Effect of a third-generation LED LCU on microhardness of tooth-colored restorative materials.

OBJECTIVE: To assess the effects of different modes of a third-generation light-curing unit (LCU) (VALO) on the microhardness of restorative materials. DESIGN: A microhybrid composite resin (Filtek(™) Z550), a giomer (Beautifil II), a compomer (Dyract eXtra) and a RMGIC (Photac(™) Fil) were used in the study. Three different modes of VALO were tested and a second-generation LCU (Elipar S10) was used as a control. The microhardness (VHN) was measured using a Vickers Hardness tester. Data were analyzed using two-way anova and post hoc Tukey's test (P < 0.05). RESULTS: The Filtek Z550 group had the highest VHN values followed by Photac Fil, Beautifil II and the Dyract eXtra at both top and bottom surfaces, however the difference between Filtek Z550 and Photac Fil was not statistically significant for the bottom surfaces (P > 0.05). Of the different curing protocols tested, the VALO LCU in Mode 3 resulted in the lowest VHN values at both top and bottom surfaces (P < 0.05). CONCLUSION: Based on the results of this study, it can be concluded that the high-power mode of the VALO LCU can be recommended for clinical applications especially in pediatric patients, as it can shorten the time required to adequately polymerize resin-based tooth-colored restorative materials.

The impact of nanosilver addition on element ions release form light-cured dental composite and compomer into 0.9% NaCl.

The aim of this paper was to identify and to assess in semi-quantified way the release of different ions from composite and compomer restorative materials subjected to 0.9% NaCl solution, which simulates the environment of the human body. In the present study, the number of ions (Al, Ag, Ba, Sr, Ti) released from dental fillings over time (one week, one month and 3 months), in different temperatures (23°C, 37°C) and depending on the materials applied (unmodified/modified with nanosilver) was investigated. The results suggest that nanosilver addition influences directly on the process of metal ion releasing into 0.9% NaCl solution. The increase in the number of counts of metal ions was observed in the solutions in which samples modified with nanosilver were kept. Higher amount of metal ion release was observed for composite samples rather than for compomer materials. The study revealed that in general the number of released metal ions increases with the time of storage (for metal ions: Ti, Ba, Sr) and at higher temperature (Ag, Ti, Ba). Reverse tendency observed for silver ion release versus incubation time may be caused by the process of silver adsorption, which takes place on the surface of analyzed material and test-tube walls, where samples were incubated.

Conversion degrees of a colored compomer in different colors utilized by various curing times.

PURPOSE: Compomers are widely used in primary teeth and are manufactured in different colors in order to make dental treatment acceptable in children. The aim of this in vitro study was to evaluate the degree of conversion (DC) of different colored compomers and of compomers with various curing times. METHODS: Sixty three cylindrical samples were prepared from a colored compomer (Twinky Star). These samples were of 7 different color groups, with 9 samples of each color. Each group was divided into 3 sub-groups, according to the curing time (20-30-40 seconds) with a light emitting diode light curing unit. The DC values from 3 different regions and depths were evaluated with a Fourier Transform Infrared Spectrometer before and after curing procedures for all groups. Data were calculated by using the baseline values; statistical analyses were done by using ANOVA test. RESULTS: Significant differences in DC results before and after curing were found among the groups (P<0.05). For all curing times, the silver colored samples showed the poorest DC results, which ranged from 13% to 18%. CONCLUSIONS: It was concluded that DC values of different colors were variable. The material properties could be improved by defining the proper polymerization time for each color.

In vitro evaluation of marginal leakage using invasive and noninvasive technique of light cure glass ionomer and flowable polyacid modified composite resin used as pit and fissure sealant.

