What ultimately matters in root canal treatment success and tooth preservation: A 25-year cohort study.

AIM: There are currently no prospective studies evaluating the long-term outcomes of non-surgical root canal treatments beyond 5 years, both in terms of treatment success and tooth preservation, and identifying factors predictive of treatment outcome. The aim of the present work was therefore to fill this gap by assessing these outcomes over time and identifying predictive variables based on systematic data collection over a 25-year period. METHODOLOGY: Data concerning the treatments (N = 2500) were systematically collected since 1990. Information was recorded among clinical, technical, radiographic and patient-related characteristics, i.e., approximately 150 variables for each treatment. The data were analysed regarding both treatment success and tooth preservation by multivariable Cox proportional hazards model, and survival curves were generated. The statistical significance level was set at 0.0125. RESULTS: In total, 56.4% of the treatments could be followed over time (0-25 years, mean = 6.5 years, median = 5 years). Survival probability decreased almost linearly for treatment success, with about 85% after 5 years and 60% after 20 years, and for tooth preservation, with about 90% at 5 years and 50% at 20 years. The variables significantly associated with treatment failure were: pre-operative pain (Hazard Ratio-HR = 1.56 [95% CI 1.23-1.97]), persistent pain (HR = 2.63 [95% CI 1.44-4.80]), good operator rating of treatment prognosis (HR = 0.46 [95% CI 0.36-0.58]), size of periapical bone radiolucency (HR = 1.88 [95% CI 1.67-2.11]), and tooth type (p = .0006). For tooth extraction, they were: combined endodontic-periodontal lesion (HR = 3.37 [95% CI 1.88-6.05]), pre-existing complication before treatment (HR = 1.67 [95% CI 1.26-2.21]), good operator rating of treatment prognosis (HR = 0.45 [95% CI 0.33-0.60]), clinical failure of root canal treatment (HR = 2.78 [95% CI 1.98-3.89]) and tooth type (p = .0012). CONCLUSION: Root canal treatment success and tooth preservation on the arch are not static outcomes, but evolve with time. Among a substantial set of potential predictors, only a small proportion was significantly predictive of treatment success and tooth preservation, most of them being disease and patient characteristics, and not technical aspects, except pre-existing complications. These observations challenge the importance frequently given to byzantine considerations related to the numerous technical details of endodontic procedures, as opposed to general concepts of good clinical practice.

Glycemic and Insulin Status in Periodontitis Patients using the Homeostasis Model Assessment (HOMA): A Pilot Study.

PURPOSE: This study aimed to compare insulin status and dysglycemia (prediabetes/diabetes) of patients with chronic (stage III, grade B) or aggressive periodontitis (stage III, grade C) to that of a healthy population. MATERIALS AND METHODS: Patients with chronic (CP, n = 16) or aggressive periodontitis (AP, n = 15) and periodontally healthy controls (n = 32) were recruited. Body mass index was calculated. Glycemia, plasma insulin, glycated hemoglobin, C-reactive protein, and lipid levels were measured in fasting. The Homeostasis Model Assessment was used to calculate the insulin sensitivity (HOMA-%S), the beta-cell function (HOMA-%B), and their hyperbolic product (HOMA-%BxS). RESULTS: The CP group showed statistically significantly insulin resistance with a lower HOMA-%S (p = 0.0003) and a reduced HOMA-%BxS (p = 0.049) despite a higher insulin level (p = 0.01) vs the control group, even after BMI adjustment. There was also a trend to dysglycemia (prediabetes/diabetes) in the chronic group. In patients with AP, no abnormalities in insulin status were observed and glycemic levels were comparable with controls. Additionally, patients in both AP and CP groups presented significantly higher CRP levels compared to those of the control group (p = 0.02). CONCLUSION: Patients with CP showed reduced insulin sensitivity, increased insulin levels but a reduced %BxS product and a trend to dysglycemia. These abnormalities were not observed in AP.

