Effect of different surface treatment protocols on the bond strength between lithium disilicate and resin cements.

Because the use of hydrofluoric acid (HF) poses health risks if handled improperly, many clinicians prefer to have the ceramic restorations pre-etched in dental laboratories. However, during the try-in procedure, the pre-etched glass-ceramic restorations may be contaminated with saliva resulting in reduced bond strength. This in-vitro study aimed to investigate the effect of different surface treatments on the bond strength of lithium disilicate (LD) glass-ceramic restorations (IPS e.max Press, Ivoclar Vivadent) to two resin cements. One-hundred eighty blocks (4X4X3mm) of LD glass-ceramic were divided into twelve groups (n = 15), of which six received Variolink Esthetic DC (VE) cement and six received RelyX Ultimate (RU) cement, following the surface treatments: G1) Control: Hydrofluoric Acid + Silane (HF + Sil); G2) Hydrofluoric Acid + Saliva + Silane (HF + S + Sil); G3) Hydrofluoric Acid + Saliva + Ivoclean + Silane (HF + S + IC + Sil); G4) Hydrofluoric Acid + Saliva + Phosphoric Acid + Silane (HF + S + P + Sil); G5) Hydrofluoric Acid + Saliva + Monobond Etch & Prime (HF + S + EP); G6) Monobond Etch & Prime (EP). Following treatment, a resin-cement cylinder (2.3 mm diameter) was built on the glass-ceramic surface, photocured (20 s), stored in distilled water (37 °C, 24 h) and submitted to the shear bond strength test. Bond strength data (MPa) were subjected to two-way ANOVA and Tukey (α = 0.01). Cement type and surface treatment had a significant effect on the bond strength (p < 0.001) (Table 4). Single-step Monobond Etch & Prime (EP) significantly improved the bond strength of resin-cements to glass-ceramic with and without saliva contamination.

Post-fatigue fracture load, stress concentration and mechanical properties of feldspathic, leucite- and lithium disilicate-reinforced glass ceramics.

Objective: To evaluate the mechanical properties of different CAD/CAM ceramic systems and the post-fatigue fracture and stress distribution when used as cemented crowns. Materials and methods: Sixty (60) CAD/CAM monolithic crowns were milled using three different ceramic materials (FD - Feldspathic [Vita Mark II]), LE - Leucite-based ceramic [IPS Empress CAD] and LD - Lithium Disilicate [IPS e.max CAD]) and adhesively cemented on resin composite dyes. Specimens were stored in distillated water (37 °C) for 7 days. After, half of the crowns were submitted to immediate fracture load test while the other half was submitted to fatigue cycling. The average cement layer of approximately 80 µm was assessed using scanning electron microscopy (SEM). The average thickness was used in the three-dimensional (3D) Finite Element Analysis (FEA). For each ceramic material, the density, Poisson ratio, shear modulus, Young modulus, fracture toughness, and true hardness were assessed (n = 3). The data was used to assess the Maximum Principal Stress throughout 3D-FEA according to each material during load to fail and post-fatigue. Data were submitted to two-way ANOVA and Tukey test (α = 0.05). Results: LD showed the highest compression load, density, shear modulus, Young modulus, fracture toughness and true hardness values. While LE presented the lowest mechanical properties values. There is no difference in the Poisson ratio between the evaluated ceramics. Conclusion: LD was susceptible to aging process but presented stronger physicomechanical properties, showing the highest post-fatigue fracture load and highest stress magnitude.

Marginal adaptation of CAD-CAM onlays: Influence of preparation design and impression technique.

