Cosmet. Sd., 52, 163-167 (May/June 2001) Abrasiveness evaluation of silica and calcium carbonate used in the production of dentifrices I. M. C. CAMARGO, M. SAIKI, M. B. A. VASCONCELLOS, and D. M. ]tVILA, Instituto de Pesquisas Energdticas e Nucleares, Centro de Qu/mica e Meio Ambiente, IPEN/CNEN-SP, Caixa Postal 11049, ZIP 05422-970, S•o Paulo, SP, Brazil. Accepted for publication March 15, 2001. Synopsis Our purpose was to apply a radiometric method to an abrasivehess evaluation in samples of silica and calcium carbonate used as an abrasive in a dentifrice, to help in a prudent selection of materials by dentifrice producers. The results of RDA (radioactive dentin abrasion) abrasivehess indices obtained for these com- pounds varied from 136 to 19. The relative standard deviations of these RDA results varied from 5.9% to 11.8%, showing a good precision in the method. Also, the results obtained indicated that the abrasivehess indices increase with the particle size of the material. A comparison between different abrasives with similar particle sizes showed that silica presents higher RDA values than calcium carbonate. INTRODUCTION Dentifrices are cosmetics used with toothbrushes to clean tooth surfaces to prevent the accumulation of stains and plaques. Therefore, they should present an appropriate abra- siveness to clean the teeth, but without causing wear. Consequently, knowledge of the characteristics of the abrasive agents used for dentifrice manufacturing is of interest to industries in order to obtain appropriate products for perfect oral hygiene without causing wear to the teeth or restorative materials. The abrasives commonly utilized in the dentifrices produced in Brazil are silica and calcium carbonate, and their quantities in dentifrices vary from 30% to 48% in mass (1,2). Among several articles related to the use of abrasives in the dentifrices, one by Boer et al. (3) evaluated the wear caused by abrasives through the method of surface profilometry and verified the correlation between abrasivehess and the particle size of abrasives. Also, these authors obtained different abrasivehess values for distinct abrasives presenting similar particle sizes, that is, the abrasive AI(OH) 3 of 7-1•m particle size showed greater abrasivehess than that presented by CaCO 3 with 8-1•m particle size. This difference in abrasivehess may be attributed to the distinct particle hardness of these two agents. Address all correspondence to M. Saiki. 163

164 JOURNAL OF COSMETIC SCIENCE Kinoshita et al. (4) examined several dentifrices by the methods of surface analyzer and scanning electron microscopy. Among the several abrasives (CaHPO 4 ß 2H20, a mix of CaHPO 4 ß 2H20 + CaHPO4, and CaSiO3) , CaSiO 3 appeared to be more abrasive than the other two. Also, Panzeri et al., (5) examined by scanning electron microscopy the particles of abrasives used in 17 dentifrices and concluded that the majority of their particles present irregular forms and heterogeneous arrangements of the particles. In this work, the abrasiveness of the samples of silica and calcium carbonate was evaluated by radiometric method. This method consisted of brushing the irradiated teeth (dentine) with an abrasive agent and reference material slurties, one at each time. The beta radioactivity of 3•p transferred from the dentine to slurties was measured using a plastic scintillatot detector. The abrasiveness index or RDA (radioactive dentine abra- sion) is the ratio of 3•p counting rates obtained for abrasive and reference material slurties (6). MATERIALS AND METHODS MATERIAL SAMPLE The materials silica and calcium carbonate were provided from industries. PROCEDURE The radiometric method applied was based on a paper by Hefferren (6). The experi- mental conditions were established in order to use the available facilities. This experi- mental procedure consisted of the following steps: Selection of the teeth. The substracts to be abraded were roots from extracted permanent human teeth. After extraction, the teeth were stored in 4% formaldehyde solution. They were cleaned by stirring in a domestic detergent solution and then were washed with water and cut, separating the crown from the root. Irradiation of roots of the teeth. The roots of the teeth immersed in formaldehyde solution were irradiated in plastic vials during a one-hour period under a thermal neutron flux of 10 •2 n/cm-2/s -• at the IEA-R1 nuclear research reactor and in a position where the temperature was lower than 40øC. After irradiation, the tooth samples were removed from the core of the reactor to avoid damage from gamma radiation. During the irradiation a part of 3•p present in the hydroxyapatite of teeth was converted to radio- active 32p. Brushing operation of the teeth. After about one week of decay time, these irradiated teeth were fixed in a mold made by dental methacrylate resin that was fitted in a sample holder (reservoir for slurry) of a brushing machine. The brushing machine was manu- factured at IPEN/CNEN-SP and was equipped with two toothbrushes made of nylon bristles of medium hardness and a stroke counter with 125 strokes/min. A pressure corresponding to 150 g could be applied on each toothbrush. Before the first brushing, the irradiated dentins were brushed with a slurry containing reference material of calcium pyrophosphate for 6000 strokes in order to reduce irregular patterns of abrasion on the surfaces of the newly mounted teeth. The number of strokes applied to each toothbrushing operation was 1000.