Twenty-four-month clinical performance of different universal adhesives in etch-and-rinse, selective etching and self-etch application modes in NCCL – a randomized controlled clinical trial

Abstract Objective The aim of this randomized, controlled, prospective clinical trial was to evaluate the performances of two different universal adhesives and one etch-rinse adhesive for restoration of non-carious cervical lesions (NCCLs). Material and Methods Twenty patients with at least seven NCCLs were enrolled. Lesions were divided into seven groups according to adhesive systems and application modes: GSE: GLUMA Universal-self-etch, GSL: GLUMA Universal-selective etching, GER: GLUMA Universal-etch-and-rinse, ASE: All-Bond Universal-self-etch, ASL: All-Bond Universal-selective etching, AER: All-Bond Universal-etch-and-rinse, SBE (Control): Single Bond2-etch-and-rinse. A total of 155 NCCLs were restored with a nano hybrid composite (Tetric N-Ceram). Restorations were scored with regard to retention, marginal discoloration, marginal adaptation, recurrent caries and post-operative sensitivity using modified United States Public Health Service (USPHS) criteria after one week, 6, 12 and 24 months. Statistical evaluations were performed using Chi-square tests (p=0.05). Results The recall rate was 81.9% after the 24-month follow-up. The cumulative retention rates for self-etch groups (GSE: 72.2%, ASE:75%) were significantly lower than other experimental groups (GSL: 93.7%, GER: 100%, ASL: 94.1%, AER: 100%, SBE: 100%) at the 24-month follow-up (p<0.05). Regarding marginal adaptation and marginal discoloration, GSE and ASE groups demonstrated more bravo scores after 6 and 12-month observations but differences were not significant (p>0.05). Only one restoration from ASL group demonstrated post-operative sensitivity at 6 and 12-month observations. No secondary caries was observed on the restorations at any recall. At the end of 24-month observations, no significant differences were detected among groups regarding any of the criteria assessed, except retention. Conclusion GLUMA Universal and All-Bond Universal showed better results in etch-and-rinse and selective etching mode compared to the self-etch mode regarding retention. Etch-and-rinse and selective etching application modes of the current universal adhesives tended to provide better clinical outcomes considering the criteria evaluated at the end of 24-month evaluation.


Introduction
Despite many patients following oral-hygiene instructions carefully, non-carious cervical lesions (NCCLs) have increased among patients in various age populations. 1 NCCLs are typically seen on the gingival third of the tooth, where the enamel is thinner and the enamel-dentin bond is weaker than in other regions, facilitating substance loss via erosion abrasion and abfraction. 2 Treatment of NCCLs is necessary because thermal and pH changes can cause severe hypersensitivity. 3 Various treatments are used to manage NCCLs, including surface-modifying agents and toothpastes that occlude dentinal tubules on superficial lesions. For moderate and deep lesions, the only option to eliminate the clinical symptoms and prevent further loss of tooth structure is restoration, usually.
Composite resin systems are often used for NCCL restoration because, due to their adhesion mechanism, they can be applied directly to these lesions without the need for retentive cavity preparation. 4 On the other hand, NCCLs typically consist of sclerotic dentin, which can prevent maximum adhesion due to its acidresistant nature. Nevertheless, self-etch adhesives may not be suitable for highly sclerotic surfaces. 5 Despite the negative effects of etch-and-rinse adhesive systems, including technical sensitivity and a greater number of steps, they appear to be more reliable than self-etch adhesives. 6,7 However, self-etch adhesives are being widely adopted, as they are more user-friendly, have a reduced number of steps and eliminate the need to use phosphoric acid. 8 Nevertheless, clinical trials have indicated that self-etch adhesives have higher rates of marginal discoloration than etch-andrinse systems and negatively influence the aesthetic appearance of restorations. 7,9 In addition, the relatively low enamel bonding strength of self-etch adhesives remains a problem; selective etching of enamel has been suggested as an option to overcome the poor enamel bond strength of self-etch adhesives and improve their clinical success.
Over the past decade, universal adhesives have been introduced to allow clinicians to choose application modes appropriate for a given situation.
These adhesives can be used in etch-and-rinse, self-etch, or selective etching modes, thus allowing clinicians to make their own judgment for different cases. Universal adhesives can also provide adhesion to multiple substrates other than tooth surfaces, including resin composites, metals, zirconia, and silicabased ceramics. 10 The current philosophy of simplifying the application process, saving time, and eliminating errors that may arise from multiple steps, has also led to the manufacturing of universal adhesives. Although these new-generation adhesives are promising, they have been subjected to only a few clinical trials considering their long-term results. 6,11 This randomized, controlled clinical study compared two different universal adhesives in three application modes in restoration of NCCLs after 24 months. The null hypothesis was that there would be no differences among study groups regarding retention, marginal discoloration, marginal adaptation, postoperative sensitivity, and secondary caries based on the United States Public Health Service (USPHS) criteria.

