Functional factors associated with continuous eruption of maxillary incisors in adulthood: A 10-year prospective...

To investigate whether functional factors estimated by the masseter muscle thickness (MMT) and the maximum occlusal force (MOF), were associated with the amount of continuous eruption of maxillary incisors in adults.

Dental casts were taken twice in 24 adult female patients during a 10-year prospective cohort study. At the first appointment, ultrasonographic measures of the MMT and MOF were recorded. The casts were scanned into a digital model and measurements of the eruption and clinical crown lengthening (CL) of the maxillary incisors were calculated after superimpositions on the palatal region. Univariate and multivariate mixed effect regression models were used to assess the single and joint role of functional factors, with presence or absence of occlusal contacts and CL on incisor eruption.

By using the linear mixed effects regression model, we observed that both the MMT and MOF were correlated with the maxillary incisor eruption. In particular, the thicker the masseter or the stronger the occlusal force, the lower the amount of eruption. Using a backward multivariable mixed effects model, the incisor eruption was correlated with the MMT combined with presence or absence of contacts and clinical CL. The amount of tooth eruption (0.32 mm on average) was positively associated with CL (0.29 mm on average); therefore, the greater the CL (gingival recession), the greater the amount of tooth eruption. The presence of occlusion contact between the maxillary incisors and their mandibular antagonists was found as an inhibitor of eruption in the multivariate model.

The functional capacity of masticatory muscles, as estimated by the MMT, plays a role in the amount of maxillary incisor eruption. The stronger the masticatory muscles, the lower the amount of eruption.