STATEMENT OF PROBLEM: Factors that may affect the marginal adaptation of computer-aided design and computer-aided manufacturing (CAD-CAM) restorations include preparation design, impression technique, and CAD-CAM system. The influence of impression technique and preparation design on CAD-CAM partial coverage restorations has not been fully addressed. PURPOSE: The purpose of this in vitro study was to investigate the influence of direct and indirect digital scanning techniques and 2 preparation designs on the marginal adaptation of CAD-CAM onlays. MATERIAL AND METHODS: Two mesio-occlusal buccal onlay preparations with reduction of the mesiobuccal cusp were made: conventional preparation (CP) with a 1.2-mm modified shoulder margin and modified preparation (MP) flat cuspal reduction without shoulder. Virtual models were generated from each preparation by using a digital scanner (BlueCam; Dentsply Sirona) from the plastic teeth (direct digital scan) or from the stone dies (indirect digital scan). Onlays were designed using a CAD-CAM system (CEREC 4.0; Dentsply Sirona), and nanoceramic resin blocks (Lava Ultimate Restorative; 3M ESPE) were milled using the CEREC MCX milling machine. Marginal discrepancy was evaluated using an optical stereomicroscope at ×25 magnification in 18 locations distributed along the margins of the preparation. The data were analyzed by using 3-way ANOVA followed by the Tukey HSD test (α=.05). RESULTS: CP presented a statistically significant reduced average marginal adaptation (59 ±50 µm) than did MP (69 ±58 µm) (P<.001). The Tukey HSD test showed the presence of a significantly larger marginal discrepancy in the mesial and buccal locations of MP when compared with CP. Regarding impression techniques, the buccal location presented the smallest average marginal discrepancy in restorations fabricated with indirect impression when compared with direct impression (42 ±33 µm and 60 ±39 µm) (P<.001). CONCLUSIONS: The results showed that conventional preparation with a modified shoulder margin presented improved marginal adaptation compared with modified preparation with flat cuspal reduction. Direct and indirect digital scanning techniques produced restorations within a clinically acceptable range; however, the indirect scanning technique resulted in the fabrication of restorations with superior marginal adaptation on the buccal location.

Retrospective clinical evaluation of ceramic onlays placed by dental students.

STATEMENT OF PROBLEM: Indirect restorations with partial or complete occlusal surface coverage have been recommended to restore teeth with weakened walls in order to prevent cusp fracture. The success of these restorations when performed by dental students is unknown. PURPOSE: The purpose of this retrospective study was to evaluate the clinical performance of adhesively bonded ceramic onlay restorations placed by third- and fourth-year dental students. MATERIAL AND METHODS: Sixty-five ceramic onlays were placed in patients between 2009 and 2015. The onlays were laboratory or chairside fabricated with a computer-aided design and computer-aided manufacturing (CAD-CAM) system, using either IPS e.max Press or IPS e.max CAD. An adhesive technique and luting composite resin agent were used to cement the restorations. Thirty-seven onlays were evaluated clinically using the modified United States Public Health Service (USPHS) criteria. Data were statistically analyzed using the Cox proportional hazards model to compare tooth type and failures and the Fisher exact and McNemar tests to compare the USPHS criteria for significant differences (α=.05). Survival probability was calculated using the Kaplan-Meier algorithm. RESULTS: Five onlays were considered to be failures and needed replacement. According to the Kaplan-Meier analysis, the estimated survival rate was 96.3% after 2 years and 91.5% at 4 years. All 5 of the failures occurred on molars (13.5%) and none on premolars (P=.025). A statistically significant difference was found for marginal discoloration between onlays placed within 0 to 3 years and 3 to 6 years (P<.05) but no differences between any other criteria. CONCLUSIONS: Ceramic onlays placed by dental students demonstrated acceptable long-term clinical performance.

Clinical evaluation of ceramic inlays and onlays fabricated with two systems: 12-year follow-up.

OBJECTIVES: The aim of this study was to evaluate the 12-year clinical performance of sintered (Duceram, Dentsply-Degussa, Dentsply International Inc., PA, USA)-D and pressable (IPS Empress, Ivoclar-Vivadent, Schaan, Leichtenstein)-IPS ceramic inlay and onlay restorations. METHODS: Eighty-six restorations were placed in 35 patients with a median age of 33 years by a single operator. The restorations were luted with dual-cured resin luting material (Variolink II, Ivoclar-Vivadent, Schaan, Leichtenstein) and Syntac Classic adhesive under rubber dam. The evaluations were conducted by two independent investigators at the baseline, 1, 2, 3, 5, and 12 years using the modified USPHS criteria. RESULTS: At the 12-year recall, 22 patients were evaluated (62.86 %), totalling 48 (55.81 %) restorations. Seven restorations were fractured (one from Duceram and six from IPS), eight restorations presented secondary caries (three from Duceram and five from IPS), nine restorations showed unacceptable defects at the restoration margin and needed repair or replacement (two from Duceram and seven from IPS), and four IPS restorations presented pulp sensitivity. CONCLUSION: Chi-square and Mann-Whitney tests revealed that IPS Empress system showed the best results for color match and surface texture (p < 0.05) but a significant worse result for fracture (p = 0.05). Wilcoxon test showed significant differences in relation to color match, surface texture, marginal discoloration, and marginal integrity between the baseline and 12-year recall for both ceramic systems. CLINICAL SIGNIFICANCE: This long-term clinical study observed that the main reasons for failure of ceramic restorations were related to fracture, recurrent caries, and decreased marginal integrity over time. Carefully monitoring of the ceramic-tooth interface may extend their clinical longevity.

