To evaluate marginal integrity of direct resin composite restorations before and after thermo-mechanical loading in vitro , and before and after 6 years of clinical service in a prospective clinical trial.
For the in vitro part, MO cavities with the proximal box beneath the cemento-enamel junction were prepared in 32 extracted human third molars. The specimens were randomly assigned to four groups ( n = 8) and received bonded resin composite restorations (two groups each Grandio bonded with Solobond M and Tetric Ceram bonded with Syntac). Specimens were subjected to three different aging protocols: 6-year water storage (WS), thermo-mechanical loading (TML; 100,000 × 50 N; 2500 × +5/+55 °C), and 6-year water storage plus thermo-mechanical loading (WS + TML). Initially and after aging, marginal qualities in enamel and dentin were evaluated using replicas at 200× magnification (SEM). For the in vivo part, 30 patients received 68 direct resin composite restorations of the same materials in a prospective clinical trial. Replicas of 11 selected subjects per group were assessed for marginal quality under a SEM at 200×.
in vitro , all initial results showed nearly 100% gap-free margins. For TML, percentages of gap-free margins dropped to 87–90% in enamel and to 58–66% in dentin ( p < 0.05). For WS, enamel margins still were at 97–99% whereas dentin margins exhibited 67–75% gap-free margins, and for WS + TML, enamel margins were at 85–87% and dentin margins at 42–52% gap-free margins. In vivo , gap-free enamel margins were reduced from initially 86–90% to 74–80% after 6 years of clinical service ( p < 0.05). Proximally exposed dentin margins were not recordable by impressions, however, clinically no considerable problems like recurrent caries or discolorations were detected.
In vitro , hydrolytic degradation supports mechanical fatigue in dentin–composite bonds over time. In vivo , wear phenomena are superimposing marginal quality aspects. Gaps between enamel and resin composite did not play a major role.
Tooth-colored materials such as resin-based composites are today the treatment option of choice for the majority of patients , primarily due to esthetic demands. It is well-proven that adhesive restorations are successful e.g. pit and fissure sealants, direct and indirect resin composites, and bonded indirect ceramic restorations . Durable adhesion to enamel and dentin still represents the fundamental prerequisite due to polymerization shrinkage of resin-based composites . Bonding to phosphoric acid etched enamel is widely accepted as clinically viable , however, in dentin it is not completely clear whether the etch-and-rinse or the self-etch approach may be more successful in obtaining durable bonds . Irrespective of this, technique sensitivity with bonded restorations remains problematic, facing a 1:12 failure rate ratio in clinical trials with identical materials but different clinical operators .
The primary goal of preclinical screening of dental materials should be to mimic the clinical situation in order to predict clinical behavior. Therefore, researchers try to predict clinical behavior of restoratives with laboratory in vitro investigations. Of course, randomized clinical trials remain the ultimate instrument for evaluating dental restoratives, however, a major problem with clinical trials is that when they give valuable results after several years of clinical service, the material under investigation may not be in the market anymore , therefore, preclinical in vitro investigations are more important than ever. However, it is still not fully understood whether these tests are able to reliably predict clinical behavior. So the aim of this investigation was to compare the preclinical results of a large marginal quality in vitro database with clinically recorded marginal qualities of the same materials.
Materials and methods
In vitro : Thirty-two intact, non-carious, un-restored human third molars, extracted for therapeutic reasons with patients’ approval, were stored in an aqueous solution of 0.5% chloramine T at 4 °C for up to 30 days. The teeth were debrided of residual plaque and calculus, and examined to ensure that they were free of defects under a light microscope at 20× magnification. Standardized class II cavity preparations, (MO, 4 mm in width bucco-lingually, 2 mm in depth at the bottom of the proximal box) with proximal margins located 1–2 mm below the cemento-enamel junction, were performed. The cavities were cut using coarse diamond burs under profuse water cooling (80 μm diamond, Komet, Lemgo, Germany), and finished with a 25 μm finishing diamond (one pair of diamonds per four cavities). Inner angles of the cavities were rounded and the margins were not beveled to deliver comparable results to previous experiments .
The prepared cavities ( n = 8) were treated with two different adhesives according to the manufacturers’ instructions ( n = 16 with Syntac, Ivoclar Vivadent, Schaan, Principality of Liechtenstein, and n = 16 with Solobond M, Voco, Cuxhaven, Germany; Table 1 ). The dentin adhesives and resin composite were polymerized with a Translux CL light-curing unit (Elipar Trilight, 3M ESPE, Seefeld, Germany). The intensity of the light was checked periodically with a radiometer (Demetron Research Corp., Danbury, CT, USA) to ensure that 600 mW/cm 2 was always delivered during the experiments. The adhesive was polymerized for 40 s prior to application of the resin composite in all cases. The resin composites Tetric Ceram (Ivoclar Vivadent; shade A2) and Grandio (Voco; shade A2) were used for all experimental restorations. Each cavity preparation was bonded with the respective adhesive and restored incrementally with the resin composite in layers up to 2 mm thickness. The increments were separately light-cured for 40 s each with the light source in contact with the edge of the cavity. Prior to the finishing process, visible overhangs were removed using a posterior scaler (A8 S204S, Hu-Friedy, Leimen, Germany). Margins were finished with flexible disks (SofLex Pop-on, 3M ESPE, St. Paul, USA).