The Journal of Prosthetic Dentistry Caiado et al Clinical Implications Phosphoric acid treatment of coronal or root canal dentin re- sults in a greater dentin tubular cross-sectional area than does treatment using a self-etching primer, and these differences may influence bond strength of resins to these areas. Statement of problem. Coronal and radicular dentin may react differently to the type of acid treatment used when bonding to these substrates. Purpose. The purpose of this study was to characterize and compare dentin morphology, tubular density, and cross- sectional area in deep coronal (around an exposed pulp horn) and root canal dentin at the cervical third in the intact state and after acid etching with phosphoric acid or self-etching dentin primer. Material and methods. Extracted, human, caries-free premolars were fixed. Smear layer-free sections (control) were obtained and divided into 3 groups: left intact, etched with phosphoric acid, or etched with a self-etching primer from a dentin bonding system. Specimens were examined using scanning electron microscopy. Tubular density and cross-sectional area were determined from the images using software. Values were submitted to multifactorial ANOVA (α=.05). Results. Tubular density was not significantly affected by acid type or by dentin location. Acid type significantly (P<.001) affected tubular cross-sectional area: phosphoric acid > self-etching resin > intact dentin, irrespective of dentin location. All acid-treated specimens showed demineralization, and irregular surface morphology was not af- fected by either acid treatment. Conclusions. Tubular density was not significantly different between deep coronal and root canal dentin nor affected by acid treatment type. Tubular cross-sectional area did not differ between deep coronal or root canal dentin, regard- less of acid treatment. Both acid types significantly increased tubular cross-sectional area at both dentin locations, phosphoric acid to a greater degree than the self-etching primer. Root canal dentin did not display peritubular dentin. (J Prosthet Dent 2010;103:352-361) The effect of acid etchant type and dentin location on tubular density and dimension Ana Carolina Rocha Lima Caiado, MSc, DDS, a Mario Fernando de Goes, PhD, MSc, DDS, b Francisco José de Souza-Filho, PhD, MSc, DDS, c and Frederick A. Rueggeberg, DDS, MS d Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil; School of Dentistry, Medical College of Georgia, Augusta, Ga This work was supported by the State of São Paulo Research Foundation (FAPESP), grant no. 05/53290-0, and The National Council for Scientific and Technological Development of Brazil (CNPq), grant no. 310845/2006-8. a Department of Restorative Dentistry, Area of Endodontics, Piracicaba Dental School, State University of Campinas. b Department of Restorative Dentistry, Area of Dental Materials, Piracicaba Dental School, State University of Campinas. c Department of Restorative Dentistry, Area of Endodontics, Piracicaba Dental School, State University of Campinas. d Section Director, Dental Material Sciences, Department of Oral Rehabilitation, School of Dentistry, Medical College of Georgia.