INTRODUCTION

Direct resin composite restorations in posterior teeth have increased worldwide,¹ either due to the prohibitions related to the use of mercury-based materials such as amalgam² or due to the increased aesthetic needs of the population.³ In this sense, a recent literature review showed that composite resin restorations are considered as the material of choice in dental schools around the world for restoring occlusal and occluso-proximal cavities in permanent teeth.⁴

Unfortunately, several clinical studies indicated that reported postoperative sensitivity (POS) after posterior resin composite restorations remains a challenge in dentistry.^5,6 The POS is related to many factors, such as the cavity preparation procedure, adhesive approach, type of resin composite used, and placement technique.^7–11

However, one of the most important factors related to the POS is the anecdotal clinical perception that use of phosphoric acid on dentin (when etch-and-rinse adhesives are applied) significantly increase the POS.¹² After etching and rinsing the dentin, the removal of the smear layer and the opening of the dentinal tubules increases the dentin permeability and their hydraulic conductance.¹³ After the adhesive system application, if the resin monomers did not correctly infiltrate in the demineralized dentin, voids occurred in the hybrid layer. Several studies showed that voids frequently occurred when the dentin was kept dry after phosphoric acid etching.^14,15 These unfilled spaces may allow dentin fluid movement, especially under external stimuli. This, in turn, sensitizes the nerve endings in the dentin tubules, and it may cause POS.¹⁶

The wet-bonding technique is a very simple technique to improve adhesive infiltration.¹⁶ In this technique, if the dentin demineralized matrix is kept fully hydrated by the clinician during the adhesive procedure, it will not cause a collapse of collagen fibrils, and free space will be available for resin infiltration.^14,15 Due to the intrinsically wet nature of dentin, it is necessary to use ethanol- or acetone-based adhesives.^15,17 Therefore, in the last three decades, wet-bonding has been the most popular technique to maintain an adequate degree of moisture for an etch-and-rinse adhesive.¹⁸

However, the popularity of wet-bonding techniques changed with the emergence of a new generation of adhesives called universal or multimode adhesives.^19,20 These adhesives are single-bottle adhesive systems similar to self-etch adhesives but include several acidic functional monomers, including 10-methacryloyloxydecyl dihydrogen phosphate (MDP) the most known among them. Functional monomers promote chemical bonding between the enamel and dentin and the indirect materials, such as glass ceramics, zirconia and metals, following a manufacturing of one product for application in different clinical situations.^21,22

To guarantee that MDP provides stable and durable interfaces, all universal adhesives must contain water, because water is essential for ionizing the acidic functional monomers that make self-etching possible.^17,23 Although, the exact amount of water content of the universal adhesives was not disclosed by the manufacturers, several studies have already claimed that universal adhesives contain approximately 10–25 wt% of water.^24–27

Due to the self-capacity of water to reexpand the air-dried and collapsed collagen mesh, for adhesive resin infiltration,¹³ keeping the dentin dry or moist after the phosphoric acid application does not make a difference in the universal adhesive’s bonding quality, which was observed in several recently published in vitro studies.^25–28 Furthermore, recent clinical studies in noncarious cervical lesions have shown that universal adhesive systems are less sensitive to dry and moist dentin, because no significant differences in terms of clinical performance (retention, marginal adaptation, or discoloration) were observed when MDP-based universal adhesives were evaluated through 3 years of follow-up.^29–33 However, all previously published clinical trials were performed on noncarious cervical lesions. Unfortunately, there is a huge regional variability of permeability, cavity format, and dentin moisture in the dentin of posterior restorations compared to the dentin walls of noncarious cervical lesions.³⁴ Therefore, it is very important to evaluate the effect of degree of dentin moisture (dry or moist) and the subsequent effect on the clinical performance of an MDP-based universal adhesive in posterior resin composite restorations.

