Fracture resistance of pressed ZLS crowns versus pressed LD crowns under thermo-mechanical cycling

Resumo Este estudo teve como objetivo avaliar a resistência à fractura do silicato de lítio reforçado com zircônio todo o material cerâmico "Celtra Press" em comparação com um "IPS e-max Press" em condições orais simuladas. Quatorze coroas cerâmicas foram fabricadas em moldes epóxi que foram duplicados a partir de moldes principais de aço inoxidável e divididos em dois grupos iguais (n=7) de acordo com o material de construção; Grupo A: Coroas fabricadas com material IPS e-max Press e Grupo B: Coroas fabricadas com material Celtra Press. As coroas foram então cimentadas nos seus moldes correspondentes com um cimento de resina auto-adesivo e submetidas a ciclos térmicos e cargas cíclicas. Em seguida, foram carregadas para fraturar numa máquina universal de ensaios. Os resultados foram tabulados e analisados estatisticamente utilizando os testes Kolmogorov-Smirnov e Shapiro-Wilk. O teste t de Student usado para comparar os valores médios. O nível de significância foi fixado em P ≤ 0,05 e intervalo de confiança de 95%. A análise estatística foi realizada utilizando o software Graph Pad Instat (Graph Pad, Inc.) para Windows. Os valores médios ± SD da resistência à fractura foram registados para o grupo Disilicate de lítio (1706,01 ±154,32 N) enquanto que os valores médios ± SD registados com o grupo celtra foram (1550,67±196,71 N). As coroas cerâmicas de silicato de lítio reforçado com zircónio produziram valores de resistência à fractura comparáveis aos das coroas cerâmicas de dissilicato de lítio e ambos os materiais testados estão dentro dos valores clinicamente aceitáveis na área posterior.

Abstract The aim of this study was conducted to assess the fracture resistance of zirconia reinforced lithium silicate all ceramic material "Celtra Press" compared to lithium disilicate one "IPS e-max Press" under simulated oral conditions. Fourteen ceramic crowns were fabricated on epoxy dies which were duplicated from stainless steel master die and divided into two equal groups (n=7) according to the material of construction; Group A: Crowns fabricated with IPS e-max Press material and Group B: Crowns fabricated with Celtra Press material. The crowns were then cemented onto their corresponding dies with a self-adhesive resin cement and subjected to thermocycling and cyclic loading. Then they were loaded to fractur in a universal testing machine. The results were tabulated and statistically analyzed using Kolmogorov-Smirnov and Shapiro-Wilk tests. Student t-test used to compare mean values. The significance level was set at P ≤ 0.05 and 95% Confidence interval. Statistical analysis was performed using Graph Pad Instat (Graph Pad, Inc.) software for windows. The mean ± SD values of fracture resistance were recorded for lithium Disilicate group (1706.01 ±154.32 N) meanwhile the mean ± SD value recorded with celtra group were (1550.67±196.71 N). Zirconia reinforced lithium silicate ceramic crowns produced comparable fracture resistance values to lithium disilicate ceramic crowns and both tested materials are within the clinically acceptable values in the posterior area.

Comparing Torque Loss in Standard Implants and Short Implants with Increased Vertical Cantilever Abutments: an In Vitro Study / Comparação da perda de torque em implantes padrão e implantes curtos com pilares cantilever verticais aumentados (in vitro)

Objectives: With regard to the prevalence of abutment screw loosening (SL) and bone height reduction, particularly in the posterior regions of the jaws, as well as the contradictory issue of applying short implants instead of surgeries, along with all preparations associated with longer implants, the present study aimed to compare the amount of torque loss in short implants with increased vertical cantilever abutments and standard ones. Material and Methods: In this experimental study, a total number of 20 implants (MegaGen Implant Co., Ltd, South Korea) with 4.5 mm diameter including 10 short implants (7 mm) and 10 standard ones (10 mm) were utilized. Using a surveyor, fixtures were perpendicularly mounted in 13×34 mm resin for short implants and 19×34 mm resin for standard ones. The abutments of the same height but different cuff heights (2.5 mm for the standard implants and 5.5 mm for the short ones) were then tightened with 30 N.cm, via a digital torque meter. To compensate the settling effect, the abutment screw was re-tightened with 30 N.cm after 10 min. Upon applying 500,000 cycles at 75 N.cm and 1 Hz along the longitudinal axis on each sample, blind reverse torque value (RTV) was measured with a digital torque meter. The data were finally analyzed using Student's t-test. Results:Both groups experienced torque loss, but there was no statistically significant difference between the case and control groups in terms of abutment SL (p = 0451). Conclusion: Short implants seem to be a good mechanical alternative in emergencies with respect to torque loss and abutment SL. (AU)

