feldspar and tungsten-carbide

Pressing esthetic demands of good looking make people undergo bleaching procedures. However, the effect of bleaching agents on esthetic restorative materials with different surface preparations has been poorly studied.. The aim of this study was to examine the effect of a homebleaching agent (carbamide peroxide: CP 38%) on the surface roughness of the polished fiber reinforced composite (FRC), overglazed, autoglazed, or polished ceramic samples.. Twenty standardized cylindrical specimens were made of each of the following groups: over-glazed, autoglazed, polished porcelain and also FRC. The test specimens exposed to the CP 38%, 15 minutes, twice a day for 2 weeks according to the manufacturer's recommendation. Six samples from each group were selected randomly to form negative controls. Surface roughness measurements (Ra, micrometer) for baseline, test and control specimens were performed by use of a profilometer. Paired t-test, Mann-Whitney test, and Kruskal-Wallis test were used for statistical analyses.. The data showed that bleaching with CP 38% significantly increased the surface roughness of all the test samples (p < 0.05). The type of surface preparation caused significant differences between the susceptibility of porcelain subgroups to bleaching (p < 0.05). The polished porcelain specimens showed the highest changes after bleaching.. CP 38% significantly increases the surface roughness of the porcelains and FRC. The type of surface condition affects the amenability of the porcelain surface to the bleaching agent. Glazed porcelains were more resistant to roughness than the polished porcelains and also the composite.. Roughening of porcelain and FRC occur following bleaching procedure. No special surface preparation of indirect esthetic restorative materials can completely preserve these materials from adverse effects of bleaching agents.

Topics: Aluminum Oxide; Aluminum Silicates; Carbamide Peroxide; Composite Resins; Dental Etching; Dental Materials; Dental Polishing; Dental Porcelain; Dental Restoration, Permanent; Esthetics, Dental; Hot Temperature; Humans; Materials Testing; Peroxides; Potassium Compounds; Surface Properties; Temperature; Time Factors; Tooth Bleaching Agents; Tungsten Compounds; Urea; Water

The aim of this study was to compare failure modes and fracture strength of ceramic structures using a combination of experimental and numerical methods.. Twelve specimens with flat layer structures were fabricated from two types of ceramic systems (IPS e.max ceram/e.max press-CP and Vita VM9/Lava zirconia-VZ) and subjected to monotonic load to fracture with a tungsten carbide sphere. Digital image correlation (DIC) and fractography technology were used to analyze fracture behaviors of specimens. Numerical simulation was also applied to analyze the stress distribution in these two types of dental ceramics.. Quasi-plastic damage occurred beneath the indenter in porcelain in all cases. In general, the fracture strength of VZ specimens was greater than that of CP specimens. The crack initiation loads of VZ and CP were determined as 958 ± 50 N and 724 ± 36 N, respectively. Cracks were induced by plastic damage and were subsequently driven by tensile stress at the elastic/plastic boundary and extended downward toward to the veneer/core interface from the observation of DIC at the specimen surface. Cracks penetrated into e.max press core, which led to a serious bulk fracture in CP crowns, while in VZ specimens, cracks were deflected and extended along the porcelain/zirconia core interface without penetration into the zirconia core. The rupture loads for VZ and CP ceramics were determined as 1150 ± 170 N and 857 ± 66 N, respectively.. Quasi-plastic deformation (damage) is responsible for crack initiation within porcelain in both types of crowns. Due to the intrinsic mechanical properties, the fracture behaviors of these two types of ceramics are different. The zirconia core with high strength and high elastic modulus has better resistance to fracture than the e.max core.

Topics: Aluminum Silicates; Ceramics; Computer Simulation; Crowns; Dental Materials; Dental Porcelain; Dental Restoration Failure; Dental Veneers; Elastic Modulus; Elasticity; Finite Element Analysis; Humans; Image Processing, Computer-Assisted; Potassium Compounds; Stress, Mechanical; Surface Properties; Tungsten Compounds; Yttrium; Zirconium

To compare the effects of two polishing systems on the surface roughness of three types of porcelain after orthodontic debonding.. A total of 90 porcelain discs were fabricated from feldspathic (n = 30), leucite-based (n = 30) or lithia disilicate-based (n = 30) ceramics. Ten samples in each group served as the control and received no surface treatment. The remaining 60 samples in three of the porcelain groups were bonded with lower incisor brackets and debonded using a testing machine in shear mode at a rate of 1 mm/minute crosshead speed. After debonding, the remaining adhesive resin was removed with a tungsten carbide bur. Then, two experimental subgroups (10 each) in each porcelain group were treated as follows: in the first subgroup, porcelain polishing wheel and polishing paste were applied, whereas in the second, polishing was performed using a series of Sof-Lex discs. The average surface roughness (Ra) of the all samples was evaluated using SPM/AFM (surface probe microscope/atomic force microscope). Data were statistically analyzed by analysis of variance for each porcelain material and polishing method.. The polishing techniques affected surface roughness significantly. There were significant differences between the groups; higher Ra values were obtained with the use of porcelain polishing wheel and polishing paste (P < .001).. The application of Sof-Lex discs can produce smoother porcelain surfaces than porcelain polishing wheel and polishing paste.

Topics: Acid Etching, Dental; Aluminum Silicates; Ceramics; Dental Bonding; Dental Debonding; Dental Etching; Dental Polishing; Dental Porcelain; Equipment Design; Humans; Lithium Compounds; Materials Testing; Microscopy, Atomic Force; Orthodontic Brackets; Potassium Compounds; Resin Cements; Surface Properties; Tungsten Compounds