Bisphenol A released and ultrastructural changes in dental composite resins

Dental composite resins may release bisphenol-A or similar molecules affecting patient health and the environment. This study measured bisphenol-A release from three commonly used in patients composite resins (Filtek™ Z350 XT, Filtek™ P60, Filtek™ Bulk Fill) immersed in three liquid mediums (artificial saliva, 0.001 M lactic acid and 15% ethanol) and assessed the changes in the surface micromorphology.The released BPA was measured by HPLC at basal time (t=0), 1 h, 1 d, 7 d and 30 d. Topographic analysis of specimens was performed by scanning electron microscopy (SEM). The data were analyzed using one-way ANOVA and Tukey post-hoc test (P < 0.05). BPA in solution increased significantly in the three DCRs immersed in 0.001 M lactic acid at all times. SEM micrographs of the specimen in 0.001 M lactic acid disclosed more structural defects than others. The surface of the three composite resins was morphologically affected by their immersion in all solutions. SEM evidenced that the dental materials underwent erosion and cracks with filler particles protruding from the surface. The morphological changes in tested dental materials produced by exposure to these solutions are potentially dangerous to patients by causing caries, infections, and partial loss of dental material.

On color adjustment potential and color blending threshold of dental composite resins.

OBJECTIVE: Color Adjustment Potential evaluates the color blending of dental Composite Resins. While Color Adjustment Potential is simple, its clinical relevance is unclear. This research aims to understand it better and to create an index for Composite Resins with meaningful clinical interpretation. MATERIALS AND METHODS: Single and double shade composite disks of various diameters and opacities were created to test the indices. Color measurements used a dental colorimeter, avoiding subjective assessments. Color Adjustment Potential analysis of each material revealed insights, leading to the creation of a new Color Blending Threshold, providing a clinically relevant numerical value for Composite Resins. RESULTS: Color Adjustment Potential's numerical significance was clarified and introduced a new index for clinical applications. Color adaptation of each test shade to all Vita shades was also calculated, useful for single-shade restorations in open and closed cavity types. CONCLUSIONS: The proposed Color Blending Threshold defines the open/closed cavity dimension that can be adequately restored with a single shade of resin composite. CLINICAL SIGNIFICANCE: Understanding how dental materials adapt to surrounding tooth colors enhances esthetic restorations, simplifies shade matching, and optimizes resin composite production. The proposed Color Blending Threshold is a parameter that directly relates to the clinical significance of a material's true color blending ability. It defines the cavity dimension that can be adequately restored with a single shade of resin composite while ensuring that the resulting color difference falls below a predetermined threshold, meeting the clinical requirements for an esthetic restoration.

[Comparative study on radio-opacity of dental composite resin materials'determination using film imaging and digital imaging].

