Effect of types of luting agent on push-out bond strength of zirconium oxide posts

ObjectiveThe aim of this study was to investigate the effect of different luting agents on the bond strength of zirconium oxide posts in root canals after artificial ageing.Material and methodsThirty single-rooted extracted teeth were collected. Post spaces were prepared. Custom milled zirconium oxide posts (Cercon, Degudent) were fabricated. Specimens were divided into 3 groups (n = 10), according to the luting agents used: group RA, conventional resin luting agent (RelyX ARC); group RU, self-adhesive resin luting agent (RelyX Unicem); and group Z, zinc phosphate luting agent (DeTrey). Specimens were subjected to thermocycling and water storage at 37 °C. Specimens were horizontally sectioned into three sections and subjected to a push-out test with 0.5 mm/min crosshead speed. The failure mode was assessed by scanning electron microscopy. Data were analysed by using 2-way ANOVA.ResultsThe following bond strength values were obtained: group RA – 8.89 MPa, group RU – 10.30 MPa and group Z – 9.31 MPa. There was no significant difference in bond strength among the groups (P = 0.500). Adhesive failure mode at the cement/post bonded interface was seen in 100%, 66.67% and 83.3% of examined sections in groups RA, RU and Z, respectively. There was no significant difference in bond strength among different root regions (P = 0.367).ConclusionThe type of luting agent had no significant effect on the push-out bond strength of zirconium oxide posts after artificial ageing.Clinical significanceConventional luting agents, such as zinc phosphate cement, seem to provide comparable retention to resin luting agents for cementing custom milled zirconium oxide posts.     

Influence of TiO2 nanoparticles on the optical properties of resin composites

ObjectivesTo determine the influence of titanium dioxide (TiO₂) nanoparticle addition on the opalescence, color, translucency and fluorescence of experimental resin composites.MethodsA light curing resin matrix was made by mixing 60 wt.% Bis-GMA and 40 wt.% TEGDMA. Silane coated glass filler (mean particle size: 1.55 μm) was added in the ratio of 50 wt.% of the resin composites. A fluorescent whitening agent was also added (0.05 wt.%). TiO₂ nanoparticles (<40 nm) were added with the concentrations of 0, 0.1, 0.25 and 0.5 wt.%. Reflected and transmitted colors of 1 and 2 mm thick specimens were measured relative to the illuminant D65 with reflection spectrophotometers. Opalescence parameter (OP), color difference (ΔE*_ab), translucency parameter (TP), fluorescence parameter (FL), and fluorescence and opalescence spectra were calculated.ResultsFor the 1 mm thick specimens measured with 3 mm × 8 mm rectangular aperture, when the concentration of TiO₂ increased from 0% to 0.5%, OP increased from 2.4 to 18.0, TP decreased from 35.4 to 13.1, and fluorescence spectra remained unchanged. Color difference between these specimens was in the range of 3.4–6.6 ΔE*_ab units. OP values were significantly influenced by the thickness of the specimens and the configuration of the spectrophotometers (p < 0.05).SignificanceAddition of TiO₂ nanoparticles significantly increased the opalescence of resin composites while leaving the fluorescence spectra unchanged; however, it significantly decreased the translucency and also changed the color (p < 0.05). Resin composites with 0.1–0.25% TiO₂ nanoparticle would simulate the opalescence of human enamel.     

Effect of pulpal pressure on the microtensile bond strength of luting resin cements to human dentin

ObjectivesThe objectives of this study were to examine the effect of pulpal pressure on the microtensile bond strength (mTBS) of luting resin cements to human dentin and the permeability of dentin surfaces pre-treated with an adhesive and a self-etching primer.MethodsCylindrical composite blocks were luted with resin cements (RelyX ARC, 3M ESPE: ARC; Panavia F, Kuraray Medical Inc.: PF; RelyX Unicem, 3M ESPE: UN) in the absence or presence of simulated pulpal pressure. The application of Adper Single Bond 2 (3M ESPE) and ED primer 2.0 (Kuraray) was performed under 0 cm H₂O. After each resin cement was applied, the pulpal pressure group was subjected to 20 cm H₂O of hydrostatic pressure for 10 min during the initial setting period. Testing for mTBS was performed on 0.9 mm × 0.9 mm sectioned beams after 24 h water-storage. Scanning electron microscopy was performed to investigate the fractured surfaces after mTBS testing and additional dentin surfaces that were treated by an etchant, ED primer 2.0 and UN. Fluid permeability was measured on dentin surfaces that were applied with Adper Single Bond 2 and ED primer 2.0.ResultsApplication of pulpal pressure reduced mTBS significantly in groups ARC and PF. Porous bonding interfaces due to water permeability through the cured adhesive were observed on fractured surfaces. Dentin surfaces that were applied with the adhesive and the primer were more permeable than smear layer-covered dentin. The mTBS of UN was significantly lower than ARC and PF regardless of the absence/presence of pulpal pressure.SignificanceFluid permeation during the initial setting period deteriorated the bonding quality of resin cements.     

