Robert R Seghi

The Ohio State University, Columbus, Ohio, United States

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Publications (77)

  • [Show abstract] [Hide abstract] ABSTRACT: For adhesively retained ceramic crown of various types, it has been clinically observed that the most catastrophic failures initiate from the cement interface as a result of radial crack formation as opposed to Hertzian contact stresses originating on the occlusal surface. In this work, a 3D failure prognosis model is developed for interface initiated failures of monolithic ceramic crowns. The surface flaw distribution parameters determined by biaxial flexural tests on ceramic plates and point-to-point variations of multi-axial stress state at the intaglio surface are obtained by finite element stress analysis. They are combined on the basis of fracture mechanics based statistical failure probability model to predict failure probability of a monolithic crown subjected to single-cycle indentation load. The proposed method is verified by prior 2D axisymmetric model and experimental data.
    Article · May 2016 · Journal of Biomechanics
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    Rafat Amer · Duygu Kürklü · Elham Kateeb · Robert R Seghi
    [Show abstract] [Hide abstract] ABSTRACT: Zirconia complete-coverage crowns are being widely used as restorations because of their improved esthetic characteristics. Data about the enamel wear potential of this ceramic after chair side adjustments are sparse.
    Full-text Article · May 2014 · Journal of Prosthetic Dentistry
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    [Show abstract] [Hide abstract] ABSTRACT: The location of dental implants and the choice of retentive attachments for implant-retained overdentures are selected based on clinician preference, expert opinion, or empirical information. Limited information is available regarding implant position and the effect on the retention and stability of 2-implant mandibular implant overdentures. The purpose of this investigation was to evaluate the effect of implant location on the in vitro retention and stability of a simulated 2-implant-supported overdenture and to examine the differences among different attachment systems. A model that simulates a mandibular edentulous ridge with dental implants in positions that approximate tooth positions, and a cobalt-chromium cast framework attached to a universal testing machine was used to measure the peak load (N) required to disconnect the attachments. Four different types of attachments (Ball/Cap, ERA, Locator, and O-Ring) were used in sequence in various positions on the model to evaluate the effect of implant location on the retention and stability of a simulated 2-implant-retained overdenture. Means were calculated, and differences among the systems, directions, and groups were identified by using a repeated measured ANOVA (α=.05). For differences observed between measurements, the Bonferroni post hoc method at the 5% level of significance was used to determine the location and magnitude of difference. The interactions between the attachment system, direction of force, and implant location were statistically significant (P=.01). The vertical retention and horizontal stability of a simulated overdenture prosthesis increased with the distal implant location up to the second premolar, and the anteroposterior stability increased with distal implant location. The attachment type affected retention and stability differently by location. Ball attachments produced the highest levels of retention and stability, followed by Locator (pink), O-Ring, and ERA (orange). The retention and stability of a 2-implant simulated overdenture prosthesis is significantly affected by implant location (P=.01) and abutment type (P=.01).
