Hardness and fracture toughness of four commercial visible light-cured composite resin veneering materials

Characterisation of Microparticle Waste from Dental Resin-Based Composites

Clinical applications of resin-based composite (RBC) generate environmental pollution in the form of microparticulate waste. Methods: SEM, particle size and specific surface area analysis, FT-IR and potentiometric titrations were used to characterise microparticles arising from grinding commercial and control RBCs as a function of time, at time of generation and after 12 months ageing in water. The RBCs were tested in two states: (i) direct-placement materials polymerised to simulate routine clinical use and (ii) pre-polymerised CAD/CAM ingots milled using CAD/CAM technology. Results: The maximum specific surface area of the direct-placement commercial RBC was seen after 360 s of agitation and was 1290 m²/kg compared with 1017 m²/kg for the control material. The median diameter of the direct-placement commercial RBC was 6.39 μm at 360 s agitation and 9.55 μm for the control material. FTIR analysis confirmed that microparticles were sufficiently unique to be identified after 12 months ageing and consistent alteration of the outermost surfaces of particles was observed. Protonation-deprotonation behaviour and the pH of zero proton charge (pH_zpc) ≈ 5–6 indicated that the particles are negatively charged at neutral pH7. Conclusion: The large surface area of RBC microparticles allows elution of constituent monomers with potential environmental impacts. Characterisation of this waste is key to understanding potential mitigation strategies.

Evaluation of Fracture Toughness, Color Stability, and Sorption Solubility of a Fabricated Novel Glass Ionomer Nano Zirconia-Silica-Hydroxyapatite Hybrid Composite Material

The aim of this study was to investigate the effects of adding a nano zirconia-silica-hydroxyapatite (nanoZrO2-SiO2-HA) composite synthesized using a one-pot sol-gel technique to a conventional glass ionomer cement (GIC), which was then characterized using X-ray diffraction (XRD). Following the characterization studies, further investigations were carried out after the addition of nanoZrO2-SiO2-HA to cGIC (GIC nanoZrO2-SiO2-HA) at various percentages (~5% to 9%) to compare their fracture toughness, color stability, and sorption- solubility in relation to cGIC (Fuji IX). The XRD diffractogram indicated the presence of peaks for ZrO2, SiO2, and HA. The fracture toughness of GIC 5%nanoZrO2-SiO2-HA was statistically higher than that of other percentages of GIC nanoZrO2-SiO2-HA and cGIC. The highest values recorded were fracture toughness ( $1.35\pm 0.15\text{MPa}.{\text{m}}^{1/2}$ ), leading to an increase of ∼57%, as compared to cGIC. Overall, the color change ( $\Delta E$ ) values for GIC 5% nano Zr-Si-HA group were lower than those of cGIC over a one-month period and were between slight and perceptible. In addition, GIC 5%nanoZrO2-SiO2-HA recorded lower sorption values ( $23.64\pm 2.3\mu \text{gm}{\text{m}}^{-3}$ ) as compared to cGIC ( $36.28\pm 2.6\mu \text{gm}{\text{m}}^{-3}$ ) and higher solubility ( $66.46\pm 2.4\mu \text{gm}{\text{m}}^{-3}$ ) as compared to cGIC ( $56.76\pm 1.6\mu \text{gm}{\text{m}}^{-3}$ ). The addition of nanoZrO2-SiO2-HA to cGIC significantly enhanced its physicomechanical properties. Based on the results of our study, GIC nanoZrO2-SiO2-HA has the potential to be suggested as a restorative dental material with diverse applications ranging from cavity restoration, core build-up, and as a luting material.

Edge chipping resistance of veneering composite resins

OBJECTIVES

To investigate the edge chipping resistance (ECR) of six veneering composite resins after different treatment protocols.

MATERIALS AND METHODS

Rectangular bar specimens were manufactured from Ceramage Incisal (CER; Shofu), dialog Vario Occlusal (DIA; Schütz Dental), Gradia Plus Heavy Body Enamel (GRA; GC Europe), in:joy incisal (INJ; Dentsply Sirona Deutschland), SR Nexco Paste Incisal (SRN; Ivoclar Vivadent), and Signum composite enamel (SIG; Kulzer). ECR was determined after five treatment protocols: (1) no treatment, (2) after storage in distilled water at 37 °C for 7 days, (3) storage in distilled water with an additional 10 000 thermal cycles (5 °C/55 °C), and hydrothermal treatment at 134 °C at a water vapor pressure of 0.2 MPa for a duration of (4) 3.5 min or (5) 23.5 min. Force was applied with the universal testing machine ZHU 0.2 (Zwick Roell) mounted with a Vickers diamond indenter until the chip fractured off the specimen and ECR values were computed by dividing the applied maximum force by the distance to the center of the applied force. Fracture analysis was performed employing light microscope imaging. Univariate and one-way ANOVA, Scheffé and Tukey-B post hoc, and partial eta squared (ƞ_p²) were computed (p < 0.05).

RESULTS

DIA presented consistently high ECR values, while CER showed low results. For some groups, seven days' storage in water and hydrothermal treatment for 3.5 min led to higher ECR results than observed in the initial state, while an additional 10 000 thermal cycles and hydrothermal treatment for 23.5 min resulted in lower ECR values.

