Provisional restorations of full crown preparations may permit more microleakage of bacteria and their products than the final castings do. However, most investigations of the sealing qualities of cemented castings have reported that they too permit dye leakage. One approach to the problem is to seal the dentin with dentin bonding agents at the completion of the crown preparation. This study evaluated the ability of six different dentin bonding agents to seal the dentin of crown preparations of human teeth in vitro using two independent techniques. The first technique quantitated fluid filtration across dentin before and after treatment with dentin bonding agents at one hour, one day, one week, and one month and after thermocycling. The second method measured silver nitrate penetration of the thin veneers of dentin bonding agents into the dentin. Both methods correlated well with each other. The best seals were obtained with Prisma Universal Bond 2 or Superbond powder plus liquid. The worst seals were found using Gluma and Superbond liquid only. Clearfil PhotoBond, Amalgambond, and Scotchbond 2 gave intermediate results. Although the dentin bonding agents tend to accumulate on chamfers, thereby increasing their thickness to 200-300 microns, the method looks promising as a simple way to protect the pulp from the consequences of microleakage.

Analysis of Variance↗

PubMedDate not supplied

The bond strength of Panavia Ex to air-abraded amalgam.

The tensile bond strengths of a resin cement, Panavia Ex, to a spherical and an admixed amalgam were measured after surface treatment with different aluminum oxide abrasive spray procedures. The type of amalgam and the brand of aluminum oxide affected the bond strength of the resin to amalgam alloy. When the spherical alloy was air abraded using 60-microns aluminum oxide prior to cementation of a Rexillium rod using Panavia, the bond strength was not significantly different from the previously reported bond strengths of Panavia to etched enamel. Significantly lower bond strengths were obtained between Panavia and the admixed amalgam alloy. These results suggest that it may be possible to place a resin-bonded prosthesis on an abutment tooth that has been restored using a spherical amalgam alloy.

Aluminum Oxide↗

PubMedDate not supplied

Effects of denture base resins on oral epithelial cells.

The current proliferation of light-polymerized denture base resins and the continual modification of their formulations make standardized biocompatibility testing a necessity. The biocompatibilities of three light-polymerized denture base resins were compared using an in vitro epithelial cell culture system. The effect of varied lengths of polymerization of denture base resin on cell toxicity was examined. This study indicated that light-polymerized denture base resins have an effect on oral epithelial cells that appears to be related to the specific formulation of the material and not to the type of polymerization required. Varying the polymerization time or light-polymerization unit appeared to have little effect.

Acrylic Resins↗

PubMedDate not supplied

Mandibular resorption and unilateral neuralgia of the inferior alveolar nerve.

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Aged↗

PubMedDate not supplied

Bond strength of Panavia EX to dental amalgam.

The tensile bond strengths of Comspan (a conventional resin used with composite-bonded prostheses) and Panavia EX (a newer adhesive bonding material) to different types of amalgam were determined. The results were compared with the tensile bond strengths of these resins to etched bovine enamel and properly prepared Rexillium III. The results showed that all of the resin-amalgam bond strengths were statistically less than those of bonding resin to etched bovine enamel or Rexillium III. Coverage of existing amalgam restorations by the metal framework with etched-metal resin-bonded retainers is contraindicated when using either the conventional bonding agent or the new adhesive bonding material, Panavia EX.

Acid Etching, Dental↗

PubMedDate not supplied

Choice of a luting agent for precision fitting castings.

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Cementation↗

PubMedDate not supplied

A predictive model for the polymerization of photo-activated resin composites.

This study investigated the relative significance of irradiation duration (20, 40, 60, or 80 seconds) and intensity; filler type (Silux Plus, a microfill or P-50, a hybrid); and shade (Universal or Gray) on the polymerization of resin composite within the depth of a simulated photopolymerized restoration. From the data, a mathematical model that predicts the extent of resin polymerization based upon the above stated variables was generated. The monomer conversion of specimens was determined by infrared spectroscopy. The results are of great clinical use and indicate that the most significant factor influencing resin composite polymerization is thickness of overlying resin composite. Both duration of exposure and light intensity demonstrate high and equal impact. Color and filler type have only minimal influence. The predictive model for resin composite polymerization provided a very good fit (r2 = .949).

Analysis of Variance↗

PubMedDate not supplied

Effect of light intensity and exposure duration on cure of resin composite.