    Full-text Article · May 2014 · The Journal of prosthetic dentistry
    [Show abstract] [Hide abstract] ABSTRACT: Introduction: There are currently limited diagnostic tools available to assess the integrity of the cement/adhesive interface beneath fixed restorations. The characteristics of the cement interface beneath ceramic restorations are of particular interest since they are believed to reinforce the ceramic. Objective: The purpose of this investigation was to determine the feasibility of using Angle Beam Ultrasonic Spectroscopy (ABUS) to assess elastic properties of the cement interface beneath dental ceramics. Methods: In this set of experiments glass plates (1/2" x 2" x 1/8") were used as dental ceramic analogs and cemented with composite resin containing 77, 53 and 30 wt% filler (F) and 0.1 or 0.2 mm thickness (T). ABUS methods were used to determine density (ρ), cement thickness (h), longitudinal modulus (l+2), and shear modulus (). The results of two independent measurements on six samples with 3 filler loads and 2 cement thicknesses are reported in the table below. Sample ρ (g/cm3) h (mm) λ+2μ (GPa) μ (GPa) 1st 2nd diff%* 1st 2nd diff% 1st 2nd diff% 1st 2nd diff% T.2F77 2.06 2.03 1.5% 0.295 0.303 2.7% 21.9 22.2 1.4% 6.69 6.82 1.9% T.2F53 1.69 1.71 1.2% 0.200 0.199 0.5% 16.0 16.2 1.3% 4.52 4.60 1.8% T.2F30 1.47 1.45 1.4% 0.168 0.168 0.0% 12.6 12.7 0.8% 3.08 3.27 6.2% T.1F77 2.00 1.96 2.0% 0.283 0.300 6.0% 21.0 21.9 4.3% 6.37 6.73 5.7% T.1F53 1.73 1.68 2.9% 0.142 0.149 4.9% 16.6 16.3 1.8% 4.80 4.89 1.9% T.1F3o 1.47 1.52 3.4% 0.158 0.151 4.4% 13.2 12.7 3.8% 3.42 3.30 3.5% Results: The results indicate that the ABUS method can be used to assess the cement thickness and effective cement modulus below glass plates. Thickness measurements by micrometer indicate good agreement with ultrasonic measurements. Conclusions: The ABUS technique has potential to be developed as a noninvasive method to determine properties of the cement layer beneath dental crowns.
    Conference Paper · Mar 2014
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    [Show abstract] [Hide abstract] ABSTRACT: Purpose: The purpose of this investigation was to evaluate the effects of number and distribution of implants upon in vitro dislodging forces to a simulated implant-supported overdenture and to examine differences between several different attachment systems. Materials and methods: An experiment was undertaken utilizing a model simulating a mandibular edentulous ridge with dental implants in positions on the model approximating tooth positions in the natural dentition. A cobalt-chromium-cast testing framework was used to measure the peak load required to disconnect an attachment. Four different types of commercially available attachments were used in various positions on the model in sequence to evaluate the effects of retention and stability of overdentures based on implant number and distribution: (1) ERA, (2) O-Ring, (3) Locator, and (4) Ball. For each group, 10 measurements were made of peak dislodging forces. Means were calculated and differences among the systems, directions, and groups were identified using a repeated measured analysis of variance (α = .05). Results: The interactions between the attachment system, direction of force, and implant number and distribution were statistically significant. Vertical dislodging forces of the simulated overdenture prosthesis increased with additional widely spaced implants. Oblique dislodging forces of the simulated prosthesis increased with additional widely spaced implants except in the two-implant model with all attachments, and in the four-implant groups with Locator attachments. Anteroposterior dislodging forces of a simulated overdenture prosthesis increased with additional widely spaced implants except in the four-implant groups with Ball and Locator attachments. Ball attachments reported the highest levels of retention and stability followed by Locator, O-Ring, and ERA. Conclusions: Within the limitations of this study, retention and stability of an implant overdenture prosthesis are significantly affected by implant number, implant distribution, and abutment type.
    Full-text Article · Nov 2013 · The International journal of oral & maxillofacial implants
  • [Show abstract] [Hide abstract] ABSTRACT: An effective spring stiffness approximation is proposed for a hexagonal array of coplanar penny shaped cracks located at the interface between two dissimilar solids. The approximation is based on the factorization of the solution on the material dissimilarity factor, the crack interaction factor and the effective spring stiffness solution for non-interacting cracks in a homogeneous material. Such factorization is exact and was validated for 2D collinear cracks between two dissimilar solids. The crack interaction factor is obtained using a recently developed model for stress intensity factors for an array of coplanar penny shaped cracks in a homogeneous material; also the material dissimilarity function recently obtained for non-interacting penny shaped crack at the interface between two dissimilar materials is employed. The obtained solution is useful for an assessment by ultrasonic measurements of the interface stiffness in bonded structures for monitoring the interfacial microdamage growth due to mechanical loading and environmental factors.
