Three-Year Clinical Evaluation of Class I Restorations in Posterior Teeth. Effects of Two Adhesive Systems

Adhesive systems are used for adhering composite resin restorations to tooth structure, contributing significantly to the control of microleakage, retention, postoperative sensitivity, staining of the margins, secondary caries, and pulpal irritation.^3,4 Manufacturers are constantly improving composite resins and their companion adhesives, making adhesion less technique sensitive and more durable.^3,4 The first adhesive system employed was the 3-step etch-and-rinse, followed by 2-step etch-and-rinse system, both requiring a previous acid etching with phosphoric acid and commonly known as total-etch adhesives.⁴ The etch-and-rinse technique may induce some problems, such as the collapse of the collagen networks following the application of etching agent, over-etching of dentin, the necessity of rinsing and the correct interpretation of the wet or dry bonding.⁵ However, for enamel adhesion, an etch-and-rinse approach using phosphoric acid remains the preferred choice, because it not only guarantees the most durable bond to enamel, but also seals and thus protects the more vulnerable bond to dentin against degradation.⁶ Furthermore, Souza-Zaroni et al⁷ reported higher bond strength values to enamel compared to dentin, which certainly influences the restoration’s chances for survival.

Self-etching adhesive systems were developed to reduce the treatment time required⁵ and to eliminate the critical step of acid conditioning, as they contain acidic monomers that simultaneously condition and prime the dental substrate.^5,8 Therefore, this approach has the advantage of demineralizing and infiltrating the tooth surface simultaneously to the same depth, theoretically ensuring complete penetration of the adhesive^3,8 and reducing postoperative sensitivity.⁵ In addition, there is no ambiguity about the remaining moisture in dentin, as these systems contain water and are not dependent on surface moisture in dentin.⁵

Then, the main challenge for dental adhesives is to provide an equally effective bond to hard tissues, as an etch-and-rinse or a self-etch approach differs significantly in the manner they deal with tooth tissue.^5,8 In vitro studies offer important data regarding the chemical and mechanical properties of dental materials commonly used by professionals in daily practice; however, they are unable to provide a direct correlation with clinical trials. Clinical conditions that commonly present in the oral environment, such as the effects of oral-hygiene habits, the presence of microorganisms, changes in temperature, and the conditions related to masticatory stress, may significantly interfere with the durability of dental materials.⁹

Therefore, well-designed clinical studies are better able to provide useful data that closely resemble actual oral conditions regarding the performance of dental materials.⁹ When considering the development of adhesive dental materials, it is necessary to conduct clinical studies to confirm past results over time.^9,10 The aim of this study was to evaluate posterior class I resin composite restorations 3 years after placement, employing a 2-step etch-and-rinse system or a 2-step self-etching adhesive system restored with a nanofilled composite resin. The null hypothesis is that neither adhesive system would differ from each other after 3 years.

Materials and Methods

The clinical effectiveness of a two-step etch-and-rinse (Adper™ Single Bond Plus [SB] [3M ESPE, 3mespe.com]), a two-step self-etching (Adper Scotchbond™ SE Plus [SE] [3M ESPE]) and nanofilled resin composite (Filtek™Supreme Plus [FS] [3M ESPE]) was evaluated in direct Class I resin composite restorations. The factors studied were marginal discoloration, marginal integrity, secondary caries, and postoperative sensitivity measured at baseline and again after 3 years based on modified US Public Health Service (USPHS) criteria (Table 1).

The researchers selected the patients for this study from Araçatuba Dental School–UNESP-Brazil, employing the following inclusion criteria: (1) permanent premolars and molars requiring class I for treating primary or secondary carious lesions, (2) at least one neighboring tooth and in occlusion to antagonistic teeth, (3) good oral hygiene, and (4) presenting amalgam restorations or composite resin restorations that needed replacing due to fractures or esthetics. The exclusion criteria was: (1) fewer than 20 teeth, (2) poor hygiene, (3) heavy bruxism habits, (4) periodontal problems and known allergic reactions against any components of the used materials, (5) pathologic pulpal diagnosis with pain (nonvital), (6) fractured or visibly cracked teeth, (7) defective restorations adjacent or opposing to the tooth, (8) rampant caries, and (9) atypical extrinsic staining of teeth or staining of any existing tooth-colored restorations

