CAD/CAM milled complete removable dental prostheses: An in vitro evaluation of biocompatibility, mechanical properties, and surface roughness.

This study compared the biocompatibility, mechanical properties, and surface roughness of a pre-polymerized polymethyl methacrylate (PMMA) resin for CAD/CAM complete removable dental prostheses (CRDPs) and a traditional heat-polymerized PMMA resin. Two groups of resin substrates [Control (RC): conventional PMMA; Test (RA): CAD/CAM PMMA] were fabricated. Human primary osteoblasts and mouse embryonic-fibroblasts were cultured for biocompatibility assays. Mechanical properties and surface roughness were compared. ANOVA revealed no difference between the resin groups in the biocompatibility assays. RA demonstrated a higher elastic modulus (p=0.002), young's modulus (p=0.002), plastic energy (p=0.002), ultimate strength (p=0.0004), yield point (p=0.016), strain at yield point (p=0.037), and toughness (p<0.0001); while RC displayed a higher elastic energy (p<0.0001). Laser profilometry concluded a rougher surface profile (p<0.0001) for RA. This study concluded that the tested CAD/CAM resin was equally biocompatible and presented with improved mechanical properties than the traditional heat-polymerized PMMA resin used in the fabrication of CRDPs.

Grinding damage assessment for CAD-CAM restorative materials.

OBJECTIVES: To assess surface/subsurface damage after grinding with diamond discs on five CAD-CAM restorative materials and to estimate potential losses in strength based on crack size measurements of the generated damage. METHODS: The materials tested were: Lithium disilicate (LIT) glass-ceramic (e.max CAD), leucite glass-ceramic (LEU) (Empress CAD), feldspar ceramic (VM2) (Vita Mark II), feldspar ceramic-resin infiltrated (EN) (Enamic) and a composite reinforced with nano ceramics (LU) (Lava Ultimate). Specimens were cut from CAD-CAM blocs and pair-wise mirror polished for the bonded interface technique. Top surfaces were ground with diamond discs of respectively 75, 54 and 18µm. Chip damage was measured on the bonded interface using SEM. Fracture mechanics relationships were used to estimate fracture stresses based on average and maximum chip depths assuming these to represent strength limiting flaws subjected to tension and to calculate potential losses in strength compared to manufacturer's data. RESULTS: Grinding with a 75µm diamond disc induced on a bonded interface critical chips averaging 100µm with a potential strength loss estimated between 33% and 54% for all three glass-ceramics (LIT, LEU, VM2). The softer materials EN and LU were little damage susceptible with chips averaging respectively 26µm and 17µm with no loss in strength. Grinding with 18µm diamond discs was still quite detrimental for LIT with average chip sizes of 43µm and a potential strength loss of 42%. SIGNIFICANCE: It is essential to understand that when grinding glass-ceramics or feldspar ceramics with diamond discs surface and subsurface damage are induced which have the potential of lowering the strength of the ceramic. Careful polishing steps should be carried out after grinding especially when dealing with glass-ceramics.

Hydrothermal degradation of a 3Y-TZP translucent dental ceramic: A comparison of numerical predictions with experimental data after 2 years of aging.

OBJECTIVES: The purpose of the study was to assess the hydrothermal resistance of a translucent zirconia with two clinical relevant surface textures by means of accelerated tests (LTD) and to compare predicted monoclinic fractions with experimental values measured after two years aging at 37°C. METHODS: Polished (P) and ground (G) specimens were subjected to hydrothermal degradation by exposure to water steam at different temperatures and pressures. The t-m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR). The elastic modulus and hardness before- and after LTD were determined by nanoindentation. RESULTS: G specimens presented a better resistance to hydrothermal degradation than P samples. Activation energies of 89 and 98kJ/mol and b coefficients of 2.0×10(-5) and 1.8×10(-6) were calculated for P and G samples respectively. The coefficients were subsequently used to predict transformed monoclinic fractions at 37°C. A good correlation was found between the predicted values and the experimental data obtained after aging at 37°C during 2 years. Hydrothermal degradation led to a significant decrease of the elastic moduli and hardness in both groups. SIGNIFICANCE: The dependency of the t-m phase transformation rate on temperature must be determined to accurately predict the hydrothermal behavior of the zirconia ceramics at oral temperatures. The current prevailing assumption, that 5h aging at 134°C corresponds to 15-20 years at 37°C, will underestimate the transformed fraction of the translucent ceramic at 37°C. In this case, the mechanical surface treatment influences the ceramic's transformability. While mild grinding could potentially retard the hydrothermal transformation, polishing after occlusal adjustment is recommended to prevent wear of the antagonist teeth and maintain structural strength.