    Article · Aug 2013 · International Journal of Solids and Structures
  • Robert R Seghi · Sadia Nasrin · Jonathan Draney · Noriko Katsube
    [Show abstract] [Hide abstract] ABSTRACT: An incompletely formed tooth is left with thin dentin walls and experiences a higher incidence of cervical root fracture that reduces the long-term overall prognosis of the tooth. Faced with these situations, clinicians have attempted to use various restorative methods to reinforce the remaining root. Various techniques have been reported, and the scientific evidence for each has been reviewed. The biomechanical considerations of reinforcing a weakened root are also reviewed, and the most current information about failure analysis, fracture characteristics of natural dentin, and in vitro test configurations used have been considered. In light of these additional considerations, some recommendations for future understanding of this complex problem have been proposed.
    Article · Mar 2013 · Journal of endodontics
  • [Show abstract] [Hide abstract] ABSTRACT: The effect of crack interactions on stress intensity factors is examined for a periodic array of coplanar penny-shaped cracks. Kachanov’s approximate method for crack interactions [Kachanov, M., 1987. Elastic solids with many cracks: a simple method of analysis. International Journal of Solids and Structures 23 (1), 23–43] is employed to analyze both hexagonal and square crack configurations. In approximating crack interactions, the solution converges when the total truncation number of the cracks is 109. As expected, due to high density packing crack interaction in the hexagonal configuration is stronger than that in the square configuration. Based on the numerical results, convenient fitting equations for quick evaluation of the mode I stress intensity factors are obtained as a function of crack density and angle around the crack edge for both crack configurations. Numerical results for the mode II and III stress intensity factors are presented in the form of contour lines for the case of Poisson’s ratio ν = 0.3. Possible errors for these problems due to Kachanov’s approximate method are estimated. Good agreement is observed with the limited number of results available in the literature and obtained by different methods.
    Article · Jan 2013 · International Journal of Solids and Structures
  • [Show abstract] [Hide abstract] ABSTRACT: A quasi-static approximation has been widely used to model ultrasonic wave interactions at imperfect interfaces between two linearly elastic materials. To simulate the reduction of static stiffness of the overall structure due to compromised interfaces (micro-cracks or micro-disbonds), the compliance of an imperfect interface to a loading is represented by continuous, uniform distributions of linearly elastic interfacial springs. In this work, a representation by normal and transverse effective spring stiffnesses of an array of non-interacting penny-shaped cracks at the interface between two dissimilar, isotropic, linearly elastic materials is obtained based on classical fracture mechanics. The results obtained are useful in estimating the disbonded area, which is critical in assessing the bond integrity and estimating the remaining life. Special care is taken to avoid crack surface interpenetration for transverse loading, and the valid loading range is obtained to assure negligibility of crack surface interpenetration for all possible ranges of isotropic, linearly elastic material combinations. For linear ultrasound applications, it is shown that the expression obtained for transverse springs can be used for most isotropic, linearly elastic material combinations, if the initial maximum crack opening displacement is more than 10 -5 of the crack radius. The obtained expressions are applied to estimate the accuracy of existing approximate models based on the analysis of penny-shaped cracks in a homogeneous material, rules of mixture, and Hertzian-based effective moduli. It is shown that for most practical material combinations the error is below 5%.
