THREE-DIMENSIONAL EVALUATION OF IMPLANT-SUPPORTED RAPID MAXILLARY EXPANSION VS. TRADITIONAL TOOTH-BORNE RAPID MAXILLARY EXPANSION USING CONE-BEAM

Transcription

1 THREE-DIMENSIONAL EVALUATION OF IMPLANT-SUPPORTED RAPID MAXILLARY EXPANSION VS. TRADITIONAL TOOTH-BORNE RAPID MAXILLARY EXPANSION USING CONE-BEAM COMPUTED TOMOGRAPHY Mary Ellen Helmkamp, D.D.S. An Abstract Presented to the Graduate Faculty of St. Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry (Research) 2012

2 Abstract Introduction: Transverse maxillary deficiency is a common problem among patients seeking orthodontic care and rapid maxillary expansion (RME) is one of the most frequent methods used by orthodontists to treat this problem. With the advent of orthodontic mini-screw implants, new appliances have been developed that use the palatal bone rather than the teeth as anchorage for the expansion appliance. Purpose: The purpose of this study is to evaluate the skeletal and dental effects of rapid maxillary expansion in the transverse plane using two different expansion appliances: a traditional tooth-supported Hyrax expander versus an implantsupported rapid maxillary expansion appliance. Materials and Methods: A sample of 11 patients who have been treated with an implant-supported RME and 18 patients who have been treated with a Hyrax RME were utilized for this study. CBCT scans were taken before treatment (T1) and immediately following full activation of the expansion appliances (T2). Defined landmarks were located on the pre- and post-treatment orientated images. Changes in pre- and post-treatment measurements were noted and differences between the two treatment groups were evaluated using the Mann-Whitney U test and independent samples t-test. Results: RME produced an increase in all the maxillary transverse dimensions at the skeletal, alveolar, and dental levels for both the implant-supported and tooth-borne Hyrax RME groups. Significant differences (p <0.05) in treatment changes were found at two parameters: maxillary base width at the level of the premolar and left premolar angulation. For both treatment groups, there was less expansion at the skeletal level than the dental level. Conclusions: Both groups showed similar results with greater expansion occurring at the dental level than skeletal level. Crown expansion was greatest followed by alveolar expansion and sutural expansion. Implant-supported RME may serve as a non-surgical alternative to traditional tooth-borne RME when anchorage to the teeth is 1

3 undesirable or unavailable. Further studies are needed to evaluate treatment differences between implant-supported expansion appliances and tooth-borne rapid maxillary expanders. 2

4 THREE DIMENSIONAL EVALUATION OF IMPLANT-SUPPORTED RAPID MAXILLARY EXPANSION VS. TRADITIONAL TOOTH-BORNE RAPID MAXILLARY EXPANSION USING CONE-BEAM COMPUTED TOMOGRAPHY Mary Ellen Helmkamp, D.D.S. A Thesis Presented to the Graduate Faculty of St. Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry (Research) 2012

5 COMMITTEE IN CHARGE OF CANDIDACY: Professor Rolf G. Behrents, Chairperson and Advisor Professor Eustaquio A. Araujo Professor Donald R. Oliver i

6 Dedication I dedicate this to my loving family, especially my parents. They have encouraged, supported and helped me every step of the way. They instilled in me the desire to dream big, work hard, and always give my very best in everything I do. I feel grateful to have such an amazing family. ii

7 Acknowledgements I would like to acknowledge a number of individuals for their contributions to this thesis. Dr. Kim for introducing me to the implant-supported rapid maxillary expander and all the advice and encouragement he gave to me along the way. Dr. Behrents for making me look at things from different and new perspectives and for helping me with organization. Dr. Araujo for his constant encouragement and advice through the entire process. Dr. Oliver for his analytical eye and attention to detail. Heidi Israel for her help in statistical analysis. iii

8 TABLE OF CONTENTS List of Tables... v List of Figures... vi CHAPTER 1: INTRODUCTION... 1 CHAPTER 2: REVIEW OF LITERATURE Growth and Development of the Maxilla... 4 Etiology of Transverse Maxillary Deficiency... 5 History of Rapid Maxillary Expansion... 7 Biomechanical Basis of Rapid Maxillary Expansion... 9 Expansion Appliances Skeletal and Dental Effects of Rapid Maxillary Expansion Bone-anchored Rapid Maxillary Expansion Summary and Statement of Thesis References CHAPTER 3: JOURNAL ARTICLE Abstract Introduction Materials and Methods Patient Selection Imaging Landmark Selection Statistics Results Discussion Conclusions References Vita Auctoris iv

9 List of Tables Table 3.1: Landmarks for transverse maxillary evaluation Table 3.2: Parameters measured for transverse maxillary evaluation Table 3.3: Comparison of maxillary transverse dimensions at T Table 3.4: Comparison of maxillary transverse dimensions at T Table 3.5: Comparison of the mean changes in maxillary transverse dimension from T1-T Table 3.6: Percentages of skeletal, alveolar, and dental expansion for both groups v

10 List of Figures Figure 3.1: Figure 3.2: Figure 3.3: Implant-supported RME design with four mini-screw implants and lingual wire extensions Implant-supported RME design with four mini-screw implants and no lingual wire extensions Implant-supported RME design with two mini-screw implants and lingual wire extensions Figure 3.4: Tooth-borne Hyrax RME Figure 3.5: Cone-beam computed tomography image orientation Figure 3.6: Figure 3.7: Cone-beam computed tomography coronal slice at the molar level with landmarks Cone-beam computed tomography coronal slice at the premolar level with landmarks vi

