Effect of dynamic loading on fracture resistance of gradient zirconia fixed partial denture frameworks.

STATEMENT OF PROBLEM: The new strength-gradient zirconia composed of 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 5-mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) has been claimed to have superior mechanical properties. However, data on the fracture resistance of 3-unit gradient 5Y-TZP and 3Y-TZP fixed partial denture frameworks are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of dynamic loading on the fracture resistance of gradient zirconia fixed partial denture frameworks. MATERIAL AND METHODS: Two standardized stainless-steel master dies were designed to simulate a mandibular left second premolar and second molar prepared to receive zirconia frameworks. The frameworks were designed with a 0.6-mm uniform wall thickness. The mesiodistal width of the connectors was 3 ±0.02 mm, and the occlusogingival height was 3 ±0.02 mm. Forty zirconia frameworks were fabricated and divided into 2 groups according to the tested materials (n=20): 3Y-TZP and gradient 5Y-TZP and 3Y-TZP. The frameworks were cemented onto their corresponding dies with a conventional glass ionomer cement. Half of the cemented frameworks in each group underwent 600 000 cycles of dynamic loading in a mastication simulator (n=10). The other half was fractured without dynamic loading (n=10). Fracture resistance measurements (N) for each framework were recorded by using a universal testing machine at a crosshead speed of 1 mm/min. A fractured framework from each group was examined by using a scanning electron microscope (SEM) at ×100 magnification. The data obtained were statistically analyzed by using 2-way ANOVA, the pairwise Tukey honestly significant difference (HSD), and simple main effect tests to detect the difference between group mean values (α=.05). RESULTS: The mean ±standard deviation of fracture load value before dynamic loading was 1919 ±193 N for the 3Y-TZP group and 908 ±99 N for the gradient 5Y-TZP and 3Y-TZP group. In addition, the mean fracture load value after dynamic loading was 1418 ±163 N for the 3Y-TZP group and 716 ±85 N for the gradient 5Y-TZP and 3Y-TZP group. The interaction between the effects of the zirconia material and dynamic loading on the fracture resistance was statistically significant (P=.002). The 3Y-TZP group had a statistically significant, higher fracture load mean value the gradient 5Y-TZP and 3Y-TZP group before and after dynamic loading (P<.001). CONCLUSIONS: The fracture resistance of 3Y-TZP frameworks was significantly higher than that of gradient 5Y-TZP and 3Y-TZP frameworks before and after dynamic loading. Dynamic loading significantly reduced the fracture resistance of 3Y-TZP and gradient 5Y-TZP and 3Y-TZP frameworks.

Effect of different surface treatments on the bond strength of milled polyetheretherketone posts.

STATEMENT OF PROBLEM: Polyetheretherketone (PEEK) can be used as a framework material for removable and fixed dental prostheses. However, information about the use of PEEK as a post-and-core restoration is scarce. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different surface treatments on the push-out bond strength of milled polyetheretherketone posts to resin cement. MATERIAL AND METHODS: Sixty intact human maxillary central incisors were selected and endodontically treated, and standardized post spaces were prepared. Sixty PEEK posts were milled from a prefabricated PEEK blank by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system and divided into 3 groups (n=15) according to the surface treatment: acid etching by using 98% sulfuric acid (AE); airborne-particle abrasion by using 50-µm Al2O3 (AA); nonthermal plasma treatment (NTP); in addition, PEEK posts (n=15) received no treatment (NT) and served as a control. All posts were bonded by using a self-adhesive resin cement. Three sections (coronal, middle, and apical) were obtained for each specimen. Push-out bond strength measurements (MPa) for each section were recorded by using a universal testing machine at a crosshead speed of 0.5 mm/min until failure occurred. The post-cement interfaces and failure modes were evaluated by using scanning electron microscopy. The data obtained were statistically analyzed by using 1-way ANOVA and the pair-wise Tukey (HSD) test to study the difference between group mean values (α=.05). RESULTS: The overall mean ±standard deviation of the push-out bond strength was 11 ±2 MPa for AE group, 6 ±1 MPa for AA group, 5 ±1 MPa for NTP group, and 3 ±1 MPa for NT group. A statistically significant difference was found among all groups subjected to different surface treatments as indicated by the ANOVA test (P<.001). The pair-wise Tukey honestly significant difference (HSD) test showed a significant difference among the AE group and all groups (P<.001); however, no significant difference was observed between the AA and NTP groups (P>.05). Moreover, a significant difference was observed among all root sections (P<.001). CONCLUSIONS: Surface treatment of PEEK posts with 98% sulfuric acid for 60 seconds showed significantly higher bond strength values than those in other groups. The bond strength of PEEK posts to resin cement was significantly higher in the coronal section than that in other sections.

