The loss of resin cement adhesion to ceramic influences the fatigue behavior of bonded lithium disilicate restorations

When partial and/or non-retentive preparation, such as those for occlusal veneers, is indicated, a proper and stable adhesion is essential. Therefore, the aim of this in vitro study was to evaluate the effect of loss of adhesion in different regions of the bonding interface on the fatigue behavior of simplified lithium disilicate restorations. For this, lithium disilicate (IPS e.max CAD) discs (1 mm thick and Ø = 10 mm) were fabricated, polished with #400-, #600-, #1200-grit silicon carbide (SiC) papers, and crystallized. As substrate, fiber-reinforced resin epoxy discs (2.5 mm thick and Ø = 10 mm) were fabricated and polished with #600-grit SiC paper. The ceramic bonding surface was treated with 5% hydrofluoric acid and a silane-containing primer (Monobond N), while the substrate was etched with 10% hydrofluoric acid followed by the application of the bonding system primers (Primer A + B). A lacquer (nail polish) was used to simulate the loss of adhesion in specific areas according to the study design to compose the testing groups: bonded (control; did not received nail polish application); - non-bonded (loss of adhesion in the whole specimen area); - margin (loss of adhesion in the ceramic margin); - center (loss of adhesion in the ceramic central area). The adhesive area of partially bonded groups was 50% of the adhesive surface. Then, the discs (n = 12) were bonded to the respective substrate using a resin cement (Multilink N), light-cured, water-stored for 90 days, and subjected to thermocycling (25,000 cycles, 5° to 55 °C) before testing. A cyclic fatigue test was run (20 Hz, initial load of 200 N for 5000 cycles, 50 N step size for 10,000 cycles each until specimen failure), and the fatigue failure load and number of cycles for failure were recorded. As complementary analysis, finite element analysis (FEA) and scanning electron microscopy analysis were performed. Kaplan-Meier log-rank (Mantel-Cox) was conducted for survival analysis. The results showed that as the loss of adhesion reaches the central area, the worse is the fatigue behavior and the higher is the stress peak concentration in the ceramic bonding surface. The bonded specimens presented better fatigue behavior and stress distribution compared to the others. In conclusion in a non-retentive preparation situation, proper adhesion is a must for the restoration fatigue behavior even after aging; while the loss of adhesion reaches central areas the mechanical functioning is compromised.

Advanced lithium disilicate: A comparative evaluation of translucency and fatigue failure load to other ceramics for monolithic restorations

The aim of this in vitro study was to evaluate the surface roughness, translucency, fatigue failure load (FFL), and number of cycles for fatigue failure (CFF) of a recently released lithia-based material called advanced lithium disilicate and three other ceramics indicated for monolithic restorations. First, ALD (advanced lithium disilicate, CEREC Tessera, Dentsply Sirona), LD (lithium disilicate, IPS e. max CAD, Ivoclar), LS (lithium silicate-disilicate, Suprinity, Vita Zahnfabrik), and 4Y-PSZ (Yttria-stabilized zirconia, IPS e.max ZirCAD MT, Ivoclar) discs (n = 15, Ø = 10 mm and thickness = 1.0 mm) were fabricated from CAD/CAM blocks/discs, A2 shade. The discs were sintered/crystallized and subsequently analyzed by a rugosimeter (Mitutoyo SJ-410) to determine Ra and Rz surface roughness parameters. Next, they were evaluated to determine the translucency parameter (TP) using a bench-top spectrophotometer (SP60, EX-Rite). The discs were subsequently cemented to glass fiber epoxy resin discs, and the specimens were tested under cyclic loading (Step-test), immersed in distilled water at a frequency of 20 Hz, with an initial cyclic load of 200 N for 5,000 cycles and increments of 50 N every 10,000 cycles until failure. Fatigue failure load (FFL) and number of cycles for fatigue failure (CFF) were recorded for subsequent Kaplan Meier analysis, with post-hoc Mantel-Cox and Weibull analysis (α = 0.05). Complementary fractographic, topographic and energy dispersive spectroscopy analyses (EDS) were performed. 4Y-PSZ showed higher survival (p < 0.05), with higher FFL and CFF (1077 N; 180,333 cycles), followed by LD (980 N; 161,000 cycles), LS (937 N; 152,333 cycles) and ALD (910 N; 147,000 cycles). No differences were observed between the tested groups regarding Weibull modulus. ALD presented TP (28.14) equal to DL (28.27) and higher than LS (25.51). All lithia-based materials had higher translucency than 4Y-PSZ (TP = 8.62) (p < 0.05). ALD appears to have a similar elemental composition to LD and LSD for oxygen and silicon. ALD and LSD have a similar zirconium content. Fractures originated on the cemented surface of the ceramic discs. Lithia-based ceramics showed lower surface roughness, with ALD (Ra = 0.04 μm; Rz = 0.66 μm) showing the lowest values (p < 0.05). Despite showing lower FFL when compared to LD and 4Y-PSZ, ALD has compatible translucency and mechanical fatigue performance with its indication for fabricating monolithic, anterior and posterior adhesively cemented single-unit restorations. However, further studies are needed to substantiate its clinical performance.

Tooth discoloration induced by endodontic sealers and cervical limit: 1-year in vitro evaluation

This laboratory study aimed to evaluate the influence of endodontic sealer and cervical limit of root filling on the discoloration of root canal treated teeth. Bovine incisors were randomly distributed into six experimental groups and control (n=21/group), according to the endodontic sealer used [AH Plus (AP); MTA Fillapex (MF) and Sealer Plus BC (SPB)] and the cervical limit of root filling [dental cervix (DC) or 2 mm in apical direction (2mm-AD)]. Tooth discoloration (ΔE) was evaluated by a digital spectrophotometer using the CIED2000 method. Color assessments were performed immediately before (baseline), 1 week, 1, 3, 6 months, and 1 year after obturation. Data were analyzed by ANOVA and Tukey's post-hoc tests (α=5%). Teeth filled with the three sealers showed perceptible tooth discoloration (ΔE≥2.7) in 1 week, maintaining similar values over time. There was a significant difference between MF and SPB sealers in the 2mm-AD groups. In addition, 2mm-AD groups promoted significantly lower discoloration than DC groups for AH (3 months) and SPB (1 and 3 months) sealer,s. Teeth filled with AP, MF, and SPB sealers displayed discoloration from 1 week to one year, with differences between MF and SPB sealers. A cervical limit of filling material at 2 mm from the dental cervix seems more advisable, promoting lower crown discoloration.

Surface properties and flexural fatigue strength of an advanced lithium disilicate

The aim of this study was to evaluate the surface properties and fatigue mechanical behavior of an advanced lithium disilicate ceramic in comparison to lithium disilicate and zirconia. First, discs (n = 15, diameter = 13.5 mm and thickness = 1.2 mm) were made from the following materials: 4Y-PSZ - 4% mol yttria-stabilized zirconia (IPS e.max ZirCAD A2); LD - lithium disilicate (IPS e.max CAD); ALD - advanced lithium disilicate (CEREC Tessera). The specimens were crystalized/sintered and subsequently analyzed by a rugosimeter (Mitutoyo SJ-410) to determine surface roughness (parameters Ra and Rz). Specimens were subjected to biaxial flexural fatigue testing using the step-test method (20 Hz; 10,000 cycles per step; initial stress of 200 MPa; and step size of 25 MPa) until specimen fracture. Statistical analyses included Shapiro-Wilk, Kruskal-Wallis, and post-hoc tests for roughness data, while survival analysis (Kaplan-Meier and Mantel-Cox) and reliability analysis (Weibull modulus) were applied to flexural fatigue strength data. Hardness (Vickers) results were submitted to analysis of variance (1-way ANOVA) and Tukey's test. Zirconia (4Y-PSZ) showed higher FFS, CFF (467 MPa and 115216 cycles) and survival compared to the other materials. ALD had the lowest FFS, CFF (215 MPa and 11,908 cycles) and survival. ALD showed lower Weibull modulus (m = 6.63 for FFS; m = 1.27 for CFF) than LD for FFS (m = 17.33), and lower than LD (m = 4.64) and 4Y-PSZ (m = 6.69) for CFF. ALD showed the lowest Ra (0.07 μm) and Rz (1.05 μm) values, while 4Y-PSZ (Ra = 0.22 μm; Rz = 1.91 μm) and LD (Ra = 0.21 μm; Rz = 2.17 μm) showed higher and similar values. Zirconia (4-YPSZ) was the hardest material, while lithia-based ceramics (LD and ALD) presented the lowest and similar hardness values. Fractures originated in surface defects in the tensile stress concentration region. ALD has lower flexural fatigue strength compared to the other tested materials, along with higher variability (lower structural reliability).

