Effect of etching and airborne particle abrasion on the microstructure of different dental ceramics

STATEMENT OF PROBLEM: The ceramic composition and microstructure surface of all-ceramic restorations are important components of an effective bonding substrate. Both hydrofluoric acid etching and airborne aluminum oxide particle abrasion produce irregular surfaces necessary for micromechanical bonding. Although surface treatments of feldspathic and leucite porcelains have been studied previously, the high alumina-containing and lithium disilicate ceramics have not been fully investigated. PURPOSE: The purpose of this study was to assess the surface topography of 6 different ceramics after treatment with either hydrofluoric acid etching or airborne aluminum oxide particle abrasion. MATERIAL AND METHODS: Five copings each of IPS Empress, IPS Empress 2 (0.8 mm thick), Cergogold (0.7 mm thick), In-Ceram Alumina, In-Ceram Zirconia, and Procera (0.8 mm thick) were fabricated following the manufacturer's instructions. Each coping was longitudinally sectioned into 4 equal parts by a diamond disk. The resulting sections were then randomly divided into 3 groups depending on subsequent surface treatments: Group 1, specimens without additional surface treatments, as received from the laboratory (control); Group 2, specimens treated by use of airborne particle abrasion with 50-microm aluminum oxide; and Group 3, specimens treated with 10% hydrofluoric acid etching (20 seconds for IPS Empress 2; 60 seconds for IPS Empress and Cergogold; and 2 minutes for In-Ceram Alumina, In-Ceram Zirconia, and Procera). RESULTS: Airborne particle abrasion changed the morphologic surface of IPS Empress, IPS Empress 2, and Cergogold ceramics. The surface topography of these ceramics exhibited shallow irregularities not evident in the control group. For Procera, the 50-microm aluminum oxide airborne particle abrasion produced a flattened surface. Airborne particle abrasion of In-Ceram Alumina and In-Ceram Zirconia did not change the morphologic characteristics and the same shallows pits found in the control group remained. For IPS Empress 2, 10% hydrofluoric acid etching produced elongated crystals scattered with shallow irregularities. For IPS Empress and Cergogold, the morphologic characteristic was honeycomb-like on the ceramic surface. The surface treatment of In-Ceram Alumina, In-Ceram Zirconia, and Procera did not change their superficial structure. CONCLUSION: Hydrofluoric acid etching and airborne particle abrasion with 50-microm aluminum oxide increased the irregularities on the surface of IPS Empress, IPS Empress 2, and Cergogold ceramics. Similar treatment of In-Ceram Alumina, In-Ceram Zirconia, and Procera did not change their morphologic microstructure.     

Influence of surface conditions and silane agent on the bond of resin to IPS Empress 2 ceramic

PURPOSE: The aim of this study was to evaluate the effect of different ceramic surface treatments on the tensile bond strength between IPS Empress 2 ceramic framework and Rely X adhesive resin cement, with or without the application of a silane coupling agent. MATERIALS AND METHODS: One hundred twenty disks were made, embedded in resin, and randomly divided into six groups: group 1 = sandblasting (100 microm), no silanation; group 2 = sandblasting (100 microm), silane treatment; group 3 = sandblasting (50 microm), no silanation; group 4 = sandblasting (50 microm), silane treatment; group 5 = hydrofluoric acid etching, no silanation; and group 6 = hydrofluoric acid etching, silane treatment. The disks were bonded into pairs with adhesive resin cement. All samples were stored in distilled water at 37 degrees C for 24 hours and then thermocycled. The samples were submitted to tensile testing. RESULTS: The use of silane improved the bond strength in relation to the groups in which silane was not applied (P < .05). The most effective surface treatment was etching with 10% hydrofluoric acid, both with (25.6 MPa) and without silane application (16.4 MPa); these values showed a statistically significant difference compared to sandblasting with 50- and 100-microm Al2O3. Sandblasting with 50-microm Al2O3, with (11.8 MPa) and without silane (5.4 MPa), demonstrated significantly higher tensile bond strength than sandblasting with 100-microm Al2O3, with (8.3 MPa) and without silane (3.8 MPa). CONCLUSION: Combined application of 10% hydrofluoric acid and silane enhanced the bond strength between the IPS Empress 2 ceramic framework and resin agent.     