OBJECTIVE: To compare the effects of different imaging methods on radio-opacity. Digital imaging and traditional film imaging were used to determine the radio-opacity of dental composite resin materials. METHODS: Fourteen dental composite resins commonly used in clinic were prepared for disc samples with thickness of 1 mm and diameter of 15 mm respectively. The aluminum step wedge was used as the reference and the disc samples were irradiated with X-rays by the traditional film imaging, phosphor imaging plate and charge-coupled device(CCD) intra-oral X-ray sensor respectively. Exposure was set at 65 kV and 7 mA, with 300 mm focus to film distance and the exposure time was 0.25 s. After developing and fixing the film, the optical density of the image of the sample and that of each step of the aluminum step wedge were measured using the densitometer. The digital image file was exported to grey scale analysis software of Adobe Photoshop® to measure the average grey value in the sample image and aluminum step wedge image. The curves were drawn corresponding to the optical density/gray value of each step of the aluminum step wedge and its thickness, and the equivalent thickness of the aluminum plate was calculated according to the optical density/gray value of the actual measured thickness of the sample, so as to evaluate the radio-opacity of dental composite resin material. RESULTS: For the same sample, the aluminum equivalent measured by traditional film imaging and two other digital imagings had significant differences among the 14 composite resins (P < 0.05), and the aluminum equivalent measured by the two digital imagings were greater than that of the traditional film. Moreover the aluminum equivalent measured by the two digital imagings was also different, and the aluminum equivalent measured by the CCD intra-oral X-ray sensor in most composite resins was larger than that measured by phosphor imaging plate. The same sample was photographed with the same imaging method, and the aluminum equivalent was different after three exposures. The standard deviation of aluminum equivalent measured by phosphor imaging plate was the largest, while that measured by CCD intra-oral X-ray sensor was the smallest. Among the 14 dental composite resin materials, the aluminum equivalent of Tetric N-Ceram and Te-Econom Plus measured by traditional film imaging and phosphor imaging plate was significantly higher than other composite resins. CONCLUSION: Based on clinical significance, three kinds of sensors designed to measure the radio-opacity of dental composite resin, the value of aluminum equivalent will change according to different types of sensors. The aluminum equivalent measured by CCD intra-oral X-ray sensor was higher than that measured by phosphor imaging plate, and the aluminum equivalent measured by phosphor imaging plate was higher than that measured by traditional film imaging. Moreover, even though the same sensor was used, the aluminum equivalent measured by multiple exposures was different. The standard deviation of the aluminum equivalent measured by phosphor imaging plate was greater than that measured by traditional film imaging and CCD intra-oral X-ray sensor. The three sensors in this study could be used for evaluating the radio-opacity of dental composite resin materials. But no matter what kind of sensor was used to measure the radio-opacity of dental composite resin, it complied to ISO 4049: 2019 standard, the materials were suitable for clinical use.

Polymerization Shrinkage of Short Fiber Reinforced Dental Composite Using a Confocal Laser Analysis.

The purpose of this study was to investigate the polymerization shrinkage of short fiber reinforced composite (SFRC) using a multicolor confocal displacement laser that can measure the polymerization shrinkage with high accuracy. The three types of SFRCs used in this study were XD (Ever X Flow Dentin), XB (Ever X Flow Bulk), and XP (EverX Posterior). In addition, CF (Clearfil majesty ES Flow) with hybrid type filler was used as a control. The measured values of the final polymerization shrinkage rate and amount of polymerization shrinkage rate when the polymerization shrinkage rate became constant (less than 0.1 µm/s) were approximated for all SFRCs. XP had a large aspect ratio of glass fiber filler and showed a significant difference from XD with a small aspect ratio (p < 0.05). There was no significant difference in the measured value of time when the polymerization contraction reached a constant speed (0.1 µm/s or less) for all SFRCs (p > 0.05). There was no significant difference in the measured values of polymerization shrinkage rate after the polymerization shrinkage reached a constant rate for all SFRCs (p > 0.05). These results show that glass fiber with large aspect ratio can alleviate polymerization shrinkage stress. The polymerization behavior of SFRC was found to be dependent on the amount of glass fiber filler, aspect ratio, and orientation.

The effect of new anti-adhesive and antibacterial dental resin filling materials on gingival fibroblasts.

OBJECTIVE: Aim of this study was to evaluate the biocompatibility of four experimental antiadhesive and antibacterial dental filling composites on human gingival fibroblasts (HGFs). METHODS: For these experimental resin composites a delivery system based on novel polymeric hollow beads, loaded with Tego Protect (Aa1), Dimethicone (Aa2), Irgasan (Ab1) and methacrylated polymerizable Irgasan (Ab2) as active agents was used. The cultured HGFs' cell integrity, proliferation, viability, collagen synthesis and cytokine release were measured. For this purpose, human gingival fibroblasts were treated with eluates from all four composites and compared with an experimental standard composite (ST). Eluate extraction times 24 h and 168 h were chosen. RESULTS: Statistical analysis was conducted via a mixed model. Both antibacterial composites reduced proliferation, collagen and cytokine synthesis significantly (p < 0.05), increasing with time of elution. Ab1 did also have a damaging effect on the membrane and on cell viability. SIGNIFICANCE: Overall, it can be concluded that the antiadhesive composites showed clear advantages over the antibacterial composites in terms of biocompatibility. This study also continues to show the potential of the new poly-pore system, as it can be used for a variety of other applications in future composite mixtures.

