Occlusal contacts on the first mandibular molar among patients with different molar relationships using cone-beam CT

Abstract:

Objective：To analyze the differences of occlusal contacts on the first mandibular molar among patients with different molar relationships and to discover its practicability. Methods：Patients who needed to take cone-beam CT in our hospital between January 2013 and June 2013 were chosen. Totally 347 patients were selected according to the excluded rules. Numbers of occlusal contacts in the mesiocclusion，middle and distal areas among A，B，C three types of the first mandibular molar were recorded. SAS9.2 was used for statistical analysis. Results：The total number of occlusal contacts among three types was compared：Ⅰtype（n=130，26.62±10.79），Ⅱtype（n=131，26.75±10.81），Ⅲ type（n=86，19.16±9.14），with statistically significant differences（H=28.346，P=0.000）. The number of occlusal contacts was fewer in Ⅲ types than in the other two types，with statistically significant differences（P<0.016 7）. The num－ber of occlusal contacts in the mesiocclusion area among three types was compared：Ⅰtype （5.62±3.56），Ⅱtype（7.96±4.06），Ⅲ type（4.47±3.61），with statistically significant differences（H=45.045，P=0.000）. There were statistically significant differences among groups（P<0.0167）. The number of occlusal contacts in the middle area among three types was compared：Ⅰtype（10.3±4.74），Ⅱtype （9.24±4.54），Ⅲ type （6.53±4.04），with statistically signifi－cant differences（H=32.390，P=0.000）. There were statistically significant differences between groups（P<0.016 7）. The number of occlusal contacts was the fewerest in Ⅲ types and there was no statistically significant difference among groups. The number of occlusal contacts in the distal areas among three types was compared：Ⅰtype（10.7±4.89），Ⅱtype（9.55±5.35），Ⅲ type（8.16±4.72），with statistically significant differences（H=12.025，P=0.002）. The number of occlusal contacts was fewer in Ⅲ types than in Ⅰtype（P<0.016 7） and there was no statistically significant difference among other groups. The number of contact A was compared：Ⅰtype（10.46±5.75），Ⅱtype（9.53±5.2），Ⅲ type（7.83±5.02），with statistically significant differences（H=8.466，P=0.015）. The number of contact A was fewer in Ⅲ type than Ⅰtype（P<0.016 7） and there was no difference among others. The number of contact B was compared：Ⅰtype（9.66±5.58），Ⅱtype（10.87±5.08），Ⅲ type（6.17±4.7），with statistically significant differences（H=39.598，P=0.000）. The number of contact B was the fewest in Ⅲ type（P<0.016 7） and there was no difference among others. The number of contact C was compared：Ⅰtype（6.49±3.46），Ⅱtype（6.34±4.63），Ⅲ type（5.16±3.39），with statistically significant differences（H=7.179，P=0.028）. The number of contact C was fewer in Ⅲ type than Ⅰtype（P<0.016 7） and there was no difference among others. Conclusion：The total occlusal contacts and contact B of type Ⅲ on the first molar are fewer than others，so there is less stability dur－ing the intercuspal occlusion position，and the cone-beam CT could be a new method to research occlusal contacts.