Biological Evaluation of the Effect of Root Canal Sealers Using a Rat Model.

Gutta-percha points and root canal sealers have been used for decades in endodontics for root canal obturation. With techniques such as single cone methods, the amount of sealer is larger, making their properties more critical. However, relatively few reports have comprehensively evaluated their biological effects. To this end, we evaluated three types of sealers, zinc oxide-fatty acid-, bio-glass- and methacrylate resin-containing sealers were considered. Their biological effects were evaluated using a rat subcutaneous implantation model. Each sealer was loaded inside a Teflon tube and implanted subcutaneously in the backs of rats. Inflammatory cells were observed around all samples 7 days after implantation and reduced after 28 days. Our results revealed that all samples were in contact with the subcutaneous tissue surrounding the sealer. Additionally, Ca and P accumulation was observed in only the bio-glass-containing sealer. Furthermore, each of the three sealers exhibited unique immune and inflammatory modulatory effects. In particular, bio-glass and methacrylate resin sealers were found to induce variable gene expression in adjacent subcutaneous tissues related to angiogenesis, wound healing, muscle tissue, and surrounding subcutaneous tissue. These results may help to understand the biological impacts of root canal sealers on surrounding biological tissues, guiding future research and comparisons with new generations of materials.

Short-Term Pain Evolution and Treatment Success of Pulpotomy as Irreversible Pulpitis Permanent Treatment: A Non-Randomized Clinical Study.

The objective of this work was to evaluate (1) the short-term evolution of pain and (2) the treatment success of full pulpotomy as permanent treatment of irreversible pulpitis in mature molars. The study consisted of a non-randomized comparison between a test group (n = 44)-full pulpotomy performed by non-specialist junior practitioners, and a control group (n = 40)-root canal treatments performed by specialized endodontists. Short-term pain score (Heft-Parker scale) was recorded pre-operatively, then at 24 h and 7 days post-operatively. Three outcomes were considered for treatment success: radiographic, clinical and global success. For short-term evolution of pain, a non-parametric Wilcoxon test was performed (significance level = 0.05). For treatment success, a Pearson Chi square or Fisher test were performed (significance level = 0.017-Bonferroni correction). There was no significant difference between test and control groups neither regarding short term evolution of pain at each time point, nor regarding clinical (80% and 90%, respectively) or global success (77% and 67%, respectively). However, a significant difference in radiographic success was observed (94% and 69%, respectively). The present work adds to the existing literature to support that pulpotomy as permanent treatment could be considered as an acceptable and conservative treatment option, potentially applied by a larger population of dentists.

Shining a light on high volume photocurable materials.

Spatial and temporal control is a key advantage for placement and rapid setting of light-activated resin composites. Conventionally, placement of multiple thin layers (<2mm) reduces the effect of light attenuation through highly filled and pigmented materials to increase polymerisation at the base of the restoration. However, and although light curing greater than 2mm thick layers is not an entirely new phenomenon, the desire amongst dental practitioners for even more rapid processing in deep cavities has led to the growing acceptance of so-called "bulk fill" (4-6mm thick) resin composites that are irradiated for 10-20s in daily clinical practice. The change in light transmission and attenuation during photopolymerisation are complex and related to path length, absorption properties of the photoinitiator and pigment, optical properties of the resin and filler and filler morphology. Understanding how light is transmitted through depth is therefore critical for ensuring optimal material properties at the base of thick increments. This article will briefly highlight the advent of current commercial materials that rationalise bulk filling techniques in dentistry, the relationship between light transmission and polymerisation and how optimal curing depths might be achieved.

Extracellular matrix-derived hydrogels for dental stem cell delivery.

