Adjunctive

Clinical Considerations in Adhesive Restorative Dentistry -- Influence of Adjunctive Procedures

Edmond R. Hewlett, DDS, and Charles F. Cox, DMD, PhD

Authors:

Edmond R. Hewlett, DDS, is an associate professor and vice chair of the Division of Restorative Dentistry at the University of California at Los Angeles School of Dentistry.

Charles F. Cox, DMD, PhD, is an associate professor in the Division of Restorative Dentistry at UCLA School of Dentistry.

Copyright 2003 Journal of the California Dental Association.

Several adjunctive procedures commonly performed during placement of adhesively bonded restorations can significantly influence a restoration’s immediate and long-term clinical performance and the maintenance of pulp vitality. This article reviews some of these procedures to highlight and characterize their potential effects on the restorative outcome and to offer suggestions for appropriately incorporating these procedures into routine clinical practice.

The complexity of resin/tooth adhesion and its numerous consequences for managing typical restorative procedures have been addressed in another article.1 In addition to issues related to inherent characteristics of the tooth substrates and adhesive systems, other variables merit consideration. Specifically, several adjunctive procedures commonly performed during placement of adhesively bonded restorations can significantly influence a restoration’s immediate and long-term clinical performance and the maintenance of pulp vitality. This article reviews some of these procedures to highlight and characterize their potential effects on the restorative outcome and to offer suggestions for appropriately incorporating these procedures into routine clinical practice.

Isolation of the Operating Field

Despite improvements in dental cements and adhesive resins, one aspect of adhesive restorative dentistry remains constant: Prevention of contamination by saliva or blood during critical steps of restoration placement is key to achieving an optimum outcome. Use of a rubber dam is still widely regarded as the most effective method of moisture control, in addition to improving visibility and access, protecting patients from aspirating or swallowing small objects, and reducing microbial transmission from patients to dental personnel (Figure 1). Even high intraoral humidity has been shown to adversely affect resin-dentin bonding, prompting yet another recommendation for rubber dam use.2,3 While some studies have suggested that survival of composite resin restorations is not necessarily enhanced by use of a rubber dam,4 the preponderance of opinion in this regard is to the contrary.5-8 Furthermore, rubber-dam isolation is not optional for air abrasion cavity preparation or CAD/CAM techniques, the latter involving direct optical imaging of prepared teeth for restoration with bonded ceramic. Evidence indicates that patients are generally not averse to rubber dam use and often prefer it for restorative procedures.9,10

Optional isolation methods include use of absorbent materials (cotton rolls, parotid shields) in conjunction with evacuator/retractor devices.11 Gingival retraction cord is also used in lieu of specialized rubber-dam retainers to improve isolation and access for cervical restorations. These methods are less effective than the rubber dam but may provide adequate moisture control in less demanding situations. In any event, field isolation during adhesive restorative procedures must be meticulously maintained.

Dealing With Contamination

The reality of day-to-day clinical practice is that saliva contamination during adhesive procedures will occasionally occur despite efforts to prevent it. It is therefore prudent to consider strategies for managing these occurrences based on interpretation of available scientific evidence. These strategies include utilizing indirect (ceramic, composite resin, cast gold) and/or nonresin-bonded alternatives (glass-ionomer restoratives and luting agents) if moisture control cannot be adequately established and maintained for direct resin procedures.

For resin bonding, it is recommended that saliva-contaminated etched enamel be rinsed, dried, and re-etched for 10 seconds.12,13 Acid-etched dentin, however, exhibits less sensitivity to saliva contamination, possibly due to the water content of saliva and the requirement of a moist dentin surface for optimum adhesion of many bonding resins.14-16 A one-second air blast to remove excess saliva without dehydrating the dentin produced bond strengths equivalent to those obtained with uncontaminated dentin.13 The long-term effect of biofilm incorporation at the dentin-resin interface under such circumstances has not been investigated.

Other reports indicate that bond strength to contaminated and re-etched dentin is similar to that for noncontaminated controls.17 In light of these various findings, it is the authors’ recommendation that etched/contaminated enamel and dentin both be dried and re-etched for a maximum of 10 seconds, with selective application of the etchant first to enamel, if possible, to minimize the additional acid contact with dentin. The rationale is that reapplication of the acid to the dentin is likely to solubilize salivary contaminants and facilitate their removal with rinsing.

