A survey of amalgam use to guide dental education curriculums.

OBJECTIVES: To identify behavioral, preferential, and professional factors influencing the use of amalgam in private practices; and to compare the incidence of the placement of amalgam versus composite resin restorations in the province of Ontario and its pedagogical implications on dental curricula. METHODS: Participants responded anonymously to a 23-question online survey about their current use of dental amalgam and composite resins as well as their opinions regarding both dental materials. The explanatory variables were associated bivariately with the outcome variables, and the most significant predictors were identified using the multivariate analysis. RESULTS: Higher percentages of amalgam use were reported among clinicians who trained in Canada only (P = .009), who graduated before 1980 (p = <.001) and who work outside private practice (p = <.001). Familiarity with amalgam was higher among clinicians who are female (p = <.001), older (p = <.001), trained only in Canada (p = .017), who graduated prior to 2000 (p = <.001), and who work in locations with populations over 100,000 (p = .042). Familiarity with composite resin was higher among clinicians who graduated more recently (p = .002). A higher percentage of females (p = <.001), younger clinicians (p = <.001), recent graduates (p = <.001), and clinicians who work in private practice (p = .043) suggested that over 50% of dental student training time be allocated to amalgam. CONCLUSIONS: Decreased amalgam use was reported by later dental graduates and private practitioners; this may be impacted by familiarity with dental amalgam. As amalgam remains a safe and effective dental material, its removal may not be prudent. Dental educators play a crucial role in the future of amalgam opinion and use.

Effect of Training Method on Dental Students' Light-Curing Performance.

The aims of this study were to evaluate 1) the effect of different light-curing training methods on first-year dental students' light-curing performance immediately after and one year after training and 2) the effect of dental student year (first vs. third year) and different light-curing training methods on students' light-curing efficacy. The study was organized into two parts, conducted in 2013 and 2014. In the first part, all students (N=66) in the first-year restorative course at a Canadian dental school were invited to participate in a light-curing activity immediately after training; after 12 months, those students (now in their second year) were asked to again perform the light-curing activity. In the second part, all the subsequent first-year students (N=75) and third-year students (N=95) were invited to perform the same light-curing activity after training. Each class was divided into three groups: the Control group received a lecture; the Tips group received the same lecture plus tips on "7 Steps to Ensure Better Light Curing"; and the Simulator group received the lecture, tips, and hands-on training using the patient simulator. In the first part of the study, all 66 students participated in the first year; 39 of those participated a year later. In the second part, all students in both years participated. For the first part, time had a significant effect on light-curing performance, with significantly higher results in the second year. When the first-year students' results were isolated, training method had a significant effect on mean and maximum irradiance values. The second part found a significant effect of training on mean (p=0.003) and maximum (p=0.021) irradiance. The interaction DDS*training was significant (p=0.037) when the after-training values were analyzed. These results point to the need for further research to determine the most effective light-curing training methods.

Effect of tooth whitening strips on fatigue resistance and flexural strength of bovine dentin in vitro.

OBJECTIVE: To determine the effects of whitening strips on bovine dentin fatigue resistance and flexural strength in vitro. MATERIALS AND METHODS: A total of eighty bovine dentin specimens (2x2x17mm) were treated with either: control glycerine gel on plastic film wrap or whitening strips containing 9.5% hydrogen peroxide. Treatment was applied for 30 minutes, twice a day, for 1- or 4-weeks. After the last treatment, ten specimens per group were randomly selected to undergo fatigue testing (106 cycles, 3Hz, 20N) while the other ten were subjected to flexural strength testing after ten days of storage in artificial saliva. Kaplan-Meier method with a log rank test, Wilcoxon test and Cox regression were used to assess fatigue test results (p<0.05). One-way ANOVA and Tukey's tests were used to compare the flexural strength results (p<0.05). RESULTS: There were significant differences in survival during the fatigue test among the groups (p<0.001). Treatment (control or bleach) was a significant factor for specimen survival (p<0.001, Exp(B) = 33.45). There were significant differences in mean flexural strength (p<0.001). No significant difference was found between "1-wk control" and "4-wk control". The mean flexural strength and fatigue resistance of the "4-wk bleach" were significantly lower than all the other groups. CONCLUSIONS: The use of whitening strips reduced the fatigue resistance and flexural strength of bovine dentin in vitro. Until the effect of whitening strips on mechanical properties of human dentin is fully elucidated, it remains prudent to advise patients to avoid excessive direct use of whitening strips on dentin.

