Biomedical subjects

Nikolaos Silikas

Publications and source records attributed to Nikolaos Silikas.

3 recordsLinked to original sources

PubMed2005

Comparative assessment of the roughness, hardness, and wear resistance of aesthetic bracket materials.

OBJECTIVE: The purpose of this study was to assess critical properties of orthodontic aesthetic bracket materials. METHOD: Samples of polycarbonate, poly(oxy)methylene, ultra high molecular weight polyethylene (UHMWPE), and polycrystalline alumina raw material used from bracket manufacturing were subjected to: (a) profilometry for the determination of Ra, Rq, Rmax and Rz roughness parameters; (b) Vickers hardness (HV50) testing; and (c) wear resistance determined by the scratch test. The results were analyzed with one-way ANOVA and Tukey multiple comparisons test at alpha=0.05 level of significance. RESULTS: The UHMWP and alumina specimens showed the highest roughness values for all parameters. The highest hardness, amongst the polymeric raw materials, was obtained from the poly(oxy)methylene appliances. Differences were also noted between the polycarbonate raw material of different manufacturers implying an effect from the manufacturing process. With the exception of alumina, the highest wear resistance was found for the poly(oxy)methylene specimens. SIGNIFICANCE: The results of this study reveal the variability among aesthetic plastic bracket raw materials, their reduced hardness and wear resistance relative to alumina as well as the inappropriateness of UHMWPE as alternative bracket material.

Aluminum Oxide↗

PubMed2005

The nature of the remaining dentin surface following application of Carisolv solution.

PURPOSE: To evaluate the effect of Carisolv solution on the topography and surface hardness of dentin. METHODS: Two separate studies were carried out. Atomic force microscopy (AFM) was employed to visualize dentin surface topography on slices of previously extracted non-carious and carious teeth following the passive application of Carisolv gel for 30- and 60-second periods. A Wallace hardness instrument was used to measure the dentin surface hardness following active caries removal with Carisolv gel and the specially designed instruments. Conventional caries removal with dental burs and non-carious dentin acted as controls for the latter study. RESULTS: AFM revealed that the passive application of Carisolv gel resulted in smoother surfaces than observed on carious and non-carious dentin. There was a statistically significant difference between the mean hardness values for non-carious and Carisolv-treated dentin (P< 0.05). There was no statistically significant difference between the non-carious and bur-treated dentin nor the Carisolv and bur-treated dentin.

Analysis of Variance↗

PubMed2004

Titanium orthodontic brackets: structure, composition, hardness and ionic release.

OBJECTIVES: The aim of the present study was to investigate the composition, morphology, bulk structure and ionic release of two brands of titanium orthodontic brackets: Orthos2 (Ormco, USA) and Rematitan (Dentaurum, Germany). METHODS: Five specimens of each group were examined with computerized X-ray microtomography, to reveal the morphology and structure of brackets, whilst resin-embedded and metallographically polished specimens were subjected to SEM/EDS analysis and Vickers microhardness measurements. Brackets were also maintained in 0.9% saline for 2 months and the ionic release in the immersion medium was determined with Inductively Coupled Plasma Atomic Emission Spectroscopy. The results of the hardness and ionic release measurements were statistically analyzed with two-way ANOVA and Tukey's test (alpha = 0.05). RESULTS: Orthos2 brackets consisted of two parts, the base (commercially pure Ti grade II) and the wing (Ti-6Al-4V alloy), joined together by laser welding, producing large gaps along the base-wing interface. The base was of lower hardness (Hv = 145), than the wing (Hv = 392) and incorporated a standard foil base-mesh pad. Rematitan brackets consisted of commercially pure Ti grade IV, with a single-piece manufacturing pattern of virtually identical hardness (p > 0.05) at the base and wings, featuring a laser-etched base-mesh pad. The hardness of the Rematitan brackets was significantly lower than the hardness of the Orthos2 wings, but double the hardness of the Orthos2 base. Released Ti levels were below the threshold level (1 ng/ml) of analysis for both materials, whilst traces of Al (3 ppm) and V (2 ppm) were found in the immersion media for Ti-6Al-4V alloy. SIGNIFICANCE: The structural and hardness differences found may influence the torque transfer characteristics from activated archwires to the brackets and the crevice corrosion potential at the base-wing interface (Orthos2). The detection of Al and V in the immersion medium (Orthos2) may imply a different biological response from the two types of Ti brackets.

Alloys↗