11 CHAPTER 1: INTRODUCTION Transverse maxillary deficiency is a common problem among patients seeking orthodontics care. It is characterized by a narrow maxilla in relation to the rest of the craniofacial structures, a narrow palatal vault, and often a posterior crossbite. According to a recent epidemiological study, the prevalence of some form of posterior crossbite in the primary dentition is 20.81%. 1 A long history of palatal expansion as a way to treat crossbites, anteroposterior discrepancies, dental crowding, and airway issues has made it a common treatment modality in most orthodontic practices today. The etiologies of transverse maxillary deficiency are numerous. It can be due to both genetic and environmental factors, soft tissue influences, cleft palate, low tongue position, CIII anteroposterior skeletal discrepancies, and habits. 2 Rapid maxillary expansion (RME) is one of the most frequent methods used by orthodontics to treat this problem. RME is based on the concept of widening the dental arch by means of opening the midpalatal suture. The concept dates back to 1860 when Angell described rapid expansion in a paper to the dental community. Since its origin, the concept of rapid maxillary expansion has been used to increase nasal permeability, correct posterior crossbites, and increase arch perimeter to relieve crowding and tooth size-arch length discrepancies. RME uses orthopedic forces to separate the two halves of the maxilla at the mid-palatal suture. 3 This is accomplished with an expansion screw that is anchored to the maxillary teeth and is typically activated 0.5 to 1 mm per day. Studies have reported various amounts of dental and skeletal expansion that occur with RME, but it is postulated that RME produces expansion that is 50% dental and 50% skeletal. 4 It is often the goal of orthodontists to maximize skeletal expansion and minimize dental expansion 1

12 in order to prevent unwanted negative side effects. Disadvantages that have been identified with traditional tooth-borne expansion appliances include limited skeletal movement, undesirable tooth movement and dental tipping, root resorption, dehiscence, and relapse. Because of these disadvantages alternative methods have been developed including implant-supported rapid maxillary expanders. These appliances anchor the expansion screw directly to the palatal bone rather than using the teeth as anchorage for the device. Skeletal anchorage devices have been successfully used in the past and include palatal distracters, implant-supported Hyrax screws, and bone anchors for maxillary protraction. 5 Only a limited number of studies have been published that test the differences between traditional tooth-borne expansion appliances versus bone-anchored expansion appliances though. Of the studies published, many have used distraction or surgically-assisted rapid maxillary expansion protocols which involve a more invasive surgical procedure for the patient. Studies using either a bone-anchored hyrax expansion screw with surgically-assisted expansion or palatal distraction have been done to compare the effects of these appliances with tooth-anchored expansion appliances. Cortese et al. found that after expansion with a palatal distractor device, there was minimal tipping of the teeth and that the main movement was of the maxillary segments themselves. 6 Likewise, studies evaluating the effects of surgically assisted expansion using bone-borne implant supported expansion appliances show minimal dental tipping, greater expansion at the level of the alveolar process than the tooth crown, suggesting greater skeletal expansion than dental expansion. 7-8 Harzer et al. found 10 degrees less molar tipping than toothsupported expansion in their study looking at the effects of direct fixation of the expansion screw to the palatal bone for RME. 9 All of these studies involved surgically-assisted expansion. 2

13 On the contrary, Lagravère et al. used cone-beam computed tomography to evaluate bone-anchored versus traditional rapid maxillary expansion in adolescents. Unlike the previous studies, Lagravère et al. concluded that the skeletal and dental changes for both groups were similar. 10 Recently, hybrid appliances using mini-implant and tooth-borne RME have been introduced as well. These appliances are cited as having the advantage of being less invasive than traditional bone-borne expansion devices that involve surgical involvement while providing the benefit of less buccal tooth tipping associated with tooth-borne expansion appliances Despite the varying conclusions that have been made in the literature regarding the differences between bone-anchored and tooth-borne rapid maxillary expansion, little research has been done evaluating implant-supported RME versus tooth-borne RME without the use of surgically assisted expansion or distraction. The purpose of this study is to use CBCT to evaluate and compare the skeletal and dental changes in the transverse dimension following rapid maxillary expansion with an implantsupported expansion appliance versus a tooth-born expansion appliance. Additionally, suture opening, alveolar expansion, tooth expansion and tooth angulation changes will be evaluated. 3

14 CHAPTER 2: REVIEW OF THE LITERATURE Growth and Development of the Maxilla In order to better understand the etiology of transverse maxillary deficiency, one should first understand the normal growth and development of the maxilla, particularly transverse growth and development. The bones of the maxilla develop entirely through intramembranous ossification. Growth occurs either by apposition of bone at the sutures or surface remodeling. 4 Growth of the soft tissues translates the maxillary complex downward and forward as bone fills in the space opened at the posterior and superior sutures. This downward and forward growth of the maxilla is accompanied by a corresponding resorption of the anterior surfaces of the maxilla by surface remodeling. 4 The midpalatal suture develops at about 12 weeks in utero and growth was originally thought to cease at around 3 years of age. 13 Latham s study of histological specimens ranging in age from 16 weeks in utero to 15 years of age, notes that although sutural growth stopped early, fusion had not occurred in any of his specimens. Growth rates in the transverse, vertical and horizontal planes vary depending on age. According to a study by Snodell et al., at the age of 6 the transverse dimension had a greater percentage of adult size than vertical measurement for males and females. 14 The transverse dimension is the first to reach adult size, followed by sagittal and vertical. Because of this fact, questions as to when the suture fuses and growth is complete becomes of importance in treatment planning. It is known that the midpalatal suture does not fuse until somewhere between the ages of years on average and even older in some cases. Bjork found that age 17 was the average age in which the median suture fused. 15 Melsen found growth of the suture of the maxilla to fuse at age 16 years in females and 18 years 4

