Effect of ACP on Bond Strength of Composite to Enamel

Amorphous calcium phosphate paste (ACP) has become increasingly popular for remineralization of tooth structure and caries prevention.  Objective:  To evaluate the shear bond strength of composite to enamel with and without the application of an ACP paste (MI-Paste, GC).  Methods: Eighty enamel sections were obtained from human third molars and mounted in PVC pipe.  A small area of the enamel was flattened using 600-grit silicon-carbide paper.    Half the specimens were left untreated (control) and half were treated with MI-Paste for 35 minutes, two times daily for 30 days. Specimens were rinsed and stored in artificial saliva at 37⁰C.  The specimens were divided into eight groups and bonded with four different bonding agents (Scotchbond Multi-Purpose, 3M/ESPE; Optibond Solo Plus, Kerr; Clearfil SE, Kuraray; Clearfil Tri-S, Kuraray).  Each bonding agent was placed on enamel specimens with and without prior treatment with MI Paste (n=10).  The bonded specimens were placed in a jig (Ultradent).   The composite (Filtek Supreme Plus, 3M/ESPE) was inserted into the mold in 2mm increments to a height of 3-4mm and cured for 20 seconds per increment.  All specimens were stored 24 hrs in 37⁰C distilled water and tested in shear in a universal testing machine (MTS Insight).  A mean shear bond strength value (MPa) and standard deviation was determined per group.  See table below.  Data was analyzed with 2-way ANOVA/Tukeys (alpha=0.05).  Results:  The 2-way ANOVA found a significant difference between groups based on surface treatment (p<0.001) but not on bonding agent (p=0.05) with no significant interaction (p=0.113).  Conclusions:  ACP (MI Paste) significantly reduced the shear bond strength of composite to enamel.