    Article · Sep 2011 · Mathematics and Mechanics of Solids
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    [Show abstract] [Hide abstract] ABSTRACT: Ceramic laminate veneers are generally fabricated with varying thicknesses ranging from 0.3 to 1 mm, depending on the need to mask discolored teeth or slightly correct the contour of malpositioned teeth. Clinical color reproduction poses a challenge because of color interaction with the underlying substrate, whether tooth structure or esthetic restorative material. The purpose of this in vitro investigation was to measure the effect of color change resulting from applying 2 shades of ceramic material, translucent (T1) and opaque (O2), to 2 shades of composite resin substrate material, light (A3) and dark (C4), on the overall color of ceramic laminates. Forty disks were fabricated. Twenty disks (15 × 0.5 mm) were cut from pressed ceramic, 10 disks for each shade (translucent and opaque). Additionally, 20 disks (15 × 4.0 mm) were fabricated from light-polymerized composite resin material, 10 disks for each shade (light and dark). The ceramic disks were bonded to the composite resin disks with clear resin cement. The specimen combinations were divided into 4 groups (n=5). Color measurements were done with a colorimeter (Minolta Chroma Meter CR-200b) configured with diffuse illumination/0-degree viewing geometry. Mean CIE lightness (L*), chroma (C*(ab)), and hue angle (h(ab)) values were obtained. A 2-way analysis of variance (ANOVA) was used to compare the means and standard deviations between the different color combinations (α=.05), followed by Tukey's HSD post hoc test for significant interactions. The 2-way ANOVA showed significant differences (P<.001) in L*, C*(ab), and h(ab) for a change in the composite resin substrate, regardless of the ceramic material shade. There was significant color change from dark to light substrate (P=.044). The mean h(ab) (SD) of dark substrate/opaque veneer was 89.62 (1.5), while the mean h(ab) of light substrate/translucent veneer was 81.23 (1.7). Within the limitations of this study, the selected color of a 0.5 mm ceramic laminate veneer was significantly affected by the change in color of the supporting substrate.
    Full-text Article · Sep 2011 · The Journal of prosthetic dentistry
    [Show abstract] [Hide abstract] ABSTRACT: Ceramic restorations exhibit delayed failure due to subcritical crack growth (SCG). Repetitive low-level loading causes pre-existing subcritical flaws to grow slowly until failure occurs.SCG parameters have been estimated for only a few commercial dental ceramics and glasses; however, few has investigated bilayered structure and how different cements may affect parameter estimates. Objective: To study the influence of different resin cements on the stress corrosion susceptibility coefficient (n) of lithium-disilicate ceramic(E-max Ivoclar) by means of dynamic fatigue method. Methods: Ceramic plates 0.65-mm in thickness were heat treated according to manufacturers' instructions. Surfaces were ground(600-grit SiC slurry), ultrasonically cleaned, etched(5% HF acid), rinsed and air dried. Before cementation, silane (Silane Primer,Kerr) was applied to the ceramics and a uniform layer of cement was obtained from either N(Nexus 2 Kerr) or U(Unicem 3M/ESPE).The bonded specimens were tested by a dynamic fatigue method (equibiaxial ring-on-ball of ring testing apparatus) in a water bath at room temperature by fracturing 10 specimens of each cement at different cross-head speed. The break stress was determined for the bilayer and monolayer plates (Rosenstiel et al 1993). Strength data were analyzed by means of weibull statistics and Tukey's test (alpha=0.05). Results: Linear regression analysis of log stress-rate versus log stress was performed to calculate the coefficient(n) according to ASTM-C1368 .The table below shows results of biaxial strength(weibull mean and shape parameter) at different cross-head speed. Treatment (.01mm/min) (.1mm/min) (1mm/min) (n)-value Etch/Si/U(U) 257(8) 302(9) 333(6) 17.518 Etch/Si/N(N) 206(6) 255(5) 323(5) 10.695 No treatment(A) 340(8) 4024(9) 431(8) 14.265 Conclusion: Within the limitation of this study and the limited sample size, different values of (n) were obtained, but there were no statistical difference between them. Strength values for untreated group(A) were higher than other groups. Further work with larger sample size should be done to determine resin cement influence on (SCG) parameters.