15 in males, while Snodell et al. found that transverse growth was completed for the majority of females at age 15 and 17 years for males. 14 This is important in the timing of rapid maxillary expansion treatment, as it is expected to be successful in patients that have not reached the age in which their midpalatal suture has fused. Implant studies by Bjork and Skieller state that growth in the median suture is the most important factor in growth in the width of the maxilla. Their studies show that in general the two maxillae rotate in relation to each other in the traverse plane during development, while at the same time the maxilla shifts forward in the sagittal plane and rotates, forward or backward, in the vertical plane. From ages 10 to adulthood, the width of bilateral implants increased.9 mm in the anterior region and 3.0 mm in the posterior region. This indicates a greater amount of transverse growth posteriorly than anteriorly. 15 Similar findings were found by Korn and Baumrind in their implant study on transverse development of the human jaws between ages 8.5 and 15.5 years. They concluded that transverse widening was greater in the more posterior part of the palate and found annual growth rates that closely corresponded to the rates found by Bjork and Skieller. 16 Gandini and Buschang s study using metallic implants found maxillary width increases that were 0.1 mm/yr less than previous studies. The authors attributed this difference to the growth potential of their treatment groups which were 14 years of age at the initiation of treatment. 17 Etiology of Transverse Maxillary Deficiency Transverse maxillary deficiency is characterized by a narrow maxilla in relation to the rest of the craniofacial structures, a narrow palatal vault and often the presence of a unilateral or 5

16 bilateral posterior crossbite or dental crowding. Both posterior crossbite and dental crowding are some of the easily recognizable signs of maxillary deficiency. Estimates of the percentage of children and adolescents exhibiting a posterior crossbite vary in the literature. The Division of Health Statistics of the U.S. Public Health Service estimated the prevalence of various malocclusions in a large scale survey in Proffit notes that this survey (NHANES III) found the prevalence of posterior crossbite among all races, genders, and age to be 9.1% of the U.S. population. 4 This is similar to Helm s estimate of the prevalence of unilateral or bilateral crossbites in 9.4% of boys and 14.1% of girls. 18 Others have estimated anywhere from 1.0% to 23.5% of children as having a posterior crossbite in the primary dentition. 1 According to a more recent epidemiologic study by da Silva et al., 20.81% of children have some form of posterior crossbite in the primary dentition. 1 Despite the variation over the exact incidence of posterior crossbites, orthodontists are routinely confronted with the challenge of correcting a transverse maxillary deficiency and etiology is an important consideration in treatment planning. Posterior crossbites can be dental or skeletal in origin or a combination of both. Likewise, the discrepancy may originate in the maxilla or the mandible or a little of both. Haas makes an important point in distinguishing true maxillary deficiency from relative maxillary deficiency. Relative maxillary deficiency occurs when the maxilla is the correct size compared with the upper face, but the mandible is too large resulting in a posterior crossbite. On the other hand, true maxillary deficiency is characterized by a small maxilla and constriction of the buccal tooth segments, indicating a true undersized maxilla A narrow maxilla can be due to genetic or environmental factors or a combination of both. 2 Possible causes include cleft palate, soft tissue influences, true skeletal transverse discrepancy between the maxilla and mandible, non-nutritive sucking habits, open mouth 6

17 posture, low tongue position, Class III anteroposterior skeletal discrepancies, and abnormal function. 2 Treatment is individualized based on the nature of the discrepancy, etiology, and skeletal maturity of the patient. History of Rapid Maxillary Expansion The concept of widening the dental arch by means of opening the midpalatal suture dates back to 1860 when Angell described rapid expansion of the upper arch in a paper he presented to the dental community. In the first issue of Dental Cosmos in 1860, he wrote of an apparatus that at the end of two weeks, the jaw was so widened as to leave a space between the front incisors, showing conclusively that the maxillary bones had been separated. 21 This concept of splitting the suture to expand the maxilla flourished during the early 1900s. These years have been referred to as the maxillary expansion years by both orthodontists and rhinologists. It was during this time that rhinologist Brown, as well as many others, promoted maxillary expansion for the purpose of increasing nasal permeability and obtaining greater nasal width Pfaff supported this concept with the opinion that expansion of the dental arch lowered the palatal vault and induced straightening of the nasal septum. 24 Indications for RME are widespread in the literature. These include lateral discrepancies resulting in unilateral or bilateral crossbites, anteroposterior discrepancies, cleft lip and palate and to gain arch length. Rapid maxillary expansion as a means of increasing arch width and perimeter became a popular area of investigation resulting in numerous clinical and animal studies on the subject in the mid-1900s. Cleall et al. 25 published a paper indicating that strong expansion forces applied to the maxilla of a growing Macaca rhesus monkey resulted in the 7

