Influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns using three-dimensional finite element analysis.@*METHODS@#A maxillary second premolar was scanned by Micro-CT and a three-dimensional finite element model of ceramic endocrown with 1 mm thickness of base was established. A model without base was also established as a negative control. Four kinds of conventional base materials with different elastic modulus were adopted: light cure glass ionomer(3M Vitrebond, 3 657 MPa), flowable composite resin(3M Filtek Z350XT Flowable Restorative, 7 300 MPa), high strength glass ionomer(GC Fuji Ⅸ, 13 130 MPa), and posterior composite resin(3M Filtek P60, 19 700 MPa). With a 200 N force loaded vertically and obliquely, the distribution and magnitude of stress in the tooth tissue and adhesive layer were investigated by three-dimensional finite element analysis.@*RESULTS@#The maximum von Mises stress values(vertical/oblique) in dentin and adhesive layer were measured as follows: (1) no base material: 19.39/70.49 MPa in dentin and 6.97/17.97 MPa in adhesive layer; (2) light cure glass ionomer: 19.00/69.75 MPa in dentin and 6.87/16.30 MPa in adhesive layer; (3) flowable composite resin: 18.78/69.33 MPa in dentin and 6.79/16.17 MPa in adhesive layer; (4) high strength glass ionomer: 18.71/69.20 MPa in dentin and 6.74/16.07 MPa in adhesive layer; (5) posterior composite resin: 18.61/69.03 MPa in dentin and 6.70/16.01 MPa in adhesive layer. Under the same loading condition, models with different elastic moduli of base materials had similar stress distribution patterns. The von Mises stress of tooth tissue was mainly concentrated in the tooth cervix. Under oblique load, the regions where von Mises stress concentrated in were similar to those under a vertical load, but the values increased. The stress concentration in the tooth cervix was alleviated in models with base materials compared with the model without base material. The maximum von Mises stress in the tooth tissue and adhesive layer decreased when the elastic modulus of base materials increased and got close to that of dentin.@*CONCLUSION@#The posterior composite resin of which the elastic moduli is high and close to that of dentin is recommended as base material for premolar endocrowns to alleviate the concentration of stress in tooth cervix and adhesive layer.

Evaluation and Comparison of the Transverse Strength of Two Heat Cure Denture Base Resins Repaired with Auto Polymerizing Resin by Wetting with Methyl Methacrylate (MMA) at Different Time Intervals - An In vitro Study.

Aims: Fracture of dentures is a common clinical finding in daily prosthodontic practice, resulting in great inconvenience to both the patient and the dentist. A satisfactory repair should be costeffective, simple to perform, and quick. This study evaluated and compared the transverse strength of two heat cure denture base resins repaired with auto polymerizing resin by wetting with methyl methacrylate (MMA) at different time intervals. Materials and Methods: Stellon and Trevalon denture base materials were used in the study. A total of 200 heat cure acrylic resin specimens (100 specimens each of Stellon and Trevalon acrylic material) with the dimensions of (65 mm x 10 mm x 3 mm) were prepared. The specimens were divided with 10 specimens for each of the test groups (n =10). The test groups were designated as Group A through J. Repair gap of 2 mm was prepared in the centre of the specimen. The repair surface of the specimens were wetted with MMA at different time intervals (1, 2, 3, 4, 5, 10, 15 and 30 minutes) and repaired by using auto polymerizing resin. The transverse strength of the repaired specimens was tested by a 3 point bending test. All data was statistically analyzed with one-way ANOVA, differences within the groups were analyzed by independent sample t -test. Results: The results showed that the significant difference between the specimens wetted with MMA at different time intervals. A gradual increase was shown in the mean transverse strength of repaired specimens wetted from 1 minute to 5 minutes in Stellon and from 1 minute to 10 minutes in Trevalon. Conclusion: Wetting the repair surfaces with MMA for a period of more than 5 minutes and 10 minutes in case of Stellon and Trevalon respectively increases the incidence of adhesive failure in the repaired specimens.

Cuspal deflection of directly or indirectly restored teeth / Deflexão cuspídea de dentes restaurados direta ou indiretamente

Objective: The aim of this study was to evaluate the cuspal deflection of teeth restored directly and indirectly. Material and Methods: Forty sound maxillary premolar teeth were restored with composite and different base materials. Wide mesial-occlusal-distal cavity preparations were performed, with isthmus width of one third of the distance between the cuspal tips, 3 mm occlusal and a 5 mm interproximal preparation height. The teeth were divided into 4 groups (n = 10), according to the restoration type: G1) GIC-DCR (1 mm glass ionomer cement base and direct restoration using nanoparticulate composite); G2) FL-DCR (1 mm base of flowable composite resin and direct restoration using nanoparticulate composite); G3) GIC-ICR (1 mm glass ionomer cement base and indirect restoration using nanoparticulate composite GIC base); G4) FL-ICR (1 mm base of flowable composite resin and indirect restoration using nanoparticulate composite). The specimens were submitted to compressive load of 50 N on the buccal and lingual cusps, in a universal testing machine. The lingual cusp microstrain (με) measurements were executed by strain gauges. Results: The Kruskal-Wallis (5%) test was used and showed there were no significant differences among the microstrain values for the four study groups (G1 = 1250; G2 = 1075; G3 = 1279; G4 = 937). Conclusion: It could be concluded that the restorative techniques and the bases employed did not show any influences in cuspal deflection

Objetivo: O objetivo deste trabalho foi avaliar, por meio de medidores de tensão, a deflexão cuspídea sofrida por dentes restaurados, direta e indiretamente, com resinas compostas e diferentes materiais de base. Material e Métodos: Para o preparo dos corpos-de-prova (CP) foram utilizados 28 dentes pré-molares humanos íntegros, extraídos por razões ortodônticas que tiveram suas raízes embutidas em poliuretano de densidade semelhante a do osso e suas raízes recobertas por um espaçador visando simular o espaço referente ao ligamento periodontal. Na etapa seguinte os dentes receberam preparos cavitários do tipo mésio-ocluso-distais amplos e então restaurados direta e indiretamente com resina composta e dois diferentes materiais de base/forramento, resina flow e cimento de ionômero de vidro. Para a realização das medidas de deflexão das cúspides foram utilizados extensômetros lineares elétricos colados à face lingual de cada dente e submetidos a uma carga de 50 N aplicada por uma ponta romba de diâmetro de 3,0 mm, que promoveu compressão simultânea nas vertentes triturantes das cúspides vestibular e lingual, numa máquina universal de ensaios. Resultados: Foi realizado o teste de Kruskall-Wallis (5%) de significância e não foram encontradas diferenças estatísticamente significantes entre os grupos (G1 – 1250; G2 = 1075; G3 = 1279; G4 = 937). Conclusão: Pode-se concluir que o tipo de restauração bem como o tipo de base empregados nesse estudo não alteram a deflexão cuspídea dos dentes com restaurações amplas.