Resin cement coating reverts the machining damage on the flexural fatigue strength of lithium disilicate glass-ceramic

This study evaluated the effect of resin cement coating with high and low viscosities on the flexural fatigue strength of machined lithium disilicate glass-ceramic. Discs (IPS e.max CAD; Ivoclar Vivadent) were prepared and divided according to the surface condition (machining [M]-CEREC inLab; and polishing [P]-laboratory procedures), resin cement coating (with or without), and cement viscosity (high [H] and low [L]). The ceramic bonding surface was etched/primed by a one-step primer application followed by resin cement application (Variolink N base + high or low viscosity catalyst; Ivoclar Vivadent). Biaxial flexural fatigue strength was evaluated on a piston-on-three-ball set by the step-test method (n = 15) (initial stress: 60 MPa; incremental steps: 20 MPa; 10,000 cycles/step, at 20 Hz). Weibull statistics were used for fatigue data. Contact angle, topographic, and fractographic analysis were also performed. Machining produced statistically lower contact angle than polishing and a significant detrimental effect on the fatigue behavior (σ₀ M = 247.2 [246.9-268.3]; σ₀ P = 337.4 [297.8-382.4]). Machined groups followed by resin cement coating (σ₀ MH = 297.9 [276.0-321.5]; σ₀ Ml = 301.2 [277.1-327.4]) behaved similarly to the polished and coated groups (σ₀ PH = 342.0 [308.9-378.5]; σ₀ PL = 357.3 [324.7-393.1]), irrespective of the cement viscosity. Therefore, cement coating has able to revert the detrimental effects of the machining on the fatigue strength of lithium disilicate glass-ceramic. High and low viscosity cements behaved similarly in the improvement of CAD-CAM lithium disilicate fatigue strength.

Biaxial flexure strength and physicochemical characterization of a CAD/CAM lithium disilicate ceramic: effect of etching time, silane, and adhesive applications

OBJECTIVE

To evaluate the effect of different acid etching time and bonding agent (silane and/or adhesive system) on biaxial flexural strength and physico-chemical properties of a lithium disilicate ceramic.

MATERIAL AND METHODS

One hundred twenty ceramic discs were made and divided into 8 groups (n = 15) according to factors "etching time" (20 and 120 s) with hydrofluoric acid (HF) and "bonding agent" (C, no bonding agent; S, silane, A, adhesive; and SA, silane + adhesive). After surface treatment, a resin cement layer was applied to the surface and all specimens were subjected to biaxial flexural strength (BFS) test with treated surfaces loaded in tension (1 mm/min). The Weibull analyses and complementary analyses were also performed. Statistical analysis was done with 2-way ANOVA and the Tukey test (α = 0.05).

RESULTS

ANOVA revealed that the factors "etching time" (p = 0.0003) and "bonding agent" (p = 0.007) were statistically significant. In the overall analysis, the HF120S group (272.02 ± 35.30A MPa) presented significantly higher BFS than that of HF120C (218.45 ± 17.15CD MPa) and HF20S (228.40 ± 37.83BCDMPa). On the other hand, the HF20A group (208.92 ± 31.16D MPa) had significantly lower BFS than HF120S (272.02 ± 35.30A), HF120A (254.42 ± 26.87ABC) and HF120SA (259.30 ± 36.55AB) groups (Tukey). The Weibull modulus (m) of all groups was significantly different from each other (p = 0.000).

CONCLUSIONS

Regardless of etching time, the application of silane alone is sufficient to increase the flexural strength of glass ceramic, eliminating the need for the application of adhesive systems. Moreover, if only silane or adhesive is applied, 120-s HF application should increase the flexural resistance of the lithium disilicate ceramic.

CLINICAL SIGNIFICANCE

Applications of adhesive systems after silanization can be suppressed from the surface treatment protocol of glass ceramics, since it does not improve their mechanical strength.

Adhesive application after ceramic surface treatment is detrimental to load-bearing capacity under fatigue of a lithium disilicate glass-ceramic

OBJECTIVE

To evaluate whether an adhesive application after surface treatment on a lithium disilicate ceramic (LD) has an influence on its load-bearing capacity under fatigue.

METHODS

LD discs (Ø= 10 mm; thickness= 1 mm) were allocated into 8 groups (n= 15), considering 3 factors: "ceramic surface treatment" - HF: hydrofluoric acid + universal primer application; or MEP: single-component ceramic primer; "adhesive application" - with or without; and "aging protocol" - baseline: 24 h to 7 days; or aging: 180 days of storage + 25,000 thermal cycles. The LD discs were adhesively bonded to glass fiber-reinforced epoxy resin discs (Ø= 10 mm; thickness= 2 mm) and stored according to the condition and each group. Cyclic fatigue testing (initial load= 100 N; step size= 100 N until600 N and after step size= 25 N to failure; 10,000 cycles/step; 20 Hz frequency) was performed. Fractographic and adhesive interface analyzes were also performed. The collected data were then analyzed by Kaplan Meier and Mantel-Cox tests and One-way ANOVA.

RESULTS

The adhesive application in the baseline condition had no influence on the load-bearing capacity under fatigue when the HF surface treatment was performed, however, adhesive application for the MEP treatment led to worse results than without it. The adhesive application in the aged condition showed worse fatigue outcomes for both treatments. All specimens presented radial cracks. MEP treatment followed by adhesive application presented the thickest luting layer.

CONCLUSION

The adhesive application after surface treatments of a lithium disilicate glass-ceramic is detrimental to its load-bearing capacity under fatigue when adhesively luted onto a supporting substrate.

Color and translucency stability of CAD/CAM restorative materials

Aim: This study assessed the color and translucency stability of a polymer infiltrated ceramic network (PICN) and compared it with a resin composite (RC) and a feldspathic ceramic (FEL). Methods: Disc-shaped samples of a PICN (Vita Enamic), a feldspathic ceramic (Vitablocks Mark II), and a resin composite (Brava block) were prepared from CAD/CAM blocks. PICN and RC surfaces were finished with a sequence of polishing discs and diamond paste. FEL samples received a glaze layer. The samples were subjected to 30-min immersions in red wine twice a day for 30 days. CIEL*a*b* coordinates were assessed with a spectrophotometer at baseline and after 15 and 30 days of immersion. Color alteration (ΔE00) and translucency parameter (TP00) were calculated with CIEDE2000. Average roughness was measured before the staining procedures. Color difference and translucency data were analyzed with repeated-measures ANOVA and Tukey’s tests. Roughness was analyzed with the Kruskal-Wallis test. Results: Roughness was similar among the experimental groups. All materials had their color alteration significantly increased from 15 to 30 days of staining. PICN reached an intermediate ΔE00 between FEL and RC at 15 days. PICN revealed a color alteration as high as the composite after 30 days. No statistical difference was observed regarding translucency. Conclusion: PICN was not as color stable as the feldspathic ceramic at the end of the study. Its color alteration was comparable to the resin composite when exposed to red wine. However, the translucency of the tested materials was stable throughout the 30-day staining.

Influence of testing environment on static fatigue behavior of a glass and a polycrystalline ceramic

It aims on evaluate the effect of the test environment on static fatigue behavior of lithium disilicate-based (LD), and yttrium oxide-stabilized zirconia (YSZ) ceramics. Specimens of LD (IPS e.max CAD, Ivoclar Vivadent) and YSZ (IPS e.max ZirCAD MO, 3 mol% Y2O3, Ivoclar Vivadent) were randomly allocated into three groups: tested in air, inert (paraffin oil, Sigma Aldrich) or distilled water. The static fatigue test (n=15) was performed using a piston-on-three ball assembly, adapted from ISO 6872, as follows: starting load 100 N for LD and 300 N for YSZ; loading application time set to 1 hour for each loading step; step size of 50 N for LD and 100 N for YSZ, applied successively until fracture. Data from static fatigue strength (MPa) and time to fracture (hours) were recorded. Fractographic analysis was executed. Survival analysis corroborates absence of influence of environment on static fatigue outcomes (fatigue strength, time to fracture and survival rates) for YSZ. For LD, specimens tested in air presented statistically superior survival rate and static fatigue strength (p= 0.025). In regards of time to fracture, LD tested in air were superior than when tested in distilled water (p=0.019) or inert (p=0.017) environments. No statistical differences for Weibull modulus were observed. Failures started on the tensile stress surface. Thus, the test environment did not affect slow crack growth (SCG) mechanisms during static fatigue test of YSZ ceramics, but it plays a significant role for the static fatigue behavior of lithium disilicate-based glass ceramics, indicating a high susceptibility to SCG.