Objetivos: Considerando a prevalência de afrouxamento de parafuso dos pilares, redução da altura óssea especialmente nas regiões posteriores, a questão contraditória da aplicação de implantes curtos em vez de cirurgias e todos os preparos associados a implantes mais longos, este estudo buscou comparar implantes curtos com pilares cantilever verticais aumentados e implantes padrão na quantidade de perda de torque. Material e métodos: Neste estudo experimental, foram utilizados 20 implantes (Megagen, Coreia do Sul) com diâmetro de 4,5 mm, incluindo 10 implantes curtos (7 mm) e 10 implantes padrão (10 mm). A fixação foi realizada perpendicularmente em uma resina 13 × 34 mm para implantes curtos e uma resina 19 × 34 mm para implantes padrão, usando um topógrafo. Os pilares da mesma altura, mas com diferentes comprimentos de manguito (2,5 mm para os implantes padrão e 5,5 mm para os implantes curtos) foram apertados com 30 N, utilizando um torquímetro digital. Para compensar o efeito de sedimentação, o parafuso do pilar foi reapertado com 30 N após 10 min. Depois de aplicar 500.000 ciclos a 75 N e 1 Hz ao longo do eixo longitudinal em cada amostra, o valor de torque reverso cego foi medido com um medidor de torque digital. Os dados foram analisados pelo teste t de Student. Resultados: Todos os grupos tiveram perda de torque, mas não houve diferença estatisticamente significativa entre os grupos caso e controle em termos de afrouxamento do parafuso do pilar (p = 0451). Conclusão: Os implantes curtos parecem ser uma boa alternativa mecânica em emergências em termos de perda de torque e afrouxamento do parafuso do pilar. (AU)

Influence of CAD/CAM Material and Preparation Design on the Long-term Fracture Resistance of Endocrowns Restoring Maxillary Premolars / Influência do material de CAD / CAM e tipo de preparo na resistência à fratura a longo prazo de coroas endodônticas adesivas na restauração de pré-molares superiores

Objective: To evaluate the effect of different occlusal preparation designs and CAD/CAM materials on the fracture resistance of maxillary premolars end crowns. Materials and Methods: sixty-four endodontically treated upper first premolars were randomly divided into four groups according to ceramic materials (Vita Enamic and IPS emax CAD) and occlusal preparation designs (Anatomical and horizontal butt joint). After teeth preparation, the restorations were all made by CAD/CAM system (Cerec MCXL). Half of each group had undergone cyclic fatigue testing of 105 cycles with 50N loading force at a frequency of 0.5Hz in a mechatronic chewing simulator machine, and then all samples were loaded to fracture using a universal testing machine with a cross head speed of 0.5 mm/min recording the fracture resistance values in N . The specimens were measured and statistically analyzed using using three-way analyses of variance (ANOVA), followed by serial two-way and one-way ANOVAs at each level of the study. P-values were adjusted for multiple comparisons using BENFORRONI correction and the significance level was set at P ≤ 0.05 for all tests. Results: Vita Enamic endocrowns showed higher fracture resistance values than IPS e max specimens. Conclusions: Vita Enamic endocrowns with anatomical preparations were found to be more favourable restoring endodontically treated maxillary premolars (AU)

Objetivo: Avaliar o efeito de diferentes tipos de preparo oclusal e materiais CAD/CAM na resistência à fratura de coroas endodônticas adesivas em pré-molares. Materiais e Métodos: Sessenta e quatro primeiros pré-molares superiores tratados endodonticamente foram divididos randomicamente em quatro grupos de acordo com os materiais cerâmicos (Vita Enamic e IPS emax CAD) e tipos de preparo oclusal (Recobrimento Incisal Anatômico e Horizontal). Após o preparo dental, as restaurações foram confeccionadas pelo sistema CAD/CAM (Cerec MCXL). Metade de cada grupo foi submetido a testes de fadiga cíclica de 105 ciclos com força de carga de 50N a uma frequência de 0,5Hz em uma máquina simuladora de mastigação mecatrônica, e então todas as amostras foram submetidas a fratura por uma máquina de teste universal com uma velocidade de 0,5 mm / min registrando os valores de resistência à fratura em N. As amostras foram medidas e analisadas estatisticamente usando análises de variância de três fatores (ANOVA), seguidas por ANOVAs de dois fatores e de um fator em cada nível do estudo. Os valores de p foram ajustados para comparações múltiplas usando a correção BENFORRONI e o nível de significância estabelecido foi de P ≤ 0,05 para todos os testes. Resultados: Coroas endodônticas adesivas da Vita Enamic mostraram maiores valores de resistência à fratura do que as amostras de IPS emax. Conclusões: Verificou-se que as coroas endodônticas adesivas da Vita Enamic com preparos com recobrimento incisal anatômico foram mais favoráveis para restaurar os pré-molares superiores tratados endodonticamente (AU)

Fracture load of nano-ceramic composite material for anterior endocrown restorations / Carga de fratura de material compósito nano-cerâmico para restaurações endocrown anteriores

Objective: to evaluate ability of Nano Ceramic Composite endocrown to withstand occlusal forces when used in the anterior region. Material and Methods: eighty endodontically treated maxillary central incisors teeth were randomly divided into two main groups according to the restoration type. Forty of these teeth were post, core and crown restorations and 40 were endocrown restorations. Then they were divided by halves into two subgroups according to the material used 20 were made with Lava Ultimate and the other 20 with IPS e.max. Each subgroup was then further subdivided into two divisions according to the remaining tooth structure above the CEJ (n = 10): 2 mm and 0.5 mm above the CEJ. After teeth preparation, the restorations were all made by CAD/CAM system (Cerec MCXL). All samples had undergone cyclic fatigue testing, and then loaded to fracture using a universal testing machine. The specimens were measured and statistically analyzed using Mann-Whitney test for comparing the mean changes between the groups. Results: Lava Ultimate showed higher mean fracture load values than IPS e.max specimens. Conclusions: endocrowns were found to be more favorable when used on endodontically treated teeth than the conventional post, core and crown restorations.(AU)

