Understanding the Effect of Thermal Treatment on the Physico-Mechanical Properties of Light-Cured Composites for use in Indirect Restorations.

OBJECTIVES: To study the potential benefits of a post-cure thermal treatment on key physico-mechanical properties of light-cured resin-based composites for use in indirect restorations, a CAD/CAM composite block being used as control. MATERIAL AND METHODS: Six commercial composites were light-cured before being thermally treated in a furnace at 90°C during 15 minutes (CAD/CAM composite used as a control). The properties measured with or without thermal treatment were: degree of conversion, flexural strength, elastic modulus, Vickers microHardness, organic mass content and eluted and absorbed mass before and after storage in ethanol. The data were analysed using one-way ANOVA, and Weibull distributions. RESULTS: A general increase in the properties measured was observed for all materials after thermal treatment, except a general decrease in mass elution and absorption (most statistically significant: p⟨0.05). Weibull analysis showed a tendency (p⟩0.05) of increased reliability of the flexural strength after thermal treatment for all materials. CONCLUSION: The present data revealed clear physico-mechanical improvements after thermal treatment of light-cured composites. Such method could hence be beneficially used to produce indirect restorations as compared to stratifying and light-curing the same composites in situ. However, most properties of the control CAD/CAM composite were higher, but CAD/CAM technologies aren't available everywhere.

Investigating the limits of resin-based luting composite photopolymerization through various thicknesses of indirect restorative materials.

OBJECTIVE: To determine the limitations of using light-curable resin-based luting composites (RBLCs) to bond indirect ceramic/resin-composite restorations by measuring light transmittance through indirect restorative materials and the resulting degree of conversion (DC) of the luting-composites placed underneath. METHODS: Various thicknesses (0-4mm) and shades of LAVA Zirconia and LAVA Ultimate were prepared and used as light curing filters. A commercial, light curable RBLC, RelyX Veneer (control) was compared with four experimental RBLCs of the following composition: TEGDMA/BisGMA (50/50 or 30/70wt%, respectively); camphorquinone/amine (0.2/0.8wt%) or Lucirin-TPO (0.42wt%); microfillers (55wt%) and nanofillers (10wt%). RBLCs covered with the LAVA filter were light-cured for 40s, either with the dual-peak BluephaseG2 or an experimental device emitting either in the blue or violet visible band. The samples were analyzed by Raman spectroscopy to determine DC. Light transmittance through the filters was measured using a common spectroscopy technique. RESULTS: All the factors studied significantly influenced DC (p<0.05). RBLCs with increased TEGDMA content exhibited higher DC. Only small differences were observed comparing DC without filters and filters ≤1mm (p>0.05). For thicknesses ≥2mm, significant reductions in DC were observed (p<0.05). Transmittance values revealed higher filter absorption at 400nm than 470nm. A minimal threshold of irradiance measured through the filters that maintained optimal DC following 40s irradiation was identified for each RBLC formulation, and ranged between 250-500mW/cm2. SIGNIFICANCE: This work confirmed that optimal photopolymerization of RBLCs through indirect restorative materials (≤4mm) and irradiation time of 40s is possible, but only in some specific conditions. The determination of such conditions is likely to be key to clinical success, and all the factors need to be optimized accordingly.

Influence of composition on setting kinetics of new injectable and/or fast setting tricalcium silicate cements.

OBJECTIVES: New commercial tricalcium silicate based cements were elaborated to improve handling properties and setting time. The goals of the present work were: (i) to determine the composition of the new injectable and/or fast setting calcium silicate based cements, and (ii) to investigate the impact of the differences in composition on their setting kinetics. METHODS: The materials considered were Angelus MTA™, Biodentine™, MM-MTA™, MTA-Caps™, and ProRoot MTA™ as control. Elemental composition of materials was studied by Inductively Coupled Plasma-Atomic Emission Spectroscopy and X-ray Energy Dispersive analysis, whereas phases in presence were analyzed by Micro-Raman spectroscopy and X-ray Diffraction analysis and cement surface by Scanning Electron Microscope. Setting kinetics was evaluated using rheometry. RESULTS: Elemental analysis revealed, for all cements, the presence of three major components: calcium, silicon and oxygen. Chlorine was detected in MM-MTA, MTA-Caps and Biodentine. Different radio-opacifiers were identified: bismuth oxide in ProRoot MTA, Angelus MTA and MM-MTA, zirconium oxide in Biodentine and calcium tungstate (CaWO4) in MTA-Caps. All cements were composed of di- and tri-calcium silicate, except Biodentine for which only the latter was detected. Major differences in setting kinetics were observed: a modulus of 8×10(8)Pa is reached after 12min for Biodentine, 150min for MM-MTA, 230min for Angelus MTA and 320min for ProRoot MTA. The maximum modulus reached by MTA-Caps was 7×10(8)Pa after 150min. SIGNIFICANCE: Even if these cements possess some common compounds, major differences in their composition were observed between them, which directly influence their setting kinetics.