Matrix metalloproteinase inhibitor modulates esterase-catalyzed degradation of resin-dentin interfaces.

OBJECTIVE: Assess the modulating effect of matrix metalloproteinase (MMP) inhibition on simulated human salivary enzyme (SHSE)-catalyzed degradation of interfacial fracture-toughness (FT) of self-etched and total-etched resin-dentin interfaces. METHODS: Miniature short-rod FT specimens (N=10/group) containing a resin composite bonded to human dentin, using a self-etch (Easy Bond, EB) or a total-etch (Scotchbond, SB) adhesives, were prepared with and without application of an MMP inhibitor (galardin). Specimens were non-incubated or incubated in phosphate buffered saline (PBS) or SHSE for 7, 30, 90, or 180-days. FT data were obtained using a universal testing machine. Incubation media were analyzed by high performance liquid chromatography (HPLC) for the presence of a 2,2-bis-[4-2(2-hydroxy-3-methacryloxypropoxy)phenyl]-propane (bisGMA)-derived degradation product, bis-hydroxy-propoxy-phenyl-propane (bisHPPP). Fractographic analysis was performed by scanning electron microscopy and image processing software (ImageJ). Statistical analysis was performed by ANOVA and Tukey's (p<0.05). RESULTS: More bisHPPP was detected in SHSE vs. PBS for both adhesive systems (p<0.05). EB specimens yielded no difference in FT and failed preferentially in the resin after >30-days (p<0.05). SB specimens yielded lower FT values after 180-days with SHSE ±galardin vs. 0-days/no-galardin (p<0.05) and failed preferentially in the hybrid-layer after >30-days (p<0.05). Galardin mildly modulated the change in fracture mode for both systems. SIGNIFICANCE: Esterase-catalyzed degradation of total-etch interfaces is modulated by MMP-inhibition, however, self-etch interfaces possess greater biostability under simulated intra-oral conditions, regardless of MMP inhibition. This could be related to different chemical compositions and/or mode of adhesion.

Fracture toughness of chairside CAD/CAM materials - Alternative loading approach for compact tension test.

OBJECTIVE: This in-vitro study determined plane-strain fracture toughness (KIC) of five different chairside CAD/CAM materials used for crown fabrication, following alternative innovative loading approach of compact tension test specimens. METHODS: Rectangular-shaped specimens were cut from CAD/CAM blocks (n=10): Vita Mark II (Vident) (VMII); Lava-Ultimate (3M/ESPE) (LU); Vita Enamic (Vident) (VE); IPS e.max CAD (Ivoclar Vivadent); crystallized and un-crystallized (E-max and E-max-U, respectively); and Celtra Duo (Dentsply) fired and unfired (CD and CD-U, respectively). Specimens were notched with thin diamond disk prior to testing. Instead of applying tensile loading through drilled holes, a specially-made wedge-shaped steel loading-bar was used to apply compressive load at the notch area in Instron universal testing machine. The bar engaged the top » of the notch before compressive load was applied at a cross-head speed of 0.5mm/min. Fracture load was recorded and KIC calculated. Data was statistically-analyzed with one-way ANOVA at 95% confidence level and Tukey's tests. RESULTS: Means and SDs of KIC in MPam(1/2) for VMII, LU, VE, E-max, E-max-U, CD and CD-U were: 0.73 (0.13), 0.85 (0.21), 1.02 (0.19), 1.88 (0.62), 0.81 (0.25), 2.65 (0.32) and 1.01 (0.15), respectively. ANOVA revealed significant difference among the groups (p<0.001). CD and E-max had significantly highest mean KIC values. SIGNIFICANCE: Mean KIC values of the tested materials varied considerably, however, none of them reached mean KIC of dentin (3.08MPam(1/2)) previously reported. For E-max and CD, specimens firing significantly increased mean KIC. The modified test arrangement was found to be easy to follow and simplified specimen preparation process.

Effect of Bleaching Treatment on Fatigue Resistance and Flexural Strength of Bovine Dentin.