Adhesion of composite resin to dentin is significantly reduced if saliva contamination occurs after adhesive application. This result was obtained for contamination of adhesive with saliva both prior to and after polymerization.18 Saliva contaminants were not rinsed off in this study. Unpolymerized adhesive resin presumably acts as at least a partial barrier to direct saliva contact with etched enamel and dentin by virtue of its hydrophobic properties. Removal of saliva and resin with a compressed air blast followed by reapplication and polymerization of the resin is therefore recommended. An exception, however, is the hydrophilic primer component of multiple-bottle adhesives. It is not likely that these solutions fit the hydrophobic barrier hypothesis. These products should therefore be avoided in favor of single-component adhesives or nonresinous materials in situations at higher risk for saliva contamination.

Contamination after polymerizing either the adhesive resin or a composite resin increment has also been shown to reduce bond strength to subsequent increments17 as well as fracture toughness of the final restoration.19 Removal of salivary contaminants from polymerized resin surfaces is thus recommended. As simple drying seems to be inadequate,17 scrubbing of the contaminated and dried surface with adhesive resin followed by resin thinning/removal with compressed air is offered as an empirical recommendation.

Caries Detector Dyes

Characterization of dentinal caries has revealed a zone of demineralization at the advancing front of the lesion that precedes actual bacterial infection of the substrate.20 A technique for using a basic fuchsin red stain to differentiate between the infected dentin and the bacteria-free demineralized zone was developed in the late 1970s21 and has given rise to several protein dye products marketed for caries detection. Designed to dye denatured collagen, these indicators are purportedly useful for facilitating thorough caries removal while preventing unnecessary removal of non-infected demineralized dentin. They also aid visualization of remaining caries in minimally invasive cavities when tooth structure is preserved at the expense of convenience form.

In vitro studies indicate that use of these dyes does not significantly affect composite bonding to enamel and dentin.22,23 A review of caries detector dyes,24 however, cites several studies that call the accuracy of these agents into question. Of particular concern is a tendency for the dyes to render false positives along the dentinoenamel junction25 and at circumpulpal sites.26 This differential uptake of stain was explained by the higher proportion of organic matrix normally present in these areas.26 Furthermore, due to lack of true specificity for caries among these dyes, absence of stain does not guarantee elimination of bacteria.

In light of these findings, clinicians are cautioned as to the potential for unnecessarily aggressive removal of dentin when a caries detector dye is used as the sole basis for this clinical decision.24 The value of tactile and visual means for caries detection should not be discounted. This issue underscores the highly variable nature of dentin as a resin bonding substrate, and, in the authors’ opinion, validates the routine use of the “sandwich technique” -- replacement of dentin with glass-ionomer -- in resin restorations involving deep caries excavations.1,27

Dentin Desensitizers

Various types of products are available for treatment of hypersensitivity associated with noncarious cervical lesions and gingival recession. Along with fluorides and oxalate crystal solutions, a third group of desensitizers can be described as dentin bonding derivatives. These typically consist of a hydrophilic resin primer (usually 35 percent HEMA) in solution with an antibacterial agent (chlorhexidine or benzalkonium chloride). In addition to topical application use, some of these derivatives are recommended by manufacturers for use in the total-etch dentin bonding protocol, typically applied to moist dentin between etching and priming, to reduce post-operative sensitivity. Anecdotal reports of their efficacy in this application are common, and this comes as no surprise. Application of these products to etched moist dentin is tantamount to priming, the additional antibacterial component notwithstanding. It is likely that a more thorough dentin hybridization is resulting, thus highlighting the importance of this critical step. It is also likely that the same effect can be obtained simply by extending the application time for the primer component of one’s adhesive system of choice. In spite of the apparent compatibility of HEMA-containing desensitizers and adhesive systems, isolated examples of material-specific incompatibility have been reported.28

Cavity Disinfection

Treatment of cavity preparations with commercially available antibacterial solutions is purported to reduce the incidence of postoperative sensitivity by elimination of viable bacteria and their toxins from the restorative interface. Chlorhexidine and benzalkonium chloride are again the commonly used active ingredients. Modes of use vary: before etching, after etching, rinsing off or not rinsing. The obvious question of effect on resin bond to dentin and enamel has been addressed with in vitro studies. Reports reflect a highly material-specific nature to this issue with significant effects on bonding in some cases.29,30 Use of a chlorhexidine cleanser before etching was shown not to affect bonding to enamel or dentin.31 Another study, however, reported reduced dentin bond strengths when a chlorhexidine cleanser was used before or after etching, but rinsing the cleanser off before bonding produced bond strengths similar to no-cleanser controls.32 Rinsing away cleansers prior to bonding will most likely prevent undesired material interactions.