AIM: This study compared the microleakage of light cure glass ionomer and flowable compomer as pit and fissure sealant, with and without tooth preparation. MATERIALS AND METHODS: One hundred premolars that were extracted for orthodontic purpose were used. After adequate storage and surface debridement, the teeth were randomly divided into four groups. In Group I and III, the occlusal surfaces were left intact, while in Group II and Group IV, tooth surfaces were prepared. Teeth in Group I and Group II were sealed with Light cure glass ionomer, whereas flowable compomer was used to seal teeth in Group III and IV. The sealed teeth were then immersed in dye. Subsequently, buccolingual sections were made and each section was examined under stereomicroscope for microleakage followed by scoring. RESULTS: In group I, microleakage score ranged from 2 to 4 with mean of 3.64 (±0.757), while in group II the range was observed to be 1-4 with mean of 2.88 (±1.236). Group III recorded a range of 0-4 with the mean of 2.20 (±1.443) while 0-2 and 0.60 (±0.707) being the range and mean observed, respectively, for group IV. CONCLUSION: Flowable compomer placed after tooth preparation showed better penetration and less marginal leakage than the light cure glass ionomer.

Comparison of curing depth of a colored polyacid-modified composite resin with different light-curing units.

OBJECTIVE: To compare the depth of cure (DoC) of a colored polyacid-modified composite resin (PAM-C) with a traditional PAM-C and a fine hybrid composite resin using different light-curing units and different radiant energies. METHOD AND MATERIALS: The DoC of the PAM-C Twinky Star (Voco, all shades), the PAM-C Glasiosite (Voco), and the composite resin Z100 (3M ESPE) shades A2 and A4 was determined using a penetrometer test method. The materials were cured in bulk using a halogen-based unit (Elipar Trilight, E = 18 J/cm2 and E = 32 J/cm2; 3M ESPE) and an LED curing unit (Elipar Freelight 2, E = 20 J/cm2; 3M ESPE) in split stainless steel molds. Immediately after curing, the height (mm) of the cured material was measured and taken as the DoC. Ranking of means was performed by Student-Newman-Keuls multiple comparison test, and statistically significant differences among mean values were detected with ANOVA. RESULTS: Mean DoC for all materials and shades varied as follows: 4.705 to 8.870 mm (E = 32 J/cm2); 3.672 to 8.050 mm (E = 20 J/cm2); and 4.090 to 7.357 mm (E = 18 J/cm2). Two-way ANOVA revealed that the DoC depended significantly (P < .001) on the shade of the material and the curing device. Moreover, there was a significant interaction (P < .001) between the latter, indicating that the effect of the energy densities differed quantitatively among the shades. CONCLUSIONS: In this study, DoC differed significantly among the materials and the shades. Twinky Star shade blue showed the highest DoC compared to Glasiosite and Z100 shades A2 and A4. The curing device with the highest energy density exhibited the highest curing depths.

Effects of high-intensity curing lights on microleakage under orthodontic bands.

INTRODUCTION: Our objective was to compare the effects of 3 light-curing units (LCUs) (quartz-tungsten-halogen [QTH], light-emitting diode [LED], and plasma-arc curing [PAC]) on the microleakage patterns of a polyacid-modified composite (PAMC) for band cementation between the cement-enamel and the cement-band interfaces from the buccal, lingual, occlusal, and gingival margins. METHODS: Sixty freshly extracted third molars were randomly divided into 3 groups of 20 teeth each. Microetched molar bands were cemented in all groups with the PAMC (Ultra Band-Lok, Reliance Orthodontic Products, Itasca, Ill) and cured for 30 seconds with the QTH (Hilux 350, Express Dental Products, Toronto, Ontario, Canada), for 20 seconds with the LED (Elipar Freelight 2, 3M Espe, Seefeld, Germany), or for 6 seconds with the PAC (Power-Pac, American Medical Technologies, Hannover, Germany). A dye penetration method was used for microleakage evaluation. Microleakage was determined with a stereomicroscope for the cement-band and cement-enamel interfaces from the buccal and lingual sides at the occlusal and gingival margins. Statistical analyses were performed with the Kruskal-Wallis and Mann-Whitney U tests. The level of significance was set at P <0.05. RESULTS: The gingival sides in the LED and PAC groups had higher microleakage scores compared with those observed on the occlusal sides at both the cement-band and cement-enamel interfaces. The buccal sides had similar microleakage values compared with those on the lingual sides for the cement-enamel and cement-band interfaces in all LCU types. Statistical comparisons showed that there were statistically significant differences among the investigated LCUs at the cement-enamel interface (P <0.05). Post hoc comparisons showed statistically significant microleakage differences between the PAC (median, 0.950 mm), the QTH (median, 0.383 mm) (P <0.01), and the PAC and the LED (median, 0.558 mm) (P <0.05) LCUs at the cement-enamel interfaces. CONCLUSIONS: The high-intensity curing device PAC is associated with more microleakage than the LED and QTH at the cement-enamel interface.

