| ObjectivetTo detect the chemical interaction of malic(MA), tartaric(TA) and citric acid(CA) with synthetic hydroxyapatite, the evidence of chemosorption of the acids to calcium of dental hard tissue and to observe the etching ability of the acids to tooth hard tissue.Materials and MethodsThe synthetic hydroxyapatite sample or Ca(OH)2 powder was shaken with a series of standard aqueous solutions (15w/v%) of MS CA or alcohol-aqueous (50:50) solution of TA for 24h at room temperature. The precipitate and the mother solution were separated, and they were dried in a vacuum over silica gel. Fourier transform infrared spectrophotometric (FTIR) measurement were performed for the dried precipitate and the desiccated powder of mother solution. The resultant products of acid with hydroxyapatite or Ca(OH)2 were analyzed with XRD to determine what kind of reaction products were formed.A couple of enamel and dentin disk were as control(untreated with acid).The surfaces of 3 tooth disks were treated with 15% MA, TA CA separately for 1 minutes, and the treated surfaces were washed with water spray. The other 3 tooth disks were also treated with three acid aqueous solution separately for the same time without washing. All of the specimens were dried and detected by Attenuated Total Reflectance (ATR) to verify the bonding evidence of the carboxylic acids to the dental surface. Tooth disks were also etched with 15% MAx TA or CA for 0, 15, 30, 60, 120s, 36% H3PO4 for 15,30s, and then rinsed, dried and gold-sputtered, in preparation for SEM observations.ResultsThe FTIR spectra showed carboxylate in the CA-filtrate; u ascoo.l584cm1, vsCOO-l408cm"1 and u c=ol724cm"' were observed in MA-solid materials;u as coo-1589cm"' ? uscoo- 1386cm"1 were detected in TA-solid-materials, and u ascoo- 1573m"? u scoo.1411cm"1 appeared in the TA-filtrate. The XRD analyses showed that the precipitable prudctions were mixture of HA and carboxylic calcium expect the precipitation of CA and HA, which was testified HA. The XRD data indicated that the reaction of MAN TA and CA with HA produced calcium carboxylateIt was detected with ATR that carboxylic acid were chemically bonded to the dental-hard tissue interfaces, as demonstrated by the characteristic absorption band for COO". The SEM micrographs indicated that the enamel surfaces treated with tartaric acid for 15s and 30s , malic acid and citric acid for 15s appeared inhomogeneously dull; The other treated surfaces showed a chalky appearance, similar to the clinically observed enamel surface changes after phosphoric acid etching. The micro-morphology of the etched dentin showed that the amorphous smear layers were dissolves, creates a zone of partially demineralized dentin. Lengthing etching time revealed significant changes in deeper demineralized dentin with the evidence of increased tubule diameter, and calcium malate crystals occluded dentin tubules. The diameter of dentin tubules which were treated with 15% CA was similar to those treated with 36% H3PO4.Conclusion: True chemosorption of malic, tartaric and citric acid to calcium present in dental-hard-tissue have been positively denmostrated by FT-IR, XRD and ATR. The enamel surface can be decalcified by the carboxylic acids showed a chalky appearance, smear layers were dissolved and dental tubules diameter were increased. The three kinds of carboxylic acid could be used as ingredients of self-etching primers. |
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