PURPOSE: To determine the effects of bleach on dentin fatigue resistance and flexural strength. MATERIALS AND METHODS: Eighty bovine dentin specimens (2 × 2 × 17 mm) were treated with: placebo or 10% carbamide peroxide bleach. Treatment was applied for 6 hours/day for 2 or 8 weeks. After treatment, 10 specimens per group were subjected to fatigue testing (10(6) cycles) whereas the other 10 were stored in artificial saliva as fatigue controls. The specimens undergoing fatigue were checked daily for visible signs of fracture and excluded from subsequent flexural strength tests if fractured. Fatigue control and surviving fatigued specimens were subjected to flexural strength testing. Chi-square, Kruskal-Wallis, factorial analysis of variance (p < 0.05) and Mann-Whitney (p < 0.002) tests were performed. RESULTS: There were significant differences in fatigue resistance (p = 0.003) and flexural strength rank scores (p < 0.0001) among the groups. None of the specimens in the "8-week bleach" group survived the fatigue testing. Fatigue (p = 0.005) and interaction of time and treatment (p = 0.039) were significant factors in the flexural strength results. Fatigued specimens had lower flexural strength than nonfatigued and "8-week bleach" had lower flexural strength than placebo and "2-week bleach" groups. CONCLUSIONS: Prolonged direct bleaching of bovine dentin reduces its fatigue resistance and flexural strength in vitro. Further research is needed in this area. CLINICAL SIGNIFICANCE: It remains prudent to advise patients to limit their exposure to tooth bleaching materials by avoiding direct application of bleach to exposed dentin and by minimizing the duration of bleach treatment.

The use of MDP-based materials for bonding to zirconia.

STATEMENT OF PROBLEM: A strong and stable bond between the luting resin and overlying ceramic restoration is critical to longevity, but no technique has been established for how to provide such a bond when the core material is zirconia. PURPOSE: The purpose of this study was to evaluate the effect of different materials containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP) on the bond strength to yttria-tetragonal zirconia polycrystal (Y-TZP) ceramic. MATERIAL AND METHODS: Forty Y-TZP slices (Lava) were cemented to substrates (8 groups; n=5 in each) with or without the previous application of an experimental primer (0.5% MDP) or an MDP-based adhesive (Clearfil S3 Bond Plus or Scotchbond Universal) with either an MDP (Clearfil SA) or a non-MDP (RelyX Ultimate) luting resin. Specimens were cut, stored in distilled water, and microtensile tested (5 beams per specimen) at 48 hours and again at 6 months after luting procedures. The data were analyzed by 4-way ANOVA (α=.05) and the Tukey test (α=.05). The mode of failure was classified with a stereomicroscope, and the treated surfaces were analyzed with energy-dispersive x-ray spectroscopy. RESULTS: Both adhesive (P<.001) and time (P<.001) significantly affected bond strength. The interaction of any of the factors was not significant. The use of an MDP-containing adhesive and the shorter storage time were associated with higher bond strengths. At 48 hours, an overall incidence of 50.5% of Type 1 mode of failure (adhesive at ceramic/resin interface) occurred, as opposed to 68% after 6 months of water storage. Energy-dispersive x-ray spectroscopy results showed peaks of carbon and phosphorus when MDP-based materials were used. CONCLUSIONS: The application of an MDP-based adhesive may improve bond strength to zirconia. However, microtensile bond strength results for all groups did not remain stable over 6 months.

Comparative translucency of esthetic composite resin restorative materials.

OBJECTIVE: To evaluate the translucency of currently available composites classified by their respective manufacturers as "opaque," "dentin," "body" (or "universal") and "enamel" materials. MATERIALS AND METHODS: Four disk-shaped specimens were produced using a split-ring mould (13 mm in diameter and 2 mm in thickness) from each of 39 proprietary composite restorative materials. Enamel and dentin samples of equivalent thickness were obtained from extracted human teeth. Colour values for lightness (L*), red-green chromatic coordinate (a*) and blue-yellow chromatic coordinate (b*) were recorded against standard white and black backgrounds with a Minolta CR-300 chroma meter under the standard illuminant D65. Translucency parameter values were calculated and compared using analysis of variance and the Tukey test, with significance set at p < 0.05. RESULTS: A continuum of values for the translucency parameter was obtained, ranging from the most opaque (Filtek Supreme Plus A2D) to the most translucent (Ceram X Duo E2). In general, "opaque" and "dentin" composites yielded relatively low translucency values, "body" (or "universal") composites yielded intermediate values, and "enamel" composites yielded relatively high values. However, the boundaries between these categories were not distinct, and there was some overlap. The mean value of the translucency parameter for human enamel was within the range of values for "enamel" shade composites. The individual values for specimens of human dentin were more variable (i.e., greater standard deviation around the mean) than those for human enamel. The mean value obtained for dentin was intermediate between the ranges for composites with low and intermediate translucency. CONCLUSIONS: The various categories of composite from different manufacturers yielded a wide range of translucency, with minimal distinction between the extremes in adjacent categories. The measured translucency values provided more information than the respective category types. Knowledge of the relative translucency and opacity of different commercial materials can assist clinicians in the choice of composite for clinical use.