Residual stresses explaining clinical fractures of bilayer zirconia and lithium disilicate crowns: A VFEM study

OBJECTIVE

To understand the stress development in porcelain-veneered zirconia (PVZ) and porcelain-veneered lithium disilicate (PVLD) crowns with different veneer/core thickness ratios and cooling rates. To provide design guidelines for better performing bilayer restorations with the aid of Viscoelastic Finite Element Method (VFEM).

METHODS

The VFEM was validated by comparing the predicted residual stresses with experimental measurements. Then, the model was used to predict transient and residual stresses in the two bilayer systems. Models with two different veneer/core thickness ratios were prepared (2:1 and 1:1) and two cooling protocols were simulated (Fast: ∼300 °C/min, Slow: ∼30 °C/min) using the heat transfer module, followed by stress analysis in ABAQUS. The physical properties of zirconia, lithium disilicate, and the porcelains used for the simulations were determined as a function of temperature.

RESULTS

PVLD showed lower residual stresses than PVZ. The maximum tensile stresses in PVZ were observed in the cusp area, whereas those in PVLD were located in the central fossa. The 1:1 thickness ratio decreased stresses in both layers of PVZ. Slow cooling slightly decreased residual stresses in both systems. However, the cooling rate effect was more evident in transient stresses.

SIGNIFICANCE

Slow cooling is preferable for both systems. A thinner porcelain layer over zirconia lowers stresses throughout the restoration. The different stress distributions between PVZ and PVLD may affect their failure modes. Smaller mismatches in modulus, CTE, and specific heat between the constituents, and the use of low T_g porcelains can effectively reduce the deleterious transient and residual tensile stresses in bilayer restorations.

Dentists’ Attitudes towards the Dental Ceramic Choice for Metal-Free Restorations: a Questionnaire Survey

AbstractA wide variety of dental ceramics is launched every year. Therefore, clinicians should constantly study and update themselves to correctly indicate these materials. This cross-sectional study aimed to assess the association of dentists’ academic aspects with their knowledge and the indication of dental ceramics for metal-free restorations. All the dentists from private clinics who affirmed to perform prosthetic treatments on their patients in a Southern Brazilian city were personally invited to this research to avoid dropouts. Participants answered questions related to their knowledge of different dental materials, their information sources and usage frequency of ceramic materials, and related to their academic training/education. Chi-square tests were performed to evaluate the association among the outcomes (knowledge of different materials, information sources considered for material selection and their frequencies of use) and exposure variables (time since graduation and post-graduation degree). Significant associations were also submitted to Chi-square residual analysis. A response rate of 73.3% was reached. The most known and used materials were Y-TZP and porcelain veneered zirconia, respectively, whereas the least known was leucite-based ceramic. The majority of the professionals with at least 25 years since graduation claimed not to know lithium disilicate or leucite-based ceramics, and a significant number of these professionals allow the laboratory prostheses technician to choose the restorative material. In addition, most of dentists with no post-graduation said they did not have knowledge about leucite and lithium disilicate. It was evidenced that continuing education plays an important role in the dentists’ attitudes regarding ceramic materials. Keywords: Surveys and Questionnaires. Ceramics. Prosthodontics. ResumoUma grande variedade de cerâmicas é lançada no mercado a cada ano. Portanto, os clínicos devem se manter em constante estudo e atualização para indicar corretamente o uso desses materiais. Assim, este estudo transversal teve por objetivo avaliar a associação entre aspectos acadêmicos de dentistas com seus conhecimentos e as indicações de cerâmicas dentárias para uso em restaurações livres de metal. Para isso, todos os dentistas de clínicas privadas que afirmaram realizar tratamentos protéticos em seus pacientes em uma cidade do sul do Brasil foram pessoalmente convidados a participar desta pesquisa para evitar desistências. Os participantes responderam a questões relacionadas ao seu conhecimento sobre diferentes materiais dentários, suas fontes de informação, a frequência de uso de materiais cerâmicos, e, também, sobre sua formação acadêmica. Testes qui-quadrado foram realizados para avaliar a associação entre os desfechos (conhecimento de diferentes materiais, fontes de informação consideradas para a seleção do material e sua frequência de uso) e as variáveis de exposição (tempo desde a graduação e grau de pós-graduação). As associações significativas foram submetidas à análise de resíduos do qui-quadrado. A taxa de resposta obtida foi de 73,3%. O material mais conhecido e usado foi a Y-TZP e zircônia recoberta por porcelana, respectivamente, enquanto que o material menos conhecido foi a cerâmica a base de leucita. A maioria dos profissionais com pelo menos 25 desde a graduação afirmaram não conhecer as cerâmicas a base de dissilicato de lítio ou leucita, e um significativo número desses profissionais permitem que o técnico em prótese dentária escolha o material restaurador. Ainda, a maioria dos dentistas sem pós-graduação disseram não conhecer as cerâmicas a base de dissilicato de lítio ou leucita. Concluiu-se que a educação continuada é um fator determinante nas atitudes de dentistas em relação aos materiais cerâmicos. Palavras-chave: Pesquisas e Questionários. Cerâmicas, Prótese Dentária

Extended glaze firings for porcelain-veneered zirconia: Effects on the mechanical and optical behavior

OBJECTIVE

This study evaluated the effect of dwell time (conventional or extended) and cooling protocol (fast or slow) of self-glaze firings on the mechanical (flexural strength and crack propagation) and optical (color and translucency) properties of a porcelain-veneered zirconia system.

METHODS

Bilayer disc-shaped samples were prepared (Vita VM9 + In-Ceram YZ) and divided according to the final thermal treatment: glaze firing followed by slow cooling (furnace opening at 200 °C) (G-S) or fast cooling (furnace opening at 600 °C) (G-F, manufacturer-recommended protocol), extended glaze firing (15 min of dwell time) followed by slow cooling (EG-S) or fast cooling (EG-F), or no thermal treatment (CTRL). Porcelain roughness (Ra and Rz) was measured before and after glaze firings. Color (ΔE₀₀) and translucency (TP₀₀) alteration were also evaluated. Flexural strength was measured with the piston-on-three-ball test and crack propagation analysis was performed after Vickers indentations. Complementary analyzes of crystalline phase and scanning electron microscopy were carried out.

RESULTS

Significant effect of dwell time was observed, with extended glaze leading to higher flexural strength and shorter crack lengths. Cracks of EG groups were observed to end in clusters of crystals. Color and translucency changed below perceptibility thresholds. All treatments led to a smoother surface and EG groups reached the lowest Rz values. An extra SiO₂ peak was revealed in control and EG groups. No effect of cooling protocol was found.

SIGNIFICANCE

Extended glaze firing was able to improve the resistance to crack initiation and propagation of porcelain-veneered zirconia without clinically perceptible changes in optical properties.

Effect of milling, fitting adjustments, and hydrofluoric acid etching on the strength and roughness of CAD-CAM glass-ceramics: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Whether procedures performed before the cementation of computer-aided design and computer-aided manufacturing (CAD-CAM) glass-ceramic restorations, including milling, fitting adjustment, and hydrofluoric acid etching introduce defects on the ceramic surface that affect the mechanical and surface properties is unclear.

PURPOSE

A systematic review and meta-analysis were conducted to assess the effect of milling, fitting adjustments, and hydrofluoric acid etching (HF) on the flexural strength and roughness (Ra) of CAD-CAM glass-ceramics.

MATERIAL AND METHODS

Literature searches were performed up to June 2020 in the PubMed/MEDLINE, Web of Science, and Scopus databases, with no publication year or language limits. The focused question was "Do milling, fitting adjustments, and hydrofluoric acid etching affect the flexural strength and roughness of CAD-CAM glass-ceramics?" For the meta-analysis, flexural strength and Ra data on milling, fitting adjustment, and HF etching versus control (polishing) were analyzed globally. A subgroup analysis assessed the effect of etching parameters (HF concentration and time) on the flexural strength and roughness of CAD-CAM glass-ceramics with different microstructures. Comparisons were performed with random-effect models at 5% significance.

RESULTS

Fourteen studies from 2764 potentially relevant records were included in the qualitative syntheses, and 12 in the meta-analysis. Milling and fitting adjustments increased roughness and reduced the flexural strength of CAD-CAM glass-ceramics. The effect of HF etching was dependent on the glass-ceramic microstructure, HF concentration, and etching time. For feldspathic- and leucite-reinforced ceramics, HF 5% applied for between 30 and 120 seconds increased roughness without affecting flexural strength. For lithium disilicate glass-ceramics, HF concentrations greater than 4.9% used for 20 seconds or more reduced the strength without affecting the surface roughness.

