Barium and strontium leaching from aged glass particle/resin matrix dental composites
Introduction
Dental composites consisting of a polymerizable resin matrix, reinforcing glass particle fillers, and silane coupling agents, are becoming more popular in modern dentistry.1 These glass particle/resin matrix composites have good aesthetic properties and strength, making them the most widely used materials for restorations of anterior teeth.2 The polymerizable resin matrix typically contains one or more monomers such as ethylene glycol dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA). Polymerization of the resin matrix may be chemically initiated in ‘self cure’ composites, light activated, or a combination of both. Various inorganic materials such as glass fillers are utilized as fine or micro-fine particles and serve as reinforcing components. These fillers make up the bulk of the composites and they vary in size and composition among different composites. In addition to silica (SiO2), these composites also incorporate barium (Ba) and strontium (Sr) glasses, which add X-ray opacity to facilitate radiological monitoring of the composite in vivo.
During exposure to the oral environment, dental composites are subjected to material property changes due to degradation and erosion over time. Problems include shrinkage, which could result in fracturing and lead to leakage as well as the leaching of water soluble components. These changes may result from chemical breakdown by hydrolysis,3 chemical breakdown by stress induced effects associated with swelling and applied stress,4 chemical composition changes by leaching,4 precipitation and swelling phenomena to produce voids and cracks, leaching of the interface,5 and loss of strength due to corrosion.6
Different analytical techniques have been used to analyze the elemental composition changes of the composites during their degradation in the oral environment. A change in weight of dental composites7 indicated that the source of leachable components was the uncured resin at the bottom of the specimens. Studies on the absorption of water and the leaching of inorganic ions from several commercial dental composites analyzed the elemental composition of the inorganic filler composition in the aqueous leachate by optical emission spectroscopy.8 The results showed that silicon was the major element in all the fillers except one, which had both silicon and strontium as major elements. Atomic absorption and inductively coupled plasma spectroscopies are both effective techniques9 for analyzing the leached components into the aging solution. These studies generally found that the elements prevalent at the surface of the composite were those predominantly released into the leachate solution. However, analysis of the leachate does not describe from which portion of the composite leaching occurs.
The present study evaluated elemental and structural changes on the surface and cross-sections of several dental composites after aging for several months in different solutions that simulate the oral environment. Leaching and aging propagate from the surface and cracks of a dental composite, so any composition change on the surface will eventually affect the bulk properties of dental composites. It follows that elemental surface analysis can be applied to the degradation of dental composites in the oral environment. Wavelength X-ray dispersive spectroscopy (WDS), secondary ion mass spectroscopy (SIMS), energy dispersive spectrometry (EDS), and secondary electron microscopy (SEM) are surface analysis techniques used here to study aging at the surface of these dental composites. Quantification of WDS is achieved by the use of standards combined with matrix correction factors. The penetration depth of the incident electron beam defines the analysis depth of WDS, which is much deeper than the instantaneous analysis depth of SIMS. SIMS has been used in the analysis of dental hard tissue for over two decades.10 However, it is difficult to obtain reproducible and accurate quantitative information from SIMS due to fluctuations in ionization efficiency and ion collection efficiency.11 Although absolute quantification of an element remains difficult, a relative quantitative approach is possible by using C+ (m/z 12) as an internal reference.12 The dynamic internal standard SIMS method is applied here by employing C+ (m/z 12) and CH3CO+ (m/z 43) as internal reference ions due to their ubiquitous appearance in spectra of the embedding resin. Quantification of the SIMS data is completed by preparation of specific standards of dental composites with known concentrations of Sr and Ba. Use of the WDS and SIMS methods for the analysis of dental composites are contrasted with each other and other surface analysis methods.
