INTRODUCTION

The prevalence of noncarious cervical lesions (NCCLs) varies from 5% to 85% and has been increasing in recent years due to an aging population, especially in premolars.^1-5 Among the main dental materials used for the treatment of NCCLs are resin composites. They are used to protect the affected teeth against the loss of a healthy tooth structure, to improve esthetics, and to treat dental hypersensitivity, as well as when the affected tooth is used as lateral support for a removable partial denture.^6,7

Treatment of NCCLs remains a major challenge for dentists, and studies have reported that the retention loss of NCCLs can vary from 0% to 50%.⁸ Restoration loss especially occurs because of the difficulty of dental material adhesion;⁹ a high degree of sclerosis can exist, and a high amount of minerals can impair the adequate establishment of a hybrid layer.^6,8 Besides, many studies have reported the loss of retention and marginal discoloration after cervical restorations with resin composites.^8,10 To minimize these problems, tooth surface treatment has been suggested to improve resin composite adhesion in NCCLs.^11-13

The surface treatment techniques that were proposed include surface irrigation with EDTA, adhesive application with a frictional technique, and drying the dentin before adhesive application.^11,13-15 Some studies have already evaluated the effects of surface treatment on NCCL treatment, but a question still remains about whether clinicians should consider using these approaches to improve the adhesion of resin composites. Therefore, the aim of this study was to analyze the influence of dentin surface treatments on the retention rate of resin composite restorations in NCCLs. Our hypothesis evaluated whether surface treatments could improve resin composite retention.

METHODS AND MATERIALS

The protocol of this review was registered in the PROSPERO international database for systematic reviews (CRD42014010018). This systematic review is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA Statement).¹⁶ To formulate the question from evidence-based practice, the following PICO (Population, Intervention, Comparison and Outcomes) was established: the population was patients who present with NCCLs; the intervention was dentin surface treatment (any nonconventional procedure performed prior to resin composite restoration, such as surface irrigation with EDTA, adhesive application with a frictional technique, drying the dentin before adhesive application); the comparison was teeth without dentin surface treatment; and the outcome was retention rate (complete or partial loss of the restoration). The research question was as follows: Does dentin surface treatment improve the retention rate of resin composite restorations in NCCLs?

Search Strategies

The literature search was carried out by two independent reviewers of studies published from 1940 to December 2016. Eight databases were screened, including PubMed (Medline), Lilacs, Ibecs, Web of Science, BBO, Scopus, Scielo, and The Cochrane Library, using the search strategy developed for PubMed (Medline) and adapted for other databases (Table 1). The references cited in the included papers were also checked to identify other potentially relevant articles. After the identification of articles in the databases, the articles were imported into Endnote X7 software (Thompson Reuters, Philadelphia, PA, USA) to remove duplicates.

Table 1 Search Strategy Used in PubMed (MedLine)

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Study Selection

Two authors independently assessed the titles and abstracts of all the documents. The studies were analyzed according to the selection criteria described in Table 2. Full copies of all the potentially relevant studies were identified. Those appearing to meet the inclusion criteria or for which there were insufficient data in the title and abstract to make a clear decision were selected for full analysis. The full-text papers were assessed independently and in duplicate by two authors. Any disagreement regarding the eligibility of the included studies was resolved through discussion and consensus or by a third reviewer. Only papers that fulfilled all eligibility criteria were included.

Table 2 Inclusion and Exclusion Criteria

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Data Extraction

The data were extracted using a standardized form. If there was some information missing, the authors of the included papers were contacted via e-mail to retrieve any missing data. The following data were tabulated: study design, publication year, country, number of patients, gender, age, evaluation criteria, follow-up (months), and number of teeth evaluated (Table 3). The characteristics of the included studies, such as selection criteria, surface treatment, control group, and restoration characteristics (brand, company and country), were also analyzed (Table 4).

Table 3 Description of Demographic Data, Study Design, and Main Objectives of Included Studies

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Table 4 Main Characteristics of the Included Studies

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Table 4 Main Characteristics of the Included Studies (ext.)