The effect of bleaching time on dentin fracture toughness in vitro.

STATEMENT OF PROBLEM: A recent study reported a decrease in dentin fracture toughness after the application of peroxide bleaching products to dentin in vitro. PURPOSE: The objective of the present study was to investigate this in vitro decrease in fracture toughness further by evaluating the effect of different peroxide application times on dentin fracture toughness. MATERIALS AND METHODS: Compact test fracture toughness specimens were prepared from coronal human. These were divided into five groups (N = 12) and subjected to either bleach (10% carbamide peroxide) and/or placebo gel for a total of 336 consecutive hours (0 and 336, 84 and 252, 168 and 168, 252 and 84, 336 and 0 hours of bleach and placebo application time, respectively). The gel materials were changed every 6 hours. Fracture toughness testing was done 24 hours after the end of bleaching using tensile loading at 10 mm/min. Results were analyzed by analysis of variance and linear regression (p < 0.05). RESULTS: Dentin fracture toughness after 252 and 336 hours was significantly reduced compared to the 0- and 84-hour bleach times. An association between fracture toughness and bleach time (r(2) = 0.82) with an inverse linear regression line (K(1C) = -0.0032 [hour] + 3.386) was found. CONCLUSIONS: A significant correlation was found between bleach time and dentin fracture toughness. Dentin fracture toughness was reduced over time during the 336-hour course of in vitro bleaching. CLINICAL SIGNIFICANCE: The results suggest that it would be prudent to minimize the length of time for clinical bleaching procedures when dentin is directly exposed to bleach.

Flexural strength, elastic modulus, and pH profile of self-etch resin luting cements.

PURPOSE: To determine the flexural strength, modulus of elasticity, and 24-hour pH profile of three self-etching resin luting cements and to obtain comparative data for representative conventional resin and resin-modified glass ionomer luting cements. MATERIALS AND METHODS: Three self-etching resin luting cements [RelyX Unicem (3M ESPE), Maxcem (Kerr), Embrace Wetbond (Pulpdent)] were tested and compared with two conventional resin cements [RelyX ARC (3M ESPE), Linkmax (GC)] plus two resin-modified glass ionomer luting cements [Fuji Plus (GC), RelyX Luting Plus (3M ESPE)]. Flexural strength and modulus of elasticity were determined using bar-shaped specimens (2 x 2 x 25 mm(3)) at 24 hours, using an Instron universal testing machine. Setting pH was measured using a flat-surface pH electrode at 0, 2, 5, 15, and 30 minutes and 1, 2, 4, 6, and 24 hours after mixing. Testing was performed under both dual-cured and self-cured conditions for all dual-cure cements. Data analysis included ANOVA and Tukey's test (p < 0.05). RESULTS: The self-etching cements showed similar flexural strength to the conventional resin cements, except for Embrace Wetbond self-cured, which was considerably lower. Modulus of elasticity results were both higher and lower than for conventional resin cements. All photopolymerized conventional and self-etch dual-cure cements showed markedly higher flexural strength and modulus than when solely self-cured. The resin-modified glass ionomer cements were characterized by lower flexural strength and elastic modulus. Self-etching resin cements showed lower initial pH (2.0 to 2.4) than conventional resin cements (4.8 to 5.2) and a wide range of final pH values (3.9 to 7.3) at 24 hours. One self-etching cement (Unicem) revealed a unique pH profile characterized by a more rapid rise in pH to neutrality both when dual-cured (15 minutes) and when auto-cured (1 hour). CONCLUSIONS: The self-etching resin cements evaluated in this study displayed disparate properties and cannot be considered a homogeneous group. Flexural strength properties were most uniform and were similar to those of the conventional resin cements, whereas moduli of elasticity showed greater variation. Setting pH profiles differed, depending on the brand and mode of cure, even within the same category of luting cement. All cements with dual-cure capability, both conventional and self-etch, showed significantly superior properties when photopolymerized.