Comparative study on radio-opacity of dental composite resin materials'determination using film imaging and digital imaging / 北京大学学报(医学版)

OBJECTIVE@#To compare the effects of different imaging methods on radio-opacity. Digital imaging and traditional film imaging were used to determine the radio-opacity of dental composite resin materials.@*METHODS@#Fourteen dental composite resins commonly used in clinic were prepared for disc samples with thickness of 1 mm and diameter of 15 mm respectively. The aluminum step wedge was used as the reference and the disc samples were irradiated with X-rays by the traditional film imaging, phosphor imaging plate and charge-coupled device(CCD) intra-oral X-ray sensor respectively. Exposure was set at 65 kV and 7 mA, with 300 mm focus to film distance and the exposure time was 0.25 s. After developing and fixing the film, the optical density of the image of the sample and that of each step of the aluminum step wedge were measured using the densitometer. The digital image file was exported to grey scale analysis software of Adobe Photoshop® to measure the average grey value in the sample image and aluminum step wedge image. The curves were drawn corresponding to the optical density/gray value of each step of the aluminum step wedge and its thickness, and the equivalent thickness of the aluminum plate was calculated according to the optical density/gray value of the actual measured thickness of the sample, so as to evaluate the radio-opacity of dental composite resin material.@*RESULTS@#For the same sample, the aluminum equivalent measured by traditional film imaging and two other digital imagings had significant differences among the 14 composite resins (P < 0.05), and the aluminum equivalent measured by the two digital imagings were greater than that of the traditional film. Moreover the aluminum equivalent measured by the two digital imagings was also different, and the aluminum equivalent measured by the CCD intra-oral X-ray sensor in most composite resins was larger than that measured by phosphor imaging plate. The same sample was photographed with the same imaging method, and the aluminum equivalent was different after three exposures. The standard deviation of aluminum equivalent measured by phosphor imaging plate was the largest, while that measured by CCD intra-oral X-ray sensor was the smallest. Among the 14 dental composite resin materials, the aluminum equivalent of Tetric N-Ceram and Te-Econom Plus measured by traditional film imaging and phosphor imaging plate was significantly higher than other composite resins.@*CONCLUSION@#Based on clinical significance, three kinds of sensors designed to measure the radio-opacity of dental composite resin, the value of aluminum equivalent will change according to different types of sensors. The aluminum equivalent measured by CCD intra-oral X-ray sensor was higher than that measured by phosphor imaging plate, and the aluminum equivalent measured by phosphor imaging plate was higher than that measured by traditional film imaging. Moreover, even though the same sensor was used, the aluminum equivalent measured by multiple exposures was different. The standard deviation of the aluminum equivalent measured by phosphor imaging plate was greater than that measured by traditional film imaging and CCD intra-oral X-ray sensor. The three sensors in this study could be used for evaluating the radio-opacity of dental composite resin materials. But no matter what kind of sensor was used to measure the radio-opacity of dental composite resin, it complied to ISO 4049: 2019 standard, the materials were suitable for clinical use.

Study of POSS on the Properties of Novel Inorganic Dental Composite Resin.

: Various amounts of methacryl polyhedral oligomeric silsesquioxane (POSS) were explored to be incorporated into novel nano SiO2 dental resin composites using light curing method. The scanning electron microscopy (SEM), optical microscopy, fourier transform infrared spectroscopy (FTIR), nanoindentation, nanoscratch and three-point flexure tests were performed. The volumetric shrinkage and mechanical properties such as hardness, elastic modulus, resistance, flexural strength and fracture energy were analyzed. With the additions of POSS, the volume shrinkage decreased and the mechanical properties initially increased. The effects of POSS on these properties were studied to provide a reference for clinically selecting a composite resin with excellent properties.

