Nanofilled and microhybrid composite restorations: Five-year clinical wear performances

Abstract

Objectives

To compare the clinical wear performance of nanofilled restorations (Filtek Supreme) against microhybrid restorations (Z100) in a 5-year randomized clinical trial to evaluate the wear rate and the influence of subject-, operator- and restoration-related variables on wear rate.

Materials and methods

18 Filtek Supreme and 17 Z100 restorations were placed in human molars (split-mouth-model) and bonded with Single Bond/Scotch Bond Adhesive. Restorations were recalled at baseline, 6-, 12-months and at annual intervals until 5-years of clinical service. The gypsum replicas at each recall were used for 3D-Pro-laser scanning to quantify wear and the epoxy resin replicas were observed under SEM for microwear patterns. Linear-mixed-models were used to study the influence of the different variables on the vertical and volume loss.

Results

Z100 Filtek Supreme
Vertical wear (μm/month) Generalised 0.870 0. 925
0–6 m/running-in wear 5.563 6.987
6–36 m/early stage 0.974 1.288
36–60 m/steady state 0.486 0.263
Volume loss (mm 3 /month) Generalised 0.014 0.011
0–6 m/running-in wear 0.017 0.011
6–36 m/early stage 0.006 0.005
36–60 m/steady state 0.031 0.023

Volume wear, but not the vertical wear rate of the two restorative materials were significantly influenced ( p < 0.05) by the factors such as operator, cavity type, as well as combination of operator–cavity type and quadrant type. The variations in the occlusal surface microwear patterns over time reflect the effect of biomechanics of mastication on the restorative composite.

Conclusions

The rate of vertical and volume loss of both the restoratives appear, on average, not to be constant even after the early stage wear, under the influence of certain clinical variables.

Introduction

Long-term clinical performances of resin composite restorations have been improving year by year . However, the occurrence of a high percentage of wear in the first five years of clinical service and the relatively scarce information available in literature over the clinical wear resistance is suggestive of wear resistance being one of the prime concerns in large stress-bearing restorations . With the promise of substantially reducing in vivo wear based on in vitro wear simulator studies , several manufacturers have introduced nanocomposites fabricated by different approaches . Few comparative studies of nanocomposites against the conventional composites have shown controversial results regarding the beneficial effects of nanofills on the wear resistance of nanocomposites .

The clinical results and in vivo wear performance of a nanofilled composite, Filtek Supreme compared against a microhybrid, Z100 placed in Class I and Class II cavities in a three year randomized clinical trial (RCT) were published recently . Reporting of in vivo wear involved both vertical and volume loss as recommended previously . As part of the clinical follow-up protocol of the RCT, the study participants were encouraged to return for annual follow-up visits during the fourth and fifth year following the restoration placement. Having gathered the wear data from baseline to five years for all patients in the prospective RCT, the present study sought to assess the progression of in vivo wear among all of the nanofilled and microhybrid restorations.

Although the long-term temporal pattern of resin composite restoration wear has not been thoroughly characterised, it is generally accepted that the wear curve appears non-linear with three stages. A period of rather rapid initial “running-in” wear and early stage wear with slightly increased wear rate lasting for a period of two years before the transition to a rather slower steady state wear have been observed in clinical studies , which is also consistent with the results of in vitro studies . Several factors related to the patient , operator and the restorative materials have been suggested to influence clinical wear.

This study had two objectives. The first objective was to comparatively assess the running-in wear, early stage and steady state wear rates for vertical and volume wear among the nanofilled and microhybrid restoration groups that had five-year follow-up in a RCT study. With the quantified wear rate, the next goal was to investigate the effect of material-, clinician-, and tooth-related variables on the clinical wear rates.

Materials and methods

Study population

The subjects in the present study were selected from a group of 30 dental student volunteers, by applying strict inclusion and exclusion criteria as mentioned before . 16 subjects in need of a minimum of two Class I and/or Class II restorations of comparable size involving failed restorations and primary caries perwere invited to join the study. Each subject signed an informed consent to participate in the study, which was approved by the medical ethics committee of the Catholic University of Leuven.

Restoration placement

From two restorative dentists blinded for the type of restorative materials, 16 patients received a total of 37 restorations (11 primary caries and 26 failed restorations), divided into two blocks (Class I and Class II). The filling materials listed in Table 1 – Z100 or Filtek Supreme was randomized over these blocks with the use of random number generating functions in Excel following a percent distribution of Class I versus Class II as 53:47 for Z100 and 44:56 for Filtek Supreme. Table 2 summarises the attributes of restorations and patients of this study.

