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ABSTRACT
In humans, the inappropriate occlusal vertical dimension (OVD) causes several orofacial disorders, such as bruxism and pain in the masticatory muscles and temporomandibular joint. However, it is still unclear how strictly the OVD is adjusted. To answer this question, we studied the temporal change of the OVD in bite-raised young guinea pigs. The OVD was raised by fixation of a bite-raising appliance to the lower incisors, and increased by either 3 or 1.5 mm at the first molars. After the space produced between the upper and lower molars was filled within 10 days due to eruption of the molars, the appliance was removed. In the bite-raised animals, the raised OVD was reduced until it attained that observed in the control animals, after which the OVD increased according to cranial growth. These results show that the OVD is developmentally changed and strictly controlled.
KEY WORDS: vertical dimension, bite-raised appliance, eruption, grinding, guinea pig.
Received January 15, 2002; Last revision October 20, 2002; Accepted October 30, 2002
INTRODUCTION
In humans, occlusal vertical dimension (OVD) may be set at a position appropriate to the conduct of oral functions: mastication, deglutition, and conversation. When it is increased excessively, patients often complain of headache, bruxism, pressure pain of the masticatory muscles, and pains during jaw movements and around the temporomandibular joint (Christensen, 1970). In animal studies, the excessively raised OVD induced some acute and chronic pathological changes in the oral-facial structures, including mandibular deformation (McNamara, 1973; Rowe and Carlson, 1990) and changes in muscular attachments (McNamara, 1973) and muscle fiber compositions (Paik et al., 1993; Kawasaki et al., 1997; Ohnuki et al., 1999). These findings indicate the importance of keeping an appropriate OVD. It is not clear, however, how strictly the OVD is regulated. To answer this question, we studied the temporal change of the OVD in naive control and bite-raised guinea pigs, whose teeth erupt continuously (Holmstedt et al., 1977).
MATERIALS & METHODS
All experimental procedures were approved by the Committee on Animal Research of the Osaka University Graduate School of Dentistry. Twenty-eight male Hartley guinea pigs (4-5 post-natal wks old) were used; half of them were used as controls, and in the other animals, the dimension between the upper and lower molars...