A six-year prospective randomized study of a nano-hybrid and a conventional hybrid resin composite in Class II restorations

Abstract

Objective

The objective of this 6 year prospective randomized equivalence trial was to evaluate the long-term clinical performance of a new nano-hybrid resin composite (RC) in Class II restorations in an intraindividual comparison with its well-established conventional hybrid RC predecessor.

Methods

Each of 52 participants received at least two, as similar as possible, Class II restorations. The cavities were chosen at random to be restored with an experimental nano-hybrid RC (Exite/Tetric EvoCeram (TEC); n = 61) and a conventional hybrid RC (Exite/Tetric Ceram (TC); n = 61). The restorations were evaluated with slightly modified USPHS criteria at baseline and then annually during 6 years.

Results

Two patient drop outs with 4 restorations (2TEC, 2TC) were registered during the follow-up. A prediction of the caries risk showed that 16 of the evaluated 52 patients were considered as high risk patients. Eight TEC (2 P, 6M) and 6 TC (2P, 4M) restorations failed during the 6 years. The main reason of failure was secondary caries (43%; including the failure fracture + secondary caries it increases to 57.1%). 63% of the recurrent caries lesions were found in high caries risk participants. The overall success rate at six years was 88.1%. No statistical significant difference was found in the overall survival rate between the two investigated RC.

Significance

The nano-hybrid RC showed good clinical performance during the 6 year evaluation, comparable to the well-established conventional hybrid RC.

Introduction

The use of amalgam has decreased in many countries to negligible levels during the latest decade. Advantages like aesthetics and tooth substance saving adhesive techniques increased the popularity of resin composites (RC) also in the posterior region. However, polymerization shrinkage, manifested as shrinkage stress when monomer molecules are converted into a polymer network is still considered remaining a challenge. Contraction forces exceeding the bond strength at the tooth-restoration interface affect the interfacial adaptation . The following interfacial debonding is often discussed to result in marginal staining, bacterial microleakage, secondary caries or pulpal inflammation . However, neither evidence nor a good correlation between contraction stress and clinical durability of resin composite materials has been presented. Filler particles incorporated in the resin matrix has been continuously in focus for improvements over the years. The last generation hybrid resin composites contain 0.5–1.0 μm sized filler particles of glass or zirconium completed with smaller amounts of colloidal silica particle clusters. Newer generations of hybrid resin composites have been marketed with claims that modified filler-loading and matrix monomers result in lower polymerization shrinkage, improved polish retention and aesthetics . A recent development is the application of nanotechnology in dental materials, incorporating nanofiller particles in RC and bonding systems. Nanotechnology is known as the production and manipulation of materials and structures in the range of about 0.1–100 nanometers by various physical or chemical methods . Nanofillers with sizes ranging from 5 to 200 nm have recently been developed ( ) although 40 nm particles already were present in the microfilled resin composites . The main difference is the higher filler loading of the recent materials compared to the earlier microfilled RC. Nano-hybrid and nanofilled resin composites are two types of resin composites referred to under the term “nanocomposite”. In vitro, good mechanical properties, improved surface characteristics and esthetics, better gloss retention, reduced polymerization shrinkage and diminished wear have been reported . In recently introduced RC, an approach to wet the larger surface area of the included smaller fillers is the use of prepolymerized filler made of ground RC containing microfine particles. Ergücü et al. showed that this material was the less surface-stained nanocomposite among four nano-hybrid and one nano-filled resin composite materials .

Prediction of restorative systems is mostly performed in vitro, but its value is often limited and clinical studies are required to test these materials in the oral cavity. Initial short time studies of nanocomposite materials in posterior cavities have been promising, but no differences in durability have been shown compared to conventional microhybrid resin composites . No long time clinical evaluations of nanocomposites have been reported. The aim of this study was to evaluate the long-term clinical performance of a new nano-hybrid RC (Tetric EvoCeram) containing prepolymerized filler of ground composite microfine particles, in Class II cavities and to compare with an established conventional hybrid RC (Tetric Ceram) in a split mouth study. The reference RC has a widespread use and has been evaluated in several earlier trials which enable a noninferiority/equivalence design of the trial. The null hypothesis tested was that the nano-hybrid resin composite showed different durability as its predecessor. The alternative hypothesis was that they were equally effective.