CONCLUSIONS

The flexural strength of CAD-CAM glass-ceramic is reduced by grinding procedures such as milling and fitting adjustment. Ceramic microstructure, HF concentration, and etching time determined the effect of hydrofluoric acid etching on the flexural strength and surface roughness of glass-ceramic materials.

Surface treatment and adhesion approaches on polymer-infiltrated ceramic network

Aim: To evaluate the effect of different surface treatments and adhesive approaches on the microshear bond strength of resin cement to a polymer-infiltrated ceramic network (PICN). Methods: PICN blocks were randomly assigned into 9 groups (n=10): CTRL: no treatment; HF: 5% hydrofluoric acid etching; HF-S: HF + silane; HF-S-A: HF-S + adhesive (Adper Single Bond 2); HF-UA: HF + universal adhesive (Single Bond Universal); SB: sandblasting with 50 μm Al2O3 particles; SB-S: SB + silane; SB-S-A: SB-S + adhesive; SB-UA: SB + universal adhesive. Resin cement microcylinders (Ø = 0.96 mm; height = 1 mm) (RelyX Ultimate) were built upon the PICN surface after roughness and contact angle measurements. Next, microshear bonding tests (μSBS) were performed (0.5 mm/min) after water storage (37ºC, 90 days) and thermocycling (12,000 cycles; 5ºC-55ºC). Failure modes were observed under stereomicroscope. Bond strength data were analyzed by two-way ANOVA/Tukey’s test and t-tests. Kruskal-Wallis/Dunn’s tests were conducted for roughness and contact angle data (α = 0.05). Results: A rougher surface and lower contact angles were observed for Sandblasting. HF-S (18.54 ± 2.03 MPa), SB-S (19.00 ± 1.66 MPa) and SB-UA (18.07 ± 2.36 MPa) provided the highest bond strength values, followed by the other treated groups. The CTRL group resulted in lower bond strength (7.18 ± 2.34 MPa). Conclusion: Hydrofluoric acid etching followed by silane application and sandblasting followed by silane or universal adhesive are useful clinical steps to enhance bonding to PICN. Adhesive applications after HF etching have no advantages in bonding to PICN.  

Effect of resin cement space on the fatigue behavior of bonded CAD/CAM leucite ceramic crowns

This study evaluated the influence of occlusal resin cement space on the fatigue performance of bonded-leucite crowns to a dentin-analogue material. Leucite anatomical crowns were adhesively cemented to dentin-like preparations having distinct occlusal cement space (50, 100 and 300 μm) (n = 18), and subjected to step-stress fatigue testing (150 N - 350 N; step-size: 25 N; 20,000 cycles/step; 20 Hz). Fatigue data (load and number of cycles for failure) were analyzed using Kaplan-Meier and Mantel-Cox (log-rank) tests (p <0.05). Fractographic analysis and occlusal internal space measurements were also performed. There was no significant difference for the distinct occlusal cement layer (50 μm: 289 N, 136,111 cycles; 100 μm: 285 N, 132,778 cycles; 300 μm: 246 N, 101,667 cycles). Occlusal internal space analysis showed a mean thickness of 120.4 (50 μm), 174.9 (100 μm) and 337.2 (300 μm). All failures were radial cracks originating at the ceramic-cement interface. Distinct occlusal cement spaces had no effect on the fatigue behavior of anatomical leucite crowns.

Grinding the intaglio surface of yttria partially- and fully-stabilized zirconia polycrystals restorations: Effect on their fatigue behavior

This study evaluated the effects of diamond bur grinding the intaglio surface of second (yttria partially-stabilized zirconia polycrystals, PSZ) and third-generation zirconia (fully-stabilized zirconia polycrystals, FSZ) adhesively cemented to dentin analogue substrate on the fatigue failure load, cycle number until failure, surface micromorphology and phase transformation. Disc-shaped specimens were produced from second (Katana ML-HT, Kuraray) and third-generation zirconia (Katana STML, Kuraray) and randomly allocated (n = 15) into two groups according to the intaglio surface treatment: Control - Ctrl (without grinding); Grinding - Gr (grinding at the center of the intaglio surface). The ceramic discs were adhesively cemented (Multilink Automix System) onto dentin analogue discs. Fatigue tests were executed by the step-stress method. The obtained data were analyzed by Kaplan Meier and Mantel-Cox tests. In addition, surface topography, roughness, phase transformation and fractography analyses were performed. SEM analysis showed that grinding increased the surface roughness and introduced defects in zirconia from both generations. Grinding increased the fatigue failure load, number of cycles to failure and survival rates of the second-generation zirconia statistically (control: 1373.33 N < grinding: 1600 N), while these same outcomes were reduced by grinding for the third-generation zirconia significantly (control: 766.67 N > grinding: 620 N). Thus, clinical adjustments with diamond burs damage the fatigue behavior of adhesively cemented third-generation zirconia.

Y-TZP surface treatments and their effects on the bond strength to resin cement

Aim: This study evaluated the effect of surface treatments of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics on their bond strength to a resin cement. Methods: Seventy zirconia blocks (6 × 6 × 2 mm3, IPS e.max ZirCAD) were assigned into 7 groups (n=10) – as-sintered (AS), no treatment; tribochemical silica coating + silanization (TBS; Cojet-sand; ProSil); airabrasion with 45 μm alumina particles + universal primer (AAP; Monobond®Plus); fusion sputtering (FS); SiO2 nanofilm + silanization (SN; ProSil); FS+SN+ silanization (FSSN; ProSil); FS+SN+Universal Primer (FSSNP; Monobond®Plus). Afterwards, a resin cement (RelyX™ ARC) was applied inside cylinders (Ø = 0.96 mm × 1 mm height) placed on the zirconia surfaces. Microshear bond strength tests (μSBS) were carried out (1 mm/min). Failure and phase transformation analysis were performed. Bond strength data (MPa) were subjected to Kruskal-Wallis/Mann Whitney tests. Results: TBS (27 ± 1.2) and AAP (24.7 ± 0.8) showed higher bond strengths than the other groups, followed by FSSNP (15.5 ± 4.2) and FSSN (13.3 ± 3.6). FS (3.4 ± 0.44) and SN (9.5 ± 2.7) showed the lowest values (p < 0.001). Most of the specimens exhibited an adhesive failure. Conclusion: Air-abrasion by silica-coated alumina particles followed by silanization or by alumina particles followed by universal primer resulted in the highest resin bond strength to zirconia. Fusion sputtering and silica nanofilm deposition induced low strengths. However, when these methods are applied in combination and with a primer (FSSN and FSSNP), higher bond strengths may be achieved. Low bond strengths are obtained when no zirconia treatment is performed.

The effect of extended glaze firing on the flexural fatigue strength of hard-machined ceramics

STATEMENT OF PROBLEM

It is unclear whether an extended glaze firing could improve the long-term mechanical performance of densely sintered CAD-CAM ceramics.

PURPOSE

The purpose of this in vitro study was to analyze the effect of an extended glaze firing on the flexural fatigue strength (FFS) of densely sintered milled (hard-machined) leucite-based (LEU) and lithium disilicate-based (DIS) ceramics.

MATERIAL AND METHODS

Disks were machined from ceramic blocks and divided into 6 groups (n=20) according to the material, LEU or DIS, and to the applied glaze firing: manufacturer-recommended glaze (G group), extended glaze (EG group), and control/no firing (C group). The surface roughness of the disks was measured before and after firing by using a contact profilometer, and data were compared by paired sample tests. Specimens were submitted to fatigue by using the staircase test design in water (piston-on-3 balls; 500 000 cycles, 20 Hz, and sinusoidal loading). Mean (±SD) FFS values were then calculated and analyzed by using 1-way analysis of variance and post hoc Tukey test (α=.05).

RESULTS

Surface roughness did not change after the firing (P>.05). The highest FFS value in both ceramics was obtained after EG firing (LEU-EG=80.52 ±6.3 MPa; DIS-EG=147.25 ±10.5 MPa), which was statistically superior to G firing (LEU-G=73 ±6.8 MPa, P=.003; DIS-G=134.34 ±15.6 MPa; P=.023) and C group (LEU-C=61.94 ±6.3 MPa; P<.001; DIS-C=134.13 ±17.3 MPa; P=.023).

CONCLUSIONS

EG firing optimized the biaxial flexural fatigue strength of hard-machined leucite and lithium disilicate ceramics compared with conventional glaze firing.

