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

Dental adhesion review: Aging and stability of the bonded interface

Incompletely infiltrated collagen fibrils in acid-etched dentin are susceptible to degradation. We hypothesize that degradation can occur in the absence of bacteria. Partially demineralized collagen matrices (DCMs) prepared from human dentin were stored in artificial saliva. Control specimens were stored in artificial saliva containing proteolytic enzyme inhibitors, or pure mineral oil. We retrieved them at 24 hrs, 90 and 250 days to examine the extent of degradation of DCM. In the 24-hour experimental and 90- and 250-day control specimens, we observed 5- to 6-microm-thick layers of DCM containing banded collagen fibrils. DCMs were almost completely destroyed in the 250-day experimental specimens, but not when incubated with enzyme inhibitors or mineral oil. Functional enzyme analysis of dentin powder revealed low levels of collagenolytic activity that was inhibited by protease inhibitors or 0.2% chlorhexidine. We hypothesize that collagen degradation occurred over time, via host-derived matrix metalloproteinases that are released slowly over time.

/pdf/collagen-degradation-by-host-derived-enzymes-during-aging-2jn0requum.pdf

Collagen Degradation by Host-derived Enzymes during Aging

The dentin substrate: structure and properties related to bonding.

This study compared the shear bond strengths of dentin bonding systems applied to air dried and blot (moist) dried dentin. Five systems with primers possessing hydrophilic properties were evaluated. Three contained acetone. All Bond, Amalgambond, Mirage Bond and Tenure all produced significant statistical improvement in shear bond strength values when applied to moistened dentin. Mirage Bond values quadrupled. Bond strength values with Gluma were compromised by the presence of moisture. It was concluded that acetone probably facilitated deeper and more complete penetration of resin into dentin to enhance micro-mechanical retention. Amalgambond, while free of acetone is strongly hydrophilic and is known to form substantial mechanical bonding through the formation of a resin rich superficial layer of dentin (hybridization). Gluma while hydrophilic does not appear to possess the same behavioral characteristics embodied in the other systems as evidenced from lack of a bond to moist dentin.

Moist versus dry dentin: its effect on shear bond strength.

Preservation of the morphological integrity of demineralized dentin collagen in its hydrated state may account for the success observed in wet-bonding procedures. This study investigated the micromorphological differences between moist- and dry-bonding techniques with the use of: (a) Aelitebond, an alcohol-based, water-free, single-component dentin adhesive primer system; and (b) a water-free, acetone-based experimental primer similar to the acetone-based, water-containing All-Bond 2, a two-component primer system. In the wet groups, acid-conditioned dentin surfaces were blotted so that they remained visibly moist prior to bonding. In the dry groups, dentin surfaces were air-dried for 30 sec. Following the bonding procedures, dentin discs in each group were laminated together by means of a chemical-cure resin and processed for scanning electron microscope (SEM) and transmission electron microscope (TEM) examination. Conditioning with 10% H3PO4 for 20 sec. produced complete demineralization of the outer de...

/pdf/resin-permeation-into-acid-conditioned-moist-and-dry-dentin-3gwsev4hlg.pdf

Resin Permeation into Acid-conditioned, Moist, and Dry Dentin: A Paradigm using Water-free Adhesive Primers:

The purpose of this study was to investigate the effect of air drying and remoistening of dentin on resin composite bond strength and to determine the extent to which the outermost, collagenous network and surface area of chemically conditioned dentin contributed to interfacial strength. Three components made up the experimental design: The first component comprised 12 experimental groups each containing 10 caries-free molar teeth. Shear bond strength values with dentin were measured for conditioned and non-conditioned dentin to which All-Bond 2 and BisFil were applied. The following values (MPa) were obtained for the groups conditioned with 10% phosphoric acid for 20 seconds: Group 1 (wet control) 24.20 +/- 2.03; Group 2 (10 seconds dried) 19.83 +/- 5.42; Group 3 (30 seconds dried) 11.56 +/- 4.93; Group 4 (10 seconds dried, 5 seconds. remoistened) 25.38 +/- 3.89; Group 5 (30 seconds dried, 5 seconds, remoistened) 24.66 +/- 4.54; Group 6 (5% NaOCl/wet) 25.97 +/- 3.61. For the non-conditioned groups the values were: Group 7 (wet control) 21.54 +/- 4.07; Group 8 (10 seconds dried) 14.62 +/- 3.55; Group 9 (10 seconds dried, 5 seconds remoistened) 16.95 +/- 4.04; Group 10 (5% NaOCl/wet) 13.67 +/- 4.39; Group 11 (air abrasive action) 18.78 +/- 3.62; Group 12 (air abrasive/5% NaOCl) 19.87 +/- 2.03.(ABSTRACT TRUNCATED AT 250 WORDS)

