Susana Maria Salazar Marocho
@umc.edu
Assistant Professor, Department of Biomedical Materials Science
University of Mississippi Medical Center
RESEARCH INTERESTS
Dental ceramics, fracture mechanics, fatigue, lifetime
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Pallabi Pal, Michelle A. Tucci, Lir‐Wan Fan, Ratna Bollavarapu, Jonathan W. Lee, Susana M. Salazar Marocho, and Amol V. Janorkar
Wiley
B. Moura Pereira, A. Restani Oliveira, R. Leal do Prado, A. B. Gomes de Carvalho, R. Marques de Melo, K. Singh Jodha, S. M. Salazar Marocho and G. Ávila Galhano
INTRODUCTION
Adjustments with diamond burs on the ceramic surface can affect its roughness and decrease flexural strength. This study evaluated the effect of polishing or glazing on the surface roughness and biaxial flexural strength of a zirconia-reinforced lithium silicate glass-ceramic upon adjustment with diamond burs.
METHODS
Seventy disks were prepared according to ISO 6872 and divided into seven groups (n = 10) according to different adjustments and finishing processes. Surface roughness was measured prior to biaxial flexural strength testing. The topography was analyzed using an atomic force microscope , fracture markings were identified using a stereomicroscope and representative specimens were analyzed using scanning electron microscopy.
RESULTS
The use of diamond burs significantly increased the surface roughness and decreased the strength of the evaluated ceramic (p⟨0.05). Polishing reduced the ceramic's roughness but resulted in flexural strength similar to that of the groups with wear (p⟩0.05). The glaze-treated specimens showed flexural strength statistically similar to the control group (p>0.05) but higher roughness, similar to those with wear.
CONCLUSIONS
Polishing reduced the surface roughness but did not affect the biaxial flexural strength of the ZLS ceramic. At the same time, the application of glaze after wear increased the strength.
Lisseth Patricia Claudio Contreras, Camila Silva Rodrigues, Camila Pauleski Zucuni, Luiz Felipe Valandro, Susana Maria Salazar Marocho, and Renata Marques de Melo
Wiley
PURPOSE
This study evaluated the fatigue failure load (FFL) and the number of cycles for fatigue failure (CFF) of traditional (porcelain layer up) and reversed (zirconia layer up) designs of porcelain-veneered zirconia samples prepared with heat-pressing or file-splitting techniques.
MATERIALS AND METHODS
Zirconia discs were prepared and veneered with a heat-pressed or machined feldspathic ceramic. The bilayer discs were bonded onto a dentin-analog according to the bilayer technique and sample design: traditional heat-pressing (T-HP), reversed heat-pressing (R-HP), traditional file-splitting with fusion ceramic (T-FC), reversed file-splitting with fusion ceramic R-FC), traditional file-splitting with resin cement (T-RC), and reversed file-splitting with resin cement (R-RC). The fatigue tests were performed using the stepwise approach at 20 Hz, 10,000 cycles/step, step-size of 200N starting at 600N, and proceeding until failure detection or up to 2600 N if enduring. The failure modes (from radial and/or cone cracks) were analyzed in a stereomicroscope.
RESULTS
The reversed design decreased the FFL and CFF of bilayers prepared with heat-pressing and file-splitting with fusion ceramic. The T-HP and T-FC reached the highest results, which were statistically similar between them. The bilayers prepared by the file-splitting with resin cement (T-RC and R-RC) were similar to the R-FC and R-HP groups regarding FFL and CFF. Almost all reverse layering samples failed by radial cracks.
CONCLUSIONS
The reverse layering design did not improve the fatigue behavior of porcelain veneered zirconia samples. The three bilayer techniques behaved similarly when used in the reversed design. This article is protected by copyright. All rights reserved.