Repolimento de Resina Composta Após Tratamento Clareador: Efeitos na Estabilidade de Cor e Rugosidade

Este estudo avaliou o efeito do repolimento após clareamento na estabilidade de cor e rugosidade de uma resina composta nanoparticulada. Foram confeccionados 56 espécimes em formato de disco (8 mm x 2 mm) da resina composta Filtek Z350 XT, os quais foram divididos conforme o primeiro tratamento: clareamento com peróxido de hidrogênio 35% (Total Blanc Office) ou sem clareamento. Após três sessões de contato com o gel, os grupos foram subdivididos conforme o segundo tratamento: repolimento ou sem repolimento. Então, os grupos foram novamente subdivididos conforme os meios que teriam contato por 30 dias: saliva artificial ou vinho tinto (imersões diárias de 15 min). Avaliações de cor e rugosidade foram feitas após preparação dos espécimes (F0) e após as fases de clareamento (F1), repolimento (F2) e pigmentação (F3). A alteração de cor (OE00) foi calculada pela fórmula CIEDE2000. A análise estatística foi realizada pelo teste de Análise de Variância para Medidas Repetidas e teste de Tukey como post-hoc. Após F3, o grupo clareado não repolido apresentou valores de OE00 19% maiores que o clareado repolido quando imersos em vinho tinto, porém, nenhuma diferença foi encontrada entre os grupos imersos em saliva. O repolimento promoveu diminuição de rugosidade (F1 vs. F2) na maioria dos grupos. Os dados apontaram para a conclusão de que o simples ato de repolir restaurações de resina composta imediatamente após o tratamento clareador pode ser capaz de minimizar a sua susceptibilidade à alteração de cor caso sejam submetidas a uma dieta rica em pigmentos.Palavras-chave: Cor. Agentes Clareadores Dentais. Resinas Compostas.

Resistência à Fadiga de Y-TZP Monolítica e com Recobrimento Cerâmico pelas Técnicas CAD-on e Cimentação

Este estudo objetivou avaliar a resistência à fadiga de estruturas cerâmicas compostas por Y-TZP e dissilicato de lítio, confeccionadas pelas técnicas CAD-on e cimentação em comparação com Y-TZP monolítica. Foram fabricados discos (diâmetro: 14,4 mm espessura: 1,4 mm) trilayer (infraestrutura de Y-TZP, cerâmica de fusão ou cimento resinoso e cobertura de dissilicato de lítio) e monolayer  de Y-TZP. A resistência flexural à fadiga foi determinada pelo método da escada com configuração piston-on-three-ball em água (750000 ciclos, 20 Hz). A tensão inicial (o1) foi de 60% do valor obtido com ensaio monotônico (n3) e os incrementos foram de 10% de o1. Os seguintes grupos foram testados (n20): Y-TZP (zircônia monolítica), CAD-ZT (técnica CAD-on com zircônia sob tração), CAD-DT (CAD-on com dissilicato sob tração), CIM-ZT (técnica de cimentação com zircônia sob tração), CIM-DT (cimentação com dissilicato sob tração). Foram calculados média e intervalos de confiança (IC) e a diferença estatística foi determinada com base na não-sobreposição dos IC. Houve diferença estatística entre todos os grupos. As médias de resistência à fadiga (MPa) foram: Y-TZP 405,92 (IC 397,58-414,26) CAD-ZT 377,73 (IC 374,59-380,88) CAD-DT 154,79 (IC 151,86-157,72) CIM-ZT 346,54 (IC 340,62-352,46) e CIM-DT 100,34 (IC 97,42-103,26). Conclusões: Y-TZP monolítica apresentou a maior resistência à fadiga. O método CAD-on gerou resistência à fadiga superior à cimentação. Houve influência do material sob tração, sendo que a zircônia resultou em resistência à fadiga superior.Palavras-chave: Fadiga. Cerâmica. Resistência à Tração.

Efeito do Par de Brocas e da Ordem de Usinagem na Rugosidade Superficial e na Resistência à Fadiga de Cerâmicas para CAD/CAM

O trabalho avaliou o efeito das brocas e da ordem de usinagem na rugosidade e na resistência à fadiga de cerâmicas para CAD/CAM. Dois conjuntos de pares de brocas (A e B) foram utilizados na usinagem de vinte discos de cerâmica vítrea reforçada por leucita (LEU), dissilicato de lítio (DIS) e zircônia (YZ), em sistema Cerec inLab MC XL®. Realizou-se análise de rugosidade (Ra) e ensaio de resistência à fadiga pelo método step-test. A carga inicial e o incremento de carga para cada material foram baseados em ensaio estático. Dez mil ciclos foram aplicados em cada step, a 1,4 Hz, até a falha. Teste-t indicou que Ra (μm) foi diferente (p<0,05) entre os conjuntos de brocas A e B para LEU (A: 1,73; B: 1,45) e YZ (A:1,67; B:1,90), mas nenhuma diferença foi reportada para o DIS (A: 1,78; B: 1,84). A resistência à fadiga (MPa) da YZ foi significativamente influenciada pelo par de brocas (A: 554,25; B: 459,31), mas não houve diferença para LEU (A: 69,91; B: 73,88) e DIS (A: 179,36; B:190,82). Houve correlação significativa entre ordem de usinagem e Ra para LEU (rs= -0,88) e DIS (rs=0,91). A correlação entre ordem de usinagem e resistência à fadiga foi significativa para LEU (rs=0,74) e YZ (rs=0,73). Considerando que o par de brocas pode influenciar a rugosidade e a resistência da cerâmica, sugere-se que estudos futuros realizem uma randomização estratificada dos espécimes, distribuindo, entre os grupos experimentais, espécimes usinados com diferentes brocas. Uma possível deterioração das brocas com o aumento do número de usinagens parece não ter efeito deletério na resistência das cerâmicas.Palavras-chave: Cerâmica. CAD-CAM. Fadiga

Usinagem em CAD/CAM x Técnicas de Fabricação Pré-Sinterização

Este estudo teve por objetivo avaliar e comparar o efeito de diferentes técnicas de fabricação de espécimes de cerâmica Y-TZP pré- sinterizada (usinagem em CAD/CAM Vs técnicas de fabricação in-lab) na rugosidade superficial, transformação de fase, topografia de superfície e comportamento mecânico. Para isso, discos pré-sinterizados de cerâmica Y-TZP (IPS e.max ZirCAD, Ivoclar Vivadent) foram confeccionados segundo as normas da ISO 6872-2008 para flexão biaxial de corpos cerâmicos (piston-on-three balls - 18 mm de diâmetro x 1.5 mm de espessura) através de diferentes técnicas: Machined- usinado em CAD/CAM Polished- corte com disco diamantado seguido de polimento com lixa de carbeto de silício Xfine- corte com disco diamantado seguido pelo desgaste com ponta diamantada extra-fina Fine- corte com disco diamantado seguido pelo desgaste com ponta diamantada fina Sic- corte com disco diamantado seguido pelo desgaste com lixa de carbeto de silício. Após a confecção, os discos foram sinterizados de acordo com as recomendações do fabricante e submetidos às análises de rugosidade, resistência biaxial, limite de fadiga, transformação de fase e topografia superficial. Foi observado que o processo de fabricação influenciou as características superficiais e o comportamento mecânico interferindo nos desfechos observados. O desgaste com ponta diamantada fina demonstrou ser o melhor método para mimetizar a usinagem em CAD/CAM. Nenhum conteúdo de fase monoclínica foi observado nas diferentes técnicas de confecção avaliadas.Palavras-chave: Cerâmica. Projeto Auxiliado por Computador. Zircônia.

