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

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 .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.

Bond strength of self-adhesive resin cements to tooth structure

The aim of this study was to evaluate the strength of the bond between newly introduced self-adhesive resin cements and tooth structures [i.e., enamel and dentin]. Three self-adhesive cements [SmartCem2, RelyX Unicem, seT SDI] were tested. Cylindrical- shaped cement specimens [diameter, 3 mm; height, 3 mm] were bonded to enamel and dentin. Test specimens were incubated at 37°C for 24 h. The shear bond strength [SBS] was tested in a Zwick Roll testing machine. Results were analyzed by one-way ANOVA and t-test. Statistically significant differences were defined at the alpha= 0.05 level. Bond failures were categorized as adhesive, cohesive, or mixed. The SBS values ranged from 3.76 to 6.81 MPa for cements bonded to enamel and from 4.48 to 5.94 MPa for cements bonded to dentin [p >0.05 between surfaces]. There were no statistically significant differences between the SBS values to enamel versus dentin for any given cement type. All cements exhibited adhesive failure at the resin/tooth interface. Regardless of their clinical simplicity, the self-adhesive resin cements examined in this study exhibit limited bond performance to tooth structures; therefore, these cements must be used with caution

3D innovations of cranioplasty plate construction: a case report

Titanium cranioplasty is one of the well-established and widely used techniques in restoring skull defects for optimal protection to skull internal structures and re-establishing skull conformity. Nowadays, most centres utilise computer-assisted reconstruction for manufacture of titanium plates. In this paper we presented a method for making titanium cranioplasty plates using the 3D innovation through making a 3D model. It can be stated that computer assisted production titanium plate for repairing skull defects is hassle free to patient and prosthetists, efficient and reliable, accurate and reproducible method. Furthermore, the resultant prosthesis constructed is accurately fitting