Influence Of Various Surface Conditioning Methods On The Shear Bonding Strength Of Brackets To Porcelain Surfaces

This study evaluated the effect of various surface treatments after different storage time and thermocycling on the shear bond strength of orthodontic brackets to a feldspathic porcelain surfaces. The Adhesive Remnant Index and microstructure of the treated porcelain facets were also examined. The study was divided into the following two parts:Part OneInfluence of various surface conditioning methods onthe shear bonding strength of metal bracket to porcelain surfacesPURPOSE: The aim of part one was to compare the effect of foursurface treatments and two storage conditions on the shear bonding strengthof metal bracket to porcelain surfaces and determine which conditioningmethod can offer adequate bond strength for orthodontic purpose but alsokeep porcelain intact after debonding. The microstructure of the treatedsurfaces were also examined. MATERIALS AND METHODS: 64 discshaped porcelain specimens were randomly assigned to the followingtreatments:9.6%hydrofluoric, 9.6% hydrofluoric combined with silane, 50μaluminum trioxide sandblasting followed by silane and application of silane after 37% orthophosphoric acid. Metal brackets were bonded onto each treated porcelain with light cured resin (Transbond XT,3M Corp).The samples were stored in 37°C water 1 day or 7 days, thermocycled 500 times from 5°C to 55°C.The shear bonding strengths were measured and bond failure sites were classified according to Adhesive Remnant Index system. The surface of the glazed, sandblasted, hydrofluoric and orthophosphoric acid etched porcelain were examined with scanning electron microscopy. RESULTS: The lowest shear bonding strengths value was achieved by hydrofluoric etch alone. The highest values were obtained with hydrofluoric etch or sandblasting followed by silane application. Statistically significant differences were observed among the group of orthophosphoric acid combined with silane and the other three groups. Sandblasting caused more porcelain fracture. The shear bonding strength after 7days water storage time was lower than that of lday.But the difference was small and statistically insignificant. CONCLUSION: All groups achieved adequate bonding strengths to withstand the application of orthodontic forces. Silane increased bonding strength to porcelain more significantly than mechanical retention. The optimal regimen for metal bracket bonding to feldspathic porcelain was to apply orthophosphoric acid combined with silane. Water storage and thermocycling reduced shear bonding strength.Part TwoInfluence of various surface conditioning methods on theshear bonding strength of ceramic bracket to porcelain surfacesPURPOSE: The aim of part two was to compare the effect of foursurface treatments and two storage conditions on the shear bonding strengthof ceramic bracket to porcelain surfaces and determine which conditioningmethod can offer adequate bond strength for orthodontic purpose but also keep porcelain intact after debonding. Whether the mean shear bonding strength has difference between the metal and ceramic bracket was also compared. MATERIALS AND METHODS: 64 disc shaped porcelain specimens were randomly assigned to the following treatments: 9.6%hydrofluoric, 9.6% hydrofluoric combined with silane, 50 P aluminum trioxide sandblasting followed by silane and application of silane after 37% orthophosphoric acid. Ceramic brackets were bonded onto each treated porcelain with light cured resin(Transbond XT,3M Corp).The samples were stored in 37°C water 1 day or 7 days, thermocycled 500 times from 5°C to 55°C.The shear bonding strength was measured and bond failure sites were classified according to Adhesive Remnant Index system. RESULTS: The lowest shear bonding strengths value was achieved by hydrofluoric etch alone. The highest values were obtained with hydrofluoric acid or sandblasting followed by silane application. Statistically significant differences were observed among the group of orthophosphoric acid combined with silane and the other three groups. Water storage 7days caused a lower shear bonding strength than lday.But the difference was small and statistically insignificant. The mean shear bonding strength provided by ceramic bracket with mechanical retention had no statistical difference with that of metal bracket. CONCLUSION: All groups achieved adequate bonding strengths to withstand the application of orthodontic forces .The ceramic bracket can obtain acceptable bonding to feldspathic porcelain by applying orthophosphoric acid combined with silane. There was no statistical difference between the mean shear bonding strength of the two types of brackets.In conclusion, there were almost the same effects of the four conditioned methods on the two types of bracket. All can provide adequateshear bonding strength to porcelain. It's unnecessary to deglaze the porcelain. Therefore, bonding to silane treated glazed porcelain is possible to achieve orthodontic bonding. Water storage and thermocycle can reduce bond strength.