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Kinetics of light-cure bracket bonding: power density vs exposure duration
Anestis Mavropoulos1, Maria Cattani-Lorente, Ivo Krejci
1Division of Orthodontics, University of Geneva, Geneva, Switzerland. anestis.mavropoulos@medecine.unige.ch
Summary
For orthodontic bracket bonding, total light energy is not the only factor; sufficient exposure time is crucial. Insufficient exposure, even with high power, compromises bond strength.
Area of Science:
- Dental Materials Science
- Orthodontic Technology
- Polymerization Kinetics
Background:
- Technological advancements allow for increased light power density, potentially reducing curing times.
- The polymerization kinetics of light-cured composites are complex, especially for indirect curing beneath metallic brackets.
- The hypothesis tested was that the 'total energy' concept (reciprocity of power density and duration) does not apply to orthodontic light-cure bracket bonding.
Purpose of the Study:
- To investigate whether the principle of 'total energy' applies to light-cured bracket bonding in orthodontics.
- To determine the optimal balance between light power density and exposure duration for achieving adequate bracket shear bond strength.
- To identify critical thresholds for exposure duration and power density in orthodontic bracket bonding.
Main Methods:
- Stainless steel brackets were bonded to bovine incisors using light-cured composite.
- A halogen lamp varied power density (300-3000 mW/cm²) and exposure duration to achieve specific energy densities (6000, 12000, 24000 mJ/cm²).
- Shear bond strength (SBS) and adhesive remnant index (ARI) were measured after 24-hour water storage.
Main Results:
- Bracket shear bond strength (SBS) was primarily dependent on the light cure's energy density.
- Significantly lower SBS was observed in groups receiving 6000 mJ/cm² compared to higher energy densities (P <0.01).
- The relationship between SBS and exposure duration at constant energy density followed a nonlinear regression model (r² = 0.98).
Conclusions:
- The 'total energy' concept is not applicable to orthodontic light-cure bracket bonding.
- Exposure times under 4 seconds, regardless of power density, failed to ensure sufficient bracket bond strength.
- Higher power density appears more advantageous than extended exposure duration for metallic bracket bonding, with an effective lower limit of 4 seconds exposure and an upper limit of 3000 mW/cm² power density.