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RESULTS

Search Strategy

A total of 4040 potentially relevant records were identified from all the databases, of which 1046 were duplicates. No additional studies were identified as relevant after a search of the reference lists. Figure 1 is a flowchart that summarizes the article selection process according to the PRISMA Statement.¹² After the title and abstract examination, 2971 studies were excluded because they did not meet the eligibility criteria. Of the 23 studies retained for detailed review, 16 studies were not included because 11 evaluated the restoration material without surface treatment^19-29 and five papers were in vitro studies.^30-34 A total of seven studies fulfilled all of the selection criteria and were included in the qualitative analysis.

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Risk of Bias of Included Studies

Concerning the quality assessment (Figure 2), these studies presented a low risk of bias for most of the biases that were analyzed. Only two studies^13,14 did not report blinding the participants and personnel, as well as blinding the outcome assessments.

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Meta-Analysis

A meta-analysis was performed for the six randomized clinical trials. Considerable heterogeneity was observed in this analysis (I²=55%). The analysis considering the mechanical removal of dentin surface with a bur (Figure 3A) and the application of an adhesive system in a frictional mode (Figure 3B) showed these treatments improved retention rates of the resin composite restorations in NCCLs (p<0.05). However, when considering only the application of an adhesive system in dry dentin compared with a control, no statistically significant differences were observed (Figure 3C).

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DISCUSSION

The hypothesis that was evaluated was accepted once our meta-analysis demonstrated that dentin surface treatments could improve resin composite retention in NCCLs. All studies were randomized, and in general, they presented a low risk of bias because the evidence obtained from them had high quality. Among the surface treatments suggested to improve resin composite retention, two studies evaluated the application of an adhesive system in a frictional mode.^12,26 Both studies reported that vigorous application of the adhesive system improved the retention of restorations in NCCLs. One of the studies compared two different frictional techniques, including a slight rubbing action and the vigorous application of adhesives, and the researchers concluded that the vigorous application could be a clinical approach to improve the retention of resin composite in NCCLs.²⁶ It was reported that this approach improved the bond strength of self-etch adhesives to enamel^37,38 and to dentin.^38–41 In dentin, the active adhesive system application may have improved smear layer dissolution, micromechanical interlocking and chemical interactions.⁴² Although clinical trials evaluating this approach are limited,¹⁴ the available literature suggests that adhesive application in a frictional mode could improve the retention rates of resin composite.

One of the factors that could compromise adhesion in NCCLs is the presence of dentin sclerosis, which consists of a hypermineralized dentin that has difficult resin composite adhesion.^6,43 It was reported that 54%, 22%, and 2% of NCCL presented mild, moderate, and heavy dentin sclerosis, respectively.² Alternative strategies for adhesion to sclerotic dentin have been recommended by previous researchers.⁶ It was observed that lesions were slightly roughened before adhesive system application showed lower loss rates of restoration compared with unroughened adhesives.^13,14 This difference probably occurred because these lesions had a high degree of sclerosis. In the present review, one study investigated the removal of the surface layer of sclerotic dentin through the use of a bur¹⁴ and showed no improvement in the retention and marginal staining after 24 months. On the other hand, one clinical trial showed that roughening the tooth surface with a bur prior to an etch-and-rinse or self-etch adhesive application improved retention rates after 8 years for adhesives used in both sclerotic and nonsclerotic dentin.¹³

Furthermore, many failures of restoration are due to the technique sensitivity of the adhesive systems, and some studies have questioned the technique of using moist dentin. It is necessary to preserve demineralized dentin to allow adequate resin monomer infiltration, and this sensitivity technique is a major challenge for students or inexperienced dentists.^44–46 Due to these disadvantages, other dentin surface treatments that were evaluated included the application of an adhesive system over dry and moist dentin.^15,35 It was suggested that the maintenance of demineralized dentin in a dry state could minimize the negative effects of water on hybrid layer formation.¹⁵ Additionally, universal adhesives were evaluated in two studies, and they were applied in self-etch, etch-and-rinse, and selective enamel etching modes, which allowed the clinician to decide on a specific adhesive protocol that was best suited for the cavity that was being prepared.⁴⁶ Studies that evaluated the application of these adhesives in etch-and-rinse or self-etch modes,^15,35 both in moist and dry dentin, demonstrated that the behavior of the adhesive was not dependent on the bonding strategy that was used after 18¹⁵ and 24 months.³⁵ Further studies with longer follow-up periods are needed to evaluate if dry dentin can increase the retention rate of resin composite in NCCLs.

