N Dorin Ruse

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Master's Student Supervision (2010 - 2018)
“CAD-on” interfaces - a fracture mechanics characterization (2017)

AbstractObjective: “CAD-on” crowns, consisting of CAD/CAM milled lithium disilicate (LS2) veneersglass-fused to CAD/CAM milled yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP)framework, have shown promise in increasing veneer fracture resistance. The glass fusiontechnique is purported to result in stronger bonding between veneer and framework whencompared to conventional veneering. The objective of this study was to apply fracture mechanicsmethodology to characterize the interfaces present in “CAD-on” crowns.Methods: The notchless triangular prism (NTP) specimen fracture toughness (KIC) test was usedto determine interfacial KIC. Four groups, each consisting of 6X6X6X12mm NTP specimens(n=22), were produced from IPS Emax CAD (LS2), IPS Emax ZirCAD (Y-TZP), and IPS EmaxZirPress and crystal connect™(CC) fusing glass. Groups I (Emax/CC/Emax), II (Zir/CC/Zir), andIII (Zir/CC/Emax) utilized half-size (6X6X6X6mm) NTP specimens approximated undervibration with the connecting glass and sintered according to manufacturers’ guidelines. Group IVspecimens were coated with ZirLiner and pressed with IPS Emax ingots. The specimens weretested using a computer controlled (Bluehill) Instron 4301. Results were analyzed with one-wayANOVA, Scheffé multiple means comparisons (α=0.05) and Weibull statistics. All fracturedsurfaces were characterized with a light microscope. Selected fractured interfaces werecharacterized under a scanning electron microscope.Results: Groups I-III demonstrated a cohesive mode of failure. Number and size of defectsappeared to correlate with the variability of K1C values. There were no significant differencesbetween the KIC values of the “CAD-on” interfaces. Interfacial KIC values were limited by KIC ofCC. The “CAD-on” KIC value was significantly greater than that of the ZirPress control.Conclusion: Based on the results obtained, KIC of interfaces produced during the “CAD-on”technique appear to be limited by the interfacial KIC of the connecting glass and the defectsproduced during processing. In this study, “CAD-on” produced veneers had stronger interfacialKIC than a conventionally veneered control group.

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Comparison of adherence of self-cured adhesive resin cement to lithium disilicate ceramics and ceramic resin composites using fracture mechanics (2015)

Objective : The goal of this study was to apply fracture mechanics methodology to assess the effect of surface preconditioning on the short and long term adherence between a widely used adhesive resin cement (RelyX Ultimate, 3M ESPE) and recently introduced CAD/CAM materials : two ceramic resin composites (Lava Ultimate – 3M ESPE and Enamic – Vita-Zahnfabrik) and a ceramic (IPS e.max – Ivoclar-Vivadent). Materials and Methods : Sixty specimens were prepared from each e.max and Enamic, and 120 specimens were prepared for Lava Ultimate. Ceramic resin composite blocks samples were prepared by wet cutting and grinding. Ceramic samples were prepared using the lost wax procedure and pressing. Enamic and e.max bonding surfaces were treated with hydrofluoric acid. Lava Ultimate received two surface treatments : sandblasting and Rocatec soft. All samples were bonded using an adhesive and resin cement and stored in water at 37°C. After 24h storage, half of the specimens from each group were tested to determine the interfacial KIC using an Instron universal testing machine; the remaining specimens were tested after 60d storage. Scanning electron microscopy fractographic analysis was performed on representative fractured samples from each group to determine the mode of failure. To determine the adhesive resin cement KIC, twenty specimens were prepared using a mold. Half of the specimens were tested after 24h storage in water at 37°C and the other half were tested after 60d storage. The KIC results were analyzed using two-way ANOVA followed by Scheffé multiple means comparisons. Results : Lava Ultimate had a significantly higher interfacial KIC at 24h when compared to Enamic and e.max. For Lava Ultimate, crack propagation occurred cohesively through the adhesive resin cement. In Enamic and e.max samples, crack propagation occurred cohesively within the adhesive layer. Only Enamic showed a significantly higher interfacial KIC at 60d, compared to the other groups. Lava Ultimate and e.max interfacial KIC, and cement KIC showed lower values at 60d. Conclusion : For Lava Ultimate, surface silicatisation seems to be a more effective surface treatment compared to only sandblasting. For Enamic and e.max, the application of silane coupling agent and adhesive contained in one solution does not seem to be effective.

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IPS e.max CAD and IPS e.max Press : fracture mechanics characterization (2014)