Color changes of polyetheretherketone (PEEK) and polyoxymethelene (POM) denture resins on single and combined staining/cleansing action by CIELab and CIEDE2000 formulas

PurposeThe purpose of study was to investigate the long-term effect of staining and/or cleansing solutions on the color stability of two non-metal removable partial denture materials.MethodsOne hundred disks (25×3 mm) of polyoxymethylene (POM) and polyetheretherketone (PEEK) were immersed in water, wine, coffee, cleanser and combo bath, simulating normal daily use. Color parameters in the CIELAB system was measured every 30 cycles up to 240 using a contact colorimeter and color differences estimated using ΔE_ab and ΔE₀₀ formulas. Two-way repeated measures ANOVAs and regression analyses were performed at α = 0.05.ResultsRegression analysis indicated a strong R² between color changes and number of cycles, for both materials. Tests of within-subjects effects for the ΔE_ab revealed significant differences among cycles and between the materials in the wine and coffee baths (p < 0.001). Significant materialXcycles interactions were also recorded with all staining baths. ΔE₀₀ values were lower than ΔE_ab up to 63.6%. Tests within and between-subjects effects for the ΔE₀₀ gave similar but not the same with ΔE_ab results.ConclusionsΔE₀₀ found to correlate well with ΔE_ab. Long term exposure of both materials showed a progressive discoloration in all except control baths. POM discolored more than PEEK in coffee, and combo baths but not in cleanser. Discoloration was smaller in combo bath (where a cleanser was also used) indicating the effectiveness of a cleanser to prevent long term discoloration of both materials.     

Influence of curing modes on the degree of conversion and mechanical parameters of dual-cured luting agents

PurposeTo investigate the effects of different curing modes, including tack cure, on the degree of conversion (DC) and mechanical parameters of dual-cured luting agents for all-ceramic restorations.MethodsImmediate light curing, intermittent light curing (2-s tack cure and a 1-min interval before the main cure), delayed light cuing (2-min delay) and chemical or no light curing were used to cure two dual-cured luting agents, RelyX Unicem and PermaCem 2.0, through a 1.5-mm thick lithium disilicate ceramic slide. DC (n = 3), micro-hardness (n = 5), shrinkage strain (n = 4) and shrinkage stress (n = 3) were measured under the aforementioned curing modes. The data were analyzed using two-way ANOVA and post-hoc Tukey HSD test, with the level of significance set at α = 0.05.ResultsFor both luting agents, all the light-curing modes produced similar final DC, but using chemical cure only could significantly reduce the DC. The mechanical parameters followed a similar pattern. There were positive but nonlinear correlations between DC and the other mechanical parameters, with the increase in these parameters with DC being slower initially.ConclusionsProvided adequate light curing is applied to a dual-cured luting agent, delaying the light curing or using a tack cure first to facilitate seating of a restoration may not have a significant impact on the luting agent’s final degree of conversion. However, using chemical cure only may result in inadequate cure of the luting agent and is recommended only for highly opaque restorations.     

Effect of denture cleansers on physical properties of heat-polymerized acrylic resin

