Lorenz M. Brauchli

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 decontamination procedures on shear forces after contamination with blood or saliva

INTRODUCTION Despite rapid development in adhesive technology, contamination of bonding surfaces remains a major problem. The aims of this study were to evaluate the influence of contamination on bond strength and to investigate possible decontamination procedures. METHODS Four bonding systems were evaluated for their shear bond strengths under 5 bonding situations: control (without contamination and decontamination); contamination with blood; contamination with saliva; decontamination with water and air, and repriming after blood contamination; and decontamination with water and air, and repriming after saliva contamination. The 25 specimens of each group consisted of composite blocks bonded to bovine teeth. Shear forces were measured with a testing machine after thermocycling. RESULTS The 3 composite primers showed similar behavior. With the exception of Transbond SEP (3M Unitek, Monrovia, Calif) with saliva contamination, all contaminated samples showed greatly reduced shear forces. The control and decontaminated groups showed shear forces about 20 MPa. The resin-modified glass ionomer, however, did not reach clinically sufficient bond strengths in either setup. CONCLUSIONS Decontamination with water and air and repriming is sufficient after contamination with blood or saliva. Etching again is not necessary. The bond strength of Transbond SEP was not significantly altered by saliva contamination and can be recommended for conventional bonding procedures.

Active and passive self-ligation-a myth?

OBJECTIVE To compare the frictional behavior of several self-ligating brackets with that of normal brackets both with and without tipping force-moments and in combination with different archwire dimensions. MATERIALS AND METHODS The resistance to sliding (RS) of seven self-ligating brackets, a conventional bracket, and a ceramic bracket with a low-friction clip were evaluated in combination with three different archwires and tipping force-moments of 0 and 10 Nmm. The center of rotation for the measurements was set within the center of the bracket or with a 10-mm offset. Resistance to sliding was measured using an Instron 3344 at a cross-head speed of 10 mm/min at a temperature of 36°C. RESULTS Without a tipping moment, RS increased with the active self-ligating brackets with increasing archwire size. No RS was found for any of the passive self-ligating brackets. The 10-Nmm tipping moment resulted in more RS and was similar for all bracket and archwire combinations. RS was approximately doubled when the center of rotation was located at the bracket rather than with a 10-mm offset. CONCLUSIONS RS between brackets and archwires is highly dependent on the experimental setup. Different setups can result in contradictory results. Almost 1 N of traction force is lost in RS when a moment of 10 Nmm is placed at a rotational center 10 mm from the bracket.

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.

Active and passive self-ligation: a myth? Part 1: torque control.

OBJECTIVE To determine the amount of torque expressed by various self-ligating brackets and to evaluate the influence of active clip designs. MATERIALS AND METHODS Torque moments were measured for nine different bracket types in combination with a 0.019 × 0.025 inch stainless-steel archwire. All active brackets were measured in an open and a closed configuration to evaluate the influence of the self-ligating spring clip. In addition, slot dimensions were optically measured and compared to the torque expression. RESULTS Moments between 3.1 Nmm and 22.6 Nmm were observed at an angulation of 30° between archwire and slot. The amount of torque contributed by the spring clip of active self-ligating brackets was approximately 1 Nmm; 10 Nmm of torque was achieved with most brackets with a 20°-25° angulation between archwire and slot. The slot dimensions ranged from 0.0222 inch (0.563 mm) to 0.0241 inch (0.613 mm). CONCLUSION The influence of the ligature or the active or passive self-ligating mechanism is minimal, and slot dimensions are far more important for the transmission of torque. The amount of torque exerted by the active spring clip is approximately 1/10th of the torquing moments recommended in the literature.

Shear modulus of 5 flowable composites to the EverStick Ortho fiber-reinforced composite retainer: An in-vitro study

INTRODUCTION Although fiber-reinforced composites (FRC) are now available for use as orthodontic retainers, little is known about their bonding properties. Our aim in this study was to investigate the adhesive properties of various composites to a commercially available FRC retainer. METHODS Five flowable composites (Grandio Flow [Voco GmbH, Cuxhaven, Germany], Synergy Flow [Coltène/Whaledent AG, Genf, Switzerland], Tetric Flow [Ivoclar Vivadent AG, Schaan Fürstentum, Liechtenstein], Tetric Flow Chroma [Ivoclar Vivadent AG], and Transbond LR [3M Unitek, Monrovia, Calif) were tested for their shear bond strengths to the EverStick Ortho (Stick Tech Ltd Oy, Turku, Finland) FRC retainer stick. Each group contained 15 samples and underwent 1000 aging cycles between 5 degrees C and 55 degrees C. A testing machine was used to measure the shear bond strengths at the composite-FRC interface. All specimens were visually controlled for the location of the fracture line. RESULTS Typical shear bond strengths were measured at 40 N or 8 MPa. No significant difference was found between the 5 composites (ANOVA, P < or = 0.05). The fracture line was consistently in the FRC retainer. CONCLUSIONS All composites had similar bonding characteristics, and visual inspection consistently showed fractures in the FRC retainer. Because the point of least resistance was in the retainer, we concluded that all tested composites were equally effective.

