Biomechanical Relationship Between Trunk Flexion and Mouth Opening: Pilot Study

The aim of the present study is to analyze if there is a biomechanical relationship between trunk flexion and buccal opening and to observe if there is an improvement of trunk flexion by performing the "sit and reach" test when stretching the masticatory muscles.

The study design is made up of a double-blind clinical trial with 60 participants randomly divided into two groups of 30 people each (Treatment group and Control group). Basal measurements of the mouth opening were taken with a vernier caliper and the trunk flexion measurements were taken by means of the "sit and reach" test. These measurements were carried out again after the intervention, which consisted of self-stretching of the masticatory muscles for the Treatment group and an occlusion of the mouth for the Control group. In the results there was an increase in the trunk flexion compared to the initial values in both groups (Treatment group 2.8 (1.51), Control group 1.97 (2.31) and this increase was greater in the Treatment group even though the difference with the Control group was not statistically significant. Therefore, the stretching of the masticatory muscles does not cause an immediate increase in the degree of trunk flexion measured by the "sit and reach" test. As a consequence, we cannot confirm the existence of a biomechanical relationship between trunk flexion and mouth opening.