Influence of cortical bone thickness on miniscrew microcrack formation

Area of Science:

• Orthodontics
• Biomaterials Science
• Surgical Implantology

Background:

• Orthodontic miniscrews (OMs) are crucial for anchorage in orthodontic treatments.
• Understanding the biomechanical effects of OM insertion is vital for successful treatment outcomes.
• Cortical bone thickness is a potential factor influencing the stability and osseointegration of OMs.

Purpose of the Study:

• To investigate the impact of varying cortical bone thickness on the microdamage induced by orthodontic miniscrew insertion.
• To quantify the relationship between bone thickness and the extent of surface microdamage.
• To provide data that can inform clinical decisions regarding OM placement.

Main Methods:

• In vitro insertion of orthodontic miniscrews (OMs) into porcine tibia bone with cortical thicknesses of 1.0 mm, 1.5 mm, and 2.0 mm.
• Utilized a torque-limiting screwdriver set at 18 Ncm for consistent insertion.
• Employed sequential staining and laser confocal microscopy to visualize and quantify microdamage using ImageJ software.

Main Results:

• Complete insertion of OMs was achieved in 1.0 mm bone; partial failures occurred in 1.5 mm and 2.0 mm bone.
• The 2.0 mm cortical bone group exhibited significantly greater total damage area, diffuse damage area, maximum crack length, and maximum damage radius.
• Maximum crack lengths ranged from 1.03 to 3.06 mm on entry and exit surfaces.

Conclusions:

• Increased cortical bone thickness (2.0 mm) leads to a higher incidence and severity of microdamage during OM insertion compared to thinner bone (1.0 mm).
• Minimizing cortical bone thickness at the insertion site is recommended to reduce microdamage.
• A safety zone of 3.5 mm is advised for OMs in 1.0 mm and 1.5 mm cortical bone to mitigate detrimental effects.