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PURPOSEThe aim of this study was to evaluate occlusal contacts generated by 3 different biogeneric design modes (individual (BI), copy (BC), reference (BR)) of CEREC software and to assess the designs subjectively.MATERIALS AND METHODSTen pairs of maxillary and mandibular casts were obtained from full dentate individuals. Gypsum cast contacts were quantified with articulating paper and digital impressions were taken. Then, all ceramic crown preparation was performed on the left first molar teeth and digital impressions of prepared teeth were made. BI, BC, and BR crowns were designed. Occlusal images of designs including occlusal contacts were superimposed on the gypsum cast images and corresponding contacts were determined. Three designs were evaluated by the students.RESULTSThe results of the study revealed that there was significant difference among the number of contacts of gypsum cast and digital models (P<.05). The comparison of the percentage of virtual contacts of three crown designs which were identical to the contacts of original gypsum cast revealed that BI and BR designs showed significantly higher percentages of identical contacts compared with BC design (P<.05). Subjective assessment revealed that students generally found BI designs and BR designs natural regarding naturalness of fissure morphology and cusp shape and cusp tip position. For general occlusal morphology, student groups generally found BI design "too strong" or "perfect", BC design "too weak", and BR design "perfect".CONCLUSIONOn a prepared tooth, three different biogeneric design modes of a CAD/CAM software reveals different crown designs regarding occlusal contacts and morphology.

The aim of this study was to evaluate the elemental release from a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) or 10% carbamide peroxide (CP) solutions and to determine the composition of surface oxide layer formed on alloy samples. Cylinder-shaped 15 specimens were cast from a Ni-Cr alloy and divided into three groups (n = 5). Samples were exposed either to phosphate-buffer solution, HP, or CP for 30 days, and total mass and individual elements (Ni, Cr, Mo) released into solutions were measured by means of atomic absorption spectrometry. Before and after elemental release measurements, a scanning electron microscope (SEM) accompanied by energy dispersive spectroscopy (EDS) (SEM/EDS) was used to analyze the surface morphology, and surface characterization of passive film formed on alloy samples was also performed by using X-ray photoelectron spectroscopy (XPS). The presence of bleaching agents induced the mass released compared to control group (4.9 μg/cm(2)); this effect was recorded in both HP (171.2 μg/cm(2)) and CP (59.7 μg/cm(2)). XPS data showed that Cr and Ni levels in oxide layers formed on HP group were higher, Mo level was lower than those of CP group.

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This study compared the fracture resistance of monolithic and veneered all-ceramic four-unit posterior fixed dental prostheses (FDPs) generated by computer-aided design/computer-aided manufacturing (CAD/CAM) after aging in a mastication simulator. Four-unit FDPs were designed from six different all-ceramic systems: 1) monolithic lithium disilicate (M-E), 2) monolithic zirconia (M-TZI), 3) veneered zirconia by conventional layering (V-L), 4) veneered zirconia by lithium disilicate pressing (V-P), 5) veneered zirconia by lithium disilicate fusing (CAD-F-E), and 6) veneered zirconia by feldspathic ceramic cementing (CAD-C-CB). The specimens were divided into control and aging groups (n = 10 per group). The aging process included both thermocycling and mechanical loading and was followed by fracture resistance testing. All specimens in the ME , M-TZI, and V-L groups survived; however, all specimens in the V-P group were fractured during artificial aging. The highest fracture resistance values were observed in the M-TZI group. According to the fracture resistance test, connector fractures were the most frequent type of failure. M-TZI and ME FDPs revealed no failures during aging and showed higher fracture resistance than the veneered groups. Among the veneered zirconia framework groups, V-L FDPs showed the highest success rate during aging, while the fracture resistance was similar among all the veneered zirconia groups.

Implant failure is more likely to occur in persons with medically compromising systemic conditions, such as diabetes related to high blood glucose levels and inflammatory diseases related to pH levels lower than those in healthy people. The aim of this study was to investigate the effects of lower pH level and simulated- hyperglycemia on implant corrosion as these effects are critical to biocompatibility and osseointegration. The electrochemical corrosion properties of titanium implants were studied in four different solutions: Ringer's physiological solution at pH = 7.0 and pH = 5.5 and Ringer's physiological solution containing 15 mM dextrose at pH = 7 and pH = 5.5. Corrosion behaviors of dental implants were determined by cyclic polarization test and electrochemical impedance spectroscopy. Surface alterations were studied using a scanning electron microscope. All test electrolytes led to apparent differences in corrosion behavior of the implants. The implants under conditions of test exhibited statistically significant increases in I(corr) from 0.2372 to 1.007 μAcm(-2), corrosion rates from 1.904 to 8.085 mpy, and a decrease in polarization resistances from 304 to 74 Ω. Implants in dextrose-containing solutions were more prone to corrosion than those in Ringer's solutions alone. Increasing the acidity also yielded greater corrosion rates for the dextrose-containing solutions and the solutions without dextrose.

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The comparison of the effects of the two bleaching agents at 10% showed that the alloy suffered less corrosion with CP than HP. This result was also confirmed by the SEM and XPS data. The presence of Mo on the oxide layer affected the oxide layer, leading to lower corrosion rates.