Kartikeya S. Jodha, Navleen Kaur, Susana M. Salazar Marocho, John J. Mecholsky, Seth T. Lirette, Yuanyuan Duan, and Jason A. Griggs
Elsevier BV
Rodrigo Ottoni, Susana M. Salazar Marocho, Jason A. Griggs, and Márcia Borba
Elsevier BV
W. B. Key, K. S. Jodha, N. Kaur, S. M. Salazar Marocho, J. J. Mecholsky, and J. A. Griggs
Springer Science and Business Media LLC
S. M. Salazar Marocho, P. F. Cesar, J. A. Griggs, and M. A. Bottino
Springer Science and Business Media LLC
Jaccare Jauregui-Ulloa and Susana Marocho
Quintessence Publishing
PURPOSE
To describe the current findings regarding the use of lasers to enhance the bonding properties of zirconia and to enable its debonding.
MATERIALS AND METHODS
The PudMed database was searched for literature up to July 2021. The keywords used for zirconia surface treatment were: laser irradiation; zirconia; and bond strength. For ceramic laser debonding, the keywords were: laser irradiation; ceramic; and debonding.
RESULTS
A total of 36 studies were included for zirconia surface treatment, and 12 for ceramic laser debonding. Nd:YAG, CO2, Er:YAG, Er,Cr:YSGG, and ultrashort lasers were used for surface treatment, whereas only Er:YAG and Er,Cr:YSGG lasers were applied to debond zirconia structures.
CONCLUSION
The use of laser irradiation to improve the bonding properties of zirconia depends on the type of laser and the parameters used. Among the laser types included in this review, ultrashort lasers have shown the most promising results; however, more studies are needed to prove their superiority over the other lasers for enhancing zirconia bond strength. In terms of debonding, irradiation with different lasers was effective regardless of the ceramic type; however, well-established protocols (ie, laser irradiation time and motion, laser settings) are still needed for different thicknesses and material ceramic types.
Susana M. Salazar Marocho, Mary Beth VanLandingham, Firas Mourad, Andres Pappa, and Sreenivas Koka
MDPI AG
The chance to critically and microscopically inspect the quality of bonded restorations once they are delivered to the patient after several pre-cementation steps is rare or nonexistent. Replicas of in-service restorations can provide a wealth of information on the integrity of the restorations and moreover make it possible to bring this information to the laboratory for further detailed analysis. This study aimed to characterize the epoxy replicas of 27 cemented monolithic yttria-stabilized zirconia crowns of the maxillary and mandibular arch to assess surface roughness, topography, and symmetry. The topography of the facial, lingual, and occlusal/incisal surfaces of each crown was observed under the optical microscope and further characterized using the scanning electron microscope. Surface roughness measurements were performed using the atomic force microscope. The optical microscope was used to measure the golden proportion and visible width of the anterior maxillary crowns. Surface damage consistent with unpolished adjustment was identified mostly in the occlusal surface of the posterior teeth. Other irregularities, such as scratch marks, small pits, and coarse pits were also found. The surface roughness had great variability. Not all of the anterior maxillary and mandibular teeth followed the golden proportion concept. This study design allows in vitro characterization of in-service restorations. It provides a framework for using replicas for early identification of patterns or features that can trigger fracture and for analysis of morphology and symmetry.
Michelle A. Tucci, Yilianys Pride, Suzanne Strickland, Susanna M. Salazar Marocho, Ramon J. Jackson, Joshua R. Jefferson, Alejandro R. Chade, Raymond J. Grill, and Bernadette E. Grayson
Mary Ann Liebert Inc
Nearly all persons with spinal cord injury (SCI) will develop osteoporosis following injury, and further, up to 50% of all persons with SCI will sustain a fracture during their lives. The unique mechanisms driving osteoporosis following SCI remain unknown. The cannabinoid system modulation of bone metabolism through cannabinoid 1/2 (CB1/2) has been of increasing interest for the preservation of bone mass and density in models of osteoporosis. Using a thoracic vertebral level 8 (T8) complete transection in a mouse model, we performed daily treatment with a selective CB2 receptor agonist, HU308, compared with SCI-vehicle-treated and naïve control animals either immediately after injury for 40 days, or in a delayed paradigm, following 3 months after injury. The goal was to prevent or potentially reverse SCI-induced osteoporosis. In the acute phase, administration of the CB2 agonist was not able to preserve the rapid loss of cancellous bone. In the delayed-treatment paradigm, in cortical bone, HU308 increased cortical-area to total-area ratio and periosteal perimeter in the femur, and improved bone density in the distal femur and proximal tibia. Further, we report changes to the metaphyseal periosteum with increased presence of adipocyte and fat mass in the periosteum of SCI animals, which was not present in naïve animals. The layer of fat increased markedly in HU308-treated animals compared with SCI-vehicle-treated animals. Overall, these data show that CB2 agonism targets a number of cell types that can influence overall bone quality.
