The relationship between cure depth and transmission coefficient of visible-light-activated resin composites

Preparation of Al-doped mesoporous silica spheres (Al-MSSs) for the improvement of mechanical properties and aging resistance of dental resin composites

OBJECTIVE

The purpose of this study was to synthesize Al-doped mesoporous silica spheres (Al-MSSs) and evaluate the effect of them as functional fillers on the mechanical properties and aging resistance of dental resin composites.

METHODS

Al-MSSs were prepared by a two-step method. The effect of Al-MSSs on the performance of the composites was evaluated using neat resin matrix, commercial composites 3M Z350XT and samples containing mesoporous silica spheres (MSSs) and nonporous silica spheres (NSSs) as control. The neat resin matrix consisted of resin monomer (Bisphenol A glycerolate dimethacrylate/triethylene glycol dimethacrylate, 49.5/49.5, wt%) and photoinitiator (camphor quinone/Ethyl-4-dimethylaminobenzoate, 0.2/0.8, wt%). The mechanical properties (flexural strength, flexural modulus, compressive strength and microhardness) of them were evaluated by a universal testing machine and microhardness tester. The mechanical stabilities of the prepared composites in wet environment were evaluated by immersing them in deionized water at 37 °C. In addition, we evaluated the effect of Al-MSSs on other properties of the dental resin composites such as polymerization shrinkage, degree of conversion, curing depth, contact angle, water sorption and solubility according to ISO 4049: 2019.

RESULTS

The synthesized Al-MSSs possessed good dispersibility with an average particle size of about 505 ± 16 nm. The mechanical properties of resin composites gradually increased with the increase of the loading amounts of inorganic fillers. The reinforcing effect of Al-MSSs was similar to that of MSSs and better than that of the NSSs groups at the same filler loading. After aging in deionized water at 37 °C for 30 days, the mechanical properties of all resin composites decreased. However, the decrease percentage of the composites filled with Al-MSSs was significantly lower than the other groups, indicating that the stability of the dental composites in wet environments was significantly improved by the Al-MSSs fillers. Furthermore, Al-MSSs had no obvious influence on the biocompatibility and other properties of dental resins.

SIGNIFICANCE

The prepared Al-MSSs could effectively improve the mechanical properties and aging resistance without sacrificing other physic-chemical properties of dental resin composites.

Zeolite/Polymer Composites Prepared by Photopolymerization: Effect of Compensation Cations on Opacity and Gas Adsorption Applications

The fabrication of structured zeolite adsorbents through photopolymerization-based 3D printing which offers a solution to the limitations of conventional shaping techniques has been demonstrated but many parameters still need to be optimized. In this study, we studied the influence of zeolite compensation cations on the photopolymerization and the composite's properties. Modified zeolites (LTA 4 A and FAU 13X exchanged with K+ , Li+ , Sr2+ , Ca2+ or Mg2+ ) were incorporated in PEGDA with BDMK as photoinitiator, and the formulation was cured under mild conditions (LED@405 nm, room temperature, under air). Our results indicate that the nature of zeolite compensation cations affects the colorimetric properties of polymer/zeolite composites: a better translucency parameter results in higher depth of cure. After calcination at 650 °C and complete removal of PEGDA, pure zeolitic monoliths were tested for adsorption of gas molecules of interest (carbon dioxide, dichlorobenzene and water). Structured 4 A and 13X monoliths obtained by 3D printing exhibit comparable adsorption capacity to commercial beads prepared from the same zeolites. This study enhances our understanding of the photopolymerization process involved in the production of polymer/zeolite composites. These composites are used in the fabrication of zeolitic objects through 3D printing, offering potential solutions to various environmental and dental challenges.

Strong-field THz radiation-induced curing of composite resin materials in dentistry

Dental caries is listed as one of the three major non-communicable diseases by the World Health Organization, and its main treatment method is to restore it by filling it with resin. At present, the visible light-cure method has the problems of non-uniform curing and low penetration efficiency, which makes the bonding area easy to develop marginal leakages, thus leading to secondary caries and requiring repeated treatment. In this work, through the strong terahertz (THz) irradiation-weak THz detection technique, it is found that the strong THz electromagnetic pulses can accelerate the curing process of the resin, and the weak-field THz spectroscopy can be used to monitor this dynamic change in real time, which will greatly promote the potential application of THz technology in dentistry.

Radical photoinitiation with LEDs and applications in the 3D printing of composites

Radical initiation upon LED light irradiation is discussed herein as well as its application in additive manufacturing. The ability of manufacturing complex structures, freedom of design, low energy consumption, fast prototyping, and excellent spatial resolution are the main benefits of the 3D printing technology by photopolymerization. Therefore, the 3D printing of composites through photopolymerization processes is developing rapidly in the academia and industry, and has been a turning point of additive manufacturing (AM). In the present review, an overview of radical initiation with LEDs (i.e., the photopolymerization LED technology, the photoinitiating systems, and the polymerizable media) and of the main 3D printing methods by photopolymerization, materials, and their applications in different fields has been carried out. As a challenging topic, the issue of light penetration in a filled matrix for the access to composites is discussed, including the light transmittance of the composite, the mismatch of the refractive index between the filler and the monomer, the factors of the filler, and the adverse influence of low light penetration on the 3D printing process. In particular, the popular applications of 3D printing by photopolymerization in biomedical science, electronic industry, materials for adsorption, and 4D printing are discussed. Overall, this review gives an overview of the 3D printing of polymer matrix composites through photopolymerization processes as a benchmark for future research and development.

Analysis of transmittance and degree of conversion of composite resins

The objective of this study was to evaluate and correlate light transmittance (T), initial degree of conversion (IDC), and degree of conversion after 24 hr (DC24) for 22 composite resins (CR) for enamel and dentin use. The transmittance (n = 10) was measured with a spectrometer at a wavelength of 468.14 nm. The degree of conversion (DC; n = 5) was measured with Fourier Transform Near-Infrared Spectroscopy before polymerization, immediately after photoactivation, and 24 hr after photoactivation. Both sets of values are provided as percentages. ANOVA and Games-Howell (α = 5%) tests showed that Filtek Supreme Ultra gave the highest T values of all enamel CRs, while Esthet-X HD presented the lowest. Meanwhile, Venus diamond gave the highest values of all dentin CRs, while Esthet-X HD gave the lowest. For IDC and DC24, ANOVA showed differences between individual CRs and the two CR types (p < .0001). Despite the limitations of this study, it can be concluded that there was no correlation between T and either IDC or DC24 (p > .05); however, IDC and DC24 were strongly correlated (p < .05) by Pearson's correlation. That being said, as a higher DC reflects better mechanical properties, certain conclusions can be drawn about overall performance. The best IDC values were observed for the Opallis enamel resin and the Opallis and Premise dentin resins. Meanwhile, the best DC24 values were observed for the Opallis, Charisma, and Premise enamel resins and the Opallis and Premise dentin resins. Degree of conversion and light transmittance showed differences between composite resin types (enamel and dentin) and brands. It is important to know at the moment of composite choice taking into account mechanical and optical properties.

