不同形态的氧化锆陶瓷桩对牙本质应力的三维有限元分析

目的:通过三维有限元分析的方法模拟牙体组织的力学组成,分析不同形态的氧化锆陶瓷桩修复上颌中切牙后对周围剩余牙本质的应力分布规律。方法:根据成年男性上颌中切牙的标准数据,通过ANSYS 12.0软件直接建立平行桩、锥形桩、末端锥形桩3种不同形态的氧化锆陶瓷桩修复上颌中切牙的三维有限元模型;对建立的模型进行网格划分;通过加载边界条件,设定模型主参数以及加载静态载荷;分析牙本质内的Von Mises应力的分布规律,观察不同形态的桩核对其周围剩余牙本质的影响。结果:成功建立了不同形态的氧化锆陶瓷桩核和牙根的三维有限元模型;柱形桩和锥形桩的牙本质应力分布沿牙本质界面向牙颈部逐渐增大达高峰,末端锥形桩应力最高峰在根末1/3;锥形桩所受的牙本质应力大于柱形桩,且锥度越大,受到的应力也相应越大。结论:柱形桩组所受应力值均小于锥形桩组,末端锥形桩组在牙根部应力值最大;选择氧化锆材料时,柱形桩为最佳设计。     

Influence of prefabricated post material on restored teeth: fracture strength and stress distribution

AIMS: This work studied how prefabricated intraradicular post material affects the mechanical performance of restored teeth. The effect of using two different materials (glass fiber and stainless steel) with significantly different elastic moduli was studied. METHODS: A combined theoretical and experimental method was used: first, an experimental fracture strength test was performed on 60 extracted human maxillary central incisors. The teeth were decoronated, treated endodontically and restored, 30 with glass fiber posts and 30 with stainless steel posts. The data were recorded and the results compared using an ANOVA test. Then, the finite element technique was used to develop a model of the restored tooth. For both post systems, the model allowed for the study of stress distribution patterns on the restored tooth under external loads. RESULTS: For teeth restored with stainless steel posts, a significantly lower failure load was found, as compared with those teeth restored with glass fiber posts (520 N versus 803 N). The estimated distributions confirmed a worse mechanical performance on teeth restored using stainless steel posts, with a high stress concentration due to the significant difference between the elastic moduli of the steel and the surrounding materials. CONCLUSION: Within the limitations of this study, post systems, where the elastic modulus of the post is similar to that of dentin and core, have a better biomechanical performance.     

An ex vivo study of the effects of retained coronal dentine on the strength of teeth restored with composite core and different post and core systems

AIM: To investigate the fracture resistance and fracture patterns of teeth restored with composite cores supported by different pre-fabricated post systems and different heights of remaining coronal dentine. METHODOLOGY: Four groups of 30 single rooted teeth were used. Each group was divided into three subgroups of 10 teeth each and restored with carbon fibre, glass fibre, or Radix titanium posts luted with dual cure resin cement. The control group A had no retained coronal dentine. Groups B, C and D had 2, 3 and 4 mm of retained buccal and lingual coronal dentine, respectively. Teeth were tested to failure using an Instron Universal Testing Machine. Subsequently, the fracture mode of specimens was recorded. RESULTS: Teeth with retained dentine were more resistant to fracture (P = 0.001). Tooth fracture resistance was not significantly different between groups B, C and D. Within group A, titanium posts were associated with higher fracture resistance than fibre posts. Within the other groups, tooth fracture resistance was not related to post material. Within groups C and D, fracture resistance of teeth restored with carbon fibre posts was significantly higher than those restored with glass fibre posts. The dominant fracture mode in group A was core and vertical oblique root fracture whilst a combination of core, coronal dentine and root fracture occurred in the other groups. CONCLUSIONS: Fracture resistance of teeth increased with the presence of retained coronal dentine. The use of glass and carbon fibre posts did not improve the fracture resistance or the fracture pattern of teeth when compared with metal titanium posts regardless of the presence of retained coronal dentine. The dominant fracture pattern of teeth was not related to the amount of retained dentine if it was >2 mm high.     