AR Oliveira, KS Jodha, SM Salazar Marocho, and GA Galhano
Operative Dentistry
SUMMARY This study aimed to characterize the surface topography, effect of polishing on surface roughness, residual stresses, and hardness in two glass-ceramic veneers. Fifty-two (52) upper incisors were collected, prepared, and scanned for ceramic veneers. Half of the teeth were restored with veneers made up of feldspathic ceramic (FE), and the other half with zirconia-reinforced lithium silicate ceramic (SZ). All the veneers were designed and milled using a CAD/CAM system and later cemented following the manufacturer's guideline. An optical microscope analyzed the topography of the specimens before and after polishing. The surface roughness was measured using the roughness meter (n=12) and the topographical analysis was carried out using an atomic force microscope (n=6). The residual stresses and Vickers' hardness were evaluated by the indentation method in a micro-hardness indenter (n=6). The surface roughness was analyzed using a three-way analysis of variance (ANOVA) followed by a post hoc Tukey test. The Student t-test was used to compare the residual stresses and hardness between the two ceramics. The topographical analysis revealed that both glass-ceramic veneers had similar percentages of specimens with cracks, before (34.6%) and after (42.3%) polishing. The surface roughness decreased after polishing (p<0.001), and the polishing smoothed out the surface of the veneers. The zirconia-reinforced lithium silicate veneer had a lower roughness as compared to the feldspathic one after polishing, while the residual stresses (p=0.722) and hardness (p=0.782) were statistically similar for both ceramic veneers.
Kartikeya S. Jodha, Susana M. Salazar Marocho, Susanne S. Scherrer, and Jason A. Griggs
Elsevier BV
OBJECTIVES
Previous studies have shown that the fracture toughness of ceramics can be determined from the fractal dimensions (D) of their fracture surfaces and that the surface should be leveled to obtain an accurate D measurement. This study was to determine the effects of leveling operations and distance from the failure origin on the D values.
METHODS
Twelve clinically failed zirconia implants from four different manufacturers: Axis Biodental (n=7), Z-Systems (n=3), Straumann (n=1), and Swiss Dental Solutions (n=1) were obtained from one of the authors and thoroughly cleaned. Epoxy replicas were made of three locations along the crack path in the center region of each fracture surface (near origin (O), hackle (H), and near compression curl (CC)) using a light body polyvinyl siloxane impression material. Surfaces were scanned in ScanAsyst mode with a scan size of 5μm×5μm and a scan rate of 0.592Hz using the atomic force microscope. The surface scans were then leveled using 1st order flattening operation in the AFM analysis software. The height data before and after the operation were imported into a custom MathCAD script, and FRACTALS software was used to determine the D value by Minkowski Cover algorithm, which was shown previously to be the algorithm with the highest precision. A Wilcoxon signed-rank test, two-way repeated-measures ANOVA, and one-way repeated-measures ANOVA were performed as detailed below.