Objetivo: Avaliar a capacidade do compósito nanocerâmico endocrown para suportar forças oclusais quando usado na região anterior. Material e Métodos: Oitenta incisivos centrais superiores tratados endodonticamente foram divididos aleatoriamente em dois grupos principais, de acordo com o tipo de restauração. Quarenta desses dentes receberam restaurações com retentor intrarradicular, núcleo e coroa e 40 receberam restaurações endocrown. Em seguida, foram divididos pela metade em dois subgrupos, de acordo com o material utilizado, sendo 20 confeccionados com Lava Ultimate e os demais 20 com IPS e.max. Cada subgrupo foi posteriormente subdividido em dois, de acordo com a estrutura dentária remanescente acima da JEC (n = 10): 2 mm e 0,5 mm acima do JEC. Após o preparo dos dentes, todas as restaurações foram realizadas pelo sistema CAD/ CAM (Cerec MCXL). Todas as amostras foram submetidas a testes de fadiga cíclica e submetidas ao esforço até a fratura em uma máquina universal de testes. As amostras foram medidas e analisadas estatisticamente pelo teste de MannWhitney para comparação das alterações médias entre os grupos. Resultados: lava Ultimate apresentaram valores médios mais altos de carga até a fratura do que as amostras IPS e.max. Conclusões: as endocrowns mostraram-se mais favoráveis quando utilizadas em dentes tratados endodonticamente do que as restaurações convencionais com retentor intrarradicular, núcleo e coroa.(AU)

Ageing assessment of zirconia implant prostheses by three different quantitative assessment techniques

PURPOSE: To evaluate the influence of cyclic loading on phase transformation of zirconia abutments and to compare the effectiveness of three different quantitative ageing assessment techniques. MATERIALS AND METHODS: Thirty two Y-TZP prostheses fabricated from two brands, InCoris ZI and Ceramill ZI, were cemented to titanium bases and equally divided into two subgroups (n=8): control group without any treatment and aged group with cyclic loading between 20 N and 98 N for 100,000 cycles at 4 Hz in distilled water at 37℃. The tetragonal-to-monoclinic phase transformation was assessed by (i) conventional x-ray diffraction (XRD), (ii) micro x-ray diffraction (µXRD), and (iii) micro-Raman spectroscopy. The monoclinic-phase fractions (M%) were compared by two-way ANOVA. RESULTS: InCoris Zi presented significantly higher M% than Ceramill Zi in both control and aged groups (P<.001). Both materials exhibited significant phase transformation with monoclinicphase of 1 to 3% more in aged groups than controls for all thre e assessment techniques. The comparable M% was quantified by both µXRD and XRD. The highest M% was assessed with micro-Raman. CONCLUSION: Cyclic loading produced significant phase transformation in tested Y-TZP prostheses. The micro-Raman spectroscopy could be used as an alternative to XRD and µXRD.

Experimental Study on Ratcheting Behavior of Defective Cartilage under Cyclic Compressive Loading / 医用生物力学

Objective To study the ratcheting behavior of defective cartilage under cyclic compressive loading, so as to explore the pattern of damage evolution for defective articular cartilage. Methods Fresh articular cartilage was obtained from the distal femur of adult porcine, and the cartilage samples with different depth of defect were applied under triangular wave cyclic loading with different parameters. Combined with non-contact digital image technology, the ratcheting strain at different layers of cartilage was obtained. Results With the increase of loading cycles numbers, the ratcheting strain at each layer of cartilage increased sharply at first, then increased slowly and tended to be stable, and the ratcheting strain decreased gradually from shallow layer to deep layer. The response of each layer to cycle number was different. The strain in shallow layer increased rapidly within 50 cycles, while the strain in middle layer increased rapidly within 100 cycles and the strain in deep layer increased rapidly within 75 cycles. The ratcheting strain in shallow and deep layers was positively correlated with the stress amplitude and defect depth, and negatively correlated with the loading rate, while hysteresis response occurreds in middle layer. Conclusions The ratcheting behavior of cartilage was affected by special structure of the cartilage. The defect caused the strain increasing in each layer of cartilage, which could easily result in the aggravation of damage. The experiment results provide references for the construction of tissue-engineered cartilage.