    Conference Paper · Mar 2011
  • [Show abstract] [Hide abstract] ABSTRACT: Explicit analytical expressions are obtained for the longitudinal and transverse effective spring stiffnesses of a planar periodic array of collinear cracks at the interface between two dissimilar isotropic materials; they are shown to be identical in a general case of elastic dissimilarity (the well-known open interface crack model is employed for the solution). Since the interfacial spring stiffness can be experimentally determined from ultrasound reflection and transmission analysis, the proposed expressions can be useful in estimating the percentage of disbond area between two dissimilar materials, which is directly related to the residual strength of the interface. The effects of elastic dissimilarity, crack density and crack interaction on the effective spring stiffness are clearly represented in the solution. It is shown that in general the crack interaction weakly depends on material dissimilarity and, for most practical cases, the crack interaction is nearly the same as that for crack arrays between identical solids. This allows approximate factorization of the effective spring stiffness for an array of cracks between dissimilar materials in terms of an elastic dissimilarity factor and two factors obtained for cracks in a homogeneous material: the effective spring stiffness for non-interacting (independent) cracks and the crack interaction factor. In order to avoid the effect of the crack surface interpenetration zones on the effective spring stiffness, the range of the tensile to transverse load ratios is obtained under the assumption of small-scale contact conditions. Since real cracks are often slightly open (due to prior loading history and plastic deformation), it is demonstrated that for ultrasound applications the results obtained are valid for most practical cases of small interfacial cracks as long as the mid-crack opening normalized by the crack length is at least in the order of 10(-5).
    Article · Feb 2011 · Mechanics of Materials
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    X Hu · W M Johnston · R R Seghi
    [Show abstract] [Hide abstract] ABSTRACT: Color information from different color-measuring systems varies during color matching in maxillofacial prosthetics. We studied the hypothesis that a non-contact measuring system and 4 contact color-measuring instruments perform comparably in accuracy and precision on measurements of pigmented maxillofacial elastomer specimens having human skin colors. Measurement comparisons in accuracy on opaque standard color patches were made in Phase I. In Phase II, the system with the best accuracy was used as the reference instrument, and comparisons in accuracy and precision on elastomer specimens were made. The CIEDE2000 color difference formula was used. Repeated-measures ANOVA with Tukey testing and linear regression analysis for CIELAB and color differences among the instruments were performed. The contact measuring systems perform differently in accuracy, possibly due to edge loss and other factors, but performed comparably in precision with the non-contact measuring instrument. This non-contact system is recommended for color measurement of maxillofacial prosthetic materials.
    Full-text Article · Dec 2010 · Journal of dental research
    [Show abstract] [Hide abstract] ABSTRACT: Microtensile bond strength testing of resin cement to prefabricated CAD/CAM composite blocks Objectives: To evaluate the effect of surface-conditioning on microtensile bond strength of resin cement (Nexus 2 Kerr) to prefabricated CAD/CAM composite blocks (Paradigm, 3M/ESPE) before and after aging. Methods: Paradigm plates 5 mm thick were sectioned from blocks as supplied. The surfaces received one of 3 treatment conditions 1- ground with 600-grit SiC slurry(600G),2-600G+sandblasting(Sb) and 3- 600G +etcheing with 5%HF and silanization (Si). Two plates with same surface treatment were bonded together with Nexus 2. The bonded specimens were then longitudinally sectioned with a diamond wire saw (Well) into approximately 0.7mm x 0.7 mm microbars or sticks. The microbars from each treatment group were equally divided into 4 groups: (1) initial bond strength (control), thermalcycled (Tc) for (2)17,000, (3)22,000 and (4)50,000 cycles between (5-55C, dwell time: 30s). The microtensile test was accomplished in a universal testing machine (crosshead speed: 0.05mm/min) using a modified testing device described by El Zohairy (2003). Results: Data were analyzed by Two-way ANOVA and Tukey's tests, α=.05. Means and standard deviations of bond strength (MPaSD) per group are listed in the table. The surface treatment condition greatly affect the TS (p<0.001) while condition was only slightly significant (p=0.02). Group 600G showed lowest bond strength and did not survive TC conditions. One of the TC groups resulted in significantly higher TBS than the others. The interaction between treatment condition and TC conditions was not significant (p=0.28). Conclusion: Sandblasting alone and chemical HF acid etching followed by silane application resulted in similar and durable TB strengths. TC Conditions Surface Tx (Initial) 0TC (TS) 17,000 TC (TS) 22,000 TC (TS) 50,000 TC (TS) 600G 1.478(3.1)C 0(0)C 0(0)C 0(0)C Sb 32.077(12.6)AB 24.45(9.58)B 27.63(10.07)AB 36.64(12.64A Si 34.575(10.5)AB 29.6(10.05)AB 28.25(7.92)AB 32.88(13.06)AB Levels not connected by the same letters are significantly different: 0(0) indicates none of the specimens survived the TC conditions
    Conference Paper · Jul 2010
  • [Show abstract] [Hide abstract] ABSTRACT: Objectives: An attractive smile has been shown to tremendously impact the perception of appearance and personality attributes. In recent years, all-ceramic restorations have been heavily utilized to improve teeth defects and discolorations. The ability to identify teeth color and further reproduce the exact match in the restoration has been a challenging process. Color measuring devices are becoming very popular among practitioners to aid in clinical shade selection. The purpose of this study was to compare variations in color differences (DE) when using 2 color matching colorimeter devices, namely, Vita Easyshade (Vident), Minolta Chroma Meter CR-200b (Minolta), and Crystaleye spectrophotometer (Olympus). Methods: Forty pressed IPS Empress ceramic disks (15x0.5 mm) of two shades (T1 and O2) were luted to 40 composite disks (15x4.0 mm) of shades (A3 and C4) using yellow (Y) shade of Nexus (NX3) resin luting cement. Color measurement was done three times for every specimen using the color matching devices, which were configured with diffuse illumination/0-degree viewing geometry. The L* a* and b* color parameters were analyzed for dependence on the materials and the devices, and DE (CIEDE2000) color difference values between the devices were obtained. Results: For each of the L* a* and b* color parameter, a statistically significant interaction (P≤0.0001) was found between the devices tested and the composite substrate studied, e.g. for the O2 shade ceramic material, the mean value was: Device Composite L* a* b* Easyshade A3 73.860.8 0.080.04 11.880.9 C4 65.440.8 -0.30.2 15.220.9 Minolta A3 71.101.39 0.660.2 72.240.9 C4 63.940.4 -0.020.04 6.400.25 Crystaleye A3 70.080.9 4.040.32 13.141.1 C4 61.081.9 1.630.1 9.280.6 Conclusion: There was a significant color difference (mean DE>5.6) between the color measuring devices. No significant differences were found between the materials or their interactions. This study is supported in part by Kerr Corp. Orange, CA, USA.
    Conference Paper · Jul 2010
    [Show abstract] [Hide abstract] ABSTRACT: Environmental conditions may negatively affect the mechanical properties of bonded glass-ceramic restorations. The bond integrity is partly responsible for the long-term durability of these restoration types. Objectives: To evaluate the microtensile bond strength (MTBS) of ProCAD (Ivoclar) and two composite resin cement before and after thermo-cycling (TC) at various intervals. Method:Ceramic plates 5 mm thick were sectioned from blocks as supplied. The surfaces were ground with 600-grit SiC slurry, ultrasonically cleaned, etched with 5%HF acid for 60 seconds, rinsed and air dried. Prior to cementation, silane (Silane Primer, Kerr) was applied to the ceramics and two plates were cemented together with either N (Nexus 2 Kerr) or U (Unicem 