Effect of light-activated bleaching on the microleakage of Class V tooth-colored restorations.

OBJECTIVE: In-office bleaching procedures utilizing highly concentrated 30%-35% hydrogen peroxide solutions or hydrogen peroxide releasing agents are used for tooth whitening. Some recommend that, to enhance the whitening process, light-activation of the bleaching agent should be performed. The current study evaluated the effect of plasma arc bleaching on the microleakage of Class V restorations restored with resin composite, compomer and resin-modified glass ionomer (RMGI). MATERIALS AND METHODS: The buccal surfaces of 72 freshly extracted premolars were prepared with Class V cavities (4 x 2.5 x 1.5 mm) extended 1 mm apical to the CEJ. The prepared teethwere randomly divided into six groups. The cavities were restored with Single Bond and Z100 resin composite (Groups 1 and 2), Prompt L-Pop and F2000 compomer (Groups 3 and 4) and Vitremer RMGI (Groups 5 and 6), respectively. They were then thermocycled for 500 cycles. The samples from Groups 1, 3 and 5 were incubated at 37 degrees C and 100% humidity. Groups 2, 4 and 6 were bleached using in-office bleaching gel and the plasma arc bleaching unit, then incubated. All samples were sealed with nail varnish and immersed in 2% basic fuschin for 24 hours. The restorations were sectioned longitudinally and microleakage was evaluated using a scale ranging from 0 to 3. The data were analyzed using the Kruskal-Wallis test (alpha = 0.05). RESULTS: No statistically significant differences between study groups were observed in both the enamel and dentinal margins (p > 0.05). CONCLUSION: Plasma arc bleaching did not significantly affect the microleakage of existing tooth-colored restorations restored with Z100 resin composite, F2000 compomer and Vitremer RMGI.

Influence of flowable materials on microleakage of nanofilled and hybrid Class II composite restorations with LED and QTH LCUs.

BACKGROUND: Class II composite restorations are more frequently being placed with margins apical to the cementoenamel junction (CEJ) and margins within the dentin are prone to microleakage. AIMS: This in vitro study was used to evaluate the influence of flowable composite and flowable compomer as gingival liner on microleakage in Class II composite restorations and compare a light-emitting diode (LED) unit with a quartz tungsten halogen (QTH) unit for light-activating composite resins. MATERIALS AND METHODS: Mesioocclusal and distoocclusal Class II cavity preparations were made in 72 sound extracted premolars. The buccolingual width was 2.5 mm and the gingival margins of all the cavities were placed 1.0 mm apical to the CEJ. The boxes were prepared 1.5 mm deep axially, making 144 slot cavities. Teeth were randomly divided into the following two groups (n = 72): (I) Universal Filtek Supreme XT; Universal Filtek Supreme XT + Flwable Filtek XT and Universal Filtek Supreme XT + Dyract Flow and (II) Filtek Z250; Filtek Z250 + Flwable Filtek XT and Filtek Z250 + Dyract Flow. Flowable materials were injected into the gingival floor of the cavity to a thickness of 1.0 mm. Each increment was cured for 20 s. One-half of the subgroups in each group were cured with QTH and the other half with LED light curing units (LCUs). After 1 week of incubation at 37 degrees C, the specimens were thermocycled (5-55 degrees C, x1500), immersed in 0.5% basic fuchsine dye for 24 h and sectioned and microleakage was evaluated at the gingival margin by two examiners using a 0-3 score scale. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests. RESULTS: The groups utilizing flowable liners had significantly less microleakage (P < 0.05). No significant difference was identified between Universal Filtek Supreme XT and Filtek Z250 composites with and without flowable materials. There was no significant between utilizing flowable composite or flowable compomer and between each similar subgroup when polymerized with either the LED or the QTH LCUs. CONCLUSIONS: A layer of flowable materials at the gingival floor of Class II composite restorations may be recommended to improve the marginal seal of a restoration.