Effect of Polymerization Time and Home Bleaching Agent on the Microhardness and Surface Roughness of Bulk-Fill Composites: A Scanning Electron Microscopy Study

OBJECTIVE

The aim of this study is to evaluate the microhardness and surface roughness of two different bulk-fill composites polymerized with light-curing unit (LCU) with different polymerization times before and after the application of a home bleaching agent.

MATERIALS-METHODS

For both microhardness and surface roughness tests, 6 groups were prepared with bulk-fill materials (SonicFill, Filtek Bulk Fill) according to different polymerization times (10, 20, and 30 s). 102 specimens were prepared using Teflon molds (4 mm depth and 5 mm diameter) and polymerized with LCU. 30 specimens (n = 5) were assessed for microhardness. Before home bleaching agent application, the bottom/top (B/T) microhardness ratio was evaluated. After bleaching agent application, the microhardness measurements were performed on top surfaces. Roughness measurements were performed in 72 specimens (n = 12) before and after bleaching application. Additionally, for SEM analyses, two specimens from all tested groups were prepared before and after bleaching agent application. The data B/T microhardness ratio before bleaching was analyzed by two-way ANOVA and Tukey's HSD test. The data from the top surface of specimens' microhardness before and after bleaching were analyzed using Wilcoxon signed-rank test, Kruskal-Wallis, Mann-Whitney U tests. The data from surface roughness tests were statistically analyzed by multivariate analysis of variance and Bonferroni test (p < 0.05).

RESULTS

The B/T microhardness ratio results revealed no significant differences between groups (p > 0.05). Comparing the microhardness values of the composites' top surfaces before and after bleaching, a significant decrease was observed exclusively in FB30s (p < 0.05). No significant differences in surface roughness values were observed when the groups were compared based on bulk-fill materials (p > 0.05) while the polymerization time affected the surface roughness of the SF20s and SF30s groups (p < 0.05). After bleaching, surface roughness values were significantly increased in the SF20s and SF30s groups (p < 0.05).

CONCLUSION

The clinicians should adhere to the polymerization time recommended by the manufacturer to ensure the durability of the composite material in the oral environment.

Microhardness and water solubility of expired and non-expired shelf-life composites

Background:

The aim of this study was to determine the Vickers hardness and water solubility of expired and non-expired shelf-life bulk-fill and conventional dental composite material.

Methods:

Four different expired (E) (after 6 months) and non-expired (N) shelf-life composite resin materials (Clearfil Majesty ES-2 Enamel, Clearfil Majesty ES-2 Dentin, Tetric N-Ceram Bulk-Fill, and Tetric N-Ceram) were used. For each tested material, seven specimens were prepared and polymerized with a light curing unit. Vickers hardness measurements were made on the top and bottom surfaces. For the water sorption test, initially all specimens were weighted, the thickness and diameter of each specimen were measured, and the average volume of specimen was calculated. Then, each specimen was immersed in distilled water and kept in an incubator for 7 days and finally weighed again.

Results:

There was not any statistically significant difference between the microhardness results of expired and non-expired shelf-life composites on the top and bottom surfaces (p > 0.05). No significant difference was determined between the non-expired shelf-life composite materials on the top surfaces (p > 0.05). Non-expired Clearfil Majesty ES-2 Dentin showed lower microhardness than non-expired Tetric N-Ceram Bulk-Fill and non-expired Tetric N-Ceram on the bottom surface (p < 0.05). Expired Clearfil Majesty ES-2 Dentin showed lower microhardness results than expired Tetric N-Ceram Bulk-Fill on the top and bottom surfaces (p < 0.05). There was not any significant difference between the water sorption results of expired and non-expired shelf-life composites (p > 0.05). Expired Clearfil Majesty ES-2 Dentin showed higher water sorption than expired Tetric N-Ceram E-TN (p < 0.05).

Conclusion:

Expiration date did not affect the microhardness and water sorption of bulk-fill and conventional composites. The hardness and water sorption of the composite materials varied depending on the type of composites.

Thermal conductivity of different colored compomers

BACKGROUND

Compomers are mostly used in primary dentition. The thermal conductivity properties of traditional or colored compomers have not been investigated in detail so far. The aim of this in vitro study was to assess and compare the thermal conductivities of traditional and colored compomers.

METHOD

Two sets of compomers - namely, Twinky Star (available in berry, lemon, green, silver, blue, pink, gold and orange shades) and Dyract Extra (available in B1, A3 and A2 shades) - were included in this study. All of the traditional and colored compomers were applied to standard molds and polymerized according to the manufacturers' instructions. Three samples were prepared from each compomer. Measurements were conducted using a heat conduction test setup, and the coefficient of heat conductivity was calculated for each material. The heat conductivity coefficients were statistically analyzed using Kruskal-Wallis and Duncan tests. Uncertainty analysis was also performed on the calculated coefficients of heat conductivity.

RESULTS

Statistically significant differences were found (p<0.05) between the thermal conductivity properties of the traditional and colored compomers examined. Among all of the tested compomers, the silver shade compomer exhibited the highest coefficient of heat conductivity (p<0.05), while the berry shade exhibited the lowest coefficient (p<0.05). Uncertainty analyses revealed that 6 out of 11 samples showed significant differences.

CONCLUSIONS

The silver shade compomer should be avoided in deep cavities. The material properties could be improved for colored compomers.

Curing effectiveness of single-peak and multi-peak led light curing units on tpo-containing resin composites with different chromatic characteristics

This study evaluated the surface microhardness of Lucirin-TPO (TPO) containing resin based composite (RBC) cured with three light-emitting diode (LED) light curing units (LCUs) (two single-peak LED and one multi-peak LED), and two different energy density (ED) (8 J/cm² and 16 J/cm²). Ninety specimens (8 mm wide and 2 mm thick) (n=5), were prepared with three different shades: translucent (T), A2 dentin (A2d), and A4 dentin (A4d). Specimens were subjected to micro-hardness Vickers measurements (Vickers Hardness Number, VHN) on both top and bottom surfaces. Hardness ratio (rHV) was also calculated. Data were analyzed using multifactorial ANOVA and Bonferroni tests (<=0.05). Results indicated that higher ED performed better than lower ED. Multi-peak LED achieved higher VHNs and rHV than single-peak LED when curing a TPO-containing RBC. A4d invariably achieved lower rHV and VHN than T and A2d. Single-peak LED achieved comparable VHNs and rHVs with multi-peak LED only curing A2d and T shades with 16J/cm².

