Modulated photoactivation methods: Influence on contraction stress, degree of conversion and push-out bond strength of composite restoratives

Objectives

Verify the influence of curing methods on contraction stress, stress rate, and degree of conversion (DC) of a restorative composite and on bond strength of composite restoratives.

Methods

For the stress test, composite (0.84 mm thick) was applied between two 5-mm diameter glass rods, mounted in a servohydraulic machine. Stress rate was taken by the value of stress/time at each second. DC was measured by micro-FTIR. Bond strength testing was performed using a push-out test. The C-factor in all tests was 3.0. Four curing methods were tested: continuous light (CL), soft-start (SS), and two pulse delay methods using different initial irradiances—150 mW/cm² (PD150) and 80 mW/cm² (PD80). Results were analyzed by ANOVA and Tukey's test (α = 0.05).

Results

Stress values ranged from 7.9 MPa (PD80) to 10.3 MPa (CL). No statistical difference was verified among CL, SS, and PD150. PD80 presented statistically lower stress values compared to CL and SS. CL presented the highest maximum stress rate, followed by SS, PD150 and PD80. Mean DC values ranged from 54.2% (PD150) to 55.9% (PD80), with no difference observed among the methods. For the bond strength test, values ranged from 26.4 MPa (CL) to 35.5 MPa (PD150). PD150 and PD80 were both statistically superior to SS and CL. SS presented statistically higher bond strength compared to CL.

Conclusions

Modulated curing methods were shown to be effective in reducing contraction stress rate and improving the strength of the bonded interface, and without compromising the DC of the restorative composite.     

Shrinkage stress in light-cured composite resins: influence of material and photoactivation mode.

OBJECTIVES: The aim of this study was to record the effect of composite type and photoactivation mode on the stresses resulting from polymerization of five established composite resins: packable (Solitaire, Solitaire 2), micro-hybrid (Aelitefil, Z100) and hybrid (Clearfil AP-X). METHODS: A mechanical testing machine was used to record the polymerization contraction stress (MPa) of cylindrical composite specimens (d=5mm; h=2mm; C-factor=1.25) at 0.1s intervals over a period of 400s. The samples were photopolymerized using a halogen light curing device under two types of light exposure: group 1, Standard (800mW.cm(-2)x60s); group 2, Exponential (logarithmic increase from 150 to 800mW.cm(-2) over 15s+800mW.cm(-2)x45s). The stress rate (SR: slope(MPa>0-60s)) and the maximum shrinkage stress (MSS: MPa(400s)) of each material (five replications) were statistically analysed by one-way ANOVA/Scheffe's test and Pearson's correlation procedure (alpha=0.05). Finally, Student's t-test (two matched series) enabled the assessment of the effect of the irradiation method on the results. RESULTS: For group 1, in decreasing order, the MSS was 1.51+/-0.07MPa (Solitaire) statistically equivalent to 1.45+/-0.06MPa (Aelitefil), 1.29+/-0.08MPa (Solitaire 2), and 1.04+/-0.03MPa (Z100) statistically equivalent to 0.92+/-0.05MPa (Clearfil AP-X). Z100 showed the highest SR (0.045+/-6x10(-3)) and Solitaire, the lowest (0.017+/-2x10(-3)). There was no correlation between SR and MSS (r<-0.33, p<0.05). For group 2, the MSS and SR values were distributed in a similar way to those from group 1. There was a negative correlation between SR and MSS (r<-0.43 and p<0.01). The exponential ramp successfully reduced the MSS (-3.9%) and SR (-11%) values. SIGNIFICANCE: There is no relationship between composite resin type, stress rate and shrinkage stress levels. The slower stress rate development, resulting from ramped light intensity, helped slightly to reduce the maximum polymerization stress.     