Effect of Water Storage and Surface Treatments on the Tensile Bond Strength of IPS Empress 2 Ceramic

PURPOSE: The aim of this study was to evaluate the effect of water storage (24 hours and 1 year) on the tensile bond strength between the IPS Empress 2 ceramic and Variolink II resin cement under different superficial treatments. MATERIALS AND METHODS: One hundred and eighty disks with diameters of 5.3 mm at the top and 7.0 mm at the bottom, and a thickness of 2.5 mm were made, embedded in resin, and randomly divided into six groups: Groups 1 and 4 = 10% hydrofluoric acid for 20 seconds; Groups 2 and 5 = sandblasting for 5 seconds with 50 microm aluminum oxide; and Groups 3 and 6 = sandblasting for 5 seconds with 100 microm aluminum oxide. Silane was applied on the treated ceramic surfaces, and the disks were bonded into pairs with adhesive resin cement. The samples of Groups 1 to 3 were stored in distilled water at 37 degrees C for 24 hours, and Groups 4 to 6 were stored for 1 year. The samples were subjected to a tensile strength test in an Instron universal testing machine at a crosshead speed of 1.0 mm/min, until failure. The data were submitted to analysis of variance and Tukey's test (5%). RESULTS: The means of the tensile bond strength of Groups 1, 2, and 3 (15.54 +/- 4.53, 10.60 +/- 3.32, and 7.87 +/- 2.26 MPa) for 24-hour storage time were significantly higher than those observed for the 1-year storage (Groups 4, 5, and 6: 10.10 +/- 3.17, 6.34 +/- 1.06, and 2.60 +/- 0.41 MPa). The surface treatments with 10% hydrofluoric acid (15.54 +/- 4.53 and 10.10 +/- 3.17 MPa) showed statistically higher tensile bond strengths compared with sandblasting with 50 microm(10.60 +/- 3.32 and 6.34 +/- 1.06 MPa) and 100 microm (7.87 +/- 2.26 and 2.60 +/- 0.41 MPa) aluminum oxide for the storage time 24 hours and 1 year. CONCLUSIONS: Storage time significantly decreased the tensile bond strength for both ceramic surface treatments. The application of 10% hydrofluoric acid resulted in stronger tensile bond strength values than those achieved with aluminum oxide.     

The influence of ceramic surface treatments on the tensile bond strength of composite resin to all-ceramic coping materials

STATEMENT OF PROBLEM: An increasing demand for esthetic restorations has resulted in the development of new ceramic systems, but the fracture of veneering ceramics still remains the primary cause of failure. Porcelain repair frequently involves replacement with composite resin, but the bond strength between composite resin and all-ceramic coping materials has not been studied extensively. PURPOSE: The purpose of this study was to evaluate the tensile bond strength of composite resin to 3 different all-ceramic coping materials with various surface treatments. MATERIAL AND METHODS: Thirty specimens (10 x 10 x 2 mm) each of lithium-disilicate ceramic (IPS Empress2 [E]), alumina ceramic (In-Ceram Alumina [I]), and zirconia ceramic (Zi-Ceram [Z]) were fabricated. Feldspathic ceramic (Duceram Plus [F]) was used as the control. Each material was divided into 3 groups (n=10), and 3 different surface treatments were performed: airborne-particle abrasion with 50-microm alumina particles (Ab); airborne-particle abrasion with 50-microm alumina particles and acid etching with 4% hydrofluoric acid (Ae); or airborne-particle abrasion with 30-microm alumina particles modified with silica acid (Si). After surface treatment of ceramic specimens, composite resin cylinders (5-mm diameter x 10-mm height) were light polymerized onto the ceramic specimens. Each specimen was subjected to a tensile load at a crosshead speed of 2 mm/min until fracture. The fracture sites were examined with scanning electron microscopy to determine the location of failure during debonding and to examine the surface treatment effects. Two-way analysis of variance and the Duncan multiple comparison test (alpha=.05) were used to analyze the bond strength values. RESULTS: There were significant differences in the bond strengths for both ceramics (P<.001) and surface treatments (P<.001) and the interaction (P<.001). The Duncan analysis yielded the following statistical subsets of the bond strength values: (FAe, ISi, EAe, ZSi) > FAb > (FSi, EAb, ESi) (IAb, IAe) > (ZAe, ZAb). The results illustrate no differences within the parentheses but statistically significant differences among the groups. CONCLUSION: Alumina and zirconia ceramic specimens treated with a silica coating technique, and lithium disilicate ceramic specimens treated with airborne-particle abrasion and acid etching yielded the highest tensile bond strength values to a composite resin for the materials tested.     

Effects of surface treatment on the microtensile bond strength of ceramic materials to dentin

This study evaluated the effects of distinct surface treatments on the micro-tensile bonding strength (microTBS) of different ceramic materials. The occlusal surfaces of eighteen human maxillary molars were flattened perpendicularly to the long axis and divided in groups based on surface treatment (sandblasting: s; hydrofluoric acid: a; tribochemical silica coating: t): DP-s, DP-a, DP-t, IE-s, IE-a, IE-t, IC-s, IC-a, IC-t) and ceramic materials (Duceran Plus: DP, IPS Empress 2: IE, In-Ceram Alumina, IC). Panavia F luting resins were used according to the manufacturers' instructions to bond ceramic materials to the exposed dentin specimens under a load of 7.5 N. After 3-day storage, microTBS was tested at a cross-head speed of 1 mm/min. Data were analyzed with ANOVA and Tukey's test. ANOVA results showed that the microTBS of DP and IC were significantly different. The microTBS of DP-a was significantly higher than those of DP-s and DP-t. The microTBS of IC-t was significantly higher than those of IC-s and IC-a. Ceramic materials with different chemical formulations and applications yielded significantly different bond strengths to human dentin and must receive distinct surface treatments accordingly.     

