Judith Ball

Mechanical behavior and clinical application of nickel-titanium closed-coil springs under different stress levels and mechanical loading cycles

INTRODUCTION The main advantage of superelastic nickel-titanium (NiTi) products is their unique characteristic of force plateaus, which allow for clinically precise control of the force. The aims of this study were to define the mechanical characteristics of several currently available closed-coil retraction springs and to compare these products. METHODS A universal test frame was used to acquire force-deflection diagrams of 24 NiTi closed-coil springs at body temperature. Data analysis was performed with the superelastic algorithm. Also, the influence of temperature cycles and mechanical microcycles simulating ingestion of different foods and mastication, respectively, were considered. RESULTS Mechanical testing showed significant differences between the various spring types (ANOVA, < or =0.05), but constant intrabatch behavior (t test). Four groups were formed according to the mechanical properties of the springs: strong superelasticity without bias stress, weak superelasticity without bias stress, strong superelasticity with bias stress, and weak superelasticity with bias stress. CONCLUSIONS In sliding mechanics, the strongly superelastic closed-coil springs with preactivation are recommended. In addition, we found that the oral environment seems to have only a minor influence on their mechanical properties.

Influence of initial strain on the force decay of currently available elastic chains over time

OBJECTIVE To investigate the dependence of force decay on the initial strain applied to currently available elastic chains. MATERIALS AND METHODS Eight different elastic chains from eight major companies were tested for force decay over a period of 3 weeks at 50% and 100% strain. They were stored in water and thermocycled between 5°C and 55°C. An Instron 3344 was used for the force measurements. RESULTS Absolute force values at 50% strain varied between 2.3 N and 4.1 N initially, and between 0.9 N and 1.6 N after 21 days. Thus, the force decay of the elastic chains varied from 37% to 75%. At 100% strain, the force values varied between 2.9 N and 4.7 N initially, and between 1.3 N and 2.1 N after 21 days of continuous strain. The force decay varied between 39% and 67%. Most force decays between 24 hours and 21 days were not significant. This information should be taken into consideration when the appropriate elastic chain is selected for clinical use. CONCLUSION A wide array of elastic chains with various force levels is available. However, differences between products of greater than 100% were measured for force decay over time.

Treatment strategies for infraoccluded dental implants

Single-tooth implants in the maxillary anterior region have the highest risk of esthetic complications from infrapositioning due to continuing maxillary growth and the eruption of adjacent teeth. Although the placement of anterior single-tooth implants should normally be postponed, particularly girls and young women with a hyperdivergent growth pattern, if an infraposition of an implant is present, then thorough examination and strategic planning are required. According to the severity, the strategic treatment options are as follows: simple retention; adjustment or replacement of the implant restoration, possibly including adjacent teeth; surgical implant repositioning by segmental osteotomy combined with osseodistraction; or submergence or removal of the implant. With the patient presented, an interdisciplinary approach that combined orthodontic alignment, surgical segmental osteotomy, distraction osteogenesis, and restorative features offered the opportunity to realign the adjacent teeth into the arch and to harmonize the gingival contour by means of continuous soft tissue enlargement and adaptation.

Force levels of 23 nickel-titanium open-coil springs in compression testing.

