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LOWER INCISOR STABILITY COMPARING TRADITIONAL BONDED RETAINERS TO THE MAGNETAINER®™ Adam W. Armstrong, D.M.D. A Thesis Presented to the Graduate Faculty of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry 2014 ® Copyright by Adam Williams Armstrong ALL RIGHTS RESERVED 2014 i COMMITTEE IN CHARGE OF CANDIDACY: Associate Clinical Professor, Donald R. Oliver Chairperson and Advisor Professor Eustaquio Araujo Associate Professor Ki Beom Kim ii DEDICATION This work is dedicated to my wonderful wife Megan. Your belief in me and constant encouragement has allowed me to accomplish my goals. I love you and will attempt to support you as much as you have supported me. To the many people who have taken a chance on me and allowed me to prove myself, Drs. Richard Simonsen, Russell Gilpatrick, and Rolf Behrents. Thank you for the opportunity to further my education and enter into the fields of dentistry and orthodontics. I will strive to make you proud. Lastly to the faculty of Saint Louis University, thank you for teaching me the skills and knowledge that I will build upon and will allow me to have a wonderful career and bright future. iii ACKNOWLEDGEMENTS This project would not have been possible without the help from the following individuals: Dr. Oliver. Thank you for your guidance and feedback during the preparation of this project and for all you have taught me both clinically and in the classroom. Dr. Rolf Behrents. Thank you for allowing me the opportunity to come to Saint Louis University and further my education. Dr. Ki Beom Kim. Thank you for your input and advice on this project and for all that you have taught me in both in the classroom and in the clinic. Dr. Eustaquio Araujo. Thank you for all of your contributions to my thesis and to my clinical education Drs. Gene and Aron Dellinger. Thank you for entrusting me with the data and study models relating to the MagneTainer®™, this project would not exist without your contributions. Dr. Heidi Israel. Thank you for your assistance with understanding the statistical analysis for this thesis. iv TABLE OF CONTENTS List of Tables. . . . . . . . . . . . . . . . . . . . . vii List of Figures. . . . . . . . . . . . . . . . . . . . viii CHAPTER 1: INTRODUCTION. . . . . . . . . . . . . . . . . .1 CHAPTER 2: REVIEW OF THE LITERATURE Magnetism and magnetic properties. . . . . . . . . ..4 Magnetic field and its properties. . . . . . . .4 Hard vs. soft magnets. . . . . . . . . . . . . .6 Magnetic properties of matter. . . . . . . . . . . .6 Types of magnets. . . . . . . . . . . . . . . . . . .7 Aluminum-nickel-cobalt magnets. . . . . . . . ..8 Ferrite magnets. . . . . . . . . . . . . . . . .8 Rare earth magnets. . . . . . . . . . . . . . ..9 Biological considerations. . . . . . . . . . . . . .11 Corrosion of rare earth magnets. . . . . . . ..11 Biological effects of magnetic fields. . . . . 14 Magnets in orthodontics. . . . . . . . . . . . . . .21 Magnetic brackets. . . . . . . . . . . . . . ..22 Space closure. . . . . . . . . . . . . . . . ..22 Molar distalization. . . . . . . . . . . . . ..23 Extrusion of teeth. . . . . . . . . . . . . . .24 Intrusion of teeth. . . . . . . . . . . . . . .24 Impacted teeth. . . . . . . . . . . . . . . . .25 Maxillary expansion. . . . . . . . . . . . . ..25 Open bite correction. . . . . . . . . . . . . .25 Magnetic functional appliances for Cl II. . . .27 Magnetic functional appliances for CL III. . . 29 Rare earth magnets for retention. . . . . . . .29 Retention. . . . . . . . . . . . . . . . . . . . . .30 Alteration of arch form. . . . . . . . . . . ..31 Periodontium and stability. . . . . . . . . .. . . 33 The role of lower incisor shape. . . . . . . ..33 The impact of pre-treatment malocclusion. . . .34 The effect of extractions on stability. . . . .35 Retainers. . . . . . . . . . . . . . . . . . . . . .36 Hawley retainers. . . . . . . . . . . . . . . .36 Vacuum-formed retainers. . . . . . . . . . . ..38 Bonded retainers. . . . . . . . . . . . . . . .39 Little’s Irregularity Index. . . . . . . . . . . . .43 Statement of thesis. . . . . . . . . . . . . . . . .44 Literature cited. . . . . . . . . . . . . . . . . . 46 v CHAPTER 3: JOURNAL ARTICLE Abstract. . . . . . . . . . . . . . . . . . . . . ..59 Introduction. . . . . . . . . . . . . . . . . . . ..61 Materials and methods. . . . . . . . . . . . . . . .63 Sample. . . . . . . . . . . . . . . . . . . . . . . 63 Technique for measurement of digital models. . . . .64 Error study. . . . . . . . . . . . . . . . . . . . .66 Statistical analysis. . . . . . . . . . . . . . . . 66 Results. . . . . . . . . . . . . . . . . . . . . . .67 Bonded retainer sample. . . . . . . . . . . . .67 MagneTainer®™ sample. . . . . . . . . . . . . .70 Findings between the samples. . . . . . . . . .74 Discussion. . . . . . . . . . . . . . . . . . . . ..75 Conclusions. . . . . . . . . . . . . . . . . . . . .76 Literature cited. . . . . . . . . . . . . . . . . ..78 Vita Auctoris. . . . . . . . . . . . . . . . . . . . . ..83 vi LIST OF TABLES Table 2.1 Development of different types of magnets . . .87 Table 3.1 Mean, median, standard deviation, and variance for the bonded retainer sample. . . . . . . . .69 Table 3.2 Paired t-tests for significance of variables of bonded retainer group. . . . . . . . . . . . ..70 Table 3.3 Pearson’s correlation for variables of bonded retainer group. . . . . . . . . . . . . . . . .71 Table 3.4 Mean, median, standard deviation, and variance for the MagneTainer®™ sample. . . . . . . . . .73 Table 3.5 Paired t-tests for significance of variables of the MagneTainer®™ sample. . . . . . . . . . . .74 Table 3.6 Pearson’s correlation for variables of the MagneTainer®™ sample. . . . . . . . . . . . . .75 Table 3.7 Paired t-tests for significant differences of variables between bonded retainer and MagneTainer®™ sample. . . . . . . . . . . . . .76 vii LIST OF FIGURES Figure 2.1 The MagneTainer®™ in place on a patient. .15 Figure 3.1 Little’s Irregularity Index and intercanine width measured using OrthoAnalyzer® software. . . . . . . . . . . . . . . . . 65 Figure 3.2 Little’s Irregularity Index and intercanine width measured using OrthoCAD® software. .65 viii Chapter 1: Introduction One of the most difficult challenges in orthodontics is retaining the teeth after orthodontic treatment has ended. This problem is not new, indeed back in 1919 C.A. Hawley, quoting a friend stated “If anyone would take my cases when they are finished, retain them and be responsible for them afterward, I would gladly give him half the fee.1” No matter how good the finished result of orthodontic treatment, the teeth tend to return to their pre-treatment positions. Many theories and ideas have been postulated as to why this is the case. And while it still cannot be said with certainty why teeth won’t remain in their post-treatment location, we do know there are several factors that contribute to non-stability of teeth. It is well known that arch perimeter or length and intercanine width decrease as a person ages.2, 3 This occurs whether or not orthodontic treatment is initiated.4-6 In fact, some of these changes are known to worsen in those who have undergone orthodontic treatment versus untreated controls.6 1 Blake and Bibby pointed out many of the changes that occur to the dental arches are part of normal human development. As they discuss, arch width increases until the permanent cuspids erupt, this is followed by a decrease in intercanine width and arch length.7 The decrease in arch length continues into the 20s, and for some individuals into their 30s at which point it slows down.6 Intermolar width is relatively stable from 13 to 20 years with a reduction of the antero-posterior dimension of the mandible over time. Incisor irregularity tends to increase during the teenage years with a more pronounced degree of irregularity seen in females.7 Nowhere in the dentition is instability more pronounced than the mandibular incisors. Studies have shown that 40% to 90% of individuals have unacceptable dental alignment of the lower incisors ten years after orthodontic treatment.6, 8-10 These findings led Little to conclude that relapse of the mandibular incisors is almost inevitable, regardless of when orthodontic treatment is initiated and the technique employed.6, 8, 9 Little also stated that the only predictable way to ensure stability of orthodontic treatment would be lifetime retainer wear.11 2 Recent trends in orthodontics are towards more bonded retainers and fewer Hawley retainers, especially in the mandibular arch.12 This allows for the orthodontist to eliminate patient compliance and to increase the length of the retention phase of treatment. A new retentive appliance known as the MagneTainer®™ is being developed by Gene and Aron Dellinger of Fort Wayne Indiana. It is a fixed, magnetic retainer made from several (10 total) neodymium iron boron magnets bonded from the mesial of the lower canine to the mesial of the contralateral canine (see figure 1). This unique design allows the retainer to function as a bonded retainer with the added ability to floss the teeth between the magnets. The purpose of this study is to determine the efficacy of the MagneTainer®™ magnetic retainer as compared to other canine-to-canine bonded retainers that are bonded to each tooth. Figure 1.1 The MagneTainer®™ in place on a patient. OSS Orthodontics, Fort Wayne Indiana 3 Chapter 2: Review of the Literature Magnetism and Magnetic Properties While it is uncertain as to exactly when and where magnetism was discovered, we do know that the ancient Romans, Greeks, and Chinese were aware of magnetism.13 Magnetism is a fundamental force of nature and is closely related to electricity. Magnetism is due to magnetic fields produced either by an electric current, or due to the natural alignment of charged particles within an element or substance.14 The effects of magnetic fields have been studied and utilized for centuries. Recently, magnets have been incorporated into orthodontic appliances. Magnetic Field and its Properties The area around a magnet where its magnetic force can be felt and measured is known as the magnetic field. Magnetic fields are concentrated on the ends or poles of the magnet, with each pole exhibiting an opposite direction of magnetic force. Like poles will repel one another and opposite poles will attract one another. The stronger a magnet is, the larger its magnetic field will be.15 4 The intensity of a magnet’s magnetic field is called its flux density or field density. Flux density is measured in units of Gauss (G), Tesla (T) and Millitesla (mT).15 Magnets are susceptible to being demagnetized if a strong enough magnetic field is applied to them. The strength of an external magnetic field needed to demagnetize a magnet is known as coercivity. Permanent magnets have a high coercivity.15 For all magnets, the amount of force between two poles is proportional to their magnitudes and inversely proportional to the square of the distance between the poles. This is known as Coulomb’s Law. Coulomb’s law must be considered when selecting a magnet to be used in an orthodontic appliance so that sufficient force is maintained through all distances that the appliance will function under.15 All magnets are susceptible to losing their magnetism if exposed to a certain temperature that varies depending on the chemical composition