CONCLUSIONS

The examined veneering composite resins differed in regard to their mechanical properties, with DIA possessing the highest resistance to chipping. While post-processing can initially increase a material's edge chipping resistance, intensified treatment protocols reduced the mechanical properties of veneering composite resins.

The effect of esterase enzyme on aging dental composites

We measured the push-out and diametral tensile strength of dental restorative composites following aging under environmental conditions relevant to the oral cavity; air (A), artificial saliva (AS), acidified (50 mM CH₃ COOH, pH = 4.7) artificial saliva (AS + HAc), and AS with esterase enzyme (AS + ENZ). Cylindrical test specimens (6.3 mm diameter by 5.1 mm long) were prepared by placing 0.3 g of nanofilled composite in an epoxy ring and cured. Twenty samples were aged in each environment for 163-186 days at 37°C. The push-out strengths (mean ± standard error of the mean [SEM], in MPa) for specimens were: A-2.4 ± 0.2, AS-7.3 ± 0.5, AS + HAc-7.2 ± 0.9, and AS + ENZ-6.0 ± 0.6. Following the push-out test, the diametral tensile strength and elasticity were immediately determined. The diametral tensile strengths (mean ± SEM, in MPa) for specimens were: A-54.0 ± 1.6, AS-31.4 ± 1.3, AS + HAc-34.3 ± 1.2, and AS + ENZ-22.5 ± 0.7. The push-out strength was lowest for the A environment due to shrinkage of the composite. The push-out strength increased significantly as water diffused into the specimens (AS and AS + HAc) but decreased significantly in the enzyme environment (AS + ENZ). The diametral tensile strength was highest for specimens in the A environment, which was significantly higher than both the AS and AS + HAc specimens and > 2× higher than the AS + ENZ specimens. The results indicated that a water environment (with or without acid) caused a significant decrease in the mechanical properties of this composite, but the greatest decrease was seen in water with esterase. This is the first study to demonstrate that esterase enzymes affect the bulk strength of a commonly used commercial dental composite. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2178-2184, 2019.

Investigation of the correlation between the different mechanical properties of resin composites

The aim of this study was to investigate the relationship between the different mechanical properties with the filler fraction of various resin composites. Mechanical properties of eighteen different resin composites were investigated in this study; flexural strength (FS), flexural modulus (FM), fracture toughness (FT), compressive strength (CS), diametral tensile strength (DTS), Barcol hardness (BH), Vickers hardness (HV), and Knoop hardness (HK). The mean values of mechanical properties and the filler fractions (V(f )) obtained from the literature and the manufacturer were analyzed using Pearson's correlation test at p<0.01. The relationships were compared with the data retrieved from previous studies. Strong correlations between Vf and BH/HV/HK and V(f) and FM were evident in the results of the present study and these results were supported by the retrieved data from previous studies. The other relationships between mechanical properties, such as that between FS and FM and between CS and HV were not significant.

A comparison of microhardness of indirect composite restorative materials

The purpose of this study was to compare the microhardness of four indirect composite resins. Forty cylindrical samples were prepared according to the manufacturer’s recommendations using a Teflon mold. Ten specimens were produced from each tested material, constituting four groups (n=10) as follows: G1 - Artglass; G2 - Sinfony; G3 - Solidex; G4 - Targis. Microhardness was determined by the Vickers indentation technique with a load of 300g for 10 seconds. Four indentations were made on each sample, determining the mean microhardness values for each specimen. Descriptive statistics data for the experimental conditions were: G1 - Artglass (mean ±standard deviation: 55.26 ± 1.15HVN; median: 52.6); G2 - Sinfony (31.22 ± 0.65HVN; 31.30); G3 - Solidex (52.25 ± 1.55HVN; 52.60); G4 - Targis (72.14 ± 2.82HVN; 73.30). An exploratory data analysis was performed to determine the most appropriate statistical test through: (I) Levene's for homogeneity of variances; (II) ANOVA on ranks (Kruskal-Wallis); (III) Dunn's multiple comparison test (0.05). Targis presented the highest microhardness values while Sinfony presented the lowest. Artglass and Solidex were found as intermediate materials. These results indicate that distinct mechanical properties may be observed at specific materials. The composition of each material as well as variations on polymerization methods are possibly responsibles for the difference found in microhardness. Therefore, indirect composite resin materials that guarantee both good esthetics and adequate mechanical properties may be considered as substitutes of natural teeth.

Influence of the interaction of light- and self-polymerization on subsurface hardening of a dual-cured core build-up resin composite

OBJECTIVE

To investigate the influence of time delay and duration of photo-activation on subsurface microhardness of a dual-cured resin composite.

MATERIAL AND METHODS

A commercially available dual-cured core build-up resin composite (Rebilda DC) was filled in cavities (diameter: 4.0 mm; height: 6.0 mm) of polystyrene molds and light-cured for 20 or 60 s either immediately after the filling procedure (time delay 0 s) or after a time delay of 30, 90, 180 or 300 s. Non-irradiated self-cured specimens served as a control group (n = 15). Specimens were stored in complete darkness and at 100% relative humidity at 37°C for 2 weeks and cross-sectioned. Knoop Hardness Numbers (KHNs) were measured six times per depth and averaged at distances of 0.25, 0.50, 1.00, 2.00, 3.50 and 5.50 mm from the light-exposed surface. Data were statistically analyzed using one- and two-way ANOVA followed by Scheffé's post-hoc test at a level of significance of 0.05.