Thus, this double-blind, randomized clinical trial evaluated the influence of dentin moisture on spontaneous and stimulated POS in posterior resin composite restorations using a universal adhesive applied in etch-and-rinse mode, after 48 hours, 7 days, and 6 and 12 months. In addition, the marginal discoloration, marginal adaptation, fracture, and recurrence of caries were evaluated by World Dental Federation (FDI) criteria after 6 and 12 months. The null hypotheses were: (1) dentin moisture does not influence the spontaneous and stimulated POS evaluated at different times (48 hours, 7 days, and 6 and 12 months) when compared to a universal adhesive applied in etch-and-rinse mode on dry dentin. (2) Dentin moisture does not influence the other evaluated clinical parameters (marginal staining, fracture, marginal adaptation, and the recurrence of caries) at different times (6 and 12 months) when compared to a universal adhesive applied in etch-and-rinse mode and used on dry dentin.

METHODS AND MATERIALS

Eligibility Criteria

Two pretrained dentists examined 63 participants to check if the subjects met the inclusion and exclusion criteria (Figure 1). The evaluations were performed using an intraoral mirror, an explorer, and a periodontal probe. Participants had to be in good general health, at least 18 years old, and present at least 20 teeth under occlusion and at least two carious lesions and/or indication of replacement restorations (fracture, secondary caries, and temporary restoration) in different hemiarches with depths ≥ 3 mm, which were diagnosed using an interproximal radiograph. As much as possible, we always tried to select participants with two cavities in the same hemiarch, the same cavity type, and the same number of cavity surfaces to be restored.

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Participants with dental prostheses, extremely poor oral hygiene, severe or chronic periodontitis, severe bruxism, parafunctional habits, continuous use of medication that may alter the perception of pain (analgesic, anti-inflammatory, etc.), and patients undergoing bleaching treatments or who were pregnant were excluded. Based on preestablished criteria, we selected 45 subjects who volunteered for this study (Figure 1).

Interventions: Restorative Procedure

The interventions were standardized by a detailed protocol, which is briefly summarized below. A preliminary dental prophylaxis of the tooth surface was performed with pumice and water in a rubber cup, with the aim of removing the salivary pellicle and any remaining dental plaque, followed by rinsing and drying. Using a shade guide, the proper shade of the resin composite was determined. Local anesthesia was applied with a 3% mepivacaine solution (Mepisv, Nova DFL, Rio de Janeiro, RJ, Brazil), and all restorations were placed under rubber dam isolation. The operators did not prepare any additional retention or bevel in the cavities.

All subjects received a minimum of two restorations, one from each experimental group, in different cavities previously selected according to the inclusion criteria. The cavity dimensions in millimeters (height, width, and depth) and the cavity geometry were also recorded. The cavity design was performed using a spherical diamond bur (#1013-1017; KG Sorensen, Barueri, SP, Brazil) mounted in a high-speed handpiece with an air–water spray. It was only applied for the removal of defective restorations or for the elimination of carious tissues (caries-infected dentin). No liner or base was used. For restoration of class II cavities, a sectional matrix system (Palodent, Dentsply Sirona) was preferentially used. However, circumferential matrix systems were used when a good adaptation could not be obtained with the sectional matrix system.

Then, an application of 34% phosphoric acid (Scotchbond Universal Etchant, 3M Oral Care, St. Paul, MN, USA) was conducted for 15 seconds in dentin/enamel, followed by rinsing with a dental syringe for 10 seconds. Afterward, in the groups assigned for dry dentin, all dentin surfaces were dried for 10 seconds at a distance of 2 cm between the tip of the air syringe and the dentin surface. At the end, the dentin surface was completely dry, without any signs of moisture. In the groups assigned for moisture dentin, only the excess water in the dentin surface was removed through air-drying for 2–4 seconds at a distance of 2 cm between the tip of the air syringe and the dentin surface. At the end, the entire dentin surface was shiny, because moisture was visible (Table 1).^29–31

Table 1: Adhesive System and Resin Composite: Composition and Application Mode

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The Single Bond Universal Adhesive (SBU; 3M Oral Care, also known as Scotchbond Universal in some countries) was shaken, and a small drop was put in a microbrush (Cavibrush, FGM, Joinville, SC, Brazil). Then, the microbrush was rubbed onto the surface of the dentin under manual pressure, followed by thinning with gentle air-drying for 5 seconds. At the end, the entire surface was light cured (Radii Cal, SDI, Victoria, Australia) for 10 seconds (1000 mW/cm²; Table 1). The resin composite Bulk Fill (3M Oral Care) was used in a single increment and photoactivated for 30 seconds (1000 mW/cm²; Radii Cal, SDI, Victoria, Australia). After finishing the restorations, the occlusal adjustment was carried out, and followed by finishing and a final polishing with fine-grained diamond tips FF (KG Sorensen, Barueri, SP, Brazil) and polishing with rubber bowls (Astropol, Ivoclar Vivadent, Schaan, Liechtenstein).

