Delayed Application Effect on Bond Strength of a Unidose Bonding Adhesive

Background

The dental adhesive used for composite restorations in the predoctoral clinic at the researchers’ institute is a single-component total-etch OptiBond™ Solo Plus (Kerr Dental, kerrdental.com) in a unidose package. Once the package is opened, the adhesive is typically used for multiple restorative procedures on the same patient. The application period after package opening ranges from a few minutes to 1 hour if a student-doctor uses the same package of adhesive for subsequent restorations. Considering that OptiBond Solo Plus is an alcohol-based adhesive, the delayed application may affect the quality of bonding due to the evaporation of alcohol. A previous study reported an ethanol-based universal adhesive had lower bond strength when evaporation was more than 50%.²

Methods

After receiving Institutional Review Board approval (14-03039-XM), the researchers collected 50 extracted human molars, which were embedded in acrylic resin. The occlusal surfaces were sectioned perpendicular to the long axis to expose flat occlusal dentin (Figure 1) and ground with 600-grit silicon carbide paper to simulate a bur-prepared surface. The teeth were randomly assigned to 5 groups (N = 10): In Group 0 (“immediate”), adhesive was used immediately after opening the vial; in Groups 20, 40, and 60, adhesive was used after the vials were left opened on the counter for 20, 40, or 60 minutes with the applicator brush left in the vial; in Group 40 (“dried”), adhesive used after the applicator brush was removed from the vial for 40 minutes and was replenished from the open vial. Dentin surfaces were etched with phosphoric acid etchant (Ultra-Etch®, Ultradent, ultradent.com) for 15 seconds, rinsed 10 seconds, and blotted before being coated with OptiBond Solo Plus (according to the 5 groups previously described) for 15 seconds and then air thinned with dry, compressed air for 3 seconds at a distance of 5 cm. The teeth were then placed under a bonding mold insert (Ultradent) shown in Figure 2, and light cured for 20 seconds using a SmartLite Max LED Curing Light (Dentsply, dentsply.com). A composite (Esthet-X® HD, shade A2, Dentsply) cylinder was built in 2 increments in the bonding mold insert (Figure 3). Each increment was light cured for 40 seconds. After removing the bonding mold insert, the bonded teeth (Figure 4) were stored in deionized water at 37 °C for 24 hours.

The specimens were subjected to a shear bond test in a universal testing machine (Instron, instron.us) at a rate of 0.5 mm per minute using a notched blade (Figure 5). Load at failure (Newton) was recorded. Shear bond strength was calculated by dividing the maximum load by the bonded area (4.448 mm²). The results were statistically analyzed using one-way ANOVA followed by Student-Newman-Keuls post-hoc test (significance level 0.05). Fracture surface images were recorded with a stereomicroscope (1.6x zoom), and fracture modes were determined (adhesive, cohesive, or mixed adhesive/cohesive) for each specimen. Fracture mode results were analyzed using a Kruskal-Wallis test.

Results

Shear bond strength values (mean ± standard deviation) and fracture modes occurrences are shown (Table 1). No significant differences in bond strength were found among the groups (ANOVA; P = .8391). Fracture modes were predominantly mixed adhesive/cohesive (>67%) in all groups (Kruskal-Wallis; P = .9725). The results showed a delay in application of up to 60 minutes after opening of the tested unidose adhesive did not produce a statistically significant difference in bond strength.

Clinical Implications

The finding that a delay in application of up to 60 minutes after opening the adhesive vial did not significantly lower shear bond strength to dentin was unexpected. Either this particular adhesive is not sensitive to evaporation or the vial shape minimizes the evaporation of the adhesive solvent. One limitation of the study was that the strength values were determined only after 24 hours. Bond strength usually decreases over time due to environmental deterioration and mechanical stresses.³ OptiBond Solo Plus was chosen for our predoctoral clinic because it is a simplified version of its predecessor, the gold standard OptiBond FL multi-bottle etch-and-rinse adhesive (Kerr Dental). Considering the modest experience of novice clinicians, an adhesive with low technique sensitivity and few application steps may help increase rates of clinical success. In our predoctoral clinic, replacement of a restoration with less than 12 months of service is recorded in the AxiUm electronic chart as “redo at no charge to the patient due to restoration failure.” The percentage of “redo at no charge” indicates a 1-year failure rate. From 2007 to 2014, the percentages of “redo at no charge” restorations placed by third- and fourth-year student-doctors averaged 0.77% per year for the anterior and 0.85% for the multiple surface posterior composite restorations. A comparable record of redone class II composite restorations was 3.6%.4 Meta-analysis of 58 clinical studies reported a mean annual failure rate of 1.46% for posterior composite restorations.⁵ Considering that skilled practitioners placed restorations in most clinical studies, the low redo rate at our predoctoral clinic is remarkable. Composite restorations are placed by using dental dams to isolate the working field. Dental dams not only prevent contamination, but also create an environment more suitable for placing composite restorations. A recent study showed several bonding agents were negatively affected by increased relative humidity.⁶ The successful clinical outcomes of the adhesive and composite materials by student doctors can likely be attributed to correctly following instructions, working under supervision, and the “forgiving” nature of the materials used.

Acknowledgments

Supported by the University of Tennessee Health Science Center College of Dentistry Alumni Endowment Fund and the Tennessee Dental Association Foundation. Materials were donated by the Dentsply and Kerr Dental.

About the Authors

James A. Lane, DDS
Assistant Professor
Department of General Practice Dentistry
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee

Samantha J. Hughey, DDS
Former dental student
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee
Private Practice
Hendersonville, Tennessee

Paul N. Gregory, DDS, MHA
Assistant Professor
Department of General Practice Dentistry
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee

Daranee Versluis-Tantbirojn, DDS, MS, PhD
Professor
Department of Restorative Dentistry
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee

James F. Simon, DDS, MSEd
Director
Division of Esthetic Dentistry
Professor, Department of Restorative Dentistry
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee

Janet Harrison, DDS
Professor and Former Chair
Department of Restorative Dentistry
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee

Antheunis Versluis, PhD
Professor and Director
Biomaterials Research
Department of Bioscience Research
College of Dentistry
University of Tennessee Health Science Center
Memphis, Tennessee