Comparative analysis of flexural strength of abraded and polished porcelain surfaces – an in vitro study

Typically, prosthodontists adjust ceramic restorations glazed surface by grinding prior to insertion. Such alterations of surfaces are necessary for the correction of occlusal interferences. We aimed to evaluate and compare the change in flexural strength of ceramic surfaces after re-glazing and polishing. This study included 40 samples of ceramic blocks that were fabricated and glazed, and then fired in accordance with the manufacturer’s recommendations. The sample was randomly divided into four groups of 10 samples each. The first group was the control group with unaltered glazed samples. The second group was abraded with an extra-fine diamond bur followed by re-glazing, and the other two groups were polished with two commercially available polishing kits after abrading them with an extra-fine diamond bur. The samples were tested for their flexural strength using a universal testing machine. On the application of the F test on the means of all the groups, a value greater than 0.05 was found, which meant that there is no statistically significant difference in flexural strength values between the groups (P-value>0.05). Since the flexural strength values of the polished group were comparable to the other groups, polishing can be used instead of re-glazing for ceramic restorations. This reduces an additional clinical appointment for the patient and saves working time.

Adhesive bond strength between orthodontic resin and acrylic surfaces

The use of orthodontic treatments in patients with temporary prostheses has been increasing, the purpose of this in vitro research is to measure the adhesive bond strength between orthodontic resin and acrylic surfaces by applying different procedures. Objective. To compare the adhesive bonding strength between orthodontic resin and acrylic surfaces under different application protocols. Methodology. Transversal, experimental, prospective study. In vitro with acrylic provisions, was carried out in the laboratory of the Faculty of Dentistry of the Universidad Veracruzana region of Veracruz. In the period of February-June of the year 2019. The sample was conformed by two control groups of specimens and four experimental ones, each group conformed by 20 specimens, in total 120 provisional ones were made in acrylic Nic Tone of quick self-cure. The tests performed by the ULTRATESTER machine were expressed in MPa. Later, the data obtained were processed in Excel tables (version) for statistical processing in SPSS version 24. Contribution. When comparing the pre-cutting protocol of acrylic surfaces with fine diamond bur and the protocol without pre-cutting, no statistically significant differences were found, therefore, this step could be omitted in clinical practice.

Mechanism of online dressing for micro-diamond grinding wheel during the ultrasound-aided electrolytic in-process dressing grinding

A high-precision continuous dressing technology, namely ultrasound-aided electrolytic in-process dressing method, was proposed in this paper, aiming at overcoming the difficulty in continuous dressing for fine diamond wheel during the super mirror processing, such as optics and aeronautics. Firstly, the influence of high-frequency ultrasonic vibration on electrolysis was analyzed on the basis of the mechanism of electrolysis. Then, the compared tests between the common electrolytic in-process dressing grinding and the ultrasound-aided electrolytic in-process dressing grinding of the grinding wheel were employed to observe the effect of dressing and the state of abrasive particle. It was found experimentally that under the latter dressing, the better dressing effect could be gained, and the number of abrasive particle per unit area, the sharpness of abrasive and the average grain protrude height were improved; meanwhile, the distribution of grains become more uniform. In addition, compared with the former dressing, the average distance between grains was decreased, and the microscopic roughness of grinding wheel physiognomy was increased in the latter dressing. Finally, the grinding experiment was carried out to illustrate the advantages of the ultrasound-aided electrolytic in-process dressing grinding. The experimental results revealed that the removal rate and machining surface quality were increased compared with the common electrolytic in-process dressing grinding.

Enamel Surface Roughness after Lingual Bracket Debonding: An In Vitro Study

The aim of the present study was to quantitatively assess changes in enamel roughness parameters before and after lingual bracket debonding. The lingual surface of 25 sound premolars extracted for orthodontic reasons was studied by 3D optical interferometric profilometry before and after debonding of lingual brackets following enamel finishing (with fine diamond) and polishing (with 12- and 20-fluted carbide burs). The roughness parameters tested were the amplitude parameters Sa and Sz, the hybrid parameter Sdr, and the functional parameters Sc and Sv. The parameter differences (after debonding-reference) were calculated, and statistical analysis was performed via a Wilcoxon signed-rank test. Statistically significantly higher values were observed in all the surface roughness parameters of enamel surfaces after finishing and polishing, with the mostly affected parameter being the Sdr. Under the conditions of the present study, the finishing and polishing instruments used after debonding of lingual noncustomized brackets created a surface texture rougher than the control in all the tested roughness parameters.

Effect of Finishing Techniques on the Junction Between the Composite Restoration and the Dental Enamel

The aim of this in vitro study was to to evaluate the impact of finishing procedures on the enamel adjacent to composite restorations and to assess if the resistance of the enamel-resin junction to leakage is affected by the use of these instruments. The surfaces of enamel at the joint with composite were observed by scanning electron microscopy, then the microleakages at the enamel margin was assessed using an optical microscope. Finishing with extra-/ ultra-fine carbide burs and extra-fine diamond burs produced a superficial abrasion to the adjacent enamel and did not seem to have a significant influence on the sealing ability of composite resin.