Structural reliability of alumina-, feldspar-, leucite-, mica- and zirconia-based ceramics

OBJECTIVES: The objective of this study was to test the hypothesis that industrially manufactured ceramic materials, such as Cerec Mark II and Zirconia-TZP, have a smaller range of fracture strength variation and therefore greater structural reliability than laboratory-processed dental ceramic materials. METHODS: Thirty bar specimens per material were prepared and tested. The four-point bend test was used to determine the flexure strength of all ceramic materials. The fracture stress values were analyzed by Weibull analysis to determine the Weibull modulus values (m) and the 1 and 5% probabilities of failure. RESULTS: The mean strength and standard deviation values for these ceramics are as follows: (MPa+/-SD) were: Cerec Mark II, 86.3+/-4.3; Dicor, 70.3+/-12.2; In-Ceram Alumina, 429. 3+/-87.2; IPS Empress, 83.9+/-11.3; Vitadur Alpha Core, 131.0+/-9.5; Vitadur Alpha Dentin, 60.7+/-6.8; Vita VMK 68, 82.7+/-10.0; and Zirconia-TZP, 913.0+/-50.2. There was no statistically significant difference among the flexure strength of Cerec Mark II, Dicor, IPS Empress, Vitadur Alpha Dentin, and Vita VMK 68 ceramics (p>0.05). The highest Weibull moduli were associated with Cerec Mark II and Zirconia-TZP ceramics (23.6 and 18.4). Dicor glass-ceramic and In-Ceram Alumina had the lowest m values (5.5 and 5.7), whereas intermediate values were observed for IPS-Empress, Vita VMK 68, Vitadur Alpha Dentin and Vitadur Alpha Core ceramics (8.6, 8.9, 10.0 and 13.0, respectively). CONCLUSIONS: Except for In-Ceram Alumina, Vitadur Alpha and Zirconia-TZP core ceramics, most of the investigated ceramic materials fabricated under the condition of a dental laboratory were not stronger or more structurally reliable than Vita VMK 68 veneering porcelain. Only Cerec Mark II and Zirconia-TZP specimens, which were prepared from an industrially optimized ceramic material, exhibited m values greater than 18. Hence, we conclude that industrially prepared ceramics are more structurally reliable materials for dental applications although CAD-CAM procedures may induce surface and subsurface flaws that may adversely affect this property.     

三种全瓷基底与其相应饰面瓷的结合性能研究

目的:测试并比较3种全瓷基底材料与其相应饰面瓷的结合强度,为临床选择合适的修复材料提供依据。方法:将成品Lava Frame、Vita In-Ceram Alumina、IPS EmpressⅡ瓷块、StarLoy钴铬合金制成长方体试件,分别在其表面烧结相应的饰面瓷,测试抗剪切强度,激光共聚焦扫描显微镜和扫描电镜观察破坏模式。结果:Lava、Vita、IPS EmpressⅡ、金瓷复合体的抗剪强度值分别为11.40±1.08、9.44±1.23、25.56±1.70、27.02±2.06MPa。IPS EmpressⅡ、金瓷复合体的抗剪切强度显著高于Lava和Vita(P<0.05);IPS EmpressⅡ与金瓷复合体的抗剪切强度差异无统计学意义(P>0.05);Lava与Vita差异无统计学意义(P>0.05)。IPS Em-pressⅡ的破坏模式以基底材料破坏为主,Lava、Vita、金瓷复合体以饰面瓷破坏为主。结论:IPS EmpressⅡ基底与饰面瓷的结合强度最高,与金瓷复合体无差别。     

Effect of surface treatment on the shear bond strength of a resin-based cement to porcelain