PurposeThis study aimed to measure the color change, surface roughness and flexural strength of heat-polymerized acrylic resin after its immersion in denture cleansers, simulating a 180-day use.MethodsThirty disk-shaped (15 mm × 4 mm) and 30 rectangular samples (65 mm × 10 mm × 3.3 mm) were prepared from heat-polymerized acrylic resin and immersed in Corega Tabs, Bony Plus, and distilled water. Color measurements (ΔE) were determined by a portable colorimeter. A surface analyzer was used to measure the roughness before and after immersion (ΔRa). The flexural strength (S) was measured using a 3-point bending test. The ΔE values were submitted to statistical analysis by the Kruskal–Wallis test, followed by Dunn's Multiple Comparisons test. The ΔRa and S values were submitted to statistical analysis by ANOVA, followed by a Student–Newman–Keuls test (α = .05).ResultsThe color changes were significantly higher for the Corega Tabs than for the control group. The mean ΔE values quantified by the National Bureau of Standards (NBS) were classified as Trace (0.0–0.5). The Bony Plus group had significantly higher surface roughness than the other groups. Corega Tabs and Bony Plus groups presented lower flexural strength than the control group.ConclusionsAlthough the color changes after the immersion in denture cleansers were clinically insignificant, the Corega Tabs group showed higher color differences. The Bony Plus group showed significantly increased surface roughness. Both effervescent tablets Corega Tabs and Bony Plus significantly diminished the flexural strength of the acrylic resin.     

Tensile bond strength of cast commercially pure titanium dowel and cores cemented with three luting agents

PurposeThe purpose of this study was to compare the tensile strength of commercially pure titanium dowels and cores cemented with zinc phosphate or resin cements.MethodsTwenty-one extracted human canines were endodontically treated. The root preparations were accomplished using Largo reamers (10 mm in depth and 1.7 mm in diameter). Acrylic resin patterns for the dowel and cores were made, and specimens were cast in commercially pure titanium (n = 7) and divided in three groups: TZ–CP Ti dowels luted with zinc phosphate luting agent, TP–CP Ti dowels luted with Panavia F and TR–CP Ti dowels luted with RelyX U100. Tensile strengths were measured in a universal testing machine at a crosshead speed of 0.5 mm/min. The results (N) were statistically analyzed by ANOVA and Tukey tests (α = 0.01).ResultsThe ANOVA indicated that there were significant differences among the groups tested. A Tukey multiple comparison procedure was performed and revealed statistically significant higher retention values for the dowel luted with RelyX U100 when compared with zinc phosphate or Panavia F.ConclusionCast commercially pure titanium dowels and cores fixed with RelyX U100 cement presented superior bond strength retention when compared to zinc phosphate and Panavia F.     

Color change of some aesthetic dental materials: Effect of immersion solutions and finishing of their surfaces

ObjectivesThe purpose of this research was to evaluate the color change of five aesthetic dental materials, before and after immersion in distilled water and blue food color solution for 7 and 21 days, and to study the effect of finishing the surfaces on any color change.MethodsDisc shaped samples of five types of light curing composite (A2) (n = 10 samples/composite) were prepared and all samples were light-cured with a Plasma Arc light cure unit for ten seconds. One side of each sample disc was finished and polished with a Super-Snap system all samples. After 24 h, color measurements of each sample were conducted using a digital spectrophotometer. Five sample discs from each composite group were immersed in 30 ml of food color solution for 7 and 21 days, while the remaining five sample discs were immersed in 30 ml of distilled water as a control. Color measurements were repeated for all samples at 7 and 21 days after immersion. The color changes were statistically analyzed using t-tests within the same group. A result was considered statistically significant at α = 0.05.ResultsThe color differences (ΔE) ranged from 0.4 to 4.66 and statistically significant differences on the finished and unfinished surfaces were observed after immersion in the food color solution for 7 days. No significant differences were found in any group after immersion in the food color solution for 21 days. The Tetric EvoCeram and Arabesk groups showed less color differences after 7 and 21 days than other composites.ConclusionFinished composite surfaces showed less coloration than unfinished surfaces after 7 days, but all surfaces (finished and unfinished) were highly colored for all composite types after 21 days.     