Effect of ceramic thickness and shade on mechanical properties of a resin luting agent.

PURPOSE: This study aimed to investigate the influence of ceramic thickness and shade on the Knoop hardness and dynamic elastic modulus of a dual-cured resin cement. MATERIALS AND METHODS: Six ceramic shades (Bleaching, A1, A2, A3, A3.5, B3) and two ceramic thicknesses (1 mm, 3 mm) were evaluated. Disk specimens (diameter: 7 mm; thickness: 2 mm) of the resin cement were light cured under a ceramic block. Light-cured specimens without the ceramic block at distances of 1 and 3 mm were also produced. The Knoop hardness number (KHN), density, and dynamic Young's moduli were determined. Statistical analysis was conducted using ANOVA and a Tukey B rank order test (p = 0.05). RESULTS: The bleaching 1-mm-thick group exhibited significantly higher dynamic Young's modulus. Lower dynamic Young's moduli were observed for the 3-mm-thick ceramic groups compared to bleaching 3-mm-thick group, and no difference was found among the other 3-mm groups. For the KHN, when A3.5 3-mm-thick was used, the KHN was significantly lower than bleaching and A1 1-mm-thick ceramic; however, no difference was exhibited between the thicknesses of the same shade. CONCLUSIONS: The dual-cured resin cement studied irradiated through the 1-mm-thick ceramic with the lightest shade (bleaching ceramic) exhibited a better elastic modulus, and there was no effect in KHN of the resin cement when light cured under different ceramic shades and thicknesses (1 and 3 mm), except when the A3.5 3-mm-thick ceramic was used. CLINICAL SIGNIFICANCE: Variolink II irradiated through ceramic with the lowest chroma exhibited the highest elastic modulus; therefore, the light activation method might not be the same for all clinical situations.

The effect of prophylactic powders on the surface roughness of enamel.

OBJECTIVE: To assess the effect of dental prophylactic methods on the surface roughness of enamel. METHODS: Enamel specimens (150) were sectioned from human molars and mounted on resin bases. This work consisted of two parts. In the first, there were eight groups (n = 15). Three groups were treated with two air-polishing devices (AP)­LM-ProPower AirLED (Mode 1 and 2) and EMS Air-Flow Handy 2­for 30 seconds and sodium bicarbonate prophylactic powder, and three other groups were treated with the two air-polishing devices using microsphere calcium carbonate prophylactic powder. The seventh group was treated with rubber-cup polishing using medium and fine grits (Oral-B prophy paste), and the eighth (control) was enamel with no surface treatment. In the second part of the work, two groups (n = 15) were subjected to treatment with the LM unit (Mode 2) and each of the abrasive powders for 5 seconds. Surface roughness (Ra) of samples was assessed using a mechanical stylus profilometer and scanning electron microscope (SEM). Statistical analysis of the data was conducted using two-way ANOVA and Tukey HSD (honest significant difference) rank order test at P = 0.05. RESULTS: Both prophylactic methods resulted in a statistically significant increase in surface roughness (P < 0.05) when compared to untreated specimens. All air-abrasive treatments for 30 seconds resulted in an increase in roughness compared to rubber-cup prophylaxis (P < 0.05). However, AP with calcium carbonate and the sodium bicarbonate for 5 seconds produced results that were not significantly different from rubber-cup prophylaxis (P > 0.05). CONCLUSION: Both types of prophylactic dental cleaning have an effect on surface roughness. The abrasiveness of APs depends upon the length of treatment and the type of powder used.

Overview of CEREC CAD/CAM chairside system.

This article describes CAD/CAM technology used in dentistry and different restorative materials used in conjunction with adhesive cementation with particular attention given to the evolution of the CEREC system, as well as various ceramics developed for this system. Advantages and limitations of materials and technique are also discussed.

Microleakage and microtensile bond strength of silorane-based and dimethacrylate-based restorative systems.