Grinding damage assessment on four high-strength ceramics.

OBJECTIVES: The purpose of this study was to assess surface and subsurface damage on 4 CAD-CAM high-strength ceramics after grinding with diamond disks of 75 µm, 54 µm and 18 µm and to estimate strength losses based on damage crack sizes. METHODS: The materials tested were: 3Y-TZP (Lava), dense Al2O3 (In-Ceram AL), alumina glass-infiltrated (In-Ceram ALUMINA) and alumina-zirconia glass-infiltrated (In-Ceram ZIRCONIA). Rectangular specimens with 2 mirror polished orthogonal sides were bonded pairwise together prior to degrading the top polished surface with diamond disks of either 75 µm, 54 µm or 18 µm. The induced chip damage was evaluated on the bonded interface using SEM for chip depth measurements. Fracture mechanics were used to estimate fracture stresses based on average and maximum chip depths considering these as critical flaws subjected to tension and to calculate possible losses in strength compared to manufacturer's data. RESULTS: 3Y-TZP was hardly affected by grinding chip damage viewed on the bonded interface. Average chip depths were of 12.7±5.2 µm when grinding with 75 µm diamond inducing an estimated loss of 12% in strength compared to manufacturer's reported flexural strength values of 1100 MPa. Dense alumina showed elongated chip cracks and was suffering damage of an average chip depth of 48.2±16.3 µm after 75 µm grinding, representing an estimated loss in strength of 49%. Grinding with 54 µm was creating chips of 32.2±9.1 µm in average, representing a loss in strength of 23%. Alumina glass-infiltrated ceramic was exposed to chipping after 75 µm (mean chip size=62.4±19.3 µm) and 54 µm grinding (mean chip size=42.8±16.6 µm), with respectively 38% and 25% estimated loss in strength. Alumina-zirconia glass-infiltrated ceramic was mainly affected by 75 µm grinding damage with a chip average size of 56.8±15.1 µm, representing an estimated loss in strength of 34%. All four ceramics were not exposed to critical chipping at 18 µm diamond grinding. CONCLUSIONS: Reshaping a ceramic framework post sintering should be avoided with final diamond grits of 75 µm as a general rule. For alumina and the glass-infiltrated alumina, using a 54 µm diamond still induces chip damage which may affect strength. Removal of such damage from a reshaped framework is mandatory by using sequentially finer diamonds prior to the application of veneering ceramics especially in critical areas such as margins, connectors and inner surfaces.

Modulation of osteoblast behavior on TiNxOy coatings by altering the N/O stoichiometry while maintaining a high thrombogenic potential.

INTRODUCTION: Titanium nitride oxide (TiNxOy) coatings are known to stimulate osteoblast proliferation and osseointegration when compared to microrough titanium implants. The objectives of the present study were to determine whether the beneficial effects of TiNxOy coatings observed with implant osseointegration are dependent on N/O stoichiometry, with the final goal of optimizing these benefits. MMS: TiNxOy coatings with various N/O compositions were deposited on microrough titanium plates (Ti-SLA, 11 × 11 mm). Human primary osteoblast (hOBs) proliferation and gene expression were analyzed for a time course of three weeks, with or without additional stimulation by 1.25 (OH)2 vitamin D3 100 nM. Platelet adhesion/activation and thrombin generation were also assessed. RESULTS: hOBs proliferation gradually increased with the amount of oxygen contained in the coatings. The effect was observed from day 7 to reach a maximum at day 10, with a 1.8 fold increase for the best coating as compared to Ti-SLA. SEM views indicated that cells adhered, spread and elongated faster on oxygen-rich TiNxOy films, while the differentiation process as well as the thombogenic potential was not affected. CONCLUSIONS: The effect of TiNxOy coatings on osteoblast is dependent on their chemical composition; it increases with the amount of oxygen. TiNxOy coatings may act as a catalyst for cell-adhesion and proliferation early after seeding. In contrast, thrombogenicity of Ti-SLA surface is not affected by TiNxOy application.