桩-粘接剂-根管内壁牙本质界面的拉曼光谱分析

目的本实验采用显微激光拉曼光谱仪观测根管内壁牙本质- 粘接剂- 桩粘接界面的物质过渡变化,了解不同粘接材料与根管内壁牙本质的结合方式,探讨不同粘接剂对桩固位力影响的原因。方法将钛桩和玻璃纤维桩分别使用磷酸锌黏固剂、玻璃离子黏固剂和树脂粘接材料粘着于离体牙根管内,用显微激光拉曼光谱仪分别测量其光谱,并与粘着前粘接底物和粘接剂的光谱进行对比,探讨粘接前后的光谱变化。结果磷酸锌黏固剂- 牙本质和玻璃离子黏固剂- 牙本质界面未见改变,而树脂- 牙本质及树脂- 玻璃纤维桩界面可见明显激光拉曼光谱混合带改变。结论显微激光拉曼光谱仪是研究修复粘接界面的有效手段。不同粘接材料与牙本质结合方式不同,本实验使用的树脂类粘接材料可渗入到根管内壁及玻璃纤维桩材料内。     

偶联剂和不同粘接剂对纤维桩粘接强度的影响

目的:利用薄片推出实验比较硅烷偶联剂和三种树脂粘接剂对纤维桩剪切粘接强度的影响.方法:60颗因牙周病等原因拔除的上颌单根前牙,根管治疗后行纤维桩修复的桩道预备.随机分为5组,每组12颗牙.分别采用下列粘接剂粘接Matchpost纤维桩:A组:Paracore粘接剂+偶联剂;B组:Paracore粘接剂;C组:Panavia F粘接剂+偶联剂;D组:Panavia F粘接剂;E组:Multilink N粘接剂+偶联剂.纤维桩粘接后,在牙根中部横向切割1.0mm层厚切片2个,在Zwick Z100材料试验机上行薄片推出试验(Push-Out Bond Test),记录失败载荷,计算剪切粘接强度,体视显微镜观察粘接失败类型.结果采用SPSS 11.5进行方差分析和χ2检验.结果:五组样本的剪切粘接强度(MPa)分别为A组:14.69±2.76;B组:9.46±3.11;C组:13.12±3.10;D组:10.40±3.30;E组:13.86±3.81,方差分析提示五组间差异有统计学意义(P <0.01).采用偶联剂处理时,Paracore粘接剂和Panavia F粘接剂与纤维桩间的剪切粘接强度均高于未用偶联剂处理者(P <0.05).采用偶联剂处理时,三种树脂粘接剂与纤维桩的剪切粘接强度间差异无统计学意义(P >0.05).五组粘接失败类型间差异有统计学意义(P <0.05),未采用硅烷偶联剂处理纤维桩表面者,出现纤维桩-粘接剂界面失败者增多.结论:在树脂粘接前,玻璃纤维桩表面氢氟酸酸蚀后,采用硅烷偶联剂处理可显著提高纤维桩与树脂粘接剂间的剪切粘接强度.     

Stress analysis of an upper central incisor restored with different posts

The effect of different anatomic shapes and materials of posts in the stress distribution on an endodontically treated incisor was evaluated in this work. This study compared three post shapes (tapered, cylindrical and two-stage cylindrical) made of three different materials (stainless steel, titanium and carbon fibre on Bisphenol A-Glycidyl Methacrylate (Bis-GMA) matrix). Two-dimensional stress analysis was performed using the Finite Element Method. A static load of 100N was applied at 45 degrees inclination with respect to the incisor's edge. The stress concentrations did not significantly affect the region adjacent to the alveolar bone crest at the palatine portion of the tooth, regardless of the post shape or material. However, stress concentrations on the post/dentin interface on the palatine side of the tooth root presented significant variations for different post shapes and materials. Post shapes had relatively small impact on the stress concentrations while post materials introduced higher variations on them. Stainless steel posts presented the highest level of stress concentration, followed by titanium and carbon/Bis-GMA posts.     

