Andrea Kaplan

Frictional resistance exerted by different lingual and labial brackets: an in vitro study

BackgroundAlthough much has been written on the implications of friction generated between orthodontic archwires and labial brackets, information on lingual brackets is still limited. Hence, we set out to investigate the frictional resistance exerted by different lingual and labial brackets, including both conventional and self-ligating designs. The effect of various factors, namely bracket/base width, slot size, inter-bracket distance, and first- (Θ cI) and second-order (Θ cII) critical contact angles were evaluated and compared.MethodsA plaster model of a pretreatment oral cavity was replicated to provide 18 (9 upper and 9 lower) identical versions. The anterior segments of each were taken, and the canine and lateral and central incisors were mounted with either lingual (7th Generation, STb, New STb, In-Ovation L, ORJ) or labial (Mini-Mono, Mini Diamond, G&H Ceramic) brackets. Mechanical friction tests were performed on each type of bracket using a universal testing machine. The maximum force necessary to displace NiTi wires of two different diameters (0.012, 0.014) was measured, using both elastic and metal ligatures with conventional brackets.ResultsThe frictional force necessary to displace the wires increased as the diameter of the wire increased in all tested brackets (p < 0.01). Friction was significantly higher (p < 0.001) with elastic ligatures, as compared with metal ones, in all conventional brackets. In the lower lingual group, significantly lower friction was generated at conventional lingual New STb brackets (p < 0.01) and ORJ lingual brackets (p < 0.05) than at self-ligating In-Ovation L lingual brackets. A significant statistical correlation between (Θ cI) and friction was detected in the lower labial bracket group.ConclusionsFriction resistance is influenced not only by the bracket type, type of ligation, and wire diameter but also by geometric differences in the brackets themselves.

Influence of polishing protocol on flexural properties of several dental composite resins

The aim of this study was to determine the influence of the finishing protocol (FP) on flexural properties of several composites (CR). Twenty composite samples (25x2x2 mm) were prepared: G1 HelimolarR; G2 Filtek™ Z350;G3TetricR N Ceram, G4 Point 4™, G5 Premisa™; G6 Esthet.XR HD, G7 ice, G8 Vit-L-escenceR, G9 GrandioR, G10 TPHR3, G11 AmelogenR Plus, G12 Brilliant Enamel; G13 Filtek™ Z100 and randomly divided into four groups according to the finishing system: C control, J JiffyR, SS Super SnapR, AA AstropolR /AstrobrushR. Each sample was polished for 10 seconds with each sequence instrument, and stored in distilled water for 24 hours, after which a three-point flexure test was applied to determine flexural strength (FS) and modulus (Flexural modulus). Data were analyzed using a two-way multivariate ANOVA and means were compared with Tukeys test. Results were: FS level CR p=0.000 with significant differences. FS level FPp= 0.093 with significant differences. In order: FM level CR p 0.00 with significant differences. FM level PS p=0.001; with significant differences. Under the study conditions, the polishing systems based on silicone rubber decreased the flexural properties of composite resins.

Ex vivo microleakage comparison between glass ionomers used as pit and fissure sealants.

The aim of this study was to evaluate in vitro the marginal microleakage of two glass ionomer materials used as pit and fissure sealants. Thirty healthy premolars extracted for orthodontic treatment were randomly assigned to two groups (n=15) and respectively sealed with two glass ionomers (Group I, Fuji VII and Group II, Fuji IX). All teeth were preserved in artificial saliva (NAF) for 10 days, thermocycled (250 cycles; 5 °C, 37 °C and 60 °C), isolated, and immersed in 2% alcohol gentian violet blue solution for 24 h. After washing, teeth were included in acrylic resin and sectioned longitudinally in a bucco-lingual direction with a Struers-Minitom cutting device. Samples were analyzed for leakage using an optical microscope (Olympus BX- 60M). TheWilliams and Winter semi-quantitative ranked scale was used to score dye penetration. In Group I the grades were distributed as follows: Grade 1, 1 sample and Grade 3, 14 samples (Mean 2.87 Median 3, SD 0.52). In Group II: Grade 0: 4 samples, Grade 1, 3 samples, Grade 2, 2 samples and Grade 3, 6 samples (Mean 1.67, Median 2, SD 1.29). Fishers exact test showed statistically significant differences between materials (p=0.006). From these results, we conclude that Fuji IX had better marginal sealing than Fuji VII when used as a pit and fissure sealant.