title: A comparison of the fracture resistances of endodontically treated mandibular premolars restored with endocrowns and glass fiber post-core retained conventional crowns.
abstract: OBJECTIVE
  Thisin-vitrostudy aimed to evaluate the fracture resistances and failure modes of endodontically treated mandibular premolars restored with endocrowns and conventional post-core retained crowns.
  
  
  METHODS
  Thirty mandibular premolars were assigned into three groups (n=10): GI, intact teeth; GE, teeth with endocrowns; GC, teeth with conventional post-core supported crowns. Except for the teeth in group GI, all specimens were cut to 1.5 mm above the cementoenamel junction and endodontically treated. Both endocrowns and conventional crowns were fabricated from lithium-disilicate blocks using a CEREC 3D CAD/CAM unit. All specimens were subjected to thermocycling and then to 45° oblique compressive load until fracture occurred. The fracture resistance and failure mode of each specimen were recorded. Data were analyzed with one-way ANOVA and LSD Post Hoc Test (α=.05).
  
  
  RESULTS
  The fracture resistances of GE and GC were significantly lower than that of GI (P<.01), while no significant difference was found between GE and GC (P=.702). As of the failure mode, most of the specimens in GE and GC were unfavorable while a higher occurrence of favorable failure mode was presented in GI.
  
  
  CONCLUSIONS
  For the restoration of mandibular premolar, endocrown shows no advantage in fracture resistance when compared with the conventional method. Both of the two methods cannot rehabilitate endodontically treated teeth with the same fracture resistances that intact mandibular premolars have.
authors.affiliation: Department of Stomatology, the Chinese PLA General Hospital, Beijing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Guo
authors.affiliation: Department of Stomatology, the Chinese PLA General Hospital, Beijing, China.
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Stomatology, the Chinese PLA General Hospital, Beijing, China.
authors.forename: Xuesheng
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Mechanical Engineering, University of Science and Technology, Beijing, China.
authors.forename: Chaoyang
authors.initials: C
authors.lastname: Sun
authors.affiliation: Department of Stomatology, the People's Hospital of Cangzhou, Hebei, China.
authors.forename: Erdong
authors.initials: E
authors.lastname: Gao
authors.affiliation: Department of Stomatology, the Chinese PLA General Hospital, Beijing, China.
authors.forename: Hongbo
authors.identifier: 0000-0002-9896-9455
authors.initials: H
authors.lastname: Li
keywords: Endocrown; Failure mode; Fracture resistance; Intact tooth; Mandibular premolar