and fabrication method of the magnet. This temperature is known as the Curie point.15 Curie point is a critical consideration for a magnet to be used intraorally as some magnets have Curie points below body temperature. Any appliance to be used intraorally 5 should also have the ability to be sterilized so a magnet with a high Curie point will be required. Hard vs. Soft magnets Hard magnets are resistant to demagnetization in the presence of a magnetic field that is stronger than its own magnetic field. Hard magnets also stay magnetic at a size of 1mm or less. Soft magnets possess properties that are opposite to hard magnets.15 Magnetic Properties of Matter Magnetic materials fall into three broad categories based on their response to an externally applied magnetic field. They are termed diamagnetic, paramagnetic, and ferromagnetic.13, 14, 16 In diamagnetic materials, the magnetic moment that is induced when a magnetic field is applied is in the opposite direction of the applied magnetic field. This occurs as the atoms in the material respond to the applied magnetic field. Diamagnetic materials have a repulsive effect that is weak in strength and demonstrate no permanent magnetism. The repulsive moment induced by an applied magnetic field disappears when the applied magnetic field is removed. Common diamagnetic materials are metallic bismuth and many 6 organic molecules that have a cyclic structure, enabling electric currents to flow through them.13, 14, 16 Paramagnetic materials are weakly attracted to an applied magnetic field. The molecules in a paramagnetic material all line up in the same direction as the applied magnetic field and a small attractive force results. Substances that contain an unpaired electron will demonstrate paramagnetism. Paramagnetism is temporary and exists only as long as an external magnetic field is applied. Iron salts and many rare-earth salts demonstrate paramagnetism. 13, 14, 16 Ferromagnetic materials are strongly attracted to an applied magnetic field. This is due to the atoms in the material lining up in a parallel fashion when a magnetic field is applied. This alignment will persist after the magnetic field is removed. Common ferromagnetic materials include iron, nickel, cobalt, chromium dioxide and alloys containing these elements. 13, 14, 16 Types of Magnets Permanent magnets are all made from ferromagnetic materials and all have a persistent magnetic field. The properties of individual magnets are related to their 7 composition and fabrication.16 Table 1 shows the development of several different types of magnets. Table 2.1 development of modified from Ravindran15 different Year of development 1910 1925 1935 1945 1950 1955 1965 1985 1993 types of magnets, Tungsten-steel Cobalt-steel Aluminum-nickel Aluminum-nickel-cobalt Aluminum-cobalt Ferrite Samarium-cobalt Neodymium-iron-boron Samarium-iron-nitride Aluminum-Nickel-Cobalt Magnets (Alnico) Alnico magnets were the first type of magnets used in biomedicine. Alnico magnets are made from cobalt, aluminum, nickel, and iron.16, 17 These magnets are available in many shapes and sizes and are widely available. Alnico magnets have several drawbacks that prevent them from being used in orthodontics. Alnico magnets are expensive, prone to demagnetization, and are not very strong for their size.15, 16 Ferrite Magnets Ferrite magnets are magnets containing salts of iron. Common ferrite magnets are iron-barium and iron-strontium. 8 Ferrite magnets are highly resistant to demagnetization and corrosion and are very inexpensive to produce. Ferrite magnets are among the most common magnets produced and have been used in many industries but are not used in orthodontics due to size constraints.15, 16 Rare Earth Magnets Rare earth magnets, so named because they contain elements from the lanthanide series of the periodic table are the most recently developed magnets. Rare earth magnets exhibit a property known as magnetocrystalline anisotropy.18 Magnetocrystalline anisotropy means that as the magnet is produced, it is made up of a single crystal that is aligned in the same direction.15, 16 This allows for much stronger magnetism. Due to magnetocrystalline anisotropy, rare earth magnets are up 20 times stronger than previously developed magnets.15 This increase is magnetic strength allows for much smaller magnets to produce higher levels of force than was previously possible. Incorporation of rare earth metals also increases the Curie temperature of the magnet.15 Clinically, this allows for rare earth magnets to be sterilized and still retain their magnetic properties. Development of rare earth magnets has allowed for many orthodontic appliances that incorporate these magnets to be 9 produced. Rare earth magnets currently exist in three main forms: Samarium-cobalt, Neodymium-iron-boron, and most recently, Samarium-iron-nitride.16, 19 Samarium-cobalt(Sm-Co) magnets were first developed in the 1960s. These magnets are very strong and have a Curie point of 600˚C. These magnets are costly to produce and are very brittle.16, 17 Neodymium-iron-boron (Nd-Fe-B) magnets are stronger, much less expensive to produce, and less brittle than Samarium-Cobalt magnets. The main disadvantages of neodymium-iron-boron magnets are a lower Curie point (from 100˚C to 200˚C depending on the grade of the magnet) than Sm-Co magnets and a very low resistance to corrosion.15, 20, 21 16, For intraoral use, Nd-Fe-B magnets must be coated. Even with these drawbacks, Nd-Fe-B magnets are still the most widely used magnet in orthodontics. Samarium-iron-nitride (Sm-Fe-N) magnets are the most recently developed rare earth magnet and offer many qualities that make them attractive for use in orthodontics. Sm-Fe-N magnets are very strong, have higher resistance to corrosion than other rare earth magnets, and have a higher Curie point (700˚C to 800˚C depending on grade) than other rare earth magnets.16 10 Biological Considerations Prior to any material being introduced into clinical practice, it must be studied for effectiveness, and more importantly for safety. The side effects of the material and its components must be evaluated to determine if they can be safely used intra-orally. All dental materials should be studied to determine if they will produce side effects at either local or systemic levels. Testing should also be done to determine if any toxic, allergic, or carcinogenic side effects exist.22 Corrosion of Rare Earth Magnets One of the main drawbacks to the use of rare earth magnets, particularly those containing neodymium is their tendency to corrode when placed in aqueous environments.22, 23 Various studies have found that while Ne-Fe-B magnets are more prone to corrosion, their corrosion byproducts are less cytotoxic than other rare earth magnets, particularly those containing cobalt.22-25 Neodymium-containing magnets corrode via oxidation of neodymium rich grains resulting in the release of oxides of neodymium.21 In their study, Bondemark, Kurol, and Wennberg used two different methods to study cytotoxicity of new, 11 clinically used, and recycled magnets Sm-Co magnets. The methods used were a Millipore filter method and an extraction method. The Millipore filter method found that the corrosion products of Sm-Co magnets were mildly cytotoxic with only one magnet showing any cytotoxicity.23 The extraction experiment yielded similar results, showing mild cytotoxicity.23 The authors also found that cytotoxicity reduced upon retesting of new magnets and after the magnets had been used clinically. These findings suggest that most corrosion occurs during the initial placement of the magnets intra-orally.23 In another study using the same testing techniques, it was shown that different types of rare earth magnets demonstrated different levels of toxicity. They found that SmCo5 magnets were highly cytotoxic while Sm2Co17 magnets were only moderately cytotoxic. Ne2Fe14B magnets were also tested and found to have negligible cytotoxicity.25 To overcome the corrosive nature of rare earth magnets, several authors have recommended that the magnets either be coated, or hermetically sealed in a protective jacket to isolate the magnets from the intra-oral environment.16, 20, 22-26 12 Various coating materials have been compared. Coatings made from nickel and from chromium have been tested and while both reduced corrosion of rare earth magnets, the nickel itself was found be by cytotoxic.26 Tsutsui et al. concluded that a chromium coating was far superior as it is biologically compatible.26 Acrylic has also been studied as a coating for rare earth magnets. When corrosion of magnets coated with acrylic were compared to uncoated magnets it was found that although an acrylic coating served as a good barrier to corrosion, corrosion was still seen and a better coating is needed.24 Parylene coating has been shown to reduce the cytotoxicity of rare earth magnets to negligible levels.25 as mentioned previously, most cytotoxic corrosion occurs very quickly after being exposed to an aqueous environment. It has been suggested that recycling previously used magnets, or soaking new magnets in water for twenty-four hours prior to use may be a good way to reduce cytotoxicity.23 When magnets coated with parylene were compared to magnets coated with polytetrafluoroethylene (PTFE) in a simulated intra-oral environment, it was found that both 13 parylene and PTFE provided protection against corrosion when compared to controls with no significant difference between the coatings.27 It two separate studies, Wilson et al. found that biofilm accumulation played a role in the corrosion of magnets. They demonstrated that the both the biofilms themselves, and the metabolic byproducts of the bacteria in the biofilms increased corrosion of rare earth magnets.20, 21 Biological Effects of Magnetic Fields A large number of studies have been conducted to determine the effects of magnetic fields on living tissue with results ranging from little to no effect28-37, to having negative effects.38-40 In a split mouth study, Bondemark, Kurol, and Larsson examined the effects of static magnetic fields on human pulp and gingival tissue. They found no change in the dental pulp or in the gingival tissue adjacent to magnets.28 In another split-mouth study, tissue response to space closure was examined comparing coil springs to magnets. No significant differences in the rate of space closure, bone formation, or epithelial thickness were shown.29 This study did show significant differences in bony resorption and 14 tetracycline uptake when compared to the control side. These findings suggest increased metabolic activity. While these findings were statistically significant, the authors suggest they were transitory and had negligible clinical side effects.29 Sato et al. studied human cultured cells (HeLa cells and human fibroblast cells) to determine the effects of static magnetic fields on these cells. They grew these cultured cells in the presence of a non-homogenous static magnetic field and observed their growth, morphology, and later DNA synthesis and content. They demonstrated that static magnetic fields had no effect on cell morphology, cell growth, DNA content, or DNA synthesis.31 In another study of the effect of magnetic field, five titanium caps were implanted into the mandibles of five dogs. Three of the caps contained rare earth magnets and two were empty. The