Comparison of the biomechanical properties of CAD/CAM individualized lingual retainers: An in vitro study

This study examined the biomechanical properties of computer-aided design/computer-aided manufacturing (CAD/CAM) retainers made of titanium and nickel-titanium (NiTi).

Four retainer types were tested: (1) twisted steel, (2) NiTi, (3) cut titanium, and (4) printed titanium. Longitudinal wires were manufactured (2-4) and subjected to a three-point bending test (3PBT). In a biomechanical bending test (BMT), retainers were designed from patient scans and applied to models in an Orthodontic Measurement and Simulation System, with the maxillary central incisor and mandibular central incisor loaded with deflections of ±0.2 mm and rotation of ±1°.

The 3PBT showed that NiTi wires exhibited a characteristic hysteresis loop, whereas the cut and printed titanium wires had different flow and yield strengths. The BMT forces during intrusive and extrusive movements were measured, and the findings revealed that in the maxilla, all CAD/CAM materials showed significant differences from the twisted steel, with NiTi differing from the cut and printed titanium. In the mandible, the forces were generally higher, with significant differences observed at 0.1-mm extrusion and 0.2-mm deflection. In addition, significant differences were observed in the mesial and distal deflections, particularly in the mandible, where the cut titanium generated the lowest forces. Twisted steel exhibited the lowest torque, whereas cut titanium exhibited the highest torque.

CAD/CAM retainers differ significantly from conventional twisted steel retainers, with notable differences between NiTi and titanium retainers, especially in the maxilla. However, these differences may be negligible in the mandible due to the shorter interdental distance.