Failure Of Composite Restorations Research Articles

Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization

Event Abstract Back to Event Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization Qiang Ye1, Linyong Song1, Xueping Ge1, Anil Misra1, 2 and Paulette Spencer1, 3 1 University of Kansas, Bioengineering Research Center, United States 2 University of Kansas, Department of Civil Engineering, United States 3 University of Kansas, Department of Mechanical Engineering, United States Introduction: In vivo biodegradation of the bond between the composite and tooth, i.e. the composite restoration’s adhesive bond layer, is considered a major contributor to premature failure of composite restorations[1]. The structure of methacrylate-based dentin adhesives suggests a general mechanism for their chemical and enzymatic degradation in oral fluids. In our previous study[2], the crosslink density of dentin adhesives can be improved with the addition of epoxide monomers. The objective of this work was to further develop a self-strengthening methacrylate-based dentin adhesive system by introducing an epoxy cyclohexyl trimethoxysilane (TS) containing both epoxy and methoxysilyl functional groups and cured by visible-light photopolymerization. Materials and Methods: Neat methacrylate monomer mixture (Scheme 1) of HEMA/BisGMA at 45/55 wt% was used as the control (C0). Experimental formulation with HEMA/BisGMA/TS (22.5/27.5/50, wt%) was used to investigate the free radical polymerization of methacrylate, ring-opening cationic polymerization of epoxy, and photoacid-induced sol-gel reaction. The polymerization behavior was monitored in-situ using real-time Fourier transform infrared spectroscopy (FTIR). The properties of copolymers at TS concentration from 5 to 35 wt% were determined using dynamic mechanical analysis (DMA). The leachables from polymer discs were determined by HPLC using a reverse phase C18 column and UV/diode array detectors. Results and Discussion: In this triple polymIn this triple polymerization system, free radical polymerization rate was the highest and the hydrolysis-condensation reaction was the slowest. In acidic environments, the fast hydrolysis reaction and the limited condensation gave rise to the self-strengthening process, which significantly improved the mechanical properties. When the TS concentration was 10-20 wt%, the copolymers became more homogeneous and the storage modulus at 70 0C reached maximum. The cumulative amounts of leached monomers were reduced significantly (Figure 1). Conclusion: With the introduction of both epoxy and trimethoxysilyl functional groups, a self-strengthening hybrid system has been developed for application as a dentin adhesive. During visible-light irradiation, a triple polymerization mechanism was involved (Figure 2). Supported by grant NIH/NIDCR R01 DE022054. Scheme 1. Chemical structures of monomers used in the formulations. Figure 1. Cumulative release of HEMA from the dentin adhesive copolymers as a function of incubation time in ethanol at 23±2 0C Figure 2. Proposed polymethacrylate-based matrix network structure and the autonomic self-strengthening process with different TS concentrations. (A1 and A2) Polymethacrylate-based network formed by free radical polymerization, cationic ring-opening polymerization, and limited photoacid-induced sol-gel reaction in dry conditions after 40 s irradiation; (B1 and B2) photoacid-induced ring-opening polymerization and sol-gel reaction after 24 h; (C1 and C2) self-strengthening process via sol-gel reaction and ring-opening polymerization in wet environment. Supported by grant R01DE022054 (PS, JSL), from the National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892.

In vitro near-infrared imaging of natural secondary caries.

Secondary caries stands as the leading reason for the failure of composite restorations and dentists spend more time replacing existing restorations than placing new ones. Current clinical strategies, and even modern visible light methods designed to detect decay, lack the sensitivity to distinguish incipient lesions, are confounded by staining on the surface and within the tooth, or are limited to detecting decay on the tooth surface. Near-IR (NIR) imaging methods, such as NIR reflectance and transillumination imaging, and optical coherence tomography are promising strategies for imaging secondary caries. Wavelengths longer than 1300-nm avoid interference from stain and exploit the greater transparency of sound enamel and dental composites, to provide increased contrast with demineralized tissues and improved imaging depth. The purpose of this study was to determine whether NIR transillumination (λ=1300-nm) and NIR cross-polarized reflectance (λ=1500-1700-nm) images can serve as reliable indicators of demineralization surrounding composite restorations. Twelve composite margins (n=12) consisting of class I, II & V restorations were chosen from ten extracted teeth. The samples were imaged in vitro using NIR transillumination and reflectance, polarization sensitive optical coherence tomography (PS-OCT) and a high-magnification digital visible light microscope. Samples were serially sectioned into 200-μm slices for histological analysis using polarized light microscopy (PLM) and transverse microradiography (TMR). The results presented demonstrate the utility of NIR light for detecting recurrent decay and suggest that NIR images could be a reliable screening tool used in conjunction with PS-OCT for the detection and diagnosis of secondary caries.