Surface change assessment of Co-Cr alloy subjected to immersion in denture cleansers

Choosing the right chemical cleanser for removable partial dentures is a challenge, because they present an acrylic and a metallic portion, which should be cleaned and not damaged. Aim: The aim of this study was to assess surface changes of cobalt chromium alloys immersed in diferente cleaners solutions: 0.05% sodium hypochlorite, 4.2% acetic acid, 0.05% sodium salicylate, sodium perborate (Corega Tabs®) and 0.2% peracetic acid. Material and Methods: One hundred and twenty circular specimens (10 mm in diameter) of two commercial available Co-Cr alloys were tested: GM 800 ® (Dentaurum) and Co-Cr® (DeguDent). The samples were randomly divided into tem experimental groups (n=10), according to the trend mark of alloy and cleaners solutions in which they were immersed, and two control groups, in which the samples of the two alloys were immersed in distilled water. Evaluations were performed through roughness measurement (rugosimeter Surftest 211, Mitutoyo), visual evaluation with stereomicroscope (Stereo Discovery 20, Carl Zeiss) and scanning electron microscope surface (JSM, 6360 SEM, JEOL), at experimental times T0 – before immersions, T1 - after one immersion, and T2 - after 90 immersions. Intergroup comparison for the effect of immersion in the different cleanser agents was evaluated through ANOVA/Tukey tests (p≤0.05). The effect of the time in the immersion of each alloy was evaluated by t-pared test (p≤0.05). The two alloys were compared using the t-Student test. Results: The analysis of roughness and microscopy showed that surface changes were significantly greater in groups submitted to 0.05% sodium hypochlorite after 90 immersions (T2). When comparing the two alloys, a similar behavior of roughness was observed for the cleaning agents. However, alloy GM 800® showed significant statistical difference for roughness variations in experimental times (Δ1 and Δ2), when immersed in sodium 0.05% hypochlorite. The number of exposures of the alloys to the cleaning agents showed a negative influence when using sodium hypochlorite solution. Conclusions: It is possible to conclude that 0.05% sodium hypochlorite has caused the greatest apparent damage to alloy surface.

Tribochemical Glass Ceramic Coating as a New Approach for Resin Adhesion to Zirconia

PURPOSE

To investigate the effects of a novel tribochemical silica coating technique with powders made from feldspathic ceramic and leucite-based ceramic on the bond strength of zirconia to resin cement before and after aging.

MATERIALS AND METHODS

Zirconia blocks were divided into 3 groups according to the material used for airborne-particle abrasion: 1) SP (control): silica-coated alumina particles; 2) FP: feldspathic ceramic powder; 3) LP: leucite glass-ceramic powder. After silanization, composite resin cylinders were cemented on the zirconia surface using a dual-curing resin cement. Prior to the shear bond strength (SBS) test, half of the samples (n = 15) were stored in distilled water for 24 h; the other half (n = 15) were submitted to aging (10,000 thermocycles of 5°C to 55°C; 150 days of water storage). The bond strength data were analyzed using two-way ANOVA and Tukey's test (α = 0.05). Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction analysis were performed.

RESULTS

The initial bond strengths did not differ significantly between the groups (p = 0.053). However, after aging procedures, airborne-particle abrasion with feldspathic ceramic powder (FP) resulted in higher values of bond strength (p = 0.0001). SEM and EDS indicated that all the treatments promoted silica deposition on the Y-TZP surface ceramic. Airborne-particle abrasion with FP and LP induced a lower percentage of the monoclinic phase.

CONCLUSION

Airborne abrasion with fine feldspathic ceramic particles is a novel tribochemical technique and appears to be suitable for improving the bond strength between zirconia and resin cements.

Color stability of ceramic laminate veneers cemented with light-polymerizing and dual-polymerizing luting agent: A split-mouth randomized clinical trial

STATEMENT OF PROBLEM

The color stability of luting agents influences the esthetics of ceramic laminate veneers. Clinical studies that have evaluated the color changes of veneers cemented to enamel with light- and dual-polymerizing resin cement are lacking.

PURPOSE

The purpose of this split-mouth randomized clinical trial was to evaluate the color change and marginal discoloration of dual- and light-polymerizing cement used for cementation of ceramic laminate veneers.

MATERIAL AND METHODS

In 10 participants, 0.3-mm-thick ceramic laminate veneers were cemented on the buccal surface of the second premolars without tooth preparation. A randomized application of light-polymerized cement was used on one side and a dual-polymerized cement on the contralateral side. The operator and participants were blinded to the activation mode. Color was evaluated by a blinded evaluator with a spectrophotometer at 24 hours and at 2, 6, 12, and 24 months after cementation. The CIELab (ΔE*_ab) and CIEDE2000 (ΔE*₀₀) formulas were used to quantify color alteration, and Δa*, Δb*, and ΔL* were calculated between the first and subsequent measurements. US Public Health Service guidelines were used to evaluate the marginal discoloration.

RESULTS

Wilcoxon tests did not show a statistical difference in ΔE*_ab and ΔE*₀₀ between the groups (P>.05). At 24 months, the median ΔE*_ab was 2.31 (interquartile ranges [IQR]: 3.34) for the light-polymerizing mode and 1.57 (IQR: 0.41) for the dual-polymerizing mode, while the median ΔE*₀₀ was 1.65 for the light-polymerizing mode (IQR: 2.34) and 1.18 for the dual-polymerizing mode (IQR: 0.25). The thresholds for clinically acceptable color changes ΔE*_ab>3.46 and ΔE*₀₀>2.25 were found for both curing modes. Marginal discoloration was observed from the 2-year assessment.

CONCLUSIONS

The color stability of ceramic laminate veneers was similar for both of the polymerizing modes for all evaluated periods. Marginal discoloration increased over a 2-year period for both the light- and the dual-polymerizing modes.

CAD/CAM machining Vs pre-sintering in-lab fabrication techniques of Y-TZP ceramic specimens: Effects on their mechanical fatigue behavior

This study evaluated the effects of different pre-sintering fabrication processing techniques of Y-TZP ceramic (CAD/CAM Vs. in-lab), considering surface characteristics and mechanical performance outcomes. Pre-sintered discs of Y-TZP ceramic (IPS e.max ZirCAD, Ivoclar Vivadent) were produced using different pre-sintering fabrication processing techniques: Machined- milling with a CAD/CAM system; Polished- fabrication using a cutting device followed by polishing (600 and 1200 SiC papers); Xfine- fabrication using a cutting machine followed by grinding with extra-fine diamond bur (grit size 30 μm); Fine- fabrication using a cutting machine followed by grinding with fine diamond bur (grit size 46 μm); SiC- fabrication using a cutting machine followed by grinding with 220 SiC paper. Afterwards, the discs were sintered and submitted to roughness (n=35), surface topography (n=2), phase transformation (n=2), biaxial flexural strength (n=20), and biaxial flexural fatigue strength (fatigue limit) (n=15) analyses. No monoclinic-phase content was observed in all processing techniques. It can be observed that obtaining a surface with similar characteristics to CAD/CAM milling is essential for the observation of similar mechanical performance. On this sense, grinding with fine diamond bur before sintering (Fine group) was the best mimic protocol in comparison to the CAD/CAM milling.

Influence of the resin cement thickness on the fatigue failure loads of CAD/CAM feldspathic crowns

OBJECTIVES

to evaluate the influence of the occlusal resin cement thickness on the cyclic loads-to-failure of feldspathic crowns and to compare the results to data from monotonic tests. A large range of cement thickness (50μm and 500μm) was tested, in order to better measure the influence of this variable.

METHODS

Feldspathic ceramic crowns (Vita Mark II blocks, Vita Zahnfabrik) were bonded to dentin analog dies (G10 (NEMA grade G10, International Paper), with occlusal resin cement thicknesses of 50μm and 500μm (Multilink Automix, Ivoclar). The dies were prepared with microchannels for water transport to the cement layer. After 96-h water storage, the specimens (n=20) were submitted to cyclic loads (500,000 cycles at 20Hz; initial maximum load=40% of monotonic load, from previous data) following a staircase sensitivity design (step size=25N). Failure loads at 500,000 cycles were compared to monotonic failure loads (from a previous study with specimens produced by the same author, using the same materials, specimen configuration and cementation protocol).

RESULTS

Crowns with an occlusal cement layer of 50μm were more resistant than those cemented with 500μm (246.4±22.9N vs. 158.9±22.9N), under wet cyclic testing conditions (p<0.001). The fatigue failure loads were reduced compared to monotonic loads: to 37% of monotonic for 50μm; to 53% of monotonic for 500μm.

SIGNIFICANCE

An occlusal cement thickness of 50μm was more favorable for the structural performance of feldspathic crowns than was 500μm. Cyclic fatigue reduced failure loads well below those found under monotonic loading.

Cuspal deflection of directly or indirectly restored teeth

Objective: The aim of this study was to evaluatethe cuspal deflection of teeth restored directlyand indirectly. Material and Methods: Fortysound maxillary premolar teeth were restoredwith composite and different base materials. Widemesial-occlusal-distal cavity preparations wereperformed, with isthmus width of one third of thedistance between the cuspal tips, 3 mm occlusaland a 5 mm interproximal preparation height. Theteeth were divided into 4 groups (n = 10), accordingto the restoration type: G1) GIC-DCR (1 mm glassionomer cement base and direct restoration usingnanoparticulate composite); G2) FL-DCR (1 mm baseof flowable composite resin and direct restorationusing nanoparticulate composite); G3) GIC-ICR(1 mm glass ionomer cement base and indirectrestoration using nanoparticulate composite GICbase); G4) FL-ICR (1 mm base of flowable compositeresin and indirect restoration using nanoparticulatecomposite). The specimens were submitted tocompressive load of 50 N on the buccal and lingualcusps, in a universal testing machine. The lingualcusp microstrain (??) measurements were executedby strain gauges. Results: The Kruskal-Wallis (5%)test was used and showed there were no significantdifferences among the microstrain values for the fourstudy groups (G1 = 1250; G2 = 1075; G3 = 1279;G4 = 937). Conclusion: It could be concluded thatthe restorative techniques and the bases employeddid not show any influences in cuspal deflection.KeywordsBase materials; Cuspal defection; Composite resin; Direct restoration; Indirect restoration.

