Influence of changing the chewing region on mandibular movement

Objectives:

The purpose of this study was to investigate the changes in three-dimensional mandibular movements when the chewing region was moved from the first molar to the first premolar, due to loss of posterior occlusal supports.

Methods:

Thirty clinical residents with healthy natural dentitions were recruited as subjects. A piece of beef jerky was selected as the test food. The subjects were asked to perform 20 seconds of spontaneous chewing of the test food using either the first molar or the first premolar on the preferred chewing side. Three-dimensional trajectories of lower incisors and both condyles were analyzed using a jaw motion tracking device with six degrees of freedom, during the period between the onset and offset of electromyographic bursts from the masseter and anterior temporal muscles. The study protocol was approved by the Ethics Committee of Matsumoto Dental University (#0042) and informed consent was obtained from all the subjects.

Results:

During the EMG bursts, chewing movement from the frontal view at the lower incisors tended to be narrower during first premolar chewing in comparison with first molar chewing. When this reference point was positioned 0.5 mm below the intercuspal position in the closing phase, significant difference was found in the angle of the pathway to the intercuspal position between first premolar chewing and first molar chewing (paired t-test; p<0.05). During the EMG bursts,the condylar movements were smaller and slower on both sides, when the chewing region was changed from the first molar to the first premolar (paired t-test; p<0.01).

Conclusions:

It was suggested that the mandibular movement during mastication might be changed to adapt the premolar chewing, due to loss of posterior occlusal supports.