Comparison of CAD/CAM abutment and prefabricated abutment in Morse taper internal type implant after cyclic loading: Axial displacement, removal torque, and tensile removal force

PURPOSE: The purpose of this study was to compare computer-aided design/computer-aided manufacturing (CAD/CAM) abutment and prefabricated abutment in Morse taper internal connection type implants after cyclic loading.MATERIALS AND METHODS: The study was conducted with internal type implants of two different manufacturers (Group Os, De). Fourteen assemblies were prepared for each manufacturer group and divided into 2 groups (n=7): prefabricated abutments (Os-P, De-P) and CAD/CAM abutments (Os-C, De-C). The amount of axial displacement and the removal torque values (RTVs) were measured before and after cyclic loading (10⁶ cycles, 3 Hz with 150 N), and the tensile removal force to dislodge the abutments was measured after cyclic loading. A repeated measures ANOVA and a pattern analysis based on the logarithmic regression model were conducted to evaluate the effect of cyclic loading on the axial displacement. The Wilcoxon signed-rank test and the Mann-Whitney test was conducted for comparison of RTV reduction% and tensile removal forces.RESULTS: There was no significant difference between CAD/CAM abutments and prefabricated abutments in axial displacement and tensile removal force; however, significantly greater RTV reduction% after cyclic loading was observed in CAD/CAM abutments. The correlation among the axial displacement, the RTV, and the tensile removal force was not significant.CONCLUSION: The use of CAD/CAM abutment did not significantly affect the amount of axial displacement and tensile removal force, but presented a significantly greater removal torque reduction% than prefabricated abutments. The connection stability due to the friction at the abutment-implant interface of CAD/CAM abutments may not be different from prefabricated abutment.

Dual pitch titanium-coated pedicle screws improve initial and early fixation in a polyetheretherketone rod semi-rigid fixation system in sheep / 中华医学杂志(英文版)

Background@#Reports on the efficacy of modifications to the thread design of pedicle screws are scarce. The aim of the study was to investigate initial and early fixation of pedicle screws with a plasma-sprayed titanium coating and dual pitch in the pedicle region (dual pitch titanium-coated pedicle screw [DPTCPS]) in a polyetheretherketone (PEEK) rod semi-rigid fixation system.@*Methods@#Fifty-four sheep spine specimens and 64 sheep were used to investigate initial ( "0-week" controls) and early (postoperative 6 months) fixation, respectively. Sheep were divided into dual pitch pedicle screw (DPPS), standard pitch pedicle screw (SPPS), DPTCPS, and standard pitch titanium-coated pedicle screw (SPTCPS) groups. Specimens/sheep were instrumented with four screws and two rods. Biomechanical evaluations were performed, and histology at the implant-bone interface was investigated.@*Results@#At 0-week, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (557.0 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.61, P < 0.05; 622.6 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.43, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (343.4 ± 16.5 vs. 237.5 ± 12.9 N, t = 3.52, P < 0.05; 343.4 ± 16.5 vs. 289.9 ± 12.8 N, t = 3.12, P < 0.05; 124.7 ± 13.5 vs. 41.9 ± 4.3 cycles, t = 2.18, P < 0.05; 124.7 ± 13.5 vs.79.5 ± 11.8 cycles, t = 2.76, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (1.8 ± 0.13 vs. 3.76 ± 0.19 mm, t = 2.29, P < 0.05; 1.8 ± 0.13 vs. 2.46 ± 10.20 mm, t = 2.69, P < 0.05). At post-operative 6 months, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (908.4 ± 33.6 vs. 646.5 ± 59.4 N, t = 3.34, P < 0.05; 925.9 ± 53.9 vs. 646.5 ± 59.4 N, t = 3.37, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (496.9 ± 17.9 vs. 370.3 ± 16.4 N, t = 2.86, P < 0.05; 496.9 ± 17.9 vs. 414.1 ± 12.8 N, t = 2.74, P < 0.05; 249.1 ± 11.0 vs.149.9 ± 11.1 cycles, t = 2.54, P < 0.05; 249.1 ± 11.0 vs.199.8 ± 7.2 cycles, t = 2.61, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (0.96 ± 0.11 vs. 2.39 ± 0.14 mm, t = 2.57, P < 0.05; 0.96 ± 0.11 vs. 1.82 ± 0.12 mm, t = 2.73, P < 0.05). Resistance to toggle testing (370.3 ± 16.4 vs. 414.1 ± 12.8 N, t = 3.29, P < 0.05; 149.9 ± 11.1 vs.199.8 ± 7.2 cycles, t = 2.97, P < 0.05) was significantly lower and maximum displacement in cyclic loading (2.39 ± 0.14 vs.1.82 ± 0.12 mm; t = 3.06, P < 0.05) was significantly higher for the SPTCPS than the DPTCPS. Bone-to-implant contact was significantly increased for the DPTCPS compared to the SPPS (58.3% ± 7.0% vs. 36.5% ± 4.4%, t = 2.74, P < 0.05); there was no inflammatory reaction or degradation of coated particles.@*Conclusion@#DPTCPSs might have stronger initial and early fixation in a PEEK rod semi-rigid fixation system.

Screw loosening and changes in removal torque relative to abutment screw length in a dental implant with external abutment connection after oblique cyclic loading

PURPOSE: This study investigated the effects of abutment screw lengths on screw loosening and removal torque in external connection implants after oblique cyclic loading. MATERIALS AND METHODS: External connection implants were secured with abutment screws to straight abutments. The abutment-implant assemblies were classified into seven groups based on the abutment screw length, with each group consisting of five assemblies. A cyclic load of 300 N was applied at a 30° angle to the loading axis until one million cycles were achieved. Removal torque values (RTVs) before and after loading, and RTV differences were evaluated. The measured values were analyzed using repeated measures of analysis of variance with the Student-Newman-Keuls multiple comparisons. RESULTS: All assemblies survived the oblique cyclic loading test without screw loosening. There was a significant decrease in the RTVs throughout the observed abutment screw lengths when the abutment-implant assemblies were loaded repeatedly (P < .001). However, the abutment screw length did not show significant difference on the RTVs before and after the experiment when the abutment screw length ranged from 1.4 to 3.8 mm (P=.647). CONCLUSION: Within the limit of this experiment, our results indicate that the abutment screw length did not significantly affect RTV differences after oblique cyclic loading when a minimum length of 1.4 mm (3.5 threads) was engaged. These findings suggest that short abutment screws may yield stable clinical outcomes comparable to long screws in terms of load resistance.