The purpose of this in vitro study was to evaluate the effect of different surface treatments on the shear bond strength of a resin-based cement to porcelain. Sixty pairs of 50% aluminous porcelain discs were fabricated. In each pair, one disc measured 6 mm in diameter X 3 mm thickness (A) and the other measured 3 mm in diameter X 3mm thickness (B). The specimens were randomly assigned to 6 groups (n=10 pairs of discs), according to the surface treatment: etching with 10% hydrofluoric acid for 2 or 4 min (G1 and G2); 50-microm particle aluminum oxide sandblasting for 5 s (G3); sandblasting followed by etching for 2 or 4 min (G4 and G5) and control--no treatment (G6). A silane agent was applied to the treated surface of both discs of each pair. Bistite II DC dual-cure resin cement was applied and the B discs were bonded to their respective A discs. Specimens were stored in distilled water at 37 degrees C for 24 h and were tested in shear strength at a crosshead speed of 2 mm/min. Means in MPa were: G1: 14.21 +/- 4.68; G2: 8.92 +/- 3.02; G3: 10.04 +/- 2.37; G4: 12.74 +/- 5.15; G5: 10.99 +/- 3.35; G6: 6.09 +/- 1.84. Data were compared by one-way ANOVA and Tukey's test at 5% significance level. Bond strength recorded after 2-min acid etching was significantly higher than 4-min etching (p<0.05) and control (p<0.05), but did not differ significantly from sandblasting alone (p>0.05) or followed by etching for 2 or 4 min (p>0.05). Within the limitations of an in vitro study, it may be concluded that 2-min hydrofluoric acid etching produced a favorable micromechanical retention that enhanced resin cement bond strength to porcelain.     

Effect of ceramic surface treatment on the shear bond strengths of two resin luting agents to all-ceramic materials

The purpose of this study was to evaluate the bond strengths of some resin luting cements of two different all ceramic materials (In-Ceram, IPS-Empress). Composite cylinders 3.2 x 2 mm were prepared on the ceramic surfaces for a shear test. Four ceramic surface treatments were performed. (i). As received, (ii). grinding with diamond bur, (iii). sandblasting with 50 microm alumina grit and (iv). HF acid treatment and sandblasting with 50 microm alumina grit. Ceramic specimens were treated with one of the four methods and then cemented together with each of the two luting agents. The tested luting cements were Panavia F and Clearfil Se Bond (CSeB). The CSeB demonstrated the highest bond strength (59.95 MPa) regardless of the ceramic blocks. The average of load to fracture the In-Ceram blocks luted with Panavia F cement was 25.89 MPa. The mean shear bond strength of IPS Empress blocks luted with Panavia F cement was 10.31 MPa. Grinding the surface with a diamond bur for In-Ceram blocks luted with Panavia-F was 30.93 MPa and with CSeB was 77.04 MPa. For IPS-Empress blocks these values decreased to 12.39 MPa for Panavia-F and 30.84 MPa for CSeB. Acid etching of the surfaces with HF acid demonstrated a weak tendency to improve bond strength (In-Ceram-->Panavia-F= 14.59 MPa and CSeB=59.32 Mpa; IPS-Empress--> Panavia-F=5.85 MPa and CSeB= 23.33 MPa).     

Effects of surface treatments on bond strength of glass-infiltrated ceramic

The purpose of this study was to evaluate the effects of various surface treatments on the bond strength at the In-Ceram/resin composite interface. Ninety-eight In-Ceram specimens were divided into seven groups and exposed to various surface treatments as follows: (A) control (B) saliva contamination (C) saliva contamination plus aluminum oxide sandblasting (D) glove powder contamination (E) glove powder contamination plus aluminum oxide sandblasting (F) rough aluminum oxide sandblasting and (G) excess glass infiltration. A resin composite cylinder was cemented to each In-Ceram specimen with Panavia 21 resin luting cement. Half of the cemented specimens in each group were stored in water for 24 h, and the other half were stored in water for 2 weeks and then were thermo-cycled for 2000 cycles. Shear bond strengths (SBS) of seven specimens in each subgroup were determined and analysed using analysis of variance (ANOVA) and Tukey HSD test as well as Student's t-test. Scanning electronic microscopy was used to identify the type of bond failure. Shear bond strength was significantly decreased by saliva and glove powder contaminations (P < 0.05). Sandblasting treatment did not improve the saliva-contaminated specimens. However, the glove powder plus sandblasting group showed no significant difference in SBS compared with the control group. There was no significant difference in SBS between the excess glass-infiltrating group and the control group. The SBS was significantly decreased by rough aluminum oxide sandblasting (P < 0.05). The SBS values of groups without thermocycling were significantly greater than those of groups with thermocycling (P < 0.05). There were no significant differences among SBS values of the seven groups with thermocycling. Combined cohesive and adhesive bond failures were seen in every group. Various surface treatments or contaminants may significantly influence the bond strength of In-Ceram restorative in clinical use.     