RESULTS

Mean hardness values in all experimental groups ranged between 54.3 ± 2.1 and 58.1 ± 2.3 KHN. Light-curing did not significantly increase composite KHN at any depth measured. Delaying light exposure had no influence on KHN, irrespective of depth. A longer light-exposure time (60 versus 20 s) resulted in significantly higher KHN only at depths of 3.50 and 5.50 mm.

CONCLUSION

Photo-activation of the tested dual-cured resin composite provided no clinically relevant benefit compared to self-curing regarding the degree of hardening.

Indirect resin composites

Aesthetic dentistry continues to evolve through innovations in bonding agents, restorative materials, and conservative preparation techniques. The use of direct composite restoration in posterior teeth is limited to relatively small cavities due to polymerization stresses. Indirect composites offer an esthetic alternative to ceramics for posterior teeth. This review article focuses on the material aspect of the newer generation of composites. This review was based on a PubMed database search which we limited to peer-reviewed articles in English that were published between 1990 and 2010 in dental journals. The key words used were 'indirect resin composites,' composite inlays,' and 'fiber-reinforced composites.'

Conversion degree of indirect resin composites and effect of thermocycling on their physical properties

PURPOSE

This study evaluated the degree of conversion (DC) of four indirect resin composites (IRCs) with various compositions processed in different polymerization units and investigated the effect of thermal aging on the flexural strength and Vicker's microhardness.

MATERIALS AND METHODS

Specimens were prepared from four IRC materials, namely Gr 1: Resilab (Wilcos); Gr2: Sinfony (3M ESPE); Gr3: VITA VMLC (VITA Zahnfabrik); Gr4: VITA Zeta (VITA Zahnfabrik) using special molds for flexural strength test (N = 80, n = 10 per group) (25 x 2 x 2 mm(3), ISO 4049), for Vicker's microhardness test (N = 80, n = 10 per group) (5 x 4 mm(2)) and for DC (N = 10) using FT-Raman Spectroscopy. For both flexural strength and microhardness tests, half of the specimens were randomly stored in distilled water at 37 degrees C for 24 hours (Groups 1 to 4), and the other half (Groups 5 to 8) were subjected to thermocycling (5000 cycles, 5 to 55 +/- 1 degree C, dwell time: 30 seconds). Flexural strength was measured in a universal testing machine (crosshead speed: 0.8 mm/min). Microhardness test was performed at 50 g. The data were analyzed using one-way and two-way ANOVA and Tukey's test (alpha= 0.05). The correlation between flexural strength and microhardness was evaluated with Pearson's correlation test (alpha= 0.05).

RESULTS

A significant effect for the type of IRC and thermocycling was found (p= 0.001, p= 0.001) on the flexural strength results, but thermocycling did not significantly affect the microhardness results (p= 0.078). The interaction factors were significant for both flexural strength and microhardness parameters (p= 0.001 and 0.002, respectively). Thermocycling decreased the flexural strength of the three IRCs tested significantly (p < 0.05), except for VITA Zeta (106.3 +/- 9.1 to 97.2 +/- 14 MPa) (p > 0.05) when compared with nonthermocycled groups. Microhardness results of only Sinfony were significantly affected by thermocycling (25.1 +/- 2.1 to 31 +/- 3.3 Kg/mm(2)). DC values ranged between 63% and 81%, and were not significantly different between the IRCs (p > 0.05). While a positive correlation was found between flexural strength and microhardness without (r = 0.309) and with thermocycling (r = 0.100) for VITA VMLC, negative correlations were found for Resilab under the same conditions (r =-0.190 and -0.305, respectively) (Pearson's correlation coefficient).

CONCLUSION

Although all four IRCs presented nonsignificant DC values, flexural strength and microhardness values varied between materials with and without thermocycling.

Effect of Ultrasonic Versus Manual Cementation on the Fracture Strength of Resin Composite Laminates

Indirect composite laminates, when cemented ultrasonically, resulted in repairable failures as opposed to indirect composite laminates cemented under hand pressure.

Effect of adhesion to cavity walls on the mechanical properties of resin composites

OBJECTIVES

To evaluate the regional mechanical properties of resin composite under free and constrained conditions during polymerization.

METHODS

Forty cavities (8mm diameter and 5mm depth) were fabricated in resin blocks. Half of the cavities were bonded and the other half left un-bonded. The cavities were bulk-filled with one of the following composites: flowable composite (Palfique Estelite LV, Unifil Lo Flo), and Universal composites (Clearfil AP-X, Palfique Estelite Sigma), followed by photo-curing for 30s. After 24h storage, each specimen was sliced parallel to the long axis to harvest three slabs. The middle slab was serially sliced to harvest five sticks, which were trimmed to an hour-glass shape for measurement of regional ultimate tensile strength (UTS). The remaining semi-circular slabs were polished for microhardness measurement (KHN). Data were analyzed using three-way ANOVA followed by Tukey's HSD test and t-test (alpha=.05).