Influence of aging on bond strength of artificial teeth to denture base acrylic resins

Aim: The aim of this study was to evaluate the bond strength of artificial teeth to different types of denture base resins when submitted to thermomechanical cycling (TMC). Methods: Sixty artificial mandibular first molars (Trilux, Vipi) were randomly divided into 3 groups according to denture base acrylic resins (Vipi Wave, Vipi Cril, and Vipi Cril Plus, Vipi). The teeth were fixed onto self-polymerizing acrylic resin bars (0.5 cm2 cross-section x 2 cm height), and the set was included in a metal flask using dental stone/silicone. After the dental stone was set, the bar was removed, and the denture base resin was packed and processed according to the group studied (Vipi Wave: 180 W/20 minutes + 540W/5 minutes; Vipi Cril and Vipi Cril Plus: Water bath at 74ºC for 9h). After polymerization, the samples were divided into 2 groups (n=10), according to the TMC treatment received (simulation of 5 years of mastication or not). The samples were submitted to tensile bond strength test (1 mm/min), and the data (MPa) were statistically analyzed (2-way ANOVA, Bonferroni, α=0.05). The fracture interfaces were evaluated using a stereomicroscope (50x). Results: The bond strength results showed no statistically significant difference (p>0.05) between the resins studied. TMC was significant (p<0.05), demonstrating lower values for the bond strength of artificial teeth to Vipi Cril Plus. The predominant fracture type was cohesive in resin. Conclusions: It was concluded that there is no difference in bond strength between artificial teeth and the resins used for denture base. However, TMC decreases the bond strength values of artificial teeth and crosslink thermo-polymerizable acrylic resin

Effects of direct and indirect repair methods on microleakage in weak anterior teeth root canals / 天津医药

Objective To compare the difference of the microleakage repaired by direct method and indirect method of the funnel shaped root canal in the anterior teeth. Methods A total of 22 middle teeth at the similar size were collected, prepared into funnel root canal after finishing the root filling. The teeth were divided into A and B groups randomly, and there were 11 test pieces in each group. The root canal was repaired by direct method in group A and indirect method in group B. After 500 thermal-cold cycling and 240 000 dynamic cyclic loading,one tooth was selected in each group randomly. The microstructure were observed by scanning electron microscope (SEM). One piece of each group was randomly selected and the image of the core and the dentin was scanned by electron microscope. The remaining 20 pieces were dyed by India ink, dealt with transparent, compared and observed under the microscope. The degree of microleakage was recorded and analyzed in two groups. Results Under electron microscope, a gap can be observed in the bonding interface of group A. The gap was significantly bigger than that of group B. The leakage was significantly serious in group A than that in group B (P<0.05). Conclusion The level of microleakage of anterior teeth with flared canals, which is restored by fiber post core with the indirect method, is significantly better than that with the direct method. The indirect method has a good edge seal action and is more suitable for clinical application.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

PURPOSE: The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. MATERIALS AND METHODS: Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. RESULTS: The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). CONCLUSION: Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

Effect of cyclic loading and retightening on reverse torque value in external and internal implants

PURPOSE: The aim of this study was to evaluate the effect of cyclic loading and screw retightening on reverse torque value (RTV) in external and internal type implants. MATERIALS AND METHODS: Cement-retained abutments were connected with 30 Ncm torque to external and internal type implants. Experimental groups were classified according to implant connection type and retightening/loading protocol. In groups with no retightening, RTV was evaluated after cyclic loading for 100,000 cycles. In groups with retightening, RTV was measured after 3, 10, 100 cycles as well as every 20,000 cycles until 100,000 cycles of loading. RESULTS: Every group showed decreased RTV after cyclic loading. Before and after cyclic loading, external type implants had significantly higher RTVs than internal type implants. In external type implants, retightening did not affect the decrease in RTV. In contrast, retightening 5 times and retightening after 10 cycles of dynamic loading was effective for maintaining RTV in internal type implants. CONCLUSION: Retightening of screws is more effective in internal type implants than external type implants. Retightening of screws is recommended in the early stage of functional loading.

