title: Effect of thermo-mechanical loading on marginal quality and wear of primary molar crowns.
abstract: OBJECTIVE
  To evaluate the effect of thermo-mechanical loading (TML) on marginal quality and wear of different crown types for primary molars.
  
  
  METHODS
  Eighty extracted human primary molars were used. After preparation, five groups received different crowns (n=16): preformed metal crowns (3M ESPE) and NuSmile crowns (Orthodontic Technologies Inc.) were inserted as preformed metal crowns; as semi-preformed crowns Protemp crowns (3M ESPE) were luted; and as individually manufactured resin composite crowns Filtek Z250 (3M ESPE) and Heliomolar (Ivoclar Vivadent) were used. Specimens were subjected to 2,500 thermal cycles between 5-55(o)C and chewing simulation for 100,000 cycles at 50N at a frequency of 0.5 Hz. Before and after thermo-mechanical loading, impressions of the teeth were taken and replicas were made. The replicas received marginal quality evaluation under a SEM at x200 magnification. Occlusal wear was measured as vertical height loss using a 3-D laser scanning microscope.
  
  
  RESULTS
  After TML, all crowns were intact. The adhesively bonded crowns showed significantly better marginal quality to dentine/cementum compared with GIC luted crowns (p<0.05). Laboratory made crowns showed a good fit and nearly transition-free margins also after TML. Preformed metal crowns showed the significantly lowest wear rates compared to the resin composites (p<0.05). Among the resin composite groups, Protemp exhibited the most pronounced wear depths (p<0.05).
  
  
  CONCLUSIONS
  The different crown types under investigation showed a good performance concerning the evaluated parameters marginal quality and wear.
authors.affiliation: Department of Paediatric Dentistry, University Medical Center Giessen and Marburg, Marburg, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Krämer
authors.forename: H
authors.initials: H
authors.lastname: Rudolph
authors.forename: F
authors.initials: F
authors.lastname: Garcia-Godoy
authors.forename: R
authors.initials: R
authors.lastname: Frankenberger
mesh_terms: D000134:Acid Etching, Dental; D000180:Acrylic Resins / Q000737:chemistry; D001732:Bite Force; D002858:Chromium Alloys / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003442:Crowns; D003722:Dental Alloys / Q000737:chemistry; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D017267:Dental Prosthesis Design; D019554:Dental Restoration Wear; D003801:Dental Veneers; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D018613:Microscopy, Confocal / Q000379:methods; D008855:Microscopy, Electron, Scanning; D008963:Molar; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014094:Tooth, Deciduous
chemical_list: D000180:Acrylic Resins; D002858:Chromium Alloys; D003188:Composite Resins; D003722:Dental Alloys; D003764:Dental Materials; C444701:Filtek Z250; D005899:Glass Ionomer Cements; C513708:Heliomolar; C424245:Ketac-Molar Aplicap; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C425843:Prime and Bond NT; D019279:Resin Cements; D013193:Stainless Steel; C069714:Protemp