Decellularized mammalian extracellular matrices (ECM) have been widely accepted as an ideal substrate for repair and remodelling of numerous tissues in clinical and pre-clinical studies. Recent studies have demonstrated the ability of ECM scaffolds derived from site-specific homologous tissues to direct cell differentiation. The present study investigated the suitability of hydrogels derived from different source tissues: bone, spinal cord and dentine, as suitable carriers to deliver human apical papilla derived mesenchymal stem cells (SCAP) for spinal cord regeneration. Bone, spinal cord, and dentine ECM hydrogels exhibited distinct structural, mechanical, and biological characteristics. All three hydrogels supported SCAP viability and proliferation. However, only spinal cord and bone derived hydrogels promoted the expression of neural lineage markers. The specific environment of ECM scaffolds significantly affected the differentiation of SCAP to a neural lineage, with stronger responses observed with spinal cord ECM hydrogels, suggesting that site-specific tissues are more likely to facilitate optimal stem cell behavior for constructive spinal cord regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 319-328, 2017.

Filler characteristics of modern dental resin composites and their influence on physico-mechanical properties.

OBJECTIVE: The mechanical properties of dental resin-based composites (RBCs) are highly dependent on filler characteristics (size, content, geometry, composition). Most current commercial materials are marketed as "nanohybrids" (i.e. filler size <1µm). In the present study, filler characteristics of a selection of RBCs were described, aiming at identifying correlations with physico-mechanical properties and testing the relevance of the current classification. METHODS: Micron/sub-micron particles (> or <500nm) were isolated from 17 commercial RBCs and analyzed by laser diffractrometry and/or electron microscopy. Filler and silane content were evaluated by thermogravimetric analysis and a sedimentation technique. The flexural modulus (Eflex) and strength (σflex) and micro-hardness were determined by three-point bending or with a Vickers indenter, respectively. Sorption was also determined. All experiments were carried out after one week of incubation in water or 75/25 ethanol/water. RESULTS: Average size for micron-sized fillers was almost always higher than 1µm. Ranges for mechanical properties were: 3.775wt%) were associated with the highest mechanical properties (Eflex and σflex>12GPa and 130MPa, respectively) and lowest solvent sorption (∼0.3%). SIGNIFICANCE: Mechanical properties and filler characteristics significantly vary among modern RBCs and the current classification does not accurately illustrate either. Further, the chemical stability of RBCs differed, highlighting differences in resin and silane composition. Since Eflex and sorption were well correlated to the filler content, a simple and unambiguous classification based on such characteristic is suggested, with three levels (ultra-low fill, low-fill and compact resin composites).

Photopolymerization of highly filled dimethacrylate-based composites using Type I or Type II photoinitiators and varying co-monomer ratios.

OBJECTIVES: The use of a Type I photoinitiator (monoacylphosphine oxide, MAPO) was described as advantageous in a model formulation, as compared to the conventional Type II photoinitiator (Camphorquinone, CQ). The aim of the present work was to study the kinetics of polymerization of various composite mixtures (20-40-60-80 mol%) of bisphenol A glycidyl dimethacrylate/triethylene glycol dimethacrylate (BisGMA/TegDMA) containing either CQ or MAPO, based on real-time measurements and on the characterization of various post-cure characteristics. METHODS: Polymerization kinetics were monitored by Fourier-transform near-infrared spectroscopy (FT-NIRS) and dielectric analysis (DEA). A range of postcure properties was also investigated. RESULTS: FT-NIRS and DEA proved complementary to follow the fast kinetics observed with both systems. Autodecceleration occurred after ≈1 s irradiation for MAPO-composites and ≈5-10 s for CQ-composites. Conversion decreased with increasing initial viscosity for both photoinitiating systems. However despite shorter light exposure (3s for MAPO vs 20s for CQ-composites), MAPO-composites yielded higher conversions for all co-monomer mixtures, except at 20 mol% BisGMA, the less viscous material. MAPO systems were associated with increased amounts of trapped free radicals, improved flexural strength and modulus, and reduced free monomer release for all co-monomer ratios, except at 20 mol% BisGMA. SIGNIFICANCE: This work confirms the major influence of the initiation system both on the conversion and network cross-linking of highly-filled composites, and further highlights the advantages of using MAPO photoinitiating systems in highly-filled dimethacrylate-based composites provided that sufficient BisGMA content (>40 mol%) and adapted light spectrum are used.