RESULTS

The KHNs of all the resin composites were not significantly different between the bonded and unbonded groups at each cavity depth (p>0.05). The Ucapital TE, CyrillicS of the bonded group of flowable composites was significantly lower than those of the un-bonded group at the upper regions (p<0.05), while for universal composites, there were no significant differences in UTS between the bonded and un-bonded groups (p>0.05), although Clearfil AP-X had a trend toward lower UTS under the constrained condition at the upper regions.

SIGNIFICANCE

The UTS of resin composite decreases due to polymerization shrinkage stress when polymerized under a constrained condition, however, these effects were dependent upon regions in the cavity and the resin materials.

Fracture strength of direct versus indirect laminates with and without fiber application at the cementation interface

OBJECTIVES

This study compared the fracture strength of direct and indirect resin composite laminate veneers and evaluated the effect of a bidirectional E-glass woven fiber application at different locations at the cementation interface.

METHODS

Standard preparations on canines (N=50, 10 per group) were made using a depth cutting bur (0.7mm depth) designed for laminate veneer restorations. Forty indirect laminates using a highly filled polymeric material (Estenia) and 10 direct laminates (Quadrant Anterior Shine) were prepared according to the manufacturer's instructions. Bidirectional E-glass woven-fiber sheet (0.06mm) (Everstick) was applied at different locations at the cementation interface. The control group received no fibers. The specimens were stored in water at 37 degrees C for 1 month prior to fracture testing performed in a universal testing machine where the load was applied from the incisal direction at 137 degrees (1mm/min).

RESULTS

No significant differences were found between the five groups (P>0.01) (one-way ANOVA). While indirect laminate veneers showed mean fracture strength of 247+/-47N, direct laminate veneers revealed 239+/-104N. The use of E-glass fibers at the cementation interface at different locations did not increase the fracture strength significantly (286-313N) (P>0.01). Failure analysis showed mainly cohesive fracture of the veneer restoration (20/50) and adhesive failure between the cementation interface and the laminate with fiber exposure (19/50) covering more than half of the restorations.

SIGNIFICANCE

Direct and indirect resin composite laminate veneers showed comparable mean fracture strengths. The use of E-glass woven-fiber sheet at the cementation interface did not increase the fracture strength of the polymeric laminate veneers.

Effect of a metal priming agent on wear resistance of gold alloy-indirect composite joint

The purpose of the current study was to evaluate the effect of a metal priming agent on wear resistance of gold alloy-composite joint. Four types of plate specimen were prepared: composite (Estenia C&B or Epricord) alone, type 4 gold alloy alone, alloy-composite joint without priming agent, and alloy-composite joint bonded with a priming agent (Alloy Primer). Three-body wear test was performed using the plate specimens, gold alloy antagonist, and polymer slurry. Joined specimens with priming exhibited less wear depth (in microm; 21.0 for Estenia and 24.9 for Epricord) than the joined specimens without priming (57.8 for Estenia and 46.7 for Epricord). Wear depth of the single plate specimens when abraded with the gold alloy antagonist was ranked as follows: Estenia (9.6), gold alloy (12.8), and Epricord (19.1). It was concluded that the use of a metal priming agent at the alloy-composite interface effectively enhanced the wear resistance of the joined area when under cycled loading.

Mechanical properties and bond strength of dual-cure resin composites to root canal dentin

OBJECTIVES

To evaluate the regional mechanical properties of dual-cure resin composites and their regional bond strengths to root canal dentin.

METHODS

One of the following dual-cure resin composites was placed in artificial post spaces: Unifil Core (UC), Clearfil DC Core (DC), Build-It FR (BI), Clearfil DC Core-automix (DCA), and photo-cured for 60s. After 24h storage, each specimen was serially sliced to harvest eight hour-glass shaped specimens for measurement of regional ultimate tensile strength (UTS), and the remaining eight semi-circular slabs were polished for the measurement of Knoop Hardness Number (KHN). For the microtensile bond strength (muTBS) test, post cavities were prepared in human premolar roots, and the cavity surfaces treated with Clearfil SE Bond and photo-cured for 10s. The post spaces were then filled with one of the above resin composites and photo-cured for 60s. After 24h storage, each specimen was serially sliced into 8, 0.6x0.6 mm-thick beams for the muTBS test. The data were divided into coronal and apical regions and analyzed using ANOVA and post hoc test (alpha=0.05).

RESULTS

UTS and KHN were affected by the type of dual-cure resin composite and region (p<0.0001). There was no relationship between UTS and KHN for each material. The auto-mix type of resin composite possessed superior UTS to that of the hand-mix type. muTBS among the four composite materials were not significantly different at both apical and coronal regions (p>0.05). Regional differences in bond strengths were found for all materials (p<0.05).

SIGNIFICANCE

The UTS and KHN of the dual-cure resin composites varied among each material, however, differences in the mechanical properties of the resin core materials did not affect their adhesion to root canal dentin.

