| Objective:Taking the borderline cases of extraction and non-extraction as the research object,the TeeTester occlusion system was used to analyze the occlusal contact characteristics of borderline cases after extraction and non-extraction.The PAR index was used to evaluate the therapeutic effect,which is intended to provide a reference for determining the treatment plan in orthodontic clinic and adjusting the occlusal relationship and improving the state of the occlusion function,and provide some new ideas for the application of the PAR index.Methods:Screening of 40 patients with borderline extraction and non-extraction cases at the end of the orthodontic treatment at the Stomatological Hospital of Lanzhou University from September 2017 to September 2018(20 teeth extraction and20 non-extraction).TeeTester Bite Force Analyzer V3.2.0(Aidong Group company,China)recorded the total occlusal force(TOF),the location of the center of occlusal force(COF),and the total area of occlusal contact(TCA),the percentage of occlusal strength on the left and right sides and the asymmetry index(AOF)of the occlusal force in maximum intercuspal position;the time of occlusal separation in the protrusive and lateral occlusion movements was recorded.The recorded data were used to analyze the differences in occlusal contact characteristics between the three basic movements of the mandible after orthodontic treatment in patients with and without extraction.The PAR index items were measured by the preoperative and postoperative dental model,and the weighted scores of each item before and after treatment,the weighted PAR index total score,the weighted PAR index total score difference,and the weighted PAR index total score reduction percentage were calculated to evaluate the orthodontic treatment effect of the patient.Statistical software was used to perform paired test statistical analysis on the data of patients with borderline extraction and non-extraction.Results:1.There is a significant difference in the total occlusal force and the total area of occlusal contact between the extraction group and the non-extraction group in the maximum intercuspal position(MIP),which may be related to tooth reduction.2.In the MIP of the extraction group and the non-extraction group,there was no significant difference in the unit area force value,the right side bite strength percentage,the left side bite strength percentage,the asymmetry index of occlusal force and the center point position of occlusal force.3.There was no significant difference in the separation time of anterior extension of the occlusal joint and the separation time of the left lateral occlusion and the separation time of the right side occlusal in the protrusive and lateral occlusion movements of the extraction group and the non-extraction group.4.The extraction group was compared before and after orthodontic treatment,there were significant differences in the other 10 PAR index measurement items except the malposition of mandibular right posterior segment and left buccal occlusion relationship.5.Compared with before and after treatment,the non-extraction group had significant differences in the maxillary anterior segment and the anterior mandibular section in terms of tooth dislocation,overjet,overbite,and weighted PAR index.6.In the comparison of the PAR index before treatment of the extraction group and the non-extraction group,there were significant differences in the dislocation of the maxillary anterior teeth and the dislocation of the anterior teeth of the mandible.7.Compared with the measurement items of the PAR index after the treatment of the extraction group and the non-extraction group,there is a significant difference in the weighted total score of the PAR index.8.There was no significant difference in the evaluation of the effect level between the extraction group and the non-extraction group(?~2=2.978;P value=0.317>0.05).9.There were significant differences in the total score difference of weighted PAR index and the percentage reduction of total score of weighted PAR index between extraction group and non-extraction group.Conclusion:1.Orthodontic treatment of borderline cases with or without extraction has a significant effect on the total value of occlusal force,that is,there is a significant difference in the total occlusal force between the two groups at the end of the treatment of the extraction group and the non-extraction group,which is statistically significant.Because the total occlusal force of four premolars in extraction group is less than that of non-extraction group,it can be considered that the subtractive orthodontic treatment can cause partial loss of the total occlusal force.2.In this experiment,by comparing the total occlusal force and the total occlusal contact area between extraction group and non-extraction group in the MIP,we concluded that subtractive orthodontic treatment could also cause the loss of total occlusal contact area.3.In the treatment of borderline cases,tooth extraction is not the main factor affecting the force per unit area,that is to say,the subtractive orthodontic treatment does not affect the unit area force value,and there is no correlation between the two.4.borderline cases Whether or not the orthodontic treatment of tooth extraction can achieve the balance of bite force distribution,the extraction of teeth in borderline cases is not the main factor affecting the distribution of occlusal force.5.In the borderline case of the extraction group and the non-extraction group,there was no statistical difference between the two groups in the time of protrusion occlusal separation,the time of right occlusal separation and the time of left occlusal separation in the period of mandibular functional movement,that is to say,the incidence of occlusal interference in the functional movement of mandible at the end of orthodontic treatment in extraction group and non-extraction group was not statistically significant.6.There was no significant difference in the severity of malocclusion between the extraction group and the non-extraction group in the borderline case before treatment.In the comparison of PAR index measurement items before orthodontic treatment between extraction group and non-extraction group,there were significant differences between maxillary anterior teeth malposition and mandibular anterior teeth malposition.It can be concluded that anterior teeth malposition may be one of the influencing factors of orthodontic treatment in borderline cases.7.Both extraction and non-extraction in borderline cases can achieve the purpose of correcting malocclusion,but extraction is more conducive to adjusting the relationship between teeth and occlusion. |
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