| Food impaction is one of the common problems after crown restoration,especially between the first and second molars.It does harm to the health of the teeth and periodontal tissues in different degrees.The primary cause of food impaction is that there is a gap between the teeth.According to the occurrence of proximal gap,food impaction can be divided into two types: food impaction with proximal space and food impaction with tight proximal contact.The pathogenic factors of food impaction with proximal space are clear,which are mainly due to the loss of adjacent contact caused by caries,tooth movement and repair damage.The main treatment is to remove the etiology and restore the adjacent contact.Food impaction with tight proximal contact refers to that there is an adjacent contact relationship in the stationary state,but there may occur a transient separation of the adjacent contact area during mastication and result in food impaction.Clinically,it is often found that good adjacency contact is restored after crown restoration,but food impaction still exists during mastication,especially after crown restoration of the second molars.However,there is still a lack of comprehensive clinical investigation and research on such clinical problems.Meanwhile,the mechanism of food impaction with tight proximal contact is still unclear,and its clinical treatment mainly focuses on experiential occlusal adjustment,which lacks of scientific and normative.Therefore,it is an urgent clinical problem to find out the pathogenesis and causes of food impaction with tight proximal contact,and it is also the basis of establishing scientific and standardized diagnosis and treatment techniques.Objective:Abnormal distribution of occlusal contact after crown restoration may be closely related to the occurrence of food impaction with tight proximal contact.Based on this hypothesis,the characteristics and influencing factors of the disease were analyzed after investigating and studying the incidence,type,occurrence time,cause and other clinical characteristics of food impaction after crown restoration of the second molars through a large sample cross-sectional study.In addition,the tooth movement analysis technology based on digital technology and the quantitative analysis of occlusal contact were used to study the tooth displacement rule and occlusal contact characteristics of teeth with food impaction under occlusal state,which can be used to explore the correlation between food impaction and occlusal contact.The purpose of this study is to provide an experimental basis for elucidating the formation mechanism of food impaction with tight proximal contact after crown restoration of second molars,and to provide a new idea for clinical prevention and treatment of food impaction after crown restoration.Methods:1.A telephone follow-up was conducted to investigate for all patients who complete the crown restoration of second molars in Department of Prosthodontics,Stomatology Hospital,the Fourth Military Medical University(between 2014.1 and 2020.12)if there is food impaction after crown restoration.According to the follow-up results,the incidence of food impaction was calculated and the patients with food impaction after crown restoration of second molars were selected for inquiry and clinical examination.Including the patient’s general information,prosthesis information,information about food impaction,conditions of adjacent teeth and adjacent contact area,morphology of opposite occlusal teeth,periodontal health,etc.The proportion of classification,distribution,etiology and periodontal health of food impaction were analyzed.2.According to inclusion and exclusion criteria,20 patients in food impaction with tight proximal contact were enrolled among those who came to our hospital and complete clinical examination for food impaction after crown restoration of the second molars were conducted a quantitative study on the changes of the adjacent space and length of adjacent line under the occlusal state.The side of food impaction after crown restoration was used as the experimental group,the teeth with the same name on the other side and the bilateral teeth with the same name of healthy volunteers were used as the control group.The digital tooth movement analysis technique and three-dimensional quantitative analysis technique was used to compare and analyze the centroid distance of the first and second molar before and after occlusion,and the centroid movement and change in the length of adjacent line was calculated.3.In vivo experiments were conducted to evaluate the reliability and validity of four digital occlusal contact measurement methods: Scanning of articulating paper marks(SAP),Dental Prescale occlusion analysis system(DPO),T-scan occlusion analysis system(TSO)and Virtual occlusion constructed analysis method(VOC),providing methodological support for the quantitative analysis of occlusal contact.According to inclusion and exclusion criteria,20 healthy volunteers were recruited as subjects to test the intraclass correlation coefficient(ICC)between two measurements(2 weeks interval)by different methods to assess reliability;Pearson correlation coefficients between four digital measurement methods and the Silicone transmission analysis method(STA)were evaluated for effectiveness analysis.4.Patients in food impaction with tight proximal contact were enrolled in the study,and SAP method and VOC method were used to measure occlusal contact.The total occlusal contact area of the first and second molar occlusal surfaces,the occlusal contact area of distal/mesial beveling of the tooth and the ratio between them were calculated by using the software area measuring tool after beveling was partitioned according to the occlusal surface morphology.The results were compared with the teeth with the same name on the other side and the bilateral teeth with the same name of healthy volunteers.Results:1.In this study,a total of 1152 patients after crown restoration of second molars were followed up by telephone,including 351 cases of food impaction(30.5%).Affected by the coronavirus disease 2019,only 115 cases of them came to the hospital for clinical examination.The results showed in the position distribution of impaction,maxillary(63cases)was more than mandibular(52 cases).In the type of food impaction,the vertical food impaction was the most(51.3%),followed by mixed food impaction(39.1%),and horizontal food impaction was the least(9.6%).Food impaction with proximal space accounted for 25.9% and food impaction with tight proximal contact accounted for 74.1%.The calculus index,gingival index,periodontal probing depth and tooth looseness on the food impaction side were all worse than those on the control side,and there were statistical differences between them(P < 0.01).2.In the patients with food impaction with proximal tight contact after the crown restoration of second molars,the adjacent space of the first and second molars increased and the length of the adjacent line decreased in the occlusal state,the change of centroid distance was(0.099±0.035)mm.However,the adjacent distance became smaller and the length of the adjacency line increased in the control side,and the change of centroid distance was(-0.027±0.016)mm.The same changes were also observed in the teeth with the same name of healthy volunteers.The change of centroid distance after occlusion was less than 0,and there was no statistical differences between them.3.ICC values of the five occlusal contact measurement methods were STA>TSO>SAP>DPO>VOC.The Pearson correlation coefficients of the four digitalized methods with STA method for occlusal contact area and occlusal contact numbers were0.583 ～ 0.885 and 0.483 ～ 0.836,respectively.Regression analysis showed that the occlusal contact area obtained by SAP,VOC and TSO was linearly correlated with STA.4.Among the occlusal contact area of mesial and distal in patients with food impaction with tight proximal contact after crown restoration of second molars,SAP method showed that the occlusal contact area of the mesial surface was greater than that of the distal surface in 90% prosthesis,with a ratio of 1.55±0.60,while the mesial surface/distal surface was 0.81～0.88 in the self control group and the healthy control group.The difference between the impaction group and the control group was statistically significant.The VOC method showed that the occlusal contact area of the mesial surface was larger than that of the distal surface in 85% prosthesis,with a ratio of 1.52±0.75,while the mesial surface/distal surface was 0.80～0.84 in the self control group and the healthy control group.There was a statistically significant difference between the impaction group and the control group.Conclusions:1.The incidence of food impaction was 30.5% after crown restoration of the second molars,and the food impaction with tight proximal contact accounted for a larger proportion.2.The relative distance between the first and second molar increased and the adjacent space showed an increasing trend,while the relative distance of the teeth with same name in the control group decreased in the food impaction after crown restoration of the second molars.3.SAP method and VOC method have good stability and validity,and meet the requirements of obtaining the occlusal contact information of a single tooth position.It can be used for quantitative analysis of occlusal contact.4.Compared with the control group,the occlusal contact numbers of proximal surface were significantly more than distal surface in food impaction with tight proximal contact after crown restoration of second molars.Therefore,the torque of proximal surface was greater than distal surface and the prosthesis tends to move to the distal direction under the bite force resulting in an enlarged adjacent space.It is speculated an important cause of food impaction. |
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