory muscle activity, especially with cotton normalization, suggesting that occlusal contacts significantly influence muscle activity, potentially leading to muscle fatigue or hyperactivity.