Operator vs. material influence on clinical outcome of bonded ceramic inlays

ObjectiveThe aim of the present study was to clinically evaluate the suitability of Definite Multibond and Definite ormocer resin composite for luting of Cergogold glass ceramic inlays in a two-center trial involving two dentists.MethodsThirty-nine patients received 98 Cergogold inlays with at least one inlay luted with Definite Multibond/Definite (n = 45) and at least one inlay luted with Syntac/Variolink Ultra (n = 53) in a split mouth design. Treatments were carried out in two private practices by two operators (Operator A: n = 38; Operator B: n = 60). Forty-four cavities required caries profunda treatment, 23 cavities exhibited no enamel at the cervical margin. At baseline (2 months), and after 6, 14, 27, and 51 months of clinical service, the restorations were investigated according to modified USPHS criteria.ResultsThe drop-out rate was 3% after 4 years. After 48 months of clinical service, 21 restorations in 16 patients (9 luted with Definite, 12 with Variolink; 2 placed by operator A and 19 by operator B) had to be replaced due to inlay fracture (n = 11), tooth fracture (n = 4), hypersensitivities (n = 3), or marginal gap formation (n = 3). Seventy-seven inlays were in good condition (survival rate 89.9%, median survival time 4.2 years (95% confidence interval ±0.25; survival analysis by Kaplan–Meier algorithm). Survival rate after 4 years was 97.4% for operator A, and 75.4% for operator B (p = 0.002; Log Rank/Mantel-Cox) resulting in annual failure rates of 0.6% and 6.2%, respectively. The operators did not differently judge the clinical behaviour of the luting procedures (Mann–Whitney U-test, p > 0.05). Independent of the operator and the used luting system, the following criteria significantly changed over time: color match, marginal integrity, tooth integrity, inlay integrity, sensitivity, hypersensitivity, and X-ray control (p < 0.05; Friedman test). Significant differences between operators over the whole period were computed for the criteria marginal integrity, tooth integrity, and inlay integrity (p < 0.05, Mann–Whitney test). Differences between luting materials were only present during single recalls.SignificancesFor luting of ceramic inlays, only slight differences between the two luting systems were detectable. The operator influence on clinical outcome was clearly proven.     

Challenges in luting fibre posts: Adhesion to the post and to the dentine

Objective

To investigate the relationship between physicochemical interactions of resin luting cements with dentine and retention of fibre posts in root canals.

Self-adhesive resin cement versus zinc phosphate luting material: A prospective clinical trial begun 2003

ObjectivesThe literature demonstrates that conventional luting of metal-based restorations using zinc phosphate cements is clinically successful over 20 years. This study compared the clinical outcomes of metal-based fixed partial dentures luted conventionally with zinc phosphate and self-adhesive resin cement.MethodsForty-nine patients (mean age 54 ± 13 years) received 49 metal-based fixed partial dentures randomly luted using zinc phosphate (Richter & Hoffmann, Berlin, Germany) or self-adhesive resin cement (RelyX Unicem Aplicap, 3M ESPE, Germany) at the University Medical Center Regensburg. The core build-up material was highly viscous glass ionomer; the finishing line was in dentin. The study included 42 posterior, 5 anterior crowns and two onlays. Forty-seven restorations were made of precious alloys, 2 of non-precious alloys. The restorations were clinically examined every year. The clinical performance was checked for plaque (0–5; PI, Quigley-Hein), bleeding (0–4; PBI; Mühlemann) and attachment scores. The examination included pulp vitality and percussion tests.StatisticsMeans of scores, standard deviation, cumulative survival and complication rates were calculated using life tables.ResultsThe mean observation time was 3.16 ± 0.6 years (min: 2.0; max: 4.5 years). During that time no restoration was lost, no recementation became necessary. One endodontic treatment was performed in the self-adhesive composite group after 2.9 years. At study end bleeding (1.44 RelyX Unicem vs. 1.25 zinc phosphate) and plaque (1.64 RelyX Unicem vs. 1.0 zinc phosphate) scores showed no statistically significant difference.SignificanceThe self-adhesive resin cement performed clinically as well and can be used as easily as zinc phosphate cement to retain metal-based restorations over a 38-month observation period.     

Response of composite resins to preheating and the resulting strengthening of luted feldspar ceramic

ObjectiveThis study evaluated the influence of preheating different composite resins on their viscosity and strengthening yielded to ceramic.MethodsModulus of elasticity, Poisson’s ratio, and degree of CC conversion were measured for three restorative composite resins (Z100–microhybrid; Empress Direct–nanohybrid; Estelite Omega–supranano) and one photoactivated resin cement (RelyX Veneer). Viscosity was measured during a heating-cooling curve (25 °C–69 °C–25 °C) and also using isothermal analyses at 25 °C and 69 °C. Feldspar ceramic disks simulating veneers were bonded with the luting materials. Biaxial flexural strength, characteristic strength, and Weibull modulus were calculated at axial positions (z = 0 and z = −t₂) of the bilayers. Film thickness was measured and morphology at the bonded interfaces was observed. Data were statistically analyzed (α = 0.05).ResultsA gradual decrease in viscosity was noticed as the rheometer temperature gradually increased. Viscosity differences between the composite resins were large at the beginning of the analysis, but minor at 69 °C. At 25 °C, the composites were up to 38 times more viscous than the resin cement; at 69 °C the difference was 5-fold. CC conversion was similar between all resin-based agents. The resin cement yielded lower film thickness than the composites. All resin-based agents were able to infiltrate the ceramic porosities at the interface and strengthen the ceramic. However, the magnitude of the strengthening effect was higher for the preheated composite resins, particularly at z = −t₂.SignificanceSelection of composite resin impacts its response to preheating and the resulting viscosity, film thickness, and magnitude of ceramic strengthening.     