One-step self-etching adhesive polymerization: influence of a self-curing activator.

OBJECTIVES: The objectives of this work were to study the spatially resolved extent of photopolymerization and the final volumetric contraction of the self-etching adhesive Xeno IV (Dentsply/Caulk, Milford, DE, USA) in association with the self-curing agent Aurora (Dentsply/Caulk, Milford, DE, USA), using (1)H Stray-Field magnetic resonance imaging ((1)H STRAFI-MRI). METHODS: One-dimensional (1)H STRAFI-MRI images (projections along an axis, profiles) were acquired from the adhesive with and without Aurora, before and after solvent removal. Specimens were observed after the irradiation period recommended by the manufacturers and new profiles were recorded. Extent of polymerization and volumetric contraction were obtained by subtracting the profile of the cured adhesive from the profile of the liquid; the profiles were previously normalized using an external reference signal and the highest magnetization intensity recorded from the cured adhesive, respectively. Data were obtained in the presence of oxygen. Solvent evaporation was measured by gravimetry. RESULTS: High volumetric contraction was observed for Xeno IV and Xeno IV and Aurora mixture mainly related to solvent evaporation. A drying period favourably influenced the extent of photopolymerization of Xeno IV, which did not increase in the presence of Aurora. CONCLUSIONS: The incorporation of Aurora reduced the extent of polymerization of the one-step adhesive, probably due to the increase in the solvent content of the mixture. It may be that enhancing solvent evaporation is important in order to reach a higher extent of polymerization during the bonding procedure.

Compressive strength of esthetic restorative materials polymerized with quartz-tungsten-halogen light and blue LED.

This study compared the compressive strength of a composite resin and compomer photoactivated with a conventional quartz-tungsten halogen-light (XL 3000, 3M/SPE) and a blue light-emitting diode (LED) (SmartLite PS; Dentsply/De Trey). Forty disc-shaped specimens were prepared using a split polytetrafluoroethylene matrix (4.0 mm diameter x 8.0 mm hight) in which the materials were inserted incrementally. The curing time of each increment was of 40 s with the QTH and 10 s with the LED. The specimens were randomly assigned to 4 groups (n=10), according to the light source and the restorative material. After storage in distilled water at 37 degrees C +/- 2 degrees C for 24 h, the specimens was tested in compressive strength in a universal testing machine with load cell of 500 kgf running at a crosshead speed of 0.5 mm/min. Data (in MPa) were analyzed statistically by ANOVA and Student-Newman-Keuls test (p<0.05). For the composite resin, light curing with the QTH source did not produce statistically significant difference (p>0.05) in the compressive strength when compared to light curing with the LED source. However, light curing of the compomer with the QTH source resulted in significantly higher compressive strength than the use of the LED unit (p>0.05). The composite resin presented significantly higher (p>0.05) compressive strength than the compomer, regardless of the light source. In conclusion, the compressive strength of the tested materials photoactivated with a QTH and a LED light source was influenced by the energy density employed and the chemical composition of the esthetic restorative materials.

Cytotoxic effects of halogen- and light-emitting diode-cured compomers on human pulp fibroblasts.

