Shear bond strength of metal brackets bonded to enamel surface and two esthetic restorative materials

The orthodontist my be faced with the need to bond brackets to esthetic restorations. This is due to increasing demands of adults to orthodontic treatment. Bond strength of the brackets to the restored teeth should be within the range of clinical acceptance and without endangering the restoration during removing the brackets. So, it was necessary to evaluate the bond strength of the orthodontic brackets to these esthetic restorative materials in comparison to the natural teeth. This in-vitro study evaluated the shear bond strength(SBS) of metal orthodontic brackets to two esthetic restorative materials(malliable composite blocks (MZ100) and machinable ceramics (Vita Mark II)) using a new luting cement used for bonding (compomer). Thirty six metal orthodontic brackets were bonded to a flat buccal surface of extracted premolars, MZ100 and Vita Mark II using the same luting agent. All specimens were stored in water for 45 days then thermocycled for 500 cycles. The SBS in Mpa was measured using Instron machine. One way ANOVA showed statistically significant difference between test and control groups P=0.0006. Mann-Whitney tests revealed statistically significant difference between (SBS) of control group and MZ100 composite group P = 0.0003, Also there was statistically significant difference between the two test groups MZ100 composite and Vita Mark II (P = 0.02). However, there was no statistically significant difference between control group and Vita Mark II group( P = 0.07). This study revealed that the median of SBS for metal brackets to esthetic substrates(MZ100 =5.7 and Vita Mark II=8) was significantly lower than that of the natural teeth (9.9 MPa) but, at the same time they were within the acceptable clinical range (6-10 Mp) (6). However, the SBS of the metal brackets to the porcelain substrates was superior to that of composite. It was concluded that compomer luting cement may be used for direct bonding of orthodontic metal brackets to esthetic restorations in clinical practice