Light transmittance and polymerization kinetics of amorphous calcium phosphate composites

OBJECTIVES

This study investigated light transmittance and polymerization kinetics of experimental remineralizing composite materials based on amorphous calcium phosphate (ACP), reinforced with inert fillers.

MATERIALS AND METHODS

Light-curable composites were composed of Bis-EMA-TEGDMA-HEMA resin and ACP, barium glass, and silica fillers. Additionally, a commercial composite Tetric EvoCeram was used as a reference. Light transmittance was recorded in real-time during curing, and transmittance curves were used to assess polymerization kinetics. To obtain additional information on polymerization kinetics, temperature rise was monitored in real-time during curing and degree of conversion was measured immediately and 24 h post-cure.

RESULTS

Light transmittance values of 2-mm thick samples of uncured ACP composites (2.3-2.9 %) were significantly lower than those of the commercial composite (3.8 %). The ACP composites presented a considerable transmittance rise during curing, resulting in post-cure transmittance values similar to or higher than those of the commercial composite (5.5-7.9 vs. 5.4 %). The initial part of light transmittance curves of experimental composites showed a linear rise that lasted for 7-20 s. Linear fitting was performed to obtain a function whose slope was assessed as a measure of polymerization rate. Comparison of transmittance and temperature curves showed that the linear transmittance rise lasted throughout the most part of the pre-vitrification period.

CONCLUSIONS

The linear rise of light transmittance during curing has not been reported in previous studies and may indicate a unique kinetic behavior, characterized by a long period of nearly constant polymerization rate.

CLINICAL RELEVANCE

The observed kinetic behavior may result in slower development of polymerization shrinkage stress but also inferior mechanical properties.

Effect of preheating and shade on surface microhardness of silorane-based composites

AIM

The aim of the present study was to evaluate the effect of preheating and shade on the surface microhardness of silorane-based composites.

METHODS

Three shades of two different types of composites were evaluated: a silorane-based composite and a methacrylate-based composite. The composites were tested at 23°C, and after preheating at 55°C. Five specimens were prepared for each experimental group. The top surface of the specimens was irradiated for 20 s using an LED unit. Vickers microhardness test was used to evaluate both top and bottom surfaces of the specimens, followed by 24-h storage in the dark. Statistical analysis was performed using one-way anova and Tukey's post-hoc test at a level of significance of α = 0.05.

RESULTS

There was a significant rise in microhardness as the temperature increased from 23 to 55°C for both the top and bottom surfaces of the tested composites (P < 0.05). The C2 shade of both composites exhibited the lowest microhardness (P < 0.05), while the A2 and A3 shades did not show significant differences compared to each other (P > 0.05) Filtek Silorane presented significantly lower microhardness than Filtek Z250 (P < 0.05), regardless of the temperature, shade, or depth of measurement.

CONCLUSIONS

Preheating, shade, and composition of the tested composite resins affected their surface microhardness.

A resin composite material containing an eugenol derivative for intracanal post cementation and core build-up restoration

OBJECTIVES

To formulate and evaluate new dual cured resin composite based on the inclusion of eugenyl methacrylate monomer (EgMA) with Bis-GMA/TEGDMA resin systems for intracanal post cementation and core build-up restoration of endodontically treated teeth.

METHODS

EgMA was synthesized and incorporated at 5% (BTEg5) or 10% (BTEg10) into dual-cure formulations. Curing properties, viscosity, Tg, radiopacity, static and dynamic mechanical properties of the composites were determined and compared with Clearfil™DC Core-Plus, a commercial dual-cure, two-component composite. Statistical analysis of the data was performed with ANOVA and the Tukey's post-hoc test.

RESULTS

The experimental composites were successfully prepared, which exhibited excellent curing depths of 4.9, 4.7 and 4.2 mm for BTEg0, BTEg5 and BTEg10 respectively, which were significantly higher than Clearfil™DC. However, the inclusion of EgMA initially led to a lower degree of cure, which increased when measured at 24 h with values comparable to formulations without EgMA, indicating post-curing. The inclusion of EgMA also lowered the polymerization exotherm thereby reducing the potential of thermal damage to host tissue. Both thermal and viscoelastic analyses confirmed the ability of the monomer to reduce the stiffness of the composites by forming a branched network. The compressive strength of BTEg5 was significantly higher than the control whilst flexural strength increased significantly from 95.9 to 114.8 MPa (BTEg5) and 121.9 MPa (BTEg10). Radiopacity of the composites was equivalent to ∼3 mm Al allowing efficient diagnosis.

SIGNIFICANCE

The incorporation of EgMA within polymerizable formulations provides a novel approach to prepare reinforced resin composite material for intracanal post cementation and core build-up and the potential to impart antibacterial properties of eugenol to endodontic restorations.

Color Stability and Surface Roughness of a Laboratory-Processed Composite Resin as a Function of Mouthrinse

STATEMENT OF THE PROBLEM

Mouthrinses can cause discoloration on indirect resin composites.

PURPOSE OF THE STUDY

The purpose of the study was to investigate the effect of different mouthrinses on the color changes and surface roughness of a laboratory-processed composite.

METHODS AND MATERIALS

Fifty discs were made using GC Gradia/GC indirect composites and divided into five groups which immersed in artificial saliva and four different types of mouthrinses. The samples were immersed daily for 14 days in 20 mL of the solutions for 2 minutes twice a day (with a 12-hour interval between exposures). Measurements were carried out at four different times: 1 hour after sample preparation (t0 ), 1 day (t1 ), 7 days (t2 ), and 14 days (t3 ) after the first immersion in the solutions. The color before and after immersion was measured according to Comission Internationale de L'Eclairage (CIE L*, a*, b*) System and ΔL*, Δa*, Δb*, and ΔE* values were calculated. The surface roughness Ra (μm) of the specimens was evaluated using a profilometer.

RESULTS

There were significant differences between the groups at all time representing ΔE values (p < 0.001). At (t1 ) time representing ΔRa value, there were significant differences between the groups (p < 0.05). At (t2, t3 ) time representing ΔRa values, there were significant differences between the groups (p < 0.001). Pharmol Zn immersed specimens showed ΔE values between 1.04 and 3.67.

CONCLUSIONS

The result of this study indicated that the mouthrinses affected the color stability of indirect composites.

CLINICAL SIGNIFICANCE

Based on the results of this study, patients with resin composite restorations should be warned by the dentists about the discoloration of the restorations and the time period of the mouthrinse that will be used.

