Effects Of Unilateral First Molar Loss On Occlusion And Condyle Symmetry, And The Relationship Between Occlusion And Mandibular Asymmetry

Objective The unilateral first molar lost patients as subjects were selected, the characters of occlusal contacts and the mandibular asymmetry were applied for this study and comparing it with normal occlusion, and the relationship between occlusion and mandibular asymmetry. There were two methods to investigate the effect of unilateral first molar loss patients, in order to find harm the unilateral first molar loss on TMJ and stomatognathic system, and to guide the clinical design and evaluate the clinical efficacy of treatment programs.Method The study groups include 60 patients, which loss unilateral first molar, according to the time of the molar loss be divided into the study group 1, the study group 2, the study group 3. The study group 1 include 20 patients, which loss molar before 12 years old. The study group 2 include 20 patients, which loss molar between 12 and 18 years old. The study group 3 include 20 patients, which loss molar after 18 years old. The control groups include 60 patients, which have normal occlusion. The data of occlusal contacts of study group and control group were recorded with T-Scan III system in intercuspal position, protrusive movement and lateral movement, and compared with the data of the control groups. The data include the center of occlusal force, occlusion time which is the first upper and lower teeth contact to intercuspal position, protract disclusion time which is from intercuspal position to only anterior teeth contact, lateral disclusion time which is fromintercuspal position to only canine teeth contact. There is if have the occurrence rate of premature contact and occlusal interference, and compared with normal occlusion. Condylar, ramal and condylar-plus-ramal asymmetry index measurements were performed on the panoramic radiographs of a study group including 60 patients and a control group of 60 person, and compared with normal occlusion. The results of two groups were analyzed with statistical methods by SPSS 13.0.Results 1. The occlusion time, disclusion time, the distance between center line and center of occlusal force of study group were longer than the control groups and there were significant differences in statistical analyse, the occurrence rate of premature contact and occlusal interference in patients were higher than that of normal occlusion(P<0.05). 2. Condylar asymmetry index and ramal asymmetry index measurements of the study groups are compared with the control groups’ no statistically, and CRAI measurements were not statistically different between the groups with a unilateral first molar extracted after the age of 18 years(P>0.05), while CRAI measurements were statistically different between the groups with a unilateral first molar lossed before the age of 18 years(P<0.05).Conclusion1.There are statistically differents occlusal contact datas of the three study groups in patients with unilateral first molar missing compare with the datas of the control group. In intercuspal position, occlusal force of the molar missing is few than the no missing. As a result, patients with missing teeth on each side of tooth or unbalanced force, so it can affect the function. 2.In the control study 1 and study 2 with unilateral first molar missing patients’ s asymmetry index compared with the control group is statistically difference, therefore, the patients with early unilateral first molar missing can affect mandibular morphology, which have an effect to patients with facial morphology. 3.There is a relationship between occlusion and the mandibular symmetry. 4.This finding of study indicate that the unilateral first molar missing has an effect on the masticatory system, temporal-mandibular joint and stomatognathic system.