Alternatives in polymerization contraction stress management

Polymerization contraction stress of dental composites is often associated with marginal and interfacial failure of bonded restorations. The magnitude of the stress depends on the composite's composition (filler content and matrix composition) and its ability to flow before gelation, which is related to the cavity configuration and curing characteristics of the composite. This article reviews the variations found among studies regarding the contraction stress testing method, contraction stress values of current composites, and discusses the validity of contraction stress studies in relation to results from microleakage tests. The effect of lower curing rates and alternative curing routines on contraction stress values is also discussed, as well as the use of low elastic modulus liners. Moreover, studies with experimental Bis-GMA-based composites and recent developments in low-shrinkage monomers are described

Influence of biofilm formation on the optical properties of novel bioactive glass-containing composites

Objective. Bioactive glass (BAG) has been suggested as a possible additive for dental restorative materials because of its antimicrobial effect and potential for promoting apatite formation in body fluids. The purpose of this study was to investigate the effects of bacterial biofilm on the change of colorimetric value and translucency of novel BAG-containing composites having different initial surface roughness. Methods. Composites with 72 wt% total filler load were prepared by replacing 15% of the silanized Sr glass with BAG (65 mol % Si; 4% P; 31% Ca), BAG-F (61% Si; 31% Ca; 4% P; 3% F; 1% B), or silanized silica. Light-cured discs of 2-mm thickness (n = 10/group) were divided into 4 different surface roughness subgroups produced by wet polishing with 600 and then up to 1200, 2400, or 4000 grit SiC. CIE L*a*b* were measured and the color difference and translucency parameter (TP) were calculated before and after incubating in media with or without a Streptococcus mutans (UA 159) biofilm for 2 wks (no agitation). Results were analyzed using ANOVA/Tukey's test (alpha = 0.05). Results. All the color differences for BAG and BAG-F composite showed significant decreases with bacterial biofilm compared to media-only. The mean TP (SD) of BAG and BAG-F composite before aging [10.0 (2.8) and 8.5 (1.4)] was higher than that of the control composite [4.9 (0.8)], while the change in TP with aging was greater compared to the control with or without bacteria. BAG-F composites with the smoothest surfaces showed a greater decrease in TP under bacterial biofilm compared to the BAG composite. Significance. Highly polished dental composites containing bioactive glass additives may become slightly rougher and show reduced translucency when exposed to bacterial biofilms, but do not discolor any more than control composites that do not contain the BAG.OAIID:RECH_ACHV_DSTSH_NO:T201604274RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A080446CITE_RATE:3.931FILENAME:1-s2.0-S0109564116301026-main.pdfDEPT_NM:치의학과EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/9f1cbb0a-c9f7-4ad9-b383-423cefd49608/linkCONFIRM:

Tooth micro-hardness changes after applying bioactive glass-containing, anti-microbial sealants

The AAPD recommends placement of dental pit and fissure sealants on surfaces that are high risk or that already exhibit incipient carious lesions. Protection provided by sealants may be enhanced by the addition of ion-releasing, anti-microbial filler particles of bioactive glass. Objective: We prepared novel dental pit and fissure sealant materials containing bioactive glass (BAG) fillers and tested their ability to prevent tooth demineralization in a bacterial broth. Methods: Two types of BAG were synthesized in our lab: BAG1 (61 wt% silica - 31 wt% calcia - 4 wt% phosphate - 4 wt% flouride); and BAG2 (81 wt% silica - 11 wt% calcia - 4 wt% phosphate - 4 wt% flouride). Ultraseal XT (USXT) resin without filler was supplied by the manufacturer (Ultradent Products, Inc. South Jordan, UT). BAGs were individually incorporated into the resin (25 wt%) and provided handling properties similar to USXT. Caries-free teeth (n=5 each) were randomly assigned to three groups (BAG1-sealant, BAG2-sealant,or USXT) and sealants were placed by the same practitioner. Acid-resistant nail polish was used to cover half of the tooth surface. Teeth were immersed in a bacterial culture system of sucrose-rich brain-heart infusion (BHI) media containing Streptococcus mutans strain #25175, an acid-producing microbe and incubated at 37˚C, 5%CO2; media was changed every other day. Bacterial growth was confirmed throughout the test period. At two weeks, teeth were sectioned sagitally and microhardness testing compared changes in hardness as a function of location on the tooth. Results : Overall, the BAG2-sealant samples were significantly harder than the BAG1-sealant or USXT samples. Areas adjacent to the BAG2-sealant were harder than the original tooth surface. (ANOVA/Tukey’s; α=0.05). Conclusion: The inclusion of anti-bacterial, ion-releasing BAG as a filler component results in a harder tooth that may be better able to resist demineralization.This presentation was presented at the American Association for the Advancement of Science (AAAS) Pacific Division 93rd Annual Meeting in Boise, Idaho. It was also presented at the American Association for Dental Research Annual Conference in 2012 (AADR)

Residual stress in composites with the thin-ring-slitting approach

During polymerization, dental composites develop residual stresses that may compromise the marginal integrity and properties of the restorative. The objective of this study was to use the thin-walled ring-slitting method to measure and compare residual stresses. The hypotheses to be tested were that composites would generate different levels of residual stress based on their specific formulations and slitting times. Rings made from composites (Z100, Herculite, and Heliomolar) were cut at different times (10 min, 1 and 24 hrs) after being light-cured, and stress was measured. Residual stress was higher at the earlier cutting times, except for Heliomolar (α < 0.05). For the 10-minute and one-hour cutting groups, stress followed this order: Z100 > Herculite > Heliomolar. Early slitting was better to capture residual stress, and the thin-walled rings showed higher values than thick-walled rings and were better able to discriminate residual stress in composites