Influence of Enamel Conditioning on the Shear Bond Strength of Different Adhesives

AbstractBackground and Objective:Phosphoric acid etching is the gold standard for enamel conditioning. However, it is possible that air abrasion or a combination of air abrasion and etching might result in enhanced adhesion. The aim of this study was to investigate the effect of different enamel conditioning methods on the bond strength of six adhesives.Material and Methods:Three different enamel conditioning procedures (phosphoric acid etching, air abrasion, air abrasion + phosphoric acid etching) were evaluated for their influence on the shear bond strength of six different adhesives (Transbond™ XT, Cool-Bond™, Fuji Ortho LC, Ultra Band-Lok, Tetric® Flow, Light-Bond™). Each group consisted of 15 specimens. Shear forces were measured with a universal testing machine. The scores of the Adhesive Remnant Index (ARI) were also analyzed.Results:There were no significant differences between phosphoric acid etching and air abrasion + phosphoric acid etching. Air abrasion as a single conditioning technique led to significantly lower shear forces. The ARI scores did not correlate with the shear strengths measured. There were greater variations in shear forces for the different adhesives than for the conditioning techniques.Conclusion:The highest shear forces were found for the conventional composites Transbond™ XT and Cool- Bond™ in combination with conventional etching. Air abrasion alone and in combination with phosphoric acid etching showed no advantages compared with phosphoric acid etching alone and, therefore, cannot be recommended.ZusammenfassungHintergrund und Ziel:Phosphorsäure-Ätzung ist der Goldstandard in der Schmelzkonditionierung. Es ist jedoch denkbar, dass Sandstrahlung oder eine Kombination von Sandstrahlung und Ätzung zu einer erhöhten Schmelzadhäsion führen könnten. Ziel der vorliegenden Studie war die Untersuchung des Einflusses unterschiedlicher Schmelzkonditionierungsmethoden auf die Haftkräfte von sechs Adhäsivstoffen.Material und Methodik:Drei unterschiedliche Schmelzkonditionierungen (Phosphorsäure, Sandstrahlung, Sandstrahlung und Phosphorsäure) wurden bezüglich ihres Einflusses auf die Scherkräfte von sechs unterschiedlichen Adhäsiven (Transbond™ XT, Cool-Bond™, Fuji Ortho LC, Ultra Band-Lok, Tetric® Flow, Light-Bond™) untersucht. Jede Gruppe bestand aus 15 Proben. Die Scherkräfte wurden mittels einer Universalprüfmaschine gemessen. Zusätzlich wurde ein Adhäsiv-Rest-Index (ARI) bestimmt.Ergebnisse:Insgesamt gab es keine signifikanten Unterschiede zwischen den Gruppen Phosphorsäure-Ätzung und Sandstrahlung + Phosphorsäure-Ätzung. Sandstrahlung als alleinige Konditionierungsmethode führte zu signifikant niedrigeren Scherkräften. Die ARI-Werte korrelierten nicht mit den gemessenen Scherkräften. Die Variation der Scherkräfte war für unterschiedliche Adhäsivsysteme größer als für unterschiedliche Konditionierungen.Schlussfolgerung:Die höchsten Scherkräfte wurden für die konventionellen Komposite Transbond™ XT und Cool- Bond™ in Kombination mit konventioneller Ätzung gefunden. Sandstrahlung in Kombination mit Phosphorsäure-Ätzung zeigte keinen Vorteil gegenüber alleiniger Phosphorsäure-Ätzung und kann deshalb nicht empfohlen werden.

Influence of bending mode on the mechanical properties of nickel-titanium archwires and correlation to differential scanning calorimetry measurements

INTRODUCTION Nickel-titanium orthodontic archwires are used with bonded appliances for initial leveling. However, precise bending of these archwires is difficult and can lead to changes within the crystal structure of the alloy, thus changing the mechanical properties unpredictably. The aim of this study was to evaluate different bending methods in relation to the subsequent mechanical characteristics of the alloy. MATERIALS AND METHODS The mechanical behaviors of 3 archwires (Copper NiTi 35°C [Ormco, Glendora, Calif], Neo Sentalloy F 80 [GAC International, Bohemia, NY], and Titanol Low Force [Forestadent, Pforzheim, Germany]) were investigated after heat-treatment in a dental furnace at 550-650°C, treatment with an electrical current (Memory-Maker, Forestadent), and cold forming. In addition, the change in A(f) temperature was registered by means of differential scanning calorimetry. RESULTS Heat-treatment in the dental furnace as well as with the Memory-Maker led to widely varying force levels for each product. Cold forming resulted in similar or slightly reduced force levels when compared to the original state of the wires. A(f) temperatures were in general inversely proportional to force levels. CONCLUSIONS Archwire shape can be modified by using either chair-side technique (Memory-Maker, cold forming) because the superelastic behavior of the archwires is not strongly affected. However it is important to know the specific changes in force levels induced for each individual archwire with heat-treatment. Cold forming resulted in more predictable forces for all products tested. Therefore, cold forming is recommended as a chair-side technique for the shaping of NiTi archwires.

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.