Table 1
Description of materials used in this study.
Material Type Polymer * Fillers * Filler size * Filler content (% by volume) *
Range Mean
Z100 Microhybrid Bis-GMA, TEGDMA Zirconia, silica 0.01–3.5 μm 0.6 μm 66%
Filtek Supreme (translucent) Nano Bis-GMA, UDMA, Bis-EMA, TEGDMA SiO 2 nanoclusters and nanomers 0.6–1.4 μm 75 nm
75 nm
57.7%
Filtek Supreme (D/E/B) Nano Bis-GMA, UDMA, Bis-EMA, TEGDMA ZrO 2 /SiO 2 nanoclusters SiO 2 nanomers 0.6–1.4 μm ZrO 2 -5 nm
SiO 2 -20 nm
20 nm
59.5%
Columns with the superscript (*) contain data as disclosed in the technical product file by manufacturers.

Table 2
Distribution of attributes of restorations and patients.
Attributes Restoration characteristic
Z100 Filtek Supreme
Baseline 5 yrs Baseline 5 yrs
Number 19 19 18 18
Mandibular molar 10 10 12 12
Maxillary molar 9 9 6 6
Class I 10 10 8 8
Class II 9 9 10 10
Patient characteristic
Male 7 7 7 7
Female 9 9 9 9
Mean age ± SD 28.6 ± 6.7 33.6 ± 6.7 28.6 ± 6.7 33.6 ± 6.7

Local anesthetic admistration, appropriate enamel and dentin shades selection using the Vita shade guide under ambient lighting conditions and rubber dam isolation preceeded cavity preparation with diamond instruments in a highspeed handpiece with water spray. Position of margins of Class II restorations was within enamel and all enamel margins were beveled in this study for maximum adhesive retention and optical blending using the Sonic-Sys (KaVo Company) torpedo and hemisphere diamond coated bevel tips. A sectional matrix system (3M ESPE) wedged firmly against the approximal sides of the teeth was used for all Class II restorations. Preparations closer than 0.5 mm to the pulp were covered with Vitrebond (3M ESPE), a glass ionomer light cured liner, before bonding procedures. All-etch conditioning was performed with a phosphoric etching gel (3M Etching gel, 3M ESPE) used for 15–30 s, followed by thorough rinsing with water and gentle air drying. Two coats of Single Bond/Scotch Bond Adhesive (3M ESPE) were applied with 20 s waiting period in between the coats, followed by gentle air-drying for 10 s and finally light cured for 20 s. Resin composites were placed following the incremental technique (2 mm thick layers) and cured with the Elipar Freelight Serial No. 939800005306 (3M ESPE; ≥400 mW/cm 2 ) according to the manufacturer’s instruction for use. Finishing and polishing was accomplished using the diamond composite finishing kit (Komet GmbH, Germany) and the Sof-Lex (3M ESPE) finishing and polishing set as described previously . Fig. 1 provides clinical pictures of a typical Class I and a Class II restoration. Finally, an alginate impression was made and then a gypsum cast, from which acrylic posterior custom trays were fabricated. These custom trays were used for impression procedures at each registration session.

Fig. 1
Clinical pictures of a typical Class I and a Class II restoration.

Clinical recall

At baseline, this means after 1 month of clinical service (in order to allow running-in wear for occlusal adaptation) and at subsequent recalls, subsequent to a brief soft tissue survey and recording of gingival conditions, intra oral radiographs were taken and postoperative sensitivity, if present, was also evaluated with CO 2 snow (Fricar, Odontotest) and the sensitivity was scored as positive or negative. Each restoration was documented photographically (with and without articulation paper). Two impressions per air-dried, cotton-roll isolated tooth were taken with polyvinyl siloxane impression material using individualized custom trays. Prior to impression-making, the occlusal surface of the restored tooth was wiped with 0.5% NaOCl solution soaked gauze for 15 s followed by rinsing with water for 30 s . One impression was poured with white stone gypsum GC Fujirock EPWhite (Dental stone type IV, GC Europe, Leuven, Belgium) for laser scanning and another impression in Araldite D, Ciba Geigy (Belgium) for morphological observation complemented with SEM study. All replicas were uniformly trimmed and mounted on aluminum stubs for easy handling and repositioning.