Electrical enhancement of chlorhexidine efficacy against the periodontal pathogen Porphyromonas gingivalis within a biofilm.

Electric currents have been shown to promote the antimicrobial effectiveness of several biocides against microbial biofilms. Therefore, the objective of this work was to test the null hypothesis that low electric direct currents (DC) do not influence chlorhexidine (CHX) efficacy against the periodontal pathogen Porphyromonas gingivalis within a biofilm. A brain heart infusion medium inoculated with Streptococcus gordonii and P. gingivalis was perfused for 7 days in anaerobiosis through two modified Robbins devices (MRD) assembled in parallel. Biofilms grew on hydroxyapatite discs placed at the bottom of the MRD plugs, and were then treated for 10 min with either CHX or CHX/DC (1.5 mA or 10 mA). The bactericidal effect against biofilms was then evaluated by comparing the mean proportions of P. gingivalis killed. In the first series of experiments (CHX ± 1.5mA), the proportions of P. gingivalis killed were 81.1% for biofilms undergoing CHX and 79.1% when they were additionally treated with 1.5mA (p>0.05). In the second series (CHX ± 10mA), the viability of P.gingivalis was reduced by 87.3% with CHX and 98.9% when CHX was supplemented with 10mA (p<0.01). The null hypothesis was rejected, since a significant enhancement of the chlorhexidine 0.2% efficacy against P.gingivalis was observed when applying 10mA currents.

Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites.

In the aftermath of a major radiological accident, the medical management of overexposed individuals will rely on the determination of the dose of ionizing radiations absorbed by the victims. Because people in the general population do not possess conventional dosimeters, after the fact dose reconstruction methods are needed. Free radicals are induced by radiations in the tooth enamel of victims, in direct proportion to dose, and can be quantified using Electron Paramagnetic Resonance (EPR) spectrometry, a technique that was demonstrated to be very appropriate for mass triage. The presence of dimethacrylate based restorations on teeth can interfere with the dosimetric signal from the enamel, as free radicals could also be induced in the various composites used. The aim of the present study was to screen irradiated composites for a possible radiation-induced EPR signal, to characterize it, and evaluate a possible interference with the dosimetric signal of the enamel. We investigated the most common commercial composites, and experimental compositions, for a possible class effect. The effect of the dose was studied between 10 Gy and 100 Gy using high sensitivity X-band spectrometer. The influence of this radiation-induced signal from the composite on the dosimetric signal of the enamel was also investigated using a clinical L-Band EPR spectrometer, specifically developed in the EPR center at Dartmouth College. In X-band, a radiation-induced signal was observed for high doses (25-100 Gy); it was rapidly decaying, and not detected after only 24 h post irradiation. At 10 Gy, the signal was in most cases not measurable in the commercial composites tested, with the exception of 3 composites showing a significant intensity. In L-band study, only one irradiated commercial composite influenced significantly the dosimetric signal of the tooth, with an overestimation about 30%. In conclusion, the presence of the radiation-induced signal from dental composites should not significantly influence the dosimetry for early dose assessment.

Temozolomide-loaded photopolymerizable PEG-DMA-based hydrogel for the treatment of glioblastoma.

