J Adv Prosthodont.  2017 Dec;9(6):423-431. 10.4047/jap.2017.9.6.423.

Load-bearing capacity of various CAD/CAM monolithic molar crowns under recommended occlusal thickness and reduced occlusal thickness conditions

• Choi S
• Yoon HI
• Park EJ

• KMID: 2398046
• DOI: http://doi.org/10.4047/jap.2017.9.6.423

Abstract

PURPOSE
The goal of this study was to evaluate the fracture resistances of various monolithic crowns fabricated by computer-aided design and computer-aided manufacturing (CAD/CAM) with different thickness.
MATERIALS AND METHODS
Test dies were fabricated as mandibular molar forms with occlusal reductions using CAD/CAM. With different occlusal thickness (1.0 or 1.5 mm), a polymer-infiltrated ceramic network (Enamic, EN), and zirconia-reinforced lithium silicate (Suprinity, SU and Celtra-Duo, CD) were used to fabricate molar crowns. Lithium disilicate (e.max CAD, EM) crowns (occlusal: 1.5 mm) were fabricated as control. Seventy crowns (n=10 per group) were bonded to abutments and stored in water for 24 hours. A universal testing machine was used to apply load to crown until fracture. The fractured specimens were examined with a scanning electron microscopy.
RESULTS
The type of ceramics and the occlusal thickness showed a significant interaction. With a recommended thickness (1.5 mm), the SU revealed the mean load similar to the EM, higher compared with those of the EN and CD. The fracture loads in a reduced thickness (1.0 mm) were similar among the SU, CD, and EN. The mean fracture load of the SU and CD enhanced significantly when the occlusal thickness increased, whereas that of the EN did not.
CONCLUSION
The fracture loads of monolithic crowns were differently influenced by the changes in occlusal thickness, depending on the type of ceramics. Within the limitations of this study, all the tested crowns withstood the physiological masticatory loads both at the recommended and reduced occlusal thickness.

Keyword

Monolithic ceramic; Fracture resistance; Occlusal thickness; Zirconia-reinforced lithium silicate; Polymer-infiltrated ceramic

MeSH Terms

Ceramics
Computer-Aided Design
Crowns*
Lithium
Microscopy, Electron, Scanning
Molar*
Silicates
Water
Weight-Bearing*
Lithium
Silicates
Water

Figure

• 

  Fig. 1 Computer-aided-design (CAD) models of test supporting die (A) and definitive molar crowns with occlusal thicknesses of 1.0 mm (B).

• 

  Fig. 2 Mean and standard deviations of fracture loads of ceramic groups with the same occlusal thickness (1.5 mm). Significant differences (P < .05) between the groups were evaluated with Tukey HSD test and marked with asterisks (*). EN - Enamic, polymer-infiltrated-ceramic network, SU - Suprinity, zirconia-reinforced lithium silicate, CD - Celtra Duo, zirconia-reinforced lithium silicate, EM - e.max CAD, lithium disilicate.

• 

  Fig. 3 Means and standard deviations of fracture loads of ceramic groups with different occlusal thickness conditions (1.0 mm and 1.5 mm). Significant differences (P < .05) between the groups were evaluated with independent t-tests and marked with asterisks. EN - Enamic, polymer-infiltrated-ceramic network, SU - Suprinity, zirconia-reinforced lithium silicate, CD - Celtra Duo, zirconia-reinforced lithium silicate.

• 

  Fig. 4 SEM fracture surface image of EN crown with occlusal thickness of 1.0 mm. HL: hackle line, AL: arrest line, white star: origin of fracture, TH: twist hackle, white solid arrow: crack propagation direction (CPD), CL: cementation layer, SD: supporting die.

• 

  Fig. 5 SEM fracture surface image of EN crown with occlusal thickness of 1.5 mm. HL: hackle line, AL: arrest line, white star: origin of fracture, white solid arrow: crack propagation direction (CPD), CL: cementation layer, SD: supporting die.

• 

  Fig. 6 SEM fracture surface image of SU crown with occlusal thickness of 1.5 mm. HL: hackle line, AL: arrest line, CC: compression curl, TH: twist hackle, white star: origin of fracture, white solid arrow: crack propagation direction (CPD), CL: cementation layer, SD: supporting die.

• 

  Fig. 7 SEM fracture surface image of CD crown with occlusal thickness of 1.5 mm. HL: hackle line, AL: arrest line, CC: compression curl, TH: twist hackle, white star: origin of fracture, white solid arrow: crack propagation direction (CPD), CL: cementation layer, SD: supporting die.

• 

  Fig. 8 SEM fracture surface image of EM crown with occlusal thickness of 1.5 mm. HL: hackle line, AL: arrest line, CC: compression curl, TH: twist hackle, white star: origin of fracture, white solid arrow: crack propagation direction (CPD), CL: cementation layer, SD: supporting die.

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