A new testing protocol for zirconia dental implants.

OBJECTIVES: Based on the current lack of standards concerning zirconia dental implants, we aim at developing a protocol to validate their functionality and safety prior their clinical use. The protocol is designed to account for the specific brittle nature of ceramics and the specific behavior of zirconia in terms of phase transformation. METHODS: Several types of zirconia dental implants with different surface textures (porous, alveolar, rough) were assessed. The implants were first characterized in their as-received state by Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), X-Ray Diffraction (XRD). Fracture tests following a method adapted from ISO 14801 were conducted to evaluate their initial mechanical properties. Accelerated aging was performed on the implants, and XRD monoclinic content measured directly at their surface instead of using polished samples as in ISO 13356. The implants were then characterized again after aging. RESULTS: Implants with an alveolar surface presented large defects. The protocol shows that such defects compromise the long-term mechanical properties. Implants with a porous surface exhibited sufficient strength but a significant sensitivity to aging. Even if associated to micro cracking clearly observed by FIB, aging did not decrease mechanical strength of the implants. SIGNIFICANCE: As each dental implant company has its own process, all zirconia implants may behave differently, even if the starting powder is the same. Especially, surface modifications have a large influence on strength and aging resistance, which is not taken into account by the current standards. Protocols adapted from this work could be useful.

Adhesive restoration of anterior endodontically treated teeth: influence of post length on fracture strength.

OBJECTIVES: This study aims to evaluate the fracture resistance of endodontically treated anterior teeth restored with crowns made of composite or ceramic and retained without the use of a post (endocrowns) or with posts of 5 mm (short) and 10 mm in length (long). MATERIAL AND METHODS: Forty-eight intact maxillary incisors were selected for the study. After endodontic treatment, the crowns were sectioned 2 mm coronally to the cementoenamel junction provided with a ferrule of 2 mm. The roots were randomly divided into six groups (n = 8) according to the post length and type of coronary restoration. The crowns were fabricated with the chairside economical restoration of esthetic ceramics system. Group 1 was restored with a 10-mm glass fiber post, composite core, and a full-coverage ceramic crown (LPCer); group 2, with a 5-mm glass fiber post, composite core, and a full-coverage ceramic crown (SPCer); group 3, with a 10-mm glass fiber post, composite core, and a full-coverage composite crown (LPCpr); group 4, with a 5-mm glass fiber post, composite core, and a full-coverage composite crown (SPCpr); and groups 5 (EndoCer) and 6 (EndoCpr) were restored with ceramic and composite endocrowns, respectively. The teeth were then thermomechanically loaded in a chewing machine. After fatigue, the specimens were loaded to fracture. Data were analyzed with ANOVA and chi-square test. Mode of failure was defined as repairable or non-repairable. RESULTS: Presence of post, post length, and crown material had no significant effect on the fracture resistance. Groups restored with endocrowns presented a higher number of repairable fractures in respect to the other groups. CONCLUSIONS: Presence of a post had no effect on the restorations' fracture strength. CLINICAL RELEVANCE: Although this in vitro study has some limitations in respect to its clinical relevance, the restoration of largely destroyed anterior teeth with the use of an endocrown or a short glass fiber post might have advantages over a large glass fiber post.

In vitro bone exposure to strontium improves bone material level properties.