Of the many factors under their control, clinicians can manipulate light-exposure duration but must deal with a set intensity of light emitted from the dental curing unit. This research investigates the interdependence of exposure duration and source intensity on resin cure at various depths within a simulated light-cured resin composite restoration. This wafers of composite were obtained from a simulated cylindrical restoration such that the wafer could be removed from the top or from a distance of 1, 2, and 3 mm beneath the surface. The composites used in this study were a microfill and hybrid of Universal and Gray shades. All the data concerning filler type and shade were pooled so that generalized statements could be made regarding curing of light-activated composite in general. Specimens were cured using various source intensities and for different durations at each level within the cured cylinder. The cure of the specimens resulting from the different treatments was determined using infrared spectroscopy. The results indicate a dramatic effect of depth on the cure of composite. At depths greater than 2 mm, poor cure results, and polymerization is very susceptible to changes in light intensity and exposure duration. From these results, routine exposure times of 60 seconds are recommended using light-source intensities of at least 400 mW/cm2 as measured with a commercial dental light intensity meter. Incremental layer thickness should not exceed 2 mm, with 1 mm being ideal. Sources with intensity values less than 233 mW/cm2 should not be used because of their poor cure characteristics.

Absorption↗

PubMedDate not supplied

The influence of light exposure on polymerization of dual-cure resin cements.

This study investigated the degree of monomer conversion of four commercial dual-cure resin cements. The products were subjected to various postmix treatments: no light exposure, a 60-second exposure through Mylar only, and either a 20-second or 60-second exposure through an overlying cured wafer of composite 1.5 mm thick. The infrared spectrum of the treated specimens was recorded at specified times postmix for each cure treatment: 2, 5, 10, 30, and 60 minutes as well as after 24 hours. The degree of cure was then determined from the infrared spectra. The results demonstrate a wide range of potential cures among the various brands. Regardless of brand, the chemical component of cure was always lower than when the specimens were exposed to any lighting condition. For most resin systems tested, the cure observed 10 minutes postmix was almost equivalent to the cure after 24 hours. Despite manufacturers' claims, there is no evidence for a substantial chemically induced polymerization of dual-cure resins that occurs after light exposure is completed.

Analysis of Variance↗

PubMedDate not supplied

Factors affecting light transmission of single-use, plastic light-curing tips.

Recently, manufacturers introduced presterilized, single-use, plastic light-curing tips to be used either routinely or on patients with known or questionable communicable health concerns. The purpose of this study was to examine the effect of these single-use tips on light transmission compared to conventional fiber-optic bundles in a variety of commercial light-curing units. Also, the effects of surface contact with the plastic tips (human tissues, reflective or opaque media, and barrier films) were evaluated. Where applicable, single-use tips from two sources (Caulk/Dentsply and Demetron) were placed in commercial curing units (Optilux 150 and 500, MAX 100, Spectrum Curing Light, and 3M XL-3000), and the intensity was compared to that of the conventional glass curing tip used with that specific curing unit. Intensity readings were also made for 6 continuous minutes using plastic tips in a high-intensity curing unit to simulate veneer bonding. If the sides of the plastic tip came in contact with the operator's fingers or the patient's tongue and/or cheek during a clinical procedure, a lowering of transmitted light intensity resulted. The glow emitted from the sides of the tip when in use may be annoying to the operator. To prevent this glare, the operator may be tempted to treat the sides of the tip by painting, applying a thin polymer barrier, abrasion, or wrapping in an opaque reflective material (aluminum foil). A significant decrease in light intensity can result if plastic curing tips contact oral tissues or bare hands. Application of thin polymer barriers was found to significantly reduce light transmission value. Also, surface modification (coating with paint or surface scratches) was found to greatly reduce light intensity levels, while wrapping the tip in aluminum foil produced a very small increase. Results indicated that transmitted light intensity with use of plastic tips was dependent upon both the brand of plastic tip tested and the different photocuring units. Either a slight increase or a slight decrease in intensity was noted. Plastic tips did not degrade in transmitted intensity when exposed to the heat produced during a simulated veneering scenario. In summary, use of plastic, single-use light-curing tips can provide adequate intensity for photoactivated restorative techniques; however, the clinician must be aware of specific, clinically relevant limitations with their use. Clinicians must also note that these tips are not designed for re-use.

Analysis of Variance↗