This study´ was performed to measure the changes of the mandibular movement and the masticatory muscular activities anterior temporal and masseter muscle of both side - reflected by intentional increase of anterior guidance angle.
For this study, 5 volunteers (3 males and 2 females with average age of 24.0) were selected. Each volunteer had Angle´s classification I and did not have any missing tooth except third molar and any extensive restorations.
Metallic guide plate was made at volunteer´s working model fabricated by improved dental stone and cemented to the palatal surface of maxillary central incisor using resin cement(Panavia 21®) and then adjusted not to give any occlusal interferences at intercuspal position. The activity of masticatory muscles and the changes of mandibular movement were recorded by EMG and Sirognathograph in Biopak analysing system(Bioresearch Inc., Milwaukee, Wisconsin, USA). Measurement was done at before experiment, irnmediatley after placement, 1 week after placement, immediately after removal, and 1 week after removal.
The results were as follows:
1. Moderate phonetic disturbance and mild headache were occured to 3 volunteers for 2 days after setting and l volunteer had positive reaction to percussion and slight midline diastema. But all of these clinical signs were diappeared 1 week after removal and the other volunteer did not have any special clinical sign.
2. In the EMG of the mandibular rest position, the mean value of anterior tempotal muscle was increased immediately after placement(p<0.01) and then decreased 1 week after placement(p<0.05) and increased 1 week after removal(p<0.05) but not recovered as before experiment. The mean value of masseter muscle was decreased during the experiment period:
3. In the EMG during mandibular protrusive movement, all muscular activity was decreased during the experiment period. Reduced activity was not recovered I week after? removal(p<0.05).
4. During the habitual opening, anteroposterior movement of mandible was decreased immediately after place ment(p<0.05) and then increased 1 week after placement but not statistically significant(p>0.1). Vertical movement was not shown significant difference during the experiment period(p>0.1). Lateral movement was decreased immediately after placement(p<:0.05) and then increased 1 week after placement but not recovered as before experiment. The opening and closing velocity of mandible was shown minor changes but not statistically significant.
5. During the habitual opening, anteroposterior movement of mandible was decreased 1 week after placement(p<0.(6) and then increased immediately after removal and recovered 1 week after removal as before experiment. Vertical movement was not shown significant changes. Lateral displacement of mandible was increased continuously and recovered 1 week after removal. Opening velocity was temporarily increased immediately after removal but recovered and closing velocity was not shown significant changes.
6. During the right side chewing, anteroposterior movement of mandible was increased immediately after removal but recovered and vertical movement was not shown statistically significant results. Lateral displacement and velocity o mandible were not shown significant results.
7. During the left side chewing, the changes of mandibular movement pattern were not shown statistically significant results.
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