Fifteen patients (10 females and 5 males) between 13 and 21 years old were recruited. After 3 years, 95 restorations (14 patients) were evaluated. One patient (with 2 restorations) moved to another city and had no availability to attend the follow-up. Two calibrated operators performed the restoration procedures following the manufacturer’s instructions. The procedures were explained to the patients, and a written informed consent to participate in the study was provided by the patient or by the parents/guardians of the patient, if not of consent age. The study was approved by the Ethics Committee of the institution (process no. 2008-01502).

Restorative Procedures

Each patient had at least one restoration performed with one of the adhesive systems. All restoration procedures were performed using local anesthesia and after dental prophylaxis with a slurry of pumice and water. A rubber dam was used for all restorations, and the cavity was opened or the existing restoration removed using a No. 1092 cylindrical diamond bur (KG Sorensen, kgsorensen.com.br) mounted in a high-speed water-cooled handpiece. Beveling was not performed at the cavosurface margin. When carious lesions were found, they were removed with hand instruments and low-speed spherical drills in sizes compatible with the lesions. Deep cavities received a thin layer of modified glass-ionomer Fuji II LC® (GC America, gcamerica.com) as a liner, following the manufacturer’s instructions.

For 48 cavities, SB, a two-step etch-and-rinse, was used. The remaining 49 cavities were treated with SE, a two-step self-etching adhesive system. The distribution of adhesive systems was randomly assigned to each patient, as for the tooth to be restored.

The materials were applied according to the manufacturer’s instructions, as follows.

SB system: The entire cavity was etched with 35% Scotchbond Universal Etchant (3M ESPE) for 15 seconds in dentin and 60 seconds in enamel and rinsed with water spray for 60 seconds. After drying, the enamel surface was left completely dry and the dentin remained moist. To achieve this clinical effect, the dentin tissue was protected with a small cotton pellet while the etched cavities were dried. Adper Single Bond Plus was applied using a disposable microbrush and light cured for 10 seconds using a halogen light source, UltraLux (Dabi Atlante, dabiatlante.com.br), with an irradiance of 450 mW/cm².

SE system: The cavity preparation was rinsed with water spray and air dried. No previous etching with phosphoric acid was performed. The SE system is comprised of Liquid A and Liquid B. Liquid A was initially applied to the cavity using a disposable microbrush, immediately followed by the application of Liquid B, which was applied to the cavity for 20 seconds under moderate pressure. The adhesive was air dried for 10 seconds. A second layer of Liquid B was applied and light cured for 10 seconds using the same halogen light source with an irradiance of 450 mW/cm².

FS: The resin composite was placed using the oblique layering technique, with each layer not exceeding 2 mm in thickness. Each increment was light cured for 40 seconds using a halogen light-curing unit (UltraLux) with an irradiance of 450 mW/cm².

The composition of materials used can be found in Table 2. Occlusal adjustment was performed as marked with carbon paper (AccuFilm®, Parkell, parkell.com). The restorations were finished with a No. 1190 diamond point (KG Sorensen), followed by the use of Enhance finishing points (Dentsply, dentsply.com).

Clinical Analysis

After placement, two calibrated examiners, who were not the operators but were blinded to the adhesive system used, performed the clinical evaluations at two different times: baseline (1 week after the procedure) and after 3 years in an appropriately illuminated operative field, using a No. 5 explorer and a buccal mirror. The examiners were calibrated before the baseline evaluation using patients from the graduate clinical dentistry clinic of this university. In the case of disagreement over assessments, the examiners had to reach a consensus for the factors of marginal adaptation, marginal discoloration, the presence of secondary caries, and postoperative sensitivity, using the modified USPHS criteria (Table 1).

Statistical Analysis

Between baseline and after 3 years, the results were compared using the proportion test at a significance level of 5% (P < .05). After 3 years, both groups were compared using the statistical non-parametric Mann-Whitney U-test with a significance level of 5% (P < .05).

