Elsevier

Dental Materials

Volume 21, Issue 4, April 2005, Pages 375-383
Dental Materials

A randomized controlled study evaluating the effectiveness of a two-step self-etch adhesive with and without selective phosphoric-acid etching of enamel

https://doi.org/10.1016/j.dental.2004.05.008Get rights and content

Summary

Objectives:

The purpose of this randomized controlled clinical trial was to test the hypothesis that a two-step self-etch approach is equally effective to restore cervical class-V lesions as a self-etch approach with beforehand selective etching of enamel using phosphoric acid.

Methods:

Twenty-nine patients received two or four restorations randomly following two experimental protocols (‘paired-tooth’ study design): (1) A ‘mild’ self-etch adhesive (Clearfil SE, Kuraray) was applied following a self-etch approach on both enamel and dentin (C-SE non-etch); (2) Similar application of Clearfil SE, but including beforehand selective acid-etching of the enamel cavity margins with 40% phosphoric acid (C-SE etch). Clearfil AP-X (Kuraray) was used as restorative composite for all 100 restorations. The clinical effectiveness was recorded in terms of retention, marginal integrity and clinical micro-leakage after 2 years of clinical service.

Results:

No restoration losses were recorded. Clinical micro-leakage was slight and only rarely observed. No significant differences were found between both groups for the diverse parameters evaluated except for the number of small incisal marginal defects, which was significantly higher in the C-SE non-etch group (McNemar: p=0.0391).

Significance:

The clinical effectiveness of the mild two-step self-etch adhesive Clearfil SE was excellent after 2 years of clinical service. Although in general no difference in clinical performance was recorded when Clearfil SE was applied following either of the experimental protocols, more marginal defects at the enamel side were noticed when enamel was not beforehand etched with phosphoric acid. However, these defects were small and of clinically negligible relevance.

Introduction

Today's adhesives are applied following either an ‘etch and rinse’ or ‘self-etch’ approach [1]. Clinical trials have documented that reliable and relatively long-lasting adhesive restorations can be achieved using etch and rinse adhesives [2], [3], [4], [5], [6], [7], [8], [9]. Clinical trials investigating the effectiveness of self-etch adhesives is, however, limited [10], [11], [12], [13]. Self-etch adhesives nevertheless possess the clinical advantage that no intermediary rinse step is needed, making them more user-friendly and less technique-sensitive. Furthermore, as self-etching does not open the dentin tubules, but rather dissolves/infiltrates the tubule smear plug (in contrast to an etch&rinse approach that widely opens tubules), self-etch adhesives have been reported to induce significantly less post-operative sensitivity [11], [14], [15], [16], [17]. Among current self-etch adhesives, one- and two-step adhesives exist that depending on their acidity belong either to so-called ‘mild’ or ‘strong’ self-etch adhesives [1]. So far, a two-step application procedure outperforms the single-step procedure, as corroborated by many laboratory studies [1], [18], [19], [20], [21], [22], [23]. While a strong self-etch approach appears more favorable when bonding to enamel [1], a mild self-etch procedure that leaves hydroxyapatite within a submicron hybrid layer available for additional chemical interaction, warrants better bonding to dentin [1], [24].

Most concern remains regarding the enamel etching-capability of the relatively high-pH mild self-etch adhesives. Often in daily clinical practice, they are applied after first having selectively etched the enamel cavity margins with conventional 30–40% phosphoric acid. Indeed, mild self-etch adhesives demineralize enamel less effectively than conventional phosphoric acid-etchants that need to be rinsed off [25]. The literature is equivocal on this issue. Some studies have reported that self-etch adhesives bond less effectively to enamel than total-etch or etch&rinse systems that use phosphoric acid [26], [27], [28], [29]. Other studies have reported that both self-etch and etch&rinse adhesives perform equally well on ground enamel [25], [30], [31], [32], [33], [34]. Though the enamel-etch pattern resulting from a mild self-etch adhesive is less defined when compared to that resulting from phosphoric-acid etching [35], no correlation was found between enamel-etch morphology and shear bond strength to ground enamel [36].

Mild self-etch adhesives have also been reported to less effectively interact with dentin, in particular when prepared by a coarse-grit diamond that resulted in a rather compact, thick and thus relatively difficult to penetrate smear layer [37], [38], [39], [40]. In addition, with regard to bond durability, bonds produced by self-etch adhesives appear more vulnerable to degradation due to areas of increased permeability present at the hybridized adhesive–dentin interface complex [41]. Water was suggested to be incompletely removed and resulted in regions of incomplete polymerization and/or hydrogel formation, making the interface permeable and thus more degradation sensitive.

Though new in-vitro testing methodology tends to better predict clinical performance [1], [42], [43], clinical trials remain needed to ultimately evaluate the clinical efficacy of such self-etch adhesives. To date, clinical trials evaluating adhesives are, however, rather scarce, the main reason for which is that manufacturers often introduce a successor product to the market even before a trial on the precursor product has been completed. Another problem of clinical trials is the many clinical variables simultaneously involved [8], [44], making clear interpretations regarding clinical effectiveness of the adhesive itself often difficult or even not justified. The objective of this article is to report the 2-year results of a randomized controlled clinical trial investigating the clinical effectiveness of a representative mild two-step self-etch adhesive following a ‘paired-tooth’ study design. The actual hypothesis tested was that a two-step self-etch approach is equally effective to restore cervical class-V lesions as a self-etch approach with beforehand selective etching of enamel using phosphoric acid.

Section snippets

Materials and methods

The clinical effectiveness of Clearfil SE (Kuraray, Tokyo, Japan), representing the group of mild self-etch adhesives [1], was evaluated when applied strictly following a self-etch approach on both enamel and dentin (according to manufacturer's instructions; abbreviated as ‘C-SE non-etch’) and compared to the application of the same adhesive following the same application protocol, but after the enamel cavity margins were selectively acid-etched with 40% phosphoric acid (control; abbreviated as

Results

The clinical data for the diverse parameters evaluated are summarized in Table 2. Major parameters such as retention rate, perfect marginal integrity, absence of clinical micro-leakage, absence of sensitivity, absence of caries recurrence, preservation of tooth vitality and the overall clinical success rate are depicted as a function of time for the experimental and control group in the Fig. 1. The recall rate was 86% or higher at the different recalls for both experimental groups. Reasons for

Discussion

Non-carious mixed enamel/dentin class-V lesions were selected to test the clinical effectiveness of the two-step self-etch adhesive Clearfil SE in this study. Cervical lesions are regarded as the ideal cavities to test the clinical effectiveness of adhesives because (1) they present no macro-mechanical undercuts; (2) they require for at least 50% bonding to dentin; (3) when restored, they result in an enamel as well as dentin margin; (4) they are widely available; (5) they are usually found in

Conclusion

The clinical effectiveness of the mild two-step self-etch adhesive Clearfil SE was excellent after 2 years of clinical service. Although in general no difference in clinical performance was recorded when Clearfil SE was applied following either the experimental or control protocol, more marginal defects at the enamel side were noticed when enamel was not beforehand etched with phosphoric acid. However, these defects were small and of clinical negligible relevance. Long-term recalls are planned

Acknowledgements

This study was supported in part by Kuraray, by the fund No. KAN2002 1.5.142.02 ‘Krediet aan Navorsers’ of the Fund for Scientific Research of Flanders, and by the Toshio Nakao Chair with B. Van Meerbeek and P. Lambrechts awarded as chairholders.

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