Introduction of novel CAD/CAM fabricated esthetic interprenetrating phase ceramic orthodontic brackets; fracture and frictional resistance evaluation
Alrejaye, Hessa Sulaiman A.
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Esthetic orthodontic brackets available commercially are made of different ceramic materials: alumina, which is most commonly used, is either monocrystalline or polycrystalline and zirconia is least commonly used. These ceramic brackets showed significant drawback which limited their wide use by the orthodontic clinicians. They are associated with numerous problems; one of the major problems is excessive abrasion of opposing dentition and iatrogenic enamel damage when debonding, besides their opaque appearance. Objectives: To fabricate orthodontic brackets using a new esthetic interpenetrating phase ceramic and composite resin via CAD/CAM technology and evaluate their mechanical properties. To fabricate resin-infiltrated-spinel material and evaluate its optical and mechanical properties for use as an orthodontic bracket material. Materials and Methods: A CAD/CAM milling machine (CEREC Compact inLab, Dentsply-Sirona) was used to mill brackets with a 0.018"×0.025" slot from Vita-Enamic interpenetrating phase ceramic (Vita Zahnfabrik) and Cerasmart (GC America) composite resin block. The brackets were subjected to separate tests (torque, tipping and sliding) using a universal testing machine. The average moments necessary to fracture the brackets and the average frictional forces were determined and compared to commercially available zirconia brackets (Cercon ZirBra, Dentsply-Sirona) and alumina brackets (Ovation C, Dentsply-Sirona GAC). Additionally, Avex CX2 polycrystalline alumina (Opal Orthodontics) with a slot size 0.022"×0.028" was included in the test as well. Furthermore, MG-203 spinel powder was dry-pressed into multiple blocks, sintered at different temperatures and then infiltrated with resin. Densities at different stages were measured and recorded for comparison. Blocks were cut into disks of different thicknesses, and then tested for optical and mechanical properties. Results: The Enamic and Cerasmart brackets evaluated in this study presented adequate fracture strength compared to that necessary for torque and tipping movement reported in the literature. In addition, it demonstrated acceptable frictional behavior comparable to zirconia and polycrystalline alumina brackets. As the sintering temperature of spinel matrix increased, the fracture strength and transmission increased as well. Conclusions: Vita-Enamic and Cerasmart brackets were sufficiently strong to withstand the commonly accepted magnitudes of effectively torquing and tipping maxillary incisors dental movement without fracturing. Optical and mechanical properties of resin-infused spinel were enhanced by increasing sintering temperatures.