Effect of different photoactivation techniques on the bond strength of a dental composite

Using the push-out test, this study evaluated the bond strength of the composite resin Z250 (3M/ESPE) photoactivated with the XL2500 (3M/ESPE) quartz-tungsten-halogen light-curing unit with different curing protocols: soft-start (150 mW/cm2 for 2 s (S2), 3 s (S3), 5 s (S5), 10 s (S10) or 15 s (S15), followed by 700 mW/cm2 for 15 s; pulse-delay (150 mW/cm2 for 2 s (P2), 3 s (P3), 5 s (P5), 10 s (P10) or 15 s (P15), with a 1-min delay, followed by 700 mW/cm2 for 15 s. After storage at 37°C ± 1 for 24 h ± 1, the specimens were ground, polished and subjected to a push-out test in a universal test machine (Instron) with a cell load of 500 N at a crosshead speed of 0.5 mm/min. The data were analyzed statistically by ANOVA and Tukey's test at 5% significance level. There were no statistically significant differences (p>0.05) among the groups photoactivated using the soft-start mode. For the pulse-delay mode, P5 promoted the highest bond strength (p<0.05). Groups photoactivated with the pulse-delay mode (except for P2 and P15) presented significantly higher bond strength than those photoactivated with the soft-start. It may be concluded that the influence of initial exposure time was curing method-dependent, with the best results obtained using the pulse-delay method with 5 s in the first photoactivation cycle.     

Influence of the photoinitiator system and light photoactivation units on the degree of conversion of dental composites

The aim of this study was to observe the influence of two light polymerization units (LED or halogen light) on the degree of conversion (DC) of three dental composites with lighter shades and a different photoinitiator system. The top (T) and bottom (B) surfaces of 60 discs of composite resin (Filtek? Supreme, Filtek? Z250, Tetric? Ceram Bleach) cured either by LED or by halogen lamp (HL) were studied using an FT-Raman spectrometer. The degree of conversion (DC) was evaluated by following the changes in the intensity of the methacrylate C=C stretching mode at 1640 cm?1. The calculated DC ranged from 54.2% (B) to 73.4% (T) and from 60.2% (B) to 76.6% (T) for the LED and HL, respectively. LED and halogen devices were able to produce an adequate DC for all the resins tested.     

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

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

Effect of temperature on composite polymerization stress and degree of conversion

Objective

To test the following hypotheses: (1) degree of conversion (DC) and polymerization stress (PS) increase with composite temperature (2) reduced light-exposure applied to pre-heated composites produces similar conversion as room temperature with decreased PS.

Methods

Composite specimens (diameter: 5 mm, height: 2 mm) were tested isothermally at 22 °C (control), 40 °C, and 60 °C using light-exposures of 5 or 20 s (control). DC was accessed 5 min after light initiation by FTIR at the specimen bottom surface. Maximum and final PS were determined, also isothermally, for 5 min on a universal testing machine. Non-isothermal stress was also measured with composite maintained at 22 °C or 60 °C, and irradiated for 20 s at 30 °C. Data were analyzed using two-way ANOVA/Tukey and Student's t-test (α = 5%).

Results

Both DC and isothermal maximum stress increased with temperature (p < 0.001) and exposure duration (p < 0.001). Isothermal maximum/final stress (MPa) were 3.4 ± 2.0b/3.4 ± 2.0A (22 °C), 3.7 ± 1.5b/3.6 ± 1.4A (40 °C) and 5.1 ± 2.0a/4.0 ± 1.6A (60 °C). Conversion values (%) were 39.2 ± 7.1c (22 °C), 50.0 ± 5.4b (40 °C) and 58.5 ± 5.7a (60 °C). The reduction of light exposure duration (from 20 s to 5 s) with pre-heated composite yielded the same or significantly higher conversion (%) than control (22 °C, 20 s/control: 45.4 ± 1.8b, 40 °C, 5 s s: 45.1 ± 0.5b, 60 °C, 5 s s: 53.7 ± 2.7a, p < 0.01). Non-Isothermal conditions showed significantly higher stress for 60 °C than 22 °C (in MPa, maximum: 4.7 ± 0.5 and 3.7 ± 0.4, final: 4.6 ± 0.6 and 3.6 ± 0.4, respectively).Clinical significance: Increasing composite temperature allows for reduced exposure duration and lower polymerization stress (both maximum and final) while maintaining or increasing degree of conversion.     

