The influence of single molar crown placement on the smoothness of masticatory movement

The jerk-cost is an index that can quantify the smoothness of various movements including human body movements. A previous study reported the usefulness of jerk-cost in the evaluation of masticatory movement, and proposed that the masticatory movement of subjects with good occlusion could be explained as a maximum smooth movement. The purpose of this study was to investigate the influence of a single prosthetic molar restoration on the smoothness of masticatory movement. Fourteen adults who visited this hospital seeking a single prosthetic restoration on a molar were selected. Each subject chewed a piece of chewing gum on the molars of the treated side before and after crown placement. Movement trajectory was recorded using the Sirognathograph Analyzing System. Normalized jerk-cost (NJC) was calculated on the closing phase of each chewing cycle and was compared before and after the crown placement. After the prosthetic restoration, NJC significantly decreased (P < 0.05) in seven subjects with a crown placed on a lower molar, whereas significant changes were not observed in seven subjects with a crown placed on an upper molar. These results suggest that restoring a crown on a lower molar could significantly improve the smoothness of masticatory movement on the same side.