title: Characterization of the porosity of human dental enamel and shear bond strength in vitro after variable etch times: initial findings using the BET method.
abstract: OBJECTIVE
  (1) To quantitatively characterize human enamel porosity and surface area in vitro before and after etching for variable etching times; and (2) to evaluate shear bond strength after variable etching times. Specifically, our goal was to identify the presence of any correlation between enamel porosity and shear bond strength.
  
  
  METHODS
  Pore surface area, pore volume, and pore size of enamel from extracted human teeth were analyzed by Brunauer-Emmett-Teller (BET) gas adsorption before and after etching for 15, 30, and 60 seconds with 37% phosphoric acid. Orthodontic brackets were bonded with Transbond to the samples with variable etch times and were subsequently applied to a single-plane lap shear testing system.
  
  
  RESULTS
  Pore volume and surface area increased after etching for 15 and 30 seconds. At 60 seconds, this increase was less pronounced. On the contrary, pore size appears to decrease after etching. No correlation was found between variable etching times and shear strength. Samples etched for 15, 30, and 60 seconds all demonstrated clinically viable shear strength values.
  
  
  CONCLUSIONS
  The BET adsorption method could be a valuable tool in enhancing our understanding of enamel characteristics. Our findings indicate that distinct quantitative changes in enamel pore architecture are evident after etching. Further testing with a larger sample size would have to be carried out for more definitive conclusions to be made.
authors.affiliation: Orthodontic Graduate Program, School of Dentistry, University of California San Francisco, CA, USA.
authors.forename: Trang T
authors.initials: TT
authors.lastname: Nguyen
authors.forename: Arthur
authors.initials: A
authors.lastname: Miller
authors.forename: Maria F
authors.initials: MF
authors.lastname: Orellana
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods*; D000293:Adolescent; D000327:Adsorption; D002648:Child; D001840:Dental Bonding; D003743:Dental Enamel / Q000187:drug effects* / Q000648:ultrastructure*; D003745:Dental Enamel Permeability; D003799:Dental Stress Analysis; D006801:Humans; D016910:Orthodontic Brackets; D010756:Phosphoric Acids / Q000494:pharmacology; D016062:Porosity; D019279:Resin Cements; D033081:Shear Strength; D013499:Surface Properties
chemical_list: D010756:Phosphoric Acids; D019279:Resin Cements; C030242:phosphoric acid