The effect of surface treatment on the shear bond strength of luting cement to a glass-infiltrated alumina ceramic

PURPOSE: The aim of this study was to evaluate the effect of three different surface treatments on the bond strength of four different luting cements--three bis-GMA-based resin cements and a compomer cement--to In-Ceram. MATERIALS AND METHODS: Eight In-Ceram samples were used for each experimental group. The samples were randomly assigned three treatment conditions: (1) etching for 90 seconds with 5% hydrofluoric acid gel, (2) sandblasting (110-micron Al2O3), and (3) tribochemical silica coating. All samples were silanated following the surface treatment. The luting cements were bonded to In-Ceram specimens using Teflon tubes. All samples were thermocycled for 5,000 cycles altering between 5 and 55 degrees C with 30-second dwell times. The shear bond strength values were measured in a universal testing machine with a cross-head speed of 1 mm/min. Analysis of variance was used to analyze data. RESULTS: The mean bond strengths varied between 1.2 and 24.7 MPa. CONCLUSION: Shear bond strength of compomer cement following tribochemical silica coating was significantly lower in comparison to resin cements. Luting of In-Ceram with various resins provided varying degrees of bond strengths that were significantly increased by the tribochemical silica-coating system.     

Comparison of two bond strength testing methodologies for bilayered all-ceramics.

OBJECTIVES: This study compared the shear bond strength (SBS) and microtensile (MTBS) testing methodologies for core and veneering ceramics in four types of all-ceramic systems. METHODS: Four different ceramic veneer/core combinations, three of which were feldspathic and the other a fluor-apatite to their respectively corresponding cores, namely leucite-reinforced ceramic ((IPS)Empress, Ivoclar), low leucite-reinforced ceramic (Finesse, Ceramco), glass-infiltrated alumina (In-Ceram Alumina, Vita) and lithium disilicate ((IPS)Empress 2, Ivoclar) were used for SBS and MTBS tests. Ceramic cores (N=40, n=10/group for SBS test method, N=5 blocks/group for MTBS test method) were fabricated according to the manufacturers' instructions (for SBS: thickness, 3mm; diameter, 5mm and for MTBS: 10 mm x 10 mm x 2 mm) and ultrasonically cleaned. The veneering ceramics (thickness: 2mm) were vibrated and condensed in stainless steel moulds and fired onto the core ceramic materials. After trying the specimens in the mould for minor adjustments, they were again ultrasonically cleaned and embedded in PMMA. The specimens were stored in distilled water at 37 degrees C for 1 week and bond strength tests were performed in universal testing machines (cross-head speed: 1mm/min). The bond strengths (MPa+/-S.D.) and modes of failures were recorded. RESULTS: Significant difference between the two test methods and all-ceramic types were observed (P<0.05) (2-way ANOVA, Tukey's test and Bonferroni). The mean SBS values for veneering ceramic to lithium disilicate was significantly higher (41+/-8 MPa) than those to low leucite (28+/-4 MPa), glass-infiltrated (26+/-4 MPa) and leucite-reinforced (23+/-3 MPa) ceramics, while the mean MTBS for low leucite ceramic was significantly higher (15+/-2 MPa) than those of leucite (12+/-2 MPa), glass-infiltrated (9+/-1 MPa) and lithium disilicate ceramic (9+/-1 MPa) (ANOVA, P<0.05). SIGNIFICANCE: Both the testing methodology and the differences in chemical compositions of the core and veneering ceramics influenced the bond strength between the core and veneering ceramic in bilayered all-ceramic systems.     

Failure analysis of resin composite bonded to ceramic.

OBJECTIVE: To use fractographic principles to classify the mode of failure of resin composite bonded to ceramic specimens after microtensile testing. METHODS: A leucite-based ceramic (IPS Empress)-E1) and a lithia disilicate-based ceramic (IPS Empress2)-E2) were selected for the study. Fifteen blocks of E1 and E2 were polished through 1 microm alumina abrasive. The following ceramic surface treatments were applied to three blocks of each ceramic: (1) 9.5% hydrofluoric acid (HF) for 2 min; (2) 4% acidulated phosphate fluoride (APF) for 2 min; (3) Silane coating (S); (4) HF+S; (5) APF+S. An adhesive resin and a resin composite were applied to all treated surfaces and light cured. Twenty bar specimens for each group were prepared from the composite-ceramic blocks and stored in 37 degrees C distilled water for 30 days before loading to failure under tension in an Instron testing machine. Fracture surfaces were examined using scanning electron microscopy and X-ray dot mapping. Statistical analysis was performed using one-way ANOVA, Duncan's multiple range test, and Weibull analyses. RESULTS: Similar surface treatments were associated with significantly different bond strengths and modes of failures for E1 and E2. All fractures occurred within the adhesion zone. The microstructural difference between etched E1 and E2 ceramics was a major controlling factor on adhesion. SIGNIFICANCE: The quality of the bond should not be assessed based on bond strength data alone. Mode of failure and fractographic analyses should provide important information leading to predictions of clinical performance limits.     