caps were left in place for six months and then the animals were sacrificed and the mandibles sectioned and examined microscopically for any changes. No pathological changes were reported when the sites with magnets compared to control sites.32 In another study performed on dogs, magnetic appliances were left intraorally for six months. After six 15 months, no evidence of tissue damage was found either clinically or upon microscopic examination.33 Esformes, Kummer, and Livelli grew tissue cultures of several cells lines and also did an in-vivo study of wound and bone healing in rats. They found that magnetic fields from rare earth magnets had no effects on cell growth rate, morphology, or their ability to grow. They also found no negative effects on bone or wound healing.35 The authors were careful to state that this was a short-term study and that long-term effects of magnetic fields still need to be investigated.35 Darendeliler, Sinclair, and Kusy performed a study on tooth movement comparing both pulsed and static magnetic fields to move incisors of guinea pigs. They found that both the pulsed and static magnetic fields led to an increase in the rate of tooth movement.34 They also found bony wound healing and repair increased in the presence of both pulsed and static magnetic fields, this led the investigators to conclude that the rate of tooth movement could be increased by magnetic fields by altering bone metabolism.34 Effects magnetic fields generated by rare earth magnets on cultured osteoblasts have also been studied. The 16 osteoblasts were exposed to magnetic fields of attracting magnets as well as magnetic fields from repelling magnets. After exposing the cells to the magnetic fields for 21 days, the cells were microscopically examined. No difference in osteoblast activity was noted for any of the groups.36 Camilleri and McDonald studied the effects of intense magnetic fields (4,100G) produced by Ne-Fe-B magnets on the sagittal suture of rats. This study demonstrated that mitotic activity in the sagittal suture decreased for a brief period with a tendency to return back to normal.41 An in vitro study of human fibroblasts found that fibroblasts grown in the presence of magnetic fields showed significantly impaired attachment and growth when compared to controls.38 The authors of the study did note that the observed deleterious effects could have been due to corrosion byproducts of the magnets as no steps were taken to limit corrosion.38 Linder-Aronson, Lindskog, and Rygh designed a study done to determine the effects of static magnetic fields on gingival epithelium and alveolar bone in monkeys.39 In their study, splints were fabricated that contained SmCo rare earth magnets, for this study, the magnets were completely 17 imbedded in acrylic. The splints were left in place for fourteen weeks. Tetracycline was injected at time of splint placement, and at four weeks. At the end of their experiment, epithelium adjacent to the magnets was examined microscopically. Alveolar bone adjacent to the magnets was also examined microscopically. The authors found that the epithelium was morphologically normal but was on average two cell layers thinner when compared to controls.39 Patchy tetracycline uptake was also noted, suggesting either a decrease in osteoblast activity or an increase in osteoclast activity. As with previous studies, the authors did note that they could not rule out the possibility of corrosion byproducts being responsible for the changes seen in their experiment.39 It is likely that corrosion did occur due to the choice of acrylic to limit corrosion. As Vardimon and Mueller showed, acrylic is an inadequate barrier to corrosion of SmCo magnets.24 The same authors performed another study, this time looking at bone surface and skin reactions to magnetic fields produced by rare earth magnets. For this study, rings containing rare earth magnets were fabricated and placed externally around the tibias of rats. The rings were left in place for 2, 3, and 4 weeks after which the animals 18 were sacrificed and the tissue and bone adjacent to the magnets were examined. In this study, a reduction in the number of epithelial cells was seen as was a stimulation of bone-lining osteoblasts.40 This study was highly criticized by Blechman for several reasons.37 Blechman pointed out that in the study, the magnetic device they used did not simulate any orthodontic appliance or application. The device was constructed in a way that magnets were straddled both sides of the bone, this situation would not be encountered in an orthodontic setting. The device was also placed in a way that could have led to pressure ischemia which could explain the observed negative effects.37 DeVincenzo agreed that pressure to the underlying epithelium may have been responsible for the findings of the study.42 DeVincenzo also criticized the conclusions of Linder-Aronson and Lindskog stating that skin and bone changes in rat tibias due not necessarily apply to oral mucosa.42 Linder-Aronson, Rygh, and Lindskog did do a follow-up study with that same parameters but adding a group were the magnets were removed after eight weeks and the sacrificed eleven weeks after the rings were removed.30 This study was done to confirm the results of the first study and to 19 determine if the observed negative effects were reversible. The same changes to epithelium and surface bone were noted as in the first study. It was also determined that these effects were reversible. They concluded that side effects from rare earth magnets were negligible and reversible.30 After review of the literature regarding the safety of magnetic fields for orthodontic use, the majority of researchers have concluded that magnetic fields either produce negligible side effects or no side effects at all. 28-37 In the studies where negative side effects were noted, other possible reasons for these negative effects could not be ruled out. Cytotoxicity due to corrosion of the magnets was noted as a possible reason for the negative effects in several studies.38, 39 Poor design of the testing apparatus was also cited as a reason for observed negative effects.37, 42 After many studies, and many years of experience working with magnetic fields, Blechman concluded: “to my knowledge there has not been a single reported and documented adverse clinical effect because of these specifically therapeutic fields.”37 20 A search of the literature agrees with Blechman’s assertion that magnetic fields are safe and can be utilized for clinical benefit. Magnets in Orthodontics Magnets were first use in dentistry in 1952. These magnets were implanted in the jaws to aid in retention of full dentures.43 Magnets were also used to aid in retention of maxillofacial prosthesis.44 Magnets were first used in orthodontics by Blechman and Smiley who attached magnets to the teeth of cats and proved that teeth could be moved via magnetic forces.19 Darendeliler et al. found that pulsed electromagnetic fields could enhance the effects of both mechanical and magnetic forces on tooth movement.45 In another study, Darendeliler, Sinclair, and Kusy found that pulsed electromagnetic fields led to increased boney healing and the elimination of the lag phase of tooth movement.34 This led them to suggest that under ideal conditions, the maximum rate of tooth movement could be increased from 1mm per month to up to 3mm per month.34 Since the introduction of magnets into the field of orthodontics, magnets have been used in a wide variety of 21 appliances. Magnets have been used both to orthodontically move teeth,46-49 and for orthopedic correction.50-52 Magnetic orthodontic appliances have, in theory, several advantages over traditional appliances. Magnetic appliances reduce patient cooperation, exert continuous forces that do not decay over time, have reduced friction, exert predictable force levels, and can exert force through bone and mucosa.15, 16, 22 Magnetic Brackets Magnetic brackets were first designed by Kawata, Okada, and Horisaka.53 This design first used iron-cobalt magnets which were later replaced by chromium coated rare earth magnets.54 Kawata et al. found that these magnets could be used for mesial and distal movement of teeth as long as the interbracket distance was 3mm or less.54 While magnetic brackets were shown to effectively move teeth, this method of tooth movement has not gained wide acceptance. Space Closure Blechman and Abraham demonstrated that rare earth magnets could be used to successfully achieve both intermaxillary and intramaxillary mechanics.47 Muller 22 reported success with using magnets to close a midline diastema without using archwires.55 Muller also suggested that magnets could be used for more complicated mechanics such as rotational correction, tooth uprighting, and bodily movement.55 Molar Distalization Gianelly et al. were the first to use repelling magnets to successfully distalize first molars while the second molars were unerupted. Their appliance was a modified Nance appliance that incorporated magnets.49 They were able to distalize the first molars 3mm in seven weeks with 1mm of anterior anchorage loss.49 This design has been duplicated with similar results.48 Attempts have also been made to distalize both first and second molars using rare earth magnets. The appliance was successful but not without drawbacks. Tipping and rotation of the molars was noted as was proclination of the upper incisors.56 Bondemark, Kurol, and Bernhold compared nickel titanium springs to magnets for distalization of first and second molars.57 It was found that while the magnets were able to distalize molars, the coil springs achieved greater 23 amount of distalization with more consistent force levels and less loss of force. They concluded that nickel-titanium springs were a more efficient means of distalizing maxillary first and second molars.57 Extrusion of Teeth McCord and Harvie used attractive magnets to extrude a damaged incisor to aid in its eruption.58 Bondemark et al. also used rare earth magnets to extrude teeth where the crowns had fractured.59 They reported success in extrusion of the remaining portion of the tooth with no soft tissue dehiscence, root mobility, or root resorption. They also found no coronal bone loss or need to reshape the bone prior to a final restoration being placed.59 Intrusion of Teeth Magnetic appliances have also been combined with a corticotomy to intrude posterior teeth that had supererupted.60 The supererupted teeth were able to be intruded without extruding the adjacent teeth. Similarly, rare earth magnets encased in acrylic bite blocks have been used to intrude posterior teeth.61 24 Impacted Teeth Magnetic traction of impacted teeth was first reported by Sandler, et al. An impacted canine was surgically exposed and a magnet was bonded to the tooth surface. A second magnet was embedded in a removable acrylic appliance.62 Darendeliler, and Friedli used a similarly designed appliance to erupt an impacted canine as well.63 Magnetic traction of impacted canines offers many advantages over traditional mechanics. No hooks or elastics need to be used, fewer adjustments are needed, and reactivation is not necessary.16 Maxillary Expansion Vardimon et al. were the first researchers to attempt using magnets to expand the maxilla in monkeys.64 Darendeliler, Strahm, and Joho also used magnetic appliances for maxillary