A comparative study of gold UCLA-type and CAD/CAM titanium implant abutments

PURPOSE: The aim of this study was to evaluate the interface accuracy of computer-assisted designed and manufactured (CAD/CAM) titanium abutments and implant fixture compared to gold-cast UCLA abutments. MATERIALS AND METHODS: An external connection implant system (Mark III, n=10) and an internal connection implant system (Replace Select, n=10) were used, 5 of each group were connected to milled titanium abutment and the rest were connected to the gold-cast UCLA abutments. The implant fixture and abutment were tightened to torque of 35 Ncm using a digital torque gauge, and initial detorque values were measured 10 minutes after tightening. To mimic the mastication, a cyclic loading was applied at 14 Hz for one million cycles, with the stress amplitude range being within 0 N to 100 N. After the cyclic loading, detorque values were measured again. The fixture-abutment gaps were measured under a microscope and recorded with an accuracy of +/-0.1 microm at 50 points. RESULTS: Initial detorque values of milled abutment were significantly higher than those of cast abutment (P.05). After cyclic loading, detorque values of cast abutment increased, but those of milled abutment decreased (P<.05). There was no significant difference of gap dimension between the milled abutment group and the cast abutment group after cyclic loading. CONCLUSION: In conclusion, CAD/CAM milled titanium abutment can be fabricated with sufficient accuracy to permit screw joint stability between abutment and fixture comparable to that of the traditional gold cast UCLA abutment.

Efeito da altura do pilar, de diferentes cimentos e das ciclagens térmica e mecânica sobre a resistência máxima à tração de infraestruturas metálicas cimentadas / Effect of abutment height, different cements, thermocycling and cyclic loading on the ultimate tensile strength of cement-retained/implant-supported cast restorations

Este estudo avaliou (1) o efeito da altura do pilar, dos diferentes cimentos e da termociclagem e (2) o efeito dos diferentes cimentos e da ciclagem mecânica sobre a resistência máxima à tração (RMT) de restaurações implantossuportadas cimentadas. Pilares de titânio (UCLA), com alturas de 4,0 e 6,0 mm (1), ou 4,0 mm (2), foram torqueados com 32 N.cm a análogos de implantes HI. Infraestruturas em Co-Cr, jateadas com óxido de alumínio 50 µm foram cimentadas com: Fosfato de Zinco- FZ; RelyX Luting 2- RXL2; C & B Cement- C&B; RelyX U100- RXU100 e RelyX Temp NE- RXTNE. Os conjuntos foram submetidos aos ensaios de tração (0,5 mm/min) após: 1- armazenagem em saliva artificial a 37 ºC durante 24 h (controle), 2- termociclagem (10.000 ciclos, 5,0 e 55 °C, 30 s de imersão), ou 3-ciclagem mecânica (106 ciclos, 140 N, 15 Hz). Os dados foram analisados por (1) 3-way ANOVA e Dunnett, e (2) 2-way ANOVA e Tukey HSD (α=0,05). Independentemente da altura do pilar, não houve diferença nos resultados dos grupos sem termociclagem (p≥0,05). Após termociclagem, houve aumento (p<0,05) na RMT nos pilares de 6,0 mm. Após ciclagem mecânica, houve diminuição (p<0,05) nos resultados de RMT produzidos por RXL2. A altura do pilar influenciou os resultados do RXL2, que produziu RMT mais elevada com os pilares de 6,0 mm. Com exceção do RXL2, a ciclagem mecânica não comprometeu a RMT das infraestruturas cimentadas. Em determinadas condições, o RXTNE produziu RMT semelhante à alguns cimentos finais

This study evaluate (1) the effect of abutment height, different cements and thermocycling, and (2) the effect of different cements and cyclic loading on the ultimate tensile strength (UTS) of cement-retained/implant-supported cast restorations. UCLA-type abutments with 4.0 and 6.0-mm height (1), or 4.0-mm height (2) were torqued to with 32 N.cm to internal hexagon dental implant replicas. Copings casted in Co-Cr, sandblasted with 50-µm aluminum oxide particles were cemented with: Zinc Phosphate- ZP; RelyX Luting 2- RXL2; C & B Cement- C&B; RelyX U100-RXU100 and RelyX Temp NE- RXTNE. The assemblies were submitted to the tensile test (0.5 mm/min) after: 1- storage in artificial saliva at 37 °C for 24 h (control), 2-thermocycling (10,000 cycles, 5.0 and 55 ºC, 30-s dwell time), or 3- cyclic loading (106 cycles, 140 N, 15 Hz). Data were analyzed by (1) 3-way ANOVA and Dunnett tests, and (2) 2-way ANOVA and Tukey HSD tests (α=0.05). Regardless of the abutments' heights, no significant differences were found among the UTS of the nonthermocycled groups (p≥0.05). After thermocycling, an increasing in the UTS was observed for the 6.0-mm abutments (p<0.05). After cyclic loading, the UTS values produced by RXL2 were decreased (p<0.05). The abutment's heights used affected the RXL2 results, which produced higher results with the 6.0-mm abutments. With the exception of RXL2, cyclic loading did not detrimentally affect the UTS of the cemented castings. In some conditions, the provisional cement RXTNE produced similar UTS to some definitive cements

Effect of cyclic loading on axial displacement of abutment into implant with internal tapered connection: a pilot study / 대한치과보철학회지