Glioblastoma is the most frequent primary malignant brain tumor in adults. Despite treatments including surgery, radiotherapy and chemotherapy by oral Temozolomide (TMZ), the prognosis of patients with glioblastoma remains very poor. We hypothesized that a polyethylene glycol dimethacrylate (PEG-DMA) injectable hydrogel would provide a sustained and local delivery of TMZ. The hydrogel photopolymerized rapidly (<2min) and presented a viscous modulus (≈10kPa). TMZ release kinetic presented two phases: a linear burst release of 45% of TMZ during the first 24h, followed by a logarithmic release of 20% over the first week. The in vivo tolerability study showed that the unloaded hydrogel did not induce apoptosis in mice brains nor increased microglial activation. In vivo, the anti-tumor efficacy of TMZ-hydrogel was evaluated on xenograft U87MG tumor-bearing nude mice. The tumor weight of mice treated with the photopolymerized TMZ hydrogel drastically decreased compared with all other groups. Higher apoptosis (located at the center of the tumor) was also observed. The present study demonstrates the potential of a photopolymerizable TMZ-loaded hydrogel to treat glioblastoma.

The effect of ultra-fast photopolymerisation of experimental composites on shrinkage stress, network formation and pulpal temperature rise.

OBJECTIVES: to complement our previous work by testing the null hypotheses that with short curing times and high DC, TPO-based resin composites would exhibit (1) higher polymerization stresses and consequently display (2) higher temperature rise and (3) higher flexural modulus, flexural strength and hardness, compared to a conventional CQ-based experimental composite. METHODS: Two experimental resin composites using either Lucirin-TPO or camphorquinone/DMAEMA as photoinitiators were prepared. Light curing was carried out using spectral outputs adapted to the absorption properties of each initiator. Different irradiation protocols were selected (0.5, 1, 3, 9 s at 500, 1000 and 2000 mW/cm(2) for Lucirin-TPO based composites and 20 or 40 s at 1000 mW/cm2 for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured in real time by means of FT-NIR spectroscopy. Pulpal temperature rise (ΔT) was studied in a tooth model. Polymerization stress was monitored using the Bioman instrument. For cured specimens, flexural modulus and flexural strength were determined using a three point bending platform and Vickers hardness was determined with a microhardness indentor on samples prior to and after 24 h incubation in 75/25 ethanol/H2O. Premolars were restored with both materials and microleakage at the teeth/composite interfaces following restoration was assessed. RESULTS: Lucirin-TPO-based composites irradiated at radiant exposures of 3 J/cm(2) and more exhibited significantly higher DCs, associated with increased flexural moduli and hardness compared to CQ-based composites. For an ultra-short irradiation time of 1 s at 1000 mW/cm(2), TPO-composites displayed similar polymerization stresses compared to CQ-controls with yet a 25% increase for flexural modulus and 40% increase for hardness measured after EtOH/H2O sorption. Higher stress rates were however observed in all curing protocols compared to CQ-composites. Microleakage was similar between TPO and CQ-composites irradiated at 1000 mW/cm(2) for 3 and 20 s respectively, while a significant increase was observed for TPO-composites irradiated for 1 s. ΔT measured through a 0.6 mm thick dentin layer were all below 5.5°C; TPO-composites exhibited similar or lower values compared to controls. SIGNIFICANCE: The use of Lucirin-TPO in resin composites along with appropriate curing conditions may allow for a major reduction of irradiation time while improving mechanical properties. The amount of stress observed during polymerization in TPO-based composites can be similar to those using CQ and the cohesion at the restoration-tooth interface was not affected by short curing times. Contrary to other studies, we found that the temperatures increases measured during polymerization were all well below the 5.5°C threshold for the pulp.

Hypoxia modulates the differentiation potential of stem cells of the apical papilla.

