Residual stresses in bilayer dental ceramics.

Department of Dental Biomaterials, College of Dentistry, University of Florida, Gainesville, FL 32610, USA.
Biomaterials (Impact Factor: 7.6). 07/2005; 26(16):3235-41. DOI: 10.1016/j.biomaterials.2004.08.025
Source: PubMed

ABSTRACT It is clinically observed that lithia-disilicate-based all-ceramic fixed partial dentures (FPD) can fail because of the fragmentation of the veneering material. The hypothesis of this study is that the global residual stresses within the surface of those veneered FPDs may be responsible for partial fragmentation of the veneering ceramic. Bilayer and monolithic ceramic composites were prepared using a lithia disilicate based (Li2OSiO2) glass-ceramic core and a glass veneer. A four-step fracture mechanics approach was used to analyze residual stress in bilayered all-ceramic FPDs. We found a statistically significant increase in the mean flexural strengths of bilayer specimens compared with monolithic glass specimens (p < or = 0.05). There was a statistically significant difference between the mean longitudinal and transverse indentation-induced crack sizes in bilayer specimens (p < or = 0.05), which indicates the existence of residual stress. Global residual stresses in the veneer layer, calculated using a fracture mechanics equation, were determined to be responsible for the increased strength and observed chipping, i.e., spallation in bilayer ceramic composites.

1 Bookmark
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the effect of differential coping designs on the stress distributions of an all-ceramic crown on, the upper central incisor under varying loads. 3D finite element models with three differential coping designs of an all-ceramic crown on, the upper central incisor were constructed using CAD (computer aided design) software. The coping, designs included: CC (conventional coping), MCL (modified coping without veneer coverage in lingual, surface) and MCM (modified coping without veneer coverage in lingual margin). Loading that, simulated the maximum bite force (200N) was applied to the crown at differential locations (incisal, edge, lingual fossa and lingual margin). The first principal stress values for the full crown were, calculated and expressed as stress intensity in MPa. The simulations showed the stress distribution tendencies of the all-ceramic crown with, differential coping materials were similar. The stress concentration was found in the cervical region, coping/veneer layer interface and the loading area for both the coping layer and the veneer layer. Maximal stress value was observed in the loading area. Stress values varied for the three types of, coping designs; however, compared with CC and MCM, MCL exhibited the lowest stress values. Modified coping without veneer coverage in the lingual side (MCL) proved promising in, preventing all-ceramic crown failures that originate from veneering porcelain, especially under, abnormal occlusal force.
    Dental materials: official publication of the Academy of Dental Materials 10/2013; · 2.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the microtensile bond strength between two all-ceramic systems; lithium disilicate glass ceramic and zirconia core ceramics bonded with their corresponding glass veneers.
    The journal of advanced prosthodontics 06/2014; 6(3):151-6.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This in vitro study was designed to investigate the influence of the veneer and cyclic loading on the failure behavior of lithium disilicate glass-ceramic (LDG) crowns on maxillary first molar. Sixty-four LDG crowns were divided into 4 groups (n=16). Thirty-two monolithic crowns were fabricated from IPS e.max Press (M), and the remaining bilayered crowns using cut-back technique and conventional manual layering technique from IPS e.max Press/Ceram (B). Monolithic or bilayered crowns were subjected to single-load-to-fracture (SLF) testing using a universal testing machine, before (M1 and B1) and after exposure to sliding-contact fatigue (SCF) testing (M2 and B2), consisting of 1,200,000 mechanical cycles (Fmax=98N). Data were statistically analyzed using two-by-two factorial design ANOVA. Fractographic analysis was performed to determine the fracture modes of the failed specimens. The mean fracture load values (N±S.D.) for M1, B1, M2 and B2 were 2686±628N, 1443±327N, 2133±578N and 1464±419N, respectively. Significant differences were found between the failure loads of all groups (P<0.001), except between groups B1 and B2. Bulk fracture initiating from the occlusal surface is the primary failure mode of monolithic and veneered LDG crowns. Cracking that initiated from core-veneer interfacial defects and ultimately resulted in bulk fracture is another major failure origin of veneered all-ceramic crowns. Veneer application resulted in significantly lower fracture load values compared to monolithic LDG crowns. Cyclic loading is an accelerating factor contributing to fracture for monolithic LDG crowns but not for bilayered ones.
    Dental materials: official publication of the Academy of Dental Materials 12/2013; · 2.88 Impact Factor