Biomedical subjects

Christiana Gioka

Publications and source records attributed to Christiana Gioka.

8 recordsLinked to original sources

PubMed2006

Orthodontic latex elastics: a force relaxation study.

The objectives of this study were to assess the force relaxation of latex elastics occurring within 24 hours of extension and to estimate the extension required to reach the reported force. Five specimens of various manufacturers' latex elastics size and force levels were mounted on a custom-made setup capable of monitoring force levels in real time with a continuous mode and without operator intervention. The percentage of force relaxation was estimated from the initial and 24-hour levels, and the results were analyzed with one-way analysis of variance and the Tukey test at alpha = 0.05 level of significance. The elastics showed force relaxation in the order of 25%, which consisted of an initial high slope component and a latent part of decreased rate. Most relaxation occurred within the first 3-5 hours after extension, regardless of size, manufacturer, or force level of the elastic. The overall as well as the initial relaxation curves were fitted to equations, which described the variation of force with time. Elastic extension to achieve the reported force was found to range between 2.7 and five times the original length. Latex elastics show force relaxation in the order of 25%, which consists of an initial high slope component and a latent part of decreased rate. Most relaxation occurs within the first 3-5 hours after extension, regardless of size, manufacturer, or force level of the elastic. The empirical rule of "3" shows remarkable variation, ranging from 2.7 to five.

Elasticity↗

PubMed2005

Light-cured or chemically cured orthodontic adhesive resins? A selection based on the degree of cure, monomer leaching, and cytotoxicity.

PURPOSE: The purpose of this study was to estimate the degree of cure and monomer leaching of a light-cured and a chemically cured (no-mix) adhesive and to assess their biologic properties. MATERIAL: The degree of cure of adhesive specimens prepared with a procedure identical to the clinical bonding process was assessed by infrared spectroscopy. The adhesives were then immersed in normal saline solution for 2 months, and the residual monomer leached from the adhesives was quantitatively and qualitatively analyzed by liquid chromatography. The effect of the immersion media on human gingival fibroblasts' viability and proliferation was also evaluated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and deoxyribonucleic acid (DNA) synthesis assays, respectively. The results were analyzed by analysis of variance and Tukey test (alpha = .05). RESULTS: No difference was found between the 2 adhesives with respect to their degree of cure and the amount of triethylene glycol dimethacrylate released; no diglycidyl dimethacrylate monomer was detected in the eluent. However, significant qualitative changes in the composition of the substances eluted from the 2 adhesives were observed. CONCLUSIONS: Whereas no cytotoxic effect was shown for either immersion media, a moderate reduction in the DNA synthesis was obtained by both adhesives, implying a minor cytostatic effect. Further research is required to assess the long-term biologic properties of adhesives, including potential estrogenic action.

Analysis of Variance↗

PubMed2005

Premolar bracket position revised: proximal and occlusal contacts assessment.

AIM: To assess the effect of conventional bracket slot vertical position (4 mm from incisal edge) on crown spatial orientation relative to adjacent and opposing teeth through proximal contact balance and occlusal contacts assessment. MATERIAL AND METHODS: Forty patients were divided into two groups; in the first group, brackets were bonded 4 mm from the intact incisal edge; in the second group, bracket position was determined individually by transferring the maximum embrasure difference to the bracket slot height difference. The difference of proximal contacts between premolars and molars was measured. Bite registration with the use of articulating paper was also performed on all patients. Traces indicating contact between premolar maxillary lingual cusps and opposing mandibular fossa of the first and second premolars were evaluated. Differences with respect to the distribution of unbalanced proximal contacts and negative contacts between the two bonding schemes were analyzed with the chi-square test at P = .05 level of significance. RESULTS: Aligning the bracket slot with the center of the clinical crown (FA point) consistently produced unbalanced proximal contacts in excess of 1 mm, as well as increased absence of occlusal contacts. CONCLUSION: Positioning the bracket slot on the center of the premolar crown may result in marginal ridge discrepancy between the premolars and molars and lack of occlusal contacts with opposing dentition. This may be due to the height difference noted between the buccal and lingual cusp of the premolars, as well as variation in molar tube or band placement. Functional occlusal analysis should be integrated in the finishing stages of treatment to facilitate proper premolar crown position.

Adolescent↗

PubMed2004

Materials-induced variation in the torque expression of preadjusted appliances.

