J Adv Prosthodont.  2017 Dec;9(6):416-422. 10.4047/jap.2017.9.6.416.

Fracture load and survival of anatomically representative monolithic lithium disilicate crowns with reduced tooth preparation and ceramic thickness

• Nawafleh N
• Hatamleh M
• Öchsner A
• Mack F

• KMID: 2398045
• DOI: http://doi.org/10.4047/jap.2017.9.6.416

Abstract

PURPOSE
To investigate the effect of reducing tooth preparation and ceramic thickness on fracture resistance of lithium disilicate crowns.
MATERIALS AND METHODS
Specimen preparation included a standard complete crown preparation of a typodont mandibular left first molar with an occlusal reduction of 2 mm, proximal/axial wall reduction of 1.5 mm, and 1.0 mm deep chamfer (Group A). Another typodont mandibular first molar was prepared with less tooth reduction: 1 mm occlusal and proximal/axial wall reduction and 0.8 mm chamfer (Group B). Twenty crowns were milled from each preparation corresponding to control group (n=5) and conditioned group of simultaneous thermal and mechanical loading in aqueous environment (n=15). All crowns were then loaded until fracture to determine the fracture load.
RESULTS
The mean (SD) fracture load values (in Newton) for Group A were 2340 (83) and 2149 (649), and for Group B, 1752 (134) and 1054 (249) without and with fatigue, respectively. Reducing tooth preparation thickness significantly decreased fracture load of the crowns at baseline and after fatigue application. After fatigue, the mean fracture load statistically significantly decreased (P < .001) in Group B; however, it was not affected (P>.05) in Group A.
CONCLUSION
Reducing the amount of tooth preparation by 0.5 mm on the occlusal and proximal/axial wall with a 0.8 mm chamfer significantly reduced fracture load of the restoration. Tooth reduction required for lithium disilicate crowns is a crucial factor for a long-term successful application of this all-ceramic system.

Keyword

Fatigue; Lithium disilicate; Tooth preparation; Thermocycling; Fracture load

MeSH Terms

Ceramics*
Crowns*
Fatigue
Lithium*
Molar
Tooth Preparation*
Tooth*
Lithium

Figure

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  Fig. 1 Preparation of crown holders according to the specimen cup of the chewing simulator. Epoxy resin die is positioned in its corresponding place in the silicon mould with a hole created using metal pin to fix the specimen during testing (A), the mould is filled with acrylic resin (B), the metal pin and specimen holder are removed from the mould (C).

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  Fig. 2 Specimens undergoing thermal mechanical testing in the chewing simulator (A), tripod occlusal contact of the spherical indenter during single load to fracture test (B & C).

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  Fig. 3 Fracture modes as presented after fracture test. Fracture runs mesiodistally through the central fossa (A), Fracture runs mesiodistally and through the lingual groove (B), Fracture runs mesiodistally, through the mesiobuccal and lingual grooves (C).

• 

  Fig. 4 Graph showing linear correlation between fracture mode (number of fractured pieces) and fracture force.

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