3M/ESPE). The bonded specimens were then longitudinally sectioned with a diamond wire saw (Well) into approximately 0.7mm x 0.7 mm microbars or sticks. The microbars from each cement group were equally divided into four test groups: Group A: initial bond strength (control) Groups B, C, D and E were thermocycled (TC) in distilled water baths between 5C and 55C with a 30 seconds dwell time, for 12,000, 17,000, 22,000 and 50,000 cycles respectively. The MTB strengths were determined using methods described by El Zohairy (2003). Results: Data were analysed by 2 way ANOVA and the results indicated that both cement type (p<.001) and TC conditions (p<.001) significantly affected the resulting MTBS. The interaction between cement type and TC conditions was also significant (p=.005). The results are summarized in the table below. Group NA NB NC ND NE UA UB UC UD UE Mean(SD)= 53.9 (14.6)A 12.6 (8.1)C 12.6 (7.1)C 15.1 (9.0)C 13.5 (7.8)C 53.8 (14.4)A 31.1 (18.2)B 23.1 (10.9)C 32.5 (13.4)B 30.3 (11.4)B Group means with the same letters were not significantly different at the 0.05 alpha level. Conclusions: Thermocycling significantly decreased the MTBS for both cement types. Cement U was significantly less affected by thermocycling than cement N
    Conference Paper · Mar 2010
  • Yaou Wang · Noriko Katsube · Stanislav I. Rokhlin · Robert R. Seghi
    [Show abstract] [Hide abstract] ABSTRACT: The stress intensity factor (SIF) of a half-penny shaped crack normal to the interface in the top layer of a three-layer bonded structure is obtained by the finite element method for a wide range of parameters. To obtain a simple estimate of the SIF, the method of reduction of an idealized cracked trilayer domain to that of a corresponding bilayer domain has been introduced based on the notion of an equivalent homogeneous material substitution for the two bottom layers. The results obtained are utilized in estimating the SIF of a small crack at the interface in a trilayer structure subjected to an indentation load based on the stress calculations in a corresponding uncracked structure. The simplification method may be useful in predicting brittle failure initiating from interfacial flaws in layered structural components with complex geometries that would normally require extensive computational modeling.
    Article · Nov 2009 · Engineering Fracture Mechanics
    [Show abstract] [Hide abstract] ABSTRACT: Objectives: Fractographic analysis of failed ceramic crowns has indicated that the failure initiation site commonly originates at the ceramic-cement interface in the form of a radial crack. The goal of this work is to determine the influence of the cement type on radial crack formation and hence the fatigue life of model ProCAD ceramic restorations. Methods: Fifty four ceramic plates approximately 1mm thick were sectioned from CEREC blocks (ProCAD, Ivoclar) with a diamond wheel saw, ground flat with a 600 grit SiC slurry and etched with 5% HF acid for 1 min. The ceramic plates were silanated (Silane Primer, Kerr) and arbitrarily divided into two equal groups. The silanated ceramic plates were luted to flattened human molar teeth with either Cement A (Nexus, Kerr) or Cement B (Unicem, 3M ESPE) following manufacturers instructions. The trilayer specimens were subjected to cyclic vertical indentation loading (300N max) at a rate of 1.6 Hz. The specimens were examined at 0.5, 1, 2, 3, 4 and 5 million cycles under magnification and transillumination. Observation of a radial crack in the ceramic indicated failure and the number of cycles to failure was recorded. The data was analyzed using survival analysis methods (JMP 7, SAS Institute) Results: The log-rank test between groups indicates that there was a significant difference (p<.001) between the survival curves of the two groups. Cement B resulted in significantly fewer ceramic fractures than cement A after 5 million loading cycles. Further work is needed to determine the mechanism responsible for this dramatic difference. Conclusions: The cement type can significantly influence the fatigue life of ProCAD ceramics in vitro. This work supported by NIDCR R21-DE14719
    Conference Paper · Apr 2009