Reduced polymerization stress of MAPO-containing resin composites with increased curing speed, degree of conversion and mechanical properties.

OBJECTIVES: The degree and rate of photopolymerization in resin-based dental composites will significantly affect polymer network formation and resultant material properties that may determine their clinical success. This study investigates the mechanical properties, the generation of stress from polymerization, tooth cusp deflection and marginal integrity of experimental resin composites that contain different photoinitiators. METHODS: Experimental light-activated resin composites (60vol% particulate filled in 50/50mass% bis-GMA/TEGDMA) were formulated using a monoacylphosphine oxide (MAPO) photoinitiator and compared with a conventional camphoroquinone (CQ)-based system. Similar radiant exposure was used (18Jcm(-2)) for polymerization of each material although the curing protocol was varied (400mWcm(-2) for 45s, 1500mWcm(-2) for 12s and 3000mWcm(-2) for 6s). Degree and rate of polymerization was calculated in real-time by near infrared spectroscopy and the generation of stress throughout polymerization measured using a cantilever beam method. Flexural strength and modulus were acquired by three-point bend tests. Standardized cavities in extract pre-molar teeth were restored with each material, the total cuspal deflection measured and post-placement marginal integrity between the tooth and restoration recorded. RESULTS: Generally, MAPO- exhibited a significantly higher degree of conversion (72±0.8 to 82±0.5%) compared with CQ-based materials (39±0.7 to 65±1.6%) regardless of curing protocol (p<0.05) and MAPO-based materials exhibited less difference in conversion between curing protocols. CQ-based materials exhibited between ∼85 and 95% of the maximum rate of polymerization at <15% conversion, whereas MAPO-based RBCs did not approach the maximum rate until >50% conversion. Higher irradiance polymerization had a significant deleterious effect on the mechanical properties of CQ-based materials (p<0.05) whereas MAPO-based materials exhibited increased strength and modulus and were less affected by the curing method. Total cuspal deflection in restored extracted teeth was higher for CQ- compared with MAPO-based materials cured at the lowest irradiance curing protocol (12.9±4.0 and 8.3±1.5µm) and similar at 3000mWcm(-1) for 6s (10.1±3.5 and 9.0±1.5µm). A significant decrease in marginal integrity was observed for CQ-based RBCs cured at high irradiance for short exposure time compared with that of the MAPO-based RBC cured using a similar protocol (p=0.037). SIGNIFICANCE: Polymer network formation dictates the final properties of the set composite and the use MAPO photoinitiators may provide an effective restorative material that exhibits higher curing speeds, increased degree of conversion, strength and modulus without compromise in terms of polymerization stress and marginal integrity between tooth and restoration.

Benefits and limitations of adding hyperbranched polymers to dental resins.

Volumetric shrinkage reduction is a constant challenge in the improvement of dental resins. The inclusion of hyperbranched polymers (HBPs) with modified functionalities (hydroxyl, propionate, and methacrylate) instead of conventional dimethacrylate monomers has the potential to reduce shrinkage, but can also affect other properties. The null hypothesis was that the addition of HBPs (from 5 to 40 mass%) to a 50/50 mass% Bis-GMA/TEGDMA mixture reduces shrinkage without affecting degree of conversion, elastic modulus, glass transition temperature, Wallace hardness (before/after ethanol storage), and viscosity. This hypothesis was rejected, since HBP incorporation significantly affected most properties either negatively or positively. When HBP amounts in the resin were increased, the following general trends were observed: Volumetric shrinkage decreased significantly (p < 0.0001), down to about one-third of the control value at 40% HBP; Wallace hardness (both before and after ethanol) and viscosity increased progressively, while elastic modulus showed a parabolic profile, with a maximum at 10% HBP; and finally, degree of conversion and glass transition temperature were relatively stable, regardless of the HBP content. These results indicate that HBPs with modified end groups might be interesting substitutes for Bis-GMA/TEGDMA.