Materials and methods

Experimental design

Fifty-two patients, 27 women and 25 men, with a mean age of 53 years (29–82) participated in the study. During September–December 2003, all adult patients, visiting one of the author’s PDHS’s clinic, who at the yearly examination needed two or four extensive Class II restorations, were invited to join the study. The subjects were representative for the patients attending Swedish dental practises as in most of our earlier trials . All patients invited participated in the study. No participant was excluded because of high caries activity, periodontal condition or parafunctional habits. Reasons for placement were replacements of old amalgam fillings because of fracture, secondary caries or aesthetic reasons and primary caries. All teeth were in occlusion. Each patient received at least one pair of Class II restorations, a nano-hybrid and a conventional hybrid RC restoration, in order to make an intra-individual comparison possible. The cavities within the pair were chosen to match each other concerning size and localization. The two RC tested were placed in the two cavities of each pair (61 pairs) at random performed by casting a coin. The sample size, extending 50 restorations per group at baseline, was based on power calculations in our earlier clinical trials, based on a 5% difference as margin of inferiority after at least four years of follow-up. The rather extensive restorations were placed: 49 in premolars (maxilla 27, mandibula 22), and 73 in molars (maxilla 39, mandibula 34). The majority of cavities had dentin bordered proximal cervical margins. Each patient provided informed consent to participate in the study, which was approved by the ethics committee of the University of Umeå.

Clinical procedure

Operative procedures were performed under local anesthesia if necessary. Existing restorations and/or caries were removed under constant water cooling. No bevels were prepared and no calcium hydroxide base was placed. The operative field was carefully isolated with cotton rolls and suction device. For all Class II cavities a thin metallic matrix was used and carefully wedging was performed with wooden wedges (Hawe Neos, Switzerland). The cavities were conditioned with a 37% phosphoric acid total etch technique. The acid gel was first placed on the enamel, while the dentin part of the cavity was conditioned during the last five seconds of the 15 s etching time. The cavity was then thoroughly rinsed with air–water spray during about 20 s and carefully dried taking care not to over-dry the dentin. All materials were applied according to the manufacturer’s instructions. The two step etch-and-rinse enamel-dentin bonding system Excite (Ivoclar Vivadent AG, Schaan, Liechtenstein; Lot F53516) was applied with a minimal time of 20 s. The primer was cured with the Astralis 7 light-curing unit (Ivoclar Vivadent AG) at high intensity. The cavities in each individual were as described earlier randomly distributed to be restored with either the experimental nano-hybrid RC TEX-2 (Ivoclar Vivadent AG; Lot F 31516, color A3), in 2004 marketed as Tetric EvoCeram (TEC) during the second year of the study or the conventional hybrid RC Tetric Ceram (TC; Ivoclar Vivadent AG; Lot F 57791, color A3 or A 3.5). The RC’s were applied in layers of maximally 2–3 mm with if possible an oblique layering technique. Each layer was light-cured for 20 s. Normally, two or three layers were required to restore the cavity. After checking the occlusion/articulation, the final polishing was performed with fine diamond or carbide finishing burs to remove gross excess, followed by polishing with the Enhance finishing system (DeTrey/Dentsply, Konstanz, Germany) or Shofu brownie points (Shofu Co, Japan) and proximal finishing strips. The first author (JvD) placed all restorations.

The nano-hybrid RC Tetric EvoCeram contains dimethacrylates (16.8 wt%, small quantities of nano-additives such as rheological modifiers and organic pigments (0.8%). Fillers have an average particle size of 0.6 μm, range 40–3000 nm, 82.5 wt%, 69 vol% . The fillers included are barium glass (50.6%), Ba–Al–F–B-silicate (5%), SiO 2 40 nm (5), mixed oxide 0.2 1 μm, ytterbium trifluoride (17%), prepolymers (47%). The prepolymer technique has been used earlier in RC like Heliomolar (Ivoclar Vivadent AG). These are milled microfilled composite to the grain size of traditional macrofillers. The predecessor of the nano-hybrid, the conventional hybrid RC Tetric Ceram is a highly filled hybrid small-particle resin composite, with an average particle size of 1 μm . The material contained filler with a mean size 0.7 μm, 62 vol%: silanized barium glass (50.6 wt%), mixed oxides (5 wt%), silanized barium alumino-fluorosilicate glass (5 wt%), silanized high-dispersed silica 40 nm (1 wt%), and ytterbium trifluoride (17 wt%). The monomers consisted of Bis-GMA (8.3 wt%), urethane dimethacrylate (7.7 wt%) and TEGDMA (4.4 wt%).

