A Comparative Study On Retromolar Space In Adult With Different Sagittal Facial Types

Objective: The purpose of this study was to measure the retromolar space in mandible and maxilla by using cone-beam computed tomography(CBCT)imaging,and to compare the relationship of the retromolar space and the third molar eruption patterns among adults with various sagittal facial types,in order to provide guidance for the individualized design of treatment plans.Material and Methods: From September 2020 to September 2022,145 normodivergent patients who met the inclusion criteria were selected from the Liao Ning,the retromolar space in the four quadrants of each patient were treated as four samples,as 360 images were included in this study.The experimental group was divided into Skeletal Class I group,Skeletal Class II group,Skeletal Class III group according to their Wits values;the control group was set as individual normal occlusion,and according to the third molar angulation(θ),the maxillary third molar was divided into mesial,distal and vertical impacted groups;the mandibular third molar was divided into mesial,horizontal and vertical impacted groups.The functional Cusp Line of the maxillary first and second molars was used as reference lines.The distance from the second molar to the edge of the cortex was measured at the level of the cemento-enamal junction(CEJ),the root bifurcations,the distance from the root bifurcations(2,4,6 mm).The functional Cusp Line of the mandibular first and second molars and the median sagittal line were used as reference lines.The shortest distances between the inner lingual cortex of the mandibular body and second molar root was measured at the level of the cemento-enamal junction(CEJ),the root bifurcations,the distance from the root bifurcations(2,4,6mm).Statistical analysis of all measured parameters was performed using the SPSS 22.0 software package.Result:1.Three dimensional measurement of maxillary retromolar space in different sagittal facial types by using CBCT1.1 At the level of the CEJ,the level of the root bifurcations,the level of the distance from the root bifurcations(2,4,6mm),compare with the Skeletal Class I group、Skeletal Class III group and individual normal occlusion,the retromolar space values of the Skeletal Class II group was the longest,the values of the Skeletal Class III group was the smallest,and there were statistical difference(P <0.05);the measured values of retromolar space in each group was minimum at the level of the CEJ,the measured gap value increases as the measurement level moves up;1.2 The third molar was divided into mesial,distal and vertical impacted groups,and the measured values of the vertical impacted group was longer than the mesial and distal impacted group,and there were statistical difference(P <0.05);the difference between the mesial and distal impacted group has no statistical significance(P> 0.05).2.Three dimensional measurement of mandibular retromolar space in different sagittal facial types by using CBCT2.1 Based on the occlusal line and sagittal line,the retromolar space at the level of the CEJ,the level of the root bifurcations,the level of the distance from the root bifurcations(2,4,6mm),the measured values of the Skeletal Class III group was longer than Skeletal Class I group,Skeletal Class II group and individual normal occlusion,the Skeletal Class II group has the smallest retromolar space,and there were statistical difference(P <0.05);the retromolar space has the largest measured values at the level of the CEJ,and the measured gap value decreases as the measured level moves down;2.2 The third molar was divided into mesial,horizontal and vertical impacted groups,and the measured value of the vertical impacted group was longer than the mesial and horizontal impacted group,and there were statistical difference(P <0.05);the difference between the mesial and horizontal impacted group has no statistical significance(P> 0.05).Conclusion:1.At each measurement level of maxillary second molar,the Skeletal Class II patients have the longest retromolar space;Skeletal Class III patients have the smallest measured value,so the patients with Skeletal Class II have a larger space in the posterior area of maxilla,which can provide more space to provide distal displacement.Patients with Skeletal Class III are adviced to explicit the values of retromolar space when pushing the molar backward;2.Compared with Skeletal Class I patients,Skeletal Class II patients,and the patients with individual normal occlusion,the measured values of patients with Skeletal Class III are longer in each plane,and patients with Skeletal Class II were smaller in each plane.Patients with Skeletal Class III have a larger space in the posterior area of mandible,which can provide more space to provide distal displacement,and patients with Skeletal Class II should pay attention to the limitation of the lingual bone cortex of mandibular molar;3.At the level of CEJ,the measurement values of posterior space of maxillary molars were the smallest in patients.so,when pushing the maxillary molar backward,more attention should be paid to the anatomical limit of the level of CEJ;the measurement values of posterior space of mandibular molars were the smallest at the level of 6mm,when pushing the mandibular molar backward,more attention should be paid to the lingual cortex of the mandible.4.The third molar eruption patterns will have different effects on the distal movement of the molar.In the vertical impacted group,the retromolar space is longer than others,which means the vertical group has larger retromolar space to provide distal displacement.so the influence of the third molar on retromolar space should not be ignored.