Effect of different initial light intensity by the soft-start photoactivation on the bond strength and Knoop hardness of a dental composite

This study evaluated the bond strength (push-out method) and Knoop hardness of Z250 composite resin, photoactivated with XL 2500 curing unit, using different protocols: continuous mode (700mW/cm(2) for 20s) (CO); soft-start (50 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS1); soft-start (100 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS2); soft-start (150 mW/cm(2) for 5 s, followed by 700mW/cm(2) for 15s) (SS3); soft-start (200mW/cm(2) for 5s, followed by 700mW/cm(2) for 15s) (SS4); soft-start (250mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS5); soft-start (300 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS6). For the push-out test, the specimens were tested in a universal testing machine at a crosshead speed of 0.5 mm/min. For the hardness test, the specimens were polished for the hardness measurements, using a 50 g load for 15 s. Data were submitted to ANOVA and Tukey's test (alpha=5%). The results of bond strength showed that the SS3 group obtained the highest bond strength when compared to the CO group. There were no significant differences among the other modes in relation to the other groups. Regarding the other results in hardness, there were no significant differences among the groups in the surface region and up to 4 mm depth.     

Contraction stress related to degree of conversion and reaction kinetics

Polymerization shrinkage of composites bonded to cavity preparations generates stress on the tooth/restoration interface. The purpose of this study was to verify the influence of degree of conversion and speed of polymerization reaction on contraction stress. We prepared experimental composites with different curing rates by varying the concentration of inhibitor (butylated hydroxytoluene). We verified the effect of degree of conversion by submitting one of the composites to different photo-activation times. Contraction stress was monitored for 10 minutes in a tensilometer. Fourier-transformed infrared spectrometry was used for assessment of the degree of conversion. Volumetric shrinkage was determined by means of a mercury dilatometer. Degree of conversion and volumetric shrinkage showed a non-linear relationship with energy density. Degree of conversion showed a pronounced influence on stress. Increased inhibitor concentration reduced curing rate and contraction stress in composites, without compromising the final degree of conversion.     

Effect of different photoactivation methods on the polymerization depth of a light-activated composite

This study verified the polymerization depth of the composite Z100 (3M Dental Products) by Knoop Hardness test using four photoactivation methods. Twenty cylindrical specimens (5 mm in diameter by 5 mm in height) were prepared in a metallic mold and photoactivated by one of the four methods: continuous light (520 mW/cm2 for 40 seconds); stepped light (150 mW/cm2 for 10 seconds followed by 520 mW/cm2 for 30 seconds); intermittent light (cycle of 1 second, 1/2 second with the light on and 1/2 second with the light off for 60 seconds at 520 mW/cm2) and Xenon plasma are (1370 mW/cm2 for 3 seconds). Knoop hardness measurements were obtained on the surface, at the depths of 1.5 mm, 2.5 mm, 4.0 mm and at the bottom area by the HMV-2000 microhardness, with a load of 50 grams for 30 seconds. Twenty-five indentations were performed in each sample, and a total of five samples were prepared for each photoactivation method. The obtained values were submitted to ANOVA and Tukey's test at the 5% significance level. The results indicated that (1) for the continuous light method, the values of hardness were statistically superior in the surface area when compared to other areas. For the other methods, there were no statistical differences between the surface area and 1.5 mm; (2) the continuous and stepped light methods showed the highest mean Knoop Hardness Number in all areas; (3) the Xenon plasma are method was not statistically different from continuous and stepped light ones on the surface at 1.5 mm and 2.5 mm of depth. However, a great decrease in hardness was observed in the deeper areas; (4) the intermittent light method showed intermediate results.     

The effect of different light-curing units on fatigue behavior and degree of conversion of a resin composite.