In situ surface modification on dental composite resin using 2-methacryloyloxyethyl phosphorylcholine polymer for controlling plaque formation.

Composite resins (CRs) are widely used as dental restorative materials for caries treatment. They cause problems of secondary caries since Streptococcus mutans stays in the dental plaque, which the surface exists and produces acidic compounds during metabolism. The dental plaque depositions are induced by the protein adsorption on the surface. Therefore, suppression of protein adsorption on the surface of the CRs is important for inhibiting the formation of plaque and secondary caries. In this study we developed a surface treatment to provide an antibiofouling nature to the CRs by chemical reaction with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers in the oral cavity during dental treatment. To carry out the photochemical reaction on the remaining polymerizable groups of CRs, we synthesized the MPC polymer with a polymerizable group in the side chain. The MPC polymer could bind on the surfaces of the CRs chemically under dental treatment procedures. The treated surface showed significant resistance to oral protein adsorption and bacterial adhesion even when the surface was brushed with a toothbrush. Thus, we concluded that the photochemical reaction of the MPC polymer with the CRs in the oral cavity was good for making an antibiofouling surface and preventing secondary caries.

Study of Two-Body Wear Performance of Dental Materials.

INTRODUCTION: The purpose of this study was to evaluate the two-body wear resistances of natural enamel and four dental materials in vitro. METHODS: The testing machine was modified to form a type of pin-on-disk wear test apparatus. Four dental material specimens (Au-Pd alloy, Ag-Pd alloy, FiltekTMP60 and FiltekTMZ350 composite resins) and enamel were used as the pins, and a steatite ceramic grinding wheel was used as the abrasive counter face. The wear volume loss and the rigidity value was measured. The worn surface and the element analysis of the debris were analyzed. RESULT: The wear volume loss of Au-Pd alloy and its steatite antagonists were the nearest to those of the dental enamel. SEM microphotographs showed that, the main wear mechanism of the dental materials was abrasive and adhesive wear. CONCLUSIONS: Au-Pd alloy had good wear resistance and was more suitable for dental applications than other three dental materials.

Effect of low-shrinkage monomers on the physicochemical properties of experimental composite resin.

This study was conducted to determine whether novel experimental low-shrinkage dimethacrylate co-monomers could provide low polymerization shrinkage composites without sacrifice to degree of conversion, and mechanical properties of the composites. Experimental composites were prepared by mixing 28.6 wt% of bisphenol-A-glycidyl dimethacrylate based resin matrix (bis-GMA) with various weight-fractions of co-monomers; tricyclo decanedimethanol dacrylate (SR833s) and isobornyl acrylate (IBOA) to 71.4 wt% of particulate-fillers. A composite based on bis-GMA/TEGDMA (triethylene glycol dimethacrylate) was used as a control. Fracture toughness and flexural strength were determined for each experimental material following international standards. Degree of monomer-conversion (DC%) was determined by FTIR spectrometry. The volumetric shrinkage in percent was calculated as a buoyancy change in distilled water by means of the Archimedes' principle. Polymerization shrinkage-strain and -stress of the specimens were measured using the strain-gage technique and tensilometer, respectively with respect to time. Statistical analysis revealed that control group had the highest double-bond conversion (p < .05) among the experimental resins tested. All of the experimental composite resins had comparable flexural strength, modulus, and fracture toughness (p > .05). Volumetric shrinkage and shrinkage stress decreased with increasing IBOA concentration. Replacing TEGDMA with SR833s and IBOA can decrease the volumetric shrinkage, shrinkage strain, and shrinkage stress of composite resins without affecting the mechanical properties. However, the degree of conversion was also decreased.

Effects of silane-modified fillers on properties of dental composite resin.