PURPOSE: To evaluate the axial displacement of implant-abutment assembly after cyclic loading in internal tapered connection system. MATERIALS AND METHODS: External butt-joint connection implant and internal tapered connection implant were connected with three types of abutment for cement-retained prostheses, i.e. external type abutment (Ext group), internal tapered 1-piece abutment (Int-1 group), and internal tapered 2-piece abutment (Int-2 group). For each group, 7 implants and abutments were used. The implantabutments assemblies were clamped into the implant holder for vertical loads. A dynamic cyclic loading was applied for 150 +/- 10 N at a frequency of 4 Hz. The amount of axial displacement of the abutment into the implant was calculated at each cycle of 0, 5, 10, 50, 100, 1,000, 5,000, and 10,000. A repeated measures analysis of variance (ANOVA) for the overall effect of cyclic loading and the pattern analysis by linear mixed model were used for statistical analysis. Differences at P<.05 were considered statistically significant. RESULTS: The mean axial displacement after 10,000 cycles were 0.714 +/- 0.488 microm in Ext group, 5.286 +/- 1.604 microm in Int-1 group, and 11.429 +/- 1.902 microm in Int-2 group. In the pattern analysis, Int-1 and Int-2 group showed continuous axial displacement at 10,000 cycles. There was no declining pattern of axial displacement in the Ext group. CONCLUSION: The pattern of linear mixed model in Ext group showed no axial displacement. There were continuous axial displacements in abutment-implant assemblies in the Int-1 and Int-2 group at 10,000 cycles. More axial displacement was found in Int-2 group than in Int-1 group.

Effect of cement type on microleakage of cast post-and-core systems under cyclic loading / Efeito do tipo de cimento na microinfiltração de núcleos metálicos fundidos submetidos à fadiga cíclica

Objective: The purpose of this study was to compare the microleakage of four cements in cast post-andcoresystems under cyclic loading. Materials and methods: Sixty-four human premolars were sectionedat the cement-enamel junction, endodontically treated, and divided into four groups (n = 16). Cast postsand cores were fabricated for root segments and were cemented with zinc phosphate cement (Harvard),resin-modified glass ionomer (Fuji PLUS), dual-cured phosphate methacrylate resin cement (Panavia F),or a dual-cured resin cement (Variolink II). All specimens underwent thermal cycling for 1.500 cycleswith 5 °C and 55 °C, with a dwelling time of 12 seconds. Half of the specimens of each group were subjectedto cycling loading with 50 N at 1.2 Hz for 750,000 cycles. Specimens were then immersed in 5%basic fuchsin solution for 24 hours. Specimens were sectioned, visualized by stereomicroscope under40x magnification and scored for dye penetration. The ratio between the length of the interface and thelength of dye penetration was also determined. Microleakage differences between the four cements were analyzed by Kruskal-Wallis test, and the effect of fatigue was analyzed with Mann-Whitney nonparametrictest (α =.05). Results: No failures occurred during fatigue testing. The zinc phosphate cement showedsignificantly higher microleakage values compared to other cements under both unloaded and loadedconditions (p = .007 and p = .006). Fatigue significantly increased the microleakage in all groups (p < .05).Conclusions: The microleakage values for the resin cements and the resin-modified glass ionomer weresimilar and significantly less than those of zinc phosphate, irrespective of loading. Fatigue loading increasedthe microleakage values for all the cements.

Objetivo: O objetivo deste estudo foi comparar a microinfiltração de pinos e núcleos de preenchimento metálicoscimentados com quatro diferentes materiais. Materiais e Métodos: 64 pré-molares humanos foram seccionadosna junção cemento-esmalte, tratados endodonticamente e divididos em quatro grupos (n = 16). Pinos enúcleos metálicos fundidos foram fabricados e cimentados com cimento de fosfato de zinco (Harvard), cimentode ionômero de vidro modificado (Fuji Plus), cimento resinoso dual de metacrilato fosfato (Panavia F) e cimentoresinoso dual (Variolink II). Todos os espécimes foram submetidos à ciclagem térmica (1.500 ciclos a 5-55 °C, 12segundos de banho). Metade dos espécimes de cada grupo foi submetida a uma carga cíclica de 50 N a 1,2 Hz emum total de 750.000 ciclos. Após a ciclagem, os espécimes foram imersos em solução de fucsina básica 5% por24 horas, seccionados, visualizados sob aumento de 40x e ranqueados quanto à penetração do corante. A proporçãoentre o comprimento da interface e o comprimento da penetração do corante foi também determinada.As diferenças de infiltração entre os quatro cimentos foram analisadas por teste de Kruskal-Wallis e o efeito dafadiga foi analisado por teste não paramétrico de Mann-Whitney (α = 0,05). Resultados: Não ocorreram falhasdurante o teste de fadiga. O cimento de fosfato de zinco mostrou valores de infiltração significativamente maiorescomparados aos demais cimentos na ausência ou presença da fadiga (p = 0,007 e p = 0,006). A fadiga elevousignificativamente a microinfiltração em todos os grupos (p < 0,05). Conclusões: Os valores de microinfiltraçãopara os cimentos resinosos e para o cimento de ionômero de vidro modificado foram similares e inferiores àquelesdo cimento de fosfato de zinco, independente da aplicação do teste de fadiga. A fadiga elevou os valores de microinfiltraçãopara todos os cimentos.