Effect of EDTA conditioning upon the retention of fibre posts luted with resin cements

Aim To determine if a final rinse with EDTA improves the short‐term in‐tooth retentive strength of adhesively luted fibre‐reinforced composite posts. Methodology Six different commercial fibre post systems were tested. Post spaces in extracted human anterior teeth were irrigated with either 6% NaOCl or 6% NaOCl followed by 17% EDTA. Posts were luted using the manufacturer’s recommended bonding agent and luting cement. Two different sizes of post were tested for each post system. After 24 h of storage, the retentive strength of the post to the tooth (14 per group, 336 total) was tested using a pull‐out technique. Three‐way anova and the Student–Newman–Kuels test were used to test the effects of irrigation regimen, post size and post brand on the retentive strength of the fibre post. Results Almost every sample failed at the interface between dentine and luting cement. Irrigation method did not have any significant effect (P > 0.14) for any group other than ParaPost Fibre White (P < 0.001). The overall retention of a post appeared to be correlated to the amount of surface texture on the post; the smooth ICEPost was the least retentive brand, the textured FibreKor and the ParaPost Fibre White posts were moderately retained, and the threaded Flexi‐Post Fibre and the Flexi‐Flange Fibre posts were the most retentive brands tested. For all brands, larger diameter posts were more retentive than smaller diameter posts (P < 0.008). Conclusions A final rinse of EDTA did not improve the short‐term retention of fibre posts except for ParaPost Fibre White.     

SEM evaluation of the cement layer thickness after luting two different posts

PURPOSE: To verify with SEM the cement layer thickness and uniformity of resin-relined translucent fiber posts (anatomic posts) and standard translucent fiber posts. MATERIALS AND METHODS: On 20 extracted maxillary anterior teeth, the roots were endodontically treated and prepared for the insertion of a fiber post. Translucent fiber posts (DT) were luted with a dual-curing resin cement (Duo-Link) in 10 specimens (group 1) after the canal walls had been treated with the One-Step bonding system. In the other 10 specimens (group 2), experimental anatomic posts (Anatomic Post'n Core) were tested. To these posts, a layer of light-curing resin is added to allow for a pre-cementation relining of the post, aimed at improving its fit into the endodontic space. For luting, the same adhesive-resin cement combination of group 1 was used. All the roots were sectioned and prepared for SEM observations. At the 1-mm, 4.5-mm, and 8-mm level of each root, cement thickness was measured, and the presence of gaps or voids within the luting material or at its interfaces was evaluated. A statistical analysis was performed to test the significance of differences in the cement layer thickness around the two types of post and at different levels of the same type of post. RESULTS: In the presence of anatomic posts, the cement layer was significantly thinner and more uniform at the coronal and middle level of the root. In both groups, voids and bubbles were detected within the luting material, within the abutment material, and between fiber post and cement. Gaps were also visible between post and relining material. CONCLUSIONS: The resin cement thickness was significantly lower in the anatomic post group than in the control group (standardized posts), except at the apical third of the canal, where there was no statistically significant difference. A good adaptation of anatomic posts was evident in all of the specimens.     

Effect of the timing of radiation therapy on the push-out strength of resin cement to root dentine

This study investigated the effect of radiation timing on the bond strength of resin cement to intraradicular dentine. Fifty human teeth were distributed into 5 groups (n = 10): Control (nonirradiated teeth), Before-RCT (teeth irradiated before root canal treatment), After-CH (teeth irradiated after canal preparation and placement of calcium hydroxide intracanal dressing), After-RCT (teeth irradiated after completion of root canal treatment) and After-FPL (teeth irradiated after luting of a glass fibre post). Each tooth received 70 Gy irradiation. The roots were sectioned for push-out strength testing. After-RCT and After-FPL groups had significantly lower push-out strength than the control at the middle third (p < 0.05). Control and After-CH groups had a higher percentage of cohesive dentine failure. Radiotherapy after root canal obturation and post luting adversely affected the adhesiveness of resin cement to intraradicular dentine. Teeth irradiated before root canal treatment and after placement of calcium hydroxide had the best performance.     