The effect of silanization on the mechanical, chemical, and physical properties of dental composites was investigated. Silica fillers were obtained from colloidal silica solution, Ludox® HS-40 and they were silanized by using 3-methacryloxypropyl trimethoxysilane (MPTMS) in an acidic media. Mineralogical and chemical structures of unsilanized and silanized fillers were determined by using XRD and FT-IR analyses. The modification of unsilanized/silanized fillers were investigated by performing XPS and TGA analyses. The morphological evaluations, surface area, and particle size measurements were performed by using SEM, BET, and Zeta-Sizer, respectively. Eventually, pure and amorphous silica fillers were obtained. Furthermore, the weight percentage of the silane in silica/silane structure was compatible with theoretical values. SEM images, surface area, and particle size measurements showed that agglomeration tendencies of silanized fillers were lower compared to silanized fillers because of the MPTMS addition. Experimental composites (5/10/10/5BisGMA/HEMA/UDMA/TEGDMA resin reinforced with 70wt% silanized/unsilanized SiO2) were fabricated into 4mm diameter×6mm thick discs for compressive strength (CS), angular flexural strength (AFS), curing depth (CD), and polymerization shrinkage (PS) on a 25×2×2mm rectangular Teflon mold for flexural strength (FS) and modulus of elasticity (E) tests. The curing depth (CD) and degree of polymerization percentage (DP) of composites were determined. Consequently, results showed that mechanical properties and DP of composite resins can be greatly influenced by silanization as a result of the organic matrix-inorganic filler interface bonding formed by silane structures. Despite of these findings, silanization of the SiO2 was not effected DC and PS values.

Mechanical properties of contemporary orthodontic adhesives used for lingual fixed retention.

OBJECTIVE: The aim of the present study was to test the mechanical properties of different adhesives used in orthodontics for fixed retainers and to investigate their possible interrelations. MATERIALS AND METHODS: Specimens of six different adhesive resins were prepared: Transbond XT, Transbond LR and an experimental BPA-free orthodontic adhesive, as well as IPS Empress Direct (IPS-ED), ZNano and Accolade. The mechanical properties tested were Martens hardness (HM), indentation modulus (EIT), the ratio of elastic to total work, commonly known as elastic index (ηIT) and Vickers hardness (HV). These properties were determined using instrumented indentation testing according to ISO 14577-2002. The results of the aforementioned properties were statistically compared with one-way ANOVA-test and Student-Newman-Keuls multiple comparison test at a=0.05, while possible correlations among the properties tested were analyzed by Pearson correlation. RESULTS: Significant differences were identified among all the materials tested for HM, with Transbond LR presenting the highest value. This resin presented the highest EIT too. Significant EIT differences were identified among the materials and only ZNano and IPS-ED showed no significant differences for this property. Transbond LR and ZNano showed higher HV values. ZNano demonstrated the highest elastic index. Pearson analysis showed a strong positive correlation between HM and EIT (0.970), HM and HV (0.837), and EIT and HV (0.695), while a weak negative correlation was found between EIT and elastic index (-0.505). CONCLUSIONS: The materials tested demonstrated significant differences in their mechanical properties, and thus differences in their clinical performance are anticipated.

Recomendaciones para el empleo práctico de resinas compuestas en restauraciones estéticas / Recommendations for the use of composite resins in esthetic restorations

