Assessment of Retentive Strength Orthodontic Bands Cemented with ACP-ModifiedGI

Objectives: One of the problems concerning banding in orthodontics is the formation of decalcified areas around the bands. To prevent demineralization, amorphous calcium phosphate (ACP)-containing cements have been introduced recently. The aim of this study was to evaluate the retention strength of ACP-containing glass-ionomer cement (GIC) for band fixation. Methods: 120 extracted human mandibular third molars were embedded in acrylic resin blocks, leaving the buccal surface of the crowns parallel to the base of the molds. The teeth were randomly divided into four groups of 30. Groups 1 and 3 were banded using conventional GIC and groups 2 and 4 using ACP-containing orthodontic cement. Thereafter, the samples were maintained in the incubator in stilled water and at a temperature of 37°C for 48 hours. Groups 1 and 3 immediately, and groups 2 and 4 after thermo cycling (5000 cycles,5° to 55°C),were examined for retention strength, using universal testing machine (cross-head speed of 1 mm/min).The data were analyzed using variance analysis (ANOVA) and Tukey test via SPSS. Results: The highest retention strength (mean: 1.5140 MPa) belonged to group 1 (with conventional GI cement and without thermo cycling), and the lowest retention strength (mean: 1.1695 MPa) belonged to group 2 (ACP-containing GI cement with thermo cycling). According to Tukey test results, the difference between group 1 and groups 2 and 3 was significant (P<0.05). The difference between group 2 and groups 1 and 4 was also significant (P<0.05). Conclusions: Although retention strength decreased when ACP was added to GI cement,after thermo cycling,retention strength of the samples banded by ACP-containing GI was remarkably higher to a point that it had no significant difference with the retention strength of GI cement group without thermo cycling.It seems that in the oral cavity ACP-containing GI cement has sufficient strength to endure the forces upon posterior teeth.