| Clinically, residual roots and crowns with flared roots are often found in anteriorand premolars teeth, which over-flared shaped and badly damaged. Currently, Themethod post-core restoration system is the most common way to preserve resdual rootsand crowns. The long-term effect of restoration is not satisfiactory beause of the poorretention and resistance forms of the residual root and crown. Restoration failures suchas root and post fracture, post-core dislodgment can be found, clinically, which can beinduced by the high elastic modulus of post-core materials, the poor adaption of postwith root, the polymerization shrinkage of resin materials and the complexity of theclinical operation. It’s also a challenge to restore the residual roots and crowns withflared roots for a clinical doctor. The survival of natural root can not only reserveperiodontal ligament proprioception, but also reduce the numbers of missing teeth andedentulous pain of the patient. Therefore, in order to maintain residual crown and rootas much as possible and prolong the life of restorations, clinicians need to solve theproblem that exploring a better way to restore the residual roots and crowns. In recentyears, a new post-core restoration is advocated to repair the flared roots, which iscomposed of master and accessory post. There are many advantages of the new repairsystem, such as the low elastic modulus like dentine, good adaption to the flared roots,less amount of resin cement, the low polymerization shrinkage and the easily clinicaloperation. At present, the domestic and overseas study about the repair system mainlyfocused on the flexural performance in basic research, and found that it can improve thetooth root fracture, but its clinical application is seldom reported. Now, clinicians paymore attention to the long-term effect of the restoration of residual root and crown. Can fiber post combined with accessory post restoration system achieve a long-term repaireffect? Can its stress delivery method help to reduce stress concentration? How is themicroleakage actually? How is the effect? These problems need further research toillustrate.Methods like FEM, penetration, and SEM were used to research the stressdistuibution regular of the dentin, the root corconal clousure, and its restoration effectwhen to ues the fiber post-core system combined with accessory posts. The target of thisresearch is to provide biomechanical, basic research and clinical reference for theexpanding application of the new repair system. This thesis consists of three parts:Part One: Stress analysis of maxillary central incisor with flared rootcanal using fiber post-core restoration combined with accessory postsThe maxillary central incisor tooth and alveolar bone of a healthy male wasscanned by the spiral CT, and the information of the image was obtained accurately.Three-dimensional finite element model of the normal maxillary incisor and periodontaltissue was established by software Mimics and Geomagic, and different height of dentincollar, master fiber post, accessory fiber post, crown, adhesive cement models wasestablished by Solidworks software. In accordance with the same dentin collar width0.5mm, different height of collar are divided into0mm,1mm,2mm groups; accordingto different post-core materials, there were metal post, single fiber post, master andaccessory fiber post groups; According to different occlusal state were divided into twogroups: the same loading angle45°, different loading force value (60N,80N,100N,120N,150N) and the same load value100N, different loading angles (0°,30°,45°,60°,90°). The aim of the study is to analysis dentin stress distribution of post-corerestoration under different conditions. The results are as follows: Compared with metalpost, master and accessory fiber post group can reduce apical dentin stress concentration,and achieve a uniform stress distribution, which is similar to single fiber post and hadno significant difference. With the increases of dentin collar height, the peak stress indentin decreased, and the same as the area of high stress distribution. The change ismost obvious when the height rose from0mm to1mm, which VonMises stressdecreased by3.94%and the maximum tensile stress is reduced by4.18%; In the sameload angle45°and60N～150N force range, compared with single post, the group ofmaster and acessory fiber post can rise the peak stress in the neck of root, but there is no significant difference between them; Two groups of the peak stress increased with therise of force value, the dentin Von Mises was up to42.469MPa stress, and both in thenormal range that the dentin could bear; In the same load value100N and the load angleof0°～90°range, dentin peak stress of master and accessory fiber post group is slightlylarger than the single fiber post, and there was no obvious difference. When the loadingangle is90°, the maximum principal stress value of dentin was54.153MPa that reachedthe maximum value of tensile stress, which suggesting that the dentin stress distributionwas closely related to the load angle.These