Results

At baseline, all restorations received an Alpha score for the marginal discoloration and marginal integrity. After 3 years, marginal discoloration received an Alpha score for 53.19% of the restorations performed with the SB system and for 52.08% of those restorations performed with the SE system (Figure 1). Marginal integrity received an Alpha rating for 65.96% and 68.75% of the restorations performed with SB and SE systems, respectively (Figure 2). The remaining restorations received Bravo ratings for all variables. None of the restorations was categorized as Charlie or Delta or were lost at the 3-year evaluation. Postoperative sensitivity was observed in 8 restored teeth (5 SB; 3 SE) at baseline, but no sensitivity was found at the 3-year follow-up. Also, no secondary caries were verified around the restorations at the 3-year evaluation. The Alpha percentage score was calculated for the patients with both SB and SE restorations. The application of a percentage test found statistically significant differences when comparing the baseline and the 3-year values for marginal discoloration with the SB and SE systems; however, no statistically significant difference was observed for marginal integrity with both adhesive systems after 3 years.

At 3 years, the results were submitted to a Mann-Whitney U-test, with a significance level of 5%. The results demonstrated no statistically significant differences between the teeth restored with the SB and SE systems for marginal discoloration (P = .7880) and marginal integrity (P = .8132) at 3 years.

Discussion

The clinical success of adhesive restorative procedures is directly related to the use of an accurate technique of applying the adhesive system, including the steps for insertion, polymerization, finishing, and polishing.⁹ After 3 years, marginal discoloration decreased from a 100% Alpha score at baseline to 53.19% and 52.08% scores for SB and SE systems, respectively. Findings from previous reports also revealed an increase of marginal discoloration.^9,11

The SE system would result in a higher amount of marginal discoloration than the SB system due to the fact that self-etch adhesive system did not provide the same degree of enamel porosity and resin penetration as that created by phosphoric-acid etching,^3,12 leading to a general trend toward lower enamel bond strengths for self-etch adhesives when compared with etch-and-rinse systems.⁶ Interfacial staining may be the result of food pigmentation and/or a shallow enamel-etching pattern, which has been associated with a poor enamel etching ability of self-etch adhesives,¹³ even for the SE system.¹³

The SE system presents a pH level below 1 and, thus, can be categorized as a strong self-etch adhesive.¹⁴ A unique characteristic of the SE system is the color change during the successive application of the two liquids.¹⁴ Self-etching is initiated only as soon as the yellow acidic monomer solution (Liquid B) is applied and mixed with the HEMA-water solution (Liquid A).¹⁴ After air-drying to remove all excess water, Liquid B is reapplied as the actual adhesive resin,¹⁴ which is quite different from SB. That requires phosphoric acid to be followed by priming and bonding at the same time (second clinical step). TEM evaluation revealed a tight interface with distinct macrotags and microtags at enamel and resin tags at dentin for SE.¹⁴ Regardless of its different manner to bond to tooth tissues and chemical composition, the present study showed a similar clinical result for SB and SE after 3 years, revealing that both adhesive systems behaved similarly to each other in the face of oral challenges.

An excess of composite resin material beyond the conditioned cavity margin, known as “overfilling,” sometimes occurs.¹⁰ This undesired effect, even when slight, may contribute to the presence of small marginal fractures and staining, which could have led to Bravo scores for marginal integrity and discoloration. Also, during mastication, class I and class II restorations are submitted to higher mechanical stresses than class III, class IV, or class V. Crushing of hard foods on occlusal surfaces may have contributed to stresses at the overfilling area, increasing microleakage in enamel,¹⁵ which may be a reason that made marginal integrity and discoloration decline after 3 years. However, the restorations with Bravo scores were still considered clinically acceptable based on the rigorous criteria used and did not require repair or replacement.

The ratio of the bonded surface area to the unbounded or free surface area is called the cavity configuration, or C-factor.¹⁶ Cavities with high C-factors, such as class I, increase the risk for interfacial failures.^16,17 When polymerization shrinkage stress of resin composite is higher than bond strength, a rupture of the interface can occur.¹⁸ Therefore, the strength of the adhesive interaction with tooth structure should be able to counteract the polymerization stresses¹⁹ as it may cause deleterious effect on marginal integrity, gap formation, and damage the marginal seal of the bonded restorations.²⁰ Lower bond strength was reported in cavities with high C-factor¹⁸ and produced the highest gap formation.²¹ All together, these occurrences definitely could have affected the authors’ results by regarding marginal integrity and discoloration.