Bonding of fibre-reinforced composite post to root canal dentin

OBJECTIVE: The aim of this study was to determine bonding properties of two types of fibre-reinforced composite (FRC) posts cemented into root canals of molars. Serrated titanium posts served as reference. METHODS: Prefabricated carbon/graphite FRC posts with cross-linked polymer matrix and individually formed glass FRC posts with interpenetrating polymer network (IPN) polymer matrix were compared. The crowns of extracted third molars were removed and post space (diameter: 1.5mm) was drilled, etched and bonded. The posts were treated with dimethacrylate adhesive resin, light-polymerized and cemented with a dual-polymerizing composite resin luting cement. After thermocycling (6000x) the samples were cut into discs of thicknesses: 1, 2 and 4mm (n=12/group). Push-out force was measured by pushing the post from one end. Assessment of failure mode was made under a stereomicroscope (1, adhesive failure between post and cement; 2, cohesive failure of post-system; 3, adhesive failure between cement and dentin). RESULTS: The push-out force increased with increased height of dentin disc in all groups (ANOVA, p<0.001). In the 4mm thick dentin discs the individually formed glass FRC posts showed highest push-out force and the difference to that of the titanium posts was significant (ANOVA, p<0.001). The other differences were not statistically significant. None of the individually formed glass FRC posts showed adhesive failures between the post and the cement. CONCLUSIONS: Contrary to the other posts, there were no adhesive (post-cement) failures with the individually formed glass FRC posts, suggesting better interfacial adhesion of cement to these posts.     

An in vitro evaluation of a prototype CFRC prefabricated post developed for the restoration of pulpless teeth

Carbon fibre reinforced carbon (CFRC) in the form of a prefabricated post has recently been developed and is theoretically acceptable for consideration in an endodontic post-retained crown system. This study compared four different types of postcore system cemented into 40 extracted anterior human teeth. The test groups consisted of CFRC posts cemented with a composite resin luting agent, and used with either a cast gold alloy core (Group B) or a composite resin core (Group C). Two existing post-core techniques were used as controls for comparison with the CFRC groups. One control was a prefabricated wrought precious alloy post having a cast gold alloy core, and cemented with zinc phosphate cement (Group A). The other was a prefabricated stainless steel post with a composite resin core, and cemented with a composite resin luting agent (Group D). All specimens were restored with a gold alloy crown and tested to failure with an obliquely applied compressive load at 130 degrees in an Instron using a cross-head speed of 5 cm min-1. The results showed that post-retained crowns using a prefabricated CFRC post exhibited properties comparable with, and in some cases better than, those of existing prefabricated posts. The mode of failure of specimens restored with a CFRC post was more favourable to the remaining tooth tissue than was that of specimens restored with a metallic post.     

The finite element analysis of the effect of ferrule height on stress distribution at post-and-core-restored all-ceramic anterior crowns

The purpose of this study was to compare the effect of ferrule with different heights on the stress distribution of dentin and the restoration-tooth complex, using the finite element stress analysis method. Three-dimensional finite element models simulating an endodontically treated maxillary central incisor restored with an all-ceramic crown were prepared. Three-dimensional models were varied in their ferrule height (NF: no ferrule, 1F: 1-mm ferrule, and 2F: 2-mm ferrule). A 300-N static occlusal load was applied to the palatal surface of the crown with a 135° angle to the long axis of the tooth. In addition, two post and core materials with different elastic modulus were evaluated. The differences in stress transfer characteristics of the models were analyzed. Maximum stresses were concentrated on force application areas (32.6–32.8 MPa). The stress values observed with the use of a 2-mm ferrule (14.1/16.8 MPa) were lower than the no-ferrule design (14.9/17.1 MPa) for both the glass fiber-reinforced and zirconium oxide ceramic post systems, respectively. The stress values observed with zirconium oxide ceramic were higher than that of glass fiber-reinforced post system. The use of a ferrule in endodontically treated teeth restored with an all-ceramic post-and-core reduces the values of von Mises stresses on tooth-restoration complex. At rigid zirconium oxide ceramic post system, stress levels, both at dentin wall and within the post, were higher than that of fiber posts.     