OBJECTIVE: To evaluate the microleakage and bond strengths (microTBS) of silorane-based (SBC) and dimethacrylate-based (DBC) restorative systems. The null hypotheses are: 1) there is no difference in microleakage between the resin composites and the adhesive systems tested at the enamel and dentin margins; 2) there is no significant difference in microTBS between the composite restorative systems using self-etch and etch-and-rinse adhesive versions. METHODS AND MATERIALS: Microleakage: Class V cavity preparations with cervical margin in dentin were performed on pristine extracted human molars and were randomly distributed among the following three groups: Group 1-DBC/etch-and-rinse adhesive system (Filtek™ Supreme Ultra/Adper™ Single Bond Plus, 3M ESPE, www.3MESPE.com); Group 2-SBC/self-etch adhesive (Filtek LS Low Shrink Posterior Restorative System/LS self-etch adhesive, 3M ESPE); Group 3-DBC/self-etch adhesive (Filtek Supreme Ultra/ Adper Easy Bond Self-Etch, 3M ESPE). Restorations were thermocycled and immersed in 0.2 percent methylene blue dye for 24 hours. Samples were assessed visually under 10x magnification; microTBS: Bond sticks (0.9 mm2) were prepared from each group and tested on a universal testing machine. RESULTS: The Kruskal-Wallis test revealed no significant difference in microleakage among the experimental groups at the enamel margin (P=0.191). At the dentin margins, silorane/self-etch restorative system showed significantly less leakage than the dimethacrylate/etch-and-rinse restorative system (P=0.008). Tukey's B rank order test showed that the dimethacrylate/etch-and-rinse restorative system presented the highest microTBS. CONCLUSIONS: SBC/self-etch system showed less microleakage at the dentin margins, while DBC/etch-and-rinse system presented higher bond strength.

CAD/CAM technology and esthetic dentistry: a case report.

Advances in dental materials as well as in computer technology have made CADCAM-fabricated restorations not just possible in dentistry but plentiful. When using CADCAM systems, operators can fabricate restorations from several materials, including ceramics, metal alloys, and various composites. This case report describes the replacement of a porcelain-layered zirconia-based (coping) crown on a left lower cuspid that presented with a veneering ceramic chipping on a lithium-disilicate CADCAM-fabricated crown. It demonstrates how all-ceramic systems offer a promising alternative in the restoration of anterior teeth.

Shear bond strength of resin cement bonded to alumina ceramic after treatment by aluminum oxide sandblasting or silica coating.

PURPOSE: To evaluate the shear bond strength and bond durability between a dual-cured resin cement (RC) and a high alumina ceramic (In-Ceram Alumina), subjected to two surface treatments. MATERIALS AND METHODS: Forty disc-shaped specimens (sp) (4-mm diameter, 5-mm thick) were fabricated from In-Ceram Alumina and divided into two groups (n = 20) in accordance with surface treatment: (1) sandblasting by aluminum oxide particles (50 µm Al(2) O(3) ) (SB) and (2) silica coating (30 µm SiO(x) ) using the CoJet system (SC). After the 40 sp were bonded to the dual-cured RC, they were stored in distilled water at 37°C for 24 hours. After this period, the sp from each group were divided into two conditions of storage (n = 10): (a) 24 h-shear bond test 24 hours after cementation; (b) Aging-thermocycling (TC) (12,000 times, 5 to 55°C) and water storage (150 days). The shear test was performed in a universal test machine (1 mm/min). RESULTS: ANOVA and Tukey (5%) tests noted no statistically significant difference in the bond strength values between the two surface treatments (p = 0.7897). The bond strengths (MPa) for both surface treatments reduced significantly after aging (SB-24: 8.2 ± 4.6; SB-Aging: 3.7 ± 2.5; SC-24: 8.6 ± 2.2; SC-Aging: 3.5 ± 3.1). CONCLUSION: Surface conditioning using airborne particle abrasion with either 50 µm alumina or 30 µm silica particles exhibited similar bond strength values and decreased after long-term TC and water storage for both methods.

Diametral tensile strength of composite core material with cured and uncured fiber posts.

The aim of this study was to determine the influence of different types of posts and post head designs on the fracture resistance of a composite resin core material using the diametral tensile strength (DTS ). Seventy-five disc specimens were prepared using a composite core and prefabricated glass fiber posts and were divided into four test groups and one control group (n=15). The use of fiber posts reduced the DTS of the composite core material; the DTS value of the control material was significantly higher (p=0.05) than all of the test groups.

Accuracy of mechanical torque devices for implants used in Brazilian dental offices.

The purpose of this study was to determine the accuracy of mechanical torque devices in delivering target torque values in dental offices in Salvador, Brazil. A team of researchers visited 16 dental offices, and the clinicians applied torque values (20 and 32 Ncm) to electronic torque controllers. Five repetitions were completed at each torque value and data were collected. When 20 Ncm of torque was used, 62.5% of measured values were accurate (within 10% of the target value). For 32 Ncm, however, only 37.5% of these values were achieved. Several of the tested mechanical torque devices were inaccurate.

Hardening of a dual-cure resin cement using QTH and LED curing units.