In rats treated with strontium ranelate, the ultimate load of intact bone is increased and associated with changes in microstructure and material level properties. Evaluation by micro-computed-tomography-based finite element analysis has shown that these changes independently contribute to the improvement of bone strength induced by strontium ranelate treatment. However, the mechanism by which Sr ion acts on bone material level properties remains unknown. The vertebrae of intact female rats were exposed overnight to 0.5, 1 or 2M chloride salt solutions of Sr, Ca and Ba. The latter two were used to assess the specificity of Sr. Bone material level properties were evaluated by measuring hardness, elastic modulus and working energy in a nanoindentation test. Wavelength dispersive X-ray spectroscopy provided semi-quantitative elemental analysis and mapping. Incubation with Sr rendered bone stiffer, harder and tougher. Among the divalent ions tested, Sr had the greatest effect. Sr affinity was also assessed on in vivo treated bone specimens. After in vitro exposure, the highest improvements were observed in ovariectomized rats. However, anti-osteoporotic treatments did not influence the capacity of Sr to modify bone material level properties. Our findings demonstrated that in vitro incubation with Sr selectively improved bone material level properties, which may contribute to the macroscopic increase of bone properties observed under Sr therapy.

TiNOx coatings on roughened titanium and CoCr alloy accelerate early osseointegration of dental implants in minipigs.

INTRODUCTION: Titanium nitride oxide (TiNOx) coatings are known for their biocompatibility, hardness and high resistance to corrosion and wear. Further, they can be applied by plasma vapor deposition onto a wide variety of metallic, mineral, or organic substrates. In cell cultures, TiNOx coatings applied onto SLA (sandblasted, large grit, acid etched)-roughened titanium surfaces increased human primary osteoblast proliferation by 1.5 times in the first 2 weeks after seeding, while maintaining a high degree of cell differentiation. Therefore, the objectives of the present study were (i) to determine whether these findings would translate into the enhanced osseointegration of TiNOx-coated implants in vivo and (ii) to compare the osseointegration of Ti-SLA (titanium-SLA) and CoCr-SLA (cobalt-chromium-SLA) implants coated with TiNOx. METHODS: Forty-eight cylinders made of Ti-SLA, Ti-SLA-TiNOx (TiNOx-coated Ti-SLA) and CoCr-SLA-TiNOx (TiNOx-coated CoCr-SLA) were implanted into the lower jawbone of 8 minipigs. The bone-to-implant contact was determined after 1 week, 2 weeks, 1 month and 3 months. RESULTS: Osseointegration proceeded normally on all 3 surfaces, with equal activity after the first week of healing. After 2 weeks, bone-to-implant contact was 1.8 times higher on TiNOx coatings, either deposited on Ti or on CoCr. These differences fell off after 1 and 3 months of healing. CONCLUSIONS: When compared to standard SLA titanium, TiNOx coatings enhance implant osseointegration during the first month of healing. Furthermore, this stimulating effect is independent of the substrate, leading to similar results whether the coating is applied onto SLA-Ti or onto SLA-CoCr.

Low temperature degradation of a Y-TZP dental ceramic.

Bars of Y-TZP ceramic for dental restorations were subjected to hydrothermal degradation via in vitro exposure to water steam at 140°C for 7 days. X-ray diffraction, atomic force microscopy and scanning electron microscopy techniques were applied to observe and quantify the tetragonal-monoclinic (t-m) phase transformation associated with the process. Nanoindentation was used to assess the ceramic's mechanical properties before and after hydrothermal degradation. Texture associated with martensitic t-m transformation was observed at the grain surface. The t-m transformation followed nucleation-and-growth kinetics, with predominance of the nucleation process. The transformation occurred within a layer of 6 µm below the surface. Mechanical properties deteriorated with hydrothermal degradation, resulting in a 30% reduction of Young's modulus and hardness. A strong correlation was found between the increasing monoclinic fraction and the decline in mechanical response. It was thus concluded that the emergence of the monoclinic phase and the associated microcracking were the most likely causes for the degradation of mechanical properties.

Fatigue behavior in water of Y-TZP zirconia ceramics after abrasion with 30 µm silica-coated alumina particles.