RESULTS
The data were not normally distributed (S-W p≤0.05), so a non-parametric repeated measures test (Wilcoxon signed-rank test) was selected. The median D values before and after leveling were 2.161 and 2.174, respectively. There was a significant difference before and after leveling (p<0.001). The two-way repeated-measures ANOVA showed no significant difference among the D values for different implant brands (p=0.66) and scanning locations on the fracture surface (p=0.83). After eliminating the implant brand as a factor, the data passed normality and equal variance tests (S-W p=0.88, BF p=0.15). The mean D values and standard deviations from the three locations (O, H, CC) were 2.183±0.031, 2.179±0.024, and 2.175±0.018, respectively. One-way repeated measures ANOVA showed no significant effect of scanning location (p=0.74).
SIGNIFICANCE
The leveling operation successfully removed the tilt without decreasing surface tortuosity, as it increased the D values significantly. The fractal dimension was the same at the three locations on the fracture surfaces. This means that hackle and compression curl regions can be used to determine fracture toughness when the failure origin has been lost.
Bhuvaneswari Gurumurthy, Michelle A. Tucci, Lir‐Wan Fan, Hamed A. Benghuzzi, Pallabi Pal, Gene L. Bidwell, Susana M. Salazar Marocho, Zelma Cason, David Gordy, and Amol V. Janorkar
Wiley
The goals of this study are to evaluate the ability of the multicomponent collagen-elastin-like polypeptide (ELP)-Bioglass scaffolds to support osteogenesis of rat mesenchymal stem cells (rMSCs), demonstrate in vivo biocompatibility by subcutaneous implantation in Sprague-Dawley rats, monitor degradation noninvasively, and finally assess the scaffold's ability in healing critical-sized cranial bone defects. The collagen-ELP-Bioglass scaffold supports the in vitro osteogenic differentiation of rMSCs over a 3 week culture period. The cellular (rMSC-containing) or acellular scaffolds implanted in the subcutaneous pockets of rats do not cause any local or systemic toxic effects or tumors. The real-time monitoring of the fluorescently labeled scaffolds by IVIS reveals that the scaffolds remain at the site of implantation for up to three weeks, during which they degrade gradually. Micro-CT analysis shows that the bilateral cranial critical-sized defects created in rats lead to greater bone regeneration when filled with cellular scaffolds. Bone mineral density and bone microarchitectural parameters are comparable among different scaffold groups, but the histological analysis reveals increased formation of high-quality mature bone in the cellular group, while the acellular group has immature bone and organized connective tissue. These results suggest that the rMSC-seeded collagen-ELP-Bioglass composite scaffolds can aid in better bone healing process.
SusanaMaría Salazar Marocho, TacianaMarco Ferraz Caneppele, DanielMaranha Rocha, MariaAmelia Máximo Araujo, and MárciaCarneiro Valera
Medknow
BACKGROUND
Abrasive wear is one of the most common type of wear that not only affect teeth, as also dental restorations. Thus to investigate one of the etiological factors as tooth brushing procedure is clinical relevant in order to select the best material combination that may prevent damage of resin dental restoration's abrasion.
AIMS
This study evaluated the influence of tooth brushing on mass loss and surface roughness of direct Venus (Vs) and indirect Signum (Sg) resin composites, with and without a surface sealant, Fortify (F).
MATERIALS AND METHODS
Twenty-four specimens were prepared with each resin composite, using their proprietary curing units, according to manufacturer's instructions. All the specimens were polished and ultrasonically cleaned in distilled water for 5 minutes. Half of the specimens of each resin (n = 12) were covered with F (Vs F and Sg F ), except for the control (C) specimens (Vs C and Sg C ), which were not sealed. Mass loss (ML) as well as surface roughness (Ra ) was measured for all the specimens. Then, the specimens were subjected to toothbrush-dentifrice abrasion, using a testing machine for 67.000 brushing strokes, in an abrasive slurry. After brushing simulation, the specimens were removed from the holder, rinsed thoroughly and blot dried with soft absorbent paper. The abrasion of the material was quantitatively determined with final measurements of ML and surface roughness, using the method described above.