OBJECTIVE: The aim of this study was to determine the cytotoxic effects of three different compomers (Dyract AP, Compoglass, and Hytac) cured using a halogen light-curing unit (LCU) and a light-emitting diode (LED) LCU on human pulp fibroblasts. METHODS: Specimens of three compomers were added to human pulp fibroblast cultures. Cytotoxicity was evaluated over 96 h using the agar overlay method. RESULTS: All three compomers tested were found to be moderately cytotoxic to human pulp fibroblasts, regardless of whether they were cured using halogen or LED LCUs. The decolorization zone of Hytac was significantly larger than those of the other compomers tested (P < 0.05). Dyract AP and Compoglass specimens showed greater decolorization when cured with LED than with halogen LCUs (P < 0.05). CONCLUSION: Compomers are potentially toxic to human pulp fibroblasts, and the type of curing unit may affect compomer toxicity.

Compressive strength of esthetic restorative materials polymerized with quartz-tungsten-halogen light and blue LED

This study compared the compressive strength of a composite resin and compomer photoactivated with a conventional quartz-tungsten halogen-light (XL 3000, 3M/SPE) and a blue light-emitting diode (LED) (SmartLite PS; Dentsply/De Trey). Forty disc-shaped specimens were prepared using a split polytetrafluoroethylene matrix (4.0 mm diameter x 8.0 mm hight) in which the materials were inserted incrementally. The curing time of each increment was of 40 s with the QTH and 10 s with the LED. The specimens were randomly assigned to 4 groups (n=10), according to the light source and the restorative material. After storage in distilled water at 37oC ± 2oC for 24 h, the specimens was tested in compressive strength in a universal testing machine with load cell of 500 kgf running at a crosshead speed of 0.5 mm/min. Data (in MPa) were analyzed statistically by ANOVA and Student-Newman-Keuls test (p<0.05). For the composite resin, light curing with the QTH source did not produce statistically significant difference (p>0.05) in the compressive strength when compared to light curing with the LED source. However, light curing of the compomer with the QTH source resulted in significantly higher compressive strength than the use of the LED unit (p>0.05). The composite resin presented significantly higher (p>0.05) compressive strength than the compomer, regardless of the light source. In conclusion, the compressive strength of the tested materials photoactivated with a QTH and a LED light source was influenced by the energy density employed and the chemical composition of the esthetic restorative materials.

Este estudo comparou a resistência à compressão de uma resina composta e de um compômero, fotoativados com luz halógena convencional de quarto-tungstênio (QTH) (XL 300, 3M/SPE) e LED azul (SmartLite PS; Dentsply/De Trey). Foram confeccionados 40 espécimes em forma de disco usando uma matriz bipartida de politetrafluoretileno (4,0 mm de diâmetro x 8,0 mm de altura) em que o material foi inserido incrementalmente. O tempo de polimerização de cada incremento foi de 40 s para a luz halógena convencional e de 10 s para o LED. Os espécimes foram aleatoriamente alocados em 4 grupos (n=10), de acordo com a fonte de luz e com o material restaurador. Depois de armazenadas em água destilada a 37°C ± 2°C por 24 h, a resistência à compressão dos espécimes foi testada em uma máquina universal de ensaios com célula de carga de 500 kgf a uma velocidade de carregamento de 0,5 mm/min. Os dados (em MPa) foram analisados estatisticamente por ANOVA e teste de Student-Newman-Keuls (p<0,05). Para a resina composta, a fotopolimerização com luz halógena não produziu diferença estatisticamente significante (p>0,05) em sua resistência à compressão quando comparada à fotopolimerização com LED. Contudo, a fotopolimerização do compômero com a luz halógena resultou em uma resistência à compressão significativamente maior que a feita o LED (p>0,05). A resina composta apresentou resistência à compressão significativamente maior que a do compômero, independente da fonte de luz. Concluiu-se que a resistência à compressão dos materiais fotopolimerizados com luz halógena e LED foi influenciada pela densidade de energia empregada e pela composição química dos materiais restauradores estéticos.