Effect of silica coating combined to a MDP-based primer on the resin bond to Y-TZP ceramic

The aim of this study was to evaluate the influence of silica coating and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based primer applications upon the bonding durability of a MDP-based resin cement to a yttrium stabilized tetragonal zirconia (Y-TZP) ceramic. Ninety-six Y-TZP tabs were embedded in an acrylic resin (free surface for adhesion: 5 × 5 mm(2)), ground finished and randomly divided into four groups (N = 24) according to the ceramic surface conditioning: (1) cleaning with isopropanol (ALC); (2) ALC + phosphoric acid etching + MDP-based primer application (MDP-primer); (3) silica coating + 3-methacryloyloxypropyl trimethoxysilane (MPS)-based coupling agent application (SiO2 + MPS-Sil); and (4) SiO2 + MDP-primer. The MDP-based resin cement was applied on the treated surface using a cylindrical mold (diameter= 3 mm). Half of the specimens from each surface conditioning were stored in distilled water (37 °C, 24 h) before testing. Another half of the specimens were stored (90 days) and thermo-cycled (12,000 x) during this period (90 d/TC) before testing. A shear bond strength (SBS) test was performed at a crosshead speed of 0.5 mm/min. Two factors composed the experimental design: ceramic conditioning strategy (in four levels) and storage condition (in two levels), totaling eight groups. After 90 d/TC (Tukey; p < 0.05), SiO2 + MDP-primer (24.40 MPa) promoted the highest SBS. The ALC and MDP-primer groups debonded spontaneously during 90 d/TC. Bonding values were higher and more stable in the SiO2 groups. The use of MDP-primer after silica coating increased the bond strength.

Evaluation of procedures employed for the maintenance of removable dentures in elderly individuals

PURPOSE

The objective of the present study was to evaluate the behaviour of the wearers of removable dentures in relation to cleaning and maintaining the prosthesis.

MATERIALS AND METHODS

Two hundred and thirty-one people were interviewed, most of whom were females, over 60 years of age and participants in the Center for Integrated Study and Support to the Elderly.

RESULTS

After analysing the responses, it was verified that most people brush their dentures three times a day using dentifrice and only go to the clinician when they have a complaint. They do not receive follow-up appointments for checkups, do not use immersion cleaners for their dentures and do not remove their dentures during the night.

CONCLUSIONS

It was concluded that the study sample did not receive proper orientation for the conservation of removable dentures, which may consequently reduce the useful life of dentures and cause social and functional problems.

Effects of surface treatments and storage times on the tensile bond strength of adhesive cements to noble and base metal alloys

This work evaluated two resin cements and a glass-ionomer cement and their bond strength to gold-palladium (Au-Pd), silver-palladium (Ag-Pd), and nickel-chromium-beryllium (Ni-Cr-Be) alloys, utilizing three surface treatments over a period of six months. Eight hundred ten pieces were cast (in a button shape flat surfaces) in one of three alloys. Each alloy group was assigned to three other groups, based on the surface treatment utilized. Specimens were fabricated by bonding similar buttons in using one of three adhesive cements. The 405 pairs were thermocycled and stored in saline solution (0.9% NaCl) at 37 degrees C. The tensile bond strengths were measured in a universal testing machine after storage times of 2, 90, or 180 days. The highest mean bond strength value was obtained with the base metal alloy (10.9 +/- 8.6 MPa). In terms of surface treatment, oxidation resulted in the highest mean bond strength (13.7 +/- 7.3 MPa), followed by sandblasting (10.3 +/- 5.5 MPa) and polishing (3.0 +/- 6.4 MPa). Panavia Ex (13.2 +/- 9.3 MPa) showed significantly higher bond strengths than the other two cements, although the storage time reduced all bond strengths significantly.

Efficacy and safety of acetaminophen and naproxen in the treatment of tension-type headache. A randomized, double-blind, placebo-controlled trial

The objective of this study was to evaluate and compare the efficacy and safety of single doses of acetaminophen (paracetamol) 1000 mg and naproxen 375 mg vs. placebo over a six-hour period in the treatment of tension-type headache. The treatments were compared in a randomized, double-blind, multicentre, placebo-controlled study. Efficacy was evaluated using four standard analgesic summary endpoints (the sum of pain intensity differences from baseline, the maximum pain intensity from baseline, the sum of the pain relief scores, and the maximum pain relief score). Both acetaminophen 1000 mg and naproxen 375 mg were significantly superior to placebo (P<or=0.009 and P<or=0.021, respectively) but not significantly different from each other (P>or=0.498) for these four endpoints. For example, the mean sum of pain intensity differences from baseline was 9.14+/-0.34 for acetaminophen 1000 mg and 8.81+/-0.35 for naproxen 375 mg compared with 7.42+/-0.34 for placebo. Other efficacy endpoints (percentage of responders (pain reduced to none) at two hours, onset of meaningful relief, time to use of rescue medication and subject's overall impression of study medication) showed similar trends. A significantly larger mean pain intensity difference from baseline was observed for acetaminophen 1000 mg (1.13) than for naproxen 375 mg (0.95) (P=0.036) at one hour after treatment. There was no significant difference among the treatment groups in the incidence of adverse events (P=0.730). In summary, the results of this well-controlled, double-blind study demonstrate that over-the-counter acetaminophen 1000 mg and prescription naproxen 375 mg are effective and well tolerated in the treatment of tough (moderate-to-severe) tension-type headache.

M3 muscarinic acetylcholine receptors regulate cytoplasmic myosin by a process involving RhoA and requiring conventional protein kinase C isoforms

Although muscarinic acetylcholine receptors (mAChR) regulate the activity of smooth muscle myosin, the effects of mAChR activation on cytoplasmic myosin have not been characterized. We found that activation of transfected human M3 mAChR induces the phosphorylation of myosin light chains (MLC) and the formation of myosin-containing stress fibers in Chinese hamster ovary (CHO-m3) cells. Direct activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate (PMA) also induces myosin light chain phosphorylation and myosin reorganization in CHO-m3 cells. Conventional (alpha), novel (delta), and atypical (iota) PKC isoforms are activated by mAChR stimulation or PMA treatment in CHO-m3 cells, as indicated by PKC translocation or degradation. mAChR-mediated myosin reorganization is abolished by inhibiting conventional PKC isoforms with Go6976 (IC50 = 0.4 microM), calphostin C (IC50 = 2.4 microM), or chelerythrine (IC50 = 8.0 microM). Stable expression of dominant negative RhoAAsn-19 diminishes, but does not abolish, mAChR-mediated myosin reorganization in the CHO-m3 cells. Similarly, mAChR-mediated myosin reorganization is diminished, but not abolished, in CHO-m3 cells which are multi-nucleate due to inactivation of Rho with C3 exoenzyme. Expression of dominant negative RhoAAsn-19 or inactivation of RhoA with C3 exoenzyme does not affect PMA-induced myosin reorganization. These findings indicate that the PKC-mediated pathway of myosin reorganization (induced either by M3 mAChR activation or PMA treatment) can continue to operate even when RhoA activity is diminished in CHO-m3 cells. Conventional PKC isoforms and RhoA may participate in separate but parallel pathways induced by M3 mAChR activation to regulate cytoplasmic myosin. Changes in cytoplasmic myosin elicited by M3 mAChR activation may contribute to the unique ability of these receptors to regulate cell morphology, adhesion, and proliferation.