OBJECTIVE: The use of a 30 µm alumina-silica coated particle sand (CoJet™ Sand, 3M Espe), has shown to enhance the adhesion of resin cements to Y-TZP. The question is whether or not sandblasting 30 µm particles does negatively affect the fatigue limit (S-N curves) and the cumulative survival of Y-TZP ceramics. METHOD: Four zirconia materials tested were: Zeno (ZW) (Wieland), Everest ZS (KV) (KaVo), Lava white (LV) and Lava colored (LVB) (3M Espe). Fatigue testing (S-N) was performed on 66bar of 3 mm × 5 mm × 40 mm with beveled edges for each zirconia material provided by the manufacturers. One half of the specimens were CoJet sandblasted in the middle of the tensile side on a surface of 5 mm × 6 mm. Cyclic fatigue (N=30/group) (sinusoidal loading/unloading at 10 Hz between 10% and 100% load) was performed in 3-point-bending in a water tank. Stress levels were lowered from the initial static value (average of N=3) until surviving 1 million cycles. Fatigue limits were determined from trend lines. Kaplan-Meier survival analysis was performed to determine the failure stress at the median percentile survival level for 1 million of cycles before and after sandblasting. The statistical analyses used the log-rank test. Characterization of the critical flaw was performed by SEM for the majority of the failed specimens. RESULTS: The fatigue limits "as received" (ctr) were: LV=720 MPa, LVB=600 MPa, KV=560 MPa, ZW=470 MPa. The fatigue limits "after CoJet sandblasting" were: LV=840 MPa, LVB=788 MPa, KV=645 MPa, ZW=540 MPa. The increase in fatigue limit after sandblasting was 15% for Zeno (ZW) and Everest (KV), 17% for Lava (LV) and 31% for Lava colored (LVB). The KM median survival stresses in MPa were: ZW(ctr)=549 (543-555), ZW(s)=587 (545-629), KV(ctr)=593 (579-607), KV(s)=676 (655-697), LVB(ctr)=635 (578-692), LVB(s)=809 (787-831), LV(ctr)=743 (729-757), LV(s)=908 (840-976). Log-rank tests were significantly different (p<0.001) for all sandblasted groups vs. the "as received" except for Zeno (Wieland) (p=0.295). Failures started from both intrinsic and machined flaws. SIGNIFICANCE: 30 µm particle sandblasting did significantly improve the fatigue behavior of three out of four Y-TZP ceramic materials and can therefore be recommended for adhesive cementation procedures. This study was supported in part by grants from the Swiss Society for Reconstructive Dentistry (SSRD) and 3M Espe.

Surface roughness and EDS characterization of a Y-TZP dental ceramic treated with the CoJet™ Sand.

OBJECTIVES: (1) To determine the surface roughness and material loss of a Y-TZP ceramic before and after tribochemical grit blasting and (2) to characterize the changes in elemental surface composition and the phase transformations after tribochemical treatment. METHODS: Machined bar shaped specimens (Zeno, Wieland) were subdivided into three groups. After grit blasting for 10, 20 and 30s respectively, half of the specimens of each group were ultrasonically cleaned in ethanol for 10min. The other half was rinsed with a water spray. Surface roughness was measured using an electro-mechanical profilometer. The elemental composition of the samples was obtained by energy dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) was used for phase transformations determination. RESULTS: The median Ra increased significantly from 0.24 to 0.32-0.38µm after grit blasting. Augmentations were also noted for R(max), R(v) and R(p). The highest roughness parameters were, obtained for water sprayed specimens and samples abraded for 30s. Loss of material ranged between 1 and 3µm for 30s grit blasting. Tetragonal and cubic phases were identified in 'as machined' specimens. Grit blasting resulted in domain switching and lattice deformations. The elemental composition comprised Si and Al. The duration of grit blasting did not significantly, influence the atomic percentages of Si or Al. Significantly lower values for both Si and Al were noted, after ultrasonic cleaning. SIGNIFICANCE: Grit blasting with CoJet™ Sand resulted in an increase of surface roughness, a removal of maximum 3µm of material and coated the surface with submicron silica and alumina particles.

