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.

	Microtensile Bond Strength MPa (st dev)
Bonding Agent	Recommended Storage	High-Heat Storage
iBond	50.50 (24.86)	40.10 (11.27)
Optibond Solo	47.54 (17.99)	27.95 (12.71)
Clearfil SE	43.50 (16.27)	42.44 (10.07)