Patient selection and study design
This was a randomized, controlled clinical trial.

Restorative procedures
Patients received dental prophylaxis and oral hygiene instructions 1 week before treatment. Twenty participants with a mean age of 49 years (age range 36-63) received 155 restorations.
All of the NCCLs were restored by the same operator. At least seven lesions were restored at each patient seen, and randomization of different adhesivesystem groups was performed using a random number table. Another clinician who was not involved in the research protocol prepared the details of the allocation. A rubber cup in a slow-speed handpiece was used to clean all lesions before restoring. Afterwards, the lesions were washed and dried, but not desiccated. The NCCLs were isolated by cotton rolls before application.
The adhesive and restorative materials were placed according to the manufacturers' recommendations ( Figure 1). All lesions were isolated using cotton rolls before restoring.

Results
In total, 155 restorations of NCCLs were performed in 20 patients (13 female, 7 male) ( were at the maxillary arch, at premolars (54.1%). The characteristics of NCCLs are shown in Table 3. Recall rates were 100% at the 6-and 12-month evaluations and 81.9% at the 24-month evaluation.

Retention rates
All of the restorations in the etch-and-rinse groups (GER, AER, and SBE) were scored as Alpha for retention at the 6-, 12-, and 24-month visits (

Marginal adaptation
With regard to marginal adaptation, the GSE and ASE groups tended to receive more Bravo scores at 6 (55.6%, 47.1%), 12 (62.5%, 50%), and 24 months (76.9%, 58.3) than the other groups. However, the differences among the groups were not statistically

Secondary caries
No secondary caries were found in any of the restorations during the 24-month evaluation period.

Discussion
In this study, when universal adhesives with self- The provisional acceptance criteria for enamel and dentin adhesives according to the American Dental Association (ADA) are maximal 5% restoration loss or microleakage at a 6-month recall. 11,12 In addition, the cumulative incidence of clinical failures should be tested in two independent clinical studies, and failure rates at 18 months must be lower than 10% for retention and microleakage. In this study, GLUMA Universal and All-Bond Universal adhesives had rates of retention loss in self-etch mode higher than the rates considered acceptable by the ADA. Similar to our findings, Brackett, et al. 18 20 Universal adhesives have been developed from self-etch adhesives and are referred to as "multimode" because they can be used in self-etch, selective etch, and etch-and-rinse modes on various adherent substrates, including enamel, dentin, metal alloys, and ceramics. 21,22 Laboratory studies that evaluated In addition, thin layers of adhesives are more sensitive to inhibition of polymerization by oxygen. 28 One clinical trial reported that an acetone-based adhesive system had a lower retention rate than an ethanol-based adhesive system at 36 months, and did not meet the ADA requirement for an acceptable failure rate. 7,29 However, this study showed no differences between ethanol-and acetone-based universal adhesives in any of the criteria examined during the 24-month evaluation.
The acidity of adhesives also differs, which may affect clinical performance. An in vitro study 30 investigated a self-etch adhesive with a mild pH in different modes (etch-and-rinse and self-etch) and found that the self-etch mode results were inferior to those of the etch-and-rinse mode. Conversely, a systematic review 31 of the clinical performance of adhesives found that mild two-step self-etch adhesives resulted in the best clinical bonding effectiveness in NCCLs, whereas the results for strong self-etch (pH<1.5) and two-step etch-and-rinse adhesives were unsatisfactory. One long-term clinical study compared a strong self-etch adhesive to a mild self-etch adhesive and concluded that there was no significant difference in their performance at 6 years. The present study found no difference between mild (GLUMA Universal) and ultra-mild (All-Bond Universal) universal adhesives used in self-etch mode.
An important finding of this investigation was that the rates of marginal discoloration were especially high in restorations placed using universal adhesives in self-etch mode, which was attributed to the lower bonding ability of self-etch adhesives to unetched enamel than to etched enamel. 32 In addition, the methacrylate copolymers in the resin composites are hydrophilic, which causes water sorption from the oral environment when exposed externally to salivary fluids and internally to underlying hydrated dentin. 33  Although the evaluation period in their study was longer than in the present study, their results are consistent with our findings. In contrast, Lawson, et al. 6 (2015) reported that Single Bond Universal showed similar results in both etch-and-rinse and self-etch modes at a 24-month evaluation. The retention rates for selfetch mode at 36 (89%) and 24 months (94.9) were very high compared to the present study. Although

Conflict of Interest
The authors declare no conflicts of interest.