Examination After Restorative Procedure

Spontaneous POS was the primary clinical outcome analyzed, and it was assessed at 48 hours, 7 days, and 6 and 12 months, using the VAS and NRS, as previously described. The stimulated POS was also evaluated (secondary outcomes) at 7 days, 6 months, and 12 months. At each time, the restoration was evaluated for sensitivity caused by air application, vertical and horizontal percussion, and cold and heat stimulation, as described in the initial evaluation. The final values of spontaneous POS were divided into two categories: percentage of patients who reported POS at least once during treatment (absolute risk) and overall POS intensity over 48 hours, 7 days, 6 months, and 12 months. Furthermore, in the 6- and 12-month return visits, the clinical outcomes, such as marginal staining, fracture, marginal adaptation, and recurrence of caries, were evaluated using the World Dental Federation (FDI)^{37, 38} criteria (Table 2).

Table 2: World Dental Federation (FDI) Criteria Used for Clinical Evaluation (Hickel and others)^37,38

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Table 2: World Dental Federation (FDI) Criteria Used for Clinical Evaluation (Hickel and others)^37,38

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Characteristics of the Participants and Cavities

No modifications were performed in the experimental protocols, and they were implemented exactly as planned. Twenty-seven women and 18 men participated in this study. The mean age of the participants was 30.0 ± 8.20 years. Ninety restorations were placed, 45 for each group. The restorations were distributed into class I (75) and class II (15) cavities (Table 3). The homogeneity of cavity characteristics between the study groups can be seen in Table 3. Seven participants did not attend the 6 and 12 months recall, because they moved to another city (Figure 1).

Table 3: Characteristics of the Research Subjects, Dental Arches and Cavities Per Group

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RESULTS

POS Evaluation

A higher risk and intensity of spontaneous POS for both groups occurred up to 48 hours after restoration placement, with statistically significant differences for other evaluation times (Table 4, p<0.02; Table 5, p>0.01) However, no statistically significant difference was found for the risk and intensity of spontaneous POS in each period when dry and moist dentins were compared (Tables 4 and 5; p>0.58). It is noteworthy that, in a 1-week evaluation period, the intensity of spontaneous POS was considered mild when measured through the VAS and NRS scales (Table 5).

Table 4: Number of Patients with Spontaneous POS/Total During 12 Months of Follow-up, as well as the Absolute Risk of POS

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Table 5: Intensity of Spontaneous POS Experienced by Patients During 7 Days of Follow-Up

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After 1 week, 6 months, and 12 months, a few participants reported experiencing stimulus POS, with no statistically significant difference when dry and moist dentin were compared (Table 6; p>0.59). However, no participants needed to take oral medication to reduce POS. When the cavities’ characteristics were evaluated, the type of cavity, the number of surfaces, and the cavity depth did not show any significant differences (Table 7; p>0.58).

Table 6: Number of Patients who Experienced Provoked Pre- and Postoperative/Total to Different Stimulus in the Baseline and 7 Days Follow-Up

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Table 7: Number of Patients (%) who Experienced Spontaneous Postoperative Sensitivity up to 48 Hours Follow-up According to the Characteristics of Dental Arches and Cavities

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Other Clinical Parameters

Fourteen restorations showed small marginal discrepancies after the 12-month recall, with no statistical difference between the dry and moist dentin groups (Table 8; p=1.0). Five restorations showed some marginal fractures after the 12-month recall, with no statistical difference between the groups (Table 8; p=0.72). Five restorations showed some marginal discolorations after the 12-month recall. Once again, no statistical difference between dry and wet dentin groups was observed (Table 8; p=0.45). No restorations had recurrent caries at the 12-month recall (Table 8; p=1.0).

