Clinical randomized controlled study of Class II restorations of a highly filled nanohybrid resin composite (4U)

Transcription

1 Clinical randomized controlled study of Class II restorations of a highly filled nanohybrid resin composite () One year report JWV van Dijken, Professor Director Clinical Research Biomaterial Research Group Umeå Sweden

2 2 I. AIM Two year clinical evaluation of a highly filled nanohybrid resin composite (Nordenta, Sweden) in posterior cavities. II. INVESTIGATORS Investigation of the Class II restorations is done by the investigators Professor JWV van Dijken, Biomaterial Research Group Umeå and Associate Professor Ulla Pallesen, Copenhagen, Denmark. Professor van Dijken having in addition the function and responsibility of the principal investigator. III. BACKGROUND Resin composites have replaced amalgam almost totally during the last years as restorative in posterior teeth. Adhesive bonding and aesthetics made the material popular despite its main remaining disadvantage, polymerization shrinkage. During curing of the monomers, a network of polymers is formed which becomes rigid due to increasing cross-linking of the polymer chains. Due to decreasing mobility, further shrinkage results in a strain on the composite and cavity margins. This stress may results in marginal deficiencies, enamel fractures, cuspal movements and cracked cusps. Resulting gap formation can result in post-operative sensitivity, microleakage and secondary caries. Increasing C-factor may result in greater stresses due to larger number of bounded surfaces. Posterior Class I and Class II cavities will therefore show the highest stress formation. Highly filled resin composites do have a decreased volume of methacrylate monomers which will influence the polymerization shrinkage and probably reduce the polymerization stress. Recently, such a highly filled resin composite was marketed (Nordenta, Sweden). Since the introduction of the enamel etch technique by Buonocore (1955), adhesive techniques have been developed to such an extent that they are now involved in most of the clinical procedures. The heterogenuos composition of the dentin tissue with organic and inorganic material, its hydrophilicity and the presence of a smear layer after cutting made it more difficult substrate to bond to than the enamel tissue. Bonding to dentin has now become a more reliable clinical procedure since the introduction of more hydrophylic monomers, which can infiltrate the moist dentin surface. Most of the last generation

3 3 adhesive systems including an etchant are very technique sensitive, time consuming and the multi-bottle systems increase the risk for allergic reactions. In the self-etching primer approach, the etchant, primer and sometimes also adhesive are combined, and are directly applied on the smear layer. These systems are based on infiltration and modification of the smear layer by acidic monomers or by dissolving of the smear layer and demineralizing of the underlying outer layer of the dentin. IV. REASONS FOR THE INVESTIGATION IN HUMAN SUBJECTS At present, only laboratory data are available of the properties of the highly filled resin composite. Concerning the clinical behaviour, no evaluations of its durability have been performed. V. MATERIALS AND METHODS During october december 213, adult patients attending the Biomaterial Clinical Research clinic at the PDHS, Dental School Umeå, who did need at least two similar Class II or two similar Class I restorations, were asked to participate in the follow up. Female patients, who were pregnant were excluded. All patients were informed on the background of the study and the follow up evaluations according to the rules at the Dental School Umeå. Concomitant treatment is given to the patients in conformity with normal clinical routines at the Dental School Umeå, which was approved by the ethics committee of the University of Umeå (Dnr 7-152M). Reasons for placement of the resin composite restorations were primary or secondary carious lesions, fracture of old amalgam fillings or replacement because of aesthetic or other reasons. In total, 11 restorations (55 pairs) were placed, distributed as shown in Table 1. The restorations were placed in 42 patients, 23 men and 19 women, mean age 56.4 yr (31-85). Table 1. Distribution and size of the experimental restorations. Surfaces Mandibula Maxilla Total Premolars Molars Premolars Molars 2 surfaces surfaces Total After removal of the amalgam restoration and/or caries excavation according to the principles of