Knoop hardness depth profile of polyacid-modified composite resins.

OBJECTIVES: To determine the hardness versus depth profile of several polyacid-modified composite resins (PAM-Cs) as a function of shade (A2, A4) and compare the depth of cure (DoC) based on these profiles with that previously obtained with the scraping and penetrometer methods. METHOD AND MATERIALS: Samples of 6 PAM-Cs (Hytac, 3M ESPE; F2000, 3M ESPE; Glasiosite, Voco; Dyract, Dentsply DeTrey; Dyract AP, Dentsply DeTrey; Compoglass F, Vivadent) and 3 composite resins (Herculite Enamel XRV, Kerr; Z100, 3M ESPE; Durafill VS, Heraeus Kulzer) with shades A2 and A4 were light-cured in bulk in split stainless steel molds (thickness ranging from 0.5 to 3.5 mm in steps of 0.5 mm). The Knoop hardness of the irradiated top (KHN(surface)) and nonirradiated bottom (KHN(bottom)) surfaces was determined as a function of sample thickness using a microhardness tester. RESULTS: Regression analysis demonstrated that for a given material, KHN(bottom) equals KHN(surface) up to a specific depth (= DoC) depending on the material and shade and then decreases linearly with increasing depth. The decrease of the KHN per unit depth differs significantly among materials and shades. According to a regression analysis, the scraping and penetrometer methods overestimate the DoC of PAM-Cs compared to the method based on the change of the hardness indentation with depth. CONCLUSIONS: Shade A2 results in greater values of DoC than shade A4, the effect depending quantitatively on the formulation of the material. Some formulations of PAM-Cs do not reach a DoC of 2 mm, a layer recommended to be applied in the incremental technique. The DoC as determined according to ISO 4049:2000 apparently is based on a lower degree of polymerization corresponding to a KHN of 80% of the irradiated surface.

Network competition in a resin-modified glass-ionomer cement.

UNLABELLED: Attempts have been made to improve the mechanical properties and convenience of use of glass-ionomer cement (GIC) by various modifications, in particular by including a free radical-polymerizable component ("resin-modified" GIC, RMGIC). Necessarily, the one replaces part of the other, but the chemistry suggests that the formation of each network separately would inhibit diffusion and thus the other reaction. OBJECTIVE: To ascertain whether interference occurs between the components of an RMGIC by variation of the irradiation regime. MATERIALS AND METHODS: Cylindrical specimens (6 mm x 3 mm diameter) of one brand of RMGIC (Shades A3, D2; Fuji II LC, GC; capsules) were prepared in ptfe moulds. After machine-mixing for 10s, each of the three increments was irradiated from the top for various times (0-60s). In addition, extra irradiation from the bottom; from the bottom before, and from the side after, ejection from the mould; the same using two curing lamps; and at various delays after mixing (0-18 h), with four replicates of each. After exposure, or as appropriate, specimens were wrapped tightly in aluminium foil for dry storage in the dark at 37 degrees C for testing at 24h after mixing. Specimens with evident defects were replaced before testing. RESULTS: No increase in strength was found beyond the recommended 20-s irradiation, indeed further exposure reduced the strength. For top-only irradiation, strength rose from the unirradiated value (66+/-9 MPa) to a peak at 20s (215+/-25 MPa), after which it declined steadily. Adding bottom irradiation gave a small decrease in peak value (194+/-36 MPa); adding side irradiation reduced it substantially (113+/-7 MPa). Delay for 2 min gave a marked reduction (155+/-15 MPa), declining to the unirradiated value at 18 h (70+/-15 MPa). No effect due to shade was detected. SIGNIFICANCE: Competition between network-forming reactions leads to a sensitive balance between the two, and a critical optimum irradiation: too much may be detrimental, as is delay. The essential compromise involved in such mixed chemistry jeopardizes reliability. It is advisable to follow the duration of exposure prescribed by the manufacturer to achieve optimal performance.

