title: Masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial crowns with and without coverage of compromised cusps.
abstract: OBJECTIVE
  To evaluate preparation designs of compromised cusps and whether or not they influence masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial-coverage restorations (PCRs) luted on mandibular molars.
  
  
  METHODS
  Sixty-four caries-free molars were equally divided into four groups. Control group NP received no preparation (NP). Group B-IN received a basic inlay (IN) preparation with buccal (B) cusp conservation and occlusal reduction of both lingual cusps. Group B-ON was prepared in the same way, except buccal cusps were prepared with an angle of 45 degrees to the occlusal plane (buccal onlay). Group B-OV preparation was similar to group B-ON, but buccal cusps received a further shoulder preparation on the buccal aspect (buccal overlap). Forty-eight all-ceramic IPS e.max Press PCRs were fabricated and luted adhesively. Specimens underwent mouth-motion fatigue (1.2 million cycles, 1.6 Hz, 49 N) and 5500 thermal cycles (5 degrees C/55 degrees C). Fracture patterns were observed. Surviving specimens were loaded until fracture. Marginal discrepancies were examined.
  
  
  RESULTS
  Only one specimen of group B-ON fractured during fatigue. Median fracture loads (N) [IQR = x(.25) - x(.75)]: group NP = 1604 N [1182-1851 N], group B-IN = 1307 N [1262-1587N], group B-ON = 1396 N [817-1750N], group B-OV = 1205 N [1096-1542N]. No significant differences in fracture resistance were found between restored molars and unprepared teeth (p _ 0.18). Different preparation designs showed no significant influence on PCR fracture resistance. Mouth-motion fatigue caused a significanty decrease of marginal accuracy in groups B-IN (p = 0.009) and B-ON (p = 0.008). Marginal discrepancy values of groups B-IN and B-OV were significantly different after fatigue (p = 0.045).
  
  
  CONCLUSIONS
  Ceramic coverage of compromised cusps did not demonstrate an increase of fracture resistance after fatigue when compared to less invasive partial-coverage restorations. However, enhanced exposure of restoration margins to occlusal wear could result in more extensive marginal discrepancies.
authors.affiliation: Department of Periodontology and Implant Dentistry, Department of Biomaterials and Biomimetics, New York University College of Dentistry, New York, NY 10010, USA. christian.stappert@nyu.edu
authors.forename: Christian F J
authors.initials: CF
authors.lastname: Stappert
authors.forename: Pia
authors.initials: P
authors.lastname: Abe
authors.forename: Volker
authors.initials: V
authors.lastname: Kurths
authors.forename: Thomas
authors.initials: T
authors.lastname: Gerds
authors.forename: Jörg R
authors.initials: JR
authors.lastname: Strub
mesh_terms: D001732:Bite Force; D002484:Cementation; D003737:Dental Cavity Preparation / Q000379:methods; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D006801:Humans; D007284:Inlays; D008409:Mastication / Q000502:physiology; D008422:Materials Testing; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D019228:Tooth Crown / Q000473:pathology; D014082:Tooth Fractures / Q000503:physiopathology
chemical_list: C508050:IPS e.max Press; D019279:Resin Cements; D003776:Dental Porcelain; C103502:Variolink