Bond strength of orthodontic brackets to composite restorative materials

Objectives:

To evaluate the SBS of orthodontic brackets to composite restorative materials using various orthodontic bonding systems.

Methods:

60 metallic orthodontic brackets Elite Opti-Mim (Ortho Organizers)  were used.  20 brackets were bonded to tooth-shaped samples of Filtek A 110(3M-ESPE) composite ( Group A ).20 brackets to similar samples with Filtek Z 250(3M-ESPE) composite (Group B) and 20 to human premolars ( Group C) as controls. The brackets were bonded to 10 teeth in each group by composite [ Illuminate -Ortho Organizers] adhesiveX or resin modified glass- ionomer [Fuji Ortho LC –GC International] adhesiveY.  Samples were stored in water at 37^oC for 24h then tested for SBS using a Hounsfield tensometer.  Failure mode was evaluated

microscopically. The results were analysed with Multifactor ANOVA and the Newman-Keuls post hoc test.

Results:

Shear bond strengths

Samples	Bonding system	Strength (MPa)	SD (MPa)
Group A	X Y	5.06 10.17	1.66 2.19
Group B	X Y	5.87 9.16	1.99 3.56
Group C	X Y	5.70 10.38	2.65 3.84

Failure for B with X was mainly adhesive between bracket and bonding system.  Failure for A with X and Y and for B with Y was mainly cohesive. In group C failures of X were cohesive/adhesive and of Y, mainly cohesive.

Conclusion:

RMGIC adhesive gave a higher SBS in both experimental groups and the control group, compared to that with composite (p<0.05).  These values are satisfactory for clinical situations. Failure mode tended to be cohesive failures in most cases.

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