Effect of different composite modulation protocols on the conversion and polymerization stress profile of bulk-filled resin restorations

ObjectiveThe aim of this in vitro study was to test the effect of different composite modulation protocols (pre-heating, light-curing time and oligomer addition) for bulk filling techniques on resin polymerization stress, intra-pulpal temperature change and degree of conversion.MethodsClass I cavities (4 mm depth × 5 mm diameter) were prepared in 48 extracted third molars and divided in 6 groups. Restorations were completed with a single increment, according to the following groups: (1) Filtek Z250XT (room temperature – activated for 20 s); (2) Filtek Z250XT (at room temperature – activated for 40 s); (3) Filtek Z250XT (pre-heated at 68 °C – activated for 20 s); (4) Filtek Z250XT (pre-heated at 68 °C – activated for 40 s); (5) Filtek BulkFill (at room temperature – activated for 20 s); (6) Filtek Z250XT (modified by the addition of a thio-urethane oligomer at room temperature – activated for 40 s). Acoustic emission test was used as a real-time polymerization stress (PS) assessment. The intra-pulpal temperature change was recorded with a thermocouple and bottom/top degree of conversion (DC) measured by Raman spectroscopy. Data were analyzed with one-way ANOVA/Tukey's test (α = 5%).ResultsPre-heating the resin composite did not influence the intra-pulpal temperature (p = 0.077). The thio-urethane-containing composite exhibited significantly less PS, due to a lower number of acoustic events. Groups with pre-heated composites did not result in significantly different PS. Filtek BulkFill and the thio-urethane experimental composite presented significantly higher DC.SignificanceResin composite pre-heating was not able to reduce polymerization stress in direct restorations. However, thio-urethane addition to a resin composite could reduce the polymerization stress while improving the DC.     

Optical influence of the type of illuminant,substrates and thickness of ceramic materials

ObjectivesThe present study is an instrumental evaluation of the optical influence of the type of illuminant, substrate and different thickness on the color of dental ceramics.MethodsThirty ceramic disks were prepared from IPS-Empress and IPS-Empress2 in three different thicknesses (1.5, 2.0 and 2.5 mm). Disks made of composite resin; silver–palladium alloy and gold were used as substrates. The disks with a 1.5 mm thickness were placed on a neutral gray photographic paper and measured with a spectrophotometer under three illuminants: daylight (D65), incandescent light (A) and fluorescent light (F6). All ceramic disks were combined with the substrate disks and a spectrophotometer was used to measure the coordinates of lightness (L*) and chromaticity (a* and b*). Two-way ANOVA (p < 0.05) was used to analyze the combinations of ceramics, substrates and illuminants tested considering the coordinates of lightness (L*) and chromaticity (a* and b*), and also differences of color (ΔE), lightness (ΔL*), chromaticity values (Δa* and Δb*).ResultsFor the illuminants tested, the results present significant differences for coordinates of chromaticity a* and b*, suggesting a metamerism effect. In combination with the substrates, the results present statistical differences in all the tested conditions, especially where there is no ceramic substructure.SignificanceThe presence of discolored tooth remnants or metallic posts and cores can interfere with the desired aesthetic result, based on the selection of color aided by a single luminous source. Thus, the substrate color effect, thickness of the ceramic materials and type of illuminant are important factors to be considered during the clinical application of the ceramic systems.     