18 breakdown of the midpalatal suture and eventual restoration of normal sutural morphology. Likewise, Haas pig study indicated that the midpalatal suture could indeed be opened to a degree sufficient to cause a widening of the dental arch and an increase in intranasal capacity. 23 In the same publication, Haas clinical study described the direction of opening of the suture, effect on the surrounding structures and the corresponding buccal inclination of the mandibular teeth. In the 1950s, following Bjork s protocol, Krebs implant studies showed an increase in dental arch width that was about half of the basal maxillary segments and noted rotation of the maxillary segments in the frontal plane. 26 Haas became one of the leaders in research regarding palatal expansion at that time and wrote numerous articles on the effects of palatal expansion. In an article in 1970, Haas noted the specific skeletal effects of rapid palatal including a triangular pattern of opening with the apex being in the nasal cavity. 27 He also noted that the procedure produced forward and downward movement of the maxilla and downward and backward rotation of the mandible. 27 Many other authors have verified the finding that rapid maxillary expansion causes the palatal shelves to rotate upon opening resulting in the rotation of the palatal processes, alveolar processes and teeth around the midpalatal suture. 28 Starnbach elaborated on this concept by looking at the effects of rapid maxillary expansion on the entire craniofacial skeleton and the dental changes that resulted, noting that not only do changes in the midpalatal suture occur but histologic changes are also seen in the zygomaticomaxillary suture and the zygomaticotemporal sutures as well. 28 Rapid maxillary expansion has also been used to alleviate tooth size-arch length discrepancies as an alternative to extractions, providing additional space in the arch to relieve crowding. With rapid maxillary expansion, studies show an increase in arch perimeter of 8

19 4-4.7 mm in maxilla and 2.5 mm in the mandible According to Adkins et al., RME with Hyrax appliances produce an increase in maxillary arch perimeter at the rate of approximately 0.7 times the change in first premolar width. 29 Biomechanical Basis of Rapid Maxillary Expansion Bell summed up the mechanics of rapid maxillary expansion simply when he reported, If the applied transverse forces are of sufficient magnitude to overcome the bioelastic strength of the sutural elements, orthopedic separation of the maxillary segments can occur. 31 This is the basis of rapid maxillary expansion. At the same time, expansion appliances compress the periodontal ligament, bend the alveolar processes, tip the anchor teeth, and gradually open the midpalatal suture when the forces exceed the limits needed for orthodontic tooth movement. 32 Typically, rapid maxillary expansion is done with a jackscrew at the rate of mm per day, while slow maxillary expansion is done at a rate of 1 mm per week. According to Isaacson, a single activation of the expansion screw produces 3-10 pounds of force, with a smaller load being produced per activation in younger patients as compared with more mature patients. 3 The midpalatal suture becomes more interdigitated with age and therefore heavier forces are needed to overcome the partially interlocked suture in older adolescents and adults. These forces decay rapidly following activation, but the rate of decay decreases within several minutes. 3 Active expansion usually takes place for 2-3 weeks followed by 3-6 months of the appliance being left in place as the suture reorganizes. According to Isaacson, the main resistance to rapid maxillary expansion is not just the midpalatal suture but the other maxillary articulations. 3 The maxilla articulates with ten other 9

20 bones in the face and cranium and resistance to midpalatal suture opening is partly due to this, especially the zygomatic and sphenoid bones. 32 In order to minimize dental tipping and get a more linear opening of the midpalatal suture, the rigidity of both the expansion screw and wires joining it to the teeth should be as high as possible. Braun discusses the fact that the moments induced by the dentomaxillary centers of resistance and the moment-to-force ratios at the centers of resistance are reduced as the rigidity of the appliance is increased. 33 For this reason Braun advises against using an acrylic interface with the teeth as this is less stiff than stainless steel wires. Expansion Appliances The rationale behind rapid maxillary expansion is that the orthopedic forces exerted by the expansion appliance can, up to a certain age, open the midpalatal suture and widen the palate. Although it has been documented that expansion appliances in some form or another have been used since the 1860s, regular use of the appliance did not become popular until Haas introduced his expansion appliance in the 1950s. The Haas expander consists of a metal framework with an expansion screw in the palatal vault, bands on the first molars and premolars, an acrylic pad on the palatal tissue and buccal soldered bars as well to maximize anchorage and promote suture opening. 27 According to Haas, the split acrylic palatal appliance is superior in that the orthopedic force is resisted by the inclined walls of the palatal vault, alveolar process, and teeth resulting in less tooth movement and a more orthopedic movement than other expansion appliances that do not have an acrylic pad on the palatal shelves

21 An alternative to the Haas appliance is the hygienic or Hyrax expander developed by Biederman. This appliance was developed in response to the soft tissue irritation often seen with the Haas appliance. 34 The Hygienic appliance consists of four orthodontic bands placed on the maxillary first molars and premolars with a expansion screw in the middle of the palate and a.040 buccal wire connecting the molar to the premolar bands on the buccal side of the teeth. Like the Haas appliance, activation is two turns per day and a retention period of 3 months. According to Biederman, the main advantages of the hygienic appliance are patient comfort, easier hygiene, and prevention of lesions to the palatal mucosa. The Haas and Hyrax expansion appliances are the most widely used and studied appliances. The main difference is simply the presence or absence of the acrylic pad which some say has a large effect of the amount of skeletal versus dental expansion that is achieved. Garib et al. performed a study evaluating the differences between the two appliances by means of computed tomography (CT). They concluded that both appliances produced significant increases in all transverse dimensions with a decreasing upward expanding effect. 35 It was determined that both appliances produced similar orthopedic effects, while the tooth-tissue borne expander produced a greater change in the axial inclination of the supporting teeth especially the premolars. 35 More recently, expansion appliances have been developed that use mini-screw implants to secure the expansion screw directly to the palate, reducing the forces being placed directly on the teeth. Obviously this form of RPE, has been developed in an effort to maximize skeletal expansion and minimize dental tipping. The idea of avoiding direct forces on the teeth in order to maximize the orthopedic effect is the basis of bone-anchored rapid maxillary expanders, although appliance designs can vary greatly. Palatal distractors have been developed as an 11