不同材料不同形态桩核修复上颌中切牙牙本质应力的有限元分析

Sun Jing,Tel：021-66313725     

The evaluation of displacement resistance of glass FRC posts to root dentine using a thin slice push-out test

Aim  To investigate and compare the displacement resistance of glass fibre reinforced composite (FRC) posts to root dentine after luting with different adhesive systems.
Methodology  A total of 32 noncarious extracted human mandibular premolars were prepared for post-cementation using the FRC Postec system (Ivoclar Vivadent, Schaan, Liechtenstein) and divided into four groups ( n  = 8). The posts in each group were luted with one or other of the following materials. Group 1: Variolink II/Excite DSC (etch-and-rinse, dual-curing), group 2: Clearfil Esthetic Cement/ED Primer II (self-etch, dual-curing), group 3: Multilink/Multilink Primer (self-etch, chemical-curing) and group 4: Multilink Sprint (self-adhesive, dual-curing). Specimens were sectioned to obtain slices with the post in the centre and with the root dentine overlaid by the autopolymerizing acrylic resin on each side. The displacement resistance was measured using a Universal Testing Machine at a crosshead speed of 0.5 mm min⁻¹. The displacement resistance of the specimens were calculated and expressed in MPa. Data were analysed with one-way anova and post hoc Tukey's test ( P  < 0.05).
Results  Mean (SD) values of displacement resistance data in MPa are as follows: group 1, 12.08 (2.13); group 2, 12.39 (2); group 3, 11.3 (1.23); group 4, 14.29 (1.84). There were statistically significant differences amongst the groups ( P  = 0.021). A statistically significant difference was observed for the displacement resistance values between groups 3 and 4 ( P  = 0.015), that is between Multilink/Multilink Primer and Multilink Sprint.
Conclusions  Glass FRC posts luted with self-adhesive luting system exhibited higher displacement resistance than when luted with chemical-curing self-etch luting system.     

Influence of prefabricated post dimensions on restored maxillary central incisors

The aim of this study was to test the following hypothesis: biomechanical performance (fracture strength and stress distribution) of restored teeth is less sensitive to post diameter and post length when using glass fibre posts than when using stainless steel posts. First, an experimental fracture strength test was performed on 80 extracted human maxillary central incisors. Teeth were decoronated, treated endodontically and restored (40 with glass fibre posts and 40 with stainless steel posts), and the length and diameter of the posts varied uniformly. Failure loads were recorded and results were compared using an ancova analysis. Secondly, the finite element technique was used to develop a model of the restored tooth. The post diameter had a significant effect on the biomechanical performance of teeth restored with stainless steel posts. Lower failure loads were found as post diameter increased. However, the post diameter of those teeth restored with glass fibre posts, and the post length for both post systems under consideration, did not affect the biomechanical performance of restored teeth to a significant degree. The stress distributions predicted by the developed model corroborated these findings, confirmed the assumed hypothesis, and permitted the proposal of the use of glass fibre posts to achieve a restorative technique that is less sensitive to post dimensions, and thus more robust.     

FEM analysis of different dental root canal-post systems in young permanent teeth

AIM: Aim of this work was to carry out a comparative evaluation of the structural behaviour of different root canal posts (cylindrical, conical and triple conical) fitted in a second lower bicuspid and subjected to compression and bending test. MATERIALS AND METHODS: This study has been carried out by numerical method of structural analysis of finite elements (FEM, Finite Element Method). Different tridimensional models were obtained by CAT images of an extracted tooth, endodontically treated, filled with guttapercha and triple conical glass post. Images have been elaborated by a software for images (Mimics and Ansys) and CAD (Rhinoceros 3 D). In the models a II Class restoration has been virtually created. In the numerical simulation dental tissues (enamel, dentine and root cement), guttapercha, root canal cement, different posts, different techniques of cementation and crown restoration (composites and adhesive systems) have been considered. RESULTS: Strain distributions in dental tissues, in root canal cement and in posts have been compared. The equivalent tensions and the single components (traction, compression and cut) have been analysed. In all examined posts, the most strained part is resulted the coronal one, even if the total tension, in the different tooth-post analyzed systems, resulted uniformly distributed. A similar behaviour was shown by the root canal cement. CONCLUSIONS: According to the analyzed conditions of bond and load, varying according to the geometry of the considered posts, our results confirm that there is no substantial difference of deformation in posts, root canal cement and treated tooth.     