4 4 adhesive dentistry, the operative field was carefully isolated with cotton rolls and suction device. No bevel was placed. For all Class II cavities a thin metallic matrix was used and carefully wedging was performed with wooden wedges (Kerr/Hawe Neos, Switzerland). The cavities were cleaned by a thoroughfull rinsing with water or cleaning agents if necessary. No Ca(OH)2 or base of other materials was used. The cavities in each individual pair of cavities were randomly distributed to be restored with either the experimental resin composite (Nordenta, Sweden) or the control resin composite Filtek Supreme XTE (3M ESPE, Germany). The Scotchbond Universal bonding system (3M ESPE) was used for both restorations in order to have the restorative material as only variable. After rinsing of the cavities with water, application of this adhesive in both cavities was performed according to the manufacturer s instructions. After dispension into a CliXdish, the adhesive was applied twice in the cavity wetting all cavity surfaces uniformly. After a 2s gently agitating, the solvent was evaporated thoroughly during at least 5s. Curing was then performed with a well controlled light curing unit for at least 1s. The resin composites were applied with a 2-3mm layering technique using selected resin composite instruments (Hu Friedy). Every increment was light cured for at least 2s. The restorations were placed by one experienced operator (JvD). After checking the occlusion/articulation and contouring with finishing diamond burrs, the final polishing were performed with the Shofu polishing system (brownie). Evaluation The restorations were evaluated at baseline (after performance of the restorations, within 2 weeks after placement) and at one year by assessing the following parameters: secondary caries, anatomic form, marginal adaptation, marginal discoloration, surface roughness and color match assessed by using the earlier mentioned slightly modified US Public Health Service criteria (Cvar & Ryge; 1971; van Dijken, 1986). These criteria can easily be transferred to the original USPHS criteria. Postoperative sensitivity was reported by the participants. Follow-up registrations will be performed at 1, and 2 years. Participants were instructed to contact the clinic immediately should any discomfort occur. Statistical analysis: The characteristics of the restorations are described by descriptive statistics using cumulative frequency distributions of the scores. The relative frequencies of

5 5 the adhesive restorations can also be compared with earlier reported studies performed and evaluated under similar clinical conditions. The experimental and control restorative techniques were compared intra-individually with the non parametric Friedman two-way analysis of variance test. VII. RESULTS At one year all 11 posterior restorations were evaluated. 42 patients received one or two pairs of restorations, 55 pairs in total. No drop outs were registered. At baseline the handling characteristics of both materials were satisfactory and without clinical problems. No postoperative sensitivity was reported by the participants at baseline or at the one year recalls. 96.4% of the restorations were registered as acceptable. Four failed restorations were observed during the first year, two (2 molar teeth) and 2 (1 premolar and 1 molar) teeth. The reasons for failure are shown in Table 3. Two defects, small chip fractures, were observed in two other restorations (2 molar restorations, ) which were recontoured and polished. The annual failure rate of both resin composites for the investigated Class II restorations was 3.6%. The baseline and one year modified USPHS scores for the evaluated clinical variables of the and restorations are given as relative frequencies (%) in Table 4. The differences seen between the two experimental restorations for the evaluated variables in the posterior cavities were not significant.

6 6 VIII. CONCLUSIONS Good handling characteristics were observed for both resin-based composite systems. Both materials showed an overall clinical success rate of 96.4% after the first year giving an annual failure rate of 3.6%. No significant differences were observed between the two materials. Umeå, JWV van Dijken Professor

7 7 Table 2. Criteria for direct clinical evaluation; Modified Ryge criteria (van Dijken 1986) Category Score (acceptable/unacceptable Criteria Anatomical form The restoration is contiguous with tooth anatomy 1 Slightly under- or over-contoured restoration; marginal ridges slightly undercontoured; contact slightly open (may be self-correcting); occlusal height reduced locally 2 Restoration is undercontoured, dentin or base exposed; contact is faulty, not self-correcting; occlusal height reduced; occlusion affected 3 Restoration is missing partially or totally; fracture of tooth structure; shows traumatic occlusion; restoration causes pain in tooth or adjacent tissue Marginal adaptation Restoration is contiguous with existing anatomic form, explorer does not catch 1 Explorer catches, no crevice is visible into which explorer will penetrate 2 Crevice at margin, enamel exposed 3 Obvious crevice at margin, dentin or base exposed 4 restoration mobile, fractured or missing Color match Very good color match 1 Good color match 2 Slight mismatch in color, shade or translucency 3 Obvious mismatch, outside the normal range 4 Gross mismatch Marginal discoloration No discoloration evident 1 Slight staining, can be polished away 2 Obvious staining can not be polished away 3 Gross staining Surface roughness Smooth surface 1 Slightly rough or pitted 2 Rough, cannot be refinished 3 Surface deeply pitted, irregular grooves Caries No evidence of caries contiguous with the margin of the restoration 1 Caries is evident contiguous with the margin of the restoration

8 8 Table 3. Failed restorations during the one year evaluation, tooth type, year and reason of failure Tooth Year of Reason of failure type failure / M 1 Composite fracture Scotchbond Universal M 1 Composite fracture Filtek Supreme XTE/ P 1 Composite fracture Scotchbond Universal M 1 Tooth fracture

9 9 Table 4. Scores at baseline and one year for the evaluated (Scotchbond Universal/) (55) and (Scotchbond Universal/ )(55) Class II restorations, given as relative frequencies (%) Anatomical form Marginal 1 adaptation Color match Marginal 1 discoloration Surface roughness Caries