Influence of ceramic surface conditioning and resin cements on microtensile bond strength to a glass ceramic

STATEMENT OF PROBLEM: It is not clear how different glass ceramic surface pretreatments influence the bonding capacity of various luting agents to these surfaces. PURPOSE: The purpose of this study was to evaluate the microtensile bond strength (microTBS) of 3 resin cements to a lithia disilicate-based ceramic submitted to 2 surface conditioning treatments. MATERIAL AND METHODS: Eighteen 5 x 6 x 8-mm ceramic (IPS Empress 2) blocks were fabricated according to manufacturer's instructions and duplicated in composite resin (Tetric Ceram). Ceramic blocks were polished and divided into 2 groups (n=9/treatment): no conditioning (no-conditioning/control), or 5% hydrofluoric acid etching for 20 seconds and silanization for 1 minute (HF + SIL). Ceramic blocks were cemented to the composite resin blocks with 1 self-adhesive universal resin cement (RelyX Unicem) or 1 of 2 resin-based luting agents (Multilink or Panavia F), according to the manufacturer's instructions. The composite resin-ceramic blocks were stored in humidity at 37 degrees C for 7 days and serially sectioned to produce 25 beam specimens per group with a 1.0-mm(2) cross-sectional area. Specimens were thermal cycled (5000 cycles, 5 degrees C-55 degrees C) and tested in tension at 1 mm/min. Microtensile bond strength data (MPa) were analyzed by 2-way analysis of variance and Tukey multiple comparisons tests (alpha=.05). Fractured specimens were examined with a stereomicroscope (x40) and classified as adhesive, mixed, or cohesive. RESULTS: The surface conditioning factor was significant (HF+SIL > no-conditioning) (P<.0001). Considering the unconditioned groups, the microTBS of RelyX Unicem was significantly higher (9.6 +/- 1.9) than that of Multilink (6.2 +/- 1.2) and Panavia F (7.4 +/- 1.9). Previous etching and silanization yielded statistically higher microTBS values for RelyX Unicem (18.8 +/- 3.5) and Multilink (17.4 +/- 3.0) when compared to Panavia F (15.7 +/- 3.8). Spontaneous debonding after thermal cycling was detected when luting agents were applied to untreated ceramic surfaces. CONCLUSION: Etching and silanization treatments appear to be crucial for resin bonding to a lithia disilicate-based ceramic, regardless of the resin cement used.     

The effect of different etching times of acidulated phosphate fluoride gel on the shear bond strength of high-leucite ceramics bonded to composite resin

STATEMENT OF PROBLEM: A 10-minute treatment with acidulated phosphate fluoride (APF) gel has been used as an alternative in ceramic surface etching before repairing with composite resin. However, the optimal etching time for APF gel is still unknown. PURPOSE: The purpose of this study was to determine the in vitro shear bond strengths of composite resin on high-leucite ceramics after APF gel treatment over different time periods. MATERIAL AND METHODS: One hundred and twenty high-leucite ceramic (Empress 1) specimens (12 mm in diameter and 1.5 mm thick) were prepared and divided into 12 groups (n=10). Ten experimental groups were surface treated with 1.23% APF gel, each group receiving 1 to 10 minutes of etching time in 1 minute increments. One group was treated with 9.6% hydrofluoric acid for 4 minutes and the final group received no treatment and served as a control. The surface condition of the treated specimens was analyzed under a scanning electron microscope (SEM). All specimens received a silane application and were bonded to a composite resin Filtek (Z250) cylinder with an adhesive system (Scotchbond Multi-Purpose Plus adhesive) and then stored in 100% humidity at 37 degrees C for 24 hours before shear bond strength testing in a universal testing machine. Mean bond strengths (MPa) were analyzed with 1-way ANOVA and the Tukey HSD test (alpha=.05). RESULTS: Hydrofluoric acid etching produced the highest mean shear bond strength (SD) between composite resin and the ceramic (17.64 (1.48) MPa). Overall, APF gel etching produced lower bond strengths. No significant difference in mean bond strength (SD) was observed between etching with hydrofluoric acid and etching with APF gel for 7 to 10 minutes (15.21 (1.93) to 17.33 (1.43)). The lowest mean shear bond strengths (SD) were recorded in the untreated group (7.61 (1.03) MPa) (P<.05). CONCLUSIONS: Within the limitations of this study, shear bond strength values between composite resin and high-leucite ceramics after etching with 1.23% APF gel for 7 to 10 minutes were not significantly different than that after etching with 9.6% hydrofluoric acid for 4 minutes.     