High irradiance curing and anomalies of exposure reciprocity law in resin-based materials.

OBJECTIVES: The aim of this work was to investigate the effect of high irradiance curing on resultant degree of conversion of 'flowable' resin composites and their counterpart higher viscosity paste materials. METHODS: Five commercial flowable materials (Venus; Heraeus Kulzer, Synergy D6; Coltene, Premise; Kerr, Grandio; Voco and Gradia; GC Corp) and their counterpart higher viscosity restorative versions were tested. Specimens were cured with a halogen Swiss Master Light (EMS, Switzerland) using five different curing protocols with similar radiant exposure (18J/cm(2)): 400mW/cm(2) for 45s, 900mW/cm(2) for 20s, 1500mW/cm(2) for 12s, 2000mW/cm(2) for 9s and 3000mW/cm(2) for 6s. Degree of conversion (DC) was measured in real time by Fourier transform near infrared spectroscopy (FT-NIRS). RESULTS: Three- and subsequent two way ANOVA testing revealed significant differences (p≤0.02) with respect to "composite type" and "cure protocol" for DC for all 5 product comparisons. Supplementary one-way ANOVA also revealed significant differences between curing protocols (p<0.05). The majority of higher viscosity resin composite paste materials exhibited similar DC regardless of curing protocol. However, a significant decrease in DC for specimens cured at 3000mW/cm(2) for 6s compared with 400mW/cm(2) for 45s was observed for the flowable materials, Grandio (41±0.36 and 62±1.15%, respectively) and Venus (44±0.44 and 67±0.44%, respectively). Conversely, other flowable materials exhibited little or no significant differences between curing modes. Generally, a higher degree of conversion was observed for flowables compared with their more viscous counterpart, except at high irradiance for those materials where a reciprocal relationship with exposure time was not observed. CONCLUSIONS: The validity of exposure reciprocity law and final degree of conversion depends on several factors, amongst which resin viscosity and filler content were important. Practitioners should be aware of the importance of resin composite constituents and irradiation protocols. Information on material composition and appropriate radiation sources by manufacturers may assist practitioners with the selection of appropriate curing protocols for specific material/light curing unit combinations with the aim of reducing the incidence of under-cured restorations and the clinical impact thereof.

Photoinitiator type and applicability of exposure reciprocity law in filled and unfilled photoactive resins.

OBJECTIVES: To test the influence of photoinitiator type and filler particle inclusion on the validity of exposure reciprocity law. MATERIALS AND METHODS: 50/50 wt% Bis-GMA/TEGDMA resins were prepared with equimolar concentrations of camphorquinone/DMAEMA (0.20/0.80 mass%) (CQ) or Lucirin-TPO (0.42 mass%), and were used either unfilled or filled to 75 mass%. Specimens were cured with a halogen Swiss Master Light (EMS, Switzerland) using four different curing protocols: 400 mW/cm² for 45 s as reference protocol (18 J/cm²), 1500 mW/cm² for 12 s (18 J/cm²), 3000 mW/cm² for 6 s (18 J/cm²) and 3 s (9 J/cm²). Degree of conversion (DC) was measured in real time for 70 s by FT-NIRS and temperature rise using a thermocouple. Depth of cure was determined with a penetrometer technique. RESULTS: With respect to DC and depth of cure, exposure reciprocity law did not hold for any tested material, except for the depth of cure of filled CQ-based materials. At similar radiant exposure, DC was significantly higher (p<0.05) for all unfilled and filled TPO-based materials compared with CQ-based materials. As exposure time was reduced and irradiance increased, TPO-based materials exhibited higher DC whilst an opposite trend was observed for CQ-based materials (p<0.05). For similar curing regimes, depth of cure of CQ-based materials remained significantly greater than that of TPO-based materials. Adding fillers generally reduced DC, except at higher irradiance for CQ-based materials where a positive effect was observed (p<0.05). SIGNIFICANCE: The validity of exposure reciprocity law was dependent on several factors, among which photoinitiator type and filler content were important. Lucirin-TPO is a highly reactive and efficient photoinitiator, which may allow the potential for a reduction in curing time of TPO-based photoactive materials in thin sections.

Irradiation modes' impact on radical entrapment in photoactive resins.

