The limited durability of resin-dentin bonds severely compromises the longevity of composite resin restorations. Resin-dentin bond degradation might occur via degradation of water-rich and resin sparse collagen matrices by host-derived matrix metalloproteinases (MMPs). This review article provides overview of current knowledge of the role of MMPs in dentin matrix degradation and four experimental strategies for extending the longevity of resin-dentin bonds. They include: (1) the use of broad-spectrum inhibitors of MMPs, (2) the use of cross-linking agents for silencing the activities of MMPs, (3) ethanol wet-bonding with hydrophobic resin, (4) biomimetic remineralization of water-filled collagen matrix. A combination of these strategies will be able to overcome the limitations in resin-dentin adhesion.

The purpose of this study was to evaluate the effect of different etching times on microtensile bond strength (µTBS) to dentin both initial and after thermocycling with 3 different types of total-etching adhesives.

Fifty four teeth were divided into 18 groups by etching times (5, 15, 25 sec), adhesives types (Scotchbond Multipurpose (SM), Single Bond (SB), One-Step (OS)), and number of thermocycling (0, 2,000 cycles).

Flat dentin surfaces were prepared on mid-coronal dentin of extracted third molars. After exposed fresh dentin surfaces were polished with 600-grit SiC papers, each specimen was acid-etched with 35% phosphoric acid (5, 15, 25 sec) and bonded with 3 different types of total etching adhesives respectively. Then, hybrid composite Z-250 was built up. Half of them were not thermocycled (control group) and the others were subjected to 2,000 thermocycle (experimental group). They were sectioned occluso-gingivally into 1.0 × 1.0 mm² composite-dentin beams and tested with universal testing machine at a crosshead speed of 1.0 mm/min.

Within limited data of this study, the results were as follows

1. There was no statistically significant difference in µTBS between the thermocycled and non-thermocycled groups, except for both SM and SB etched for 25 sec.

2. In thermocycled SM and SB groups, bond strength decreased by extended etching time.

In total etching systems, adhesive durability for dentin could be affected by type of solvents in adhesive and etching time. Especially, extended etching time may cause deteriorate effects on bond strength when ethanol-based adhesive was used.

To evaluate the effect of vital tooth bleaching agent and alcohol pretreatment on dentin bonding, flat dentin windows were produced on the buccal side of the crowns of fifty-five extracted, human premolars. A bleaching gel, Opalescence® with 10% of carbamide peroxide (Ultradent Product, USA) was daily applied on the teeth of three experimental groups for six hours for 10 consecutive days, while teeth of a control group were not bleached. After 6 hours of bleaching gel application, the specimens were washed and stored in saline until the next day application. After application of One-step® dentin bonding agent (Bisco, USA), Z-250® resin (3M-ESPE, USA) was bonded to dentin with a mount jig. Shear bond strength was measured with an Instron machine (Type 4202, Instron Corp., USA) after 24 hours. The results were analyzed using one-way ANOVA and Duncan's multiple range test at p < 0.05.

Immediate bonding group showed significantly lower bond strength than un-bleached control group (p < 0.05).

Ethanol-treated group showed significantly higher bond strength compared to immediate bonding group (p < 0.05). However, the bond strength of the ethanol treatment group was lower than that of the un-bleached control group (p < 0.05).

There were no significant difference in shear bond strength between the 2-week delayed bonding group and the ethanol-treated group (p > 0.05) and between delayed bonding group and un-bleached control group (p > 0.05).

In the condition of the present study, it seems that alcohol pretreatment after bleaching procedure can reduce the adverse effect of vital bleaching agent on dentin bonding.