| For the past few years,the application of all-ceramic restoration,which has a good biocompatibility,ideal wear resistance and unique aesthetic effects in clinical practice,became more and more widely.The dental all-ceramic contains porcelain veneers,ceramic inlays,all-ceramic crowns and so on.However,all-ceramic restorations need strict tooth preparation and appropriate bonding methods as well as materials,otherwise micro leakage or even loss of the prostheses and other adverse consequences may emerge.In addition,the preparation of all-ceramic restoration is significantly greater than traditional restoration,the pulp injury caused by the lack of existing knowledge in three-dimensional morphology of teeth is common in the clinic,resulting in great losses to the patients.Therefore,it is necessary to systematically analyze the three-dimensional morphology of the teeth,and to master the bonding area about enamel and dentin of anterior and posterior teeth after preparation and provide scientific basis for the rational selection of bonding method in clinical,meanwhile the remaining tooth tissue thickness and other important parameter after preparation should be accurately understood to provide reference for improving clinical preparation,the above work has important significant in improving the clinical repair effect and avoiding adverse complications.In previous studies,studies on tooth preparation and tooth morphology is uncommon,and there are the following problems: Firstly,the measurement means is relatively backward,for example,the slide gauge and other tools can only measure the thickness of tooth preparation and other simple indicators;Secondly,big difference appears between research object and clinical practice,for example,the preparation is measured by weighing the artificial resin teeth.The latest digital technology can reconstruct and measure the three-dimensional model accurately,but the technology applied to studying the relationship between the three-dimensional structure of permanent tooth and the preparation of dental all-ceramic has not been reported.Purpose:In this study,human maxillary central incisors and mandibular first molars were collected as the research object.the reduction of preparations,Bonding area and other parameters were studied by Micro CT,reverse engineering and 3D printing between three types of all-ceramic restorations to investigate the interrelationship between tooth preparation and dental structure to provide scientific guidance for clinical operation.Methods:A total of fifteen samples of maxillary central incisors and ten mandibular first molars were collected,then scanned and reconstructed by Micro CT and reverse engineering software.The reconstructed three-dimensional model of upper incisors and mandibular first molars were printed by 3D printing.A total of forty-five random samples were randomly divided into three groups(n = 15 each): group A : porcelain veneer,group B:all porcelain crown,group C:the blank control group;mandibular first molar each tooth printed four dental samples,a total of forty,were randomly divided into four groups,each group contains ten specimens,group D:the whole porcelain crown,group E:MOD(Mesial-Occlusal-Distal)all-ceramic inlay,group G:blank control group.The samples were prepared according to the group.Micro CT and Mimics software were used to reconstruct the samples before and after the preparation.Geomagic software was used to measure the parameters such as the amount of preparation and the area of the teeth.The data were analyzed by SPSS19.0 software.Results:1.Successfully reconstructed a three-dimensional delicate model of human maxillary central incisor and mandibular first molar preparations:porcelain laminate veneer,all-ceramic crown,ceramic inlays for medial-occlusal cavity and MOD all-ceramic inlay,the quantity of reduction was measured by the formula as following for the first time:quantity of reduction =(control group crown volume-experimental group crown volume)/(control group crown volume-crown volume of the pulp bed)× 100% was used for the first time to measure the quantity of reduction,the consequences are as below:1)maxillary central incisor :all-ceramic crown(56.93 ± 3.47)%,porcelain veneer(28.35 ± 4.35)%,the quantity of reduction in all-ceramic crown was double of porcelain veneer,the significant difference in quantity of reduction occurs(P <0.05).Pearson