Effect of different fabrication techniques on the marginal precision of polyetheretherketone single-crown copings.

STATEMENT OF PROBLEM: Demand is increasing for polyetheretherketone (PEEK) as a fixed dental prosthesis core material. However, information is lacking about how the precision of these restorations is affected by the fabrication procedures. PURPOSE: The purpose of this in vitro study was to evaluate the influence of different fabrication techniques on the marginal precision of PEEK single-crown copings. MATERIAL AND METHODS: A stainless-steel master die was designed to simulate a prepared mandibular second molar to receive ceramic crowns. Thirty PEEK copings were fabricated and divided into 3 groups (n=10) according to the fabrication technique: milled from a prefabricated PEEK blank by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system (PC); pressed from prefabricated PEEK pellets (PP); and pressed from PEEK granules (PG); in addition, 3-mol yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) copings (n=10) were produced by using the same CAD-CAM system and served as a control. Marginal precision measurements (in µm) were recorded at 4 reference points on each coping by using a digital microscope. The data obtained were statistically analyzed by using 1-way ANOVA and the pair-wise Tukey (HSD) test to study the difference between group mean values (α=.05). RESULTS: The overall mean ±standard deviation marginal gap at the marginal opening for the copings was 78 ±10 µm for PEEK granules copings, 72 ±9 µm for PEEK pellet copings, 45 ±6 µm for PEEK CAD-CAM copings, and 43 ±1 µm for the 3Y-TZP CAD-CAM control. A statistically significant difference was found between the milled and pressed copings as indicated by the ANOVA test (P<.001). The pair-wise Tukey honestly significant difference (HSD) test showed a nonsignificant difference (P>.05) between milled 3Y-TZP and milled PEEK copings; moreover, no significant difference was observed between the PEEK copings pressed from pellets or granules (P>.05). CONCLUSIONS: The marginal precision of PEEK CAD-CAM-fabricated copings showed significantly lower mean marginal gap values than PEEK pressed copings. The marginal gap mean values recorded were all within a clinically acceptable range (120 µm).

Flexural strength of small connector designs of zirconia-based partial fixed dental prostheses.

STATEMENT OF PROBLEM: Partial fixed dental prostheses with a small connector size are required for optimal esthetics and limited interarch space; however, final strength is endangered. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different connector designs on the flexural strength of simulated 3-unit partial fixed dental prostheses made of yttria-stabilized tetragonal zirconia polycrystalline using computer-aided design and computer-aided manufacturing technology. MATERIAL AND METHODS: To simulate a 3-unit partial fixed dental prosthesis, 20 rectangular bar-shaped specimens were fabricated with dimensions of 4 ± 0.05 mm (H) × 4 ± 0.05 mm (W) × 30 0.5 mm (L). Each bar specimen had 2 constricted parts on both sides, representing the connector and defining a central pontic of 10 ± 0.10 mm in length. The specimens were divided into 4 groups according to the connector diameter and design, as follows: SR: 2 mm (H) × 3 mm (W) round 0.6 mm radius of curvature; SS: 2 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature; CR: 3 mm (H) × 3 mm (W) round 0.6 mm radius of curvature; and CS: 3 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature. An additional 5 specimens were fabricated with no constriction and served as the control group. The specimens were subjected to a 3-point flexural strength test in a universal testing machine with a crosshead speed of 0.5 mm/min until failure. Scanning electron microscopic and photomicrograph images were used to examine the fracture surfaces. Two-way ANOVA and the Tukey-Kramer post hoc test were used to analyze the data (α = .05). RESULTS: The mean flexural strength for SR 2 mm (H) × 3 mm (W) round 0.6 mm radius of curvature (583.6 ± 49.7 MPa) was significantly higher than that of SS, which was 2 mm (H)× 3 mm (W) sharp 0.1 mm radius of curvature (502.8 ± 23.3 MPa). Similarly, the mean flexural strength for CR was 3 mm (H) × 3 mm (W) round 0.6 mm radius of curvature (682.9 ± 36.8), which was significantly higher than that of CC, 3 mm (H) × 3 mm (W) sharp 0.1 mm radius of curvature (486.7 ± 35.6 MPa). CONCLUSIONS: The flexural strength of the yttria-stabilized tetragonal zirconia polycrystalline-based ceramics was affected by the connector dimension and design. The 2-round connector design was more able to withstand occlusal forces than the sharp design. The 3-connector design with a minimum cross section of 2 × 3 mm is recommended for anterior fixed dental prostheses, provided it has a round curvature.

Accuracy of ceramic restorations made with two CAD/CAM systems.

