Rohit C. L. Sachdeva

Mechanical properties and clinical applications of orthodontic wires

This review article describes the mechanical properties and clinical applications of stainless steel, cobalt-chromium, nickel-titanium, beta-titanium, and multistranded wires. The consolidation of this literature will provide the clinician with the basic working knowledge on orthodontic wire characteristics and usage. Mechanical properties of these wires are generally assessed by tensile, bending, and torsional tests. Although wire characteristics determined by these tests do not necessarily reflect the behavior of the wires under clinical conditions, they provide a basis for comparison of these wires. The characteristics desirable in an orthodontic wire are a large springback, low stiffness, good formability, high stored energy, biocompatibility and environmental stability, low surface friction, and the capability to be welded or soldered to auxiliaries. Stainless steel wires have remained popular since their introduction to orthodontics because of their formability, biocompatibility and environmental stability, stiffness, resilience, and low cost. Cobalt-chromium (Co-Cr) wires can be manipulated in a softened state and then subjected to heat treatment. Heat treatment of Co-Cr wires results in a wire with properties similar to those of stainless steel. Nitinol wires have a good springback and low stiffness. This alloy, however, has poor formability and joinability. Beta-titanium wires provide a combination of adequate springback, average stiffness, good formability, and can be welded to auxiliaries. Multistranded wires have a high springback and low stiffness when compared with solid stainless steel wires. Optimal use of these orthodontic wires can be made by carefully selecting the appropriate wire type and size to meet the demands of a particular clinical situation.

Evaluation of the consolidation period during osteodistraction using computed tomography.

The use of distraction osteogenesis offers an alternative approach to the correction of craniofacial deformities. However, little is known with respect to the appropriate length of the consolidation period for the newly formed bone. The objective of this study was to evaluate, by quantitative computed tomography, the regenerate bone produced during osteodistraction of the dog mandible at three different consolidation times. Twelve skeletally mature male beagle dogs were equally separated into three experimental groups. Each dog underwent 10 mm of bilateral distraction osteogenesis to lengthen the mandible. After the distraction period, the bone was allowed to consolidate for 4, 6, or 8 weeks, at which time the animals were sacrificed and the mandibles harvested for computed tomographic imaging. The results demonstrate a significantly lower mean bone density of the regenerate in the 4 week group when compared with either the 6 or 8 week groups (P < .01). There was no significant difference, however, in mean bone density between the 6 and 8 week groups.

Changes in contact angles as a function of time on some pre-oxidized biomaterials

Interfaces between biomaterials, tissue and body fluids such as blood play a key role in determining the nature of the interaction between biomaterials and the living organism. The wettability of these biomaterials in relationship to their microenvironment is an important factor to consider when characterizing surface behaviour. The measure of the contact angle between a fluid and material surface can be used to define wettability for that particular microenvironment.In this study, pure Ti, Ti6AI4V alloy, austenitic and martensitic Ni-Ti alloys, pure Ni, AISI Type 316L stainless steel, Co-Cr alloy, and α-alumina were investigated. All metallic materials were mechanically polished and oxidized at 300 °C for 30 min in pure oxygen. Oxide films formed on the surfaces of these materials were examined under the electron microscope and their crystalline structures were identified by the electron diffraction method. The initial contact angle (ϑo) and its changes (δϑ/δt) as a function of time in 1% NaCl solution drop were measured.The results of this study indicated that (i) Ti and its alloys were covered with mainly TiO2 (tetragonal structure), (ii) NiO (cubic structure) was found on pure Ni, (iii) the spinel type oxide (cubic structure) was formed on both 316L stainless steel and Co-Cr alloy, (iv) TiO2 (except for oxides formed on Ti6AI4V alloy) showed a rapid spreading characteristic in 1% NaCl solution; while (v) a relatively slow spreading behaviour was observed on the cubic structure oxides.

Effects of shot-peening on surface contact angles of biomaterials

It was shown previously that (i) if the surface of a biomaterial is covered with TiO2 (tetragonal structure oxide), it shows a high initial contact angle and a high change rate in contact angle (i.e. a higher spreading process); while (ii) cubic structure oxides show relatively lower spreading rates in 1% NaCl solution at 25°C. Shot-peening has been applied to biomaterials (especially titanium and its alloys) to improve their fatigue strength. It is well known that shot-peening causes surface roughening. The effects of surface roughness on wettability are not well documented. Therefore, in the present study, the effects of shot peening on the initial contact angle and changes in it as a function of time, were investigated. In addition, the spontaneous half-cell potential of all tested biomaterials were measured to correlate the wettability phenomenon to initial surface chemistry. Pure titanium and its alloys, including Ti-6AI-4V and NiTi alloys, AISI Type 316L stainless, Co-Cr alloy, and pure nickel, were mechanically polished, shot-peened and pre-oxidized at 300°C for 30 min in pure oxygen. It was found that (i) shot-peening homogenized the surface conditions in terms of initial contact angles, (ii) TiO2 oxide shows a higher spreading coefficient, while cubic structure oxides show a lower value, and (iii) the spreading coefficient was correlated to the magnitude of the spontaneous half-cell potential.

Nonsurgical correction of a Class II malocclusion with a vertical growth tendency

Malocclusion, with a superimposed vertical growth tendency, is often difficult to treat without a combined surgical orthodontic approach. Certain situations, however, may preclude surgery as a treatment option. The following case report demonstrates the use of orthodontic mechanotherapy alone in successfully treating a patient that exhibited a Class II Division I malocclusion with a high mandibular plane angle and vertical growth tendency.