Evaluation of Er,Cr:YSGG laser irradiation for debonding of zirconia hybrid abutment crowns from titanium bases.

To evaluate the efficacy of Er,Cr:YSGG laser irradiation on the removal of zirconia hybrid abutment crowns (HAC) from ti-bases and investigate the effects of laser output power and zirconia generation on debonding time and fracture resistance of crowns. A hundred monolithic zirconia HACs were fabricated by using 4Y-TZP and 5Y-TZP materials and subsequently cemented onto the ti-bases with a resin luting agent. Each zirconia group was further divided into 5 subgroups according to the debonding procedure as control (no debonding), 4.5 W-, 5 W-, and 6 W-laser irradiation, heat processed (n = 10). Er,Cr:YSGG laser (Waterlase MD; Biolase Technology Inc., Irvine, CA) was used on a noncontact hard tissue mode at a 20-Hz repetition rate and 140-μs pulse duration with 50% water and 50% air. Debonding durations were recorded for each specimen, and modes of failure were investigated. Crowns were re-cemented on their corresponding ti-bases, and HACs were subjected to fracture strength test. Debonding duration and fracture strength data were statistically analyzed. Fractured zirconia crown surfaces of ti-bases were examined under the scanning electron microscope. 5Y-TZP crowns were debonded from ti-bases in significantly lower durations in comparison with 4Y-TZP crowns for all output powers [4.5 W (P = 0.001), 5 W (P = 0.002), and 6 W (P = 0.0014)]. For both 4Y-TZP and 5Y-TZP materials, debonding duration was significantly decreased with the increase in laser output power (P ≤ 0.001 for 4Y- and 5Y-TZP). In comparison with 4Y-TZP heat-processed group to the 4Y-TZP laser-irradiated groups, no significant differences were detected in terms of fracture strength (P > 0.05), while heat-processed crowns exhibited significantly lower fracture strength values than those of control group (P = 0.006). All debonding procedures significantly reduced fracture strength values of 5Y-TZP crowns in comparison with the control group (P ≤ 0.001). The common failure type was the adhesive failure between the zirconia crown and resin cement for all groups. SEM evaluation showed no visible damage caused by laser irradiation or heat application. The use of Er,Cr:YSGG laser irradiation is an efficient way to retrieve zirconia crowns from ti-bases. The higher the output power of the laser, the shorter the bonding procedure. The debonding duration and fracture strength of the crown were affected by the zirconia generation. Debonded 5Y-TZP zirconia crowns should not be reused due to the decrease in mechanical strength values.