The immediate bonding effectiveness of contemporary adhesives is quite favorable, regardless of the approach used. In the long term, the bonding effectiveness of some adhesives drops dramatically, whereas the bond strengths of other adhesives are more stable. This review examines the fundamental processes that cause the adhesion of biomaterials to enamel and dentin to degrade with time. Non-carious class V clinical trials remain the ultimate test method for the assessment of bonding effectiveness, but in addition to being high-cost, they are time- and labor-consuming, and they provide little information on the true cause of clinical failure. Therefore, several laboratory protocols were developed to predict bond durability. This paper critically appraises methodologies that focus on chemical degradation patterns of hydrolysis and elution of interface components, as well as mechanically oriented test set-ups, such as fatigue and fracture toughness measurements. A correlation of in vitro and in vivo data revealed that, currently, the most validated method to assess adhesion durability involves aging of micro-specimens of biomaterials bonded to either enamel or dentin. After about 3 months, all classes of adhesives exhibited mechanical and morphological evidence of degradation that resembles in vivo aging effects. A comparison of contemporary adhesives revealed that the three-step etch-and-rinse adhesives remain the 'gold standard' in terms of durability. Any kind of simplification in the clinical application procedure results in loss of bonding effectiveness. Only the two-step self-etch adhesives approach the gold standard and do have some additional clinical benefits.

http://www.endoexperience.com/documents/DeMunketalDurabiltyofadhesionJDR.pdf

A Critical Review of the Durability of Adhesion to Tooth Tissue: Methods and Results

Bonding to tooth tissue can be achieved through an "etch&rinse," "self-etch" or "glass-ionomer" approach. In this paper, the basic bonding mechanism to enamel and dentin of these three approaches is demonstrated by means of ultramorphological and chemical characterization of tooth-biomaterial interfacial interactions. Furthermore, bond-strength testing and measurement of marginal-sealing effectiveness (the two most commonly employed methodologies to determine "bonding effectiveness" in the laboratory) are evaluated upon their value and relevance in predicting clinical performance. A new dynamic methodology to test biomaterial-tooth bonds in a fatigue mode is introduced with a recently developed micro-rotary fatigue-testing device. Eventually, today's adhesives will be critically weighted upon their performance in diverse laboratory studies and clinical trials. Special attention has been given to the benefits/drawbacks of an etch&rinse versus a self-etch approach and the long-term performance of these adhesives. Correlating data gathered in the laboratory with clinical results clearly showed that laboratory research CAN predict clinical effectiveness. Although there is a tendency to simplify bonding procedures, the data presented confirm that conventional three-step etch&rinse adhesives still perform most favorably and are most reliable in the long-term. Nevertheless, a self-etch approach may have the best future perspective. Clinically, when adhesives no longer require an "etch&rinse" step, the application time, and probably more importantly, the technique-sensitivity are substantially reduced. Especially "mild," two-step self-etch adhesives that bond through a combined micromechanical and chemical interaction with tooth tissue closely approach conventional three-step systems in bonding performance.

Buonocore memorial lecture, adhesion to enamel and dentin: current status and future challenges

Systematic review of the chemical composition of contemporary dental adhesives

Dental adhesion review: Aging and stability of the bonded interface

http://webdelprofesor.ula.ve/odontologia/robertramirez/PDF/1.pdf

State of the art of self-etch adhesives

Two-year clinical effectiveness of a self-etch adhesive in cervical lesions

Tooth-cavity preparation contributes to a large extent to the quality of the direct posterior composite restoration, the so-called hidden quality of the restoration. Indeed, the effect of a poor cavity design is not immediately visible after placement of the restoration. To correctly prepare a cavity for a posterior composite restoration, the tooth to be restored should first be profoundly biomechanically analyzed. Here, the forces that work on the tooth during occlusion and articulation, and the amount and quality of the remaining tooth structure determine the cavity form. In addition, the dental tissues must be prepared in order to receive the best possible bond of the adhesive and subsequent restorative composite. A well-finished cavity preparation enables the restorative composite to adapt well, providing a good marginal seal to the direct benefit of the clinical lifetime of the posterior composite restoration. Finally, it is highly recommendable to isolate the teeth with rubber-dam before starting with the cavity preparation, as this increases the visibility of the operating field and allows the operator to work in a more precise way.

Effective Protocol for Daily High-quality Direct Posterior Composite Restorations. Cavity Preparation and Design.

PURPOSE To evaluate the effect of the type and concentration of photo-initiator on the long-term bonding efficacy to dentin in terms of mini-interfacial fracture toughness (mini-iFT). MATERIALS AND METHODS The bonding efficacy of the one-step self-etch (SE) adhesive Clearfil S3 Bond Plus and four derivative experimental adhesives (Leuven University Bond [LUB]), which were similar in composition except for the (co)photo-initiators (all prepared by Kuraray Noritake), containing 2.0 wt% camphorquinone (CQ) and 2.0 wt% EDMAB (LUB-CQ/amine_high), 0.35 wt% CQ and 0.35 wt% EDMAB (LUB-CQ/amine_low ), 2.0 wt% TPO (LUB-TPO_high), and 0.35 wt% TPO (LUB-TPO_low), was measured using a mini-iFT approach after being aged for 6 months and 1 year by water storage at 37°C (control: 1 week mini-iFT). The mini-iFT specimens were loaded until failure in a 4-point bending device to determine the interfacial fracture toughness (KIc). All fractured specimens were evaluated using scanning electron microscopy (SEM). RESULTS The mini-iFT of Clearfil S3 Bond Plus and the adhesives with high photo-initiator concentrations was not significantly different at 6 months, although it dropped significantly at 1 year. For each storage period, the mini-iFT of the adhesives with high photo-initiator concentrations was not significantly different from that of the commercial adhesive, in contrast to the significantly lower mini-iFT measured for adhesives with low concentrations of photo-initiator. SEM fracture analysis revealed that the adhesives with high concentrations of photo-initiator most frequently failed at the top of the hybrid layer at 1 week, while this failure pattern shifted to the bottom of the hybrid layer after aging. CONCLUSION A one-step self-etch adhesive should contain photo-initiator in a sufficiently high concentration, as this directly improves its immediate and long-term bonding efficacy to dentin. While the mini-iFT remained stable up to 6 month of aging for both the commercial and the adhesive with a high concentration of photo-initiator, the mini-iFT was found to decrease after 1 year of aging.

Bart Van Meerbeek

Papers

Two-year clinical effectiveness of a self-etch adhesive in cervical lesions

Effective Protocol for Daily High-quality Direct Posterior Composite Restorations. Cavity Preparation and Design.

Polymerization Efficacy Affects the Long-term Mini-interfacial Fracture Toughness.

The effect of a gradient of elastic modulus on the thickness of the hybrid layer

Adhesion to tooth enamel and dentin: a view on the latest technology and future perspectives