OBJECTIVES: The aim of this study was to investigate the effect of different light-curing units and irradiation modes on the mechanical fatigue strength and degree of conversion of a restorative resin composite. METHODS: Conventional halogen, plasma arc and blue LED light-curing units were used for polymerization of a resin composite (Tetric) Ceram, Ivoclar, Vivadent, Liechtenstein). Initial fracture strength (FS) and flexural fatigue limit (FFL) as well as degree of conversion (DC) were measured. The FFL was determined under cyclic loading for 10(5) cycles in terms of a staircase approach. The specimens were stored for 14 days in 37 degrees C distilled water prior to testing. The curing efficiency was observed with Fourier transform infrared micromultiple internal reflectance spectroscopy. The measurements were carried out at 0.5 and 2.5 mm distance from the directly irradiated surface after 14 days storage in dark and dry conditions at 37 degrees C. RESULTS: The highest FS, FFL and DC were observed from high energy curing devices and from extended curing intervals. The conventional halogen light exhibited the most homogenous in-depth curing efficiency along with a low loss of mechanical resistance under cyclic fatigue. SIGNIFICANCE: Evaluation of flexural fatigue limit and curing efficiency correlate in terms of decreased mechanical strength due to insufficient light-curing intervals or light intensities. Initial promising fracture strengths do not correlate with a clinically more relevant fatigue loading and with the in-depth degree of conversion, both accounting for a significantly reduced strength performance.     

Effect of resin liners and photoactivation methods on the shrinkage stress of a resin composite

Purpose: This study was undertaken to evaluate the effect of three different photoactivation methods on the polymerization shrinkage stress of a resin composite using different resin liners.
Materials and Methods: Three photoactivation methods using a quartz-tungsten-halogen light were evaluated: continuous light, soft start, and intermittent light. Three lining groups were tested: one or three coats of adhesive, and flowable composite. The stress was measured using a universal testing machine. After the stress measurement, Knoop hardness numbers (KHNs) were evaluated to verify indirectly the degree of conversion of the composite using the three photoactivation methods. The data were submitted to analysis of variance and Tukey's test (   p < .05  ).
Results: Intermittent light was always associated with statistically lower stress values when compared with continuous light. Statistical differences were not observed when continuous light and soft start were compared. The use of a flowable composite liner significantly reduced the stress generation when compared with the use of one adhesive coat. The three adhesive coats groups showed intermediate stress values. The hardness test showed no statistical difference between that achieved with continuous light and soft start. These two methods showed statistically higher KHNs when compared with results with intermittent light.

CLINICAL SIGNIFICANCE

Photoactivation using intermittent light may lead to a significant reduction in shrinkage stress levels. This effect could be attributed to a significant reduction of the polymerization rate and/or a decrease in the degree of conversion. The use of a flowable composite liner reduced the stress levels when compared with levels when one coat of adhesive was used. This is possibly related to the higher thickness of the flowable composite layer.     

Diametral tensile strength of composite resins submitted to different activation techniques

The aim of this study was to evaluate the diametral tensile strength (DTS) of composite resins submitted to different curing techniques. Four composite resins were tested in this study: Targis (Ivoclar), Solidex (Shofu), Charisma (Heraeus-Kulzer) and Filtek Z250 (3M Espe). Sixty-four cylindrical specimens were prepared and divided into eight groups according to each polymerization technique (n = 8). The indirect composite resins (Targis and Solidex) were polymerized with their respective curing systems (Targis Power and EDG-lux); Charisma and Filtek Z250 were light-cured with conventional polymerization (halogen light) and additionally, with post-curing systems. Specimens were stored in artificial saliva at 37 degrees C for one week. DTS tests were performed in a Universal Testing Machine (0.5 mm/min). The data were statistically analyzed by ANOVA and Duncan tests. The results were (MPa): Z250/EDG-lux: 69.04 feminine; Z250/Targis Power: 68.57 feminine; Z250/conventional polymerization: 60.75b; Charisma/Targis Power: 52.34c; Charisma/conventional polymerization: 49.17c; Charisma/EDG-lux: 47.98c; Solidex: 36.62d; Targis: 32.86d. The results reveal that the post-cured Z250 composite resin showed the highest DTS means. Charisma composite presented no significant differences when activation techniques were compared. Direct composite resins presented higher DTS values than indirect resins.     