Color stability, surface roughness and microhardness of composites submitted to mouthrinsing action

Objective

The purpose of this study was to evaluate the effect of mouth rinse solutions on color stability, surface roughness and microhardness of two composite resins.

Material and Methods

Fifty test specimens of each composite (Filtek Z250 and Z350; 3M ESPE) were made using a teflon matrix (12x2 mm). Color, surface roughness and Knoop microhardness baseline measurements of each specimen were made and specimens (n=10) were immersed in 5 mouth rinse solutions: G1: distilled water (control), G2: Plax Classic, G3: Plax alcohol-free; G4: Periogard, and G5: Listerine. Final measurements of color, roughness and microhardness were performed and the results submitted to statistical analysis (2-way ANOVA, Bonferroni's test; p<0.05).

Results

The most significant color change was observed for Z250 when immersed in Listerine (p<0.05). Z350 showed greater color change when immersed in Plax alcohol-free (p<0.05), but with no significant difference for Listerine (p>0.05). With regard to roughness, both composites showed significant changes when immersed in Listerine in comparison with Plax alcohol-free (p<0.05). Microhardness of Z350 was shown to be significantly changed when the composite was immersed in Plax alcohol-free (p<0.05).

Conclusion

Composite changes depended on the material itself rather than the mouth rinse solution used.

Relationships between conversion, temperature and optical properties during composite photopolymerization

Optical properties of composite restoratives, both cured and uncured, are of obvious importance in a procedure reliant on photoactivation, since they may affect light transmission and therefore materials conversion upon which mechanical properties and ultimate clinical performance are dependent. The objective of the present study was to evaluate simultaneous, real-time conversion, and the development of the temperature and optical properties. The dimethacrylate resin (Bis-GMA/TEGDMA 70/30mass%) was prepared at three filler loading (0, 35 or 70mass%: no fill, low and high fill, respectively) combined with three initiator concentrations (CQ/EDMAB: 0/0, 0.2/0.8 or 1.0/1.6mass%). Specimens were exposed to either low (50mWcm(-2)) or high (500mWcm(-2)) irradiance. Simultaneous conversion (near-IR peak area), temperature (thermocouple) and visible light transmission (UV-vis spectroscopy) measurements were conducted throughout the polymerization process. The refractive index of the resin rises linearly with conversion (r(2)=0.976), producing a refractive index match between resin/filler at approximately 58% conversion in these materials. The percentage increase in light transmission during conversion was greater for increasing filler levels. Higher CQ content led to maximum light transmission at slightly higher levels of conversion (60-65% and 50-55% for the high and low filled materials, respectively). The broad distribution of filler concentrations allows for the clinically relevant generalization that highly filled composites not only jeopardize absolute light transmission, conversion and depth of cure, but also demonstrate the complex interrelationship that exists between materials, processing conditions and the optical properties of dental composites.

Microhardness of composite resins at different depths varying the post-irradiation time

Objective:

The purpose of this study was to assess the microhardness of posterior composite resins at different depths varying the post-irradiation time.

Materials and methods:

For each composite resin [Solitaire 2 (SO) - Heraus Kulzer, P60 (P) - 3M, Prodigy Condesable (PC) - Kerr, Surefil (S) - Dentsply and Alert (A) - Pentron], 6 specimens (3 mm in diameter; 4mm high) were prepared using a black polyurethane cylindrical matrix. The resins were inserted in a bulk increment and light cured for 40 seconds. Microhardness was analyzed at different depths (top, 0.4 mm, 1.0 mm, 2.0mm, 3.0 mm and 4.0 mm) and at two moments (20 minutes and 24 hours after light-curing). Data were analyzed by ANOVA and Tukey's test (p<0.05).

Results:

Overall, microhardness means decreased significantly with the increase of depth, being lower in the first moment tested. P, S and PC showed the highest microhardness means.

Conclusion:

It may be concluded that the tested composite resins presented a gradual decrease of microhardness as depth increased and this drop was more accentuated for depths beyond 2 mm. For all materials, higher microhardness means were recorded 24 hours after light activation. P60 yielded the best results at the different depths evaluated.

The effect of resin shades on microhardness, polymerization shrinkage, and color change of dental composite resins

The present study sought to evaluate the effect of resin shades on the degree of the polymerization. To this end, response variables affected by the degree of polymerization were examined in this study - namely, microhardness, polymerization shrinkage, and color change. Two commercial composite resins of four different shades were employed in this study: shades A3, A3.5, B3, and C3 of Z250 (Z2) and shades A3, A3.5, B3, and B4 of Solitaire 2 (S2). After light curing, the reflectance/absorbance, microhardness, polymerization shrinkage, and color change of the specimens were measured. On reflectance and absorbance, Z2 and S2 showed similar distribution curves regardless of the resin shade, with shade A3.5 of Z2 and shade A3 of S2 exhibiting the lowest/highest distributions. Similarly for attenuation coefficient and microhardness, the lowest/highest values were exhibited by shade A3.5 of Z2 and shade A3 of S2. On polymerization shrinkage, no statistically significant differences were observed among the different shades of Z2. Similarly for color change, Z2 specimens exhibited only a slight (DeltaE*=0.5-0.9) color change after immersion in distilled water for 10 days, except for shades A3 and A3.5. Taken together, results of the present study suggested that the degree of polymerization of the tested composite resins was minimally affected by resin shade.

Comparison of translucency between indirect and direct resin composites

OBJECTIVES

To measure the translucency of indirect and direct resin composites after curing, and to determine the influence of material and shade group combination on these properties.

METHODS

BelleGlass NG (BG, indirect resin composite) and Estelite Sigma (ES, direct resin composite), each composed in three shade groups (EN, OD and TL for BG; BS, AS and OP for ES) of 16 shades were investigated. Resin composite was packed into a mold (BEC) and was cured with a light-curing unit (CWL). Secondary curing was performed in a proprietary curing chamber (CIC) for BG material. Color was measured at the BEC, CWL and CIC conditions in the CIELAB scale using a spectrophotometer. Translucency parameter (TP) was calculated as the color difference between a specimen over a white and a black background.

RESULTS

TP values before curing were in the range of 7.7 (BG-OD) to 16.9 (ES-AS), and those after curing were in the range of 10.0 (BG-OD) to 21.5 (BG-EN). TP values of both materials were influenced by curing (p<0.05). There were significant difference in the TP values by the material and shade group combination, and the following homogenous subsets were found based on Tukey multiple comparison test: BG-OD<ES-OP<BG-TL=ES-AS=ES-BS<BG-EN (p<0.05).

CONCLUSIONS

BG material showed a wider range of TP values than ES, which would improve shade-matching capability of this material. Translucency should be considered when neighboring teeth are treated with different types of resin composites.