22 alternative to tooth-borne expansion appliances as well. 7-8, Some of the first appliances to utilize this concept were variations of palatal distracters to expand the palate in adult patients after surgical osteotomy. Cortese developed an appliance consisting of four 8 mm mini-screw implants that secure 2 titanium miniplates and a titanium jackscrew to the palate. 6 Likewise, Lagrevère used a bone-anchored maxillary expander that consisted of an expansion screw and 2 stainless steel onplants secured to the palate by 2 mini-screw implants. 10 Likewise, hybrid appliances utilizing mini-screw implants and tooth-borne RME have been developed as well These more recent alternatives to the traditional tooth-borne appliances could serve as possible future replacements for the Haas and Hyrax appliances if the orthopedic effects of these appliances prove to be superior. Skeletal and Dental Effects of Rapid Maxillary Expansion The exact dental and skeletal effects of rapid maxillary expansion have been studied extensively and, although skeletal expansion is the goal of treatment, a significant amount of dental expansion occurs as well. Because of the difficulty in comparing samples that have large variations in age, size, retention protocol, and the amount of expansion accomplished, clinical studies have reported varying amounts of skeletal versus dental expansion. Proffit notes that the expansion achieved with RME is 50% skeletal and 50% dental. This is supported by numerous studies including Podessor s evaluation of the effects of RME in growing children using computed tomography. This study found actual skeletal expansion to vary from 25% to 53% of the total expansion. 18 Chung and Font found that 9.7% of the first premolar expansion and 4.3% of the first molar expansion was due to buccal crown tipping. 38 In a study by Ghoneima et al 12

23 using CT to evaluate changes with RME, they concluded that although significant increases occur in most dental and skeletal measurements, dental tipping explained most of the expansion. 39 Skeletally, RME separates the midpalatal suture as the two halves of the palate rotate laterally forming a triangular or wedge shaped pattern of opening. The widest areas of expansion are located anteriorly from an occlusal view and apically from a frontal view ,27-28,33,40-41 Numerous studies have found the center of rotation for the maxilla in the area of the frontonasal suture. 22,27,33 It is thought that the two palatal halves rotate around a point located near the frontonasal suture. 22 With RME, the maxilla moves in a forward and downward direction and the mandible is thought to move downward and backward, opening the mandibular plane 22, 38,42 angle. Arch perimeter gains can be attributed to rapid maxillary expansion as well. Geran et al. notes a significant increase in arch perimeter in the maxilla and mandible compared to controls. 30 Dentally, there is buccal movement of the posterior teeth and alveolar processes. Because the appliance is anchored to the teeth, buccal tipping of the dentition is one of the most common and undesirable side effects of RME. Schiffman and Tuncay published a meta-analysis that summarized the long term changes documented in the maxillary expansion literature from The results of their metaanalysis gave an average immediate expansion of 6.0 mm which relapsed to 4.71 mm after short term retainer wear, then further reduced to 3.88 mm after the retention period. In the long term, expansion was only 2.4 mm. Their conclusion was that this amount was no greater than documented with normal growth and no useful expansion beyond normal growth is achieved in the long term

24 In a separate meta-analysis by Lagravère et al. in 2006, the immediate changes with rapid maxillary expansion were looked at. Immediate dental changes in the transverse dimension included an increase of mm in maxillary intermolar width, 5.35 mm increase in intercanine width, and a 3.1 degree increase in intermolar angulation. 44 The mandibular intermolar width increase was only.49 mm and was not statistically significant. Skeletally, the nasal cavity width increased 2.14 mm and the left and right jugale width increased 2.73 mm. Overall, the greatest dental and skeletal changes occurred in the transverse dimension. On average, 6.7 mm of expansion was noted as measured between the maxillary molar crowns, while 4.5 mm of expansion was noted at the maxillary molar root apexes supporting the claim that RME using tooth-anchored appliances will cause tipping of the teeth. The average tipping of the teeth was 3 degrees. 44 Additionally, significant skeletal increases for maxillary interalveolar width measured from the buccal plates increased 2-3 mm, showing a large portion of the true expansion must be dental rather than skeletal. In a systematic review published by Lagravère et al. in 2005, the long-term dental arch effects of rapid maxillary expansion were evaluated and the following conclusions were made. Rapid maxillary expansion resulted in a significant long-term maxillary molar width increase as well as consistent maxillary cuspid arch width expansion of mm. Less mandibular molar and cuspid expansion was attained in adults compared to children and significant gains in arch perimeter of 6mm in the maxilla and 4.5 mm in the mandible were attained in adolescents, and no anteroposterior or vertical changes were associated with RME. 45 Recently, studies utilizing cone-beam computed tomography (CBCT) rather than two dimensional radiographs to evaluate the skeletal and dental effects of RME have become more abundant. Garrett et al evaluated the skeletal and dental effects of the maxilla after RME using 14