INTRODUCTION: Stem cells from the apical papilla (SCAP) are a population of mesenchymal stem cells likely involved in regenerative endodontic procedures and have potential use as therapeutic agents in other tissues. In these situations, SCAP are exposed to hypoxic conditions either within a root canal devoid of an adequate blood supply or in a scaffold material immediately after implantation. However, the effect of hypoxia on SCAP proliferation and differentiation is largely unknown. Therefore, the objective of this study was to evaluate the effect of hypoxia on the fate of SCAP. METHODS: SCAP were cultured under normoxia (21% O2) or hypoxia (1% O2) in basal or differentiation media. Cellular proliferation, gene expression, differentiation, and protein secretion were analyzed by live imaging, quantitative reverse-transcriptase polymerase chain reaction, cellular staining, and enzyme-linked immunosorbent assay, respectively. RESULTS: Hypoxia had no effect on SCAP proliferation, but it evoked the up-regulation of genes specific for osteogenic differentiation (runt-related transcription factor 2, alkaline phosphatase, and transforming growth factor-ß1), neuronal differentiation ( 2'-3'-cyclic nucleotide 3' phosphodiesterase, SNAIL, neuronspecific enolase, glial cell-derived neurotrophic factor and neurotrophin 3), and angiogenesis (vascular endothelial growth factor A and B). Hypoxia also increased the sustained production of VEGFa by SCAP. Moreover, hypoxia augmented the neuronal differentiation of SCAP in the presence of differentiation exogenous factors as detected by the up-regulation of NSE, VEGFB, and GDNF and the expression of neuronal markers (PanF and NeuN). CONCLUSIONS: This study shows that hypoxia induces spontaneous differentiation of SCAP into osteogenic and neurogenic lineages while maintaining the release of the proangiogenic factor VEGFa. This highlights the potential of SCAP to promote pulp-dentin regeneration. Moreover, SCAP may represent potential therapeutic agents for neurodegenerative conditions because of their robust differentiation potential.

Physico-mechanical characteristics of commercially available bulk-fill composites.

OBJECTIVES: Bulk-fill composites have emerged, arguably, as a new "class" of resin-based composites, which are claimed to enable restoration in thick layers, up to 4mm. The objective of this work was to compare, under optimal curing conditions, the physico-mechanical properties of most currently available bulk-fill composites to those of two conventional composite materials chosen as references, one highly filled and one flowable "nano-hybrid" composite. METHODS: Tetric EvoCeram Bulk Fill (Ivoclar-Vivadent), Venus Bulk Fill (Heraeus-Kulzer), SDR (Dentsply), X-tra Fil (VOCO), X-tra Base (VOCO), Sonic Fill (Kerr), Filtek Bulk Fill (3M-Espe), Xenius (GC) were compared to the two reference materials. The materials were light-cured for 40s in a 2mm×2mm×25mm Teflon mould. Degree of conversion was measured by Raman spectroscopy, Elastic modulus and flexural strength were evaluated by three point bending, surface hardness using Vickers microindentation before and after 24h ethanol storage, and filler weight content by thermogravimetric analysis. The ratio of surface hardness before and after ethanol storage was considered as an evaluation of polymer softening. Data were analyzed by one-way ANOVA and post hoc Tukey's test (p=0.05). RESULTS: The mechanical properties of the bulk-fill composites were mostly lower compared with the conventional high viscosity material, and, at best, comparable to the conventional flowable composite. Linear correlations of the mechanical properties investigated were poor with degree of conversion (0.090.8). Softening in ethanol revealed differences in polymer network density between material types. CONCLUSION: The reduction of time and improvement of convenience associated with bulk-fill materials is a clear advantage of this particular material class. However, a compromise with mechanical properties compared with more conventional commercially-available nano-hybrid materials was demonstrated by the present work. SIGNIFICANCE: Given the lower mechanical properties of most bulk-fill materials compared to a highly filled nano-hybrid composite, their use for restorations under high occlusal load is subject to caution. Further, the swelling behaviour of some of the bulk-fill materials may be a reason for concern, which highlights the critical requirement for a veneering material, not only to improve aesthetic quality of the translucent material, but to reduce the impact of degradation.

Ultra-fast light-curing resin composite with increased conversion and reduced monomer elution.

