Peter Brockhurst

Bonding of resin composite to carbon dioxide laser-modified human enamel

OBJECTIVES Irradiation of enamel with carbon dioxide (CO2) laser energy alters physical and chemical properties of the enamel surface, and these lasers hold promise for conditioning enamel for bonding of adhesive restorations. This laboratory study examined the influence of laser irradiation parameters on the shear bond strength obtained for laser etching using a hybrid composite. METHODS Standardized surfaces prepared on 110 non-carious intact extracted anterior teeth were exposed to CO2 laser energy (9 different laser exposure parameters) or etched with orthophosphoric acid. RESULTS Laser treatment under defined conditions (power density 2380 W/cm2, energy density 23.8 J/cm2) resulted in a bond strength of 30.0 +/- 4.7 MPa, which exceeded that obtained for acid etching (17.9 +/- 4.3 MPa, p < 0.0001). Cohesive failure occurred within the bonding resin in this group. SIGNIFICANCE These data indicate that CO2 laser etching may enhance the bonding of resin composite to human enamel.

Disinfection of dental stone casts: Antimicrobial effects and physical property alterations

OBJECTIVES The purpose of this study was to evaluate the effectiveness of disinfecting solutions incorporated into dental stone casts against a standard and representative group of microorganisms and to note changes in the physical properties of the casts. METHODS Irreversible hydrocolloid impressions were contaminated individually with Escherichia coli, Staphylococcus aureus, Enterobacter cloacae, Pseudomonas aeruginosa, Klebsiella pneumoniae, Actinobacter calcoaceticus, Bacillus subtilis, Mycobacterium phlei and Candida albicans. Four readily available disinfecting solutions (glutaraldehyde, povidone-iodine, chlorhexidine and sodium hypochlorite) were added to the die stone mix used to pour up the impressions. The set cast surfaces were swabbed at 1 h and 24 h, the samples plated on agar and incubated at 37 degrees C for 24 h and 3 d for M. phlei. Subsequently, colony forming units were counted. The physical properties assessed were setting time, setting expansion, compressive strength, detail reproduction and delayed expansion of the stone. RESULTS Only glutaraldehyde and povidone-iodine killed all contaminating microorganisms within 1 h, while the 1:5 dilution of sodium hypochlorite solution was equally effective after 24 h. Two percent glutaraldehyde was the most effective disinfectant with the least adverse effects on the physical properties of the set cast. Although povidone-iodine caused a decrease in the compressive strength of the set cast, it can be considered to be a sound alternative. SIGNIFICANCE This study supports the concept of incorporating disinfectants into model stone as a standard operating procedure for impressions of unknown history and, most sensibly, all dental impressions.