25 CBCT. These authors found that orthopedic or skeletal expansion accounted for 55% of the total expansion at the first premolar, 45% at the second premolar, and 38% at the first molar. Alveolar tipping accounted for 6% at the first premolar, 9% at the second premolar, and 13% at the first molar. Dental tipping accounted for 39% of the expansion at the first premolar, 46% at the second premolar, and 49% at the first molar. Alveolar and dental tipping were greater posteriorly than anteriorly. 40 On the contrary, Kartalian et al. used CBCT and found no statistically significant amount of relative dental tipping, but did find significant alveolar tipping as compared to controls. 46 The angle of the alveolus significantly increased on average by approximately 5 degrees in the RME group, while the alveolar angulation of the control groups decreased by an average of 2.84 degrees. This study found no changes in relative dental tipping as the teeth remained relatively constant in their angulation, while previous studies found dental tipping changes anywhere from 2.5 to 6 degrees. 44,47 Furthermore, the author notes that the posterior teeth actually moved in a slightly lingual direction due to denture uprighting after the expansion. While there is significant literature on the skeletal and dental effects of RME, the exact values and percentages of skeletal and dental changes vary greatly. This is due to a number of factors that make comparing samples and studies difficult, including variations in expansion appliance design, activation protocol and methods of assessing the expansion. Bone-anchored Rapid Maxillary Expansion Traditional tooth-borne expansion appliances have been effectively used for decades to correct transverse maxillary deficiencies, yet this treatment is not without negative side effects. 15

26 Disadvantages have been identified with traditional tooth-borne expansion appliances including limited skeletal movement, undesirable tooth movement, root resorption, dehiscence, a decrease 5,10, in the thickness of the buccal cortical plate and relapse. Because of these disadvantages, alternative methods have been developed including the implant-supported rapid maxillary expander. These appliances anchor the expansion screw directly to the palatal bone, avoiding direct tooth contact. Likewise, bone-anchored expansion appliances may be indicated when a patient has missing or compromised posterior permanent teeth and periodontal concerns, providing an alternative when traditional RME cannot be used. Skeletal anchorage devices have been successfully applied in patients in the past. These include palatal distracters for rapid palatal expansion, implant-supported Hyrax screw for RME and bone anchors for maxillary protraction. 5 To date, only a limited number of studies have been published that test the differences between traditional tooth-borne expansion appliances versus bone-anchored expansion appliances. Many of these studies used distraction or surgically assisted expansion protocols involving slightly more invasive surgical procedures. Cortese et al. used a palatal distractor device to treat severe maxillary constriction in adult patients who were to undergo surgically assisted rapid maxillary expansion. 6 The palatal distractor device was made of a titanium expansion, 2 titanium miniplates and four mini-screw implants. The procedure involved general anesthesia for a Le Fort I-type osteotomy and separation of the palate at the median line and results were evaluated using computed tomography (CT). Expansion averaged 5.1 mm at the canines, 4.5 mm at the first premolars, and 3.7 mm at the molars. The authors noted that the angular changes in the frontal plane were minimal with a maximum change of 0.8 or less at the palatal molar cusp level, suggesting that the main movement involved rotation of the maxillary segments and not the teeth themselves. 16

27 Lagravère et al. used CBCT to evaluate the transverse, vertical, and anteroposterior changes associated with bone-anchored and traditional rapid maxillary expansion in adolescents. 10 The experimental group (bone-anchored maxillary expander) consisted of an appliance with two custom-milled onplants and 2 mini-screw implants (12 x 1.5 mm) to secure the expansion appliance directly to the palatal bone. This required the reflection of the periosteum and a second surgery to remove the appliance after treatment. Long term and short term changes were evaluated and the authors found that immediately after completion of appliance activation, the skeletal and dental changes for both treatment groups were similar. The primary difference was the there was greater expansion at the maxillary first premolars in the tooth-anchored maxillary expander group. Furthermore, root apex expansion was less than crown expansion for both the bone-anchored maxillary expander group and the tooth-anchored maxillary expander subjects, resulting in significant buccal crown inclination. 10 The results of this study indicate that tooth-anchored expansion appliances and bone-anchored expansion appliances produce similar results. Tausche et al. evaluated three-dimensional changes in dental, alveolar, and skeletal structures caused by a bone-borne implant supported rapid maxillary expander device (Dresden distractor) using CT. The authors found an average increase in the transverse dimension at the alveolar bone to be 7.52 mm in the premolar region and 7.17 mm in the molar region, noting that these were greater skeletal increases than previous studies using tooth-borne expanders. 7 There was.8 mm more expansion in the premolar region and.73 mm more in the molar region as measured at the alveolar bone than at the teeth. Stated more simply, the teeth tipped 6 degrees to 9 degrees less than the alveolar process. This suggests that the tooth crowns expanded less than 17

