Failure probability, stress distribution and fracture analysis of experimental screw for micro conical abutment

Abstract The aim of this study was to evaluate the failure probability of two types of abutment screws after compressive load and to analyze the stress distribution with finite element method. Sixty (60) single-tooth implant restorations were assembled on titanium implants (e-fix, A.S. Technology - Titanium Fix). The groups were divided into Conventional screw (Screw neck 1.5 ø mm) and Experimental screw (Screw neck constricted with 1.2 ø mm). Specimens were subjected to single load to failure with compressive test according ISO 14801. The fractured specimens were subjected to stereomicroscopy for measurement of remaining screws inside the implant and characterization of fracture origin. Representative specimens were analyzed by scanning electronic microscopy. For finite element method (FEM), an identical 3D model of the two in vitro test groups were used with similar conditions (30º, 100 N load). The stress in the abutment screw was analyzed by von-Mises criteria. The results of strength means were 4132.5 ± 76 MPa and 4528.2 ± 127.2 for conventional and experimental groups, respectively. During microscopy, the mean (mm) of the remaining screw piece inside the implants were 0.97 ± 0.23 and 1.32 ± 0.12 for conventional and experimental groups, respectively. In FEM, the conventional group showed stress concentered in an unfavorable region (peak of 39.23 MPa), while the experimental group showed more stress areas but less concentration than the conventional group (36.6 MPa). In using the tested experimental geometry, the abutment screw can have its strength improved, and the origin of failure can be more favorable to clinical resolution.

Resumo O objetivo deste estudo foi avaliar a probabilidade de falha de dois tipos de parafusos para pilar protético após a compressão e analisar a distribuição da tensão com o método dos elementos finitos. Sessenta (60) restaurações unitárias foram montadas em implantes de titânio (e-fix, A.S. Technology - Titanium Fix). Os grupos foram divididos em parafusos convencionais (parafuso de pescoço 1,5 ø mm) e parafuso experimental (parafuso de pescoço estreitado com 1,2 ø mm). As amostras foram sujeitas ao teste de compressão de acordo com ISO 14801. Os espécimes fraturados foram submetidos a estereomicroscopia para a mensuração dos parafusos restantes dentro do implante e caracterização da origem da fratura. Os espécimes representativos foram analisados ​​por microscopia eletrônica de varredura. Para o método de elementos finitos (FEM), utilizou-se um modelo 3D idêntico dos dois grupos de teste in vitro com condições semelhantes (30º, 100 N). A tensão no parafuso do pilar foi analisada pelo critério de von-Mises. Os resultados de resistência a compressão foram 4132,5 ± 76 MPa e 4528,2 ± 127,2 para grupos convencionais e experimentais, respectivamente. Durante a microscopia, a média do remanescente do parafuso restante dentro dos implantes foi de 0,97 ± 0,23 e 1,32 ± 0,12 mm para os grupos convencionais e experimentais, respectivamente. Em FEM, o grupo convencional mostrou tensão concentrada em uma região desfavorável (pico de 39,23 MPa), enquanto o grupo experimental apresentou mais áreas de tensão, porém menor concentração do que o grupo convencional (36,6 MPa). Ao usar a geometria experimental testada, o parafuso do pilar pode ter sua resistência melhorada e a origem da falha pode ser mais favorável à resolução clínica.

Feldspar ceramic strength and the reinforcing effect by adhesive cementation under accelerated aging

Abstract This study evaluated the effect of the accelerated artificial aging (AAA) on feldspar ceramic strength and the reinforcing effect promoted by adhesive cementation with resin luting agent. One hundred twenty feldspar ceramic disks were obtained. Sixty disks were acid-etched, silanized, and coated with an experimental resin luting agent simulating the adhesive luting procedures. Four groups were created (n=30): uncoated ceramic (control group), uncoated ceramic submitted to AAA, ceramic coated with resin luting agent, and coated ceramic submitted to AAA. Biaxial flexural testing with ball-on-ring setup was carried out. Biaxial flexural strength (s bf , MPa), characteristic strength (s 0 , MPa), and Weibull modulus (m) were calculated for axial positions z=0 (ceramic surface) and z=−t2 (luting agent surface). Data of s bf at positions z=0 and z=-t2 were separately submitted to statistical analyses (a=0.05). The uncoated ceramic submitted to AAA had no significant difference in s bf and s 0 compared with the control group. Resin coating of the ceramic increased s bf and s 0 at z=0. The AAA increased the s bf and s 0 for the resin-coated ceramic specimens at z=0 and also the s 0 at axial position z=-t2. The structural reliability at z=0 and z=-t2 was not influenced by the variables tested. In conclusion, resin coating improved the mechanical strength of the feldspar ceramic. The AAA procedure was not effective in aging the uncoated or resin-coated feldspar ceramic specimens.