Table 8: Number of Evaluated Restorations for Dry and Moist Dentin Classified According to the World Dental Federation (FDI) Criteria (Hickel and others)^37,38

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DISCUSSION

The present randomized clinical trial evaluated POS, as well as the clinical performance of posterior bulk-fill resin composite restorations, associated with a universal adhesive applied in the etch-and-rinse mode in dry and moist dentin. The results of the present study showed that keeping the demineralizing dentin dry or moist did not significantly increase the spontaneous and stimulated POS in resin composite posterior restorations, leading us to accept the first null hypothesis. To the extent of the authors’ knowledge, this is the first study that evaluated the effect of dentin moisture on the clinical performance of resin composite in posterior restorations using a universal adhesive.

Several in vitro studies have shown that it is necessary to keep the dentin moist to achieve a proper adhesive infiltration in the demineralized dentin and, consequently, allow adequate sealing and high immediate bond strength values.^13–16 On the other hand, low bond strength values were achieved when adhesive systems were applied in dry dentin, mainly because there was shrinkage of collagen fibrils after the drying procedure.^13–16

However, universal adhesives seemed to have a different behavior when applied in dry and moist dentin.^{25,27,28,39,40} Universal adhesives can be used as a self-etch system, and the addition of water in their composition is important, because it ionizes the acidic groups, allowing the formation of hydronium ions, which etch hydroxyapatite.⁴¹ The water content of the universal adhesives is strongly related to the pH, because the water is essential for ionizing the acidic functional monomers, thus making self-etching possible.^17,41

According to the manufacturer, SBU contains approximately 10% of water.⁴² Perdigão and others³⁹ were the first to evaluate the effect of dry and moist dentin on the performance of SBU. The authors showed that the ultramorphology evaluation of the adhesive–dentin interface observed similar hybrid layer formation when SBU was applied in dry or moist dentin. The authors speculated that the water contained in SBU may be able to plasticize the collapsed collagen network, allowing for re-expansion and reopening of the interfibrillar spaces for the infiltration of resin monomers.⁴³ These results were recently confirmed through several studies.^25,27,28 For instance, Choi and others²⁵ and Tsujimoto and others²⁸ showed that the immediate bond strength and bond fatigue strength of SBU did not show any significant difference when dentin was kept dry or moist.^25,28

In addition, a second component of SBU, the presence of polyalkenoic acid copolymer, could be partially responsible for the similar clinical results observed in the present study. Actually, according to Sezinando and others⁴⁴, the presence of polyalkenoic acid copolymer in the SBU showed better immediate and 6-month bond strength results, when compared to an experimental SBU without this component. However, according to the manufacturer, the use of polyalkenoic acid copolymer provides a better moisture stability.^45,46 Therefore, we hypothesized that, due to the presence of polyalkenoic acid copolymer in the SBU, this adhesive is less sensitive to moisture variations, when dry or moist dentin conditions were simulated,^45,46 as occured in the present study. Future clinical studies need to be done to confirm this hypothesis.

All these characteristics of SBU help to explain the similarity of immediate POS, as well as POS after several times of evaluation, when the universal adhesive was applied in the dry or moist dentin. However, it’s important to mention that the spontaneous and stimulus POS was very low after 1 week, as previously demonstrated in recent clinical studies that evaluated the same commercial brand.^47,48 These results agree with a recent published meta-analysis of clinical studies,¹² indicating that POS generated immediately after placement of a restoration appears to be the result of trauma produced by restorative procedures, but usually this problem disappears after 1 week.^10,47

The percentage of POS in the present study was higher to that compared to a nonrandomized clinical study run by Guggenberger and others.⁴⁹ However, that data was only published as an abstract, which prevents us from evaluating the methodology and the underlying risk of bias of the study. Several important technical details (the type of cavity restored, resin composite, rubber dam use, finishing, and polishing procedure, etc) and study features (randomization, allocation concealment, blinding, outcome measurement, management of missing data, publication of the study protocol, etc) are not available for evaluation. All these characteristics are likely responsible for the differences between the present results and the results reported in that abstract.