expansion. They found that magnetic appliances could produce the required 250-500 grams of force needed to produce both dental and skeletal expansion.65 Open Bite Correction Dellinger was the first to introduce a magnetic appliance to correction anterior open bites via posterior 25 intrusion. Dellinger termed his appliance the Active Vertical Corrector (AVC).66 For this appliance, Dellinger used four pairs of Sm-Co repelling magnets imbedded in a removable acrylic plate to intrude upper and lower molars.66 The design of the appliance was updated and now uses Ne-FeB magnets to deliver less force using much smaller magnets.67 This device is appealing as it allows for a nonsurgical approach to treat anterior open bites. As the molars are intruded, the mandible is allowed to rotate forward and lower anterior facial height is reduced.66, 67 Darendeliler, Yuksel, and Meral developed an appliance they named the magnetic activator device IV (MAD IV).68 This appliance uses Ne-Fe-B magnets. Attractive magnets are placed at the anterior of the appliance to guide and position the mandible forward. At the same time, repulsive magnets are used to intrude the posterior teeth. The MAD IV appliance is available in three configurations, each modified to treat a different type of malocclusion.68 When the dental and skeletal effects of treatment with the MAD IV appliance were examined, the upper incisors became more upright, the lower incisors become more proclined, and the posterior teeth intruded.55 Skeletally, forward rotation of the mandible which led to a decreased 26 mandibular plane angle, decreased lower anterior facial height, and a decrease in the ANB angle were seen.55 Woods and Nanda have also shown that posterior teeth can be intruded utilizing magnetic appliances.69 Similar to previous studies, their appliance used magnets embedded in acrylic bite plates.69 Magnetic Functional Appliances for Class II Correction Magnetic Class II functional appliances are designed to work in the same manner as traditional functional appliances, by positioning the mandible to a more favorable, forward position. Magnetic appliances differ in that they use magnetic force to reposition the mandible to a new rest position.51, 70 Vardimon, et al. developed an appliance called the Functional Orthopedic Magnetic Appliance (FOMA) II. This appliance uses attractive magnets positioned anteriorly to position the mandible more forward.52 Another functional magnetic appliance was developed by Darendeliler, Chiarini, and Joho. This appliance is known as the magnetic activator device (MAD).51 The MAD is available is several varieties, the MAD I for lateral displacement51, the MAD II for Class II correction51, 27 71, 72 , the MAD III for Class III correction73, and as previously discussed, the MAD IV for open bite correction68. A retrospective study on an appliance known as the Functional Magnetic System (FMS) was done by Vardimon et al.74 They found that the Class II correction achieved by the appliance varied from region to region with more correction found in the incisors versus the molars.74 Half of the molar relationship was corrected skeletally while the other half was corrected dentally, whereas in the incisor region one third of the correction was skeletal with the remaining two thirds dental.74 An increase in lower facial height was seen and was attributed mainly to the eruption of the lower molars. The authors also found that the net increase in Ar-Gn was larger for the FMS than the other groups, this was postulated to be due to the magnets providing a longer time in which the mandible was postured forward as compared to other functional appliances.74 When examining the effects that magnetic functional appliances had on the dentofacial complex it was found that on average, mandibular length increased 3.2mm, the angle of facial convexity decreased 2.8°, the upper and lower teeth intruded an average of 1.5 mm each, and the mandibular plane angle decreased 1.3°. During a follow-up period, the 28 authors found some relapse due to eruption, but all other changes were found to be stable.75 Magnetic Functional Appliances for Class III Correction Darendeliler, Chiarini, and Joho developed the Mandibular Activator Device (MAD) III to achieve functional orthopedic correction of Class III malocclusion.73 This device can be used with or without a reverse-pull facemask and maxillary expander. Vardimon et al. created the Functional Orthopedic Magnetic Appliance (FOMA) III to treat patients with Class III malocclusion and a midface deficiency.50 This appliance was shown to achieve midface protraction as well as advancement of the upper incisors and molars.50 Rare Earth Magnets Used for Retention The first example of a magnetic retainer is from a case report from 1999 when Springate and Sandler used neodymium-iron-boron magnets bonded to a patient’s teeth to hold a midline diastema closed.22 Others have used rare earth magnets not as retainers but to aid in the placement of bonded retainers.76-78 29 Retention Retention is the final phase of orthodontic treatment. Retention has been defined by Moyers as “the holding of the teeth following orthodontic treatment in the treated position for the period of time necessary for the maintenance of the result.79” Reidel gave a more brief definition of retention: “the holding of teeth in ideal esthetic and functional position.80” No matter the definition, retention is a difficult and often trying aspect of orthodontics, indeed, Oppenheim referred to retention not just as a difficult problem in orthodontics but as the problem in orthodontics.81 Pratt et al. stated that there are two phases to orthodontic retention which they termed the retention phase, and the post-retention phase.12 The first phase of retention, the “retention phase” is the time in which the teeth are held in their posttreatment position during which the periodontium remodels.10 On average, the periodontal ligament takes three to four months to remodel, the collagen-fiber network takes four to six months to remodel, and the supracrestal fibers take about 12 months to completely remodel.82, 83 Thus, this first stage of retention should last at least one year.12 30 The second phase of retention, the “post-retention phase” starts once the remodeling of the periodontium is complete and, according to Pratt et al. lasts the rest of the patient’s life.12 Alteration of Arch Form Most studies of archform and arch perimeter show that both should be maintained rather than altered as both have a tendency to return toward pre-treatment dimensions.84, 85 This is especially true of mandibular intermolar and intercanine widths.8, 86-88 There are some studies that have shown stability following modification of arch form and width. Mills showed that alteration of the lower archform via incisor proclination was stable in patients whose incisors were initially retroclined, had deep bites, and who also had a digit or lip entrapment habit.89 Similarly, Artun said that proclination could be stable in cases where the incisors were initially retroclined and the etiology of the retroclination could be corrected.90 Studies have also been done that suggest that arch expansion may be more stable in patients with Class II div. 2 malocclusion than Class I and Class II div. 1 malocclusions.91, 92 Blake and Bibby point out that the sample size of these studies was very small 31 and the results may not be reliable.7 This is supported by Little who showed that relapse of both intermolar and intercanine width were independent of initial malocclusion.8 Haas, and later, Sandstrom and Klapper demonstrated that alteration of arch width via expansion may be stable in some instances. They both had similar result results which showed maintenance of three to four millimeters of mandibular intercanine width and up to six millimeters of mandibular intermolar width when this change in mandibular arch width was accompanied by rapid palatal expansion.93, 94 As Blake and Bibby pointed out however, both of these studies had flaws. Both were short-term studies with small sample sizes.7 Moussa, O’Reilly, and Close who had a larger sample size, and an 8 year post-retention follow-up showed good stability of upper intercanine and upper and lower intermolar width expansion when this expansion was done in conjunction with rapid palatal expansion. Their study also showed that stability of mandibular intercanine expansion was poor and tended to relapse.95 32 Periodontium and Stability As was mentioned previously, the periodontium plays a significant role in relapse and stability. This is especially true rotational relapse.96, 97 Because the periodontium can take up to a year to completely remodel, many have suggested a surgical procedure to sever the gingival fibers immediately following orthodontic treatment. This procedure is known as circumferential supracrestal fiberotomy.98, 99 Studies done on the effects of circumferential supracrestal fiberotomy have shown a significant decrease in incisal irregularity at six, nine, and fourteen years post-treatment with no significant loss of attachment or other periodontal issues.100-103 The Role of Lower Incisor Shape Peck and Peck suggested that relapse of the lower incisors was due, at least in part to the ratio between the mesiodistal and faciolingual height and width of the lower incisors and suggested altering the dimensions of the lower incisors to correct this ratio.104 Peck and Peck’s work has been criticized for using untreated rather than treated cases. It has also been noted 33 that the cases in Peck and Peck’s study were not followed long-term these cases would likely have shown crowding if followed for a longer period of time.7 A long term study comparing treated to untreated cases demonstrated a very weak association between irregularity and faciolingual/mesiodistal ratios.105 Other studies have not only confirmed this, but have shown that less than six percent of crowding can be explained by this ratio.106-109 The Impact of Pre-treatment Occlusion Although some studies have shown that Class II div. 2 cases have shown to be more stable,91, 92 most studies do not support this finding and show that relapse is largely independent of Angle’s classification. 