Development of a low-color, color stable, dual cure dental resin.

UNLABELLED: Dual-cure (DC) resins are mainly used as cements due to high initial color (generally yellow) and large color shift (ΔE*) after polymerization as compared to light-cured resins. However, even as cements, this color shift is clinically unacceptable, especially when used to cement thin veneers. OBJECTIVE: To develop a novel DC initiator system with both lower initial color (less yellow, i.e., whiter) and smaller ΔE*. METHODS: The effect of using an allyl thiourea (T)/cumene hydroperoxide (CH) self-cure (SC) initiator system in combination with a photo-co-initiator, p-octyloxy-phenyl-phenyl iodonium hexafluoroantimonate (OPPI), in a commercial DC resin cement (PermaFlo DC, Ultradent Products, Inc.) was investigated. Initial color and ΔE* were assessed for 6 weeks in vitro under accelerated aging conditions (75°C water bath). Rockwell15T hardness was used to assess degree of cure (DoC) and the three-point bending test was used to assess mechanical properties. RESULTS: PermaFlo DC (control) was significantly harder than all experimental groups without OPPI but had up to three times higher initial color and four times greater color shift (ΔE*=27 vs. 8). With OPPI, hardness in the experimental groups increased significantly and several were comparable to the controls. Initial color and ΔE* increased slightly (ΔE*=9), but was still 3 times less than that of PermaFlo DC. DC samples containing OPPI had comparable modulus and ultimate transverse strengths to those of the controls. CONCLUSIONS: DC resins that use the T/CH initiator system are weaker but have extremely low color and ΔE*. The addition of OPPI increases DoC and mechanical properties to clinically acceptable levels and maintains extremely low color and ΔE*. SIGNIFICANCE: With this novel initiator system, DC resins potentially can now have comparable color and color stability to light-cure resins and be used in broader esthetic dental applications to improve color stability and reduce shrinkage stress in restorative composites.

Antimicrobial acrylic materials with in situ generated silver nanoparticles.

UNLABELLED: Polymethyl methacrylate (PMMA) is widely used to treat traumatic head injuries (cranioplasty) and orthopedic injuries (bone cement), but there is a problem with implant-centered infections. With organisms such as Acinetobacter baumannii and methicillin-resistant staphylococcus aureus developing resistance to antibiotics, there is a need for novel antimicrobial delivery mechanisms without risk of developing resistant organisms. OBJECTIVES: To develop a novel antimicrobial implant material by generating silver nanoparticles (AgNP) in situ in PMMA. RESULTS: All PMMA samples with AgNP's (AgNP-PMMA) released Ag(+) ions in vitro for over 28 days. In vitro antimicrobial assays revealed that these samples (even samples with the slowest release rate) inhibited 99.9% of bacteria against four different strains of bacteria. Long-term antimicrobial assay showed a continued antibacterial effect past 28 days. Some AgNP-loaded PMMA groups had comparable Durometer-D hardness (a measure of degree of cure) and modulus to control PMMA, but all experimental groups had slightly lower ultimate transverse strengths. CONCLUSIONS: AgNP-PMMA demonstrated a tremendously broad-spectrum and long-intermediate-term antimicrobial effect with comparable mechanical properties to control PMMA. Current efforts are focused on further improving mechanical properties by reducing AgNP loading and assessing fatigue properties.