Depth of cure and hardness of an indirect composite polymerized with three laboratory curing units

This study determined the hardness and curing depth of a light-activated indirect composite polymerized with three laboratory light-polymerizing units for the purpose of comparing the curing performance of the three units. A light-activated composite material for indirect application (Vita Zeta) was polymerized with three light-polymerizing units equipped with the following light sources: 1) one halogen lamp and two fluorescent lamps (alpha-Light II); 2) three halogen lamps (Twinkle HLG); and 3) one metal halide lamp (Twinkle LI). Knoop hardness and curing depth were determined for groups of five specimens using standardized testing methods. The results were compared using analysis of variance (ANOVA) and Scheffé's S intervals (alpha = 0.05). The Knoop hardness number (KHN) generated with the halogen-fluorescent unit (12.5 KHN) was significantly (P < 0.05) lower than those produced by the halogen unit (13.9 KHN) and the metal halide unit (14.2 KHN). Of the three units, the halogen-fluorescent unit exhibited the lowest depth of cure. Both the hardness and curing depth of the composite were influenced by the laboratory polymerizing units employed.

Refractive Index Mismatch and Monomer Reactivity Influence Composite Curing Depth

Limited cure depth is a drawback of light-activated composites. We hypothesize that curing light transmission and cure depth are influenced by monomer reactivity and filler/resin refractive index mismatch. Light transmission throughout cure was recorded for composites based on strontium (refractive index 1.51) or barium (refractive index 1.53) glass fillers. Fillers were mixed (70 wt%) with 4 bisphenol-A diglycidyl-ether-dimethacrylate (bis-GMA):triethylene glycol dimethacrylate (TEGDMA) formulations with refractive indices ranging from 1.4703 to 1.5370. Following polymerization, cure depth and pre- and post-cure translucency parameters were determined. Transmission changes and cure depths related to monomer reactivity and filler/resin refractive index mismatch with significant interaction. Composites became more opaque or translucent on curing. Optimizing filler/resin refractive index mismatch provides increased curing depth and assists shade-matching.

Depth of Cure of Dental Resin Composites: ISO 4049 Depth and Microhardness of Types of Materials and Shades

Achieving a high degree of cure throughout a 2 mm thickness of light-activated resin composite did not occur for many types and shades of resin composite. Clinicians should check the depth of cure by using the scraping method.

Hardness comparison of bulk-filled/transtooth and incremental-filled/occlusally irradiated composite resins

STATEMENT OF PROBLEM

Use of a bulk-fill/transtooth composite resin insertion/irradiation technique may not provide as well polymerized a restoration as when using a conventional incremental placement/irradiation technique. Little information exists as to how the hardness of restorations produced by the 2 techniques compare.

PURPOSE

The purpose of this study was to determine the effect of composite resin placement and an irradiation technique on the axial hardness at various depths in a Class I composite resin to include the influence of composite resin filler classification and shade.

MATERIAL AND METHODS

Cylindrical Class I preparations were made in 70 recently extracted human molars and restored with either a light (A1) or dark shade (A4) of a microfill, microhybrid, or nanohybrid composite resin, or with a single shade of a translucent material. Half were placed using a conventional 2-mm-thick incremental-fill/occlusal irradiation technique, and half using a bulk-fill/transtooth irradiation method (n=5). Specimens were sectioned occluso-apically and axial Knoop hardness values were obtained at depths of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm. Hardness at 0.5 mm was used as a control to compare to deeper readings. Statistical analyses consisted of multiple ANOVAs and Dunnett's post-hoc tests performed at appropriately determined significance levels.

RESULTS

For 3 multishaded materials tested, axial hardness values were relatively unaffected by composite resin shade or filler classification for the incremental technique, but were significantly affected by these factors when using the bulk-fill/transtooth irradiation method. A single shade translucent material was not affected in either the bulk or incremental condition.

CONCLUSIONS

Use of a bulk-fill/transtooth irradiation technique for composite resin placement does not result in axial hardness values equivalent to that of an incremental-fill/occlusal irradiation technique.

Effect of composite shade, increment thickness and curing light on temperature rise during photocuring

OBJECTIVES

To examine the effect of composite shade, increment thickness and curing light characteristics on the temperature rise associated with composite photocuring.

METHODS

Four shades (C2, A4, B1 and B3), four sample thicknesses (2, 3, 4 and 5 mm) of a hybrid resin composite and two curing units, one with two modes of curing, were investigated. The composite samples were packed in polytetrafluoroethylene (PTFE) moulds and cured for 40 s. Samples cured with the ramp curing mode were irradiated for only 20 s. Temperature rises on the undersurface of the curing resin composite were measured using an infrared scanning system.

RESULTS

Shade C2 produced the highest maximum temperature of all shades (56.7 degrees C). Thinner samples produced greater temperature rises (2mm induced 60.9 degrees C, 5 mm induced 45.7 degrees C). Samples cured with Optilux 501 unit produced greater temperature rises (60.9 degrees C) than those cured with Dentsply unit (56.2 degrees C).

CONCLUSIONS

There was a quantifiable amount of heat generated during visible light curing of resin composite. The amount of heat generated was influenced by shade selected, thickness of material and characteristics of the light curing unit.

The effect of nanofiller on the opacity of experimental composites

The purpose of this study was to evaluate the effect of the nanofiller in experimental composites on opacity (contrast ratio). Thirteen experimental composites were prepared with three different sizes of fillers: barium glass minifiller (1 microm; 69-76 wt %), silica microfiller (0.04 microm; 0-6 wt %), and silica nanofiller (7 nm; 0-7 wt %). After disk-type specimens were irradiated with a halogen light curing unit at 500 mW/cm(2) for 30 s, the specimens were aged for 6 h at room conditions and were stored in deionized water for 1, 7, 14, 21, 28, 56, and 84 days. The contrast ratios of the specimens were measured as a function of aging period using a spectrophotometer. The distribution morphology of the filler particles in the resin matrix was also examined using energy-filtering transmission electron microscopy. The experimental composites that contained more than 3% nanofiller had significantly lower contrast ratios (p < 0.05). The composites that contained 6 wt % nanofiller had contrast ratios 34-65% lower than the composite that did not contain nanofiller. The values of the contrast ratio from the composites that excluded microfiller were lower than the values from the composites that included microfiller. From the comparison with the 3 different sizes of filler, the contrast ratio of the composite that contained 70 wt % minifiller and 6 wt % microfiller was the highest, the contrast ratio of the composite that contained only 76 wt % minifiller was the median value, and the contrast ratio of the composite that contained 70 wt % minifiller and 6 wt % nanofiller was the lowest. When the microfiller content was decreased from 6 wt % to 0 wt %, the contrast ratio decreased 6-9%. Energy-filtering transmission electron microscopy images indicated that the contrast ratio of experimental composites is related to the distribution morphology of the filler particles in the resin matrix.