Effect of surface treatment on roughness and bond strength of a heat-pressed ceramic

STATEMENT OF PROBLEM: Bonding ceramic restorations to tooth structure relies on treatment of the ceramic intaglio surface, selection of a suitable resin luting agent, and appropriate treatment of prepared tooth structure. Various ceramic surface treatments have been advocated which produce different topographies and bond strengths, but little information is available to identify the interaction between the resulting surface topography and bond strength. PURPOSE: The purpose of this in vitro study was to evaluate the effect of surface treatments on surface roughness and bond strength to dentin and enamel of a commercially available heat-pressed dental ceramic (IPS Empress). MATERIAL AND METHODS: One hundred heat-pressed ceramic disks were fabricated according to the manufacturer's recommendations. Specimens were divided into 5 groups (n=20) and treated with 1 of the following: (1) etching with 9.5% hydrofluoric acid, (2) 50%, or (3) 60% orthophosphoric acid and airborne-particle abrasion with (4) 50-microm, or (5) 250-microm alumina for 10 seconds. Morphological changes obtained with the surface treatments were investigated with a surface texture analyzer on half of the treated specimens. Two additional specimens from each group were treated and prepared for scanning electron microscopy. The specimens were then used for a bond strength test. The treated specimens were silanated and luted with a composite resin luting agent (Nexus 2) to enamel (n=50) and dentin (n=50) surfaces with 10 specimens for each treatment group. The luted specimens were loaded to failure in a universal testing machine in the shear mode with a crosshead speed of 0.05 mm/min. The data were analyzed with 1-way ANOVA followed by the Ryan-Einot-Gabriel-Welsch Multiple Range Test (alpha=.05). RESULTS: Surface treatments resulted in significant differences for surface topography and shear bond strength (P<.001). Mean surface roughness (Ra) (SD) was (2.54 (0.21) microm) for ceramic surfaces treated with 50-microm aluminum powder. Treatment of ceramic specimens with 50% orthophosphoric acid appeared to result in a smoother surface (1.02 (0.38) microm). The highest mean bond strength (SD) to enamel (14.7 (0.6) MPa) and dentin (8.2 (1.5) MPa) was associated with hydrofluoric acid etching. The lowest mean bond strength (SD) to enamel (2.7 (0.8) MPa) and dentin (1.5 (0.1) MPa) was recorded for 50% phosphoric acid. CONCLUSIONS: Hydrofluoric acid treatment resulted in the generation of pores and grooves that produced the greatest bond strength between the ceramic and tooth dentin and enamel. Orthophosphoric acid treatment was the least effective surface treatment method evaluated. The results are applicable to only the all-ceramic/luting system evaluated.     

Relative translucency of six all-ceramic systems. Part I: core materials

STATEMENT OF PROBLEM: All-ceramic restorations have been advocated for superior esthetics. Various materials have been used to improve ceramic core strength, but it is unclear whether they affect the opacity of all-ceramic systems. PURPOSE: This study compared the translucency of 6 all-ceramic system core materials at clinically appropriate thicknesses. MATERIALS AND METHODS: Disc specimens 13 mm in diameter and 0.49 +/- 0.01 mm in thickness were fabricated from the following materials (n = 5 per group): IPS Empress dentin, IPS Empress 2 dentin, In-Ceram Alumina core, In-Ceram Spinell core, In-Ceram Zirconia core, and Procera AllCeram core. Empress and Empress 2 dentin specimens also were fabricated and tested at a thickness of 0.77 +/- 0.02 mm (the manufacturer's recommended core thickness is 0.8 mm). A high-noble metal-ceramic alloy (Porc. 52 SF) served as the control, and Vitadur Alpha opaque dentin was used as a standard. Sample reflectance (ratio of the intensity of reflected light to that of the incident light) was measured with an integrating sphere attached to a spectrophotometer across the visible spectrum (380 to 700 nm); 0-degree illumination and diffuse viewing geometry were used. Contrast ratios were calculated from the luminous reflectance (Y) of the specimens with a black (Yb) and a white (Yw) backing to give Yb/Yw with CIE illuminant D65 and a 2-degree observer function (0.0 = transparent, 1.0 = opaque). One-way analysis of variance and Tukey's multiple-comparison test were used to analyze the data (P<.05). RESULTS: Contrast ratios in order of most translucent to most opaque were as follows: Vitadur Alpha 0.60 +/- 0.03, Empress (0.5 mm) 0.64 +/- 0.01, In-Ceram Spinell 0.67 +/- 0.02, Empress 2 (0.5 mm) 0.68 +/- 0.02, Empress (0.8 mm) 0.72 +/- 0.01, Procera 0.72 +/- 0.01, Empress 2 (0.8 mm) 0.74 +/- 0.01, In-Ceram Alumina 0.87 +/- 0.01, In-Ceram Zirconia 1.00 +/- 0.01, and 52 SF alloy 1.00 +/- 0.00. CONCLUSION: Within the limitations of this study, there was a range of ceramic core translucency at clinically relevant core thicknesses. In order of decreasing translucency, the ranges were Vitadur Alpha dentin (standard) > In-Ceram Spinell > Empress, Procera, Empress 2 > In-Ceram Alumina > In-Ceram Zirconia, 52 SF alloy.     