Resumo Este estudo avaliou o efeito do envelhecimento artificial acelerado (EAA) na resistência da cerâmica feldspática e o reforço promovido pela cimentação adesiva com cimento resinoso. Cento e vinte discos de cerâmica feldspática foram obtidos. Sessenta discos foram condicionados com ácido, silanizados, e recobertos com um cimento resinoso experimental simulando os procedimentos de cimentação adesiva. Quatro grupos foram criados (n=30): cerâmica sem recobrimento (grupo controle), cerâmica sem recobrimento submetida ao EAA, cerâmica recoberta com cimento resinoso, cerâmica recoberta com cimento resinoso submetida ao EAA. O teste de resistência à flexão biaxial foi realizado utilizando o dispositivo pistão-anel. Resistência à flexão biaxial (s fb , MPa), resistência característica (s 0 , MPa), e módulo de Weibull (m) foram calculados para as posições axiais z=0 (superfície da cerâmica) e z=−t2 (superfície do cimento). Os dados de s fb em z=0 e z=−t2 foram submetidos a análises estatísticas separadamente (a=0,05). A cerâmica não recoberta submetida ao EAA não teve diferença significante na s fb e s 0 comparada com o grupo controle. O recobrimento com cimento resinoso da cerâmica aumentou a s fb e s 0 em z=0. O EAA aumentou a s fb e s 0 para os espécimes de cerâmica recobertos com cimento resinoso em z=0 e também a s 0 em z=−t2. A confiabilidade em z=0 e z=−t2 não foi influenciada pelas variáveis testadas. Concluindo, o recobrimento com cimento resinoso melhorou a resistência mecânica da cerâmica feldspática. O procedimento de EAA não foi efetivo em envelhecer os espécimes de cerâmica feldspática recobertos ou não com cimento resinoso.

Effect of Surface Roughness on the Mechanical Properties of Ceramic-Polymer Blocks for CAD/CAM Dental Restoration / 대한치과재료학회지

The effect of surface roughness of ceramic-polymer CAD/CAM blocks on the mechanical properties was investigated in this study. Commercially available Polyglass (Vericom, Korea) and Enamic (Vita, Germany) were selected for this purpose. They were cut into either (4.0×2.1×17.0) mm and (3.0×4.0×17.0) mm, followed by grinding, and polished sequentially with 6 µm and 1 µm diamond paste. Flexural strength, fracture toughness, and Weibull analysis were determined according to ISO 6872 Dentistry-Ceramic materials. The elastic moduli were calculated from a stress-strain curves under flexural loading. The statistical significances of the mechanical properties between the products and surface roughness were analyzed with ANOVA and pared t-test at a significance level of 0.05. After grinding with 6 µm diamond paste after cutting by observing with an atomic force microscope, the arithmetic average roughness decreased to 47~49% and the maximum roughness decreased to 68~69%. When polishing with 1 µm diamond paste, The average roughness decreased to 13~22% and the maximum roughness decreased to 16~19%. When the flexural load was applied, stress increased linearly and fractured without plastic deformation both Polyglass and Enamic. As the surface roughness decreased, the mechanical properties were increased both Polyglass and Enamic. However, the mechanical properties of Polyglass increased up to P3, while Enamic showed almost maximal values at E2, after that there was no significant differences between E2 and E3. It could be due to the different microstructure between two blocks used in this experiment.

A STUDY ON THE TENSILE STRENGTH OF REINFORCED VENEERING COMPOSITE RESINS FOR CROWN / 대한치과보철학회지

Recently a new generation of crown and bridge veneering resins containing submicron glass fillers was introduced. These ultrasmall particle hybrid composite materials distinguish themselves, compared with conventional microfill crown and bridge resins, through improved mechanical properties. It is claimed that these composites are suitable for metal free crowns and even bridges using fiber reinforcement. The purpose of this study was to evaluate the effect of thermal cycling on the tensile strength of the following veneering composites: Artglass(Heraeus Kulzer Co., Wehrheim, Germany), Estenia(Kuraray Co., Japan), Sculpture(Jeneric Pentron Co., Wallingford, U.S.A.), and Targis(Ivoclar Co., Schaan Liechenstein). According to manufacturer' s instructions, rectangular tensile test specimens measuring 1.5 x 2.0 x 4.5 mm were made using a teflon mold. Whole specimens were divided into two groups. One group was dried in a desiccator at 25C for 10 days, and another group was subjected to thermal cycling(10,000 x) in water(5/55 10. All test specimens were placed in a universal testing machine and loaded until fracture with a crosshead speed of 0.5mm/min. Weibull analysis and Tukey s test were used to analyze the data. The fracture surfaces of specimens were observed in SEM and the aliphatic C=C absorbance peak of Estenia and Targis resin was analyzed using Fourier transform infrared(FTIR) spectroscopy. Within the limitations imposed in this study, the following conclusions can be drawn 1. Both in drying condition and, thermal cycling condition, the highest tensile strength was observed in Estenia testing group(p<0.05). 2. The strength data were fit to single-mode Weibull distribution, and the Weibull modulus of all veneering composite resin specimens increased after thermal cycling treatment. 3. After thermal cycling test, the highest tensile strength was observed in the Estenia group, and the lowest value was observed in the Targis group. The tensile strength values showed the significant differences between each group(p<0.05). 4. The aliphatic C = C absorbance peak of Estenia and Targis resin was decreased after light curing, and there was no distinct change after thermal cycling.