Morphological field emission-SEM study of the effect of six phosphoric acid etching agents on human dentin

Jorge Perdigão, Paul Lambrechts, Bart Van Meerbeek, Ângelo R. Tomé, Guido Vanherle, Augusto B. Lopes

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Abstract

Objectives. This study evaluated the effects of six phosphoric acidetching agents on dentin, the independent variables being two acid concentrations (10% and 32%-37%) and three thickener conditions (no thickener, silica, and polymer). The tested hypothesis was that the use of different etchants with similar concentrations of phosphoric acid would result in similar depths of dentin demineralization. Methods. Thirty dentin disks were obtained from extracted human teeth by microtome sectioning. The dentin surfaces were etched with one of the etching agents, fixed, dehydrated and dried. The specimens were observed using a FE-SEM. The mean deepest demineralization of intertubular dentin was measured from the fracture surfaces of the disks. These values were analyzed by ANOVA and Duncan's test. The morphological appearance of the dentin surfaces was compared using the following observation criteria: 1) Presence of a cuff of peritubular dentin; 2) Relative thickness of the layer containing residual collagen or smear layer particles; and 3) Formation of a submicron hiatus at the bottom of the exposed collagen network. The pH of each of the etching agents was measured. A correlation analysis was made of the pH vs. the depth of dentin demineralization. Results. Silica-thickened etchants did not demineralize dentin as deeply as did polymer-thickened etchants and unthickened etchants. High magnifications revealed three distinct zones within the demineralized dentin layer: an upper porous zone of residual smear layer or denatured collagen and residual silica particles (in groups etched with silica-thickened etchants), an intermediate area with randomly oriented collagen fibers, and a lower zone with a submicron hiatus, few collagen fibers, and scattered hydroxyapatite inclusions. This hiatus was observable in all the specimens etched with the polymer-thickened etchants, in 90% of the specimens etched with the unthickened phosphoric acid liquids, and in 60% of the specimens etched with the silica-thickened gels. Significance. The results obtained suggest that similar concentrations of phosphoric acid etchants containing distinct thickeners result in different demineralization depths as well as different morphology of etched dentin.

Original languageEnglish (US)
Pages (from-to)262-271
Number of pages10
JournalDental Materials
Volume12
Issue number4
DOIs
StatePublished - 1996

Bibliographical note

Funding Information:
Based on a chapter of a thesis submitted to the graduate faculty, Catholic University of Leuven (KUL) by J. Perdigao, in partial fuI6Ihnent of the requirements for the Ph.D. degree. We thank Prof J. Vieira, Department of Ceramics and Glass, The University of Aveiro, Portugal, for extensive instrumental support. This research was supported in part by research grants from the Calouste Gulbenkian Foundation, Portugal, from the National Fund of Scientific Research, Belgium, from Ultradent Products Inc., USA, and from Bisco Dental Products, USA.

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