OBJECTIVES: To test the null hypotheses that photoactive resin composites containing a Type I photoinitiator would exhibit reduced DC or increased monomer elution at substantially short curing times compared with materials based on a Type 2 ketone/amine system. METHODS: Two experimental resin composites were prepared, using either Lucirin-TPO or camphorquinone/DMAEMA. Specimens were light-cured using appropriate spectral emission that coincided with the absorption properties of each initiator using different irradiation protocols (0.5, 1, 3, 9s at 500, 1000 and 2000mW/cm(2) for Lucirin-TPO based composites and 20 or 40s at 1000mW/cm(2) for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured by Raman spectroscopy, propagating radical concentrations were collected by means of electron paramagnetic resonance (EPR) and monomer leaching was characterized using high-performance liquid chromatography (HPLC). RESULTS: The null hypotheses were rejected, except for a single irradiation protocol (0.5s @ 500mW/cm(2)). Lucirin-TPO-based composites could cure 20 times faster and release at least 4 times less monomers in comparison to camphorquinone-based composites. At 1000mW/cm(2), and 1s irradiation time for curing times of 1s, Lucirin-TPO based composites displayed 10% higher DC. The difference in polymerization efficiency of Lucirin-TPO compared with camphorquinone-based resin composites were explained using EPR; the former showing a significantly greater yield of radicals which varied logarithmically with radiant exposure. SIGNIFICANCE: Lucirin-TPO is substantially more efficient at absorbing and converting photon energy when using a curing-light with an appropriate spectral emission and otherwise a limitation noted in several previous publications. At concentrations of 0.0134mol/L, Lucirin-TPO-based composites require a minimum light intensity of 1000mW/cm(2) and an exposure time of 1s to provide significantly improved DC and minimal elution compared with a conventional photoinitiator system. The use of a wide range of curing protocols in the current experiment has realized the significant potential of Lucirin-TPO and its impact for clinical applications, in replacement to materials using camphorquinone.

Influence of free radicals signal from dental resins on the radio-induced signal in teeth in EPR retrospective dosimetry.

In case of radiological accident, retrospective dosimetry is needed to reconstruct the absorbed dose of overexposed individuals not wearing personal dosimeters at the onset of the incident. In such a situation, emergency mass triage will be required. In this context, it has been shown that Electron Paramagnetic Resonance (EPR) spectroscopy would be a rapid and sensitive method, on the field deployable system, allowing dose evaluation of a great number of people in a short time period. This methodology uses tooth enamel as a natural dosimeter. Ionising radiations create stable free radicals in the enamel, in a dose dependent manner, which can be detected by EPR directly in the mouth with an appropriate resonator. Teeth are often subject to restorations, currently made of synthetic dimethacrylate-based photopolymerizable composites. It is known that some dental composites give an EPR signal which is likely to interfere with the dosimetric signal from the enamel. So far, no information was available about the occurrence of this signal in the various composites available on the market, the magnitude of the signal compared to the dosimetric signal, nor its evolution with time. In this study, we conducted a systematic characterization of the signal (intensity, kinetics, interference with dosimetric signal) on 19 most widely used composites for tooth restoration, and on 14 experimental resins made with the most characteristic monomers found in commercial composites. Although a strong EPR signal was observed in every material, a rapid decay of the signal was noted. Six months after the polymerization, the signal was negligible in most composites compared to a 3 Gy dosimetric signal in a tooth. In some cases, a stable atypical signal was observed, which was still interfering with the dosimetric signal.

Progress in dimethacrylate-based dental composite technology and curing efficiency.

OBJECTIVES: This work aims to review the key factors affecting the polymerization efficiency of light-activated resin-based composites. The different properties and methods used to evaluate polymerization efficiency will also be critically appraised with focus on the developments in dental photopolymer technology and how recent advances have attempted to improve the shortcomings of contemporary resin composites. METHODS: Apart from the classical literature on the subject, the review focused in particular on papers published since 2009. The literature research was performed in Scopus with the terms "dental resin OR dimethacrylate". The list was screened and all papers relevant to the objectives of this work were included. RESULTS: Though new monomer technologies have been developed and some of them already introduced to the dental market, dimethacrylate-based composites still currently represent the vast majority of commercially available materials for direct restoration. The photopolymerization of resin-based composites has been the subject of numerous publications, which have highlighted the major impact of the setting process on material properties and quality of the final restoration. Many factors affect the polymerization efficiency, be they intrinsic; photoinitiator type and concentration, viscosity (co-monomer composition and ratio, filler content) and optical properties, or extrinsic; light type and spectrum, irradiation parameters (radiant energy, time and irradiance), curing modes, temperature and light guide tip positioning. SIGNIFICANCE: : This review further highlights the apparent need for a more informative approach by manufacturers to relay appropriate information in order for dentists to optimize material properties of resin composites used in daily practice.

