Microtensile Bond Strength of Bonding Agents after High-Heat Storage

Objective:  To evaluate the effect of high-heat storage on the microtensile bond strength to dentin of three adhesive bonding agents (Clearfil SE, Kuraray; iBond, Kulzer; Optibond Solo Plus, Kerr).  Methods: The adhesive bonding agents were stored for one month at the manufacturer's recommended temperatures (refrigerated (4°C) for Clearfil SE and iBond, or room temperature (23°C) for Optibond Solo Plus). Simultaneously, the three adhesives were also stored at a high-heat temperature (43°C) in an incubator (Stericycle, Thermoforma) for one month.  Thirty extracted human third molars were divided into 6 groups of 5 teeth each.  Coronal enamel was removed (Isomet, Buehler) exposing a flat dentin surface.  The adhesives were placed according to the manufacturer's instructions and polymerized with a visible-light-curing unit (Bluephase 16i, Ivoclar). Composite (Z-250, 3M/ESPE) was incrementally placed and cured to approximately 4mm. The specimens were sectioned into 1x1mm-thick beams (Isomet 5000, Buehler).  Four beams were selected from each tooth (n=20). The beams were separated in tension by a universal testing machine (Instron Model 5543, Instron Corp) at a crosshead speed of 1 mm/min.  A mean (MPa) and standard deviation was determined per group. See table below. Data was analyzed with a two-way ANOVA/Tukey (alpha=0.05). Results:  A significant difference was found between storage conditions (p=0.001), but not between bonding agents (p=0.110).  However, a significant interaction was present (p=0.043).  T-tests were performed to determine differences between storage conditions within bonding agents (alpha=0.01).  Optibond Solo had significantly lower bond strength when stored in a high-heat environment (p=0.0003). Conclusions:  The effect of storage conditions was product specific.  One month of high-heat storage decreased the bond strength of Optibond Solo, but not iBond or Clearfil SE compared to storage conditions recommended by the manufacturer.