Section snippets
Materials and methods
Three dental composites with different glass fillers, resins and composition were evaluated: a hybrid filler (Micronew, Bisco Inc., Schaumburg, IL, USA), a microfill (Renew, Bisco), and a composite resin cement (Choice, Bisco). The glass filler particles varied in size and distribution among the three different dental composites shown in Table 1, whose glass filler and resin composition are described in Table 2. Micronew and Choice specimens contain Sr but no Ba, while Renew contains Ba but no
Results
The WDS and SIMS data of Sr/Ba content (wt%) for all samples aged in air, 50% ethanol, distilled water, and artificial saliva for 4 and 8 month samples are shown in Table 5. No SIMS data is presented for artificial saliva aging since the accumulation of ions in the composites caused uncontrollable fluctuations in the secondary ion yields. All samples showed slight decreases in Ba or Sr content between 4 and 8 months aging in air, when measured by both methods (except for Micronew measured by
Summary of results
Aging in artificial saliva caused the greatest leaching of Ba or Sr for all the specimens, compared with either lesser or no leaching for aging in ethanol and water. The Ba content (wt%) on the surface of Renew changed very little following aging in ethanol or water, but decreased from ∼17% for air aged to ∼12% in artificial saliva after 4 months aging. A greater decrease in Sr content was seen for Choice into ethanol and water: the Sr content on the surface of Choice dropped from ∼19% for air
Conclusions
All three resin-glass composites displayed the greatest leaching of Ba or Sr for aging in artificial saliva, compared with either lesser or no leaching for aging in ethanol and water. Three mechanisms are evoked to explain the leaching process. The least important leaching mechanism is simple solvent permeation, which transports ions from the matrix. The most important leaching mechanism in the artificial saliva is ion exchange, which facilitates ion loss from the sample as the aging solvents
Acknowledgements
We thank Ksenia Andronova in the Department of Restorative Dentistry, University of Illinois at Chicago (UIC) for the assistance of aging media and sample preparation, Bisco Inc. for supplying the dental composite materials, and John R. Roth in the Research Resources Center, UIC for technical assistance with the WDS, SEM, and EDS measurements. This project was supported by grant DE 07979 from the National Institute of Dental and Craniofacial Research, Bethesda, MD, USA.
References (22)
Adhesive dental materials and their durability
Inter J Adhes Adhes
(2000)- et al.
In vitro aging of composite restorative materials
Clin Mater
(1988) - et al.
Prediction of in vivo wear in posterior composites: a fracture mechanics approach
Dent Mater
(1988) - et al.
Rate of elution of leachable components from composites
Dent Mater
(1990) Teeth and bones: applications of surface science to dental materials and related biomaterials
Surf Sci Rep
(2001)- et al.
Effect of water and artificial saliva on the low cyclic fatigue resistance of cobalt-chromium dental alloy
J Prosthet Dent
(1998) - et al.
The growth and modification of materials via ion-surface processing
Surf Sci
(2002) - et al.
Polymer analysis by Auger electron spectroscopy using sectioning and cryogenic cooling
J Elec Spect Rel Phenom
(1994) Current trends in dental composites
Crit Rev Oral Biol Med
(1995)Cyclic fatigue of composite restorative materials
J Oral Rehab
(1989)
Influence of chemicals on wear of dental composites
J Dent Res
Cited by (49)
A review study on coupling agents used as ceramic fillers modifiers for dental applications
2023, Materials Today: ProceedingsExposure of staff to aerosols and bioaerosols in a dental office
2021, Building and EnvironmentCitation Excerpt :A serious health risk concerns toxic trace elements, including mercury, silver and tin from the aging of dental amalgam [4,5] and anorganic substances released from resin-based composites, cements, impression materials and pigments. In the latter case it is related to the elution of monomers and ion leaching from the surfaces [6,7]. Allergenic substances and organic solvent vapors as well as fumes present in dental offices may also pose a health risk [8].
Barium polyphosphate glasses, from structure to thermochemistry
2020, Materials Chemistry and PhysicsLeaching behaviors of computer-aided design/computer-aided manufacturing composite resin component elements immersed in water
2019, Journal of Prosthodontic Research