RESULTS
ML data were analyzed by two-way analysis of variance (ANOVA) and the analysis indicated that resin composites were not statistically different; however, the specimens sealed with F showed higher ML. Ra mean values of the groups Vs F and Sg F significantly increased.
CONCLUSION
Tooth brushing affects mainly the roughness of the direct and indirect resin composites veneered with a sealant.
Pedro Henrique Corazza, Alecsandro de Moura Silva, José Renato Cavalcanti Queiroz, Susana María Salazar Marocho, Marco Antonia Bottino, Marcos Massi, and Rodrigo Othávio de Assunção e Souza
Ovid Technologies (Wolters Kluwer Health)
Purpose:To evaluate the effect of diamond-like carbon (DLC) coating of prefabricated implant abutment on screw removal torque (RT) before and after mechanical cycling (MC). Materials and Methods:Fifty-four abutments for external-hex implants were divided among 6 groups (n = 9): S, straight abutment (control); SC, straight coated abutment; SCy, straight abutment and MC; SCCy, straight coated abutment and MC; ACy, angled abutment and MC; and ACCy, angled coated abutment and MC. The abutments were attached to the implants by a titanium screw. RT values were measured and registered. Data (in Newton centimeter) were analyzed with analysis of variance and Dunnet test (&agr; = 0.05). Results:RT values were significantly affected by MC (P = 0.001) and the interaction between DLC coating and MC (P = 0.038). SCy and ACy showed the lowest RT values, statistically different from the control. The abutment coated groups had no statistical difference compared with the control. Scanning electron microscopy analysis showed DLC film with a thickness of 3 &mgr;m uniformly coating the hexagonal abutment. Conclusion:DLC film deposited on the abutment can be used as an alternative procedure to reduce abutment screw loosening.
MA Bottino, C Bergoli, EG Lima, SMS Marocho, RO Souza, and LF Valandro
Operative Dentistry
SUMMARY Purpose To evaluate the effects of two surface treatments, aging, and two resin cements on shear bond strength between dentin and yttrium-stabilized tetragonal zirconia polycrystal ceramic (Y-TZP). Materials and Methods Eighty human molars were embedded in acrylic resin and sectioned 3 mm below the occlusal plane. These teeth and 80 cylindrical Y-TZP specimens (height, 4 mm; diameter, 3.4 mm) were divided into eight groups (n=10) using the following factors: Y-TZP surface treatment (Vi: low-fusing porcelain [vitrification] + hydrofluoric acid etching + silanization or Si: tribochemical silicatization); cementation strategies (PF: Panavia or CC: Clearfil); and storage (nonaging or aging). Bonding surfaces of 40 Y-TZP specimens received Vi treatment, and the rest received Si treatment. Half of the ceramic-tooth assemblies were cemented with Panavia, the rest with Clearfil. Shear tests were executed using 0.4-mm–thick wire at 0.5 mm/min. Data were analyzed by three-way analysis of variance and Tukey test (α=0.05). Fractures were analyzed. Results Y-TZP surface treatments did not affect bond strength (p=0.762, Vi = Si), while resin cements (p&lt;0.001, Panavia &gt; Clearfil) and aging (p=0.006, nonaging &gt; aging) showed a significant effect. Most failures were in adhesive at dentin-cement interfaces; no failure occurred between zirconia and cement. Conclusion When Y-TZP ceramic is bonded to dentin, the weakest interface is that between dentin and resin cement. The resin cement/Y-TZP interface was less susceptible to failures, owing to Y-TZP surface treatments.