Another method that was evaluated was the application of EDTA, which could dissolve the smear layer and permit a chemical bond between the primer/bond and the dentinal collagen and calcium.^47,48 As a consequence, better interaction of the adhesive with the sclerotic dentin might occur, which would improve the etching pattern and the interaction between self-etch adhesives and sclerotic dentin.^11,49,50 EDTA is widely recognized as an effective inhibitor of endogenous metalloproteinases (MMPs),⁵¹ and the application of 17% EDTA for two minutes could significantly reduce the activity of dentin MMPs.⁵² EDTA also chelates zinc and calcium ions that are essential for MMP activity.^53,54 In vitro studies have reported promising results after preliminary conditioning with EDTA, which produced a shallow demineralization of the dentin.^49,50 In this review, one study evaluated the application of 17% EDTA for two minutes prior to adhesive application and showed a significant increase in the retention rates of composite restorations in NCCLs after 18 months.¹¹ It is reported that EDTA could improve adhesion of the self-etch adhesives to sclerotic dentin^49,50,55 by producing selective dissolution of hydroxyapatite and “kidnapping” the metallic ions presented in dentin,^56,57 enhancing the interaction of the self-etch adhesive with the tissue.^49,50,55

The studies also varied in terms of the evaluation methods used for clinical assessment of the restorations of NCCLs. Most studies used the USPHS and FDI criteria.⁵⁸ The USPHS mainly evaluated marginal adaptation staining, retention, fracture, marginal discoloration, postoperative sensitivity and recurrence of caries,^13,26,35 whereas FDI evaluated esthetic properties (staining margin), functional properties (fractures and retention, marginal adaptation), and biological properties (postoperative sensitivity, secondary caries).^11,12 We used the outcome “retention rate” that both criteria analyzed, which allowed the comparisons. A recent study¹⁵ that compared both methods concluded that the FDI criteria were more sensitive to small variations in the clinical outcomes than were the USPHS criteria when evaluating restorations of NCCLs.

One limitation of our review is that the included studies presented substantial heterogeneity, which was probably due to the different surface treatments that were evaluated, follow-up periods, evaluation criteria, materials that were tested and outcomes that were assessed. This high heterogeneity and the small amount of studies regarding surface treatment in NCCLs made other comparisons difficult. Furthermore, an important factor that influences retention of NCCL restoration is the kind of adhesive system (etch-and-rinse or self-etch) used. However, due to the small number of included studies, the results of this study could not be controlled for this confounder. Further studies comparing different dentin surface treatments need to be performed to determine the best treatment option that can improve the longevity of resin composite in NCCLs.

In summary, the influence of dentin surface treatment in the retention rates of resin composite restorations in NCCLs was dependent on the strategy that was used. The application of an adhesive system in a frictional mode and the mechanical removal of dentin surfaces with a bur improved retention rates of resin composite restorations in NCCLs. Although the meta-analysis demonstrated a positive effect of treatment, only a few studies were already available in the literature, and further clinical trials are needed to determine the best treatment option. Additionally, there was not enough evidence to support this conclusion over longer-term follow-up, as the majority of included studies evaluated the outcomes for up to 24 months.

CONCLUSIONS

There is evidence in the literature suggesting that the mechanical removal of dentin surfaces with a bur and the application of an adhesive system in a frictional mode may improve the retention rates of resin composite restorations in NCCLs. However, the studies showed high heterogeneity, and additional clinical trials are needed to compare different strategies in longer-term follow-ups and determine the best treatment option for resin composite in NCCLs.