Different irradiation protocols are proposed to polymerize dental resins, and discordances remain concerning their impact on the material. To improve this knowledge, we studied entrapment of free radicals in unfilled Bis-GMA/TEGDMA (50:50 wt%) resin after light cure. The tested hypothesis was that various irradiation parameters (curing time, irradiance, and radiant exposure) and different irradiation modes (continuous and pulse-delay) led to different amounts of trapped free radicals. The analysis of cured samples (n = 3) by electron paramagnetic resonance (EPR) revealed that the concentrations of trapped free radicals significantly differed according to the curing protocol. When continuous modes with similar radiant exposure were compared, higher concentrations of trapped free radicals were measured for longer times with lower irradiance. Concerning pulse modes, the delay had no influence on trapped radical concentration. These results give new insights into the understanding of the photopolymerization process and highlight the relevance of using EPR when studying polymerization of dimethacrylate-based materials.

Investigating filler morphology and mechanical properties of new low-shrinkage resin composite types.

Three types of low-shrinkage composites are today commercially available: Ormocers, cationic ring-opening curing systems and highly filled methacrylate-based materials, which cure via free-radical polymerization mechanisms. The aim of this study was to characterize the inorganic fraction of materials belonging to each type and to compare their mechanical properties. Two Ormocers (Admira and an experimental Ormocer V35694), one ring-opening composite (Filtek Silorane) and five methacrylate-based composites [Filtek Supreme XT, Tetric EvoCeram, Grandio, Synergy D6 (Coltène-Whaledent, Langenau, Germany) and an experimental material, V34930] were tested. Inorganic fillers were quantified by thermogravimetric analysis and morphologically characterized by scanning electron microscopy. Dynamic modulus was determined by an impulse excitation technique, static elastic moduli and flexural strength by a three-point bending method. The results were analyzed using ANOVA tests (P < 0.05) and linear correlations. Grandio, V34930 and V35694 exhibited significantly higher filler mass fractions. Both dynamic and static moduli of Grandio and V34930 were significantly higher than the other materials (P < 0.05), although no significant difference in flexural strength was observed between material type (P > 0.05). From the present findings, it was suggested that V35694 and Filtek Silorane exhibit comparable properties to conventional methacrylate-based composites, although clinically the cavity type and location must guide material choice. Under high occlusal load, the use of Grandio and V34930 might be favoured. For small cavities, alternative technologies could be preferred as the need for mechanical resistance is lower and the potential for stress generation is greater.

Antibacterial activity of glass-ionomer cements, compomers and resin composites: relationship between acidity and material setting phase.

Agar diffusion testing was used with four different media to evaluate the antibacterial activity of six products (one conventional glass-ionomer cement (GIC), two light-activated glass-ionomers, two polyacid-modified resin composites and one resin composite) on Streptoccoccus mutans. Their respective antibacterial activities were also compared during and after setting. The relationship between product acidity and antibacterial activity was evaluated. All the GICs demonstrated antibacterial properties in contrast to the polyacid-modified resin composites and resin composite which did not shown any antibacterial effects. Vitrebond GIC exhibited higher antibacterial action, probably because of a cytotoxic photo-initiator diphenyliodoniumchloride. A direct relationship between material acidity and growth inhibition of S. mutans was observed.

Characterization of the inorganic fraction of resin composites.

The purposes of this study were to determine the weight fraction of filler in thirty-nine resin-based materials including flowable and packable composites, and to examine the morphology of the filler particles. The percentages of inorganic fillers by weight were determined by Thermogravimetric Analysis and by ashing in air technique at 900 degrees C. The size and shape of the filler particles were examined using scanning electron microscopy (SEM) after dissolution of the organic matrix. The weight fraction of inorganic fillers ranged between 41.6 and 84.6%. Wide variations were found among materials of the same category. Values found in the present study were sometimes different from those given by the manufacturers. The SEM photomicrographs showed various shapes, and sizes of inorganic fillers. Compared with universal hybrid restorative materials, flowable composites have lower filler loading and packable resin composites did not show higher values as claimed by some manufacturers. Various factors may explain the observed discrepancies between the manufacturer's data and our results. The silane treatment as well as the incorporation of organic material as part of the fillers of the composite could be responsible for those differences.

Treatment with removable partial dentures: a longitudinal study. Part I.