Clinical evaluation of perceptibility of color differences between natural teeth and all-ceramic crowns

ObjectivesColor matching still remains as one of the most challenging tasks in clinical dentistry. With the advancement of intraoral color matching instruments the importance of the development of color thresholds becomes increasingly important. The objective of this study was to set a gold standard for the color difference (ΔE) at which all-ceramic crowns cannot be distinguished from natural teeth.MethodAll-ceramic crowns with a zirconia coping (LAVA, 3M ESPE, St. Paul, MN, USA) and layered porcelain (Cerabien CZR, Noritake, Nagoya, Japan) fabricated to match contralateral maxillary central incisors were assessed by experienced observers. Eleven all-ceramic crowns (AC) were assessed as “excellent/perfect matches;” these crowns were then measured using a spectrophotometer and compared to their natural counterparts. Unrestored natural maxillary teeth (NT) were compared to unrestored contralateral teeth in 22 subjects. Six areas were measured in both groups to determine color differences (ΔE*).ResultsMean ΔE* value between the restorations and natural teeth was 1.6. Mean ΔE* between contralateral natural teeth was 0.9. Incisal areas of natural teeth exhibited greater differences in color than other compared areas.ConclusionA ΔE* = 1.6 represented the color difference that could not be detected by the human eye.     

Effect of water aging on microtensile bond strength of dual-cured resin cements to pre-treated sintered zirconium-oxide ceramics

ObjectivesTo evaluate the hydrolytic stability of different dual-cure resin cements when luted to zirconia ceramic.MethodsEighteen cylinder-shaped zirconia blocks (Cercon Zirconia, Dentsply) were conditioned with: Group 1, no treatment; Group 2, sandblasting (125 μm alumina–Al₂O₃-particles); Group 3, tribochemical silica coating (50 μm silica-modified Al₂O₃ particles). Ceramic blocks were duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent). Composite disks were luted to pre-treated ceramic surfaces using: (1) Clearfil Esthetic Cement (CEC; Kuraray); (2) Rely X Unicem (RXU; 3M ESPE); (3) Calibra (CAL; Dentsply Caulk). After 24 h, bonded samples were cut into microtensile sticks (1 mm²). Half of the sticks were loaded in tension until failure (cross-head speed of 0.5 mm/min). The remaining half was tested after 6 months of water storage at 37 °C. Data was analyzed with three-way ANOVA and Tukey’s test (P <0.05). Fractographic analysis was performed by SEM.ResultsAfter 24 h, bond strength of CEC to zirconia was significantly higher than that of RXU and CAL, independently from the ceramic pre-treatment (P <0.001). Using CAL, all samples failed prematurely except when luting to sandblasted surfaces. After 6 months of water aging, bond strength of CEC significantly decreased. RXU did not significantly alter bond strengths. Adhesion of sandblasted specimens luted with CAL fell over time. Micromorphological alterations were evident after water storage.SignificanceResin–ceramic interfacial longevity depended on cement selection rather than on surface pre-treatments. CEC and RXU were both suitable for luting zirconia. Water aging played an important role in the durability of zirconia-to-composite chemical bonds.     

Influence of sandblasting granulometry and resin cement composition on microtensile bond strength to zirconia ceramic for dental prosthetic frameworks

ObjectivesTo evaluate the effect of the particle size of sandblasting and the composition of the resin cement on the microtensile bond strength (MTBS) to zirconia.MethodsForty zirconia blocks (Cercon, Dentsply) were polished and randomly treated as follows: Group 1 (NT): no treatment; Group 2 (APA-I): airborne particle abrasion (Cobra, Renfert) using 25-μm aluminium-oxide (Al₂O₃)-particles; Group 3 (APA-II): APA with 50-μm Al₂O₃-particles; and Group 4 (APA-III): APA using 110-μm Al₂O₃-particles. Ceramic blocks were duplicated in composite resin. Samples of each pretreatment group were randomly divided into two subgroups depending on the resin cement used for bonding the composite disks to the treated zirconia surfaces. Subgroup 1 (PAN), which was a 10-MDP-containing luting system, used Clearfil Ceramic Primer plus Panavia F 2.0 (Kuraray) and Subgroup 2 (BIF) used Bifix SE (VOCO) self-adhesive cement. After 24 h, bonded specimens were cut into 1 ± 0.1 mm² sticks. MTBS values were obtained using a universal testing machine (cross-head speed = 0.5 mm/min). Failure modes were recorded and the interfacial morphology of the debonded microbars was SEM-assessed. Two-way ANOVA, Student–Newman–Keuls tests, and the step-wise linear regression analysis were performed with the MTBS being the dependent variable (p < 0.05).ResultsDespite the sandblasting granulometry, PAN bonded to air-abraded surfaces attained the highest MTBS and frequently showed mixed fractures. BIF recorded no significant differences in MTBS depending on the conditioning method, and registered the highest rates of premature and adhesive failures.ConclusionsThe 10-MDP-containing luting system seems to be the most suitable to bond zirconium-oxide ceramic, mainly after sandblasting.     