Monomer conversion versus flexure strength of a novel dental composite

OBJECTIVES: To quantify the monomer conversion and flexural strength of an experimental oxirane-based composite material (EXL596) compared with two, commercially available, dimethacrylate based restoratives (Z250 and Z100). METHODS: Fourier-transform infra-red spectroscopy (FTIR) was utilised to evaluate the degree of conversion (DC) (n=5) and biaxial flexure strength (BFS) testing (n=20) was used to analyse flexural strength and associated Weibull moduli (m) of each material following 0.1, 0.5, 1, 4, 24 and 48 h immersion in a lightproof waterbath maintained at 37+/-1 degrees C. RESULTS: The DC of Z250 and Z100 following 0.1, 0.5 and 1 h post-irradiation was significantly greater than the DC of EXL596 for the same immersion periods. This was manifested as a significant decrease in BFS and associated m of EXL596 compared with Z250 and Z100 for the 0.1, 0.5 and 1 h post-irradiation periods. The DC and BFS of EXL596 were significantly greater than Z250 and Z100 following 24 h immersion. CONCLUSIONS: Assessment of FTIR spectra, BFS and associated m has provided a useful method in the quantitative analysis of resin-based composite conversion. Identification of the decreased DC of EXL596 compared with Z250 and Z100 was achieved using FTIR. However, decreased conversion rates within the first hour following irradiation of EXL596 may compromise flexural strength properties (associated with a decrease in BFS and m) which may be inadequate under masticatory loading.     

Shrinkage stress developed by polymerization of composite resin

The effects of the shrinkage stress on the various cavity forms, were examined. The shrinkage stress was obtained from the displacement of the brass mold developed by polymerization of the composite resin. The shrinkage stress developed in the cavity wall, was analyzed by the finite element method, and the crack of the cylindrical silica tube filled with composite resin, was observed. The shrinkage stress 30 minutes after mixing the composite resin was reduced with the increase in the marginal angle as well as the diameter or the depth of cavity. Preparation of the bevel at the cavity margin reduced the shrinkage stress. In the case of reverse bevel, reduction of the stress was not observed within 24 hours, but in the other cases, the stress immediately decreased after hardening. The analysis by the finite element method reveoled the maximum stress at the margin, with less stress for the round, flat and reverse bevel in this order. For the observation of the cylindrical silica tube filled with composite resin, the crack was observed in the cylindrical silica tubes prepared round, flat or without bevel, it was not observed in the tube prepared reverse bevel that the crack was developed in this tube and composite resin was detached from this tube within 24 hours.     

Variation in composite degree of conversion and microflexural strength for different curing lights and surface locations

Background

Lack of irradiance-beam profile uniformity across the emission area of light-curing units (LCUs) may result in suboptimal properties of composite restorations. The authors’ objective for this study was to assess the variation in local cure of 1 composite at 3 different LCU emission area locations cured with 3 different LCUs by means of testing the degree of conversion (DC) and microflexural strength.

Evaluation of the roughness of composite resins submitted to different surface treatments

The aim of this study was to evaluate the surface roughness of restorative composite resins after polishing with aluminum oxide discs and applying an adhesive layer The following composite resins were used: Filtek Z250 (hybrid, 3MESPE, A2) and Filtek Supreme XT (nanofilled, 3M ESPE, A2E). Thirty specimens of each composite were made using a condensation silicone mold (5.0 x 2.0 mm) into which the composites were inserted and submitted to light pressure. After polymerization using the halogen light source Curing Light 2500 (3M) for 40 seconds, the specimens were assigned to the following groups: G1-Z250/CO- control, did not receive any treatment; G2-Z250/SL--the specimens underwent finishing and polishing with Sof-Lex discs; G3-Z250/ADE, application of an adhesive layer on the top of the specimen and light curing for 20 seconds. Groups G4, G5 and G6 followed the same treatment sequence, but using Filtek Supreme XT The specimens were stored in deionized water at 37 degrees C for 24 h. Three readings of surface roughness were made for each specimen. The results were submitted to variance analysis by Two-Way ANOVA Test and Tukey HSD Test. The mean values obtained were: G3 (0.2325 +/- 0.1484 microm) and G6 (0.2266 +/- 0.0463 microm), which were higher than the other groups and did not differ statistically from each other. Groups G1 (0.1023 +/- 0.0464 microm), G4 (0.1083 +/- 0.0241 microm), G5 (0.1160 +/- 0.0252 microm) and G2 (0.1360 +/- 0.0131 microm) had the lowest average roughness and did not differ statistically among each other. It was concluded that the Sof-Lex discs performed better for the surface treatment of the composites resins tested, producing similar values of surface roughness for both composites. Covering with dentin adhesive increased the surface roughness in both composites.     

