title: Contraction stress related to degree of conversion and reaction kinetics.
abstract: Polymerization shrinkage of composites bonded to cavity preparations generates stress on the tooth/restoration interface. The purpose of this study was to verify the influence of degree of conversion and speed of polymerization reaction on contraction stress. We prepared experimental composites with different curing rates by varying the concentration of inhibitor (butylated hydroxytoluene). We verified the effect of degree of conversion by submitting one of the composites to different photo-activation times. Contraction stress was monitored for 10 minutes in a tensilometer. Fourier-transformed infrared spectrometry was used for assessment of the degree of conversion. Volumetric shrinkage was determined by means of a mercury dilatometer. Degree of conversion and volumetric shrinkage showed a non-linear relationship with energy density. Degree of conversion showed a pronounced influence on stress. Increased inhibitor concentration reduced curing rate and contraction stress in composites, without compromising the final degree of conversion.
authors.affiliation: Department of Dental Materials, University of São Paulo, School of Dentistry, São Paulo, Brazil. bragar@ohsu.edu
authors.forename: R R
authors.initials: RR
authors.lastname: Braga
authors.forename: J L
authors.initials: JL
authors.lastname: Ferracane
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002084:Butylated Hydroxytoluene / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008027:Light; D008628:Mercury; D008689:Methacrylates / Q000737:chemistry; D010777:Photochemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D019163:Reducing Agents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011108:Polymers; D011109:Polymethacrylic Acids; D019163:Reducing Agents; D013729:Terpenes; C020946:triethylene glycol dimethacrylate; D002084:Butylated Hydroxytoluene; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C048339:camphoroquinone; D008628:Mercury; C049840:2-(dimethylamino)ethyl methacrylate