110-112 Deep bite relapse has been shown to be dependent on the amount of bite opening achieved during treatment. On average 30% to 50% of deep bite correction is stable.8, 114 Open bites are difficult to retain with successful stability being shown only 60% of the time.115 Uhde, Sadowsky, and Begole found that 41% of late lower incisor crowding could be explained by changes to overjet, overbite, intercanine width, and intermolar width.113 These same authors also found that the highest 34 113, single factor related to late mandibular crowding was change to intermolar width which was shown to contribute to 12.5% of post-treatment relapse.113 The Effect of Extractions on Stability Little et al. studied cases in which patients had first premolars extracted as part of their treatment plan. These cases were examined at least ten years posttreatment. Changes in arch length, intercanine width or length of treatment were found to have no association to prediction of post-treatment crowding.6, 8 In this same study, Little et al. defined the overall success of stability of treatment as having an Irregularity Index of 3.5mm or less and found a success rate less than 30% with 20% showing severe relapse.6 When this same sample was studied to attempt to find an association or prediction between dental cast measures and cephalometric measures, no association or prediction could be found.116 Studies of serial extractions in which no other treatment was done have shown varied results. In one study, patients who had serial extractions and no other treatment showed in increase in post-treatment irregularity at 10 years.9 In another study which looked at patients 20 years 35 post-treatment, relapse of crowding was seen but to a lesser extent than untreated controls.117 Similar results have also been shown when serial extractions are combined with later orthodontic treatment. Anterior relapse as high as 73% has been reported.9 Relapse is seen regardless of the serial extraction pattern. No difference in anterior relapse was seen whether the first or second premolars were extracted.118 Retainers Orthodontists today have many choices when it comes to choosing retainers for their patients. The main types of retainers are Hawley retainers, vacuum-formed retainers, and a variety of bonded retainers. According to a recent survey of members of the American Association of Orthodontics, Hawley retainers are the most commonly used, the next most common retainers are vacuum-formed retainers, and the least common retainers are bonded retainers.12 This survey also noted a trend towards less Hawley retainers and more vacuum-formed and bonded retainer use.12 Hawley Retainers Hawley retainers are available in a wide variety of designs but generally consist of an acrylic plate that 36 rests behind the teeth and contacts the lingual surface of the teeth and the gingiva and a labial wire that contacts the facial surface from canine to canine. Hawley retainers are a popular choice among orthodontists due to their adjustability and durability. Patients have shown to be more compliant to wearing Hawley retainers long-term compared to other kinds of retainers.119 The main drawbacks to Hawley retainers are fabrication time, cost and compliance in wearing. Hawley retainers are often chosen for their durability, with one author stating that Hawley retainers have lasted up to fifteen years in his practice.2 Many studies have demonstrated that Hawley retainers also offer the advantage of allowing the posterior teeth to settle which often results in more favorable intercuspation, better occlusal contacts, and improved marginal ridge alignment.12, 120, 121 It is important to note that this settling will not occur where the wire of the retainer crosses over the occlusion. If settling of the posterior teeth after treatment is desired, and a Hawley retainer is chosen, the retainer must be designed in a way to allow settling to occur. 37 Many studies have shown that Hawley retainers are not as effective in holding the anterior teeth in their posttreatment position as vacuum-formed retainers, especially the lower anterior teeth.122-124 Other studies have shown no statistically significant differences between effectiveness of Hawley retainers compared to vacuum-formed retainers.122, 125 These findings have led many clinicians to alter their retention protocols in favor of less Hawley use, especially for the mandibular teeth.12 Vacuum-formed Retainers Vacuum-formed retainers are made from clear plastic that is warmed and vacuum-formed onto a dental cast. These retainers are often chosen because they are less noticeable and cover the entire surface of the teeth. Vacuum formed retainers can be fabricated quickly and inexpensively but these retainers are not adjustable and are not as durable as other retainers. As previously mentioned, vacuum-formed retainers have been found by many studies to be more effective at retaining the lower teeth.122-124 Many clinicians now use either vacuum-formed retainers on both arches or in the lower arch with a Hawley retainer on the upper arch. Because vacuum-formed retainers cover all surfaces of the 38 teeth, settling of the occlusion is prevented. To overcome this, Lindauer and Shoff suggested modifying the lower vacuum-formed retainer to cover only canines and incisors.122 This design maximizes the strengths of the vacuum-formed retainer in holding the anterior teeth, but still allows for posterior settling to occur. Bonded Retainers Bonded retainers are made from either one wire or several wires braided or twisted together. In a study done by Baysal et al., three different wires were compared (an 0.0215” five-stranded wire, 0.016 x 0.022” eight-stranded dead-soft braided wire, and 0.0195” dead-soft coaxial wire) to determine the performance of each of the wires. They concluded that while detachment force was similar for all wires, the dead soft wires showed more deformations. They also found that pull out force was significantly higher for the five-stranded coaxial wires than for the other wires. They concluded that of the wires tested, the five-stranded coaxial wire was the best choice for bonded lingual retainers.126 Renkema et al. studied the effectiveness of a 0.0195,” 3 stranded wire (Wildcat wire, GAC International, Bohemia, NY) and found it to be an effective retainer.127 39 For bonded retainers, once the wire is chosen, the wire is bonded to the lingual surface of the teeth holding them in place. Special attention must be taken during the bonding procedure as this has shown to be very technique sensitive and the long-term survival of the retainer is dependent on good initial placement and bond strength. Studies have shown that most failures occur in the first six months after retainer placement.128 The overall failure rate varies depending on how many of the teeth the retainer is bonded to and the experience of the practitioner placing the retainer. Overall failure rates range from around 35%128, 129 to as high as 46%.130 Scheibe and Ruf found that while the failure rate varies with time, overall orthodontists had a failure rate of 40.3% while graduate students had a failure rate of 40.3%129 Their results were corroborated by Segner and Heinrici131 Bonded retainers are most commonly used on the lower arch and can be bonded to just the lower canines or to all six anterior teeth. Several considerations must be taken into account when making the decision of how many teeth the retainer should be bonded to. Bond failure and effectiveness of the retainer are the two most important factors to consider. 40 Bond failure of lower bonded retainers has shown to be higher when the retainer is bonded only to the canines.129, 132, 133 Although bond failure is higher when the retainer is bonded only to the cuspids, this may be beneficial because the patient will be more sensitive to bond failures. If the retainer is bonded to all anterior teeth, a bond failure at just one tooth may go unnoticed by the patient leading to a delay in repair an increase in the potential for relapse134. While retainers bonded only to the canines are effective at retaining the lower anterior teeth, some studies have shown an increase in incisor regularity that is higher than if the retainer is bonded to all anterior teeth.135, 136 A particular weakness of retainers bonded only to the canines is that they may allow for labial movement and rotational relapse of the anterior teeth.12, 133, 135 Many studies have been done to examine the effects that bonded retainers have on the gingiva and teeth. In theory, a wire bonded to the teeth provides a source for accumulation of biofilm which in turn, could lead to increased gingival inflammation, periodontal problems, and caries. Johnsson, Tofelt, and Kjellberg found that while plaque accumulation was increased in patients with lower bonded retainers, only 2% of their sample showed any new 41 gingival recession.137 Other studies have shown that bonded retainers have no detrimental effects to the gingiva.3, 138 Johnsson, Tofelt, and Kjellberg also noted that no demineralization or carious lesions were seen in teeth contacting the bonded retainer.137 Similar results have been found in several other studies.133, 139-141 In studying different types of wires for bonded retainers Jongsma et al. found that single-stranded wires showed less biofilm accumulation than multi-stranded wires.142 The also showed that biofilm accumulation on multistranded wires were more resistant to antimicrobials and are harder to remove via toothbrushing.142 This led them to recommend single-stranded wires for fabrication of bonded retainers. This conclusion was supported by Pazera, Fudalej, and Katsaros.134 Bonded retainers are chosen because they eliminate compliance to wear. Compliance is one of the greatest difficulties of orthodontic retention. Heyman, Grauer, and Swift found that fewer than half of their patients wore their retainers as instructed two years post-treatment.3 The disadvantages of bonded retainers are debonding, technique sensitivity of placement procedure, and that patients with bonded retainers must be continuously monitored.127 42 Little’s Irregularity Index Little’s Index was introduced by Dr. Robert Little in 1975 as a means to quantify lower incisor irregularity. Dr. Little proposed measuring the linear distance between the anatomical contact points of the lower anterior teeth (from mesial of canine to mesial of contralateral canine) to the nearest tenth of a millimeter. These differences were added together and the sum was termed the Irregularity Index.143 Since the Irregularity Index was introduced, it has gained wide acceptance and has been used in multiple studies. Little’s Irregularity Index has been used to measure initial crowding, effectiveness of orthodontic appliances at resolving incisor crowding, and a wide variety studies to determine effectiveness of different orthodontic retainers and retention protocols. Little’s Index is not free of flaws. The Index is measured by calipers on dental models that remain flat on a table. Due to this, the Index does not take into account the vertical displacement of the teeth and its impact on crowding.144 Intra-examiner variability of Little’s Index has also been shown to be high.144 Another drawback to Little’s Index is subjectivity when locating the contact points to be measured.145 Utilizing three-dimensional digital scanning 43 for intraoral scans and to create digital models has been suggested as a way to improve both the accuracy and precision of Little’s Index.144, 145 Despite the limitations of Little’s Index, it is still one of the most widely used methods to give a quantitative measure of effectiveness of orthodontic treatment, particularly effectiveness of retentive devices and retention protocols. Statement of Thesis This study will be a retrospective study to examine whether the MagneTainer®™ is as effective as canine-tocanine bonded retainers that are bonded to each tooth. Two samples will be gathered. The first sample contains 39 consecutively treated individuals treated by Dr. Aron Dellinger of Fort Wayne Indiana. This sample had the MagneTainer placed at the conclusion of full orthodontic treatment. The second sample, consisting of 41 patients will be gathered from records of patients treated at Saint Louis University’s Center for Advanced Dental Education. This sample will have had canine-to-canine retainers bonded to each tooth placed at the conclusion of full orthodontic treatment. For both samples, any individuals who had extractions, missing teeth, or spacing prior to treatment will be excluded. 