In-vitro testing of shear bond strength of orthodontic brackets bonded to different novel CAD/CAM ceramics

To evaluate the bond strength of metal and ceramic brackets bonded to different CAD/CAM ceramic substrates etched with hydrofluoric acid vs. phosphoric acid.

One hundred and twenty CAD/CAM ceramic blocks in 12 groups were fabricated from 3 different CAD/CAM ceramic materials; VITABLOCS Mark II, VITAENAMIC and IPS e.max CAD. Each ceramic material group was divided into two etching groups; one treated with 9.5% hydrofluoric acid (HFA) and the other treated with 37% phosphoric acid (PA). Sixty metal and ceramic brackets of upper right central incisor were bonded to the HFA treated blocks. Another 60 metal and ceramic brackets were bonded to the PA treated blocks. All bonded specimens were thermocycled prior to shear bond strength (SBS) testing. Then the mode of bond failure was recorded.

There was no statistically significant difference in SBS values between the three CAD/CAM ceramic materials. The HFA treated specimens presented a statistically significant higher SBS values than the PA treated specimens. Also, the SBS values of ceramic brackets were significantly higher than those of metal brackets. The adhesive remnant index (ARI) scores were 4 for most of the groups; meaning that almost no adhesive remained on the porcelain surface.

The type of the CAD/CAM ceramics does not influence SBS but HFA yield significantly higher SBS compared to PA.