Retention and failure morphology of prefabricated posts

PURPOSE: This study evaluated the effect of cement, post material, surface treatment, and shape (1) on the retention of posts luted in the root canals of extracted human teeth and (2) on the failure morphology. MATERIALS AND METHODS: Posts of titanium alloy (ParaPost XH), glass fiber (ParaPost Fiber White), and zirconia (Cerapost) received one of several surface treatments-sandblasting, CoJet treatment, application of Metalprimer II, or sandblasting followed by silane application-and were then luted in the prepared root canal of human incisors and canines (n = 10). Following water storage at 37 degrees C for 7 days, retention was determined by extraction of the posts. Failure morphology of extracted posts was analyzed and quantified stereomicroscopically. RESULTS: Type of luting cement, post material, and shape of post influenced the retention and failure morphology of the posts. Because of limited adherence of the cement to the root canal, surface treatments did not always have a positive effect on retention. CONCLUSION: Choice of luting cement was critical for all three types of posts. Parallel posts showed superior retention to tapered posts.     

Compressive and flexural behaviour of fibre reinforced endodontic posts

ObjectivesThe aim of this study was to investigate the mechanical properties of five types of fibre-reinforced composite (FRC) posts and compare them with traditional metal post.MethodsFive FRC posts and a metallic post having different geometry and type of fibre (glass, carbon or quartz fibre) were loaded to failure in compression and bending. The transverse sections of FRC posts were observed using SEM to evaluate the fracture mode and the percentage of fibres (compared with burn-off test). Densities and voids content were also evaluated.ResultsMechanical results were subjected to a one-way ANOVA and Tukey test (p < 0.05). In compression, quartz fibre posts exhibited the greater maximum load and ultimate strength, carbon fibre posts showed a poor compressive behaviour. All posts had similar compressive moduli.Carbon posts showed the highest flexural properties (p < 0.0001) while glass posts the greater maximum load. The fracture load values correlated to the diameters of posts showed a parabolic behaviour. The flexural strengths of all posts were four and seven times higher than dentine.The elastic moduli of almost all posts were similar to dentine. The compressive strengths were lower than flexural strengths. The fibre diameters ranged from 5.2 to 26 μm, the volume percentage of fibres was about 64%. The content of voids of some posts lower their mechanical behaviour.ConclusionsCompressive properties of FRC posts were lower than in bending. The flexural properties of FRC posts were higher than the metal post and similar to dentine. The mechanical behaviour is influenced by voids.     

不同材料根管桩剪切粘结强度的比较

目的:比较新型石英纤维强化树脂桩和铸造不锈钢桩与树脂类粘结剂粘结后剪切粘结强度的差异,为临床合理选择桩核系统、优化修复设计提供实验依据。方法:选用正常人离体上颌中切牙20颗随机分成两组,截冠处理并预备桩道。制作40个环氧树脂立方体模块并于中央备洞。将两组牙根固定于模块中,分别粘结石英纤维桩与不锈钢桩的一端于牙根桩道内,另一端均用自凝塑料垂直固定于模块中央。模块与力学试验机拉力杆相连,加载速度1mm/min,方向为平行于桩的长轴与牙根脱离的方向剪切牵拉。记录根管桩脱离时的最大载荷和脱落模式。结果:石英纤维桩组的剪切粘结强度(360.58N±19.12N)高于铸造不锈钢桩组(250.82N±22.34N),完全随机设计资料的t检验显示P<0.05,两者差异有显著性。结论:石英纤维桩与树脂类粘结剂的剪切粘结强度明显优于传统铸造镍铬合金桩与粘结剂;石英纤维桩可成为美容牙科修复的有效选择。     

Bond strength of fibre glass and carbon fibre posts to the root canal walls using different resin cements

The aim of the study was to evaluate the bond strength of fibre glass and carbon fibre posts in the root canal walls cemented with self-adhesive (RelyX-Unicem) and chemical (Cement-Post) resin cements. Forty maxillary canines were divided into four groups according to the cement and post used and submitted to the push-out test (0.5 mm min(-1)). The data were submitted to statistical analysis (2-way ANOVA, Bonferroni--P<0.05) and fracture analysis by Scanning Electronic Microscopy. Fibre glass presented the best results when cemented with RelyX-Unicem and Cement-Post (P<0.05). RelyX-Unicem presented the highest bond strength values for both posts (P<0.05). Fracture analysis showed predominance of cohesive fracture of post for RelyX-Unicem and adhesive fracture between dentin/cement and mixed for Cement-Post. The bond strength values were significantly affected by the type of post and cement used and the highest values were found for fibre glass posts and RelyX-Unicem.