In a controlled prospective split-mouth study, clinical behavior of two different resin composites in extended Class II cavities was observed over six years.
Thirty patients received 68 direct resin composite restorations (Solobond M + Grandio: n = 36; Syntac + Tetric Ceram: n = 32) by one dentist in a private practice. All restorations were replacement fillings, 35% of cavities revealed no enamel at the bottom of the proximal box, in 48% of cavities remaining proximal enamel width was <0.5 mm. Restorations were examined according to modified USPHS criteria at baseline, and after six months, one, two, four, and six years.
Success rate was 100% after six years of clinical service, while the drop out of patients was 0%. Neither materials nor localization of the restoration (upper vs. lower jaw) had a significant influence on clinical outcome in any criterion after six years ( p > 0.05; Mann–Whitney U -test). Molar restorations performed worse regarding marginal integrity (4 years), filling integrity (6, 12, 24, 48 months), and tooth integrity (4 and 6 years). Irrespective of the resin composite used, significant changes over time were found for all criteria recorded (Friedman test; p < 0.05). Marginal quality revealed a major portion of overhangs having been clearly reduced after the one year recall (baseline: 44%; 6 months: 65%; 1 year: 47%; 2 years: 6%; 4 years: 4%; and 6 years: 3%). Beyond the 1 year recall, negative step formations significantly increased due to wear ( p < 0.05), having been more pronounced in molars (87% bravo after 4 years) than in premolars (51% bravo after 4 years). Tooth integrity significantly deteriorated due to enamel cracks, which increased over time ( p < 0.05). Enamel chippings and cracks were significantly more frequent in molars (26% bravo after 4 years to 35% after six years) than in premolars (9% bravo after 4 years, 11% after six years). Restoration integrity over time mainly suffered surface roughness and wear (28% after one year, 75% after two years, 84% after four years, 91% after six years).
Both materials performed satisfactorily over the 6-year observation period. Due to the extension of the restorations, wear was clearly visible after six years of clinical service with 91% bravo ratings.
Cavitated carious lesions are today predominantly restored by use of resin composites . Durable adhesion to tooth hard tissues still is the fundamental prerequisite for pit and fissure sealings, direct and indirect resin composites, and bonded all-ceramic restorations . When adhesion mechanisms fail, gap formation and secondary caries corroborate clinical success of restorations .
Bonding to enamel is clinically durable at least when the etch-and-rinse approach is applied , dentin still provides inferior adhesion , but also here clinically acceptable sealing is obtainable to limit the occurrence of postoperative hypersensitivities . Although bonded resin composites have proven to durably seal dentin especially with multi-step adhesives , it is still unclear whether it is possible to maintain a stable proximal seal in Class II cavities with proximal margins extending beyond the amelocemental junction. In vitro studies give varying results after thermomechanical loading and/or long-term storage, mostly with distinct advantages for two- or three-step adhesives compared to simplified adhesive systems . Prospective clinical trials remain ultimate instruments, but preclinical in vitro investigations are still needed for experimental questions and preclinical screening .
One of the most severe problems of clinical trials covering dental materials is apparent: while affording major results after some years of clinical service, there is a certain risk that the adhesive and/or resin composite under investigation is not in the market anymore . However, it is not a matter of course that this kind of clinical trials reveals favorable results, so also catastrophic outcomes were observed when fundamental prerequisites are neglected such as hygroscopic expansion or flexural fatigue behavior . And it may be still true that, e.g. amalgam may be superior to resin composites for restoration of very extended defects .
Research and development of resin-based composites during the last decade generated different subspecies of restorative materials, such as hybrid resin composites, fine hybrid resin composites, nanohybrid resin composites, or even nano resin composites (Filtek Supreme XTE, 3M ESPE, Seefeld, Germany). Especially the latter ones entered the market with claims of less polymerization shrinkage, lowered shrinkage stress and even higher wear resistance . In most of the cases, however, a truly better clinical outcome is not proven. On the other hand, it is stated from recent in vivo results that modern nano hybrid resin composite may provide an enamel-like wear behavior .
