Evaluation of wear of contemporary flowable resin composites: an in vitro study

Abstract

OBJECTIVES: Dental wear is considered one of the reasons for composite restorations failure. Several clinical problems may arise as result of uncontrolled wear process, including compromising masticatory function, poor aesthetics, loss of interocclusal space, teeth pain and sensitivity, and tempromandibular problems. Newly released flowable composites have been introduced to the market, that are indicated for occlusal class I and II cavity restorations. The purposes of this study are (1) to evaluate the wear resistance of newly released flowable composites against two antagonists, and compare them to universal packable composite, (2) to compare the wear properties of the two different types of antagonists, (3) to evaluate mechanical and esthetic properties, including microhardness, gloss, and surface roughness, of all resin composites and correlate it to wear characteristics of the materials. MATERIALS AND METHODS: (1) Five flowable composites were used in this study: 1. Filtek Supreme Ultra Flow (3M ESPE), 2. NovaPro Flow (Nanova Biomaterials), 3. SureFil SDR Flow (Dentsply), 4. Clearfil Majesty Flow (Kuraray), and 5. G-aenial Universal Flo (GC). One universal resin composite (Filtek Supreme Ultra Universal) was used as control group. 16 Specimens were prepared from each composite by injecting into aluminum molds, then divided into two groups for two types of antagonists (n=8). The first antagonist from natural enamel cusps, the other type was from feldspar ceramic block, Vitabloc Mark II. Both were standardized and polished. After mounting the antagonists in the wear-testing machine, a uniform sliding abrasion was applied up to 200k sliding cycles. Then the measurement of dry weight, wear depth and surface roughness of the specimens and the antagonist cusps were conducted at 3 different intervals, baseline, 100k, and 200k cycles. The amount of wear was determined by measuring the weight loss and calculating volume loss. One representative sample was randomly selected from each group for scanning electron microscope examination of the surface morphology. (2) 3 samples were prepared from each resin composite material for the microhardness and gloss test. The composite specimens were finishing and polishing by Buehler grinding-polishing system for four minutes each, then rinsed and ultrasonically cleaned in distilled water for 4 minutes. The surface gloss test was performed by using Novo Curve glossmeter. Five gloss readings were taken from each specimen at different locations, and the mean value was calculated and recorded as the GU reading of each specimen. The Knoop’s microhardness was measured on a MICROMET 2003 microhardness tester. Five indentations at different locations with at least 100 μm apart were performed on each specimen. The five readings were averaged to produce a single hardness value for each specimen. RESULTS: (1) In general, statistical analysis revealed a significantly higher surface roughness and higher weight loss of all resin composites when opposed by ceramic antagonists compared to the samples opposed by enamel antagonists. Among the tested resin composites, there were significant differences in regards to specimen wear depth, weight loss, volume loss, and surface roughness, regardless of the antagonist type used. Both Filtek supreme universal and Filtek supreme ultra flow groups showed significantly deeper wear compared to the other flowable materials, regardless of the antagonist type used. Moreover, there were statistically significant differences in antagonist’s weight and height loss between the groups. The control group universal composite caused significantly higher weight and height loss of both antagonists. (2) The microhardness and gloss results demonstrated statistical significant differences between all the composite materials. Clearfil Majesty Flow and Filtek Supreme Universal groups exhibited a significantly higher surface gloss compared to the other materials with the exception of the Filtek Supreme Ultra Flow group. Filtek Supreme Universal group exhibited a significantly higher Knoop’s hardness compared to the other materials. CONCLUSIONS: Despite the limitation of this study, less weight loss and surface roughness of the flowable composites were shown when opposed by dental enamel antagonists. A significantly deeper wear was noticed on both Filtek supreme universal and flowable composites when opposed by ceramic antagonists, indicating the detrimental effect of the Feldspathic ceramic on the nanohybrid composites compared to the other nanofilled flowable composites used in the study