Evaluation

The restorations were evaluated direct after placement (baseline), 6 months, and than annually during the following 6 years by the treating dentist. At different recalls, two calibrated dentists without knowledge of earlier assessments evaluated part of the restorations. In case of different scores, the restoration was re-evaluated and a joint scoring agreed upon. Each restoration was evaluated with slightly modified USPHS (United State Public Health Service) criteria for the following characteristics: anatomical form, marginal adaptation, color matching, marginal staining, surface texture and secondary caries ( Table 1 ) . The end point of the restoration was a non-acceptable score for one of the evaluating variables. During the follow-up evaluations, the evaluators had neither knowledge of which study the too evaluated RC restorations belonged to nor of the earlier recall evaluation scores. Cohen-kappa values performed during the follow-up were >85%. Bite-wing radiographs were taken at yearly intervals. Postoperative sensitivity was noted by questioning the participants at the recalls or direct information from the participants. The caries risk for each patient was estimated by the treating clinician by means of clinical and sociodemographic information routinely available at the annual clinical examinations, e.g. incipient caries lesions and former caries histories . The IBM SPSS (Statistical Package for the Social Sciences) statistics version 19 was used to process the data. The overall performance of the experimental restorations was tested after intra-individual comparison and ranking using the Friedman’s two-way analysis of variance test . The null hypothesis was rejected at 5% level.

Table 1
Criteria for direct clinical evaluation (modified USPHS criteria; ).
Category Score Criteria
Acceptable Unacceptable
Anatomical form 0 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 0 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 0 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 0 No discoloration evident
1 Slight staining, can be polished away
2 Obvious staining can not be polished away
3 Gross staining
Surface roughness 0 Smooth surface
1 Slightly rough or pitted
2 Rough, cannot be refinished
3 Surface deeply pitted, irregular grooves
Caries 0 No evidence of caries contiguous with the margin of the restoration
1 Evidence of superficial caries, no operative treatment necessary
2 Caries is evident contiguous with the margin of the restoration, operative treatment indicated

Materials and methods

Experimental design

Fifty-two patients, 27 women and 25 men, with a mean age of 53 years (29–82) participated in the study. During September–December 2003, all adult patients, visiting one of the author’s PDHS’s clinic, who at the yearly examination needed two or four extensive Class II restorations, were invited to join the study. The subjects were representative for the patients attending Swedish dental practises as in most of our earlier trials . All patients invited participated in the study. No participant was excluded because of high caries activity, periodontal condition or parafunctional habits. Reasons for placement were replacements of old amalgam fillings because of fracture, secondary caries or aesthetic reasons and primary caries. All teeth were in occlusion. Each patient received at least one pair of Class II restorations, a nano-hybrid and a conventional hybrid RC restoration, in order to make an intra-individual comparison possible. The cavities within the pair were chosen to match each other concerning size and localization. The two RC tested were placed in the two cavities of each pair (61 pairs) at random performed by casting a coin. The sample size, extending 50 restorations per group at baseline, was based on power calculations in our earlier clinical trials, based on a 5% difference as margin of inferiority after at least four years of follow-up. The rather extensive restorations were placed: 49 in premolars (maxilla 27, mandibula 22), and 73 in molars (maxilla 39, mandibula 34). The majority of cavities had dentin bordered proximal cervical margins. Each patient provided informed consent to participate in the study, which was approved by the ethics committee of the University of Umeå.

Clinical procedure

Operative procedures were performed under local anesthesia if necessary. Existing restorations and/or caries were removed under constant water cooling. No bevels were prepared and no calcium hydroxide base was placed. The operative field was carefully isolated with cotton rolls and suction device. For all Class II cavities a thin metallic matrix was used and carefully wedging was performed with wooden wedges (Hawe Neos, Switzerland). The cavities were conditioned with a 37% phosphoric acid total etch technique. The acid gel was first placed on the enamel, while the dentin part of the cavity was conditioned during the last five seconds of the 15 s etching time. The cavity was then thoroughly rinsed with air–water spray during about 20 s and carefully dried taking care not to over-dry the dentin. All materials were applied according to the manufacturer’s instructions. The two step etch-and-rinse enamel-dentin bonding system Excite (Ivoclar Vivadent AG, Schaan, Liechtenstein; Lot F53516) was applied with a minimal time of 20 s. The primer was cured with the Astralis 7 light-curing unit (Ivoclar Vivadent AG) at high intensity. The cavities in each individual were as described earlier randomly distributed to be restored with either the experimental nano-hybrid RC TEX-2 (Ivoclar Vivadent AG; Lot F 31516, color A3), in 2004 marketed as Tetric EvoCeram (TEC) during the second year of the study or the conventional hybrid RC Tetric Ceram (TC; Ivoclar Vivadent AG; Lot F 57791, color A3 or A 3.5). The RC’s were applied in layers of maximally 2–3 mm with if possible an oblique layering technique. Each layer was light-cured for 20 s. Normally, two or three layers were required to restore the cavity. After checking the occlusion/articulation, the final polishing was performed with fine diamond or carbide finishing burs to remove gross excess, followed by polishing with the Enhance finishing system (DeTrey/Dentsply, Konstanz, Germany) or Shofu brownie points (Shofu Co, Japan) and proximal finishing strips. The first author (JvD) placed all restorations.