The use of the incremental technique certainly contributed to the good clinical results observed by Sundfeld et al⁹ and by the present evaluation, regardless of the adhesive system employed. It is important to consider that, after polymerization, class I cavity presents a three-dimensional configuration that favors the retention of restorative materials, unlike direct class IV and class V cavity designs, in which resin retention is obtained almost exclusively by the action of the adhesive system.²¹

Some restorations belonging to both adhesive systems showed slight postoperative sensitivity 1 week after the restorations (baseline), but no sensitivity was found at the 3-year follow-up. However, it has to be considered that when restoring cavities with high C-factor, the resultant stresses of composite shrinkage put resin-tooth interfaces under severe tension as there is less chance for relaxation of shrinkage stress.²² This stress causes cuspal deflection, which is associated with postoperative sensitivity due to composite polymerization shrinkage.²³ At the 3-year evaluation, no postoperative sensitivity was scored, possibly caused by hygroscopic expansion of resin composite, which was related as the main mechanism for shrinkage stress compensation.²⁴ Versluis et al²⁵ reported that polymerization shrinkage deformation was compensated by hygroscopic expansion within 4 weeks in teeth restored with Filtek Supreme Plus (3M ESPE), which may also reduce interfacial gaps and improve cavity sealing.

Restorations with secondary caries occurring 3 years after placement were not found for either adhesive system employed. The marginal imperfections, while receiving a Bravo rating, did not necessarily lead to secondary caries and revealed the successful sealing ability of both adhesive systems. Then, the null hypothesis was accepted.

Thus, it can be inferred that the clinical performance of direct class I resin composite restorations depends on the bond strength, type of bond presented by the adhesive system applied to the dental tissues, and the cavity configuration. In addition, the collaboration of patients significantly influences the longevity of restorations,⁹ a result that was observed in this study after 3 years. This certainly may have contributed to the similarities observed among the restorations analyzed after 3 years, which revealed no statistically significant differences between both the SB and SE adhesive systems. Even with the good results observed after 3 years, future assessments will be required for more precise conclusions, because marginal integrity and discoloration are affected by time.⁹ We should not exclude the possibility of appearance of secondary caries in the future and correlate it with marginal integrity and discoloration.

Conclusion

The present clinical evaluation demonstrated that class I resin restorations in posterior teeth using a two-step etch-and-rinse or a two-step self-etching adhesive system presented good performance 3 years after placement.

About the Authors

Renato Herman Sundfeld, DDS, MS, PhD
Full Professor
Department of Restorative Dentistry
Araçatuba Dental School
UNESP
São Paulo State University
Araçatuba, SP, Brazil

Lucas Silveira Machado, DDS, MS, PhD
Collaborator Professor
Department of Restorative Dentistry
Araçatuba Dental School
UNESP
São Paulo State University
Araçatuba, SP, Brazil

Diego Sucena Pita, DDS
Department of Restorative Dentistry
Araçatuba Dental School
UNESP
São Paulo State University
Araçatuba, SP, Brazil

Laura Molinar Franco, DDS, MS
PhD student
Department of Restorative Dentistry
Araçatuba Dental School
UNESP
São Paulo State University
Araçatuba, SP, Brazil

Daniel Sundfeld, DDS, MS
PhD student
Department of Restorative Dentistry
Piracicaba Dental School
UNICAMP
University of Campinas
Piracicaba, SP, Brazil

Maria Lúcia Marçal Mazza Sundefeld, PhD
Department of Pediatric and Social Dentistry
Araçatuba Dental School
UNESP
São Paulo State University
Araçatuba, SP, Brazil

Lourenço Correr-Sobrinho, DDS, MS, PhD
Full Professor
Department of Restorative Dentistry
Dental Materials Division
Piracicaba Dental School
UNICAMP
University of Campinas
Piracicaba, SP, Brazil