Effect of prolonged direct and indirect peroxide bleaching on fracture toughness of human dentin.

STATEMENT OF THE PROBLEM: The effects of prolonged exposure to peroxide bleaching agents on dentin structural integrity are uncertain. PURPOSE: To evaluate the effect of in vitro prolonged tooth bleaching on the fracture toughness (K(1C)) of human dentin. MATERIALS AND METHODS: Dentin from recently extracted molar teeth was directly or indirectly treated to simulate a prolonged at-home (10% carbamide peroxide or 3% hydrogen peroxide, 6 hours/day, 5 days/week for 8 weeks) or in-office (30% hydrogen peroxide, 1 hour/week for 8 weeks) bleaching regimen (N=8/group). Placebo gel and distilled water acted as control materials. Compact tension test specimens (approximately 4.60 x 4.50 x 1.60 mm) were prepared from coronal dentin and tensile loading was applied at a rate of 10 mm/min 24 hours after the last bleaching session. Results were analyzed using analysis of variance and Tukey's test (p < 0.05). For direct bleach application, the treatment materials were applied onto dentin that was already prepared as compact tension specimens. For indirect bleach application, bleach was applied to the enamel of intact teeth prior to specimen preparation. RESULTS: There was a significant decrease in dentin K(1C) after 8 weeks of direct bleach treatment (p < 0.05). There were no significant differences between the bleach and control groups after 8 weeks of indirect bleach treatment (p=0.19). CONCLUSIONS: The in vitro fracture resistance of dentin was reduced after the prolonged use of bleach products that were applied directly to dentin. CLINICAL SIGNIFICANCE: Caution should be considered when using bleach for prolonged treatment times in clinical cases where there is dentin exposure such as occlusal attrition or gingival recession.

Effect of direct peroxide bleach application to bovine dentin on flexural strength and modulus in vitro.

OBJECTIVES: The objective of this study was to determine the effects of carbamide peroxide (CP) and hydrogen peroxide (HP) bleaching on the flexural strength (FS) and flexural modulus (FM) of dentin. METHODS: 2x2x20mm bovine dentin specimens were immersed in the bleaching agents to simulate overnight (10 or 15% CP, 6h daily, 2 weeks), exaggerated overnight (10% CP, 6h/day, 5 days/week, 2 months), daytime (6.5 or 7.5% HP, 1h daily, 3 weeks) and in-office (35% HP, 1h/day, 2 days/week, 3 weeks) treatment protocols. Distilled water (DW) and a placebo gel acted as control immersion materials. After immersion, the specimens were rinsed and stored in DW. Mechanical testing was performed 24h after the last treatment using an Instron Universal Testing Machine with a crosshead speed of 0.75 mm/min. The results were analyzed by ANOVA and Tukey's tests (p<0.05). RESULTS: There were significant reductions in the FS and FM of dentin after 2-week and 2-month exposures to CP. There were no significant differences in the FS or the FM of the dentin among the HP treatment and control groups. CONCLUSIONS: Direct in vitro application of CP bleaches caused significant decreases in dentin FS and FM. Similar decreases were not observed among the HP-treated dentin groups, which were exposed to shorter treatment times. Further research is needed to determine the effect of CP and HP on dentin in vivo.

Flow, strength, stiffness and radiopacity of flowable resin composites.

OBJECTIVE: This study was undertaken to characterize 9 currently available proprietary flowable composites with respect to key properties of flow, flexural strength, stiffness (modulus of elasticity) and radiopacity. METHODS: Seven proprietary flowable composites (Aelite Flo, Filtek Flow, Heliomolar Flow, PermaFlo, Revolution Formula 2, Tetric Flow, Wave) and 2 flowable compomers (Compoglass Flow, Dyract Flow) were evaluated. A universal hybrid composite (Filtek Z250) and a restorative compomer (Dyract AP) were used as controls. Standard mechanical testing of 25 x 2 x 2 mm bar specimens was carried out at 24 hours and 1 month. Flow testing used a fixed volume of material under consistent loading, and radiopacity was measured simultaneously for all materials using disk specimens of 1 mm thickness. RESULTS: As expected, flowable composites showed higher flow and lower mechanical properties than the controls. Moduli of the composites were approximately 50% or less of the moduli of control materials, which indicates high flexibility. Flexural strengths approached that of the control composite. Flow properties varied widely. The material Tetric Flow had the highest radiopacity, above that of enamel and the control composite. Lowest radiopacity, below or equivalent to that of dentin, was shown by Wave and Revolution Formula 2. CONCLUSIONS: The flowable materials possessed a wide range of mechanical and physical properties. Their lower mechanical properties suggest that they should not be used in bulk in areas of high occlusal loading. Within intracoronal restorations, clinicians are advised to use materials with high radiopacity. A wide range of fluidity options is available. The clinical applications and performance of these materials require further study.