Objective: To determine fracture toughness (KIC) and fatigue crack propagation (FCP) parameters for IPS e.max CAD and IPS e.max Press. Materials and methods: For KIC determinations, 20 (6x6x6x12mm) notchless triangular prism (NTP) specimens of IPS e.max CAD and IPS e.max Press were prepared. IPS e.max CAD blocks were cut, ground and then crystallized, while IPS e.max Press ingots were pressed into molds obtained from wax prisms. Each specimen was mounted into a holder and custom grips were used to attach the holder to a computerized universal testing machine (Instron model 4301). The assembly was loaded in tension at a crosshead speed of 0.1mm/min and KIC was calculated based on the recorded maximum load at fracture. Fractured surfaces were characterized using scanning electron microscopy (SEM). The results were statistically analyzed using Weibull statistics and t-test (⍺=0.05).For FCP characterization, a pilot test was done with three Plexiglas NTP samples. A pre-crack was initiated in one of the specimen edges. Several lines were scribed on the side of the specimen to monitor crack propagation. The specimens were mounted in the holder and then attached to custom grips on a servo hydraulic fatigue-testing machine (Instron model 8511). A strain gauge was attached to these grips to monitor crack opening displacement. Each specimen was cyclically loaded in tension (Mode I) in a load range between 1 and 20 N and crack length was monitored and filmed using a high definition video recorder (SONY HDR-XR550V) attached to a microscope (Edmund Scientific Co, Barrington, NJ). Video recording was terminated once catastrophic fracture of the specimen occurred. Cyberlink Power Director and Image J software were used in data analysis.Results: KIC values were significantly higher for IPS e.max Press than IPS e.max CAD. The pilot FCP tests on Plexiglas revealed limitations with regards to the applicability of NTP specimen KIC test to FCP studies due to the presence of a trapezoidal crack front in the specimens.Conclusion: IPS e.max Press is superior to IPS e.max CAD in KIC. Further research should be conducted to evaluate the feasibility of using a trapezoidal crack front in FCP studies.

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Mechanical properties of dental resin composite CAD/CAM blocks (2014)

Objective: The goal of this study was to determine the flexural strength (σf), flexural modulus (Ef) and fracture toughness (KIC) of two new commercially available nano-ceramic resin composite CAD/CAM blocks (Lava Ultimate and Enamic) and compare them to those of a widely-used ceramic CAD/CAM block (IPS e.max), that served as a control, in order to evaluate the clinical suitability of the former. Materials and Methods: Fifty bars of Lava Ultimate and Enamic and twenty-five bars of e.max were made for three-point bending testing (to determine σf and Ef). Testing was completed on an Instron machine whereby a force was applied at a constant crosshead speed of 1 mm/min until failure occurred. Twenty-four 6x6x6x12 mm equilateral triangular prisms were fabricated from Lava Ultimate and Enamic and twelve from e.max for fracture toughness (KIC) testing using the notchless triangular prism specimen (NTP) KIC test. Half of the prepared Lava Ultimate and Enamic samples were stored in 37°C water for 30 days prior to testing, to analyze the aging effect. Weibull statistics were used to evaluate the characteristic strength and the reliability of each material. Two-way ANOVA and post-hoc Scheffé comparisons were used to further analyze the results.Results: The σf, Ef and KIC of Lava Ultimate and Enamic were considerably lower than that of IPS e.max. Aging of Lava Ultimate and Enamic lowered the σf by 27 % and 12 % but increased the KIC by 10 % and 40 %, respectively. Aging also significantly lowered Ef of both samples. The σf of Enamic was statistically significantly lower than that of Lava Ultimate, while the Ef of Enamic was statistically significantly higher. Only in the aged samples were significant differences between KIC detected.Conclusion: When compared to conventional resin composites, the presence of ceramic nano-particles in Lava Ultimate and Enamic did not greatly improve σf or KIC of these materials. The flexural modulus of Enamic was greatly improved to levels not seen before in dental resin composites. Based on the mechanical testing results obtained in this study, their consideration and clinical use should be similar to that of conventional dental resin composites.

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Surface preparation effect on bonding to e.max cad : a fracture mechanics approach (2014)

Objective: To assess the effect of surface preconditioning on the short and long term interfacial fracture toughness (KIC) of IPS e.max CAD and an adhesive resin luting cement.Material and Methods: The materials selected for this study were from Ivoclar-Vivadent, Liechtenstein: e.max CAD blocks, Multilink implant, Mono Bond Plus, and IPS Ceramic Etching Gel. Eighty (4x4x4x4 mm) triangular prisms were cut from IPS e.max CAD blocks, crystallized and then randomly assigned to two different surface treatment groups: a) machined, using a 60 µm diamond bur (Henry Schein, Germany) and b) machined, as in group a followed by 20 s 5 % HF acid-etching. After surface treatment, all specimens were silane-treated for 60 s and the cement was used to bond two identical specimens of each group, following the manufacturer’s instructions. All 40 specimens were stored in water at 37 °C until testing. After 24 hours storage, 10 specimens from each group were tested to determine interfacial KIC using a universal testing machine (Instron 4311, Instron Canada, Canada); the other 10 specimens were tested after 60 days water storage. SEM fractographic analysis was performed on representative fractured KIC samples from each group to assess the type of failure, i.e. adhesive, cohesive, or mixed. To determine ARC KIC, twenty (4x4x4x8 mm) triangular prisms were prepared using a mould. Half of the specimens were tested after 24 hours storage in water at 37 °C and the other half were tested after 60 days.The KIC results were analyzed using univariate ANOVA followed, if warranted, by Scheffé multiple means comparisons. The statistical analysis was conducted at =0.05, using SPSS (SPSS for Windows, version 12.0; Chicago, IL).Results: The machined/etched group had a significantly higher interfacial KIC at 24 hours. Crack propagation occurred through the adhesive resin and the resin-ceramic interface.Conclusions: The higher KIC was achieved with HF acid etching. Storage in 37 °C water for 60 days led to a deterioration of both cement KIC and cement-mediated interfacial KIC.Clinical significance: IPS e.max CAD/CAM crowns should be etched with HF acid prior to cementation. However, the durability of the bond decreased upon ageing.

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