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.MethodsModel composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level.ResultsComposites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values.SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.     

Influence of pigments and opacifiers on color stability of silicone maxillofacial elastomer

ObjectivesTo determine the effects of opacifiers and silicone pigments on the color stability of silicone A-2000 maxillofacial prosthetic elastomers subjected to artificial aging.MethodsSeventy-five groups (n = 5) were made by various combinations (5%, 10%, and 15%) of four dry earth opacifiers (Georgia kaolin, Gk; calcined kaolin, Ck; Artskin white, Aw; titanium white dry pigment, Td); and 1 silicone pigment white (Sw) with one of 5 silicone pigments (no pigment (control), red (Pr), yellow (Py), burnt sienna (Po), and a mixture of Pr + Py + Po). A reflection spectrophotometer was used for color measurements. Color differences (ΔE*) between baseline and after an energy exposure of 450 kJ/m² in an artificial aging chamber were calculated. A ΔE* = 3.0 was used as 50:50% acceptability threshold in result interpretation, while ΔE* = 1.1 was used as 50:50% perceptibility threshold. Means were compared by Fisher's PLSD intervals at the 0.05 level of significance. Color differences after aging were subjected to three-way analysis of variance.ResultsYellow ochre mixed with all opacifiers at all intervals had increased ΔE* values significantly from 0.7–2.1 up to 3.8–10.3. When mixed groups were considered, at 5%, Gk exhibited the smallest color changes, followed by Td < Aw = Sw < Ck, respectively. At 10%, Aw < Td < Gk < Sw = Ck. At 15%, Td < Aw < Gk = Sw < Ck (< indicates p < 0.0001 and = indicates p > 0.05). The smallest color differences, observed for opacifier groups, were recorded for Gk at 5%, and Td and Aw at 10% and 15%. Overall, 15% Td exhibited the smallest, whereas 5% Ck exhibited the most pronounced color change after artificial aging. All ΔE* values were below the 50:50% acceptability threshold, indicating acceptable color stability. Color differences for 10% and 15% of Aw and Td were below 50:50% perceptibility thresholds, indicating excellent color stability.ConclusionSilicone pigments mixed with 10% and 15% Artskin white and titanium white dry pigment opacifiers protected silicone A-2000 from color degradation over time. Yellow silicone pigment significantly affected color stability of all opacifiers especially silicone pigment white and calcined kaolin.     

Influence of surface treatments and resin cement selection on bonding to densely-sintered zirconium-oxide ceramic

ObjectivesTo evaluate the effect of surface conditioning on the microtensile bond strength of zirconium-oxide ceramic to dual-cured resin cements.MethodsEighteen cylinder-shaped zirconium-oxide ceramic blocks (Cercon^® Zirconia, Dentsply) were treated as follows: (1) Sandblasting with 125 μm aluminum-oxide (Al₂O₃) particles; (2) tribochemical silica coating using 50 μm Al₂O₃ particles modified by silica; (3) no treatment. Each ceramic cylinder was duplicated in composite resin (Tetric Evo Ceram, Ivoclar-Vivadent) using a silicon mold. Composite cylinders were bonded to conditioned ceramics using: (1) Calibra (Densply Caulk); (2) Clearfil Esthetic Cement (Kuraray); (3) Rely × Unicem (3 M ESPE). After 24 h bonded specimens were cut into microtensile sticks that were loaded in tension until failure. Data were analyzed using two-way ANOVA and Student–Newman–Keuls test for multiple comparisons (p < 0.05). Failure mode was recorded and the interfacial morphology of debonded specimens was observed using a scanning electron microscope (SEM). Surface topography and ceramic average surface roughness were analyzed under an atomic force microscope (AFM).ResultsSignificant changes in zirconia surface roughness occurred after sandblasting (p < 0.001). Bond strength of Clearfil cement to zirconia was significantly higher than that of Rely × Unicem and Calibra, regardless of the surface treatment (p < 0.001). When using Calibra, premature failures occurred in non-treated and silica coated zirconia surfaces.SignificanceThe phosphate monomer-containing luting system (Clearfil Esthetic Cement) is recommended to bond zirconia ceramics and surface treatments are not necessary.