Introducción: la población, solicita con frecuencia restauraciones compatibles con los estándares de la estética dental y ello en ocasiones se dificulta dada la diversidad de materiales restauradores existentes y técnicas para su aplicación. Objetivo: proponer recomendaciones para el empleo práctico de las resinas compuestas fotopolimerizables en restauraciones estéticas de dientes anteriores y posteriores. Métodos: se realizó un estudio de revisión bibliográfica sobre técnicas para el empleo de resinas compuestas en restauraciones estéticas. Esto se llevó a cabo a través de Scopus, SciELO, Hinari, Medline y 45 revistas científicas indexadas de manera manual. El estudio se circunscribió a 89 artículos y 3 libros que enfocaron esta temática de manera más integral. Se reagruparon todos los documentos revisados y se procesaron según revista científica de origen y año de publicación. Integración de la información: las recomendaciones incluyeron la valoración individual de la estética del paciente, selección del tipo de resina a emplear, selección del color, profilaxis y pulido de la superficie de trabajo, preparaciones cavitarias con o sin confección de biseles, protección o no del complejo dentino pulpar, grabado ácido, lavado y enjuague del ácido grabador, aplicación del adhesivo, inserción y manipulación de la resina compuesta, polimerización y acabado de la restauración. Consideraciones finales: los tratamientos curativos y estéticos son muy variado en el campo de las resinas compuestas fotopolimerizables, por lo cual resulta útil seguir, entre otras, las recomendaciones de realizar limpieza de la superficie de trabajo, seleccionar el color y tipo de resina indicados en cada caso, realizar preparaciones cavitarias mínimas con biseles (si es necesario), emplear incrementos en la realización de las restauraciones, polimerizar evitando grandes reacciones de contracción, y pulir adecuadamente las restauraciones(AU)

Introduction: patients often request the performance of restorations compatible with the standards of dental esthetics. This is sometimes hampered by the great variety of restoring materials and techniques for their application. Objective: propose recommendations for the use of photopolymerizable composite resins in esthetic restorations of anterior and posterior teeth. Methods: a bibliographic review was performed about techniques for the use of composite resins in esthetic restorations. The search was conducted in the databases Scopus, SciELO, Hinari and Medline, as well as 45 manually indexed scientific journals. The reviewers selected the 89 papers and 3 books which approached the topic in a more comprehensive manner. All the documents reviewed were arranged and processed by scientific journal and year of publication. Data integration: recommendations included the following topics: individual assessment of the patient's esthetic considerations, selection of the resin type to use, selection of color, prophylaxis and polishing of the work surface, cavity preparation with or without beveling, protection or not of the dentin-pulp complex, acid engraving, washing and rinsing of the engraving acid, application of the adhesive, insertion and manipulation of the composite resin, polymerization and finishing of the restoration. Final considerations: there is a great variety of curative and esthetic treatments based on the use of photopolymerizable composite resins. Therefore, it would be advisable to follow these recommendations, among others: clean the work surface, select the appropriate resin color and type, perform as few beveled cavity preparations as possible (only if required), apply increments while carrying out the restoration, polymerize avoiding great contraction reactions, and polish the restorations appropriately(AU)

Análisis comparativo in vitro del grado de filtración marginal de restauraciones de resina compuesta realizadas con dos métodos de grabado ácido distintos / In vitro comparative analysis of microleakage in composites resin restorations made with a conventional and a modified acid etch technique

La técnica de grabado ácido en esmalte representa el hito que marca la puerta de entrada para el establecimiento de la odontología adhesiva. Producto de que el sustrato adamantino pudiese presentar comportamiento refractario a la técnica convencional de grabado ácido es que se plantea una técnica en dos tiempos operatorios, la cual pudiese disminuir dicho comportamiento resistente al grabado ácido y combatir así el fenómeno de la filtración marginal de las resinas compuestas. En este estudio se utilizaron 30 terceros molares sanos, en los cuales se realizaron cavidades clases V en las caras vestibulares y linguales/palatinas, las cuales fueron obturadas con resina compuestas utilizando técnica de grabado ácido convencional y técnica de grabado ácido en dos tiempos operatorios, respectivamente. Estos especímenes fueron sometidos a un proceso de termociclado en presencia de un agente colorante marcador. Luego de un proceso de termociclado, las muestras fueron cortadas transversalmente para evaluar el porcentaje de penetración del agente marcador. El análisis de los resultados demostró que las restauraciones realizadas con técnica de grabado ácido en dos tiempos operatorios presentaron menores valores de filtración marginal, existiendo diferencias significativas entre ambos grupos estudiados.