STATEMENT OF PROBLEM: Different types of CAD/CAM systems are currently available, but information regarding which system produces the best marginal fit is lacking. PURPOSE: The purpose of this study was to evaluate the effect of 2 different CAD/CAM systems (Cerec inLab, Kavo Everest) on the marginal fit of 2 types of zirconia-based and lithium disilicate crowns. MATERIAL AND METHODS: Forty zirconia-based and lithium disilicate crowns, 20 each, were fabricated with the Cerec inLab and Everest CAD/CAM systems on a specially designed stainless steel die to ensure the standardization of specimen shape and dimensions. The vertical marginal fit for all tested crowns was evaluated by using a digital microscope at ×100 magnification, and the data were tabulated and statistically analyzed with 2-way ANOVA, followed by the Tukey honestly significant difference (HSD) test with a confidence level of .05 to determine the mean differences. RESULTS: The results showed that the CAD/CAM technique, ceramic type, and their interaction had a statistically significant effect on the mean marginal fit of both ceramic types tested. CONCLUSIONS: Better marginal fit values were exhibited by the Everest CAD/CAM technique for both ceramic types tested.

Three-dimensional assessment of internal adaptation measurement of three cad/cam ceramic systems.

This study aimed to evaluate the internal adaptation of three different computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic crowns. The internal adaptation of a polymer-infiltrated ceramic network material (Vita Enamic [VE]) was compared to two machinable glass-ceramics; Zirconia-reinforced lithium silicate (Vita Suprinity [VS]) and a lithium disilicate glass-ceramic (IPS e.max. CAD). Thirty human premolars of average size were prepared (n=10 each group) by computer numerical control to fulfill the criteria of all-ceramic crown design. Optical impressions were taken for each tooth preparation using the CAD/CAM scanner. Thirty crowns were fabricated using CAD/CAM system and divided into three groups (IPS e.max, VE, and VS). To assess the internal fit of tested crowns, the gap between the intaglio of each crown and the corresponding tooth surface was evaluated using a 3D digital scanner using the Triple-scan Protocol. One-way ANOVA followed by Tukey Post Hoc statistical tests were used to statistically analyze results of the internal fit. There was a statistically significant difference for all groups at the four axial walls (p = 0.000002). For total internal fit between groups, comparisons showed a statistically significant difference between all tested groups (p=0.000002). When each pair of groups was statistically compared with each other, all pair comparisons showed a statistically significant difference. IPS e.max CAD had the best internal fit, followed by Vita Enamic, then Vita Suprinity. For all ceramics tested, values of internal fit of all ceramics tested were within the clinically acceptable range.

Effect of metal selection and porcelain firing on the marginal accuracy of titanium-based metal ceramic restorations.

STATEMENT OF PROBLEM: Titanium is the most biocompatible metal used for dental casting; however, there is concern about its marginal accuracy after porcelain application since this aspect has direct influence on marginal fit. PURPOSE: The purpose of this study was to determine the effect that metal selection and the porcelain firing procedure have on the marginal accuracy of metal ceramic prostheses. MATERIAL AND METHODS: Cast CP Ti, milled CP Ti, cast Ti-6Al-7Nb, and cast Ni-Cr copings (n=5) were fired with compatible porcelains (Triceram for titanium-based metals and VITA VMK 95 for Ni-Cr alloy). The Ni-Cr alloy fired with its porcelain served as the control. Photographs of metal copings placed on a master die were made. Marginal discrepancy was determined on the photographs using an image processing program at 8 predetermined locations before airborne-particle abrasion for porcelain application, after firing of the opaque layer, and after firing of the dentin layer. Repeated-measures 2-way ANOVA was used to investigate the effect of metal selection and firing stage, and paired t tests were used to determine the effect of each firing stage within each material group (alpha=.05). RESULTS: ANOVA showed that both metal selection and firing stage significantly influenced the measured marginal discrepancy (P<.001), and there was interaction between the 2 variables (P<.001). Student-Newman-Keuls multiple comparison tests showed that there were significant differences between any 2 metals compared, at each stage of measurement. Paired t tests showed that significant changes in marginal discrepancy occurred with opaque firing on milled CP Ti (P=.017) and cast Ti-6Al-7Nb alloy (P=.003). CONCLUSIONS: Titanium copings fabricated by CAD/CAM demonstrated the least marginal discrepancy among all groups, while the base metal (Ni-Cr) groups exhibited the most discrepancy of all groups tested.