Kinetics of light-cure bracket bonding: power density vs exposure duration.

INTRODUCTION: Recent technologic advances make it possible to increase the light power density to reduce the necessary exposure duration. The kinetics of polymerization are complex. The special case of indirectly curing the thin layler of composite below the metallic bracket base further increases this complexity. It was hypothesized that the concept of "total energy,"--the reciprocity between power density and exposure duration--does not hold for orthodontic light-cure bracket bonding. METHODS: Stainless steel brackets were bonded on deciduous bovine incisors with a standard light-cured composite. A calibrated, powerful halogen lamp allowed for modification of power density from 300 to 3000 mW/cm2. Metallic brackets were bonded in 8 groups of 20 incisors each with various combinations of power densities and exposure durations to obtain 3 levels of energy density (6000, 12000, and 24000 mJ/cm2). Another group of 20 incisors served as the positive control with a conventional powerful halogen lamp (1000 mW/cm2) for 40 seconds. After storage for 24 hours at 37 degrees C in water, the bracket shear bond strength (SBS) and the adhesive remnant index (ARI) were measured. RESULTS: It was confirmed that bracket SBS mainly depends on the energy density of the light cure. All groups with an energy density of 6000 mJ/cm2 had significantly lower SBS than the groups with higher energy densities (P <0.01). The dependence of SBS on exposure duration for the same energy density followed an exponential model of nonlinear regression (r2 = 0.98). CONCLUSIONS: The concept of "total energy" does not hold for orthodontic light-cure bracket bonding. An exposure time of less than 4 seconds, irrespective of the power density, cannot guarantee sufficient bracket bond strength. There seems to be an advantage of power density over exposure duration in the context of metallic bracket bonding. These results show that, for an efficient light-cure bracket bonding, there is an absolute lower limit of exposure duration (4 seconds) and an upper limit of useful power density (3000 mW/cm2).

Push-out bond strengths of endodontic posts bonded with different resin-based luting cements.

PURPOSE: To compare the push-out bond strengths of endodontic posts bonded with different resin-based luting cements and to verify that bond strengths did not vary with cement thickness. METHODS: 48 root canals were shaped using 6% NiTi rotary files, obturated with gutta-percha and AH Plus sealer and prepared for post cementation using Panavia F, Parapost cement, SuperBond and Unicem Rely X. All roots were sectioned into 0.7 mm thick slices and digital photographs of each slice were analyzed using Scion Image to measure the surface area of the luting cement. The root slices were stressed to failure at 1 mm/minute using a push-out test. Push-out strength was calculated as the force at failure divided by the bonded surface area. Least squares linear regression analysis was used to assess the effect of cement thickness on bond strength. Fractured specimens were further observed under the SEM. RESULTS: Mean push-out bond strengths were: Panavia F (8.8 +/- 3.6 MPa), Parapost cement (9.1 +/- 4.4 MPa) SuperBond (14.6 +/- 2.9 MPa) and Rely X Unicem (12.4 +/- 3.3 MPa). The Panavia F and the Parapost cement were not significantly different from each other, but both were significantly lower (P < or = 0.05) than SuperBond and Rely X Unicem. Although there were large variations in cement thickness, the cementation of fiber posts with thicker cement layers did not affect the performance of the adhesive luting cements applied to root canal dentin.

Hydrothermal and mechanical stresses degrade fiber-matrix interfacial bond strength in dental fiber-reinforced composites.

