Reproducibility and accuracy of machine bent 3- and 6-stranded twistflex lingual fixed retainers-An in-vitro-study

Area of Science:

• Orthodontics and Dental Technology
• Biomaterials Engineering

Background:

• Evaluating the precision of automated fabrication processes for orthodontic appliances is crucial for clinical success.
• Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) offers potential for precise retainer fabrication.

Purpose of the Study:

• To assess the accuracy of a retainer bending machine in replicating CAD/CAM designed orthodontic retainers.
• To quantify deviations between machine-bent and master CAD/CAM retainer designs.

Main Methods:

• Digitally designed canine-to-canine retainers were fabricated ten times each using the Bender II machine with 3- or 6-stranded twistflex wire.
• Master retainers were created from CAD/CAM coordinates, and bent retainers were digitized and superimposed for deviation analysis.
• Deviations were measured in transverse, sagittal, and vertical dimensions; statistical analysis used a mixed linear model.

Main Results:

• Mean deviations were 0.22 mm (transverse), -0.01 mm (sagittal), and 0.48 mm (vertical).
• Lower retainers were significantly more precise than upper retainers across all dimensions (P < 0.001).
• 3-stranded twistflex wires demonstrated significantly greater accuracy than 6-stranded wires (P < 0.05).

Conclusions:

• Clinically relevant deviations exist between CAD/CAM designed and machine-bent retainers.
• Accuracy is influenced by jaw location and wire type, with implications for clinical application.