  • [Show abstract] [Hide abstract] ABSTRACT: Objectives: Ceramic restorations have become a standard procedure in prosthodontic rehabilitation. Several color-matching devices have been marketed for clinical shade selection and verification of the restoration color before final cementation. The purpose of this in vitro study was to compare the color determination differences resulting from using two colorimeters. Methods: Forty ceramic pressed IPS Empress disks (15.0x0.5 mm) of shades T1 and O2 were luted to 40 composite disks (15.0x4.0 mm) of shades A3 and C4 using two shades of Nexus (NX3) resin cement (clear-CL and yellow-Y). The specimen combinations were divided into 8 groups (n=5). Color measurement was done using the Vita Easyshade (Vident) and the Minolta Chroma Meter CR-200b colorimeter (Minolta), configured with diffuse illumination/0 viewing geometry. CIE lightness (L*), chroma (Cab*) and hue angle (hab*) values were obtained. Results: Mean L*, Cab*, and hab* are listed below: Groups (n=5) L* Cab* hab* Minolta Vita Minolta Vita Minolta Vita T1-A3-CL 64.60.7 70.81.0 7.30.6 11.01.7 92.81.4 91.81.2 T1-A3-Y 67.20.5 72.30.4 9.10.7 12.31.0 81.21.7 85.80.9 T1-C4-CL 62.00.3 67.70.6 6.60.1 11.10.8 96.61.1 93.50.5 T1-C4-Y 59.80.4 63.10.7 6.90.2 13.30.6 87.50.8 89.90.6 O2-A3-CL 69.61.1 75.21.3 6.00.6 10.61.0 96.41.7 93.70.6 O2-A3-Y 71.10.3 75.00.5 7.80.3 11.80.7 83.71.0 87.70.8 O2-C4-CL 67.50.9 72.10.8 5.30.5 10.21.0 97.70.9 93.60.7 O2-C4-Y 65.60.4 67.60.2 5.50.2 13.10.7 89.61.5 89.91.3 Four-way ANOVA showed that when all of the three major color directions (L*, Cab*, and hab*) were analyzed, each one of the factors studied (ceramic, composite, cement, and color measuring device) was either a statistically significant factor (P<0.05) alone or in an interaction with one or more other factors. Conclusion: Digital color determination may be extremely beneficial for clinical shade selection, but consistency factors still need to be evaluated. This study is supported in part by Kerr Corp. Orange, CA, USA.
    Conference Paper · Apr 2009
    [Show abstract] [Hide abstract] ABSTRACT: Objectives: Fractographic analysis of failed ceramic crowns has indicated that the failure initiation site commonly originates at the ceramic-cement interface. The goal of this work is to examine the feasibility of developing laboratory and computer modeling techniques for predicting lifetime of bonded ceramic restorations. Methods: Two parameters (k, m) characterizing the distribution of the surface flaws for leucite-reinforced glass-ceramic ProCAD are determined based on the ball-on ring biaxial flexure tests and the fracture mechanics based failure probability model. Two parameters (n, B) characterizing the slow crack growth rate for ProCAD are determined from constant stress-time to failure analysis of ceramic plates in the biaxial test mode. By combining the stress distribution at the bottom of ceramic layer with these 4 experimentally determined parameters, survival probability for trilayered specimens are predicted as a function of loading cycles. The predictions are compared against the experimental cycles to failure (radial crack initiation) data for actual ceramic plates bonded to human molars with two ceramic thicknesses (1.0 and 1.6 mm) and two maximum loads (300 and 240 N). Results: Restorations in group A (n=12, Pmax=240 N, th=1.6mm) are subjected to 10 million cycles with no failure. The corresponding survival probability prediction remains 100% and matches experimental data. Restorations in group B (n=18, Pmax=300 N, th=1.0mm) are subjected to 5 million cycles and the theoretical survival prediction matches the lower end of the Kaplan-Meier 95% confidence level of the experimental data. The group A restoration represents clinically relevant thickness and loading range, and our simulated clinical experiments appear to demonstrate the soundness of current clinically suggested guidelines. Conclusion: Theoretical survival probability predictions for two cases with different maximum load range and thickness quantitatively match experimentally obtained survival distributions. The model, therefore, has demonstrated its potential as a useful life prediction tool for ceramic restorations.
    Conference Paper · Apr 2009