The aim of this study was to evaluate the effectiveness of an oral rehabilitation by removable partial denture (RPD). Between 1983 and 1994, 629 patients were provided with an RPD at the Dental School of the Université catholique de Louvain. All the RPDs were constructed with a cobalt-chromium framework. All the treatments were provided by dental students under the supervision of clinical instructors. At recall time (1998-2000), 269 patients could not be reached neither by telephone nor by mail and 27 had died. Consequently, 333 patients were called for clinical examination and 254 of these (76.3%) actually attended. For a total of 292 RPDs fitted for these 254 patients, 218 (74.7%) were still being worn at the time of the check-up. Seventy-four dentures were considered to be 'failures', either because they were replaced by another RPD or by a complete denture, or because they had actually never been worn. The statistical analysis (Mantel-Haenszel and Kaplan-Meier) shows that the number of failures is significantly higher at the lower jaw compared with the upper jaw. Most of the failures are attributable to RPDs with free-end saddles and, in particular, to class I mandibular dentures. The patients are wearing their denture(s) mostly continuously (63.6%) and award a high degree of satisfaction to their denture. In general, the results recorded may be considered as very satisfactory, all the more so as we have no regular recall procedures established at our school and as check-up asked for spontaneously by the patients in the course of the period of observation are most of the time occasional or non-existent.

Treatment with removable partial dentures: a longitudinal study. Part II.

The aim of this study was to evaluate the effectiveness of an oral rehabilitation by removable partial denture (RPD). Between 1983 and 1994, 629 patients were provided with an RPD at the Dental School of the Université catholique de Louvain. All the RPDs were constructed with a cobalt-chromium framework. All the treatments were provided by dental students under the supervision of clinical instructors. At recall time (1998-2000), 269 patients could not be reached neither by telephone nor by mail and 27 had died. Consequently, 333 patients were called for clinical examination and 254 of these (76.3%) actually attended. For a total of 292 RPDs checked 1893 persistent teeth were listed, with 804 serving as abutments; more than half (57.6%) of these were crowned, for which 51 debondings were recorded. For the period of observation we listed 79 abutments lost (37 at the upper jaw and 42 at the lower jaw), i.e. 9.8% of the total number of abutments. No relation could be established between the type of the abutments (natural or crowned teeth) and the losses observed (Test of Mantel-Haenszel: P=0.9496). In the upper jaw, the percentage of abutments lost was significantly higher in the presence of free-end edentulous areas as compared with bounded edentulous areas (Test of Mantel-Haenszel: P=0.0002); this difference does not appear for the lower jaws (P=0.9558). If we deduct the 25 abutments related with the 11 non-worn RPDs and the 79 abutments lost, no change becomes apparent for 92.2% of the maxillary abutments and for 85.8% of the mandibular abutments. For the 1089 other teeth, we observed the loss of 40 teeth and the appearance of caries or new fillings for 95 teeth. The fractures of cast clasps represent 3.4%.

Interfacial layer characterization in dental composite.

Nowadays, dental resins find increasing use by practitioners. However, photopolymerization of such resins is limited to a so-called 'depth of cure'. To face this problem, dentists superimpose resin layers of limited depth. This technique raises the problem of the quality of interlayer. This paper aims at screening different cases of adhesion at the interface. Shear strength of such interfacial layers is tested in shear mode in various conditions (with or without an oxygen-inhibited layer, or contaminated by saliva or water). Unexpectedly, the presence of an oxygen-inhibition on the first layer, as assessed using micro-Raman spectroscopy, induces higher shear strength. In this case, a cohesive break occurs while an adhesive one is observed in all the other cases.

Raman scattering determination of the depth of cure of light-activated composites: influence of different clinically relevant parameters.

The purpose of this research was to determine the depth of cure of light-activated composites in relation with different clinically relevant parameters. A Raman spectroscopic method has been used. The measurement of cure is made on a relative basis by comparing the vibration band of the residual unpolymerized methacrylate C=C bond at 1640 cm-1 against the aromatic C=C stretching band at 1610 cm-1 used as an internal standard. The information gained draw attention to the importance of light transmission during the exposure. The influence of sample's thickness on the depth of cure is illustrated by a second order polynomial regression. The shade and translucency of the resin composite also modify the light transmission and thus have a significant influence on the degree of conversion. Moreover the light-source intensity and the distance from the curing tip are important parameters of influence. A significant reduction of the depth of cure is observed for all sample thickness of resin composite tested when using a light device with an intensity of 300 mW cm-2 as well as using a distance from the curing tip higher than 20 mm.

Dynamic and static moduli of elasticity of resin-based materials.