Usually, the POS measured by randomized and independent clinical trials ^10,47,48 are higher than the percentage of POS measured by the studies conducted by manufacturers. The risk of POS sensitivity of bulk-fill composites, when associated to universal adhesives in randomized clinical trials, are quite variable in the literature. For instance, Tardem and others⁴⁷ and Yazici and others⁵⁰ showed lower rates of POS (2%–4%) than the present study. On the other side, the results of the present study are similar to Costa and others¹⁰ and Afifi and others,⁵¹ as they reported risk rates of 19% and 26%, respectively. Several methodological differences could explain these different results. Reis and others,¹² in a systematic review of POS in posterior restorations, observe a great variation among the way researchers assess the POS. This fact makes difficult the comparison between results of difference randomized clinical trials, and efforts need to be done to standardize the measurement of POS in posterior restorations.

It is worth mentioning that the enamel was also kept wet in the moist dentin group. In the past, dentists were taught to dry enamel vigorously after rinsing off the acid etchant in order to check for an adequately etched aspect of enamel.³⁶ This was not a concern when a universal adhesive was used, because, even with dry or moist enamel, some studies showed that there are not differences in terms of immediate and long-term bond strength as well as bond fatigue strength with the enamel.^27,28 Actually, no significant differences in terms of marginal discrepancies were observed at the 12-month follow-up when enamel or dentin margins were kept dry or moist, as well as other parameters, leading the authors to partially accept the second null hypothesis.

Furthermore, no significant difference was observed when dry and moist dentin were compared after 6 and 12 months of clinical evaluation, when other clinical parameters (fracture and recurrence of caries) were compared, leading the authors to partially accept the second null hypothesis. The present and previous studies indicate that the use of a bulk-fill resin composite could be considered an interesting alternative to restore posterior teeth. Unfortunately, the results of the present study are difficult to compare with the previous literature, because this is the first study to evaluate the effect of dentin moisture on the clinical performance of a universal adhesive associated with a bulk-fill composite. However, some studies showed similar clinical performance when evaluating SBU applied in moist dentin in posterior restorations in comparison with the present ones.^47,48

In general, the results of the present study in posterior resin composite restorations are similar to clinical studies of noncarious cervical lesions when SBU was evaluated.^29–31 In these studies, no significant clinical differences were observed when universal adhesive systems were applied in the etch-and-rinse mode in dry and moist dentin for 3 years after follow-up.^29–31 Despite all clinical differences, the results of the present study are in agreement with previous ones showing excellent clinical performances of SBU when posterior restorations, as performed in the present study, are compared with noncarious cervical restorations in terms of morphological and physiological differences.^34,50

Regarding the characteristics of the cavities, it was possible to show that the risk of spontaneous POS was not correlated with the complexity of the restoration (class I or II and the number of restored surfaces), which was previously observed in several studies.^7,9,51 Although it is expected that more extensive cavities (cavities with more surfaces involved) showed more POS when compared with more simple cavities, there is not a consensus in the literature,^7,9,51 because a fewer number of restorations has been evaluated. Related to the cavity depth, the same controversial results were found.^47,52 Future systematic reviews of clinical studies in posterior restorations need to be evaluate the effect of these variables (number of restored surfaces and cavity depth) to confirm the hypothesis.

There are some limitations in the present clinical study. Only short-term (6- and 12-month) follow-up results were described. Future long-term clinical evaluation needs to be done to confirm the effect of dry or moist dentin on other clinical parameters (marginal adaptation, marginal discoloration, fracture, and recurrence of caries, among others). In this study, only a universal adhesive was evaluated. Unfortunately, as each universal adhesive contains a specific composition, these results could not be extrapolated for all universal adhesives, specifically those with less water in their compositions.^25,27,28 Similarly, some studies showed that, if an over-wet dentin was simulated, the adhesive performance of SBU was affected.^26,53 However, the authors believe that the results of the present study will encourage researchers to investigate the same concept for other universal adhesive systems, and then a body of evidence will be produced around the concept of wet/dry dentin bonding for universal adhesives. Therefore, to increase the external validity of the concept herein demonstrated for other adhesive systems, other randomized clinical trials are recommended.

CONCLUSIONS

The moisture of dentin did not influence POS or the clinical performance in posterior bulk-fill composite restorations when associated with an MDP-containing universal adhesive applied in etch-and-rinse mode.