title: Morphology and structure of polymer layers protecting dental enamel against erosion.
abstract: OBJECTIVE
  Human dental erosion caused by acids is a major factor for tooth decay. Adding polymers to acidic soft drinks is one important approach to reduce human dental erosion caused by acids. The aim of this study was to investigate the thickness and the structure of polymer layers adsorbed in vitro on human dental enamel from polymer modified citric acid solutions.
  
  
  METHODS
  The polymers propylene glycol alginate (PGA), highly esterified pectin (HP) and gum arabic (GA) were used to prepare polymer modified citric acids solutions (PMCAS, pH 3.3). With these PMCAS, enamel samples were treated for 30, 60 and 120s respectively to deposit polymer layers on the enamel surface. Profilometer scratches on the enamel surface were used to estimate the thickness of the polymer layers via atomic force microscopy (AFM). The composition of the deposited polymer layers was investigated with X-ray photoelectron spectroscopy (XPS). In addition the polymer-enamel interaction was investigated with zeta-potential measurements and scanning electron microscopy (SEM).
  
  
  RESULTS
  It has been shown that the profilometer scratch depth on the enamel with deposited polymers was in the range of 10nm (30s treatment time) up to 25nm (120s treatment time). Compared to this, the unmodified CAS-treated surface showed a greater scratch depth: from nearly 30nm (30s treatment time) up to 60nm (120s treatment time). Based on XPS measurements, scanning electron microscopy (SEM) and zeta-potential measurements, a model was hypothesized which describes the layer deposited on the enamel surface as consisting of two opposing gradients of polymer molecules and hydroxyapatite (HA) particles.
  
  
  CONCLUSIONS
  In this study, the structure and composition of polymer layers deposited on in vitro dental enamel during treatment with polymer modified citric acid solutions were investigated. Observations are consistent with a layer consisting of two opposing gradients of hydroxyapatite particles and polymer molecules. This leads to reduced erosive effects of citric acid solutions on dental enamel surfaces.
authors.affiliation: Chair of Materials Science, Faculty of Physics and Astronomy, Friedrich-Schiller-University Jena, Löbdergraben 32, Jena, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Beyer
authors.forename: Jörg
authors.initials: J
authors.lastname: Reichert
authors.forename: Bernd W
authors.initials: BW
authors.lastname: Sigusch
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
authors.forename: Klaus D
authors.initials: KD
authors.lastname: Jandt
mesh_terms: D000464:Alginates / Q000737:chemistry; D019343:Citric Acid / Q000737:chemistry / Q000494:pharmacology*; D003743:Dental Enamel / Q000187:drug effects*; D017886:Durapatite / Q000737:chemistry; D006170:Gum Arabic / Q000737:chemistry; D006801:Humans; D008855:Microscopy, Electron, Scanning; D008964:Molar, Third; D010368:Pectins / Q000737:chemistry; D056951:Photoelectron Spectroscopy; D011108:Polymers / Q000737:chemistry*; D019946:Propylene Glycol / Q000737:chemistry; D020011:Protective Agents / Q000494:pharmacology*; D014077:Tooth Erosion / Q000517:prevention & control*
chemical_list: D000464:Alginates; D011108:Polymers; D020011:Protective Agents; D019343:Citric Acid; D019946:Propylene Glycol; D010368:Pectins; D006170:Gum Arabic; D017886:Durapatite