title: [Influence of alveolar bone heights on fracture resistance and pattern of post and core restored maxillary premolars].
abstract: OBJECTIVE
  To evaluate the influence of different alveolar bone heights on fracture resistance and pattern of post and core restored maxillary premolars.
  
  
  METHODS
  Forty-eight maxillary premolars were randomly divided into 6 groups (8 teeth in each group) for different alveolar bone heights and different post and core materials. Group A: fiber post and core and normal alveolar bone height. Group B: Ni-Cr cast post and core and normal alveolar bone height. Group C: fiber post and core with 2 mm alveolar bone height reduction. Group D: Ni-Cr cast post and core with 2 mm alveolar bone height reduction. Group E: fiber post and core with 4 mm alveolar bone height reduction. Group F: Ni-Cr cast post and core with 4 mm alveolar bone height reduction. All of the teeth were restored with Ni-Cr cast crowns. Fracture resistances were tested and the failure modes were examined.
  
  
  RESULTS
  The mean fracture resistances were (762.49 ± 84.91) N for group A, (794.26 ± 72.61) N for group B, (517.69 ± 80.30) N for group C, (543.50 ± 62.88) N for group D, (219.91 ± 43.20) N for group E, and (196.16 ± 41.08) N for group F. The ratios of favorable fractures were 100.0% for group A, 37.5% for group B, 75.0% for group C, 12.5% for group D, 50.0% for group E, and 0 for group F.
  
  
  CONCLUSIONS
  The alveolar bone height has a significant impact on fracture resistance and modes of post and core restored maxillary premolars. With the reduction of alveolar bone height, the fracture decreases and the fracture mode tends to be unfavorable.
authors.affiliation: Department of Prosthodontics, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Luo
authors.forename: Li-li
authors.initials: LL
authors.lastname: Zhang
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yu-hua
authors.initials: YH
authors.lastname: Liu
authors.forename: Jun
authors.initials: J
authors.lastname: Xu
mesh_terms: D001641:Bicuspid; D006801:Humans; D011176:Post and Core Technique; D014082:Tooth Fractures