title: In vitro fracture load of monolithic lithium disilicate ceramic molar crowns with different wall thicknesses.
abstract: OBJECTIVE
  The objective of this in vitro study was to assess the effect of wall thickness on the fracture loads of monolithic lithium disilicate molar crowns.
  
  
  METHODS
  Forty-eight extracted molars were prepared by use of a standardized preparation design. Lithium disilicate crowns (e.max CAD, Ivoclar/Vivadent, Schaan, Liechtenstein) of different wall thicknesses (d = 0.5, 1.0, and 1.5 mm; n = 16 for each series) were then constructed and milled (Cerec MC-XL, Sirona, Bensheim, Germany). After placement of the teeth in acrylic blocks (Technovit, Heraeus Kulzer, Hanau, Germany), the crowns were adhesively luted (Multilink, Ivoclar Vivadent). In each series, eight crowns were loaded without artificial aging whereas another eight crowns underwent thermocycling (10,000 cycles, THE-1100, SD Mechatronik) and chewing simulation (1.2 million cycles, Willytec CS3, SD Mechatronik, F max = 108 N). All specimens were loaded until fracture on one cusp with a tilt of 30° to the tooth axis in a universal testing machine (Z005, Zwick/Roell). Statistical assessment was performed by use of SPSS 19.0.
  
  
  RESULTS
  Crowns with d = 1.0 and 1.5 mm wall thickness did not crack during artificial aging whereas two of the crowns with d = 0.5 mm wall thickness did. The loads to failure (F u) of the crowns without aging (with aging) were 470.2 ± 80.3 N (369.2 ± 117.8 N) for d = 0.5 mm, 801.4 ± 123.1 N (889.1 ± 154.6 N) for d = 1.0 mm, and 1107.6 ± 131.3 N (980.8 ± 115.3 N) for d = 1.5 mm. For aged crowns with d = 0.5 mm wall thickness, load to failure was significantly lower than for the others. However, differences between crowns with d = 1.0 mm and d = 1.5 mm wall thickness were not significant.
  
  
  CONCLUSIONS
  Fracture loads for posterior lithium disilicate crowns with 0.5 mm wall thickness were too low (F u < 500 N) to guarantee a low complication rate in vivo, whereas all crowns with 1.0 and 1.5 mm wall thicknesses showed appropriate fracture resistances F u > 600 N.
  
  
  CONCLUSIONS
  The wall thickness of posterior lithium disilicate crowns might be reduced to 1 mm, thus reducing the invasiveness of the preparation, which is essential for young patients.
authors.affiliation: Department of Prosthodontics, Section for Biomaterial Research, University Hospital Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany.|Private Dental Office, Bad Schoenborn, Germany.
authors.forename: Bodo
authors.initials: B
authors.lastname: Seydler
authors.affiliation: Department of Prosthodontics, Section for Biomaterial Research, University Hospital Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rues
authors.affiliation: Department of Prosthodontics, Section for Biomaterial Research, University Hospital Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany.
authors.forename: Denise
authors.initials: D
authors.lastname: Müller
authors.affiliation: Department of Prosthodontics, Section for Biomaterial Research, University Hospital Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany. marc_schmitter@med.uni-heidelberg.de.
authors.forename: Marc
authors.initials: M
authors.lastname: Schmitter
mesh_terms: D003442:Crowns; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D006801:Humans; D066298:In Vitro Techniques; D008964:Molar, Third
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain
references.citation: Eur J Orthod. 2011 Aug;33(4):427-33
references.pmid: 21062965
references.citation: Dent Mater. 2008 Nov;24(11):1556-67
references.pmid: 18466964
references.citation: J Dent. 2012 Feb;40(2):154-62
references.pmid: 22197634
references.citation: J Dent Res. 2010 Oct;89(10):1051-6
references.pmid: 20660796
references.citation: Dent Mater J. 2008 May;27(3):422-6
references.pmid: 18717171
references.citation: Zahn Mund Kieferheilkd Zentralbl. 1978;66(2):125-32
references.pmid: 150164
references.citation: J Am Dent Assoc. 2008 Sep;139 Suppl:8S-13S
references.pmid: 18768903
references.citation: J Am Dent Assoc. 2012 Mar;143(3):234-40
references.pmid: 22383203
references.citation: Schweiz Monatsschr Zahnmed. 2004;114(2):115-9
references.pmid: 15119706
references.citation: Dent Mater. 2006 Nov;22(11):1008-13
references.pmid: 16375961
references.citation: J Prosthet Dent. 1986 Dec;56(6):666-71
references.pmid: 3464748
references.citation: Quintessence Int. 2006 Apr;37(4):253-9
references.pmid: 16594356
references.citation: J Prosthet Dent. 2006 Feb;95(2):117-23
references.pmid: 16473085
references.citation: Int J Prosthodont. 2000 Sep-Oct;13(5):387-91
references.pmid: 11203659
references.citation: J Prosthet Dent. 2003 Apr;89(4):374-80
references.pmid: 12690350
references.citation: Clin Oral Investig. 2013 Sep;17(7):1765-72
references.pmid: 23135425
references.citation: Arch Oral Biol. 1998 Apr;43(4):305-11
references.pmid: 9839706
references.citation: J Dent Res. 2002 Jun;81(6):433-8
references.pmid: 12097438
references.citation: Eur J Prosthodont Restor Dent. 2009 Jun;17(2):73-7
references.pmid: 19645308
references.citation: J Dent Res. 2012 Mar;91(3):305-10
references.pmid: 22205635
references.citation: J Prosthodont. 2008 Jul;17(5):370-7
references.pmid: 18355164
references.citation: Adv Dent Res. 1992 Sep;6:82-9
references.pmid: 1292468
references.citation: J Dent Res. 2009 Apr;88(4):382-6
references.pmid: 19407162
references.citation: Int J Prosthodont. 2010 Sep-Oct;23(5):434-42
references.pmid: 20859559
references.citation: Eur J Orthod. 2010 Feb;32(1):71-7
references.pmid: 19684125
references.citation: Int J Prosthodont. 2007 Jul-Aug;20(4):383-8
references.pmid: 17695869
references.citation: Int J Periodontics Restorative Dent. 2002 Jun;22(3):241-9
references.pmid: 12186346
references.citation: J Prosthodont. 2009 Dec;18(8):649-55
references.pmid: 19682214
references.citation: Acta Odontol Scand. 1977;35(6):297-303
references.pmid: 271452