44 Dental casts from pre-treatment, debond, and two years post-treatment will be digitized and a Little’s Index will be taken on these digital models at each time point. The dependent variable will be the change in Little’s Irregularity Index from debond to two years post-treatment. 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A clinical assessment of the active vertical corrector—a nonsurgical alternative for skeletal open bite treatment. Am J Orthod. 1986; 42836. 67. Dellinger EL, Dellinger EL. Active vertical corrector treatment—long-term follow-up of anterior open bite treated by the intrusion of posterior teeth. Am J Orthod Dentofacial Orthop. 1996; 145-54. 68. Darendeliler MA, Yüksel S, Meral O. Open-bite correction with the magnetic activator device IV. J Clinical Orthod. 1995; 569-76. 69. Woods MG, Nanda RS. Intrusion of posterior teeth with magnets: an experiment in growing baboons. Angle Orthod. 1988; 136-50. 70. Darendeliler MA, editor Use of magnetic forces in growth modification. Seminars in Orthodontics; 2006: Elsevier. 51 71. Darendeliler M, Joho J. Class II bimaxillary protrusion treated with magnetic forces. J Clinical Orthod. 1992; 361-8. 72. Yüksel S, Kaygisiz E, Ulusoy Ç, Keykubat A. Posttreatment evaluation of a magnetic activator device in Class II high-angle malocclusions. Eur J Orthod. 2010; 120. 73. Darendeliler M, Chiarini M, Joho J. Early class III treatment with magnetic appliances. J Clinical Orthod. 1993; 563-9. 74. Vardimon AD, Köklü S, Iseri H, Shpack N, Fricke J, Mete L. An assessment of skeletal and dental responses to the functional magnetic system (FMS). Am J Orthod Dentofacial Orthop 2001; 416-26. 75. Kalra V, Orth D, Burstone CJ, Nanda R. Effects of a fixed magnetic appliance on the dentofacial complex. Am J Orthod Dentofacial Orthop. 1989; 467-78. 76. Hahn W, Fricke J, Fricke-Zech S, Zapf A, Gruber R, Sadat-Khonsari R. The use of a neodymium–iron–boron magnet device for positioning a multi-stranded wire retainer in lingual retention—a pilot study in humans. Eur J Orthod. 2008; 433-6. 77. Hahn W, Wasser-Merkel W, Lange K, Gruber RM, KubeinMeesenburg D, Ihlow D. Accuracy of fit of 3-to-3 retainers after adhesive fixation using a neodymiumiron-boron magnet chain. J Orofac Orthop. 2011; 381-8. 78. Yadav S, Upadhyay M, Patil S, Keluskar KM. Use of RareEarth Magnets for Bonding Lingual Retainers. J Clinical Orthod. 2008; 349-50. 79. Moyers RE. Handbook of orthodontics for the student and general practitioner: Year Book Medical Publishers Chicago; 1973. 80. Riedel R, Graber T. Current orthodontic concepts and techniques. Graber TM, WB Saunders Co. 1969. 81. Oppenheim A. The crisis in orthodontia Part I 2. Tissue changes during retention. Skogsborg's septotomy. International Journal of Orthodontia and Dentistry for Children. 1934; 759-69. 52 82. Reitan K. Clinical and histologic observations on tooth movement during and after orthodontic treatment. Am J Orthod. 1967; 721-45. 83. Singh P, Grammati S, Kirschen R. Orthodontic retention patterns in the United Kingdom. J Orthod. 2009; 11521. 84. McCauley DR. The cuspid and its function in retention. Am J Orthod and Oral Surgery. 1944; 196-205. 85. Riedel RA. A review of the retention problem. Angle Orthod. 1960; 179-99. 86. Sadowsky C, Schneider BJ, BeGole EA, Tahir E. Long-term stability after orthodontic treatment: nonextraction with prolonged retention. Am J Orthod Dentofacial Orthop. 1994; 243-9. 87. Gardner SD, Chaconas SJ. Posttreatment and postretention changes following orthodontic therapy. Angle Orthod. 1976; 151-61. 88. Kahl-Nieke B, Fischbach H, Schwarze CW. Treatment and postretention changes in dental arch width dimensions— a long-term evaluation of influencing cofactors. Am J Orthod Dentofacial Orthop; 368-78. 89. Mills J. The long-term results of the proclination of lower incisors. Brit Dent J. 1966; 355-63. 90. Årtun J, Krogstad O, Little RM. Stability of mandibular incisors following excessive proclination: a study in adults with surgically treated mandibular prognathism. Angle Orthod. 1990; 99-106. 91. Riedel R, Brandt S. Dr. Richard A. Riedel on retention and relapse. J Clinical Orthod. 1976; 454. 92. Shapiro PA. Mandibular dental arch form and dimension: treatment and postretention changes. Am J Orthod. 1974; 58-70. 93. Haas A. Long-term posttreatment evaluation of rapid palatal expansion. Angle Orthod. 1980; 189-217. 94. Sandstrom RA, Klapper L, Papaconstantinou S. Expansion of the lower arch concurrent with rapid maxillary expansion. Am J Orthod Dentofacial Orthop. 1988; 296302. 53 95. Moussa R, O'Reilly MT, Close JM. Long-term stability of rapid palatal expander treatment and edgewise mechanotherapy. Am J Orthod Dentofacial Orthop. 1995; 478-88. 96. Reitan K. Tissue Rearrangement During Retention Of Orthodontically Rotated Teeth. Angle Orthod. 1959; 105-13. 97. Edwards JG. A study of the periodontium during orthodontic rotation of teeth. Am J Orthod. 1968; 44161. 98. Brain WE. The effect of surgical transsection of free gingival fibers on the regression of orthodontically rotated teeth in the dog. Am J Orthod. 1969; 50-70. 99. Edwards JG. A surgical procedure to eliminate rotational relapse. Am J Orthod. 1970; 35-46. 100. Edwards JG. A long-term prospective evaluation of the circumferential supracrestal fiberotomy in alleviating orthodontic relapse. Am J Orthod Dentofacial Orthop. 1988; 380-7. 101. BOESE LR. Fiberotomy and reproximation without lower retention, nine years in retrospect: part I. Angle Orthod. 1980; 88-97. 102. BOESE LR. Fiberotomy and reproximation without lower retention 9 years in retrospect: part II. Angle Orthod. 1980; 169-78. 103. Fricke LL, Rankine CA. Comparison of electrosurgery with conventional fiberotomies on rotational relapse and gingival tissue in the dog. Am J Orthod Dentofacial Orthop. 1990; 405-12. 104. PECK S, PECK H. Crown dimensions and mandibular incisor alignment. Angle Orthod. 1972; 148-53. 105. Gilmore CA, Little RM. Mandibular incisor dimensions and crowding. Am J Orthod. 1984; 493-502. 106. Mills LF. Arch width, arch length, and tooth size in young adult males. Angle Orthod. 1964; 124-9. 107. Keene A, Engel G. The mandibular dental arch, part IV: prediction and prevention of lower anterior relapse. Angle Orthod. 1979; 173-80. 54 108. Smith RJ, Davidson WM, Gipe DP. Incisor shape and incisor crowding: a re-evaluation of the Peck and Peck ratio. Am J Orthod. 1982; 231-5. 109. Puneky PJ, Sadowsky C, BeGole EA. Tooth morphology and lower incisor alignment many years after orthodontic therapy. Am J Orthod. 1984; 299-305. 110. Bishara SE, Chadha J, Potter RB. Stability of intercanine width, overbite, and overjet correction. Am J Orthod. 1973; 588-95. 111. Bresonis WL, Grewe JM. Treatment and posttreatment changes in orthodontic cases: overbite and overjet. Angle Orthod. 1974; 295-9. 112. Elms T, Buschang P, Alexander R. Long-term stability of Class II, Division 1, nonextraction cervical facebow therapy: I. Model analysis. Am J Orthod Dentofacial Orthop. 1996; 271-6. 113. Uhde MD, Sadowsky C, Begole EA. Long-term stability of dental relationships after orthodontic treatment. Angle Orthod. 1983; 240-52. 114. Simons ME, Joondeph DR. Change in overbite: a ten-year postretention study. Am J Orthod. 1973; 349-67. 115. Hernandez JL. Mandibular bicanine width relative to overbite. Am J Orthod. 1969; 455-67. 116. Shields TE, Little RM, Chapko MK. Stability and relapse of mandibular anterior alignment: a cephalometric appraisal of first-premolar-extraction cases treated by traditional edgewise orthodontics. Am J Orthod. 1985; 27-38. 117. Perssor M, Persson E-C, Skagius S. Long-term spontaneous changes following removal of all first premolars in Class I cases with crowding. Eur J Orthod. 1989; 271-82. 118. McReynolds DC, Little RM. Mandibular second premolar extraction-postretention evaluation of stability and relapse. Angle Orthod. 1991; 133-44. 119. Pratt MC, Kluemper GT, Lindstrom AF. Patient compliance with orthodontic retainers in the postretention phase. Am J Orthod Dentofacial Orthop. 2011; 196-201. 55 120. Sauget E, Covell Jr DA, Boero RP, Lieber WS. Comparison of occlusal contacts with use of Hawley and clear overlay retainers. Angle Orthod. 1997; 223-30. 121. Hoybjerg AJ, Currier GF, Kadioglu O. Evaluation of 3 retention protocols using the American Board of Orthodontics cast and radiograph evaluation. Am J Orthod Dentofacial Orthop. 2013; 16-22. 122. Lindauer SJ, Shoff RC. Comparison of Essix and Hawley retainers. J Clinical Orthod. 1998; 95. 123. Rowland H, Hichens L, Williams A, Hills D, Killingback N, Ewings P, Clark S, Ireland AJ, Sandy JR. The effectiveness of Hawley and vacuum-formed retainers: a single-center randomized controlled trial. Am J Orthod Dentofacial Orthop. 2007; 730-7. 124. Demir A, Babacan H, Nalcacı R, Topcuoglu T. Comparison of retention characteristics of Essix and Hawley retainers. Korean J Orthod. 2012; 255-62. 125. Barlin S, Smith R, Reed R, Sandy J, Ireland AJ. A retrospective randomized double-blind comparison study of the effectiveness of Hawley vs vacuum-formed retainers. Angle Orthod. 2011; 404-9. 126. Baysal A, Uysal T, Gul N, Alan MB, Ramoglu SI. Comparison of three different orthodontic wires for bonded lingual retainer fabrication. Korean J Orthod. 2012; 39-46. 127. Renkema AM, Renkema A, Bronkhorst E, Katsaros C. Longterm effectiveness of canine-to-canine bonded flexible spiral wire lingual retainers. Am J Orthod Dentofacial Orthop. 2011; 614-21. 128. Taner T, Aksu M. A prospective clinical evaluation of mandibular lingual retainer survival. Eur J Orthod. 2012; 470-4. 129. Scheibe K, Ruf S. Lower bonded retainers: survival and failure rates particularly considering operator experience. J Orofac Orthop. 2010; 300-7. 130. Pandis N, Fleming PS, Kloukos D, Polychronopoulou A, Katsaros C, Eliades T. Survival of bonded lingual retainers with chemical or photo polymerization over a 2-year period: a single-center, randomized controlled 56 clinical trial. Am J Orthod Dentofacial Orthop. 2013; 169-75. 131. Segner D, Heinrici B. Bonded retainers–clinical reliability. J Orofacial Orthop. 2000; 352-8. 132. Lumsden KW, Saidler G, McColl JH. Breakage incidence with direct bonded lingual retainers. J Orthod. 1999; 191-4. 133. Zachrisson BU. Clinical experience with direct-bonded orthodontic retainers. Am J Orthod. 1977; 440-8. 134. Pazera P, Fudalej P, Katsaros C. Severe complication of a bonded mandibular lingual retainer. Am J Orthod Dentofacial Orthop. 2012; 406-9. 135. Zachrisson BU. Long-term experience with direct-bonded retainers: update and clinical advice. J Clinical Orthod. 2007; 728-37. 136. Renkema A-M, Al-Assad S, Bronkhorst E, Weindel S, Katsaros C, Lisson JA. Effectiveness of lingual retainers bonded to the canines in preventing mandibular incisor relapse. Am J Orthod Dentofacial Orthop. 2008; 179-180. 137. Johnsson AC, Tofelt LN, Kjellberg H. Subjective evaluation of orthodontic treatment and potential side effects of bonded lingual retainers. Swedish Dent J. 2007; 35-44. 138. Booth FA, Edelman JM, Proffit WR. Twenty-year followup of patients with permanently bonded mandibular canine-to-canine retainers. Am J Orthod Dentofacial Orthop. 2008; 70-6. 139. Andrén A, Asplund J, Azarmidohkt E, Svensson R, Varde P, Mohlin B. A clinical evaluation of long term retention with bonded retainers made from multi-strand wires. Swedish Dent J. 1997; 123-31. 