Mutlu Özcan, Pedro Henrique Corazza, Susana Maria Salazar Marocho, Silvia Helena Barbosa, and Marco Antonio Bottino
Springer Science and Business Media LLC
ObjectivesThis study evaluated the microtensile bond strength (MTBS) of non-aged and aged resin-based composites (RBC) (nanohybrid and nanofilled) after two surface conditioning methods, repaired using the composite of the same kind or a microhybrid composite.Materials and methodsNanohybrid (Tetric EvoCeram—TE) and nanofilled (Filtek Supreme—FS) RBC blocks (5 × 5 × 6 mm) (N = 128) were fabricated and randomly divided into two groups: (a) no ageing (control group) and (b) ageing (5.000 thermocycling, 5–55 °C). RBC surfaces were polished by up to 1,200-grit silicone carbide papers and conditioned with either (a) air abrasion with 30-μm SiO2 particles (CoJet Sand) for 4 s + silane coupling agent (ESPE-Sil) + adhesive resin (VisioBond) (n = 16) or (b) adhesive application only (Multilink A+B for TE; Adper ScotchBond 1XT for FS) (n = 16). In half of the groups, repair resin of the same kind with the RBC and, in the other half, a different kind of composite (microhybrid, Quadrant Anterior Shine—AS) with its corresponding adhesive (Quadrant UniBond) was used. The specimens were submitted to MTBS test (0.5 mm/min). Data were analysed using three-way ANOVA and Tukey's tests. Degree of conversion (DC) of non-aged and aged resin composites (TE, FS) (n = 3 per group) was measured by micro-Raman analyses.ResultsRBC type (p = 0.001) and ageing affected the MTBS results significantly (p = 0.001). Surface conditioning type did not show significant difference (p = 0.726), but less number of pre-test failures was experienced with the CoJet system compared to adhesive resin application only. Repair strength on aged TE showed significantly less (p < 0.05) MTBS than for FS. FS repaired with the same kind of RBC and adhesive resin presented the highest cohesive failures (43 %). DC was higher for TE (71 %) than for FS (58 %) before ageing.ConclusionOn the aged RBCs, less favourable repair strength could be expected especially for nanohybrid composite. For repair actions, RBC surface conditioning could be accomplished with either adhesive resin application only or with CoJet system, providing that the latter resulted in less pre-test failures.Clinical relevanceClinicians could condition the resin surface prior to repair or relayering with either CoJet system or adhesive resin application only, depending on the availability of the system.
S. M. Marocho, M. Ozcan, R. Amaral, M. Bottino and L. Valandro
PURPOSE
This study evaluated the microtensile bond strength (µTBS) of 3 different resin cements to lithium-disilicate ceramic using two assemblies: ceramic-cement-ceramic (CCC) and ceramic-cement-dentin (CCD).
MATERIALS AND METHODS
The bonding surfaces of lithium disilicate ceramic blocks (5 × 5 × 4 mm) (Nblock = 90) were etched with 4% hydrofluoric acid for 20 s and silanized. Flat dentin surfaces of human third molars were conditioned according to the respective manufacturer's specifications for three types of resin cements (ML: Multilink, Ivoclar-Vivadent; PF: Panavia F, Kuraray; SB: Super Bond C&B, Sun Medical). While one set of ceramic blocks (n = 30) was cemented to another equal set (CCC assembly), another set of ceramic blocks (n = 30) was cemented on flat dentin (CCD assembly). The bonded specimens were stored in distilled water at 37°C for 24 h, and then sectioned along the x- and y-axes to obtain nontrimmed beam specimens. The beam specimens were randomly divided into two conditions: dry condition (DC - immediate testing); and aging condition (AC - thermocycling 12,000 times + water storage for 150 days). The µTBS bond strength test was performed using a universal testing machine (1 mm/min). After debonding, the substrate and adherent surfaces were analyzed using a scanning electron microscope to categorize the failure types. The data were statistically evaluated using 2-way ANOVA and Tukey's test (5%).
