Revisiting the intensity output of curing lights in private dental offices.

In a survey published in 1994, it was reported that nearly 30% of dental office curing lights had an intensity output (power density) of < 200 mW/cm2. This study was designed to examine the types of curing lights and the adequacy of the intensity output in the same localities after 10 years. A total of 161 curing lights in 65 dental offices located in 2 metropolitan areas in Texas were examined for the following variables: types of light, power density, resin build-up on the tips, and size of the tips. Two new radiometers were used to measure the outputs. The average intensity output for each light was placed in 5 categories ranging from < 150 mW/cm2 to > 500 mW/cm2. Of 161 lights examined, 127 (78.9%) were halogen, 22 (13.6%) were lightemitting diodes (LEDs), and 12 (7.4%) were plasma arc curing (PAC) lights. The intensity outputs (mW/cm2) of all examined lights were placed into 5 groups: (1) < 149 = 1.8% of lights; (2) 150 to 249 = 8.6%; (3) 250 to 349 = 6.2%; (4) 350 to 499 = 18.6%; and (5) >500 = 64.0%. Build-up on the tip was: none (23%), light (49.7%), moderate (12.4%), and heavy (13.7%). A comparison of the results of this study with the 1994 survey report shows an overall improvement in the intensity output in dental offices. LED and PAC lights constituted 21.2% of curing lights in this survey.

A new surface sealant for polishing composite resin restorations.

Achieving a smooth and lustrous surface in a timely fashion, using fewer steps, is a desirable feature for direct esthetic restorations. Eliminating the oxygen-inhibition layer and converting it to a glaze layer removes any need for further polishing. This is more applicable to small restorations where reshaping and recontouring can be achieved before light-curing. Mechanical methods for the conversion of the oxygen-inhibition layer to a glazed surface include the use of a clear matrix and an oxygen-barrier gel. A new method has been developed to totally eliminate the formation of the oxygen-inhibition layer by chemical means. This includes the use of a highly reactive, multifunctional, acrylate-based, light-cured surface sealant and glaze, BisCover. This surface sealant may be applied to the surface of restorations before light-curing or after a brief curing. Additionally, it may be applied to the surface of a polymerized and reshaped restoration to remove the need for polishing. Existing composite resin restorations--hybrid or microfilled--as well as provisional acrylic restorations appear well polished and lustrous when surface sealant is applied and cured. Studies have shown that the microhardness of microfilled composite resin is not adversely affected by the use of a surface sealant.

LED and halogen lights: effect of ceramic thickness and shade on curing luting resin.

The purpose of this study was to measure and compare the hardness of a light-cured luting resin cured under different shades and thicknesses of porcelain with a halogen and a light-emitting diode (LED) light. Square (11 mm x 11 mm) specimens of a commercially available porcelain with thicknesses of 1 mm and 2 mm were fabricated. Two shades of porcelain--A1 representing a high-value, low-chroma porcelain and C4 representing a low-value, high-chroma porcelain--were used to fabricate specimens. Composite luting resin, 0.5 mm in thickness, was placed under each porcelain specimen and light-cured for 30 or 60 seconds with LED or halogen light. The degree of polymerization of resin cement was determined by measuring the microhardness. The control group in this study was a 0.5-mm composite luting resin cured under clear Mylar matrix. No significant differences were recorded between surface hardness of control subgroups and LED subgroups cured for 30 or 60 seconds. A lower hardness value was recorded for 2-mm C4 porcelain cured for 30 and 60 seconds with the halogen light. Although a cumulative comparison of surface hardness revealed similar results for both lights, the LED light provided more consistent results than the halogen light.

Clinical evaluation of etched porcelain onlays: a 4-year report.

Etched porcelain-bonded-to-enamel restorations (porcelain veneers) have demonstrated a low incidence of debonding, fracture, microleakage, and discoloration. In addition, laboratory and short-term clinical studies have shown satisfactory results with posterior etched porcelain-bonded restorations. This study evaluated the 4-year clinical performance of posterior all-ceramic onlays and overlays bonded with a dual-cure luting resin and a self-cure acetone-based dentinal adhesive. Twenty-one posterior porcelain overlay restorations were fabricated from a high-leucite-content porcelain and bonded to the teeth of 12 adults using a dual-cure luting resin and an acetone-based self-cure N(P-tolyl) glycine-glycdyl methacrylate (NTG-GMA), pyromellitic acid dianhydride and 2-hydroxyethyl methacrylate (PMDM) dentinal adhesive. Restorations were examined for retention, marginal caries, marginal microleakage, sensitivity, discoloration, restorative fracture, and patient satisfaction. Data collected at 4 years revealed 100% retention of the restorations with no marginal discoloration, marginal ditching, caries, or sensitivity. A small gap (Ryge UPHS rating of Bravo) was detected at the facial margin of one restoration but was not sufficient enough to require repair or replacement. Each patient reported a very high level of satisfaction with the restorations. This study demonstrates that porcelain overlays with supragingival margins entirely on enamel that rely primarily or entirely on bonding for their retention can provide excellent esthetics, good function, and perhaps long-term durability if properly designed, fabricated, and bonded. Porcelain overlays fabricated from high-leucite-content porcelain bonded to sound enamel and dentin with a dual-cure luting resin and a fourth generation dentinal adhesive provide satisfactory clinical results and high patient satisfaction.

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.