Mini-Implant Screws for Bone-Borne Anchorage: A Biomechanical In Vitro Study Comparing Three Diameters.

Area of Science:

• Orthodontics
• Biomaterials Engineering

Background:

• Rapid maxillary expansion (RME) is a common orthodontic procedure to widen the palate.
• Mini-implants offer skeletal anchorage for RME, potentially improving outcomes.
• Understanding the mechanical limits of mini-implants is crucial for predictable treatment.

Purpose of the Study:

• To evaluate the maximum strength and aperture supported by mini-implant screws of different diameters.
• To compare the mechanical performance of 1.8mm, 2.0mm, and 2.2mm diameter mini-implants in a simulated RME model.

Main Methods:

• Fifteen Hyrax expander appliances anchored by mini-implants of three diameters (1.8mm, 2.0mm, 2.2mm) were tested in artificial bone blocks.
• A custom device simulated mid-palate disjunction, and expanders were activated until screw failure.
• Measurements included activations to failure, maximum supported strength, and maximum aperture.

Main Results:

• No significant differences in activations to maximum strength were observed between groups.
• Slightly significant differences in aperture were found between 1.8mm and 2.0mm groups (P=.048).
• A significant difference in maximum supported load was noted between 1.8mm and 2.2mm groups (P=.039).

Conclusions:

• The tested mini-implant screws, regardless of diameter, exceeded the forces and apertures typically required for clinical RME.
• The anchorage system demonstrated robust mechanical properties suitable for rapid maxillary expansion procedures.