Effect of surface treatments of laboratory-fabricated composites on the microtensile bond strength to a luting resin cement

The purpose of this study was to evaluate the influence of different surface treatments on composite resin on the microtensile bond strength to a luting resin cement. Two laboratory composites for indirect restorations, Solidex and Targis, and a conventional composite, Filtek Z250, were tested. Forty-eight composite resin blocks (5.0 x 5.0 x 5.0mm) were incrementally manufactured, which were randomly divided into six groups, according to the surface treatments: 1- control, 600-grit SiC paper (C); 2- silane priming (SI); 3- sandblasting with 50 mm Al2O3 for 10s (SA); 4- etching with 10% hydrofluoric acid for 60 s (HF); 5- HF + SI; 6 - SA + SI. Composite blocks submitted to similar surface treatments were bonded together with the resin adhesive Single Bond and Rely X luting composite. A 500-g load was applied for 5 minutes and the samples were light-cured for 40s. The bonded blocks were serially sectioned into 3 slabs with 0.9mm of thickness perpendicularly to the bonded interface (n = 12). Slabs were trimmed to a dumbbell shape and tested in tension at 0.5mm/min. For all composites tested, the application of a silane primer after sandblasting provided the highest bond strength means.

Fracture toughness of resin-modified glass ionomer restorative materials: effect of powder/liquid ratio and powder particle size reduction on fracture toughness

OBJECTIVES

The objectives of the current investigation were two-fold: (1) to examine the effect of different powder/liquid (P/L) ratios on the fracture toughness of commercial resin-modified glass ionomer cement and conventional glass ionomer cement, and (2) to evaluate the effect of powder size reduction on the fracture toughness of experimental resin-modified glass ionomers in order to improve their physical properties.

METHODS

The P/L ratios of the glass ionomer and resin-modified glass ionomers were varied from the manufacturer's recommended ratio to 2.0 and 1.0 by weight. The powder particle sizes for the experimental resin-modified glass ionomers tested were 2, 5, 10 and 25 micro m in diameter. Fracture toughness was determined on ring-shaped specimens with a fatigued pre-crack.

RESULTS

The fracture toughness of the resin-modified glass ionomers was significantly higher (p<0.005) than that of the glass ionomer and was not greatly influenced by the P/L ratio. For the experimental resin-modified glass ionomers, it was observed that fracture toughness gradually decreased as the powder particle size became finer.

SIGNIFICANCE

The resin components in the liquid play an important role in the improvement of the physical properties of the resin-modified glass ionomer. A reduction in the powder particle size of up to 10 micro m, which resulted in a smoother surface, can maintain high fracture toughness. The high fracture toughness values of the resin-modified glass ionomer may be one of the factors contributing to a favorable clinical outcome in high stress-bearing areas.

Fracture toughness and microhardness of a composite: do they correlate?

OBJECTIVES

Chipping and bulk fracture are major contributors in clinical failures of composite restorations. Fracture toughness (K(Ic)) quantifies susceptibility for fracture, but experimental determination is complicated. It would be beneficial for the dental community if a relatively simple experiment, such as microhardness (HK), could be used to screen composites for fracture resistance. This study explores a possible correlation between K(Ic) and HK.

METHODS

Composite cylinders (4mm diameter and approximately 7 mm long) were cured for five combinations of light intensity (I, microm W/cm(2)) and curing time (T, s) to achieve a range of different total light energy densities (I x T=100 x 10, 100 x 20, 300 x 20, 300 x 40, and 700 x 60 microm W s/cm(2)). A chevron-notch was cut in the median plane of the cylinders for the fracture toughness test, which was executed in a displacement control mode at 6 micro m/s cross-head speed (sample size 4). Knoop hardness was determined at the median plane of the cylinders (sample size 6). The tests were performed 15 min and 24h after curing.

RESULTS

Both the K(Ic) and HK increased with increased light energy density and storage time. Linear regression analysis indicated a strong correlation between HK and K(Ic) tested at the same time period (R(2)=0.97 and 0.90 for 15 min and 24h, respectively). The correlation became weaker between the different storage times (R(2)=0.71), indicating a change in fracture toughness and/or microhardness mechanisms.

CONCLUSION

Fracture toughness of a composite cannot be simply extrapolated from microhardness.

Light-polymerized compomers: coefficient of thermal expansion and microhardness

STATEMENT OF PROBLEM

The relationship between the filler content, coefficient of thermal expansion, and microhardness of commercial light-polymerized compomers has not been fully investigated.

PURPOSE

This study evaluated the effect of filler content on the coefficient of thermal expansion and microhardness of 3 commercially available light-polymerized compomers.

MATERIAL AND METHODS

Five specimens each from 3 commercially available compomers (Compoglass F, Elan and F2000) were evaluated. Linear thermal expansion (microm/ degrees C) was measured with a thermomechanical analyzer in the temperature range 20 degrees to 80 degrees C with increments of 10 degrees C. Standardized specimens were prepared in a metal die (1.5 x 2 x 12 mm) and polymerized for 40 seconds at 700 mW/cm(2) light intensity. The microhardness of 5 specimens from each of 3 compomers were measured with a Vickers hardness tester under a 15-second dwell time and 200-g load conditions. The specimens were polymerized at 700 mW/cm(2) intensity for 40 seconds after placing the compomers into a round aluminum mold. Differences in thermal expansion and microhardness among the compomers evaluated were statistically analyzed by use of one-way analysis of variance at P<.01 significance level, with differences assessed by use of Duncan's multiple range post hoc test.