The nano-hybrid RC Tetric EvoCeram contains dimethacrylates (16.8 wt%, small quantities of nano-additives such as rheological modifiers and organic pigments (0.8%). Fillers have an average particle size of 0.6 μm, range 40–3000 nm, 82.5 wt%, 69 vol% . The fillers included are barium glass (50.6%), Ba–Al–F–B-silicate (5%), SiO 2 40 nm (5), mixed oxide 0.2 1 μm, ytterbium trifluoride (17%), prepolymers (47%). The prepolymer technique has been used earlier in RC like Heliomolar (Ivoclar Vivadent AG). These are milled microfilled composite to the grain size of traditional macrofillers. The predecessor of the nano-hybrid, the conventional hybrid RC Tetric Ceram is a highly filled hybrid small-particle resin composite, with an average particle size of 1 μm . The material contained filler with a mean size 0.7 μm, 62 vol%: silanized barium glass (50.6 wt%), mixed oxides (5 wt%), silanized barium alumino-fluorosilicate glass (5 wt%), silanized high-dispersed silica 40 nm (1 wt%), and ytterbium trifluoride (17 wt%). The monomers consisted of Bis-GMA (8.3 wt%), urethane dimethacrylate (7.7 wt%) and TEGDMA (4.4 wt%).

Evaluation

The restorations were evaluated direct after placement (baseline), 6 months, and than annually during the following 6 years by the treating dentist. At different recalls, two calibrated dentists without knowledge of earlier assessments evaluated part of the restorations. In case of different scores, the restoration was re-evaluated and a joint scoring agreed upon. Each restoration was evaluated with slightly modified USPHS (United State Public Health Service) criteria for the following characteristics: anatomical form, marginal adaptation, color matching, marginal staining, surface texture and secondary caries ( Table 1 ) . The end point of the restoration was a non-acceptable score for one of the evaluating variables. During the follow-up evaluations, the evaluators had neither knowledge of which study the too evaluated RC restorations belonged to nor of the earlier recall evaluation scores. Cohen-kappa values performed during the follow-up were >85%. Bite-wing radiographs were taken at yearly intervals. Postoperative sensitivity was noted by questioning the participants at the recalls or direct information from the participants. The caries risk for each patient was estimated by the treating clinician by means of clinical and sociodemographic information routinely available at the annual clinical examinations, e.g. incipient caries lesions and former caries histories . The IBM SPSS (Statistical Package for the Social Sciences) statistics version 19 was used to process the data. The overall performance of the experimental restorations was tested after intra-individual comparison and ranking using the Friedman’s two-way analysis of variance test . The null hypothesis was rejected at 5% level.

Table 1
Criteria for direct clinical evaluation (modified USPHS criteria; ).
Category Score Criteria
Acceptable Unacceptable
Anatomical form 0 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 0 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 0 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 0 No discoloration evident
1 Slight staining, can be polished away
2 Obvious staining can not be polished away
3 Gross staining
Surface roughness 0 Smooth surface
1 Slightly rough or pitted
2 Rough, cannot be refinished
3 Surface deeply pitted, irregular grooves
Caries 0 No evidence of caries contiguous with the margin of the restoration
1 Evidence of superficial caries, no operative treatment necessary
2 Caries is evident contiguous with the margin of the restoration, operative treatment indicated
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Nov 28, 2017 | Posted by in Dental Materials | Comments Off on A six-year prospective randomized study of a nano-hybrid and a conventional hybrid resin composite in Class II restorations
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