28 the alveolar bone, most likely due to application of direct force to the bone and the torque effect of the brackets. 7 Hansen et al. conducted a similar study with the aim of carrying out a three-dimensional analysis of the teeth, alveolar, and skeletal structures during bone-borne, surgically-assisted rapid maxillary expansion. CT showed a transverse expansion of 5.55 mm in the alveolar process of the premolar region and 4.87 mm in the molar region. Width increases were 6.07 mm in the premolar region and 5.71 mm in the molar region. Buccal tipping of the teeth was minimal, only degrees in the premolars and degrees in the molar region. Like Tausche et al. concluded, this is most likely due to the direct transfer of expansion forces to the bone and the torque of the brackets. 8 Harzer et al. published a pilot study of two females treated hyrax expansion screws with palatal anchorage. Bilateral osteotomy and splitting of the midpalatal suture was performed under general anesthesia and the hyrax expansions screw was directly fixed on one side with a titanium implant and on the other side with an osteosynthesis screw. The authors concluded that direct fixation of the hyrax expansion screw at the palatal bone for RME was an effective alternative to tooth-supported appliances and had 10 degrees less molar tipping than toothsupported expansion. 9 Advantages of implant-supported rapid maxillary expansion appear to be less dental tipping and more skeletal expansion, shorter treatment times, increased anchorage for expansion, and less periodontal effects. Varying conclusions have been made regarding the claim of the superiority of implant-supported RME versus traditional tooth-borne RME though and future 18

29 studies on the subject are indicated, especially with regard to bone-borne non-surgically assisted RME. Summary and Statement of Thesis Rapid maxillary expansion has been successfully used to treat transverse maxillary deficiencies by orthodontists for many years and researchers have been trying to quantify the exact dental and skeletal effects of this treatment. Although effective in correcting posterior crossbites and relieving dental crowding due to arch length discrepancies, undesirable side effects have been noted with both tooth and tissue-borne RME treatments. These include limited skeletal expansion, buccal crown tipping, undesirable tooth movements, and root resorption. Because of these side effects, alternatives to the traditional Haas or Hyrax tooth-borne appliances have been introduced, particularly the implant-supported RME. Implant-supported rapid maxillary expanders differ from the Hyrax expander in that the appliance does not have anchorage on the teeth. The goal is to decrease dental and alveolar tipping, root resorption, and dehiscence while increasing the orthopedic effect. Little research has been done comparing the effects of these two appliances without the use of surgical intervention. The purpose of this study is to use CBCT images to compare and contrast the skeletal and dental changes that occur in the transverse dimension following rapid maxillary expansion with these two appliances. Additionally, suture opening, alveolar bending, and molar and premolar angulation changes will be evaluated. 19

30 References 1. da Silva Filho OG, Santamaria M Jr, Capelozza Filho L. Epidemiology of posterior crossbite in the primary dentition. J Clin Pediatr Dent. 2007;32(1): Malandris M, Mahoney EK. Aetiology, diagnosis and treatment of posterior cross-bites in the primary dentition. Int J Paediatr Dent May;14(3): Isaacson RJ, Ingram A. Forces produced by rapid maxillary expansion II. Forces present during treatment. Angle Orthod Oct;34(4): Proffit WR, Henry W. Fields, Jr. Contemporary Orthodontics. Third. Mosby, Inc Wehrbein H, Göllner P. Skeletal anchorage in orthodontics--basics and clinical application. J Orofac Orthop Nov;68(6): Cortese A, Savastano M, Savastano G, Papa F, Howard CM, Claudio PP. Maxillary constriction treated by a new palatal distractor device: surgical and occlusal evaluations of 10 patients. J Craniofac Surg Mar;21(2): Tausche E, Hansen L, Hietschold V, Lagravère MO, Harzer W. Three-dimensional evaluation of surgically assisted implant bone-borne rapid maxillary expansion: a pilot study. Am J Orthod Dentofacial Orthop Apr;131(4 Suppl):S Hansen L, Tausche E, Hietschold V, Hotan T, Lagravère M, Harzer W. Skeletally-anchored rapid maxillary expansion using the Dresden Distractor. J Orofac Orthop Mar;68(2): Harzer W, Schneider M, Gedrange T. Rapid maxillary expansion with palatal anchorage of the hyrax expansion screw--pilot study with case presentation. J Orofac Orthop Sep;65(5): Lagravère MO, Carey J, Heo G, Toogood RW, Major PW. Transverse, vertical, and anteroposterior changes from bone-anchored maxillary expansion vs traditional rapid maxillary expansion: a randomized clinical trial. Am J Orthod Dentofacial Orthop Mar;137(3):304.e1 12; discussion Wilmes B, Nienkemper M, Drescher D. Application and effectiveness of a mini-implant- and tooth-borne rapid palatal expansion device: the hybrid hyrax. World J Orthod. 2010;11(4): Lee K-J, Park Y-C, Park J-Y, Hwang W-S. Miniscrew-assisted nonsurgical palatal expansion before orthognathic surgery for a patient with severe mandibular prognathism. Am J Orthod Dentofacial Orthop Jun;137(6): Latham RA. The development, structure and growth pattern of the human mid-palatal suture. J. Anat Jan;108(Pt 1):