RESULTS

The coefficients of thermal expansion of Compoglass F (54.17 +/- 0.54 microm/ degrees C), Elan (40.94 +/- 0.78 microm/ degrees C) and F2000 (24.43 +/- 89 microm/ degrees C) were almost linear in the temperature range 25 degrees to 80 degrees C for all 3 compomers (r >.99). Inverse correlations between the %wt of filler and the coefficient of thermal expansion (r = -0.98, P<.0001), as well as between the microhardness and the coefficient of thermal expansion (r = -0.98, P<.0001) were observed. On the other hand, a linear correlation between the %wt of filler and microhardness of compomers was exhibited (r = -0.96, P<.0001). The microhardness values for Compoglass F, Elan, and F2000 were 43.82 +/- 1.62, 58.16 +/- 1.90, and 72.94 +/- 3.29, respectively.

CONCLUSION

Within the limitations of this study, an inverse correlation between percent weight of filler and coefficient of thermal expansion, and a linear correlation between percent weight of filler and microhardness was observed for the evaluated compomers.

[Correlation between degree of conversion, microhardness and inorganic content in composites]

The purpose of this study was to evaluate the correlation between degree of conversion and microhardness in dental composites, as well as the effect of the inorganic content and type of photo-curing unit on these parameters. Three indirect composites (Artglass, Solidex and Zeta LC) were polymerized by means of three different laboratorial units (UniXS, Solidilite and an experimental device). For each material, fifteen samples were prepared using a metal matrix. The degree of conversion was analyzed by means of infrared spectroscopy, and microhardness was also assessed. The inorganic content was measured by means of thermogravimetric analysis (TGA). The Pearson s test was carried out in order to determine correlations. The degree of conversion of Artglass ranged from 37.5% to 79.2%, and its microhardness, from 32.4 to 50.3 (r = 0.904). The degree of conversion of Solidex ranged from 41.2% to 60.4%, and its microhardness, from 33.3 to 44.1 (r = 0.707). The degree of conversion and the microhardness of Zeta LC ranged from 62.0% to 78.0% and from 22.6 to 33.6, respectively (r = 0.710). It was concluded that the utilization of different photo-curing units caused variations on the degree of conversion, as a result of specific characteristics of each unit. For each material, there was strong correlation between the degree of conversion and microhardness. In addition, when different materials were compared, microhardness was more affected by filler content than by the degree of conversion.

Mechanical properties and radiopacity of experimental glass-silica-metal hybrid composites

OBJECTIVES

Experimental glass-silica-metal hybrid composites (polycomposites) were developed and tested mechanically and radiographically in this fundamental pilot study. To determine whether mechanical properties of a glass-silica filled two-paste dental composite based on a Bis-GMA/polyglycol dimethacrylate blend could be improved through the incorporation of titanium (Ti) particles (particle size ranging from 1 to 3 microm) or silver-tin-copper (Ag-Sn-Cu) particles (particle size ranging from 1 to 50 microm) we measured the diametral tensile strength, fracture toughness and radiopacity of five composites.

METHODS

The five materials were: I, the original unmodified composite (control group); II, as group I but containing 5% (wt/wt) of Ti particles; III, as group II but with Ti particles treated with 4-methacryloyloxyethyl trimellitate anhydride (4-META) to promote Ti-resin bonding; IV, as group I but containing 5% (wt/wt) of Ag-Sn-Cu particles; and V, as group IV but with the metal particles treated with 4-META. Ten specimens of each group were tested in a standard diametral tensile strength test and a fracture toughness test using a single-edge notched sample design and five specimens of each group were tested using a radiopacity test.

RESULTS

The diametral tensile strength increased statistically significantly after incorporation of Ti treated with 4-META, as tested by ANOVA (P=0.004) and Fisher's LSD test. A statistically significant increase of fracture toughness was observed between the control group and groups II, III and V as tested by ANOVA (P=0.003) and Fisher's LSD test. All other groups showed no statistically significant increase in diametral tensile strength and fracture toughness respectively when compared to their control groups. No statistically significant increase in radiopacity was found between the control group and the Ti filled composite, whereas a statistically significant increase in radiopacity was found between the control group and the Ag-Sn-Cu filled composite as tested by ANOVA (P=0.000) and Fisher's LSD procedure.

SIGNIFICANCE

The introduction of titanium and silver-tin-copper fillers has potential as added components in composites to provide increased mechanical strength and radiopacity, for example for use in core materials.

Analysis of composite type and different sources of polymerization light on in vitro toothbrush/dentifrice abrasion resistance

OBJECTIVES

This study examined toothbrush/dentifrice abrasion of a photo-activated prosthetic composite (dentin and enamel variations) for the purpose of evaluating the influence of polymerization sources on abrasive wear.

METHODS

A photo-activated prosthetic composite material (Artglass) was assessed. Dentin and enamel variations were polymerized using a proprietary photo-curing unit with two xenon stroboscopic lamps (UniXS), and other enamel specimens were polymerized either with a laboratory photo-curing unit with three fluorescent tubes or with a high intensity unit with two metal halide lamps. All specimens were stored in water for 14days and subjected to toothbrush/dentifrice abrasion (350g vertical load) using an abrasive slurry (Colgate Fluoriguard) and a toothbrush (Oral-B 40). The amount of vertical loss and the surface roughness of the specimens after 20,000 strokes were determined by profilometer. Average values of groups of five specimens were compared using analysis of variance (ANOVA) and Sheffe's S intervals (p<0.05).