INTRODUCTION Open-coil springs are commonly used auxiliaries in fixed orthodontic appliance therapy. Space opening for impacted or heavily crowded teeth as well as distalization of molars all require specific force levels. It is the aim of the current study to present an overview of the mechanical properties of currently available nickel titanium (NiTi) closed coil springs. MATERIAL AND METHODS Twenty-three NiTi open-coil springs were compressed by 25% and 50% of their original length at a controlled temperature of 36°C. Force deflection diagrams were registered using an Instron 3344 (Instron Corp, Wilmington, De). Five samples of each coil spring were measured and evaluated for their mean force as well as their superelastic characteristics. RESULTS Almost all coil springs showed a linear behavior in the force deflection diagram. Only a few open-coil springs (GAC light, medium, and heavy [Dentsply GAC, Bohemia, NY] and RMO 12 × 45 [Rocky Mountain Orthodontics, Denver, Colorado]) showed a superelastic behavior with a clear force plateau, also indicated by their high ratio of variance. The results of the tested open-coil springs allow the clinician to choose springs with mean forces between 0.25 N (3M Unitek light; 3M Unitek, St. Paul, Minn) and 1.3 N (GAC heavy) for a compression of 25% and 0.64 N (3M Unitek light) to 2.9 N (OrthoOrganizers 14 × 37 [OrthoOrganizers, Carlsbad, Calif], Dentaurum Rematitan strong [Dentaurum, Ispringen, Germany]) for a compression of 50%. CONCLUSIONS Superelastic behavior was rarely observed with open-coil springs. The clinician can therefore not rely on the force range indicated without considering the amount of compression of the coil spring.

Laser Conditioning of Enamel with the Erbium YAG and the CO2 Laser.Bond Strength and Surface Structure

Introduction: Acid etching is the standard procedure for enamel conditioning. However it leaves a demineralized surface, which is prone to caries. This is a major disadvantage especially in combination with a fixed orthodontic appliance and reduced oral hygiene. Therefore it was the aim of this study to evaluate the effect of an Erbium:YAG laser as well as a CO2 laser on bond strength and enamel surface structure. Material and methods: 90 freshly extracted bovine incisors were used as substitutes for human enamel. One group of 30 samples was bonded following conventional acid conditioning and served as the control group. The two other groups were conditioned with an Erbium:YAG laser or a CO2 laser. All samples were tested for shear forces with a universal testing machine (Instron 4444). PMMA (polymethylmethacrylate) cylinders were used as shear bodies. SEM (scanning electron microscope) images were taken to compare the effect of the conditioning methods on the enamel surface. Results: There was a significant difference between the shear forces attained with conventional etching (16.5 MPa), the Erbium:YAG laser (6.2 MPa) and the CO2 laser (3.3 MPa). However due to large standard deviations in the groups conditioned with laser, no significant difference was observed between the Erbium:YAG laser and the CO2 laser. The SEM images revealed a micro-retentive relief for both lasers, but the surface treated with the Erbium:YAG laser showed cracks in the enamel. Conclusion: Conventional acid etching showed a superior bond strength in comparison with both the laser conditioning methods. Of concern were the fissures observed in the enamel surface treated with the Erbium:YAG laser.

Bond Strengths of Metal, Ceramic and Polymer Brackets in Combination with Different Enamel Preconditioning Methods

Introduction: Adhesive technology is widely spread throughout the different specialities of dentistry. In orthodontics the bonding of brackets accounts for a significant percentage of time in practice routine. Bond strength is dependent on several factors such as enamel conditioning, adhesive technology and the material and construction of the bracket base. It was the intention of the present study to investigate the bond strength in relation to the above mentioned parameters. Method: Four different brackets (metal, ceramic, polymer, fiber reinforced polymer) were evaluated for their bond strength during tensile testing with a universal testing machine using a conventional composite (Transbond MIP, XT) and in the case of the fiber reinforced bracket additionally a specially designed adhesive (Quick-Bond). Enamel conditioning was achieved with conventional etching, air-abrasion or a combination of both techniques. ARI (adhesive remnant index) scores were evaluated. Results: There were significant differences between the types of enamel conditioning. All brackets showed significantly lower bonding forces when the enamel was prepared with air-abrasion alone. Metal brackets had the highest bonding strength and the fiber reinforced composite brackets with the conventional adhesive the lowest. The ARI scores showed good correlation to the bonding forces, with low bonding forces presenting as a detachment at the enamel-adhesive interface. Conclusion: Air-abrasion alone showed significantly lower bonding forces than enamel conditioning with etching for all bracket types. This finding was independent of the bracket material, base design or adhesive system.