Quantification of all-ceramic crown margin surface profile from try-in to 1-week post-cementation

To use profilometry to assess the margin surface profile of all-ceramic crowns (ACC’s) at try-in and 1-week after cementation with dual-cured resin (DC, RelyX ARC, 3 M ESPE, St. Paul, MN, USA), self-adhesive dual-cured resin (SADC, RelyX Unicem, 3 M ESPE), light-cured resin (LC, RelyX Veneer, 3 M ESPE) or chemically cured resin-modified glass ionomer (RMGI, RelyX Luting Plus, 3 M ESPE) luting cement. Methods: Forty, sound, extracted, human, premolar teeth underwent a standardised preparation for ACC’s. IPS Empress (Ivoclar-Vivadent, Liechtenstein) crowns of standard dimensions were fabricated and 10 luted with each cement and stored in water for 7 days. Three groups of serial profiles were taken, the first of the tooth preparation, the second of the crown margins at try-in and lastly of the crown margins after cementation and 7 days water storage. Results: There were no significant differences in the crown margin surface profile between the four cement groups at try-in. The change in crown margin position between try-in and post-cementation was significantly greater for DC than for LC and RMGI. SADC was not significantly different to the other cements. There were no significant differences in the crown margin extensions between the four cement groups, however most of the IPS Empress ACC’s in this study were underextended but this was not statistically significant. Conclusions: IPS Empress ACC’s seated more fully with LC and RMGI than with DC cement

Fracture strength of machined ceramic crowns as a function of tooth preparation design and the elastic modulus of the cement

Objectives: To determine, by means of static fracture testing the effect of the tooth preparation design and the elastic modulus of the cement on the structural integrity of the cemented machined ceramic crown-tooth complex. 
Methods: Human maxillary extracted premolar teeth were prepared for all-ceramic crowns using two preparation designs; a standard preparation in accordance with established protocols and a novel design with a flat occlusal design. All-ceramic feldspathic (Vita MK II) crowns were milled for all the preparations using a CAD/CAM system (CEREC-3). The machined all-ceramic crowns were resin bonded to the tooth structure using one of three cements with different elastic moduli: Super-Bond C&B, Rely X Unicem and Panavia F 2.0. The specimens were subjected to compressive force through a 4 mm diameter steel ball at a crosshead speed of 1 mm/min using a universal test machine (Loyds Instrument Model LRX.). The load at the fracture point was recorded for each specimen in Newtons (N). These values were compared to a control group of unprepared/unrestored teeth. 
Results: There was a significant difference between the control group, with higher fracture strength, and the cemented samples regardless of the occlusal design and the type of resin cement. There was no significant difference in mean fracture load between the two designs of occlusal preparation using Super-Bond C&B. For the Rely X Unicem and Panavia F 2.0 cements, the proposed preparation design with a flat occlusal morphology provides a system with increased fracture strength. 
Significance: The proposed novel flat design showed less dependency on the resin cement selection in relation to the fracture strength of the restored tooth. The choice of the cement resin, with respect to its modulus of elasticity, is more important in the anatomic design than in the flat design. © 2013 Academy of Dental Materials.

Effect of the crown design and interface lute parameters on the stress-state of a machined crown-tooth system: A finite element analysis

The effect of preparation design and the physical properties of the interface lute on the restored machined ceramic crown-tooth complex are poorly understood. The aim of this work was to determine, by means of three-dimensional finite element analysis (3D FEA) the effect of the tooth preparation design and the elastic modulus of the cement on the stress state of the cemented machined ceramic crown-tooth complex. The three-dimensional structure of human premolar teeth, restored with adhesively cemented machined ceramic crowns, was digitized with a micro-CT scanner. An accurate, high resolution, digital replica model of a restored tooth was created. Two preparation designs, with different occlusal morphologies, were modeled with cements of 3 different elastic moduli. Interactive medical image processing software (mimics and professional CAD modeling software) was used to create sophisticated digital models that included the supporting structures; periodontal ligament and alveolar bone. The generated models were imported into an FEA software program (hypermesh version 10.0, Altair Engineering Inc.) with all degrees of freedom constrained at the outer surface of the supporting cortical bone of the crown-tooth complex. Five different elastic moduli values were given to the adhesive cement interface 1.8 GPa, 4 GPa, 8 GPa, 18.3 GPa and 40 GPa; the four lower values are representative of currently used cementing lutes and 40 GPa is set as an extreme high value. The stress distribution under simulated applied loads was determined. The preparation design demonstrated an effect on the stress state of the restored tooth system. The cement elastic modulus affected the stress state in the cement and dentin structures but not in the crown, the pulp, the periodontal ligament or the cancellous and cortical bone. The results of this study suggest that both the choice of the preparation design and the cement elastic modulus can affect the stress state within the restored crown-tooth complex.

