The association between maximum mouth opening and sociodemographic factors among Saudi adults: a cross-sectional study

Introduction Maximum mouth opening (MMO) is an essential clinical measurement for evaluating mandibular function and temporomandibular joint mobility. Establishing normative values across populations is crucial for the accurate diagnosis of trismus and for guiding oral and maxillofacial interventions. This study aimed to determine the mean MMO among Saudi adults and to examine its association with sociodemographic and anthropometric variables. Methods A cross-sectional study was conducted among 400 adults in Qassim, Saudi Arabia. MMO was measured using a digital caliper with triplicate readings averaged for analysis. Sociodemographic and anthropometric data were recorded. Group differences in MMO were assessed using one-way analysis of variance (ANOVA), followed by Tukey post hoc testing for variables with statistically significant ANOVA results, in addition to Monte Carlo-adjusted chi-square tests for categorical comparisons. A multivariable linear regression model was performed to identify independent predictors of MMO. Results The mean of MMO was 45.7 ± 6.9 mm (median: 46.3 mm; range: 28.0–66.3 mm). ANOVA showed significant differences in MMO by gender ( p < 0.0001) and height ( p < 0.0001), with males and taller individuals exhibiting greater mouth opening. No significant differences were found across age, weight, or BMI categories. In the multivariable regression model, height remained the only significant independent predictor of MMO ( β = 0.154, p = 0.008), while gender showed a non-significant trend. Age and weight were not associated with MMO. Discussion In this adult Saudi population, MMO was primarily influenced by height, with males showing larger values. Age, weight, and BMI were not significant predictors. These findings support using sex and stature-adjusted reference values to improve trismus diagnosis and clinical decision-making. Further research incorporating craniofacial measures is recommended to refine normative standards.