Pulp Capping

Several classic direct pulp capping studies have reported on the biological success of calcium hydroxide (Ca(OH)2)-containing materials to promote pulp healing.33-38 Until the late-1980s, many researchers speculated on the unique capacity of Ca(OH)2 to “stimulate” dentin bridge formation following a pulp exposure. Other studies since that time, however, have demonstrated that in the absence of bacterial contamination, many restorative materials are biologically compatible against exposed pulps and can provide an environment conducive to dentin bridge formation.39-42

Concerns over pulp injury during “total etching” of enamel and dentin with phosphoric acid during routine resin restorative procedures have long been dispelled.43-48 The controversy of in vivo total etching and resin bonding of exposed pulps, however, continues.49-52 Data citing deleterious effects on pulp are in disagreement with many other studies that have reported soft-tissue healing followed by eventual dentin bridge formation after direct capping with total etch and resin bonding.39,47,49,50-57 Histologic and clinical data from these studies show that most adhesive systems are biologically comparable to Ca(OH)2 when placed onto exposed vital pulps provided that proper hemorrhage control, cavity disinfection, and prevention of microleakage around the final restoration have been accomplished.

Dentin bridges have been reported to contain multiple tunnel defects that allow for the migration of Ca(OH)2 particles and bacteria into the pulp tissues.39,58 Persistence of these particles (along with microleakage) causes immediate inflammation, which may eventually lead to necrosis and periapical pathology. Gwinnett and Cox likened the persistence of these Ca(OH)2 particles to the “passing of a bag of marbles down through successive generations of a family.”59 Additionally, the presence of resin globules in dentinal tubules and pulp tissues a few days after adhesive placement, and in giant cells of the pulp at 90 days, has been reported.60 TEM data from this study are similar to that of others that showed phagocytosis of Ca(OH)2 particles within various types of pulp cells subjacent to the exposure.61

Studies of pulp capping with different adhesive resin systems continue to convey varied findings, with some authors reporting poor-to-disastrous histological results and others reporting high rates of biological success with some of the same adhesive bonding systems. The cause of these disparate findings is unclear. One aspect of this dilemma is clear, however: When analyzing results from the numerous in vivo studies showing successful healing and dentin bridging, factors of technique-sensitivity continually emerge as most significant for the clinician to be aware of and manage.

Presence of dentin chip fragments and Ca(OH)2 particles62 and persistence of the coagulum-clot at the exposure site63 have been shown to disturb and alter the healing sequence of exposed dental pulps. Accordingly, the importance of cleaning the wound site to remove inflammation-producing debris and bacteria has been stressed.63-65 Effectiveness of a 3 percent to 5 percent solution of sodium hypochlorite (NaOCl) in this regard, as well as removing blood coagulum from pulp exposure sites, has been demonstrated.66-69 Furthermore, ongoing studies by Cox and colleagues indicate that proper clinical placement of a medical-grade NaOCl solution provides for control of pulp hemorrhage with no associated damage to the normal underlying tissues. The importance of hemorrhage control prior to adhesive resin bonding has been clearly shown.70 Presence of blood, pulp tissue exudates, or salivary proteins contaminating dentin will severely inhibit dentin-resin hybridization, allowing bacterial microleakage at the nonbonded interface, likely leading to pulp inflammation and eventual necrosis.

Summary

Procedural aspects of adhesive restoration placement can have greater influence on restoration longevity and pulp vitality than the choice of restorative materials used. Clinicians are urged to execute common adjunctive procedures such as those described here in an appropriate, meticulous manner to manage the technique-sensitivity inherent in adhesive restorative dentistry.

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Legend

Figure 1. The importance of effective isolation during adhesive restorative procedures cannot be overstated (photo courtesy of Dr. R.G. Stevenson, III).