Dentin bond strength after air drying and rewetting.

PURPOSE To identify ultrastructural features resulting from possible primer-water interaction when a two-bottle, acetone- and alcohol-based dentin adhesive (All-Bond 2) was applied to acid-conditioned dentin in the presence of excess water. MATERIALS AND METHODS Three groups (3-second dry, visibly moist, overwet), each comprising eight dentin discs prepared from human third molars, were established and bonded with All-Bond 2 under different degrees of surface moisture. Variations in the ultrastructural appearance of the resin-dentin interface from laboratory demineralized and epoxy resin embedded disc pairs were examined either with en bloc ruthenium red pre-staining alone or further stained with uranyl acetate and lead citrate. RESULTS Displacement of water by the volatile primer solvents resulted in the formation of a layer of resin-impregnated dentin in the three groups. Interaction of the primer with water following the evaporation of the volatile primer solvents resulted in phase separation of the primer components. Ultrastructural features observed within the previously water-filled blister-like spaces on the dentin surface in the visibly moist and overwet groups recapitulated what was observed within partially water-filled dentin tubules in the 3-second dry group. The overwet phenomenon appeared to be a result of emulsion polymerization, involving irreversible interaction of water-soluble bifunctional primer components with those that are water-immiscible, through the formation of micelles, resulting in the absence of total interfacial integrity.

The overwet phenomenon : a transmission electron microscopic study of surface moisture in the acid-conditioned, resin-dentin interface

Using a stereoscopic clearing protocol and scanning electron microscopy, we investigated the extent and nature of microleakage in a total-etch, current-generation dentin adhesive by a wet-bonding technique under different handling conditions. The hypotheses were that inadequate light curing of the primer or incomplete drying of the primer solvent might adversely affect the sealing ability of an acetone-containing adhesive system. The study consisted of three experimental groups: (I) a control group with an adequate light source and with the primer solvent completely dried; (II) an "inadequate-light" group; and (III) an "incomplete evaporation of primer solvent" group. The extent of microleakage after silver staining and clearing of the specimens was scored based on a modified five-point scale. Nonparametric statistical analysis (Kruskal-Wallis ANOVA) followed by a multiple comparison test (Dunn test) indicated significant differences among the three groups (p < 0.05). SEM examination of the restorative interface revealed that microleakage appeared to be initiated from the bonding resin-hybrid layer interface in all three groups, representing the weak link in the adhesive system. In addition, microleakage was characterized by 5 zones, each delineating a stage in a continuous array of progressively deleterious microleakage patterns variously distributed among the three groups. It was suggested that, while the bonding resin-hybrid layer interface represented the intrinsic weakness in an already much improved dentin adhesive, extrinsic factors such as the adequacy of the curing light and, more importantly, complete removal of the primer solvents can and should be avoided to preserve the structural integrity of the marginal seal.

/pdf/variability-in-microleakage-observed-in-a-total-etch-wet-nkk2ejxf9r.pdf

Gwinnett Aj

Papers

Moist versus dry dentin: its effect on shear bond strength.

Resin Permeation into Acid-conditioned, Moist, and Dry Dentin: A Paradigm using Water-free Adhesive Primers:

Dentin bond strength after air drying and rewetting.

The overwet phenomenon : a transmission electron microscopic study of surface moisture in the acid-conditioned, resin-dentin interface

Variability in Microleakage Observed in a Total-etch Wet-bonding Technique under Different Handling Conditions