correlation analysis suggest that there was no correlation between the two types of restoration(P> 0.01).2)mandibular first molar:all-ceramic crown(36.21 ± 6.42)%,ceramic inlays for medial-occlusal cavity(5.75 ± 1.35)%,ceramic inlays for MOD(11.93 ± 1.76)%,the quantity of reduction:all-ceramic crown > ceramic inlays for MOD > ceramic inlays for medial-occlusal cavity,and the tooth structure removal for all-porcelain crown is 3 times greater than MOD,6 times greater than ceramic inlays for medial-occlusal cavity.There were significant differences among the three ceramic restorations(P <0.05).2.The three-dimensional model of the dentinal nucleus-root structure of maxillary central incisor and mandibular first molar was successfully reconstructed,and the bonding area of different all-ceramic restorations were measured as follows:1)maxillary central incisor :all-ceramic crown(128.85 ± 11.73)mm~2,porcelain veneer(97.15 ± 9.98)mm~2,there was significant departure in the bonding area between the two groups(P <0.05).porcelain veneer :the area of enamel adhesive was(54.80 ± 12.70)mm~2,the dentin was(42.35 ± 9.62)mm~2,the enamel adhesive area> dentin,there was significant difference in the adhesive area between the dentin and the enamel adhesive area(P <0.05),there is statistically significant correlation between all-ceramic crown and veneer area(P <0.05).2)mandibular first molar:all-ceramic crown(169.96 ±10.56)mm~2,ceramic inlays for medial-occlusal cavity(40.27 ± 3.93)mm~2,ceramic inlays for MOD(81.94 ± 3.45)mm~2,All-ceramic crown area> ceramic inlays for MOD > ceramic inlays for medial-occlusal cavity,which all-ceramic crown bonding area was 2 times more than MOD,4 times more than ceramic inlays for medial-occlusal cavity.There were significant differences among the three ceramic restorations(P <0.05).ceramic inlays for medial-occlusal cavity : enamel adhesive area(29.96 ± 5.79)mm~2,dentin adhesive area(10.31±5.12);MOD all-ceramic inlay:enamel adhesive area(56.32 ± 4.89)mm~2,dentin adhesive area was(25.57 ± 6.11)mm~2,there was significant difference in enamel and dentin adhesive area both of ceramic inlays for medial-occlusal cavity and MOD all-ceramic inlay respectively(P <0.05);there was significant difference in enamel and enamel、dentin and dentin adhesive area between ceramic inlays for medial-occlusal cavity and MOD all-ceramic inlay respectively(P <0.05);The Pearson correlation examine showed that the correlation in enamel bonding area for two kinds of all-ceramic inlay makes no sense(P> 0.05),so was dentin bonding area.3.The upright range between pulp chamber and leftover dentine were shown.The distance from mesial medullary angle to incisal edge,distal pump angle to incisal border.From mesial pulp angle to mesial adjacent surface and from distal medullary angle to distal adjacent surface was(2.86 ± 1.23)mm,(2.63 ± 1.33)mm,(0.97 ± 0.51)mm,(1.20 ± 0.40)mm,the distance from pulp chamber to incisal edge was more than pulp chamber to adjacent surface.The difference between the mesial and the distal medullary angle to the cutting point has no statistically significant(P>0.05),the difference between the mesial and the distal medullary angle to adjacent surface has no statistically significant(P >0.05)and there was significant difference between the other groups(P <0.05).The results between the medulla and the distal pulp to incisal edge have significant correlation(P <0.05).There was no significant correlation of the distance between the medulla and the distal pulp horn to the adjacent surface(P> 0.05)Conclusion:1.Beside other all-ceramic restorations,the reduction of all-ceramic crown was most,resulting in the highest risk of pulp injury,and the remaining tooth tissue in mesial pulp was less than normal.Clinical preparation should pay attention to mesial pulp horn exposure.2.After porcelain veneers preparation,enamel area exposed was greater than dentin for maxillary central incisor,dentin tissue was distributed over the dental neck and the cut edge of the tooth,suggesting that universal adhesives should be used,or bonding respectively according to different tissue.3.The edge of two kinds of all-ceramic inlays for mandibular first molar was consisted of enamel,and the exposed enamel area of the preparation interface is larger than dentin.It is suggested that the enamel bonding should be used. |
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