Evaluating the Type of Light Transmittance in Mono Crystalline, Poly Crystalline and Sapphire Brackets- An Invitro...

Most of the patients seek orthodontic treatment to improve the smile, which improves the facial profile by means of fixed appliances i.e., brackets and wires. The brackets are of different types like stainless steel and ceramic. Ceramic brackets were considered as aesthetic appliance which was divided into mono-crystalline, polycrystalline and sapphire brackets. The light transmittance might influence the degree of curing adhesive material in mono crystalline, polycrystalline and sapphire brackets.

The aim of the present study was to evaluate the translucency and intensity of three different aesthetic brackets (mono crystalline, poly crystalline and sapphire ceramic brackets) and to determine their influence on shear bond strength of the brackets. The adhesive remnant index was also measured after debonding of the brackets from the tooth surface.

Twenty six samples each of monocrystalline, polycrystalline and sapphire brackets (total 78 ceramic brackets) were used for the study. The bracket samples were subjected to optical fluorescence test using spectrofluorometer to measure the intensity of the brackets. Seventy eight extracted premolar teeth were procured and divided into 3 groups. The brackets were then bonded to the tooth using Transbond XT (3M Unitek) light cure composite material and cured with new light cure unit (Light Emitting Diode) of wood pecker company (400-450nm) for 30 seconds, and these samples were subjected to shear bond strength test with Instron Universal Testing Machine (UNITEK-94100) with a load range between 0 to 100 KN with a maximum cross head speed of 0.5mm/min. ARI (Adhesive Remnant Index) scores were evaluated according to Artun and Bergland scoring system using stereomicroscope at 20x magnification.

The light absorption values obtained from spectrofluorometeric study were 3300000-3500000 cps for group 1 (monocrystalline ceramic brackets), 6000000-6500000 cps for Group 2 (polycrystalline ceramic brackets) and 2700000 -3000000 cps for Group 3 (sapphire ceramic brackets) i.e., Group 2 showed the highest light absorption and the least translucency followed by groups 1 and 3. Shear bond strength results were 2.4 mpa, 1.9 mpa and 3.6 mpa for groups 1,2 and 3 respectively. Superior shear bond strength was recorded in group 3 (sapphire ceramic brackets). ARI results showed that group 3 had increased bond between bracket adhesive interfaces when compared to the other 2 groups.

From this study, it has been concluded that sapphire ceramic brackets (Group 3) was superior in translucency and shear bond strength followed by monocrystalline and polycrystalline ceramic brackets.