Mechanical properties of CAD/CAM fabricated esthetic orthodontic brackets and introduction of extremely low profile miniature zirconia and shaded brackets
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Available commercial ceramic brackets are made of alumina either monocrystalline or polycrystalline. One major drawback of these brackets is fracture during archwire torsion or tipping. Another drawback is that each type comes in one shade only: transparent or translucent. Objectives: To fabricate orthodontic brackets from different esthetic materials and evaluate their mechanical properties; to introduce extremely low profile miniature zirconia brackets and evaluate their torsional fracture strength; also, to fabricate brackets in shades comparable to natural tooth shades, and compare them to commercial ceramic brackets under different lights. Materials and Methods: CAD/CAM technology was used to mill brackets from: ParadigmTM MZ100 and LavaTM Ultimate resin composite; Mark II feldspathic porcelain; and In-Ceram® YZ zirconia. The brackets were subjected to two separate tests (torque and tipping). The average moments necessary to fracture the brackets were determined and compared to those of commercial alumina brackets, Mystique® MB and Resolve®. Also, miniature zirconia brackets were fabricated and subjected to torsion till failure. Static fatigue test was performed on standard YZ, MZ100, and Mystique brackets. Brackets were fabricated using CAD/CAM in shade A3 materials: MZ100; Lava Ultimate; and Mark II. Zirconia and alumina brackets were also fabricated and colored. Adobe Photoshop software was used to determine ΔE values between the brackets and A3 acrylic teeth from digital images taken under three different lights (daylight, fluorescent, and incandescent). The shaded brackets were compared to commercial alumina brackets: Inspire ICETM; Radiance PlusTM; Avex® CX; and Mystique® MB. Results: Standard zirconia brackets had the highest torsional and tipping strength among the tested esthetic brackets. Miniature zirconia brackets showed comparable or even statistically significantly higher resistance to archwire torsion than commercial alumina brackets. Standard zirconia brackets showed the highest survival rate of 83%. Under daylight, Radiance Plus and Lava Ultimate brackets had the smallest mean ΔE values. Lava Ultimate brackets had the smallest mean ΔE under fluorescent and incandescent light. Conclusions: Esthetic brackets can be fabricated in extremely low profile and smaller dimensions from zirconia with fracture strength comparable to the bulkier commercial alumina brackets. Also, brackets can be produced in natural tooth shades enhancing their esthetic appearance.