Mechanical properties and the hierarchical structure of bone

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

http://webdelprofesor.ula.ve/odontologia/robertramirez/PDF/17.pdf

Resin composite--state of the art.

Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature

OBJECTIVES
The magnitude and kinetics of polymerization shrinkage, together with elastic modulus, may be potential predictors of bond failure of adhesive restorations. This study examined these properties in visible-light-cured resins, in particular new flowable composites and filled adhesives.


METHODS
Polymerization shrinkage values were obtained by digital video imaging before and after light-curing; shrinkage kinetics were obtained by the "deflecting disk" method and the elastic modulus by analysis of the fundamental period of vibration.


RESULTS
Flowable composites generally showed higher shrinkage than traditional non-flowable composites, while more densely filled adhesives presented lower shrinkage than lightly filled or unfilled resins. The elastic moduli of flowable composites were in the low-medium range, whilst the hybrid composites showed the highest values and the microfilled the lowest. More densely filled adhesives were more rigid than lightly filled and unfilled adhesives. The kinetics behavior was material dependent, mainly characterized by the coefficient of near-linear contraction between 10 and 40% of the final shrinkage and the time to reach 75% of the final shrinkage.


SIGNIFICANCE
The higher shrinkage of flowable composites over that of hybrids may indicate a potential for higher interfacial stresses. However, their lower rigidity may be a counteracting factor. The microfilled composite showed low shrinkage and low rigidity, a combination that may prove less damaging to the interface. As the kinetics parameters tended to be material specific, no specific class of materials should be seen as more stress inducing until studies determine the relative importance of each examined parameter. The performance of adhesive resins as stress buffers also remains unpredictable.

Polymerization shrinkage and elasticity of flowable composites and filled adhesives

A classification of dental composites according to their morphological and mechanical characteristics

Purpose To evaluate the microtensile bond strength (microTBS) of eleven contemporary adhesives to dentin, including three one-step self-etch systems, four two-step self-etch systems, three two-step total-etch systems, and one three-step total-etch system. Materials and methods Resin composite (Z100) was bonded to flat, mid-coronal dentin from 33 extracted human third molars using the adhesives strictly according to the respective manufacturer's instructions. After storage overnight in 37 degrees C water, the bonded specimens were sectioned into 3 to 6 slabs of approximately 1 mm thickness and 2.5 mm width. They were then trimmed into an hourglass shape resulting in an interface area of approximately 1 mm2, and subsequently subjected to microTBS testing with a crosshead speed of 1 mm/min. Results The microTBS varied from 30.0 MPa for the one-step self-etch adhesive Prompt L-Pop 2 (ESPE) to 63.1 MPa for the three-step total-etch adhesive OptiBond FL (Kerr), the latter being the only one that significantly differed from all other microTBS values. Although not significantly different, one-step self-etch adhesives tended to have lower microTBS than two-step self-etch and two-step total-etch adhesives. Specimen failures during sample preparation occurred with Prompt L-Pop 2 (4 pretesting failures out of 17 specimens) and NRC/Prime & Bond NT (7 pretesting failures out of 14 specimens). Conclusion Adhesives with simplified application procedures, either following a total-etch or self-etch approach, produced lower bond strengths to dentin than a conventional three-step total-etch adhesive. Some concern exists regarding the consistency in bonding effectiveness to dentin of some self-etch adhesives.

Guido Vanherle

Papers

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

Polymerization shrinkage and elasticity of flowable composites and filled adhesives

A classification of dental composites according to their morphological and mechanical characteristics

Microtensile bond strength of eleven contemporary adhesives to enamel

Adhesives and cements to promote preservation dentistry