140. Årtun J. Caries and periodontal reactions associated with long-term use of different types of bonded lingual retainers. Am J Orthod. 1984; 112-8. 141. Gorelick L, Geiger AM, Gwinnett AJ. Incidence of white spot formation after bonding and banding. Am J Orthod. 1982; 93-8. 57 142. Jongsma MA, Pelser FD, van der Mei HC, Atema-Smit J, van de Belt-Gritter B, Busscher HJ, Ren Y. Biofilm formation on stainless steel and gold wires for bonded retainers in vitro and in vivo and their susceptibility to oral antimicrobials. Clin Oral Investig. 2013; 1209-18. 143. Little RM. The irregularity index: a quantitative score of mandibular anterior alignment. Am J Orthod. 1975; 554-63. 144. Macauley D, Garvey TM, Dowling AH, Fleming GJ. Using Little's Irregularity Index in orthodontics: outdated and inaccurate? J Dent. 2012; 1127-33. 145. Dowling AH, Burns A, Macauley D, Garvey TM, Fleming G. Can the intra-examiner variability of Little's Irregularity Index be improved using 3D digital models of study casts? J Dent. 2013; 1271-80. 58 Chapter 3: Journal Article Abstract Introduction: Retention has long been one of the most challenging aspects of orthodontic treatment. Difficulties with retention have led many to conclude that the only way to retain the teeth in their post-treatment positions is long-term retention. The MagneTainer®™ is a newly developed magnetic retainer bonded to the lower anterior teeth for long-term retention. Purpose: This study examines the efficacy of the MagneTainer®™ as compared to canine-tocanine retainers bonded to each tooth. Materials and Methods: Using digital models of 39 patients who had the MagneTainer®™ placed at debond and 41 patients who had canine-to-canine retainers placed at debond, Little’s Irregularity Index was calculated prior to treatment, at placement of retainers, and two years post-placement. The groups were compared to see if any significant differences exist. Results: Significant differences within each group were seen for changes in Little’s Index and space discrepancy at two years compared to debond. The only significant differences between the groups were related to intercanine width. Correlations were found between initial intercanine width, initial space deficiency, and initial Little’s Index. Little’s Index and a modified tooth mass 59 arch length discrepancy were shown to have a strong, positive correlation. Conclusions: The differences found within each group were all less than 0.5mm. There are no significant differences in the effectiveness of bonded canine-to-canine retainers bonded to each tooth and the MagneTainer®™. Little’s Index and a modified tooth mass arch length discrepancy are both good measures of initial crowding for this sample 60 Introduction Retention is considered by many practitioners to be one of the most difficult aspects of orthodontic treatment. Oppenheim actually referred to retention not just as a problem in orthodontics but as the problem in orthodontics.1 Natural changes to the dental arches that occur during ageing and maturation are known to contribute to the problem of post-treatment relapse, particularly decreases to arch length and intercanine width.2, 3 These changes have been shown to occur in both treated and untreated individuals4-6, some studies have even shown that decreases in arch length and intercanine width are worse for those who have undergone orthodontic treatment.6 The lower anterior teeth have been shown to be the most prone to relapse with many studies showing 40% to 90% of patients treated orthodontically to have unacceptable incisor alignment 10 years after treatment.6, 8, 11-13 These studies led Little to conclude that the only way to ensure long-term stability would be lifetime retainer wear.11 In a recent survey of retention methods of members of the American Association of Orthodontists, a trend towards more bonded, and fewer Hawley retainers was seen.7 One of 61 the main advantages of bonded retainers is that patient compliance is reduced. Blechman and Smiley were the first to use magnets to move teeth.14 Beginning in the late 1980s and continuing into the early 1990s, many magnetic appliances with a wide variety of applications have been developed. Magnets have been used to distalize, intrude, extrude, align, and even retrieve impacted teeth.15-28 Magnets have also been used for orthopedic correction of both Class II and Class III malocclusion.29-34 Magnetic appliances exert continuous forces that can be measured and do not decay over time, have reduced friction, and can exert their force through bone and mucosa.35-37 Studies have shown that both magnets themselves and the magnetic fields they produce are effective and safe for use intra-orally as long as the magnets are isolated from the intra-oral environment by either being coated or encased in a protective covering.38-47 A new retentive appliance known as the MagneTainer®™ is being developed by Gene and Aron Dellinger of Fort Wayne Indiana. It is a fixed, magnetic retainer made from 10 neodymium iron boron magnets bonded from the mesial of the lower canine to the mesial of the contralateral canine. 62 This unique design allows the retainer to function as a bonded retainer with the added ability to floss the teeth between the magnets. The purpose of this study is to determine the efficacy of the MagneTainer®™ magnetic retainer as compared to other canine-to-canine bonded retainers that are bonded to each tooth. Materials and Methods Sample For this study, two samples were gathered. The first sample was acquired from patients consecutively treated by Dr. Aron Dellinger of Fort Wayne Indiana. These patients had the MagneTainer®™ placed at the time of orthodontic appliance removal. Digital study models acquired using an iTero® (Align Technology, Inc., San Jose California) intraoral scanner were taken at initiation of treatment, appliance removal, and two years post-retainer placement were gathered. This sample consisted of 44 patients. The second sample was acquired from patients treated at the Saint Louis University Center for Advanced Dental Education (Saint Louis, Missouri). These patients all had bonded canine-to-canine retainers where each tooth was bonded placed at the time of orthodontic appliance removal. 63 Study models from initiation of orthodontic treatment, appliance removal, and two years post-retainer placement were digitized using the 3Shape® R700 desktop scanner (3Shape A/S, Copenhagen, Denmark). This sample consisted of 44 patients. Exclusion criteria included spacing at initiation of treatment, extractions, and incomplete or inadequate records. After applying exclusion criteria, six patients were excluded from the MagneTainer®™ group, and three were excluded from the bonded retainer group. Technique for Measurement of Digital Models Because the samples were acquired in different ways, different software was required to analyze the digital models. The MagneTainer®™ sample was analyzed using OrthoCAD® software (Align Technology, Inc., San Jose California)and the bonded retainer sample was analyzed using OrthoAnalyzer® software from 3Shape® (3Shape A/S, Copenhagen, Denmark). Although the software differed, the same measurements were made for each individual in the sample. For each time point (start, debond, 2 years postretainer placement) Little’s Irregularity Index and intercanine width were measured (see figures 3.1 and 3.2). 64 Figure 3.1 Little’s Irregularity Index and Intercanine width measured using OrthoAnalyzer® software from 3Shape® (3Shape A/S, Copenhagen, Denmark) Figure 3.2 Little’s Irregularity Index and Intercanine Width measured using OrthoCAD® (Align Technology, Inc., San Jose California) software. 65 A modified tooth mass arch length discrepancy was also measured at each time point. The widths of the anterior teeth were measured and summed yielding the tooth mass of the anterior teeth. The arch length was measured from the distal one canine to the distal of the contralateral canine. The difference between the anterior tooth mass and anterior arch length was then calculated. Error Study Five patients were randomly selected from each sample to be re-measured. All variables in both samples had intraclass correlation values of 0.85 or above. Statistical Analysis Paired t-tests were run using SPSS® software (IBM Corporation, Armonk, New York). Tests were run to determine any differences between and within groups initially, at appliance placement and two-years post appliance placement. Pearson’s correlation coefficients were also measured to determine the relationship, if any between Little’s Irregularity Index, intercanine width, and the modified tooth mass arch length discrepancy. 66 Results Bonded Retainer Sample Table 3.1 shows descriptive statistics for the bonded retainer sample. Statistical analysis via paired t-tests within the bonded retainer group showed significant differences for Little’s Irregularity Index at debond compared to Little’s Irregularity Index at two years. Significant differences were also found between the modified tooth mass arch length discrepancy at debond and two years post-retainer placement (see table 3.2). Table 3.1 Mean, median, standard deviation, and variance for the bonded retainer sample. (LI=Little’s Index, ICW=Intercanine width, Space=Modified tooth mass arch length discrepancy) Mean Initial LI Debond LI LI Difference from Initial 2 Year LI LI Difference from Debond LI 2Yr difference from Initial Initial ICW Debond ICW ICW Difference from Initial ICW 2Yr ICW 2Yr Difference From Initial ICW 2Yr Difference from Debond Initial Space Debond Space Debond Space Diff. From Initial 2Yr Space 2Yr Space Difference from Initial 2Yr Space Difference from Debond Median 6.15 0.56 5.61 0.90 0.41 5.24 25.45 26.96 1.95 26.70 1.71 0.40 -2.69 -0.45 3.08 -0.67 2.78 0.34 67 5.00 0.46 4.75 0.63 0.29 4.48 25.35 27.08 1.79 26.97 1.5 0.29 -2.5 -0.36 2.77 -0.70 2.62 0.31 Standard Deviation 4.16 0.36 4.09 0.56 0.38 4.11 1.64 1.51 1.26 1.42 1.05 0.40 2.87 0.43 2.04 0.45 2.04 0.25 Variance 17.29 0.13 16.79 0.31 0.14 16.86 2.68 2.29 1.58 2.01 1.09 0.16 8.23 0.19 4.17 0.21 4.16 0.06 The mean initial Little’s Irregularity Index for the bonded retainer sample was 6.15mm with mean initial intercanine width of 25.45mm. The modified tooth mass arch length discrepancy showed an average -2.69mm of space deficiency prior to treatment. After orthodontic treatment the Little’s Index was reduced to an average of 0.56mm, the intercanine width was expanded an average of 1.51mm. The modified tooth mass arch length discrepancy showed an average of -0.45mm of space at debond. Two years post-retainer placement, the Little’s Irregularity to changed 0.9mm, this was a change of 0.34mm. The intercanine width relapsed an average of 0.4mm and the modified tooth mass arch length discrepancy showed an average 0.34mm of space loss. Table 3.2 Paired t-tests for Little’s Irregularity Index at debond and two years postretainer placement as well as modified tooth mass arch length discrepancy at debond and 2 years post-retainer placement. Both tests were significant with a p-value of 0.05 Mean LI Debond LI 2Yr Space Debond Space 2Yr 0.56 0.90 -0.45 -0.67 Standard Deviation 0.36 0.56 0.43 0.45 Mean Difference 0.56 0.90 -0.45 -0.67 t-value 10.02 10.41 -6.57 -9.49 Significance 0.00 0.00 0.00 0.00 The changes to both Little’s Irregularity Index space measured via the modified tooth mass arch length were shown to be significant. 