RESULTS
While the mean µTBS of CCC assemblies were significantly influenced by the cement type (p < 0.05) and aging (p < 0.05), CCD assemblies showed a significant effect of the cement (p < 0.05) but not the aging (p > 0.05). Without aging (DC), the mean µTBS (MPa) of SB (26.9) and PF (26.9) were significantly higher than ML (18.5) (p < 0.05). For CCC after aging (AC), SB (26.6) showed higher mean µTBS than those of PF (16.4) and ML (18.5) (p < 0.05). However, in CCD after AC, no significant difference was found between the groups (p > 0.05). In both CCC and CCD assemblies, pre-test failures were the least with SB cement. Regardless of the resin cement type employed and storage conditions, adhesive failures ranged between 35.3% and 88.9%, cohesive failures in cement between 2.3% and 35.3%, and cohesive failures in ceramic between 3.3% and 6.8%.
CONCLUSION
SB resin cement demonstrated the highest bond strength to a lithium disilicate ceramic in both tests assemblies with and without aging conditions.
Susana María Salazar Marocho, Mutlu Özcan, Regina Amaral, Luiz Felipe Valandro, and Marco Antonio Bottino
Springer Science and Business Media LLC
ObjectivesThe aim of this study was to evaluate the effect of different seating forces during cementation in cement–ceramic microtensile bond strength (μTBS).Materials and methodsForty-five blocks (5 × 5 × 4 mm3) of a glass-infiltrated alumina-based ceramic (In-Ceram Alumina) were fabricated according to the manufacturer’s instructions and duplicated in resin composite. Ceramic surfaces were polished, cleaned for 10 min in an ultrasonic bath, silica coated using a laboratory type of air abrasion device, and silanized. Each treated ceramic block was then randomly assigned to five groups (n = 9) and cemented to a composite block under five seating forces (10 g, 50 g, 100 g, 500 g, and 750 g) using a dual-cured resin cement (Panavia F). The ceramic–cement–composite assemblies were cut under coolant water to obtain bar specimens (1 mm × 0.8 mm2). The μTBS tests were performed in a universal testing machine (1 mm/min). The mean bond strengths values were statistically analyzed using one-way ANOVA (α ≤ 0.05).ResultsDifferent seating forces resulted in no significant difference in the μTBS results ranging between 13.1 ± 4.7 and 18.8 ± 2.1 MPa (p = 0.13) and no significant differences among cement thickness.ConclusionsExcessive seating forces during cementation seem not to affect the μTBS results.Clinical relevanceExcessive forces during the seating of single all-ceramic restorations cementation seem to display the same tensile bond strength to the resin cement.
Roberto Elias Campos, Carlos José Soares, Paulo S. Quagliatto, Paulo Vinícius Soares, Osmir Batista de Oliveira, Paulo Cesar Freitas Santos-Filho, and Susana M. Salazar-Marocho
Wiley
PURPOSE
This in vitro study investigated the null hypothesis that metal-free crowns induce fracture loads and mechanical behavior similar to metal ceramic systems and to study the fracture pattern of ceramic crowns under compressive loads using finite element and fractography analyses.
MATERIALS AND METHODS
Six groups (n = 8) with crowns from different systems were compared: conventional metal ceramic (Noritake) (CMC); modified metal ceramic (Noritake) (MMC); lithium disilicate-reinforced ceramic (IPS Empress II) (EMP); leucite-reinforced ceramic (Cergogold) (CERG); leucite fluoride-apatite reinforced ceramic (IPS d.Sign) (SIGN); and polymer crowns (Targis) (TARG). Standardized crown preparations were performed on bovine roots containing NiCr metal dowels and resin cores. Crowns were fabricated using the ceramics listed, cemented with dual-cure resin cement, and submitted to compressive loads in a mechanical testing machine at a 0.5-mm/min crosshead speed. Data were submitted to one-way ANOVA and Tukey tests, and fractured specimens were visually inspected under a stereomicroscope (20×) to determine the type of fracture. Maximum principal stress (MPS) distributions were calculated using finite element analysis, and fracture origin and the correlation with the fracture type were determined using fractography.