Influence of resin composite shade and location of the gingival margin on the microleakage of posterior restorations

OBJECTIVE

The objective of this in vitro study was to evaluate the influence of resin composite shade and location of the gingival margin (enamel or dentin) on the microleakage of proximal restorations on posterior teeth.

METHODS AND MATERIALS

Sixty freshly extracted human third molars were prepared with standardized Class II box-shaped cavities with proportional size and shape, with distal gingival margins located on the enamel and mesial gingival margins on dentin. The teeth were randomly divided into 6 groups according to resin shade (n=10): G1-Incisal; G2-A1; G3-A2; G4-A3; G5-A3.5; G6-A4. The cavities were restored with a total-etch 1-bottle adhesive system and microhybrid resin composites inserted in 4 increments, light cured for 20 seconds through the occlusal surface, then an additional 60 seconds for each surface. After 1 week of immersion in distilled water, the specimens were thermocycled (500 cycles, 5 degrees -55 degrees C, 30 seconds dwell time), sealed with nail polish and immersed in 0.5% basic fuschin solution for 24 hours. The restorations were sectioned longitudinally, and microleakage was evaluated using a 0-3 score scale.

RESULTS

Data were subjected to Kruskal-Wallis and Wilcoxon tests at p<0.05. No statistically significant differences between groups were observed regarding the shade of resin composite (p=0.8570). When margins (enamel or dentin) were considered separately, statistically significant differences were observed between groups (p<0.0001), with enamel margins exhibiting lower degrees of microleakage.

CONCLUSION

The variation of resin composite shades utilized in this study did not influence the microleakage of Class II restorations. However, the location of the gingival margin influenced the microleakage.

Change of Color and Translucency by Light Curing in Resin Composites

For the precise shade matching of resin composite materials, clinicians should always be aware of the color change caused by light curing.

Relative curing degree of polyacid-modified and conventional resin composites determined by surface Knoop hardness

OBJECTIVES

The aim of the present study was to investigate the relative curing degree at a depth of 2 mm of several polyacid-modified composites (PAM-Cs) as a function of shade.

METHODS

The Knoop hardness of the irradiated top and non-irradiated bottom surfaces of 2 mm thick samples of the PAM-Cs Hytac, F2000, Glasiosite, Dyract, Dyract AP, and Compoglass F and of the resin composites Z100, Herculite Enamel XRV, and Durafill VS, were determined for shades A2 and A4.

RESULTS

The top and bottom hardness of F2000 and Glasiosite ranged between that of the two composites Herculite and Z100. Compoglass, Dyract and Dyract AP had a lower top and bottom hardness than the hybrid composites, but higher than that of the microfilled composite Durafill. The top hardness of Hytac compared with that of the first group, whereas the bottom hardness compared with the second group. The bottom-to-top KHN ratio reflecting the relative curing degree at a depth of 2 mm was less than 80% for the two shades of Hytac and Compoglass as well as for the A4 shade of Dyract AP and Herculite.

SIGNIFICANCE

A hard top surface of a PAM-C is not an indication of adequate in depth polymerization. Shade A2 results in significantly greater values for the curing degree compared to shade A4, the effect depending quantitatively on the formulation of the material. Some formulations of PAM-C do not reach an adequate curing degree at a depth of 2 mm so that it is recommended to apply the incremental technique even in box-only cavities with layers of maximum 2 mm.

Abrasion resistance of composites polymerized by light-emitting diodes (LED) and halogen light-curing units

This study compared the abrasion resistance of direct composite resins cured by light-emitting diodes (LED) and halogen light-curing units. Twenty specimens (12 mm in diameter; 1.0 mm thick) of each composite resin [TPH (Dentsply); Definite (Degussa); Charisma (Heraus Kulzer)] were prepared using a polytetrafluoroethylene matrix. Ten specimens per material were cured with the LED source and 10 with the halogen lamp for 40 s. The resin discs were polished, submitted to initial surface roughness reading (Ra initial - mum) in a roughness tester and stored in water at 37°C for 15 days. The specimens were weighed (M1) and submitted to simulated toothbrushing using slurry of water and dentifrice with high abrasiveness. After 100 minutes in the toothbrushing simulator, the specimens were cleaned, submitted to a new surface roughness reading (Ra final - mum) and reweighed (M2). Mass loss was determined as the difference between M1 and M2. Data were recorded and analyzed statistically by one-way ANOVA and Tukey Test at 5% significance level. The composite resin with greater size of inorganic fillers (TPH) showed the lowest mass loss and surface roughness means, indicating a higher resistance to toothbrush abrasion (p<0.05). Definite cured with LED presented the least resistance to toothbrush abrasion, showing the highest means of surface roughness and mass loss (p<0.05). The LED source did not show the same effectiveness as the halogen lamp for polymerizing this specific composite resin. When the composite resins were cured a halogen LCU, no statistically significant difference was observed among the materials (p>0.05). It may be concluded that the type of light-curing unit and the resin composition seemed to interfere with the materials' resistance to abrasion.

Influence of light curing source on microhardness of composite resins of different shades

INTRODUCTION

The evolution of light curing units can be noticed by the different systems recently introduced. The technology of LED units promises longer lifetime, without heating and with production of specific light for activation of camphorquinone. However, further studies are still required to check the real curing effectiveness of these units.

PURPOSE

This study evaluated the microhardness of 4 shades (B-0.5, B-1, B-2 and B-3) of composite resin Filtek Z-250 (3M ESPE) after light curing with 4 light sources, being one halogen (Ultralux - Dabi Atlante) and three LED (Ultraled - Dabi Atlante, Ultrablue - DMC and Elipar Freelight - 3M ESPE).

METHODS

192 specimens were distributed into 16 groups, and materials were inserted in a single increment in cylindrical templates measuring 4mm x 4mm and light cured as recommended by the manufacturer. Then, they were submitted to microhardness test on the top and bottom aspects of the cylinders.

RESULTS

The hardness values achieved were submitted to analysis of variance and to Tukey test at 5% confidence level. It was observed that microhardness of specimens varied according to the shade of the material and light sources employed. The LED appliance emitting greater light intensity provided the highest hardness values with shade B-0.5, allowing the best curing. On the other hand, appliances with low light intensity were the least effective. It was also observed that the bottom of specimens was more sensitive to changes in shade.

CONCLUSION

Light intensity of LED light curing units is fundamental for their good functioning, especially when applied in resins with darker shades.

Effect of light dispersion of LED curing lights on resin composite polymerization

PURPOSE

This study evaluated the effect of light dispersion of halogen and LED curing lights on resin composite polymerization.