Spectral spatial electron paramagnetic resonance imaging as a tool to study photoactive dimethacrylate-based dental resins.

Photopolymerizable dimethacrylate-based dental resins, which are widely used in the current routine dental practice, show a very strong EPR signal. This signal has already been studied by EPR spectroscopy, but not by EPR imaging. The spectrum is quite complex due to hyperfine splitting and to the presence of two radical species, which is a priori not favorable to EPR imaging. In this work, the robustness of EPR imaging was investigated, both in the spatial and spectral-spatial modes, to characterize this type of material using small resin samples. The images produced using standard deconvolution and filtered backprojection procedure did not display any noticeable artifact. They also reflected the expected density of free radicals in two types of resin, photopolymerized with two different light irradiances. Moreover, the spectral-spatial imaging mode provided a complete spectrum for each pixel, which enabled to delineate the different distributions of the two radical species inside the samples. EPR imaging offered a different information compared to the usual degree of conversion measured by Raman spectrometry. These results suggest that EPR imaging could be used as a complementary tool to further characterize the dimethacrylate-based resins used in dental practice or for other applications.

New insight into the "depth of cure" of dimethacrylate-based dental composites.

OBJECTIVES: To demonstrate that determination of the depth of cure of resin-based composites needs to take into account the depth at which the transition between glassy and rubbery states of the resin matrix occurs. METHODS: A commercially available nano-hybrid composite (Grandio) in a thick layer was light cured from one side for 10 or 40 s. Samples were analyzed by Vickers indentation, Raman spectroscopy, atomic force microscopy, electron paramagnetic imaging and differential scanning calorimetry to measure the evolution of the following properties with depth: microhardness, degree of conversion, elastic modulus of the resin matrix, trapped free radical concentration and glass transition temperature. These measurements were compared to the composite thickness remaining after scraping off the uncured, soft composite. RESULTS: There was a progressive decrease in the degree of conversion and microhardness with depth as both properties still exhibited 80% of their upper surface values at 4 and 3.8 mm, respectively, for 10 s samples, and 5.6 and 4.8 mm, respectively, for 40 s samples. In contrast, there was a rapid decrease in elastic modulus at around 2.4 mm for the 10 s samples and 3.0 mm for the 40 s samples. A similar decrease was observed for concentrations of propagating radicals at 2 mm, but not for concentrations of allylic radicals, which decreased progressively. Whereas the upper composite layers presented a glass transition temperature - for 10 s, 55°C (±4) at 1 mm, 56.3°C (±2.3) at 2 mm; for 40 s, 62.3°C (±0.6) at 1 mm, 62°C (±1) at 2 mm, 62°C (±1.7) at 3 mm - the deeper layers did not display any glass transition. The thickness remaining after scraping off the soft composite was 7.01 (±0.07 mm) for 10 s samples and 9.48 (±0.22 mm) for 40 s samples. SIGNIFICANCE: Appropriate methods show that the organic matrix of resin-based composite shifts from a glassy to a gel state at a certain depth. Hence, we propose a new definition for the "depth of cure" as the depth at which the resin matrix switches from a glassy to a rubbery state. Properties currently used to evaluate depth of cure (microhardness, degree of conversion or scraping methods) fail to detect this transition, which results in overestimation of the depth of cure.