RESULTS
Mean values of fracture resistance (N) for all groups were: CMC: 1383 ± 298 (a); MMC: 1691 ± 236 (a); EMP: 657 ± 153 (b); CERG: 546 ± 149 (bc); SIGN: 443 ± 126 (c); TARG: 749 ± 113 (b). Statistical results showed significant differences among groups (p < 0.05) represented by different lowercase letters. Metal ceramic crowns presented fracture loads significantly higher than the others. Ceramic specimens presented high incidence of fractures involving either the core or the tooth, and all fractures of polymer crown specimens involved the tooth in a catastrophic way. Based on stress and fractographic analyses it was determined that fracture occurred from the occlusal to the cervical direction.
CONCLUSIONS
Within the limitations of this study, the results indicated that the use of ceramic and polymer crowns without a core reinforcement should be carefully evaluated before clinical use due to the high incidence of failure with tooth involvement. This mainly occurred for the polymer crown group, although the fracture load was higher than normal occlusal forces. High tensile stress concentrations were found around and between the occlusal loading points. Fractographic analysis indicated fracture originating from the load point and propagating from the occlusal surface toward the cervical area, which is the opposite direction of that observed in clinical situations.
Susana Maria SALAZAR MAROCHO, Renata Marques de MELO, Luis Guilherme Scavone MACEDO, Luiz Felipe VALANDRO, and Marco Antonio BOTTINO
Japanese Society for Dental Materials and Devices
The aim of this study was to evaluate, in vitro, the biaxial flexural strength (ISO 6872) of a feldspathic ceramic (VM7, Vita Zahnfabrik) coated with a resin cement with different thicknesses and polymerization mode. Control groups consisted in VM7 with and without acid etching with 10% hydrofluoric acid for 1 min. Experimental groups comprised VM7 etched, silanated and coated with Variolink II (Ivoclar Vivadent) cement, that was polymerized through the porcelain in light-cure and dual-cure modes, with thickness ≤150 µm or >150 µm. The specimens (n=15) were subjected to the biaxial flexural strength essay and analyzed fractographically. Parametric (Dunnet, Anova 2-way, Tukey) and non-parametric tests (Weibull) were used to evaluate results. Ceramic disks coated with resin cements of either activation modes and thicknesses exhibited higher flexural strength while the Weibull moduli did not present significant differences for a confidence interval of 95%.
Susana M. Salazar Marocho, André R. Studart, Marco A. Bottino, and Alvaro Della Bona
Elsevier BV
OBJECTIVES
Evaluate the flexural strength (sigma) and subcritical crack growth (SCG) under cyclic loading of glass-infiltrated alumina-based (IA, In-Ceram Alumina) and zirconia-reinforced (IZ, In-Ceram Zirconia) ceramics, testing the hypothesis that wet environment influences the SCG of both ceramics when submitted to cyclic loading.
METHODS
Bar-shaped specimens of IA (n=45) and IZ (n=45) were fabricated and loaded in three-point bending (3P) in 37 degrees C artificial saliva (IA(3P) and IZ(3P)) and cyclic fatigued (F) in dry (D) and wet (W) conditions (IA(FD), IA(FW), IZ(FD), IZ(FW)). The initial sigma and the number of cycles to fracture were obtained from 3P and F tests, respectively. Data was examined using Weibull statistics. The SCG behavior was described in terms of crack velocity as a function of maximum stress intensity factor (K(Imax)).
RESULTS
The Weibull moduli (m=8) were similar for both ceramics. The characteristic strength (sigma(0)) of IA and IZ was and 466MPa 550MPa, respectively. The wet environment significantly increased the SCG of IZ, whereas a less evident effect was observed for IA. In general, both ceramics were prone to SCG, with crack propagation occurring at K(I) as low as 43-48% of their critical K(I). The highest sigma of IZ should lead to longer lifetimes for similar loading conditions.
SIGNIFICANCE
Water combined with cyclic loading causes pronounced SCG in IZ and IA materials. The lifetime of dental restorations based on these ceramics is expected to increase by reducing their direct exposure to wet conditions and/or by using high content zirconia ceramics with higher strength.