UCSF

BACKGROUND:

The bonding protocol of the dental substrate is essential for successful adhesive restorations. Dental adhesive systems can be classified into two categories: etch-and-rinse (total-etch) and self-etch systems. Highly absorbed 9.6μm CO2 short-pulsed laser prototype irradiation has successfully shown enhancement of enamel caries resistance in laboratory and prospective, randomized controlled clinical studies. Recently, a 9.3µm microsecond short-pulsed CO2-laser was introduced to the dental profession. In addition to caries preventive procedure, this laser can be used for tooth preparation and osseous surgery.

OBJECTIVES:

The objective of this study was to evaluate the CO2 9.3µm short-pulsed laser irradiation influence on shear bond strength of composite to enamel and dentin.

METHODS:

200 enamel and 210 dentin samples were irradiated with a 9.3μm carbon-dioxide laser (Solea, Convergent Dental; Needham, MA) with energies enhancing caries resistance for ablation of enamel and dentin. A 5th generation etch-and-rinse bonding agent OptiBond Solo Plus [OptiBondTE] (Kerr Corporation; Orange, CA) and Peak Universal Bond light-cured adhesive [PeakTE] (Ultradent Products) were used on both ablated enamel and dentin. A 6th generation self-etch system Scotchbond Universal [ScotchbondSE] (3M ESPE, St. Paul, MN) and Peak SE self-etching primer with Peak Universal Bond light-cured adhesive [PeakSE] were used on both ablated enamel and dentin. Clearfil APX (Kuraray, New York, NY) composite was bonded to the samples, and after 24 hours storage at 37°C, a single plane shear bond test was performed to determine enamel and dentin bond strengths.

RESULTS:

Using the caries preventive setting on enamel resulted in increased shear bond strength values for all bonding agents except for self-etch PeakSE with a slight, statistically non-significant 16.3% decrease. The highest overall bond strength to caries preventive-treated enamel was seen with PeakTE (41.29±6.04MPa), presenting a 6.6% increase over the not laser treated control.

To ablated enamel, etch-and-rinse systems achieved higher bond strength values than the self-etch systems. PeakTE showed the highest shear bond strength with 35.22±4.40MPa (90.9% of the not laser treated control). OptiBondTE reached 93.8% of the control bond strength values. The self-etch system PeakSE presented significantly lower bond strength (41.7 to 53.9% of control value), ScotchbondSE showed a non-significant increase of the bond strength after enamel ablation.

After ablation of dentin the shear bond strength values ranged between 19.15±3.49MPa for OptiBondTE and 43.94±6.47MPa for PeakSE. The shear bond strength was significantly lower (57.2 and 75.4% of the not laser treated control values) for all bonding systems.

CONCLUSION:

Etch-and-rinse systems achieve consistently high bond strengths to short-pulsed CO2 9.3μm laser-ablated enamel. After irradiation with the highest recommended energy for laser dentin removal, PeakSE reached 43.9±6.5MPa bond strength followed by 36.0±7.4MPa for PeakTE and 25.3±3.8MPa for ScotchbondSE. Following dentin ablation, all bonding agents reached higher shear bond strength values than the reported required minimum value.