title: Ceramic inlays: is the inlay thickness an important factor influencing the fracture risk?
abstract: OBJECTIVE
  It is still unclear whether the inlay thickness is an important factor influencing the fracture risk of ceramic inlays. As high tensile stresses increase the fracture risk of ceramic inlays, the objective of the present finite element method (FEM) study was to biomechanically analyze the correlation between inlay thickness (T) and the induced first principal stress.
  
  
  METHODS
  Fourteen ceramic inlay models with varying thickness (0.7-2.0 mm) were generated. All inlays were combined with a CAD model of a first mandibular molar (tooth 46), including the PDL and a mandibular segment which was created by means of the CT data of an anatomical specimen. Two materials were defined for the ceramic inlays (e.max(®) or empress(®)) and an occlusal force of 100 N was applied. The first principal stress was measured within each inlay and the peak values were considered and statistically analyzed.
  
  
  RESULTS
  The stress medians ranged from 20.7 to 22.1 MPa in e.max(®) and from 27.6 to 29.2 MPa in empress(®) inlays. A relevant correlation between the first principal stress and thickness (T) could not be detected, neither for e.max(®) (Spearman: r=0.028, p=0.001), nor for empress(®) (Spearman: r=0.010, p=0.221). In contrast, a very significant difference (p<0.001) between the two inlay materials (M) was verified.
  
  
  CONCLUSIONS
  Under the conditions of the present FEM study, the inlay thickness does not seem to be an important factor influencing the fracture risk of ceramic inlays. However, further studies are necessary to confirm this.
authors: School of Dentistry, University of Munich, München, Germany. cholberg@med.lmu.de
authors: Christof
authors: C
authors: Holberg
authors: Ingrid
authors: I
authors: Rudzki-Janson
authors: Andrea
authors: A
authors: Wichelhaus
authors: Philipp
authors: P
authors: Winterhalder
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D003198:Computer Simulation; D017076:Computer-Aided Design; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007284:Inlays; D008334:Mandible / Q000033:anatomy & histology; D008422:Materials Testing; D008953:Models, Anatomic; D008954:Models, Biological; D008963:Molar / Q000033:anatomy & histology; D010513:Periodontal Ligament / Q000033:anatomy & histology; D012307:Risk Factors; D013314:Stress, Mechanical; D013499:Surface Properties; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003776:Dental Porcelain