Effect of mode of polymerization of bonding agent on shear bond strength of autocured resin composite luting cements.

PURPOSE: There have been anecdotal reports of low bond strength with autocured resin composite materials, particularly when light-cured bonding agents that combine primer and adhesive in a 1-bottle preparation are used. The objective of this study was to determine if the mode of polymerization of the bonding agent influences the strength of the attachment of autocured resin composite luting cements to dentin. METHODS: The shear bond strength of 2 resin luting cements, Calibra and RelyX ARC, polymerized by autocuring, in combination with 4 different bonding agents, Scotchbond Multipurpose Plus, Prime & Bond NT, IntegraBond and Single Bond, polymerized to bovine dentin by light-curing, autocuring or dual-curing, was determined. The pH of each bonding agent and its components was measured. Two-way analysis of variance was used to test the effect of cement and adhesive on shear bond strength. For each bonding agent, the adhesive variable combined the factors product brand and mode of polymerization. With significant interaction among the above variables, the least square means of the 16 combinations of resin cement and adhesive were compared. RESULTS: There was no consistent relationship between shear bond strength and mode of polymerization of the bonding agent. Significant differences in bond strength were specific to the proprietary brand of bonding agent. The pH of the bonding agent depends on the manufacturer's formulation, and low pH may contribute to low bond strength. CONCLUSIONS: The low in vitro bond strength occurring with some combinations of bonding agent and resin cement could be clinically significant.

Mechanical and physical properties of contemporary dental luting agents.

STATEMENT OF PROBLEM: New luting agents, particularly with adhesive capability, are being introduced in an attempt to improve clinical success. Independent studies of basic comparative data are necessary to characterize these materials in relation to mechanical and physical properties. PURPOSE: The purpose of this study was to compare the flexural strength, modulus of elasticity, and radiopacity and pH of representatives of 5 types (categories) of luting agents. MATERIAL AND METHODS: The luting agents included a zinc phosphate, a conventional and a resin-modified glass ionomer, 2 dual-polymerizing resins ("photopolymerized" after mixing and "unphotopolymerized" conditions), and an auto-polymerizing resin. The specimens were prepared and the testing was conducted by 1 person to maximize standardization. Flexural strength (MPa) and modulus of elasticity (GPa) were determined on bar-shaped specimens (2 x 2 x 20 mm) at 24 hours and 3 months (n = 8). Radiopacity (mm Al) was measured by exposing 1 mm thick specimens along with an aluminum step wedge (n = 4). pH was measured using a pH electrode immediately after mixing; at 1, 5, 15, 30 minutes; and at 1, 2, 4, 6, and 24 hours (n = 4). The data were subjected to statistical analyses with analysis of variance and Duncan's multiple range test (P<.05). RESULTS: The resin luting agents (64 to 97 MPa) showed higher flexural strength than all other materials tested (7 to 27 MPa), with the "photopolymerized" (83 to 97 MPa) conditions higher than "unphotopolymerized" (64 to 81 MPa) (P<.0005). Zinc phosphate was the most radiopaque (6.4 mm Al) (P<.0001) and provided the highest rigidity (9.2 GPa) (P<.05). The autopolymerization resin cement was the most radiolucent (1.1 mm Al) (P<.0001). Zinc phosphate and conventional glass ionomer cements were the most acidic immediately after mixing (pH 1.5 to 2.2) but were the least acidic after 24 hours (pH 6.4 to 6.8) (P<.0001). CONCLUSIONS: Within the limitations of this study the data showed a wide variation of material properties. The dual-polymerization resin luting agents tested showed the best combination of mechanical and physical properties combined with the highest setting pH. Photopolymerization of these resin-based materials was necessary to maximize strength and rigidity.