| Indirect prosthesis is usually utilized to repair teeth with unsatisfactory effect from direct filling.In clinical practice,inlay repair and full crown are commonly opted to repair them.Compared with the full crown,it has the advantage of preserving as many remaining tooth tissues as possible.With the development of bonding technology,inlay has been used as an indirect prosthetic prosthesis after dental restoration.However,we still need residual tooth tissues to provide sufficient resistance.The inlay can be produced from different materials,such as metal and ceramic.The development of computer aided design/manufacturing(CAD/CAM)techniques allow the application of ceramic materials in this respect because of their good biocompatibility.The high elastic modulus of porcelain material requires a certain thickness to withstand the pressure of occlusion,and the usual recommended thickness is 1.5-2mm.A return visit of 187 all ceramic inlays in 17 years by Otto and others showed that the success rates were 88.7% and in the failed cases,inlay fracture accounted for 62% and 14% fracture of the teeth accounted for 14% of them.Extracted first molar teeth from mandibular jaw were examined by 3D reconstruction and finite-element analysis before and after restoration.Stress distribution of bulk teeth and restoration were analyzed from different loads and directions.The aim was to establish experimental basis for clinical inlays restoration and provide data from return visit.Objectives and Methods:1.Micro-computer tomography along with Mimics software and ANSYS software were used to establish the 3D model of mandibular first molar with the crown and to simulate the occlusal abrasion after restorations of the occlusal surface using porcelain veneer.Under the constraint by aveolar bone,load of 600 N,225N vertical and 225 N at 45 degrees were applied on various sites of the crown.The stress distribution and the maximum equivalent stress value of the hard tissues of the teeth were analyzed and compared.2.Stress analysis of class II cavities on mandibular first molar after root canal treatment: 3D model of the teeth was estabilished and class II cavities were simulated.600 N of maximum bite force,225 N of ordinary chewing force at vertical,horizontal and 45 degrees were applied on various sites of the teeth crown repaired by two inlays,respectively.Stress distribution and maximum equivlent stress of the teeth and two inlays were examined.3.280 cases of CAD / CAM made porcelain inlay repair treatment in Dental Hospital of The Fourth Medical University were interviewed.After 1~3 years of application,clinical examination and X-ray images were taken to assess the early and long-term effects.Result1.In the vertical loading,the stress from occlusal abrasion concentrated mainly in the distance,and descended to the near.The stress on the buccal concentrated at the alveolar ridge of the tooth neck.The stress of the inlay after repair was similar to that of the nonworn teeth,which concentrated mainly on the proximal cheek apex and decreased to the root.In oblique loading,the stress of the teeth after wear concentrated mainly on the distal lingual side,decreasing to the middle and the buccal side.The stress concentrated on the flat alveolar ridge in the neck of the distal middle teeth,and the stress distribution was more diffused.After inlay repair,the stress of the inlay mainly concentrated on the apex of the distal and middle cheeks,followed by the proximal and middle buccal tips,and the stress decreased from the buccal tip to the side of the tongue and the root.Results suggest that the stress of the porcelain veneer appears mainly at the inlay,and the stress of the tooth is greatly reduced.2.Inlay repair is feasible for the teeth with the thickness of residual denture greater than 2mm.For a small number of side walls,we can choose a larger elastic modulus of repair,and the inlay bears most of the loading force.It plays a part of protection,easy to stress and concentrate.When the thickness of the buccal wall was 3mm,there was no direct loading on the prosthesis during daily chewing.The maximum equivalent stress of the interface of the prosthesis came from the nearest loading point on the edge of the prosthesis.When the inlay cavity was prepared,the occlusal contact point could be avoided as far as possible,and the occlusal point of the repair body was as uniform as possible,hence reducing the failure probability of the body and increasing its service life.3.According to statistical analysis,the success rate reached 97.70%,93.48% and 93.07% for return visits after 1,2 and 3 years,respectively.This is in accordance with that of the literature.It is proved that inlay repair is a reliable repair body.There was no significant difference in the use of inlay repair in the treatment of posterior tooth defect with both the pulp and the root canal.Conclusion1.After inlay restoration,the major stress was concentrated on inlay,which bears most of the load,while less force was transferred to tooth body,therefore inlay repair is a better choice after dental attrition.2.For those teeth which depth of remaining tooth tissue more than 2mm,inlay restoration is feasible.If less lateral wall is remained,we can choose those prosthesis with bigger elasticity modulus,which can sustain most of the load,protect the site of stress concentration.3.Reserve axis wall tooth tissue as much as possible,increase resistance of the tooth.4.When preparing for inlay,try to avoid of the occlusal contacts,at the same time,try to average the occlusal contact on the inlay,decrease of the rate of tooth loss,increase its longevity. |
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