MATERIALS AND METHODS

One halogen (Optilux 501, SDS/Kerr, Orange, CA, USA) and five light-emitting diode (LED) curing lights (SmartLite iQ, Dentsply Caulk, Milford, DE, USA; LEDemetron 1, SDS/Kerr; FLASHlite 1001, Discus Dental, Culver City, CA, USA; UltraLume LED 5, Ultradent Products, South Jordan, UT, USA; Allegro, Den-Mat, Santa Maria, CA, USA) were used in this study. Specimens (8 mm diameter by 2 mm thick) were made in polytetrafluoroethylene molds using hybrid (Z100, 3M ESPE, St. Paul, MN, USA) and microfill (A110, 3M ESPE) composite resins. The top surface was polymerized for 5 seconds with the curing light guide tip positioned at a distance of 1 and 5 mm. Degree of conversion (DC) of the composite specimens was analyzed on the bottom surface using micro-Fourier Transform Infrared (FTIR) spectroscopy (Perkin-Elmer FTIR Spectrometer, Wellesley, PA, USA) 10 minutes after light activation. DC at the bottom of the 2 mm specimen was expressed as a percentage of the mean maximum DC. Five specimens were created per curing light and composite type (n=5). Percent mean DC ratios and SDs were calculated for each light under each testing condition. Data were analyzed by analysis of variance (ANOVA)/Tukey's test (alpha = .05). A beam analyzer (LBA-700, Spiricon, Logan, UT, USA) was used to record the emitted light from the curing lights at 0 and 5 mm distances (n=5). A Top Hat factor was used to compare the quality of the emitted beam profile (LBA/PC, Spiricon). The divergence angle from vertical was also determined in the x- and y-axes (LBA/PC). Mean values and SDs were calculated for each light under each testing condition (0 and 5 mm, x- and y-axes) and analyzed by a two-way ANOVA/Tukey's test (alpha = .05).

RESULTS

For DC ratios, significant differences were found based on curing light and curing distance (p < .05). At 1 mm, Optilux 501 and FLASHlite 1001 produced significantly higher DC ratios with the hybrid resin composite. No differences were found among lights with the microfill at 1 mm. At 5 mm, SmartLite iQ, FLASHlite 1001, LEDemetron 1, and UltraLume LED 5 produced significantly higher DC ratios with the hybrid resin composite, whereas LEDemetron 1 and SmartLite iQ produced significantly higher DC ratios with the microfill resin composite. The UltraLume LED 5, Allegro, and Optilux 501 had significant reductions in mean DC ratios at curing distances of 1 and 5 mm with both resin composite types. For dispersion of light, significant differences were found in Top Hat factor and divergence angle (p < .001). SmartLite iQ had overall the highest Top Hat factor and lowest divergence angle of tested lights. A linear regression analysis relating pooled DC with pooled Top Hat factors and divergence angles found a very good correlation (r2 = .86) between dispersion of light over distance and the ability to polymerize resin composite.

CLINICAL SIGNIFICANCE

The latest generation of LED curing lights provides DC ratios similar to or better than the halogen curing light at a curing distance of 5 mm. Dispersion of light plays a significant role in the DC of resin composite. To maximize curing effectiveness, light guides should be maintained in close proximity to the surface of the light-activated restorative material.

How filler properties, filler fraction, sample thickness and light source affect light attenuation in particulate filled resin composites

OBJECTIVE

It was hypothesized that by standardizing variables such as light sources, filler types and filler surface treatment, it should be possible to use Beer-Lambert's law to predict light absorption in visible light-cured dental composites.

METHODS

Mixture of 50 wt% bisGMA and 50 wt% TEGDMA to which a photo-initiator (0.35 wt% champhorquinone) and a co-initiator (0.7 wt% of dimethylaminoethylmethacrylate) was prepared. Three different filler types (HBB, SBB and KU) were added to that mixture in eight different volume percentage. Filler particles were either silane surface treated or not. Specimens were made with thicknesses of 1-5 mm. Total number of 1200 specimens were made for this study. Light transmission was obtained for halogen source and laser lights, which made the number of observations 2400. The absorbance values of the different materials were analyzed in Matlab with respect to the differences in filler fraction and sample thickness.

RESULTS

The obtained results revealed that of the two light sources, more light was absorbed by the composite when the laser light was used. Among different filler types, the HBB filler absorbed most light and the KU filler the least. There were significant differences (p < 0.05) in light absorption between all three filler types.

SIGNIFICANCE

By comparing the modeled surfaces generated by Matlab for different materials it was possible to determine how different variables such as filler type, filler surface treatment and light source affect light attenuation. The characteristic of incident light affected the light absorbance, meaning that not only the composite's composition needs to be considered in light absorption studies of dental composites.

Colour and translucency of opaque-shades and body-shades of resin composites

The purpose of this study was to evaluate the optical properties--not only the translucency but also the colours--of opaque-shade resin composites. The CIELAB parameters (L*, a* and b*) of disks of A2 and opaque A2 (OA2) shades of Charisma (Heraeus-Kulzer), Solare (GC) and Filtek Supreme (3M) were evaluated on backings of black, white and the material itself to calculate the translucency parameter (TP) and the colour differences (delta E*) between A2 and OA2. A two-way analysis of variance (anova) for the TP indicated a less statistically significant TP value in the OA2 shade than the A2 shade for all products. As for the products, Charisma showed a statistically greater TP value than the other two products. Regarding the delta E* between A2 and OA2, all the products revealed clinically perceptible colour differences (delta E* > 3.3). Hence, we must take the colour differences of opaque-shade resin composites into consideration, as well as the translucency of the materials, for a clinically acceptable colour match of the restoration.

Photoinitiator dependent composite depth of cure and Knoop hardness with halogen and LED light curing units

Light curing units (LCUs) are used for the polymerization of dental composites. Recent trends in light curing technology include replacing the halogen LCUs with LCUs using light emitting diodes (LEDs) reducing curing times and varying the LCUs light output within a curing cycle. This study investigated the time dependence of the Knoop hardness and depth of cure of dental composites polymerized with a halogen LCU (Trilight) and two LED LCUs (the commercial Freelight and custom-made LED LCU prototype). The halogen LCU was used in the soft-start (exponential increase of output power) and standard mode. Four dental composites (Z100, Spectrum, Definite, Solitaire2) were selected, two of them (Definite, Solitaire2) contain co-initiators in addition to the standard photoinitiator camphorquinone. The depth of cure obtained with the Trilight in the standard mode was statistically significantly greater (p < 0.05) than that obtained with the LED LCUs for all materials and curing times. The custom made LED LCU prototype (LED63) achieved a statistically significantly greater depth of cure than the commercial LED LCU Freelight for all materials and curing times. There was no statistical difference in Knoop hardness at the 95% confidence level at the surface of the 2 mm thick sample between the LED63 or Trilight (standard mode) for the composite Z100 for all times, and for Spectrum for 20s and 40s curing time. The composites containing co-initiators showed statistically significantly smaller hardness values at the top and bottom of the samples if LED LCUs were used instead of halogen LCUs. The experiment revealed that the depth of cure test does not and the Knoop hardness test does discriminate between LCUs, used for the polymerization of composites containing photoinitiators in addition to camphorquinone.