OBJECTIVE: This study evaluated the surface hardness of a resin cement (RelyX ARC) photoactivated through indirect composite resin (Cristobal) disks of different thicknesses using either a light-emitting diode (LED) or quartz tungsten halogen (QTH) light source. MATERIAL AND METHODS: Eighteen resin cement specimens were prepared and divided into 6 groups according to the type of curing unit and the thickness of resin disks interposed between the cement surface and light source. Three indentations (50 g for 15 s) were performed on the top and bottom surface of each specimen and a mean Vickers hardness number (VHN) was calculated for each specimen. The data were analyzed using two-way ANOVA and Tukey-Kramer test was used for post-hoc pairwise comparisons. RESULTS: Increased indirect resin disk thickness resulted in decreased mean VHN values. Mean VHN values for the top surfaces of the resin cement specimens ranged from 23.2 to 46.1 (QTH) and 32.3 to 41.7 (LED). The LED curing light source produced higher hardness values compared to the QTH light source for 2- and 3-mm-thick indirect resin disks. The differences were clinically, but not statistically significant. Increased indirect resin disk thickness also resulted in decreased mean VHN values for the bottom surfaces of the resin cement: 5.8 to 19.1 (QTH) and 7.5 to 32.0 (LED). For the bottom surfaces, a statistically significant interaction was also found between the type of curing light source and the indirect resin disk thickness. CONCLUSION: Mean surface hardness values of resin cement specimens decreased with the increase of indirect resin disk thickness. The LED curing light source generally produced higher surface hardness values.

Adhesive cementation of etchable ceramic esthetic restorations.

This article describes the different materials and techniques that are used for adhesive cementation. Particular attention is given to treatments suitable for dentin, as well as the selection of surface treatments for various restorative materials. Factors related to the durability and stability of the adhesive process, as well as the clinical and laboratory procedures required for cementation, are also discussed.

Intensity of quartz-tungsten-halogen light polymerization units used in dental offices in Brazil.

PURPOSE: To determine the intensity of quartz-tungsten-halogen light polymerization units in dental offices in El Salvador, Brazil. MATERIALS AND METHODS: A team of researchers visited 100 offices in 2003. The team measured light intensity with a radiometer. The age and make of the units and the availability of light meters were recorded. RESULTS: One hundred twenty quartz-tungsten-halogen units were tested. Intensity ranged from 10 to 1,000 mW/cm2, with mean of 255.8 mW/cm2. Almost half (48%) of the units had values equal to or less than 200 mW/cm2. Their age ranged from 1 to 21 years. None of the offices had light meters. CONCLUSIONS: Clinicians should periodically monitor light intensity and carry out maintenance on their light polymerization units.

Hardening of dual-cure resin cements and a resin composite restorative cured with QTH and LED curing units.

OBJECTIVE: The aim of this study was to determine the effects of light intensity and type of light unit (quartztungsten-halogen [QTH] or light-emitting diode [LED]) on the hardening of various resin cements and a resin composite restorative. METHODS: Disk specimens were prepared from 4 dual-cured resin cements (Variolink II, Calibra, Nexus 2 and RelyX ARC). Two QTH light-curing units (Visilux 2, at 550 mW/cm2, and Optilux 501, at 1,360 mW/cm2) and a LED unit (Elipar FreeLight, at 320 mW/cm2) were used for curing. Specimens were light-cured or dual-cured for 10, 30 or 40 seconds with 1 of the 3 light units (curing applied to upper surface only) and were tested 24 hours after curing. Additional cement specimens were self-cured and tested at 15, 30 and 60 minutes and at 24 hours. Testing consisted of measurement of Knoop hardness number (KHN) for each specimen. Six KHN values were obtained for the upper surface only of the various cement specimens in each test group. Disk specimens 2.5 mm thick were also prepared from a resin composite restorative (XRV Herculite). These were light-cured as above, and KHN measurements were obtained for both the upper and the lower surfaces. Mean KHNs were determined, and data were analyzed with analysis of variance. RESULTS: The groups were significantly different (p < 0.05). High-intensity light curing resulted in the highest KHN values for all materials with any of the 3 light-curing times. For the cements, LED light curing (with both dual-curing and light-curing modes) resulted in hardness values similar to those achieved with conventional QTH light curing, although there were some exceptions. However, both LED and conventional QTH light curing resulted in inferior hardening of lower surfaces of the XRV Herculite specimens at the 3 curing times. For all cements except Nexus 2, self-curing resulted in significantly lower hardness values than dual curing. The self-curing mechanism of Variolink II cement needed a longer time to activate than those of the other cements. CONCLUSIONS: High-intensity light curing and longer curing times resulted in the highest KHNs. The LED curing unit was associated with the lowest hardness values for lower surfaces of the resin composite restorative.