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Lien W.,U.S. Air force | Roberts H.W.,U.S. Air force | Platt J.A.,Indiana University | Vandewalle K.S.,U.S. Air force | And 2 more authors.
Dental Materials | Year: 2015

Background: Elucidating the microstructural responses of the lithium disilicate system like the popular IPS e.max® CAD (LS2), made specifically for computer-aided design and computer-aided manufacturing (CAD-CAM), as a temperature-dependent system unravels new ways to enhance material properties and performance. Objective: To study the effect of various thermal processing on the crystallization kinetics, crystallite microstructure, and strength of LS2. Methods: The control group of the LS2 samples was heated using the standard manufacturer heating-schedule. Two experimental groups were tested: (1) an extended temperature range (750-840°C vs. 820-840°C) at the segment of 30°C/min heating rate, and (2) a protracted holding time (14min vs. 7min) at the isothermal temperature of 840°C. Five other groups of different heating schedules with lower-targeted temperatures were evaluated to investigate the microstructural changes. For each group, the crystalline phases and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Differential scanning calorimeter (DSC) was used to determine the activation energy of LS2 under non-isothermal conditions. A universal testing machine was used to measure 3-point flexural strength and fracture toughness, and elastic modulus and hardness were measured by a nanoindenter. A one-way ANOVA/Tukey was performed per property (alpha=0.05). Results: DSC, XRD, and SEM revealed three distinct microstructures during LS2 crystallization. Significant differences were found between the control group, the two aforementioned experimental groups, and the five lower-targeted-temperature groups per property (p <0.05). The activation energy for lithium disilicate growth was 667 (±29.0)kJ/mol. Conclusions: Groups with the extended temperature range (750-840. °C) and protracted holding time (820-840. °C H14) produced significantly higher elastic-modulus and hardness properties than the control group but showed similar flexural-strength and fracture-toughness properties with the control group. In general, rapid growth of lithium disilicates occurred only when maximum formation of lithium metasilicates had ended. © 2015. Source


Heintze S.D.,Ivoclar Vivadent
Dental Materials | Year: 2013

Dental adhesive systems should provide a variety of capabilities, such as bonding of artificial materials to dentin and enamel, sealing of dentinal tubules, reduction of post-operative sensitivity and marginal sealing to reduce marginal staining and caries. In the laboratory, numerous surrogate parameters that should predict the performance of different materials, material combinations and operative techniques are assessed. These surrogate parameters include bond strength tests of various kinds, evaluation of microleakage with tracer penetration between restorative and tooth, two-dimensional analysis of marginal quality with microscopes and mapping of the micromorphology of the bonding interface. Many of these tests are not systematically validated and show therefore different results between different research institutes. The correlation with clinical phenomena has only partly been established to date. There is some evidence, that macrotensile and microtensile bond strength tests correlate better with clinical retention of cervical restorations than macroshear and microshear bond tests but only if data from different test institutes are pooled. Also there is some evidence that marginal adaptation has a moderate correlation in cervical restorations with clinical retention and in Class II restorations (proximal enamel) with clinical marginal staining. There is moderate evidence that microleakage tests with dye penetration does not correlate with any of the clinical parameters (post-operative hypersensitivity, retention, marginal staining). A rationale which helps the researcher to select and apply clinically relevant test methods in the laboratory is presented in the paper. © 2012 Academy of Dental Materials. Source


Lien W.,U.S. Air force | Lien W.,Indiana University | Roberts H.W.,U.S. Air force | Platt J.A.,Indiana University | And 3 more authors.
Dental Materials | Year: 2015

Background Elucidating the microstructural responses of the lithium disilicate system like the popular IPS e.max® CAD (LS2), made specifically for computer-aided design and computer-aided manufacturing (CAD-CAM), as a temperature-dependent system unravels new ways to enhance material properties and performance. Objective To study the effect of various thermal processing on the crystallization kinetics, crystallite microstructure, and strength of LS2. Methods The control group of the LS2 samples was heated using the standard manufacturer heating-schedule. Two experimental groups were tested: (1) an extended temperature range (750-840°C vs. 820-840°C) at the segment of 30°C/min heating rate, and (2) a protracted holding time (14 min vs. 7 min) at the isothermal temperature of 840°C. Five other groups of different heating schedules with lower-targeted temperatures were evaluated to investigate the microstructural changes. For each group, the crystalline phases and morphologies were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Differential scanning calorimeter (DSC) was used to determine the activation energy of LS2 under non-isothermal conditions. A universal testing machine was used to measure 3-point flexural strength and fracture toughness, and elastic modulus and hardness were measured by a nanoindenter. A one-way ANOVA/Tukey was performed per property (alpha = 0.05). Results DSC, XRD, and SEM revealed three distinct microstructures during LS2 crystallization. Significant differences were found between the control group, the two aforementioned experimental groups, and the five lower-targeted-temperature groups per property (p < 0.05). The activation energy for lithium disilicate growth was 667 (±29.0) kJ/mol. Conclusions Groups with the extended temperature range (750-840°C) and protracted holding time (820-840°C H14) produced significantly higher elastic-modulus and hardness properties than the control group but showed similar flexural-strength and fracture-toughness properties with the control group. In general, rapid growth of lithium disilicates occurred only when maximum formation of lithium metasilicates had ended. © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. Source


Patent
Ivoclar Vivadent | Date: 2012-05-09

Milling strategies for machining dental ceramic materials are provided that reduce milling time while maintaining strength, accuracy and marginal integrity.


Patent
Ivoclar Vivadent | Date: 2011-07-14

A microwave oven for the thermal treatment of at least one dental restoration part comprises a firing chamber inside which the dental restoration part as well as at least one susceptor that may be moved or rotated by means of a drive motor and that substantially is disc-shaped, are disposed, and a microwave radiation source that indirectly heats the dental restoration part with the aid of the susceptor, wherein the susceptor at least partially is microwave-tight and wherein the microwave radiation source is arranged below the susceptor.

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