IADR Abstract Archives
Contact Fracture Test of Monolithic Hybrid Ceramics for Bruxism
Objectives: The purpose of this study was to determine the minimum thickness required for an implant-supported, monolithic hybrid ceramic crown used in the mandibular posterior area of patients with bruxism.
Methods: 40 Vita Enamic (VE) disc specimens with four different occlusal thicknesses (0.8, 1.2, 1.6 and 2.0 mm) were produced using a computer-aided design/computer-aided manufacturing system and cemented on a stiff (zirconia) or soft (polyamide) substrate of 4-mm thick. The five specimens in each group were subjected to compressive loading by a MTS machine until fracture or a maximum load of 800 N was reached. The tested specimens were examined using optical coherence tomography and scanning electron microscopy. Eight finite element models comprising the four different occlusal thicknesses and two substrates under a combination of vertical and sliding loads were simulated.
Results: The fracture resistance of the specimens was significantly different between the two substrates (P< 0.001) and positively associated with specimen thickness (r = 0.597 and 0.896 for the soft and stiff substrate, respectively). Specimens on the soft substrate had lower fracture loads, while cone cracks were observed in specimens on 1.2-mm thick stiff substrate prior to final fracture (see figure below). The finite element analysis confirmed that specimens on the stiff substrate had lower maximum principalstress values than those on the soft substrate. For the maximum principal stress not to exceed the flexural strength of VE, a stiff substrate and a minimum thickness of 2.0 mmis required for the prostheses.
Conclusions: For patients with bruxism, monolithic VE crowns on zirconia (stiff) substrate in the posterior implant area should have a minimum thickness of 2.0 mm.
Methods: 40 Vita Enamic (VE) disc specimens with four different occlusal thicknesses (0.8, 1.2, 1.6 and 2.0 mm) were produced using a computer-aided design/computer-aided manufacturing system and cemented on a stiff (zirconia) or soft (polyamide) substrate of 4-mm thick. The five specimens in each group were subjected to compressive loading by a MTS machine until fracture or a maximum load of 800 N was reached. The tested specimens were examined using optical coherence tomography and scanning electron microscopy. Eight finite element models comprising the four different occlusal thicknesses and two substrates under a combination of vertical and sliding loads were simulated.
Results: The fracture resistance of the specimens was significantly different between the two substrates (P< 0.001) and positively associated with specimen thickness (r = 0.597 and 0.896 for the soft and stiff substrate, respectively). Specimens on the soft substrate had lower fracture loads, while cone cracks were observed in specimens on 1.2-mm thick stiff substrate prior to final fracture (see figure below). The finite element analysis confirmed that specimens on the stiff substrate had lower maximum principalstress values than those on the soft substrate. For the maximum principal stress not to exceed the flexural strength of VE, a stiff substrate and a minimum thickness of 2.0 mmis required for the prostheses.
Conclusions: For patients with bruxism, monolithic VE crowns on zirconia (stiff) substrate in the posterior implant area should have a minimum thickness of 2.0 mm.
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