Cytotoxic effects of dental bonding substances as a function of degree of conversion

ObjectivesRecently, we found that dental bonding substances tested alone or in combination with composites are far more cytotoxic than composite materials alone. These data are in line with several cytotoxicity reports but contradict in vivo studies showing the beneficial effects of bonding materials. The aims of the present study were to develop a preparation method for composite specimens modelling conditions in the oral cavity and to analyse the influence of bonding substances on the cytotoxicity of six different composite materials.MethodsCylindrical composite specimens were prepared in polyethylene blocks containing 5 mm diameter cylindrical holes (cylinder height 2 mm), covered with a polyethylene foil and light cured from one end for 40 s. In a second series of experiments, composite specimens were combined with bonding materials. Bonding was applied onto the polyethylene foil in one or two layers and light cured according to the manufacturers’ instructions. Subsequently, polyethylene moulds were placed on top of the bonding materials and composites prepared as described above. After unilateral light curing from the top of the cylindrical holes, visual confirmation of adherence at the base was obtained. Specimens were added to the cultures immediately after production or after preincubation for 7 days under cell culture conditions. Specimens were incubated with L-929 fibroblasts for 72 h and cell numbers determined by flow cytometry. To evaluate the degree of conversion (DC) of bonding materials cured with and without air inhibition a third series of experiments was performed. FTIR spectroscopic measurements were made on thin-films of dentin-bonding agents, cured under both an-aerobic and aerobic conditions, to determine degree of conversion.ResultsCytotoxicities of all six tested composites were significantly different (p < 0.0001) and diminished after 7 days of preincubation (p < 0.0001). Bonding substances had no statistically significant influence on the cytotoxicity of composite materials (p = 0.159). A highly significant statistical reduction in the degree of conversion for each resin cured under air inhibition conditions was documented (p < 0.01).SignificanceOur study demonstrates that cell culture toxicity data are highly model dependent and that internationally standardized test protocols for toxicity screening of dental materials in line with the existing standards are clearly needed to obtain comparable results.     

Two-body wear resistance and degree of conversion of laboratory-processed composite materials

PURPOSE: The purpose of this investigation was to evaluate the relative 2-body abrasive wear and degree of conversion of 4 laboratory-processed composites (Targis, Concept, belleGlass, and Artglass) and 2 direct placement composites (Herculite and Heliomolar) after 7 days of storage. MATERIALS AND METHODS: Human enamel was used as a positive control for 2-body abrasive wear, and 10 cylindric specimens (3.5-mm diameter, 8-mm height) of each material were prepared and stored in distilled water at 37 +/- 2 degrees C for wear testing. Relative 2-body abrasive wear rates were determined using a 30-micron diamond disk and a 2-body pin-on-disk apparatus. Subsequently, 3 polymerized specimens that had been stored in sealed polyethylene vials for 7 days were prepared for degree of conversion testing. The degree of conversion was determined on an infrared spectrometer using standard baseline techniques and various internal standards. RESULTS: Statistical analysis using analysis of variance and the Tukey-Kramer multiple range test indicated significant differences between several of the materials tested for both 2-body abrasive wear and degree of conversion. CONCLUSION: Concept exhibited significantly less 2-body abrasive wear compared to the direct and indirect composites (P < 0.01). Concept and belleGlass exhibited a mean degree of conversion that was significantly higher than any of the other composites tested (P < 0.01).