68 The mean change in Little’s Index was 0.34mm. It must be remembered that the Little’s Index measures discrepancy between all contact points from the mesial of one canine to the contralateral canine. Thus, this change of 0.34mm is distributed among the contact points of all six anterior teeth. The mean change in space was 0.23mm. This means that on average, 0.23mm of space loss was seen at two years post-retainer placement. As with the Little’s Index, this space loss is distributed among all six anterior teeth. Pearson’s correlation coefficients were calculated for Little’s Index, intercanine width, and the modified tooth mass arch length discrepancy to see if any relationship existed between these variables. The results of these tests can be found in table 3.3 Table 3.3 Pearson’s correlation for initial Little’s Index to initial intercanine width, intercanine width change to Little’s Index at two years, and initial Little’s Index to initial space measured via a modified tooth mass arch length discrepancy Correlation Coefficient Significance (2-tailed) -0.317 0.044 0.451 0.003 -0.831 0.000 LI initial to ICW initial ICW change from 2yrs to debond to LI at 2yrs Initial LI to initial space 69 A statistically significant correlation was found between initial Little’s Index and initial intercanine width. These variables show a negative, moderate correlation. As intercanine width decreases, there is a moderate correlation to a larger Irregularity Index. Change in intercanine width was shown to correlate moderately to Little’s Index at two years post-retainer placement. As intercanine width changes, the Irregularity Index gets larger. A strong, negative correlation was shown between initial space as measured by the modified tooth mass arch length discrepancy and initial Little’s Index. This is expected, as the amount of available space in the arch decreases, more crowding is expected and a larger Irregularity Index should be expected as well. The degree of this correlation also shows that the modified tooth mass arch length discrepancy and Little’s Irregularity Index agree as to the amount of crowding of the anterior teeth. MagneTainer®™ Sample Table 3.4 shows descriptive statistics for the bonded MagneTainer®™ sample. Statistical analysis via paired ttests within the MagneTainer®™ group showed significant 70 differences for Little’s Irregularity Index at debond compared to Little’s Irregularity Index at two years. Significant differences were also found between the modified tooth mass arch length discrepancy at debond and two years post-retainer placement (see table 3.5). Table 3.4 Mean, median, standard deviation, and variance for the MagneTainer®™ sample. (LI=Little’s Index, ICW=Intercanine width, Space=Modified tooth mass arch length discrepancy) Initial LI Debond LI LI Difference from Initial 2 Year LI LI Difference from Debond LI 2Yr difference from Initial Initial ICW Debond ICW ICW Difference from Initial ICW 2Yr ICW 2Yr Difference From Initial ICW 2Yr Difference from Debond Initial Space Debond Space Debond Space Diff. From Initial 2Yr Space 2Yr Space Difference from Initial 2Yr Space Difference from Debond Mean Median 6.62 0.71 5.98 0.87 0.28 5.76 26.55 28.72 2.31 28.25 1.97 0.62 -1.63 -0.45 2.07 -0.97 2.14 0.59 6.05 0.55 5.25 0.80 0.20 5.05 26.40 28.75 1.95 28.00 1.65 0.50 -1.30 -0.40 1.40 -0.80 1.30 0.40 Standard Deviation Variance 4.33 0.65 4.21 0.49 0.27 4.27 2.39 1.63 1.73 1.66 1.64 0.60 2.64 0.41 1.89 0.96 1.93 0.90 18.70 0.42 17.69 0.245 0.08 18.22 5.76 2.64 2.98 2.81 2.69 0.36 6.99 0.17 3.60 0.92 3.71 0.81 The mean initial Little’s Irregularity Index for the MagneTainer®™ sample was 6.62mm with mean initial intercanine width of 26.55mm. The modified tooth mass arch length discrepancy showed an average -1.63mm of space deficiency prior to treatment. After orthodontic treatment the Little’s Index was reduced to an average of 0.71mm, the intercanine width was 71 expanded an average of 2.31mm. The modified tooth mass arch length discrepancy showed an average of -0.45mm of space at debond. Two years post-retainer placement, the Little’s Irregularity changed to 0.87mm, this was a change of 0.16mm. The intercanine width relapsed an average of 0.62mm and the modified tooth mass arch length discrepancy showed an average 0.59mm of space loss. Table 3.5 Paired T-tests for Little’s Irregularity Index at debond and two years postretainer placement as well as modified tooth mass arch length discrepancy and debond and 2 years post-retainer placement for the MagneTainer®™ group. Both tests were significant with a p-value of 0.05 Mean Standard Mean t-value Significance Deviation Difference LI Debond LI 2Yr Space Debond Space 2Yr 0.71 0.87 -0.44 0.64 0.49 0.41 0.71 0.87 -0.44 6.77 10.85 -6.66 0.00 0.00 0.00 -0.92 1.02 -0.92 -5.47 0.00 The changes to both Little’s Irregularity Index space measured via the modified tooth mass arch length were shown to be significant. The mean change in Little’s Index was 0.16mm. It must be remembered that the Little’s Index measures discrepancy between all contact points from the mesial of one canine to the contralateral canine. Thus, this change of 0.16mm is distributed among the contact points off all six anterior teeth. 72 On average, 0.48mm of space loss was seen at two years post-retainer placement. As with the Little’s Index, this space loss is distributed among all six anterior teeth. Pearson’s correlation coefficients were calculated for Little’s Index, intercanine width, and the modified tooth mass arch length discrepancy to see if any relationship existed between these variables. The results of these tests can be found in table 3.6 Table 3.6 Pearson’s correlation for initial Little’s Index to initial intercanine width and initial Little’s Index to initial space measured via a modified tooth mass arch length discrepancy Correlation Coefficient Significance (2-tailed) LI initial to ICW initial Initial LI to initial space -0.37 0.023 -0.480 0.002 A significant correlation was found between initial Little’s Index and initial intercanine width. These variables show a negative, moderate correlation. As intercanine width decreases, there is a moderate correlation to a larger Irregularity Index. A moderate, negative correlation was shown between initial space and initial Little’s Index. The degree of this correlation was not as large as for the bonded retainer group. 73 Findings Between the Two Samples Paired t-tests were run comparing each variable from the bonded retainer sample to the MagneTainer®™ sample to see if any statistical differences existed. Significant differences were found for initial intercanine width, intercanine width at debond, and change in intercanine width at two years vs. debond (see table 3.7) Table 3.7 paired t-tests for the significant differences between groups. ICW=intercanine width. Mean Standard Deviation t-value Significance Bonded Retainer Initial ICW 25.30 1.46 -2.60 0.01 MagneTainer®™ Initial ICW 26.55 2.39 -2.60 0.01 Bonded Retainer Debond ICW 26.94 1.56 -4.21 0.00 MagneTainer®™ Debond ICW 27.72 1.63 -4.21 0.00 Bonded Retainer ICW change 0.39 0.40 -2.59 0.014 0.62 0.60 -2.59 0.014 From Debond to 2yrs MagneTainer®™ ICW change From Debond to 2yrs The MagneTainer®™ group initial intercanine width was, on average 1.25mm larger than the bonded retainer group. The average expansion of the mandibular canines was 0.64mm for the bonded retainer group and 1.17mm for the MagneTainer®™ group. The average intercanine relapse at two years post-retainer placement was 0.39mm for the bonded retainer group and 0.62mm for the MagneTainer®™ group. No significant differences were found for Little’s Index or 74 modified tooth mass arch length discrepancy at any time point. Discussion While significant differences for Little’s Irregularity Index and a modified tooth mass arch length discrepancy were seen within the groups, no such differences were found between the groups. The differences that were found within the groups were all <0.5mm. The significant differences between the groups that were found were all related to intercanine width. The MagneTainer®™ sample had, on average, a larger intercanine width than the bonded retainer sample. The MagneTainer®™ sample’s intercanine width was also expanded more than the bonded retainer group. This did not translate into significant differences in Little’s Index or space discrepancy at debond or at two years. As has been mentioned previously, both intercanine width and arch length are known to decrease with time. Following both samples for a longer period of time may yield different results than are presently available from this relatively short-term study. Correlation coefficients among the variables within each group show expected results in terms of intercanine width and available space. As the intercanine width 75 decreased, less space was available and the Little’s Irregularity Index was higher. A correlation was also seen between Little’s Irregularity Index and the modified tooth mass arch length discrepancy, this was strongly correlated for the bonded retainer group and moderately correlated for the MagneTainer®™ group. This shows that these two measures agree in showing the amount of crowding present initially. For the bonded retainer sample, a correlation was also seen for the change in intercanine width at two years post-retainer placement compared to intercanine width at debond and the Little’s Irregularity Index. The purpose of this study was to determine if the MagneTainer®™ was as effective as a canine-to-canine bonded retainer that is bonded to each tooth. In terms of Little’s Irregularity Index and a modified tooth mass arch length discrepancy, we must fail to reject the null-hypothesis that there is a difference in effectiveness between the MagneTainer®™ and canine-to-canine retainers that are bonded to each tooth. Conclusions 1. There is no difference in effectiveness of a canineto-canine retainer bonded to each tooth and the MagneTainer®™ at two years post-retainer placement, 76 2. Little’s Irregularity Index and a modified tooth mass arch length discrepancy agree in terms of measuring initial crowding, and 3. 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Bulletin of the Hospital for Joint Diseases Orthopaedic Institute. 1980; 81-7. 46. Papadopulos M HI, Gerber B, Rahn B, Rakosi T. Biologic effects of static magnetic fields on osteoblast cells in culture. Eur J Orthod. 1990; 490. 47. Blechman AM. Comments on static magnetic fields. Am J Orthod Dentofacial Orthop. 1991; 18A-20A. 82 VITA AUCTORIS Adam Armstrong was born in Bountiful, Utah on April 4th, 1980 and has an older brother and sister as well as a younger brother and sister. Adam attended Brigham Young University and graduated with a Bachelor of Science in Nutritional Science in 2006. Adam continued his education as a member of the inaugural class of Midwestern University’s College of Dental Medicine earning his DMD in 2012. He began his orthodontic training in the spring of 2012 at Saint Louis University. Adam has been married to his wife Megan since 2003 and they have four children together. Adam will graduate from Saint Louis University in December 2014 completing his Masters of Science in Dental Medicine. Upon graduation, Adam will return to Arizona with his family and join a private orthodontic practice in Phoenix, Arizona. 83