Theoretical analysis on microwave heating of oil–water emulsions supported on ceramic, metallic or composite plates

A detailed theoretical analysis has been carried out to study efficient heating due to microwaves for one-dimensional (1D) oil–water emulsion samples placed on various ceramic, metallic (reflective) and ceramic–metallic composite supports. Two typical emulsion systems are considered such as oil-in-water (o/w) and water-in-oil (w/o). A preliminary study has been carried out via average power vs emulsion thickness diagram to estimate microwave power absorption within emulsion samples for various cases. The maxima in average power, also termed as ‘resonances’, are observed for specific emulsion thicknesses and the two consecutive resonances of significant magnitudes are termed as R1 and R2 modes. For both o/w and w/o emulsions, it is observed that microwave power absorption is enhanced in presence of metallic and composite supports during both R1 and R2 modes. The efficient heating strategies characterized by ‘large heating rates’ with ‘minimal thermal runaway’ i.e. uniform temperature distributions within the sample have been assessed for each type of emulsion. Based on the detailed spatial distributions of power and temperature for various cases, SiC-metallic composite support may be recommended as an optimal heating strategy for o/w samples with higher oil fractions (0.45) whereas metallic and Alumina-metallic composite supports may be favored for samples with smaller oil fractions (=0.3) during R1 mode. For w/o samples, SiC-metallic composite support may be suitable heating strategy for all ranges of water fractions during R1 mode. During R2 mode, metallic and Alumina-metallic composite supports are favored for both o/w and w/o emulsion samples. Current study recommends the efficient way to use microwaves in a single mode waveguide and the heating strategy can be suitably extended for heating of any other emulsions for which dielectric properties are easily measurable or available in the literature.

The effect of simvastatin on bone formation and ceramic resorption in a peri-implant defect model

Experimental use of statins as stimulators of bone formation suggests they may have widespread applicability in the field of orthopaedics. With their combined effects on osteoblasts and osteoclasts, statins have the potential to enhance resorption of synthetic materials and improve bone ingrowth. In this study, the effect of oral and local administration of simvastatin to a 0 tricalcium phosphate (beta TCP)-filled defect around an implant was compared with recombinant human bone morphogenetic protein 2 (rhBMP2). On hundred and sixty-two Sprague-Dawley rats were assigned to treatment groups: local application of 0.1, 0.9 or 1.7 mg of simvastatin, oral simvastatin at 5, 10 or 50 mg kg(-1) day(-1) for 20 days, local delivery of I or 10 mu g of rhBMP2, or control. At 6 weeks rhBMP2 increased serum tartrate-resistant acid phosphatase 5b levels and reduced PTCP area fraction, particle size and number compared with control, suggesting increased osteoclast activity. There was reduced stiffness and increased mechanical strength with this treatment. Local simvastatin resulted in a decreased mineral apposition rate at 6 weeks and increased fibrous area fraction, PTCP area fraction, particle size and number at 26 weeks. Oral simvastatin had no effect compared with control. Local application of rhBMP2 increased resorption and improved mechanical strength whereas simvastatin was detrimental to healing. Oral simvastatin was ineffective at promoting either ceramic resorption or bone formation. The effect of statins on the repair of bone defects with graft substitute materials is influenced by its bioavailability. Thus, further studies on the optimal delivery system are needed. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The effect of osteogenic growth factors on bone growth into a ceramic filled defect around an implant

Currently available synthetic bone substitutes perform poorly compared to autograft. It is hoped that by adding osteogenic growth factors to the materials, new bone formation could be increased and the clinical outcome improved. In this study, IGF-1, bFGF and TGFbeta1, alone and in combination, were absorbed onto a carrier of P-tricalcium phosphate (PTCP) and implanted into a defect around a hydroxyapatite-coated, stainless steel implant in the proximal tibia of rat in a model of revision arthroplasty. Animals were sacrificed at 6 and 26 weeks for routine histology and histomorphometry and mechanical push out tests. The results show that only bFGF had a significant effect on ceramic resorption. The groups that received bFGF and bFGF in combination with TGFbeta1 had smaller and fewer betaTCP particles remaining in the defect at 6 and 26 weeks. No growth factor combination significantly enhanced new bone formation or the mechanical strength of the implant. These results indicate that, of the growth factors tested, only bFGF had any beneficial effect on the host response to the implant, perhaps by delaying osteoblast differentiation and thereby prolonging osteoclast access to the ceramic. (C) 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.

Photocatalytic evolution of hydrogen and oxygen from ceramic wafers of commercial titanias

Several commercial titania photocatalyst powders were formed into thin (ca. 350 mu m), 25 mm diameter ceramic wafers, sputter deposited with Pt on one side. The activities of each of the ceramic wafers were tested for hydrogen and oxygen evolution from aqueous sacrificial systems. The commercial sample PC50 (Millennium Chemicals, UK) yielded reproducible ceramic wafers with high activity for water photoreduction. Many of the ceramic wafers displayed low water photo-oxidation activities; however, these were greatly increased with addition of a NiO co-catalyst. In a selected case, hydrogen evolution activity was compared between a PC50 wafer and an identical weight of platinised PC50 powder suspension. (C) 2010 Elsevier B.V. All rights reserved.

A simple and low-cost method for the preparation of self-supported TiO2-WO3 ceramic heterojunction wafers

Robust, bilayer heterojunction photodiodes of TiO₂-WO₃ were prepared successfully by a simple, low-cost powder pressing technique followed by heat-treatment. Exclusive photoirradiation of the TiO₂ side of the photodiode resulted in a rapid colour change (dark blue) on the WO₃ surface as a result of reduction of W⁶⁺ to W⁵⁺ (confirmed by X-ray photoelectron spectroscopy). This colour was long lived and shown to be stable in a dry environment in air for several hours. A similar photoirradiation experiment in the presence of a mask showed that charge transfer across the heterojunction occurred approximately normal to the TiO₂ surface, with little smearing out of the mask image. As a result of the highly efficient vectorial charge separation, the photodiodes showed a tremendous increase in photocatalytic activity for the degradation of stearic acid, compared to wafers of the respective individual materials when tested separately.