Fiber-reinforced composites (FRCs) show great promise as long-term restorative materials in dentistry and medicine. Recent evidence indicates that these materials degrade in vivo, but the mechanisms are unclear. The objective of this study was to investigate mechanisms of deterioration of glass fiber-polymer matrix bond strengths in dental fiber-reinforced composites during hydrothermal and mechanical aging. Conventional three-point bending tests on dental FRCs were used to assess flexural strengths and moduli. Micro push-out tests were used to measure glass fiber-polymer matrix bond strengths, and nanoindentation tests were used to determine the modulus of elasticity of fiber and polymer matrix phases separately. Bar-shaped specimens of FRCs (EverStick, StickTech, and Vectris Pontic, Ivoclar-Vivadent) were either stored at room temperature, in water (37 and 100 degrees C) or subjected to ageing (10(6) cycles, load: 49 N), then tested by three-point bending. Thin slices were prepared for micro push-out and nanoindentation tests. The ultimate flexural strengths of both FRCs were significantly reduced after aging (p < 0.05). Both water storage and mechanical loading reduced the interfacial bond strengths of glass fibers to polymer matrices. Nanoindentation tests revealed a slight reduction in the elastic modulus of the EverStick and Vectris Pontic polymer matrix after water storage. Mechanical properties of FRC materials degrade primarily by a loss of interfacial bond strength between the glass and resin phases. This degradation is detectable by micro push-out and nanoindentation methods.

Thermal risks from LED- and high-intensity QTH-curing units during polymerization of dental resins.

The aim of this study was to test the ability of an infrared (IR) camera to assess temperature changes and distributions in teeth below restorations when quartz-tungsten-halogen (QTH) and light-emitting diode (LED) curing lights were used to photopolymerize the restorative material. Our hypothesis was that the higher power density and broader spectral distribution of the QTH source would cause greater increases in tooth temperature than the LED source, and that these differences would be best demonstrated with the IR camera. Cavities were prepared on human third molars and restored with a resin composite restorative material. The material was light-cured using three light-curing sources using several exposure times. The external (outside the tooth) and internal (inside the pulp chamber) temperature changes during polymerization of the composite material were recorded over 360 s with thermocouples and an IR camera. Using thermocouples the maximum increase in external temperature (+17.7 degrees C) was reported for the Swiss Master light after 20 s of curing time while the minimum temperature rise (+7.8 degrees C) was reported for the Freelight 2. Whereas a 2.6 degrees C increase in internal temperature was observed after curing 20 s with the Freelight 2, 7.1 degrees C was reported after 60 s of light exposure to Astralis 10. Infrared images showed similar trends in external-internal rises in temperature as the thermocouples, although temperatures measured by the IR were generally higher. These results indicate that the higher power density QTH sources caused greater increases in tooth temperatures than the LED source and that thermocouples may underestimate the heat applied to the tooth.

[Characterization of three light sources. Study of their efficiency]. / Caractérisation de trois sources lumineuses. Etude de leur efficacité.

Light-emitting sources are currently used to activate the setting reaction of restorative composite resins. It is well known that the polymerization extent of the resins will highly influence their clinical behavior. The monomer-polymer transformation will mostly depend on the chemical nature of the photo-initiators used and on the luminous energy given by the curing device. The aims of this study were to characterize three light curing devices and to compare their efficiency to polymerize a composite resin (SureFil). For that purpose, the emission spectra and the irradiance of a plasma arc (Flipo), a QTH visible light (Elipar Trilight), and a LEDs curing device (Elipar Freelight) were measured. Then, the depth of cure and the Vickers hardness of composite samples were evaluated, for each curing device, as a function of the exposure time. The emission spectra obtained showed the irradiance of the visible light emitted as a function of the wavelength, which was different for each light-curing device. The maximum cured depth (approximately 4 mm) give only a qualitative indication of the extent of the polymerization, as the hardness of the composite samples diminished as a function of the depth. Moreover, it strongly depended on the exposure time. Hence, to obtain a hardness of approximately 100 HV 0.5 at 2 mm depth, the illumination time must be at least of 3 s with the plasma arc Flipo, 10 s with the LEDs Elipar Freelight and 20 s with the QTH Elipar Trilight. In order to efficiently polymerize a composite resin, the emission spectra of the luminous source shall correspond with the absorption spectra of the photo-initiators. The present study showed that the LEDs Elipar Freelight is the most efficient curing device when the camphorquinone is used, as 92% of the emitted energy will be absorbed by the initiator. However, the power of this source is relatively low, hence higher exposure time shall be used.