Hydrolytic stability of experimental hydroxyapatite-filled dental composite materials C. Domingo a, * , R.W. Arcı ´s a , E. Osorio b , R. Osorio b , M.A. Fanovich a , R. Rodrı ´guez-Clemente a , M. Toledano b a Institut de Cie `ncia de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Spain b Facultad de Odontologı ´a, Universidad de Granada, Granada, Spain Received 7 August 2001; revised 2 May 2002; accepted 11 July 2002 Abstract Objectives. The purpose of this study was to analyze the behavior in water, related to mechanical properties, of experimental composites for dental restoration. Methods. The studied materials were composed of a visible-light-curing monomer mixture (Bis-GMA and TEGDMA or HEMA) and micrometric, nanometric or a mixture of both sizes hydroxyapatite particles as a reinforcing filler. Filler particles were modified with a coupling agent (citric, hydrosuccinic, acrylic or methacrylic acid or silane). The hydrolytic stability of the evaluated materials was studied through total elution and water-uptake tests. Percent net-mass variation was daily monitored and analyzed as a function of time. Mechanical performance was examined through flexural properties and Vickers hardness. Morphological surface changes were observed with scanning electron microscopy. ANOVA statistical analysis was performed (P , 0.05). Results. In general, the use of HEMA instead of TEGDMA did not substantially worsen the composite quality. Dental composites containing only nanometric particles of hydroxyapatite as a filler are unsuitable for clinical performance. Midway-filled composite resins loaded with micro-HAP particles, coated with citric, acrylic or methacrylic acid displayed low percent elution and water-uptake values. Mechanical properties were similar or even superior to those measured for silane treated particles. Significance. More research is needed to further improve the interaction of nano-HAP particles with the polymeric matrix, either as a single filler or, preferentially, mixed with micro-HAP, that will allow to increase the total loading of reinforcing filler and, hence, to improve the mechanical properties. q 2003 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved. Keywords: Dental composites; Bisphenol-a-glycidyl methacrylate; Triethyleneglycol dimethacrylate; Hydroxyethyl methacrylate; Visible-light-curing; Hydroxyapatite; Hybrid composites; Water-aging; Mechanical properties 1. Introduction Synthetic apatites are excellent biomaterials from the viewpoint of biocompatibility and they have been applied in the dental and medical fields [1–5]. Composite materials used in dental restoration consist of a continuous polymeric matrix (usually involving the visible-light-curing bisphenol-a-glycidyl methacrylate (Bis-GMA) diluted with triethyleneglycol dimethacrylate (TEGDMA) [6,7]) reinforced with a dispersed phase (barium or zinc glasses, quartz, zirconia, silica, etc. [8, 9]). The use of HAP in restorative dentistry offers several promising advantages, including, intrinsic radio-opaque response, enhanced polishability and improved wear performance. Finally, this material is less expensive than most of the fillers mentioned earlier. The main disadvantage of HAP is its high refractive index when compared to those of light-activated polymers [2,10]. In preliminary investigations into the use of HAP as a filler for dental composites, the mechanical and surface properties of different experimental materials were precisely studied [11]. The analysis showed the influence of monomer mixture (Bis-GMA plus either TEGDMA or HEMA (hydroxyethyl methacrylate)), filler particle size (nanometric or micrometric) and coupling agent (different carboxylic acids) on the performance of several midway- filled HAP composite resins. To ensure viability of these Dental Materials 19 (2003) 478–486 www.elsevier.com/locate/dental 0109-5641/03/$ - see front matter q 2003 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved. doi:10.1016/S0109-5641(02)00093-3 * Corresponding author. Tel.: 93-5801-853; fax: 93-5805-729. E-mail address: conchi@icmab.es (C. Domingo).