The acid etch technique is the fact that marks the starting point for the establishment of the adhesive dentistry era. But as the enamel structure may have a resistant behavior towards the conventional acid etch technique ,a two-step acid etch technique is presented. This would diminish the aforementioned resistant behavior of enamel to the conventional acid etch technique, and minimize as well, the marginal leakage phenomenon of the composite materials. In this study 30 sound recently extracted molars were used. Equal class V cavities preparations were made in the buccal and palatal/lingual faces of each tooth. Buccal cavities were filled with composite before the use of the conventional acid etch technique, as adhesive method, while in the lingual/palatal faces the two-step acid etch technique was used. The samples were subjected to thermal cycles in the presence of a dying agent. After the thermocycling process, the samples were cut transversely to assess the percentage of penetration of the staining agent. The analysis of the results showed that there was a significant statistical difference between both groups. Moreover the restorations made with the two-step acid etch technique presented lower values of marginal leakage.

Polymer grafted hydroxyapatite whisker as a filler for dental composite resin with enhanced physical and mechanical properties.

The objective of this study was to investigate the effect of surface graft polymerization of hydroxyapatite whisker (HW) on physical and mechanical properties of dental composite resin. Poly bisphenol A glycidyl methacrylate (Poly(Bis-GMA)) was grafted onto silanized hydroxyapatite whisker (SHW) via solution polymerization and the amount of the Poly(Bis-GMA) on the surface was effectively controlled by polymerization time. The obtained poly(Bis-GMA) grafted hydroxyapatite whisker (PGHW) with different polymer contents was filled into a resin matrix respectively, meanwhile the composites with HW and with SHW served as controls. Monomer conversion was characterized by Fourier transform infrared spectroscopy (FTIR) and volume shrinkage of the composite resin was measured with a density tester. Mechanical properties were tested with a universal testing machine. The results indicated that the composite filled with PGHW-1h (graft ratio of poly(Bis-GMA): 8.5 wt.%) showed lower shrinkage and better mechanical properties, improving flexural strength by 6.5% and 11.9% compared with SHW filled composite and HW filled composite, respectively. However, PGHW with higher graft ratios aggregated seriously and formed defects in the composite, leading to deterioration of mechanical properties. It was revealed that the poly(Bis-GMA) on the surface of PGHW acted as a functional transition layer and enhanced interfacial compatibility and interaction between whisker and resin matrix, which facilitated the dispersion of PGHW in the composite and decreased the composite shrinkage. Thus, the graft polymerization of Bis-GMA on the surface of filler might be a promising modification method for the fabrication of dental materials.

Use of FT-Raman Spectroscopy to Determine the Degree of Polymerization of Dental Composite Resin Cured with a New Light Source.

OBJECTIVES: To use the FT-Raman spectroscopy for evaluation the degree of polymerization of dental composite as a result of photo curing with a new light source in comparison to the conventional halogen light. MATERIALS AND METHODS: In this study a new light source, based on a metal-halide lamp (TOPSPOT G12) was developed at NRC-Egypt for curing dental composites. Two groups of 108 composite samples each were cured using both the new light source and a conventional halogen source, as a control source. Different samples' sizes (2x2, 3x3 and 6x3 mm(2)) were cured for different periods of time (2, 4, 8, 12, 20, and 40 seconds). The spectroscopic data were analyzed statistically by ANOVA and Duncan's multiple range test (P< .05). RESULTS: The results showed that the samples cured by the new metal-halide source produced higher polymerization rates than those cured by the halogen source. The polymerization rate was directly proportional to the exposure time and inversely proportional to the sample size, irrespective to the light source used. The results also showed that 12 seconds of metal-halide light curing produced polymerization rate comparable to or even higher than that produced by 40 seconds halogen light curing. CONCLUSIONS: The new light source produced a satisfactory degree of polymerization in a remarkable shorter curing time and it can be recommended for clinical use.