Comparative evaluation of the microhardness of 4 dental sealants.

AIM: Aim of this study was the evaluation of the microhardness of 4 dental sealants polymerised with two different curing units. METHODS: Twenty samples (5 x 5x 2 mm) were prepared with 4 different sealants; 10 samples for each group were polymerised with a plasma curing unit (Apollo 95 E DMD) and 10 with a halogen curing light (Heliolux DLX Vivadent ETS, Schaan, Liechtenstein). For each section 6 Vickers microhardness measurements were performed (VMHT 30A, Leica Wien, Austria), 3 on the surface exposed to the light and 3 on the opposite surface. After the baseline assessment all samples were stored in artificial saliva at 37 degrees C for 30, 60, 90, 180 and 360 days, and then analysed again with the microhardness indenter and observed under steromicroscope 10X (Leica DM2500 Wien, Austria). Data were then statistically analysed. RESULTS: The hybrid composite Tetric flow (group IV) showed the higher microhardness values compared to the other tested materials (group I, II, III); surfaces exposed to curing light showed higher microhardness values than opposite surfaces. Moreover, a significant microhardness reduction was observed after 30 days; values remained unmodified after 60, 90, 180 and 360 days. STATISTICS: Data were then statistically analysed with Anova test for repeated measures, with a global significance level of 0.05. CONCLUSION: Because of the good mechanical properties of dental sealants they represent the first choice materials in pits and fissures sealing.

Effect of curing time and light curing systems on the surface hardness of compomers.

This study compared the Vickers hardness of the top and bottom surfaces of two compomers (Compoglass F and Dyract AP) polymerized for 20 and 40 seconds with two different light curing systems. Five samples for each group were prepared using Teflon molds (9x2 mm) and were light-cured either with a conventional halogen lamp (Optilux 501) or LED light (LEDemetron I) for 20 or 40 seconds. After curing, all the samples were stored in distilled water for 24 hours at 37 degrees C. The Vickers hardness measurements were obtained from the top and bottom surfaces of each sample. ANOVA, Scheffé and t-test were used to evaluate the statistical significance of the results. For the top and bottom surfaces, the light curing systems and curing times tested showed no statistical difference, except for Optilux 501, which used 20 seconds for both compomers (p<0.05). There was no significant difference in the microhardness of both surfaces of Compoglass F and Dyract AP cured for either 20 or 40 seconds using LEDemetron I. With Optilux 501, the microhardness of samples cured for 40 seconds was significantly higher than 20 seconds (p<0.05).

Thermographic investigation of contemporary resin-containing dental materials.

OBJECTIVES: To measure the temperature rise induced during visible light curing of modern resin-containing dental materials and the effect of dentine sections in reducing this temperature rise. METHODS: A variety of newly introduced resin-containing materials were investigated, including flowable, packable and conventional hybrid composites, as well as a compomer and a resin modified glass ionomer material. The resin was packed into polytetrafluoroethylene (PTFE) moulds and cured for 40s. Temperature rises on the undersurface of the curing resin were measured using the Thermovision 900 infra-red scanning system. In the second part of the study, extracted, caries free teeth were sectioned into dentine disks of three thicknesses (0.7, 1.4 and 1.9 mm). Composite samples were overlaid by the disks and the insulating effect of dentine measured. RESULTS: The maximum temperature increases were: 43.1 degrees C (flowable composite), 32.8 degrees C (conventional composite), 32.8 degrees C (RMGI), 23.3 degrees C (compomer) and 22.4 degrees C (packable composite). CONCLUSIONS: There was a quantifiable amount of heat generated in resin-containing material during light curing. Dentine sections were good thermal insulators that significantly reduced temperature rises associated with resin composite photocuring.

Color stability of resin-based filling materials after aging when cured with plasma or halogen light.