RESULTS

When polymerizing with the proprietary unit, the abrasion and surface roughness of the enamel material required respective means of 34.08microm (+/-3.66) and 1.00microm (+/-0.08), and the those of the dentin material required means of 42.02microm (+/-5.62) and 1.23microm (+/-0.20). Both abrasion and surface roughness after toothbrushing of the enamel material were significantly smaller than were those of the dentin material. The abrasion of specimens polymerized with the metal halide unit required a mean of 23.89microm (+/-6.17) and demonstrated minimal wear.

CONCLUSIONS

The use of a high intensity metal halide photo-curing unit effectively enhanced the abrasion resistance of the composite. Surfaces of restorations should be covered with the enamel material in order to achieve smoothness and wear resistance.

Wear and surface roughness of current prosthetic composites after toothbrush/dentifrice abrasion

STATEMENT OF PROBLEM

Surface changes of prosthetic composites caused by toothbrushing are known, although composite materials have been improved and are now widely used for various kinds of prosthetic restorations.

PURPOSE

This study evaluated the influence of toothbrushing on abrasive wear and surface roughness of current prosthetic composites.

MATERIAL AND METHODS

Seven composite materials (Artglass, Axis, Cesead II, Conquest Sculpture, Estenia, Infis, and Targis) were assessed, and a machinable ceramic material (Cerec 2 Vitablocs) was used as a reference. Composite specimens polymerized with their proprietary curing units and sectioned ceramic specimens were stored in water for 14 days, and subsequently subjected to toothbrush-dentifrice abrasion. The amount of vertical loss and the surface roughness of each specimen after 20,000 strokes were determined with a profilometer. Average values of groups of 5 specimens were compared with ANOVA and Duncan new multiple range test.

RESULT

Significantly (P < .05) less wear was observed with respect to the Targis (10.01 microm; SD = 0.53 microm) and Estenia (13.04 microm; 1.95 microm) materials than for the other composites assessed, whereas Artglass (34.08 microm; 3.66 microm) and Conquest Sculpture (31.78 microm; 4.67 microm) materials demonstrated the most wear. The least surface roughness was exhibited by Conquest Sculpture (Ra, 0.54 microm; 0.07 microm) material, and the greatest by Cesead II (1.10 microm; 0.13 microm). Ceramic material showed a more wear-resistant (4.54 microm; 0.79 microm) and smoother (0.26 microm; 0.02 microm) surface than any of the composite materials.

CONCLUSION

Abrasion and surface roughness of the prosthetic composites caused by toothbrushing varied in accordance with the material. Type of prosthetic composite significantly influenced the surface condition after toothbrushing.

Effectiveness of polymerization of a prosthetic composite using three polymerization systems

STATEMENT OF PROBLEM

Although properties of laboratory-polymerized composite materials are influenced by the type of polymerizing unit, little information is available regarding the comparison between use of a high-intensity light source and application of secondary heat treatment.

PURPOSE

This study examined properties of a prosthetic veneering composite polymerized with 3 polymerizing systems to evaluate the effects of varying polymerization modes on hardness, solubility, and depth of cure.

MATERIAL AND METHODS

A composite material designed for a prosthetic veneer (Conquest Crown and Bridge) was polymerized using 3 methods: (1) exposure in the proprietary photopolymerizing unit with 2 halogen lamps (Cure-Lite Plus), followed by heating in an oven (Conquest Automatic Curing Unit); (2) exposure in a photopolymerizing unit with a xenon stroboscopic light source (Dentacolor XS); and (3) exposure in a photopolymerizing unit with 2 metal halide lamps (Hyper LII). Knoop hardness, water solubility, and depth of cure were determined for groups of 5 specimens, according to standardized testing methods. Data were compared using analysis of variance and the Duncan new multiple range test (P <.05).

RESULT

The hardness number generated with the metal halide unit was statistically greater than those produced by the other 2 methods, and material component released into water was minimal when the material was exposed with the metal halide unit (P <.05). Among the 3 photopolymerizing units, the metal halide unit consistently exhibited the greatest depth of cure.

CONCLUSION

Certain properties generated with the use of the high-intensity polymerizing unit exceeded those obtained from a proprietary system that requires a postheat treatment.

Curing depth of prosthetic composite materials polymerized with their proprietary photo-curing units

This study examined curing depth of eight prosthetic composite materials polymerized by means of six photo-curing units for the purpose of evaluating the curing performance of material-curing unit combinations. Each composite material was exposed with a photo-curing unit recommended by the manufacturer. The light sources of the units were halogen/fluorescent, xenon, metal halide, fluorescent, and halogen lamps, and exposure periods were 20, 30, 60, and 90 s. Curing depth of the materials was determined according to the method described by the International Organization for Standardization (ISO 4049). The results were analysed by factorial analysis of variance (ANOVA) and multiple comparison intervals. Two-factor ANOVA revealed that the depth of cure was influenced both by the material-unit combination and by the exposure period (P = 0.0001). Among the eight combinations, a hybrid composite material (Prywood color) polymerized with a metal halide curing unit (Hyper LII) exhibited the greatest depth of cure after 90-s exposure. For all combinations, longer exposure increased the depth of cure.