A novel protein-repellent dental composite containing 2-methacryloyloxyethyl phosphorylcholine.

Secondary caries due to biofilm acids is a primary cause of dental composite restoration failure. To date, there have been no reports of dental composites that can repel protein adsorption and inhibit bacteria attachment. The objectives of this study were to develop a protein-repellent dental composite by incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC) and to investigate for the first time the effects of MPC mass fraction on protein adsorption, bacteria attachment, biofilm growth, and mechanical properties. Composites were synthesized with 0 (control), 0.75%, 1.5%, 2.25%, 3%, 4.5% and 6% of MPC by mass. A commercial composite was also tested as a control. Mechanical properties were measured in three-point flexure. Protein adsorption onto the composite was determined by the microbicinchoninic acid method. A human saliva microcosm biofilm model was used. Early attachment at 4 h, biofilm at 2 days, live/dead staining and colony-forming units (CFUs) of biofilms grown on the composites were investigated. Composites with MPC of up to 3% had mechanical properties similar to those without MPC and those of the commercial control, whereas 4.5% and 6% MPC decreased the mechanical properties (P<0.05). Increasing MPC from 0 to 3% reduced the protein adsorption on composites (P<0.05). The composite with 3% MPC had protein adsorption that was 1/12 that of the control (P<0.05). Oral bacteria early attachment and biofilm growth were also greatly reduced on the composite with 3% MPC, compared to the control (P<0.05). In conclusion, incorporation of MPC into composites at 3% greatly reduced protein adsorption, bacteria attachment and biofilm CFUs, without compromising mechanical properties. Protein-repellent composites could help to repel bacteria attachment and plaque build-up to reduce secondary caries. The protein-repellent method might be applicable to other dental materials.

Assessment of the Quality of Composite Resin Restorations

Purpose: To evaluate the quality of the composite restorations. Material and Methods: A total of 246 composite restorations in 125 patients attending the Conservative Dentistry Clinics at the Faculty of Dentistry, University of Khartoum were examined. Both anterior and posterior composite restorations were included. California Dental Association Quality Evaluation System was used for the evaluation. Results: Fifty two percent of all restorations were found to be satisfactory, while the remaining 48% were not satisfactory. With regard to surface and colour criteria, colour mismatch within the range (34.8%) and slight surface roughness (26.6%) were the most common defects. The most frequent defects of the anatomical form were restoration overhang (26.8%). The majority of the restorations above 4 years old were of unacceptable anatomical form (66.7%), and their marginal integrity was less acceptable than more recent restorations (46.7%). Conclusions: Forty eight percent of the examined composite restorations needed to be replaced, and the unacceptable anatomic form was the main cause of failure of composite restorations.

Fracture toughness and microhardness of a composite: do they correlate?

Objectives. Chipping and bulk fracture are major contributors in clinical failures of composite restorations. Fracture toughness ( K Ic) quantifies susceptibility for fracture, but experimental determination is complicated. It would be beneficial for the dental community if a relatively simple experiment, such as microhardness (HK), could be used to screen composites for fracture resistance. This study explores a possible correlation between K Ic and HK. Methods. Composite cylinders (4 mm diameter and ∼7 mm long) were cured for five combinations of light intensity ( I, mW/cm 2) and curing time ( T, s) to achieve a range of different total light energy densities ( I× T=100×10, 100×20, 300×20, 300×40, and 700×60 mW s/cm 2). A chevron-notch was cut in the median plane of the cylinders for the fracture toughness test, which was executed in a displacement control mode at 6 μm/s cross-head speed (sample size 4). Knoop hardness was determined at the median plane of the cylinders (sample size 6). The tests were performed 15 min and 24 h after curing. Results. Both the K Ic and HK increased with increased light energy density and storage time. Linear regression analysis indicated a strong correlation between HK and K Ic tested at the same time period ( R 2=0.97 and 0.90 for 15 min and 24 h, respectively). The correlation became weaker between the different storage times ( R 2=0.71), indicating a change in fracture toughness and/or microhardness mechanisms. Conclusion. Fracture toughness of a composite cannot be simply extrapolated from microhardness.