Involvement of protein kinase C and protein kinase A in the muscarinic receptor signalling pathways mediating phospholipase C activation, arachidonic acid release and calcium mobilisation

The involvement of protein kinase C (PKC) and protein kinase A (PKA) in cholinergic signalling in CHO cells expressing the M3 subtype of the muscarinic acetylcholine receptor was examined. Muscarinic signalling was assessed by measuring carbachol-induced activation of phospholipase C (PLC), arachidonic acid release, and calcium mobilisation. Carbachol activation of PLC was not altered by inhibition of PKC with chelerythrine chloride, bisindolylmaleimide or chronic treatment with phorbol myristate acetate (PMA). Activation of PKC by acute treatment with PMA was similarly without effect. In contrast, inhibition of PKC blocked carbachol stimulation of arachidonic acid release. Likewise, PKC inhibition resulted in a decreased ability of carbachol to mobilise calcium, whereas PKC activation potentiated calcium mobilisation. Inhibition of PKA with H89 or Rp-cAMP did not alter the ability of carbachol to activate PLC. Similarly, PKA activation with Sp-cAMP or forskolin had no effect on PLC stimulation by carbachol. Carbachol-mediated release of arachidonic acid was decreased by H89 but only slightly increased by forskolin. Forskolin also increased calcium mobilisation by carbachol. These results suggest a function for PKC and PKA in M3 stimulation of arachidonic acid release and calcium mobilisation but not in PLC activation.

Ethanol disrupts carbamylcholine-stimulated release of arachidonic acid from Chinese hamster ovary cells expressing different subtypes of human muscarinic receptor

Ethanol disrupts signal transduction mediated by a variety of G-protein coupled receptors. We examined the effects of ethanol on arachidonic acid release mediated by muscarinic acetylcholine receptors. Chinese hamster ovary (CHO) cells transfected with the different subtypes of human muscarinic receptors (M1 to M5) were incubated with [3H]arachidonic acid ([3H]AA) for 18 hr, washed, and exposed to the cholinergic agonist carbamylcholine for 15 min. Carbamylcholine induced [3H]AA release from CHO cells expressing M1, M3, or M5, but not M2 or M4, muscarinic receptors. Dose response curves revealed that carbamylcholine stimulated [3H]AA release by up to 12-fold with an ECo of approximately 0.4 microM; maximal responses were obtained with 10 microM carbamylcholine. Exposure of M1-, M3-, or M5-expressing cells to ethanol for 5 min before stimulating with carbamylcholine reduced [3H]AA release by 40 to 65%; 50% of the maximal inhibition was obtained with an ethanol concentration of 30 to 50 mM. Ethanol did not affect basal [3H]AA release measured in the absence of carbamylcholine. Dose response curves suggest that ethanol acts as a noncompetitive inhibitor of muscarinic receptor-induced [3H]AA release insofar as maximal [3H]AA release was depressed in the presence of ethanol with no apparent change in the EC50 for stimulation by carbamylcholine. Exposure of CHO cells to 38 mM ethanol for 48 hr increased [3H]AA release induced by carbamylcholine without affecting basal [3H]AA release or altering the EC50 for carbamylcholine. These results indicate that ethanol acutely inhibits muscarinic receptor signaling through the arachidonic acid pathway in a noncompetitive manner, but chronically enhances muscarinic signaling through the same pathway.

Influence of acute and chronic ethanol treatment on muscarinic responses and receptor expression in Chinese hamster ovary cells

The influence of ethanol on the muscarinic receptor-mediated release of inositol phosphate from Chinese hamster ovary (CHO) cells stably transfected with one of the five subtypes of muscarinic acetylcholine receptor was determined. In CHO cells expressing M3 muscarinic receptors (CHO-M3), carbamylcholine increased muscarinic receptor-induced release of inositol phosphate by 150-350% following a 15-min incubation with an EC50 of approximately 30 microM. Maximal responses were obtained with 1 mM carbamylcholine, while responses to 10 mM carbamylcholine were somewhat less than maximal. Preincubation with atropine for 10 min inhibited the response with an IC50 of approximately 30 nM. CHO cells transfected with M1, M3, and M5 receptors displayed a similar pattern of activity; CHO cells transfected with M2 and M4, as well as untransfected cells, were unresponsive to carbamylcholine. Ethanol acutely inhibited the response of CHO-M3 cells to carbamylcholine by 15% at 18 mM and by 47% at 180 mM (the highest concentration examined). CHO-M3 cells were incubated with 50 mM ethanol for 48 hr. This treatment did not affect the number of cells or their protein content (113 pg/cell). The expression of M3 muscarinic receptors (determined using [3H]N-methylscopolamine) increased from 1.34 +/- 0.23 to 1.75 +/- 0.16 pmol/mg protein (P < 0.05). In contrast, carbamylcholine-stimulated release of inositol phosphate was depressed by 40-70% in four experiments. Concentration-response analyses indicated a non-competitive inhibitory mechanism. This dissociation of muscarinic receptor expression and muscarinic signaling suggests a compensatory increase in receptor expression in response to chronic inhibition of muscarinic signaling by ethanol.

Parathyroid hormone uses both adenylate cyclase and protein kinase C to regulate acid production in osteoclasts

Osteoclasts, isolated from the endosteum of 2.5- to 3-week-old chickens, were treated with acridine orange, a hydrogen ion concentration-sensitive fluorescent dye, in order to monitor changes in acid production. The adenylate cyclase inhibitor, alloxan, blocked parathyroid hormone (PTH)-stimulated acid production. Dibutyryl cyclic adenosine monophosphate, a membrane-permeant form of cyclic adenosine monophosphate, mimicked the PTH effect. Bisindolylmaleimide, a specific inhibitor of protein kinase C (PKC), blocked the initial stimulation (15, 30, and 60 min) of acid production by PTH but had no effect on long-term stimulation (120 min). Confocal microscopy of osteoclasts stained with fluorescein-conjugated bisindolylmateimide revealed a shift in location of PKC from the cytoplasm to the plasma membrane region after treatment with parathyroid hormone. The results of these studies support the hypothesis that PTH regulation of acid production in osteoclasts involves both adenylate cyclase and PKC as effectors.

Multiple G-protein involvement in parathyroid hormone regulation of acid production by osteoclasts

The involvement of multiple G-proteins in parathyroid hormone regulation of acid production was demonstrated in a highly enriched osteoclast population. Osteoclasts were isolated from the endosteum of 2.5 to 3-week-old chicken tibia using sequential enzymatic digestion. Single cell analysis of acid production was accomplished using microscope photometry and vital staining with acridine orange, a hydrogen ion concentration sensitive fluorescent dye. Lithium chloride, an uncoupler of G-proteins from their respective receptors, blocked parathyroid hormone stimulated production of acid. Cholera toxin, which permanently activates Gs-proteins, mimicked PTH stimulation. Pertussis toxin, which prevents receptor interaction with Gi- and Go-proteins, blocked both 10(-8) M and 10(-11) M PTH stimulated acid production, suggesting that the pertussis toxin-sensitive G-protein is utilized at both PTH concentrations. Immunoblots of osteoclast plasma membrane proteins, using a panel of antibodies generated against specific G-protein alpha subunits, revealed a 48 kDa Gs alpha, a 41 kDa Go alpha, a 34 kDa Gi alpha-3, and a unique 68 kDa G alpha subunit, with the 41 kDa and 34 kDa bands being the most intense. Immunoblots of osteoblast plasma membrane proteins had a substantially different profile with the most intense bands being a Gs alpha (48 kDa) and a Go alpha (36 and 38 kDa). The studies suggest the utilization of at least two different G-proteins in the parathyroid hormone regulation of acid formation by osteoclasts, a Gs and a pertussis toxin-sensitive G-protein (Go and/or Gi alpha-3).

Development of a new method for obtaining osteoclasts from endosteal surfaces

Techniques for the isolation of a highly pure population of viable osteoclasts are limited. For this reason, we developed an isolation procedure that results in a high yield of osteoclast-like cells, up to 92% pure, from 3-wk-old chicken tibias. The unique feature of the method is the migration of cells from marrow-free endosteal surfaces to vitronectin-coated plates. The cells retain the osteoclast phenotype and remain viable in culture for a minimum of 1 wk. The cells were characterized and compared to two populations of authentic avian osteoclasts, which were isolated on the basis of association with fibronectin-coated plates. The cells contained substantial amounts of tartrate-resistant acid phosphatase. Alkaline phosphatase levels were negligible, suggesting little contamination by osteoblasts. Response to parathyroid hormone, dibutyryl cyclic adenosine monophosphate, calcitonin, acetazolamide, 17 beta-estradiol, and prostaglandin E2 was evident, as detected by measuring acid production. The vitronectin-associating cells contained numerous mitochondria, had the ability to resorb bone in an in vitro bone slice assay, and specifically bound biotinylated vitronectin. At 5 d of culture, the cells demonstrated marginal multinuclearity, having two to three nuclei. A large number (approximately 1 x 10(6) cells/tibia) of viable cells that exhibit characteristics of authentic osteoclasts can be obtained by the method described. Potentially, this method could be applied to other species.