Three-dimensional assessment of internal adaptation measurement of three cad/cam ceramic systems

Abstract This study aimed to evaluate the internal adaptation of three different computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic crowns. The internal adaptation of a polymer-infiltrated ceramic network material (Vita Enamic [VE]) was compared to two machinable glass-ceramics; Zirconia-reinforced lithium silicate (Vita Suprinity [VS]) and a lithium disilicate glass-ceramic (IPS e.max. CAD). Thirty human premolars of average size were prepared (n=10 each group) by computer numerical control to fulfill the criteria of all-ceramic crown design. Optical impressions were taken for each tooth preparation using the CAD/CAM scanner. Thirty crowns were fabricated using CAD/CAM system and divided into three groups (IPS e.max, VE, and VS). To assess the internal fit of tested crowns, the gap between the intaglio of each crown and the corresponding tooth surface was evaluated using a 3D digital scanner using the Triple-scan Protocol. One-way ANOVA followed by Tukey Post Hoc statistical tests were used to statistically analyze results of the internal fit. There was a statistically significant difference for all groups at the four axial walls (p = 0.000002). For total internal fit between groups, comparisons showed a statistically significant difference between all tested groups (p=0.000002). When each pair of groups was statistically compared with each other, all pair comparisons showed a statistically significant difference. IPS e.max CAD had the best internal fit, followed by Vita Enamic, then Vita Suprinity. For all ceramics tested, values of internal fit of all ceramics tested were within the clinically acceptable range.

Resumo Este estudo teve como objetivo avaliar a adaptação interna de três diferentes coroas cerâmicas CAD/CAM (Computer-aided design/computer-aided manufacturing). A adaptação interna de um material cerâmico de rede com infiltração de polímero (Vita Enamic [VE]) foi comparada com duas cerâmicas de vidro maquináveis; silicato de lítio reforçado com zircónio (Vita Suprinity [VS]) e uma cerâmica-vidro de dissilicato de lítio (IPS e.max. CAD). Trinta dentes pré-molares humanos de tamanho médio foram preparados (n=10 cada grupo) por controle numérico computadorizado para preencher os critérios de desenho de coroa em cerâmica pura. Foram tiradas impressões ópticas para cada preparação dentária utilizando o scanner CAD/CAM. Trinta coroas foram fabricadas usando o sistema CAD/CAM e divididas em três grupos (IPS e.max, VE, e VS). Para avaliar o ajuste interno das coroas testadas, o espaço entre o entalhe de cada coroa e a superfície dentária correspondente foi avaliado usando um scanner digital 3D usando o Protocolo Triple-scan. Para analisar estatisticamente os resultados do ajuste interno, utilizou-se a ANOVA unidirecional seguida dos testes estatísticos Tukey Post Hoc. Houve uma diferença estatisticamente significativa para todos os grupos nas quatro paredes axiais (p = 0,000002). Para o ajuste interno total entre grupos, as comparações mostraram uma diferença estatisticamente significativa entre todos os grupos testados (p=0,000002). Quando cada par de grupos foi comparado estatisticamente uns com os outros, todas as comparações de pares mostraram uma diferença estatisticamente significativa. IPS e.max CAD teve o melhor ajuste interno, seguido por Vita Enamic, depois Vita Suprinity. Para todas as cerâmicas testadas, os valores de ajuste interno de todas as cerâmicas testadas encontravam-se dentro da gama clinicamente aceitável.

Effect of core and veneer thicknesses on the color parameters of two all-ceramic systems.

STATEMENT OF PROBLEM: Specific contributions of the core and the veneer thickness on the appearance of layered disk specimens are not well characterized. PURPOSE: This study examined the effect of varying core and veneer thickness on the color parameters of layered disk specimens made of 2 ceramic systems. MATERIAL AND METHODS: Disk specimens 16 mm in diameter with core/veneer thickness (mm) of 0.8/0.2 (baseline), 0.8/0.7, 0.8/1.2, 1.0/0.5, 1.3/0.2, and 1.8/0.2 were made from a leucite-reinforced ceramic (IPS Empress; 2B shade), and thickness (mm) of 0.5/0.5 (baseline), 0.5/1.0, 0.5/1.5, 0.8/0.7, 1.0/0.5, and 1.5/0.5 were made from a glass-infiltrated spinell ceramic (In-Ceram Spinell; A2 shade). Color parameters L*, a*, and b* of CIELAB color space were measured against a neutral gray background with a tri-stimulus colorimeter, and deltaE between disk group and its respective baseline group was calculated. Analysis of variance was used to determine the effect of material and core and veneer thickness on the color parameters (alpha = .05). RESULTS: Increasing the total disk thickness resulted in decrease of L* (P < .001) and an increase of a* (P < .001), b* (P < .001), and deltaE (P = .0236). For leucite-reinforced ceramic, the core thickness, veneer thickness, and their interaction exhibited significant influence on the mean values of a* and b* (P < .0028) but not on the mean values of L*. For spinell ceramic, the core thickness and veneer thickness exhibited significant influence on the mean values of L* and b* (P < .0272) but not on a*; the interaction demonstrated significant influence on b* (P = .0003) but not on L* and a*. CONCLUSION: The color appearance of the layered ceramic disk specimens is strongly influenced not only by the core thickness and veneer thickness, but also by their interaction.