Static frictional resistances of polycrystalline ceramic brackets with conventional slots, glazed slots and metal slot inserts.

AIMS: To compare the static frictional resistance of ceramic brackets with a conventional slot (Allure), a glazed slot (Mystique) and a metal slot insert (Clarity).

METHOD: Twenty five brackets of each type, with slot size 0.022 x 0.028 inch and Roth prescription were tested by sliding against straight lengths of 0.019 x 0.025 inch rectangular stainless steel wire. During the tests the brackets and wire were lubricated with artificial saliva. Static frictional forces at three different simulated binding angulations (0, 5 and 10 degrees) were measured for each type of bracket.

RESULTS: At each of the angulations tested, the Clarity brackets produced the lowest static frictional resistance. At 0 degree angulation (below the critical angle for binding) the Allure brackets produced the greatest friction. The difference in friction between the Clarity and Mystique brackets was not statistically significant. As the angulations were increased to 5 degrees the Allure brackets again produced the greatest frictional resistance, although this was not significantly higher than the Mystique brackets. The Mystique brackets produced the greatest frictional resistance at 10 degrees, but again there was no statistical difference from the Allure brackets.

CONCLUSIONS: A glazed slot ceramic bracket demonstrates low frictional resistance at non-binding angulations and compares favourably with a metal slot ceramic bracket. Increasing angulations through 5 to 10 degrees of simulated binding results in high levels of static frictional resistance such that the bracket behaves more like a conventional polycrystalline ceramic bracket.