Surface roughness of five different dental ceramic core materials after grinding and polishing

In clinical practice, core materials can be exposed after adjustments are made to previously-luted all-ceramic restorations. The purpose of this study was to evaluate the surface roughness of five different dental ceramic core materials after grinding and polishing. Five different ceramic core materials, Vita In-Ceram Alumina, Vita In-Ceram Zirconia, IPS Empress 2, Procera AllCeram, and Denzir were evaluated. Vita Mark II was used as a reference material. The surface roughness, Ra value (mum), was registered using a profilometer. The measurements were made before and after grinding with diamond rotary cutting instruments and after polishing with the Sof-Lex system. The surface of representative specimens was evaluated qualitatively using scanning electron microscopy (SEM). Results were statistically analysed using analysis of variance (anova) supplemented with Scheffè's and Bonferroni multiple-comparison tests. Before grinding, Procera AllCeram and Denzir had the smoothest surfaces, while IPS Empress 2 had the coarsest. After grinding, all materials except IPS Empress 2 became coarser. Polishing with Sof-Lex provided no significant (P > 0.05) differences between Denzir, Vita Mark II and IPS Empress 2 or between Procera AllCeram and In-Ceram Zirconia. There were no significant differences (P > 0.05) either between the ground and the polished Procera AllCeram or In-Ceram Alumina specimens. Polishing of Denzir, IPS Empress 2 and In-Ceram Zirconia made the surfaces smoother compared with the state after grinding, whereas the polishing effect on Procera AllCeram and In-Ceram Alumina was ineffective. The findings of the SEM evaluation were consistent with the profilometer readings.     

Flexural strength and fracture toughness of dental core ceramics

STATEMENT OF PROBLEM: Many different strengthened all-ceramic core materials are available. In vitro study of their mechanical properties, such as flexural strength and fracture toughness, is necessary before they are used clinically. PURPOSE: The purpose of this study was to evaluate and compare the mechanical properties of 6 commonly used all-ceramic core materials using biaxial flexural strength and indentation fracture toughness tests. MATERIAL AND METHODS: Specimens of 6 ceramic core materials (Finesse, Cergo, IPS Empress, In-Ceram Alumina, In-Ceram Zirconia, and Cercon Zirconia) were fabricated (n=25) with a diameter of 15 mm and width of 1.2 +/- 0.2 mm. For each group, the specimens were tested to compare their biaxial flexural strength (piston on 3 balls) (n=15), Weibull modulus, and indentation fracture toughness (n=10) (IF method). The data were analyzed with 1-way ANOVA test (a=.05). The Tamhane multiple comparison test was used for post hoc analysis. RESULTS: Mean (SD) of biaxial flexural strength values (MPa) and Weibull modulus (m) results were: Finesse (F): 88.04 (31.61), m=3.17; Cergo (C): 94.97 (13.62), m=7.94; IPS Empress (E): 101.18 (13.49), m=10.13; In-Ceram Alumina (ICA): 341.80 (61.13), m=6.96; In-Ceram Zirconia (ICZ): 541.80 (61.10), m=10.17; and Cercon Zirconia (CZ): 1140.89 (121.33), m=13.26. The indentation fracture toughness results showed that there were significant differences between the tested ceramics. The highest fracture toughness values (MPa x m(0.5)) were obtained with the zirconia-based ceramic core materials. CONCLUSIONS: Significant differences were found in strength and toughness values of the materials evaluated. Cercon Zirconia core material showed high values of biaxial flexural strength and indentation fracture toughness when compared to the other ceramics studied.     

Relative fracture toughness of differents dental ceramics

Although ceramics present high compressive strength, they are brittle materials due to their low tensile strength so they have lower capacity to absorb shocks. This study evaluated the fracture toughness of different ceramic systems, which refers to the ability of a friable material to absorb defformation energy. Three ceramic systems were investigated. Ten cylindrical samples (5,0mm x 3,0mm), were obtained from each ceramic material as follows: G1- 10 samples of Vitadur Alpha (Vita-Zahnfabrik); G2- 10 samples of IPS Empress2 (Ivoclar-Vivadent); G3- 10 samples of In-Ceram Alumina (Vita-Zahnfabrik). Fracture toughness values were collected upon indentation tests that were performed under a heavy load. A microhardness tester (Digital Microhardness Tester FM) utilized a 500gf load cell during 10seconds to perform four impressions on each sample. Statistically significant results were observed (ANOVA and Kruskal-Wallis tests). In-Ceram Alumina presented the highest median toughness values (2,96N/m3/2), followed by Vitadur Alpha (2,08N/m3/2) and IPS Empress2 (1,05N/m3/2). It may be concluded that different ceramic systems present distinct fracture toughness values, thus In-Ceram is capable of absorbing superior stress when compared to Vitadur Alpha and IPS Empress2.