results indicated that when compared with the metal post, single fiberpost-core restorations and fiber post and accessory fiber post-core restorations canreduce the irreversible root fracture of flared root canal that showed similar dentin stressdistribution. When the height of flared root is1mm, retaining0.5mm thickness of dentincollar can provide coupling effect, and it is better to reserve the remaining toothstructure, clinically. Under different occlusal conditions, increasing the bite force andthe load angle can increase the risk of tooth fracture in the coronal of the root, andclinical attention should be paid to avoid excessive excessive force and horizontal force.Part two: The study on microleakage of post-core restoration withfiber post combined with accessory post in maxillary central incisorteeth with flared root canal.A total of52teeth of maxillary incisors, which had been prepared with a flaredshape after root canal, were randomly divided into two groups, single fiber post group(n=26), including A1(n=20), A2(n=6); the fiber post and accessory post (n=26),including B1(n=20), B2(n=6). All of the samples were invaded in water for1month.A1, B1groups were placed in India ink dyeing for1week, after transparent process,then observed microleakage between post-core and dentain put samples in the asanamicroscope. A2, B2groups can be divided into three sections, the coronal, middle, andapical regions. Four points of dentin-cement interface were examined at each sectionunder SEM micrographs. A step scale method was established for each evaluatedcondition.,and data were analyzed using nonparametric statistical method. The resultsfound that when compared with single fiber post, the microleakage value of the fiberpost and accessory fiber post group significantly smaller (P <0.05); Two groups showeddifferent resin tag morphologies. Compared with fiber post and accessory fiber post, Single fiber post group showed obvious adhesive discontinuity in dentin interface,especially in the coronal section of the root.(P <0.05).Experimental result indicates, compared with single fiber post, fiber post combinedwith accessory post can reduce the amount of resin cement, which can reduce themicroleakage occurs of post-core system, is contribute to obtain a better closure incoronal and reduce the lossing chance of post-core system. The study provides a strongtheoretical basis for the clinical application of fiber post and accessory post.Part three: The clinical effect of fiber post combined with accessorypost in post core restoration of flared root canals—with clinical cases.According to the clinical inclusion criteria, selected in28patients, A total of37teeth with flared root canal in28patients were included．After root canal therapy，theteeth were restored with Macro-lock fiber posts, accessory posts and all ceramic crowns.Patients were followed up18-26months．Clinical examinations and radiograph weretaken to evaluate the restoration outcome, which included with the edge restorationintegrity, suitability, periodontal and periapical tissue health evaluation according to thecriteria modified from the restoration of the evaluation standard of California dentalassociation.37(100%) restoration were found to be intact; Crown fit well was91.89%,and8.11%was acceptable; Color match good by75.68%; Gum is healithy by83.79%;Neither loosening or fracture of the fiber post and resin cores, nor gap between the coreand dentin were discovered. No dislodgment or fracture of posts and roots wereobserved in all restorations. The results indicate that post core restoration with fiber postand accessory post is a convenient and effective method for preservation of residualcrown and root with flared root canal, and can be popularized in clinical application.Above all, there are many advantages of the fibre post-core restoration combinedwith accessory post repair the residual root and crown with flared roots, as flollows:1.Compared with metal post, fibre post-core restoration combined with accessory post canachieve uniform stress distribution in apex of the root, which can reduce the incidenceof irreversibility root fracture. Reserve of1mm height, the thickness of0.5mm ofdentine shoulder collar can provide a certain amount of coupling effect, and it’snecessory to keep the rest tissue of the tooth, clicially. Different state of occlusion canaffect the dentin stress distribution, and clinically, we should reduce the occlusion especially the horizontal occlusion of the post-core restoration as far as possible.2.Fiber post combined with accessory post group showed a similar stress distributioncharacteristic with single fiber post group.3. The application of accessory post canreduce the microleakage, which can achieve a good post-core coronal enclosure, andreduce the dislodgment rate of the post.4. The fiber post and accessory post restorationsystem have achieved good clinical effect, which can be used as a convenient andeffective method for preservation of residual crown and root with flared root canal. |
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