Curing depth of four composite veneering materials polymerized with different laboratory photo-curing units

Post-curing properties of composite materials are influenced by the type of base monomer, activation system, filler content, and also by the type of light source employed. This study examined curing depth of four composite veneering materials polymerized by means of two different high-intensity photo-curing units for the purpose of evaluating the curing performance of the combinations of composite material and photo-curing unit. Two microfilled and two hybrid composite materials designed for prosthetic veneer were assessed. The composite materials were cured using two photo-curing units, one with a xenon light source and one with two metal halide light sources, and exposure periods varied from 20 to 90 s. Curing depth of the materials was determined with a scraping technique described by the International Organization for Standardization (ISO 4049). Three-factor analysis of variance revealed that the depth of cure was influenced by the type of composite material as well as by the photo-curing unit, and also by the exposure period (P = 0.0001). A microfilled composite material (Dentacolor) demonstrated the greatest depth of cure (4.69 mm) after 90 s irradiation with a metal halide unit (Hyper LII). Of the two photo-curing units, the metal halide curing unit consistently exhibited greater depth of cure than the xenon curing unit (Dentacolor XS). Longer exposure increased the depth of cure for all combinations.

Properties of four composite veneering materials polymerized with different laboratory photo-curing units

This study examined properties of four composite veneering materials polymerized with two different photo-curing units for the purpose of evaluating curing performance of the combination of composite material and curing unit. Two microfilled (Dentacolor and Thermoresin LC II) and two hybrid (Cesead II and Solidex) composite materials designed for prosthetic veneer were selected. The respective light sources of the units were a xenon (Dentacolor XS) and a metal halide (Hyper L II) lamp. The composite materials were exposed with the photo-curing unit for 60 s on each side (i.e. from top and bottom). Knoop hardness, compressive strength, flexural strength, flexural modulus, water absorption and water solubility were determined according to standardized testing methods. The specimens exposed with the metal halide unit generally exhibited greater Knoop hardness number, and compressive strength and lower solubility than those exposed with the xenon unit. A microfilled material (Thermoresin LC II) cured with the metal halide unit exhibited significantly improved results for all tests as compared with the same material cured with the xenon unit.

Curing depth of a composite veneering material polymerized with seven different laboratory photo-curing units

Properties of laboratory-cured composite materials are affected by the type of activation system as well as by the photo-curing unit light source. This study examined curing depth of a composite veneering material polymerized by means of various photo-curing units with the aim of evaluating the curing performance of the light sources. A microfilled composite material designed for prosthetic veneer was cured with seven photo-curing units. The light sources of the units were halogen/fluorescent, xenon, metal halide, fluorescent, halogen, halogen and mercury lamps. Exposure periods were 20, 30, 60 and 90 s. The curing depth of the material was determined using the method described by the International Organization for Standardization (ISO 4049). Two-factor analysis of variance revealed that the depth of cure was influenced both by the type of curing unit and by the exposure period (P = 0.0001). Among the seven photo-curing units, a metal halide curing unit consistently exhibited the greatest depth of cure. For all units, longer exposure increased the depth of cure.

A metal halide light source for laboratory curing of prosthetic composite materials

A high-intensity laboratory photo-curing unit has been developed with the aim of improving the post-curing properties of composite veneering materials. This study introduces the structure of the curing unit and examines the resulting properties of a representative composite material. The curing unit is equipped with two metal halide lamps that radiate both ultraviolet and visible light. Unlike conventional metal halide lamps for industrial use, these metal halide lamps radiate an increased intensity of visible radiation. Properties of a microfilled composite veneering material cured with the new metal halide unit were ascertained. A xenon photo-curing unit was also used as a control. The specimens cured with the metal halide unit exhibited greater Knoop hardness numbers and flexural moduli as compared with those cured with the xenon unit, and also showed reduced water solubility values. These results suggest that the metal halide light source is effective in curing composite materials within a shorter period of time and with improved conversion.

Review of dental materials citations: Part B, July to December 1995

OBJECTIVE

A lag of many months occurs between journal issue publication and updates to electronic databases. The objective of this literature analysis was to identify and categorize all of the dental materials citations in biomedical journals that were published from July 1995 through December 1995.

METHODS

Seventeen primary and 51 secondary journals were searched using their tables of contents to detect and record dental materials publications from July to December of 1995. Those journals that were typically rich in dental materials articles were classified as primary ones. Citations were categorized into 17 topics and divided into subsections. The review excluded case reports, most literature related primarily to dental implants, and most articles on biomedical materials used outside of the field of general dentistry.

RESULTS

The greatest number of citations was related to topics of dentin bonding and resin-based restorative filling materials (composites and glass ionomers). There was no major change in the number of dental materials publications per year reported from 1993 (n = 786) to 1995 (n = 751).

SIGNIFICANCE

This citation list provides a comprehensive resource for use by academicians and researchers to bridge the gap between initial publication and access to electronic searching methods for major databases.