[Microhardness of resins as a function of color and halogen light]

The aim of this study was to evaluate the influence of light intensity and the influence of the color of a composite resin on Knoop hardness. Samples were confected utilizing polyester matrices with 6 mm of diameter and 2 mm of depth. The matrices were filled with composite resin (Fill Magic - Vigodent), colors A3, B3, C3, D3 and I, and light-cured by means of an Elipar light-curing unit in three different light intensities: 450 mW/cm2, 800 mW/cm2 and an increasing intensity setup of 100 mW/cm2 to 800 mW/cm2. Ninety test specimens were confected, with the standard curing time of 40 seconds. The specimens were stored at 37 +/- 1 degrees C and immersed in distillate water. The Knoop test was carried out in superficial and deep areas of the specimens. The results revealed that there was no statistical difference (Tukey) between the tested colors. However, there was statistical difference between different light intensities. The authors concluded that the color of the composite resin did not influence Knoop hardness and that the progressive intensity setup led to the best Knoop hardness.

Effect of exposure intensity and post-cure temperature storage on hardness of contemporary photo-activated composites

OBJECTIVES

The effect of variation in post-exposure storage temperature (18 vs. 37 degrees C) and light intensity (200 vs. 500mW/cm(2)) on micro-hardness of seven light-activated resin composite materials, cured with a Prismetics Mk II (Dentsply) light activation unit, were studied.

METHODS

Hardness values at the upper and lower surfaces of 2mm thick disc shaped specimens of seven light-cured resin composite materials (Herculite XRV and Prodigy/Kerr, Z100 and Silux Plus/3M, TPH/Dentsply, Pertac-Hybrid/Espe, and Charisma/Kulzer), which had been stored dry, were determined 24h after irradiation with a Prismetics Mk II (Dentsply) light activation unit.

RESULTS

Hardness values varied with product, surface, storage temperature, and curing light intensity. In no case did the hardness at the lower surface equal that of the upper surface, and the combination of 500mW/cm(2) intensity and 37 degrees C storage produced the best hardness results at the lower surface.

CONCLUSIONS

Material composition had a significant influence on surface hardness. Only one of the seven products (TPH) produced a mean hardness values at the lower surface >80% of the maximum mean upper surface hardness obtained for the corresponding product at 500mW/cm(2) intensity/37 degrees C storage temperature when subjected to all four test regimes. Despite optimum post-cure storage conditions, 200mW/cm(2) intensity curing for 40s will not produce acceptable hardness at the lower surface of 2mm increments of the majority of products tested.

Curing Dental Resins and Composites by Photopolymerization

The development and continued evolution of photopolymerizable dental materials, particularly dental composite restoratives, represent a significant, practical advance for dentistry. The highly successful integration of the light-activated curing process for dental applications is described in this review. The basic mechanisms by which the photoinitiators efficiently convert monomers into polymers are discussed along with the variety of factors that influence the photopolymerization process. The conventional camphorquinone-amine visible light photoinitiator system used in most dental restorative materials is illustrated in addition to some alternative initiator systems that have been studied for dental materials applications.

CLINICAL SIGNIFICANCE

Photopolymerization has become an integral component of the practice of dentistry. A better appreciation of the photopolymerization process as well as its potential and limitations may aid the dentist in the delivery of both esthetic and restorative dental care.

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.

Light transmittance characteristics of light-cured composite resins

OBJECTIVES

The purpose of this study was: (1) to examine the light transmittance characteristics of various shades of light-cured composite resins, and (2) to evaluate the effect of light transmittance characteristics on the color of the resins.

METHODS

Eleven shades of two composite resins were used. Specimens with four different thicknesses (0.5, 1.0, 2.0 and 3.0 mm) were prepared. The transmittance at wavelengths from 400 to 700 nm was measured. Also, the color values and the color differences among thicknesses of a specimen on the CIE L*a*b* color system were determined by a digital chroma meter. The differences in the transmittance, color values and color difference were determined by using a one-way analysis of variance (ANOVA) combined with a Tukey multiple-range test.

RESULTS

Significant differences were found in the wavelength dependence of transmittance between the two materials, and among shades of each material. The transmittances of the darker shades of one material were significantly lower at lower wavelengths than the other shades, but were nearly equal or significantly higher at higher wavelengths. There was a significant correlation between the changing ratio of transmittance and the color difference. Two materials showed significant differences in delta a* and delta b* of the chromatic component of color difference.

SIGNIFICANCE

The results of this study indicate that light transmittance characteristics, including the wavelength dependence, play an important role for the color of a composite resin. The significant difference in light transmittance characteristics among materials and shades will affect their clinical appearance.

Investigation of dual-staged polymerization and secondary forming of photopultruded, fiber-reinforced, methacrylate-copolymer composites

To develop a dual-curing monomer system for the photopultrusion of reformable (soft) composites, a microhardness assay showed that in a blend with 2,2-Bis[4-2-hydroxy-3-methacryloxypropoxy)phenyl] propane (Bis-GMA), the substitution of methyl methacrylate (MMA) for triethylene glycol dimethacrylate (TEGDMA) delayed the onset of gelation during photopolymerization. Adding lauroyl peroxide permitted the completion of polymerization thermally. This system was used to form silicate-glass-fiber-reinforced composites, with varying degrees of conversion, by photopultruding over a range of pulling speeds. Sol-gel extractions demonstrated both fully soluble and insoluble matrices. For the soluble material, gel permeation chromatography elucidated a trimodal distribution of molecular weights that corresponded to MMA, Bis-GMA, and polymeric molecules with molecular weights in the tens of thousands. Composites with matrix solubilities above about 10% wt could be swaged after photopultrusion to change the cross section from circular to rectangular before thermal processing. The effect on the final elastic modulus was small (-44GPa, as measured in flexure for 57% vol-reinforced composites); but the final flexure strength was reduced by approximately 25% to a constant of about 1.2 GPa. Morphological characteristics that were seen in the circular-sectioned precursors were observed in the swaged rectangular products as well, including flaws when swaging was conducted at matrix solubilities above about 75%.