31 14. Snodell SF, Nanda RS, Currier GF. A longitudinal cephalometric study of transverse and vertical craniofacial growth. Am J Orthod Dentofacial Orthop Nov;104(5): Björk A, Skieller V. Growth of the maxilla in three dimensions as revealed radiographically by the implant method. Br J Orthod Apr;4(2): Korn EL, Baumrind S. Transverse development of the human jaws between the ages of 8.5 and 15.5 years, studied longitudinally with use of implants. J. Dent. Res Jun;69(6): Gandini LG Jr, Buschang PH. Maxillary and mandibular width changes studied using metallic implants. Am J Orthod Dentofacial Orthop Jan;117(1): Podesser B, Williams S, Crismani AG, Bantleon H-P. Evaluation of the effects of rapid maxillary expansion in growing children using computer tomography scanning: a pilot study. Eur J Orthod Feb;29(1): Haas AJ. Long-term posttreatment evaluation of rapid palatal expansion. Angle Orthod Jul;50(3): Haas AJ. The treatment of maxillary deficiency by opening the midpalatal suture. Angle Orthod Jul;35: Angell EH. Treatment irregularities of the permanent or adult dentition. Dental Cosmos. 1860;1: Wertz RA. Skeletal and dental changes accompanying rapid midpalatal suture opening. Am J Orthod Jul;58(1): Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening of the midpalatal suture. Angle Orthod. 1961;31: Pfaff W. Stenosis of the nasal cavity caused by contraction of the palatal arch and abnormal position of the teeth: Treatment by expansion of the maxilla. Dental Cosmos. 1905;47: Cleall JF, Bayne DI, Posen JM, Subtelny JD. Expansion of the midpalatal suture in the monkey. Angle Orthod Jan;35: Krebs A. Expansion of the midpalatal suture studied by means of metallic implants. European Orthodontic Society Rep. 1958;34: Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. Am J Orthod Mar;57(3): Starnbach H, Bayne D, Cleall J, Subtelny JD. Facioskeletal and dental changes resulting from rapid maxillary expansion. Angle Orthod Apr;36(2):

32 29. Adkins MD, Nanda RS, Currier GF. Arch perimeter changes on rapid palatal expansion. Am J Orthod Dentofacial Orthop Mar;97(3): Geran RG, McNamara JA Jr, Baccetti T, Franchi L, Shapiro LM. A prospective long-term study on the effects of rapid maxillary expansion in the early mixed dentition. Am J Orthod Dentofacial Orthop May;129(5): Bell RA. A review of maxillary expansion in relation to rate of expansion and patient s age. Am J Orthod Jan;81(1): Bishara SE, Staley RN. Maxillary expansion: clinical implications. Am J Orthod Dentofacial Orthop Jan;91(1): Braun S, Bottrel JA, Lee KG, Lunazzi JJ, Legan HL. The biomechanics of rapid maxillary sutural expansion. Am J Orthod Dentofacial Orthop Sep;118(3): Biederman W. A hygienic appliance for rapid expansion. J Pract Orthod Feb;2(2): Garib DG, Henriques JFC, Janson G, Freitas MR, Coelho RA. Rapid maxillary expansion-- tooth tissue-borne versus tooth-borne expanders: a computed tomography evaluation of dentoskeletal effects. Angle Orthod Jul;75(4): Ramieri GA, Spada MC, Austa M, Bianchi SD, Berrone S. Transverse maxillary distraction with a bone-anchored appliance: dento-periodontal effects and clinical and radiological results. Int J Oral Maxillofac Surg Jun;34(4): Gerlach KL, Zahl C. Transversal palatal expansion using a palatal distractor. J Orofac Orthop Nov;64(6): Chung C-H, Font B. Skeletal and dental changes in the sagittal, vertical, and transverse dimensions after rapid palatal expansion. Am J Orthod Dentofacial Orthop Nov;126(5): Ghoneima A, Abdel-Fattah E, Eraso F, Fardo D, Kula K, Hartsfield J. Skeletal and dental changes after rapid maxillary expansion: a computed tomography study. Aust Orthod J Nov;26(2): Garrett BJ, Caruso JM, Rungcharassaeng K, Farrage JR, Kim JS, Taylor GD. Skeletal effects to the maxilla after rapid maxillary expansion assessed with cone-beam computed tomography. Am J Orthod Dentofacial Orthop Jul;134(1): da Silva Filho OG, Montes LA, Torelly LF. Rapid maxillary expansion in the deciduous and mixed dentition evaluated through posteroanterior cephalometric analysis. Am J Orthod Dentofacial Orthop Mar;107(3): Davis WM, Kronman JH. Anatomical changes induced by splitting of the midpalatal suture. Angle Orthod Apr;39(2):

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34 CHAPTER 3: JOURNAL ARTICLE Abstract Introduction: Transverse maxillary deficiency is a common problem among patients seeking orthodontic care and rapid maxillary expansion (RME) is one of the most frequent methods used by orthodontists to treat this problem. With the advent of orthodontic mini-screw implants, new appliances have been developed that use the palatal bone rather than the teeth as anchorage for the expansion appliance. Purpose: The purpose of this study is to evaluate the skeletal and dental effects of rapid maxillary expansion in the transverse plane using two different expansion appliances: a traditional tooth-supported Hyrax expander versus an implantsupported rapid maxillary expansion appliance. Materials and Methods: A sample of 11 patients who have been treated with an implant-supported RME and 18 patients who have been treated with a Hyrax RME were utilized for this study. CBCT scans were taken before treatment (T1) and immediately following full activation of the expansion appliances (T2). Defined landmarks were located on the pre- and post-treatment orientated images. Changes in pre- and post-treatment measurements were noted and differences between the two treatment groups were evaluated using the Mann-Whitney U test and independent samples t test. Results: RME produced an increase in all the maxillary transverse dimensions at the skeletal, alveolar, and dental levels for both the implant-supported and tooth-borne Hyrax RME groups. Significant differences (p <0.05) in treatment changes were found at two parameters: maxillary base width at the level of the premolar and left premolar angulation. For both treatment groups, there was less expansion at the skeletal level than the dental level. Crown expansion was greatest followed by alveolar expansion and sutural expansion. Conclusions: Both groups showed similar results with greater expansion occurring at the dental level than skeletal level. Implant-supported RME may 24