OBJECTIVES: The purpose of this study was to assess and compare the elastic moduli of 34 resin-based materials using a dynamic and a static method. The effect of water storage was also studied up to 6 months. METHODS: Five samples of each material were prepared according to ISO-4049. The dynamic moduli were first determined non-destructively from the fundamental period of the vibrating specimen, then the static moduli were determined by a three-point bending test. The percentages of fillers by weight were determined by ashing in air at 900 degrees C. RESULTS: Low values were obtained with flowable composites as well as with two packable resin composites. Correlations were found between the static and the dynamic modulus of elasticity (r = 0.94; p = 0.0001) as well as between the weight percentage of fillers and the moduli of elasticity (r = 0.82; p < 0.05 for static modulus and r = 0.90; p < 0.05 for the dynamic modulus) both at 24h. Water storage significantly affected both static and dynamic moduli of elasticity (ANOVA two factors; p < 0.05). SIGNIFICANCE: The low moduli of the flowable composites do not allow their use in posterior cavities under high stress. However, this does not exclude their use for minimally-invasive Class I cavities when the opposing tooth is stabilized to a large amount on the natural enamel. The Grindosonic method is very useful and simple for determining the dynamic moduli although it gives higher values than the static one. The elastic modulus evolution of resin-based materials after water storage is unpredictable since different patterns were observed as a function of time.

Meta-analytical review of factors involved in dentin adherence.

Literature data on adherence tests of dentin-bonding systems (DBS) may differ widely, even for the same DBS. The problem of bond testing is that materials are seldom compared with a standard, and experimental conditions often vary. We sought to identify the parameters that influence this variability. Using inclusion and exclusion criteria, we conducted a meta-analytical review of 75 articles, published between 1992 and 1996 in SCI reviews, that give bond strength data for 15 dentin-bonding agents of the so-called third and fourth generations. Seventeen selected parameters were classified into four groups: Group A includes factors related to the dentin substrate (i.e., nature of teeth); group B, composite and bonding area (i.e., composite stiffness); group C, storage conditions of the bonded samples (i.e., thermocycling); and group D, test design (i.e., crosshead speed). For each report, the experimental features, the bond strength means and standard deviations, and the failure mode were extracted and tabulated. Statistical Analysis System software was used to perform Pearson correlation analysis and analysis of variance, with bond strength as the dependent variable and experimental conditions as the independent variables. The meta-analytical review highlighted the significant influence of various parameters in the different groups: origin of dentin, types of teeth, pulpal pressure, tooth storage temperature, maximum storage time of teeth, and dentin depth in group A; type and stiffness of composite and bonding area in group B; storage of bonded samples (medium, temperature, and time) in group C, and testing mode and crosshead speed in group D. A significant positive correlation was observed between the mean bond strength and the rate of cohesive failure. It can be concluded from this study that some of these parameters should be controlled by the use of a standardized protocol. Unfortunately, the substrate-related variables are more difficult to control, even though their influence is consistent.

Fluoride release from glass-ionomer cements, compomers and resin composites.

The short and long-term fluoride release of 16 products (seven conventional glass-ionomers, five light-activated glass-ionomers, two polyacid-modified resin composites and two resin composites) commercialized as fluoride-releasing materials were measured. A potential link between the material type and its level of fluoride release was researched. The fluoride release was evaluated after different time intervals. Initial fluoride release from all materials was highest during the first 24 h and decreased sharply over the first week. Some groups of materials appeared to be significantly different after, respectively, 7 and 91 days. However, it was impossible to correlate the fluoride release of the materials by their type (conventional or resin-modified glass-ionomers, polyacid-modified resin composite and resin composite) except if we compared the products from the same manufacturer. The link between fluoride release and an acid-base reaction seems to be confirmed. The glass-ionomer composition (glass particles and polyacid's type, powder/liquid ratio) should have more influence on fluoride release than material type.

The micro-Raman spectroscopy, a useful tool to determine the degree of conversion of light-activated composite resins.

Light-activated composites are now among the most popular dental restorative materials. Nevertheless, concerns exist about the so-called depth of cure. Infrared spectroscopy (FTIR) has traditionally been used to quantify this problem by evaluating the degree of conversion of dental resins. However, Raman scattering provides an alternate method. This article describes the advantages and the limitations of micro-Raman spectroscopy, as compared to FTIR and other techniques, for calculating the local degree of conversion and the depth of cure of light-cured composites.