Therefore, the aim of this clinical trial was to investigate two different restorative material systems (i.e. adhesive and resin composite) in extended Class II cavities over six years in order to observe differences between conventional (Tetric Ceram) and partially nanofilled (Grandio) resin composites. The null-hypothesis tested was that there would be no difference between the different resin composites with their respective adhesives under investigation.
Methods and materials
Patients selected for this study met the following criteria: (1) absence of pain from the tooth to be restored; (2) possible application of rubber dam during luting of restoration; (3) no further restorations planned in other posterior teeth; (4) high level of oral hygiene; (5) absence of any active periodontal and pulpal disease; (6) restorations required in two different quadrants (split mouth design).
Thirty patients (23 females, 7 males, mean age 32.9 (24–59) years) with a minimum of two fillings to be replaced in different quadrants received at least two different restorations in a random decision according to recommendations of the CONSORT statement . Thirty-six Grandio fillings were bonded with Solobond M (Voco, Cuxhaven, Germany) and 32 Tetric Ceram restorations were bonded with Syntac (Ivoclar Vivadent, Schaan, Liechtenstein). All fillings (only Class II, 52 MO/OD, 16 MOD or more surfaces, no cusp replacements) were re-restorations made by one dentist in a private practice (31 upper bicuspids, 12 upper molars, 14 lower bicuspids, 11 lower molars). Reasons for replacement were caries ( n = 19), insufficient esthetics ( n = 2), and secondary caries ( n = 47). For all teeth receiving restorations, current X-rays (within six months of the procedure) were present. After evaluating the radiographs, 53 cavities (78%) were treated as caries profunda. Twenty-four cavities (35%) revealed no enamel at the floor of the proximal box, while 33 cavities (49%) exhibited a proximal enamel width of <0.5 mm.
All fillings were inserted in permanent vital teeth without pain symptoms. An extension for prevention was disregarded for maximal substance protection; however, the majority of restorations were previously prepared with undercuts for amalgam retention. 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. Inner angles of the cavities were rounded and the margins were not beveled. After cleaning and drying under rubber dam isolation (Coltene/Whaledent Inc., Altstätten, Switzerland), adhesive procedures were performed with Solobond M (2-step etch-and-rinse adhesive) and Syntac (4-step etch-and-rinse adhesive). The resin composite materials were applied into the cavity in layers of approximately 2 mm thickness and adapted to the cavity walls with a plugger. Each layer was light cured for 40 s (Elipar Trilight, 3M ESPE, Seefeld, Germany). The occlusal region was modeled as exactly as possible under intraoral conditions, avoiding visible overhangs. The light-emission window was placed as close as possible to the cavity margins. The intensity of the light was checked periodically with a radiometer (Demetron Research Corp., Danburg, CT, USA) and was found to be constantly above 650 mW/cm 2 .
As soon as polymerization was completed, the surface of the restoration was controlled for defects and corrected when necessary. Visible overhangs were removed with a scaler and the rubber dam was removed. Contacts in centric and eccentric occlusion were controlled with foils (Roeko, Langenau, Germany) and adjusted with finishing diamonds (Komet Dental, Lemgo, Germany), shaped with flexible discs (3M Dental, St. Paul, USA), super-fine discs (3M Dental, St. Paul, USA) and polishing brushes (Hawe-Neos Dental, Bioggio, Switzerland). A fluoride varnish (Elmex Fluid, GABA, Lörrach, Germany) was used to complete the treatment.
At the initial recall (baseline, i.e. within 2 weeks), and after six months, one, two, four, and six years, all restorations were assessed according to the modified United States Public Health Service (USPHS) criteria ( Tables 1 and 2 ) by two independent investigators using loups with 3.5× magnification, mirrors, probes, bitewing radiographs, impressions (Dimension Penta and Garant, 3M ESPE, Seefeld, Germany), and intraoral photographs. Replicas were collected for later marginal and wear analysis (studies in preparation). Recall assessments were not performed by the clinician who initially placed the restorations.