Wear analysis

Wear was measured on the mounted gypsum dies using a 3D Laser scanner (Willytec GmbH, Germany). In this technique , by aligning the three user-defined reference points, Match 3D – a specially developed image analysis software (volume, mean vertical loss, 0.5% quantiles) superimposed the 3D surface data obtained from the follow-up (6- to 60-month) images on the data points of the baseline images. Iterative matching and standard error minimizations were carried out until the standard deviation was less than 20 μm for the match to be accepted , following which the software performed digital subtraction of follow-up image from the baseline image. The generated differential image was used to quantify the wear magnitude (see Ref. for details on matching procedure) on occlusal contact area on composite (OCAC), (see Ref. for details on measurement technique). With the manual editing of the difference image after eliminating the material excess along the buccal-, lingual-fissures and beveled cavosurface margins, volume loss calculations were performed. The statistic mode of the difference images was activated to quantify the total surface volume loss (TSV loss), restorative surface volume loss (RSV loss) and enamel surface volume loss (ESV loss) in mm 3 . The product of the number of pixels contained in the digitally cut restorative area (from the surrounding enamel) and the size of the x coordinates provided the restorative surface area (RSA) and the enamel surface area (ESA).

Statistical analysis

The two materials were compared with each other by means of pairwise contrasts using an F -test. Vertical wear rate (micrometer/month) and volume loss rate (mm 3 /month) [rho] with standard error were estimated on the basis of a 60 month time period for the three composites using a linear relation; i.e. Wear = rho × time + error. A Linear mixed model, using PROC MIXED in SAS (version 9.2; Cary, NC, USA), was used to regress the outcome variables (vertical wear/volume loss) to the effects of time, age, gender, cavity type, surface area, quadrant type and operator while taking into account the correlation between the measurements coming from the same patients. Based on Akaike’s Information Criteria (AIC) model building (in Q5) was performed separately for the two restorative materials with the following covariates – cavity type, operator, surface area, tooth (upper/lower), and operator × cavity type interaction. For each analysis a model building was performed to arrive at the best fitting model (lowest AIC), with ‘operator’ as a fixed effect and single patient was included as a random effect. Statistical significance was accepted at p < 0.05. An operator effect can then only be interpreted for the two specific operators in the study. In a second analysis ‘operator’ was considered as a random variable. This corresponds to the idea that any operator (out of a population of operators) could be randomly sampled. Then results of the analysis can be generalized to any sample of operators.

Micromorphological wear

The epoxy replicas were gold sputtered, subjected to high magnification dental surgical optical microscopy (OPMI Pro ergo, Carl Zeiss surgical GmbH, Oberkochen, Germany), prior to SEM imaging. The potential samples demonstrating interesting micromorphologic features such as defined wear facets, differential wear steps, degrading margins and fractures were further explored under SEM. Quadrant-wise photomicrographs of each sample were made initially followed by thorough scanning area by area up to the magnification of 200.

Materials and methods

Study population

The subjects in the present study were selected from a group of 30 dental student volunteers, by applying strict inclusion and exclusion criteria as mentioned before . 16 subjects in need of a minimum of two Class I and/or Class II restorations of comparable size involving failed restorations and primary caries perwere invited to join the study. Each subject signed an informed consent to participate in the study, which was approved by the medical ethics committee of the Catholic University of Leuven.

Restoration placement

From two restorative dentists blinded for the type of restorative materials, 16 patients received a total of 37 restorations (11 primary caries and 26 failed restorations), divided into two blocks (Class I and Class II). The filling materials listed in Table 1 – Z100 or Filtek Supreme was randomized over these blocks with the use of random number generating functions in Excel following a percent distribution of Class I versus Class II as 53:47 for Z100 and 44:56 for Filtek Supreme. Table 2 summarises the attributes of restorations and patients of this study.

Table 1
Description of materials used in this study.
Material Type Polymer * Fillers * Filler size * Filler content (% by volume) *
Range Mean
Z100 Microhybrid Bis-GMA, TEGDMA Zirconia, silica 0.01–3.5 μm 0.6 μm 66%
Filtek Supreme (translucent) Nano Bis-GMA, UDMA, Bis-EMA, TEGDMA SiO 2 nanoclusters and nanomers 0.6–1.4 μm 75 nm
75 nm
57.7%
Filtek Supreme (D/E/B) Nano Bis-GMA, UDMA, Bis-EMA, TEGDMA ZrO 2 /SiO 2 nanoclusters SiO 2 nanomers 0.6–1.4 μm ZrO 2 -5 nm
SiO 2 -20 nm
20 nm
59.5%
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Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Nanofilled and microhybrid composite restorations: Five-year clinical wear performances
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