CAD/CAM indirect bonding trays using hard versus soft resin material: a single-blinded in vitro study.OBJECTIVES
 The present in vitro study aimed to evaluate the accuracy of three-dimensional (3D) printed indirect bonding trays consisting of hard or soft resin materials produced using computer-aided design and manufacturing (CAD/CAM).


 Forty-eight dental casts were 3D printed.  Four groups based on frontal crowding were defined and divided into hard- and soft-resin groups.  After virtual bracket positioning on the digital models, the transfer trays were 3D printed.  To evaluate the accuracy of the procedure, measurements were performed using a digital overlay of the virtual (target) bracket position and a post-bonding scan.  The horizontal, transverse, and vertical deviations and angular discrepancies were analyzed.  The loss rate was evaluated descriptively as a percentage.


 A total of 553 brackets were bonded using 24 soft and 24 resilient indirect bonding trays.  The mean deviations were of 0.05 mm (transversal), 0.05 mm (horizontal), 0.09 mm (vertical), 0.13° (angulation) in the resilient resin group and of 0.01 mm (transversal), 0.08 mm (horizontal), 0.08 mm (vertical), 0.37° (angular) in the soft resin group.  The loss rate was 6.9% and 0.7% in the hard and soft resin groups, respectively.  Angular deviations were significantly higher in the soft resin group (P = 0.009), whereas the loss rate was considerably higher in the hard resin group (P < 0.001).


 SIGNIFICANCE
 The findings indicate that indirect bonding using CAD/CAM is an accurate procedure in the laboratory setting.  Soft resins are considered favorable for loss rate and useability.
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