Proceedings of 5th International Congress on Nanoscience & Nanotechnology (ICNN2014) 22-24 October 2014, Tehran, Iran Effect of nanoparticles on wear mechanisms of hybrid dental nanocomposite Sepehr Salari a *, Sara Dadkan a , Mehrdad Khakbiz a , Mohammad Atai b a Department of Biomedical Engineering, University of Tehran, 1439955941, Iran b Polymer Science Department, Iran Polymer and Petrochemical Institute, 115/14965, Iran * s.salari@ut.ac.ir Abstract: One of the main problems of nano dental composites is their low wear resistance specially used in posterior restoratives. Many studies have been conducted on this area to recognize and increase wear resistance by changing and improving monomers, fillers and filler content. One of the newly introduce fillers in dental composites is Lanthanum Oxide nano particles. Its radiopaque property is very suitable for dental composites since radiopaque properties needed to enable rapid identification, reliable and non-destructive recognition of dental caries. In this study, the effect of lanthanum oxide nanoparticles on wear properties of dental nanocomposites has been studied. The results showed that the wear behaviour of nano-composite with less than 5% lanthanum oxide is different with higher percentages, in which composites contained lower particles as reinforcements, abrasive wear is dominated though with increasing the filler content it will change to adhesive wear mechanism. SEM and EDX was taken from wear surface and wear debris respectively to show these changes. It can be said that with increasing the nano particles more stable and strengthened transfer surfaces will be made which makes the adhesive mechanics the dominated mechanism for filler contents above 7 wt% Lanthanum oxide. Keywords: Dental composites, Lanthanum Oxide, Wear mechanisms Introduction Visible light-curable polymeric composites are most commonly used restoratives for the replacement of lost hard dental tissues [1]. Generally, a dental resin- composite contains an organic matrix and inorganic fillers by which properties of the dental composites are greatly influenced by both the properties of their fillers and chemical structure of the monomers used in the matrix phase [2]. Increasing filler content or incorporating fillers with high hardness tends to improve mechanical properties i.e. wear resistance, flexural strength and micro harness, which is essential for long durability of restorative materials [3]. When used, composite restorations were subjected to complex mastication forces with a considerable amount of flexural stresses which cause severe wear on restoratives [4]. Due to their lacking mechanical properties and wear resistance, currently developed dental composites are used mostly for anterior and rarely for posterior dental restorations [5]. There have been significant developments in resin monomers, fillers and filler/matrix coupling agents to improve wear resistance [6]. Knowing which wear mechanism is mostly responsible for wear, could help researchers to better understand and control this property of nano dental composites. Lanthanum Oxides is used to make optical glasses, to which this oxide confers increased density, refractive index, and hardness. Since they are the main element which is incorporated in dental composites to induce radiopacity, In this study Lanthanum Oxides nano-particle was used as nano-filler and the main purpose of the present study was to characterize by which mechanisms of wear usually happen for dental composites and which one is dominated by the other, Materials and method Quartz fillers were obtained from MERCK . Lanthanum Oxide, Bis-GMA, triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA) (755885), Camphoroquinone (CQ)) and N, N-dimethyl aminoethyl methacrylate (DMAEMA), all were purchased from Aldrich (England). Fillers were separately surface modified with 1 wt% ɣ- MPS. Modified fillers (MFs) were then washed three times with acetone to remove unattached Ɣ- MPSs then they were dried for 4hrs in oven with 90°C temperature. Absorbance peaks was obtained by FT-IR to determine the treatment of fillers. To reduce viscosity of monomers acetone added to the mixture of monomers. Finally MFs was added to the solution by 0, 2, 5, 7, 10 and 12.5 weight percent of filler and Quartz quantity decreased accordingly and then sonicated for 30min to separate the possible agglomerated particles. To mix Quartz and Lanthanum Oxide fillers with monomer phase and photo initiator system, all were hand mixed. Results and Discussion Fig. 1 shows the weight loss of samples versus time in which by increasing time the wear rate increased. Moreover adding more fillers resulted in decreased wear rate and makes the wear mechanisms more stable especially for filler content more than 5% of lanthanum oxides. Samples with lower nano filler are more susceptible to fillers detached from the surface which makes the resin surface in contact to abrasive pin, however detaching fillers in samples with higher nano