Fatigue fracture of different dental implant system under cyclic loading / 대한치과보철학회지

STATEMENT OF PROBLEM: Problems such as loosening and fractures of retained screws and fracture of implant fixture have been frequently reported in implant prosthesis. PURPOSE: Implant has weak mechanical properties against lateral loading compared to vertical occlusal loading, and therefore, stress analysis of implant fixture depending on its material and geometric features is needed. MATERIAL AND METHODS: Total 28 of external hexed implants were divided into 7 of 4 groups; Group A (3i, FULL OSSEOTITE(R)Implant), Group B (Nobelbiocare, Branemark System(R)Mk III Groovy RP), Group C (Neobiotec, SinusQuick(TM) EB), Group D (Osstem, US-II). The type III gold alloy prostheses were fabricated using adequate UCLA gold abutments. Fixture, abutment screw, and abutment were connected and cross-sectioned vertically. Hardness test was conducted using MXT-alpha. For fatigue fracture test, with MTS 810, the specimens were loaded to the extent of 60 - 600 N until fracture occurred. The fracture pattern of abutment screw and fixture was observed under scanning electron microscope. A comparative study of stress distribution and fracture area of abutment screw and fixture was carried out through finite element analysis. RESULTS: 1. In Vicker's hardness test of abutment screw, the highest value was measured in group A and lowest value was measured in group D. 2. In all implant groups, implant fixture fractures occurred mainly at the 3 - 4th fixture thread valley where tensile stress was concentrated. When the fatigue life was compared, significant difference was found between the group A, B, C and D (P<.05). 3. The fracture patterns of group B and group D showed complex failure type, a fracture behavior including transverse and longitudinal failure patterns in both fixture and abutment screw. In Group A and C, however, the transverse failure of fixture was only observed. 4. The finite element analysis infers that a fatigue crack started at the fixture surface. CONCLUSION: The maximum tensile stress was found in the implant fixture at the level of cortical bone. The fatigue fracture occurred when the dead space of implant fixture coincides with jig surface where the maximum tensile stress was generated. To increase implant durability, prevention of surrounding bone resorption is important. However, if the bone resorption progresses to the level of dead space, the frequency of implant fracture would increase. Thus, proper management is needed.

Screw Joint Stability under Cyclic Loading of Zirconia Implant Abutments / 대한치과보철학회지

PURPOSE: The purpose of this study was to evaluate the effect of abutment material on screw-loosening before and after cyclic loading. Among the different materials of abutments, zirconia and metal abutment were used. MATERIAL AND METHODS:: Two types of implant systems: external butt joint (US II, Osstem Implant, Korea) and internal conical joint (GS II, Osstem Implant, Korea) were used. In each type, specimens were divided into two different kinds of abutments: zirconia and metal (n = 5). The implant was rigidly held in a special holding to device ensure fixation. Abutment was connected to 30 Ncm with digital torque gauge, and was retightened in 30 Ncm after 10 minutes. The initial removal torque values were measured. The same specimens were tightened in 30 Ncm again and held in the cycling loading simulator (Instron, USA) according to ISO/FPIS 1480. Cycling loading tests were performed at loads 10 to 250 N, for 1 million cycles, at 14 Hz, (by subjecting sinusoidal wave from 10 to 250 N at a frequency of 14 Hz for 1 million cycles,) and then postload removal torque values were evaluated. RESULTS: 1. In all samples, the removal values of abutment screw were lower than tightening torque values (30 Ncm), but the phenomenon of the screw loosening was not observed. 2. In both of the implant systems, initial and postload removal torque of zirconia abutment were significantly higher than those of metal abutment (P .05). 4. In metal abutments, the removal torque ratio of GS II system (internal conical joint system) was lower than that of US II system (external butt joint system) (P .05). CONCLUSION: Zirconia abutment had a good screw joint stability in the condition of one million cycling loading.

A controlled cyclic loading on the surface treated and bonded ceramic: Staircase method / 대한치과보철학회지

STATEMENT OF PROBLEM: Effect of surface treatment of ceramic under loading does not appear to have been investigated. PURPOSE: The aim of this study was to investigate the effect of surface treatment of esthetic ceramic, which is performed to increase the bonding strength, on the fracture stress under controlled cyclic loading condition. MATERIAL AND METHODS: Sixty 1.0 mm-thick specimens were made from Mark II Vitablocs (Vita Zahnfabrik, Germany) and divided into 3 groups: polished (control), sandblasted, and etched. Specimens of each group were bonded to a dentin analog material base including micro-channels to facilitate the flow of water to the bonding interface. Bonded ceramics were cyclically loaded with a flat-end piston in the water (500,000 cycles, 15Hz). Following completion of cyclic loading, specimens were examined for subsurface crack formation and subsequent stress was determined and loaded to next specimen by the staircase method according to the crack existence. RESULTS: There were significant differences of mean fatigue limit in the sandblasted (222.86 +/- 23.42 N) and etched group (222.86 +/- 14.16 N) when compared to polished group (251.43 +/- 10.6 N) (P<.05; Wald-type pair-wise comparison and post hoc Bonferroni test). Of cracked specimens, surface treated group showed longer crack propagation after 24 hours. All failures originated from the radial cracking without cone crack. Fracture resistance of this study was very low and comparable to failure load in the oral cavity. CONCLUSION: Well controlled cyclic loading could induce clinically relevant cracks and fracture resistance of Mark II ceramic was relatively low applicable only to anterior restorations. Surface treatment of inner surface of feldspathic porcelain in the matsicatory area could influence lifetime of restorations.