The influence of curing devices and curing times on the color stability of filling resins was investigated by measuring the CIE-Laboratory-values after performing dry storage, water storage, and a Suntest (EN ISO 7491). Eight samples each of Charisma (CH), Durafill (DU), Definite (DE), and Dyract AP (DY) were light cured by using Translux Energy (TE) for 20, 40 or 60 s, or by using Apollo 95E (AP) for 3, 10 or 20 s. Minor color changes occurred for all dry stored materials, devices and curing times. The TE-cured, water-stored samples behaved similarly to the dry-stored ones, but the samples cured with AP revealed very strong color changes, mainly because of a drastic bleaching process. The bleaching of DU was significantly less than that of the other materials, but a strong white shift occurred. CH, DE, and DU showed very little (and even acceptable) discolorations after the Suntest when TE-cured. DY showed a drastically discoloration. All samples cured using AP drastically bleached and shifted to white for DU and DY but to dark for DE. In conclusion, the extent of discoloration depends on (i) the material, (ii) the test method, (iii) curing time, and (iv) the curing device. The halogen light-cured samples performed best.

A preliminary study of experimental polyacid-modified composite resins ('compomers') containing vinyl phosphonic acid.

OBJECTIVES: The aim of this investigation was to determine the properties of two novel compomers formulated with the monomer vinyl phosphonic acid (VPA). The setting properties, mechanical strength, wear characteristics and fluoride release of two experimental unshaded compomers containing VPA were determined, and compared with the commercial compomer Dyract A (shade C3). METHODS: Two novel compomers were prepared, containing, respectively, 0.24% (A) and 2.31% (B) by mass of VPA, and an appropriate amount of reactive glass filler. Their properties were compared with those of Dyract AP (shade A3). Depth of cure was determined according to the method of ISO 4049. Polymerization of model mixtures of bisGMA, TEGDMA and VPA was studied using FT Raman spectroscopy, by comparing the absorption at 1608cm(-1) (aromatic C-C bond) with that at 1313cm(-1) (CC aliphatic). Compressive and biaxial flexure strengths were determined for sets of 6 specimens stored either wet or dry. Wear was determined using a toothbrushing machine and an abrasive slurry, and fluoride release was determined following up to 6 weeks storage in aqueous media, using a fluoride-selective electrode. RESULTS: Of the model monomer mixtures, the one with the greater quantities of VPA showed lowest degrees of polymerization after irradiation for 40s. Compomer A had an acceptable depth of cure, and similar properties to Dyract AP in terms of compressive and biaxial flexure strength, and also fluoride release. Resistance to toothbrush abrasion of both of the experimental compomers was superior to that of Dyract AP. SIGNIFICANCE: These studies demonstrate that VPA can be used as the active monomer in experimental compomers, and is capable of yielding materials with properties equivalent to a commercial material, but with improved resistance to toothpaste abrasion. The level of VPA in the formulation is critical, because this monomer inhibits addition polymerization, hence must be used only in small amounts.

Surface hardness properties of resin-modified glass ionomer cements and polyacid-modified composite resins.

In this study the top and bottom surface hardness of two polyacid-modified composite resins (PMCRs), one resin-modified glass ionomer cement (RMGIC), and one composite resin were evaluated. The affect of water storage on their hardness was also investigated. The study was conducted using four different groups, each having five specimens obtained from fiberglass die molds with a diameter of 5 mm and a height of 2 mm. Measurements were made on the top and bottom surface of each specimen and recorded after 24 hours and again at 60 days. All tested materials showed different hardness values, and the values of top surfaces of the specimens were found to be higher than the bottom surface in all test groups. There was no statistical difference in the Vickers hardness (HV) values when the test specimens were kept in water storage. In conclusion Hytac displayed microhardness values higher than Vitremer and Dyract. We found the order of HV values to be Surfil > Hytac > Dyract > Vitremer, respectively. Vitremer presented the lowest microhardness level and Surfil the highest.