The purpose of this article is to comprehensively investigate the sources of variation in the expression of torque in preadjusted appliances. Variables related to properties of materials were systematically analyzed, including (1) the inability to fill the slot because of the size difference of archwires and bracket slot, (2) irregularities from the manufacturing process of brackets precluding proper engagement, (3) differences in the stiffness of wire alloys engaged to the bracket slot, (4) variations between actual and reported bracket torque values, and (5) ligation modes, all of which might account for increased third-order clearance or bracket-archwire "play." The effect of these variations on the expression of torque is discussed, and the net buccolingual inclinations are provided as a function of wire size and composition for common bracket slot-archwire combinations. Most reports published on this issue indicate a loss of torque control as high as 100% of the prescribed value. Furthermore, the fallacy of transferring the ideal crown inclination to the torque prescribed in the bracket is illustrated, along with the underestimation of the prescribed torque relative to the proper tooth crown. The realistically required torque is analyzed to its constituent components, involving tooth inclination, compensation for the slot-wire play, and incomplete ligation with elastomeric ligatures. Based on the evidence available, it is proposed that a high-torque prescription should be selected to account for the lack of full expression of the prescribed torque that occurs clinically.

Dental Alloys↗

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↗

PubMed2004

Color stability of orthodontic adhesive resins.

Color alteration of adhesive during treatment and after debonding may be implicated in long-term enamel discoloration. The aim of this study was to assess the color stability of light-cured and chemically cured adhesives subjected to artificial photoaging. Disk-shaped specimens of adhesives were colorimetrically evaluated before and after artificial photoaging using an ISO-recommended protocol. The measurement variable was the color change (deltaE) of adhesives induced by artificial, accelerated photoaging. The deltaE values derived from the two color recordings for the materials at pre- and postaging intervals were statistically analyzed with a one-way analysis of variance (ANOVA), with the adhesive brand serving as a discriminating variable. Differences among groups were further investigated using the Tukey multiple comparisons test (alpha = .05). To establish the statistical significance of the difference of the deltaE values of each adhesive and the deltaE threshold for clinical detection, a paired t-test was used (P = .05). All adhesives exhibited color change, which in some cases exceeded the clinically detectable color change limit. The extent of the color alterations of aged bonding systems may contribute to enamel discoloration after treatment.

Analysis of Variance↗

PubMed2004

Enamel surface roughness following debonding using two resin grinding methods.

The purpose of this study was to assess quantitatively the roughness of the enamel surface following debonding using two resin removal methods. The enamel surface of 30 premolar crowns was covered with black tape with a 3 mm window on the middle buccal third to standardize the area of analysis. The initial enamel surfaces were subjected to profilometry, registering four roughness parameters (Ra, Rq, Rt and Rz). The brackets were bonded to the plaster-embedded enamel surfaces with a chemically cured, no-mix adhesive, and debonded after 1 week. Resin removal in half of the specimens was performed with an eight-bladed carbide bur, and in the other half with an ultra-fine diamond bur, both attached to a high speed hand piece; a second profilometric measurement was made after resin removal. Finishing of all surfaces was achieved with Soflex discs and a third registration of roughness followed. The duration of each resin removal protocol was also recorded. The results were analysed with two-way ANOVA and the Newman-Keuls test with the two resin grinding modes and the three intervals serving as discriminating variables (n = 15). For the duration results, a one-way ANOVA was used. Significant differences (P < 0.05) were observed with respect to enamel roughness parameters between the two resin grinding methods used, while there was no consistent roughness-reducing effect of finishing with Soflex discs. Resin removal with a diamond bur was achieved in approximately half the time compared with the eight-bladed bur. The increase in most roughness variables induced by the debonding procedures was not reversed at the end of the finishing stage, regardless of the resin removal protocol used, suggesting an irreversible effect on enamel texture.

Analysis of Variance↗

PubMed2004

Plastic brackets: hardness and associated clinical implications.

AIM: To assess the Vickers hardness of plastic brackets, after in vitro aging. The morphology and structure of corresponding retrieved brackets were also studied to assess the reliability of in vitro set-up in imposing effects comparable to intraoral aging. MATERIALS AND METHODS: Four types of plastic brackets were selected. Specimens were immersed in a buffer solution to induce artificial aging; brackets of two groups were retrieved after orthodontic treatment. The wings of brackets were subjected to Knoop hardness testing, and scanning electron microscopy was employed to study the morphology and microstructure of retrieved brackets. The results were statistically analyzed by two-way analysis of variance and Tukey test (alpha = 0.05). RESULTS: Differences were identified between the brands of brackets, but not between the new and in vitro-aged appliances. The retrieved appliances showed significant reduction in hardness when compared with their as-received counterparts. Evidence of degradation was seen in the retrieved appliances. CONCLUSIONS: The inability of ex vivo experimental configuration to simulate clinical conditions is stressed; several clinical implications related to torque control, friction, and tie-wing strength of brackets are discussed.

Buffers↗