LONG-TERM STABILITY IN THE MAXILLARY AND MANDIBULAR ARCH DIMENSIONS USING RAPID PALATAL EXPANSION AND EDGEWISE MECHANOTHERAPY IN GROWING PATIENTS

Transcription

1 LONG-TERM STABILITY IN THE MAXILLARY AND MANDIBULAR ARCH DIMENSIONS USING RAPID PALATAL EXPANSION AND EDGEWISE MECHANOTHERAPY IN GROWING PATIENTS Renee Elizabeth Doyle, D.M.D. An Abstract Presented to the Graduate Faculty of Saint Louis University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Dentistry 2012

2 ABSTRACT Introduction: While the likelihood of adolescent upper arch expansion with a RPE appliance is not questioned, the amount of long-term expansion remaining after treatment is very important. Recent technological advances have allowed the generation of digital dental models from plaster casts that can be saved and viewed three-dimensionally on a computer. With the advent of such technology, digital dental models of RPE treated cases can potentially be measured with greater control and accuracy to evaluate morphologic changes over time. Purpose: The purpose of this study is to use the R700 in-office laser model scanner and OrthoAnalyzer software (3Shape, Copenhagen, Denmark) to assess the long-term stability of rapid palatal expansion followed by fixed edgewise appliances. Materials and Methods: The sample of this retrospective study consisted of 67 patients (53 females, 14 males) with an average pretreatment age of 12 years and 3 months. All patients were treated with a Haas-type RPE and nonextraction edgewise appliance therapy in a single orthodontic practice. Serial dental casts were available at three different time points: pretreatment (T 1 ), after expansion and fixed appliance therapy (T 2 ), and at long-term 1

3 recall (T 3 ). The mean duration of the T 1 -T 2 and T 2 -T 3 periods was 4 years 10 months and 11 years 0 months, respectively. The dental casts were digitized with the R700 in-office model scanner and the computed measurements were compared with untreated reference data. Results: The majority of treatment increases in the maxillary and mandibular arches were statistically significant (P <.05) and greater than expected for untreated controls. Although many measurements decreased postretention (T 2 -T 3 ), net gains persisted for all of the measurements evaluated. Conclusions: Based on the long-term stability observed in this study, it was concluded that the use of RPE therapy followed by full fixed appliances is an effective method for increasing maxillary and mandibular arch width dimensions in the growing patient. 2

4 LONG-TERM STABILITY IN THE MAXILLARY AND MANDIBULAR ARCH DIMENSIONS USING RAPID PALATAL EXPANSION AND EDGEWISE MECHANOTHERAPY IN GROWING PATIENTS Renee Elizabeth Doyle, 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 2012

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

6 DEDICATION This thesis is dedicated to my husband and parents who have supported and guided me through all my years of education. To my amazing husband, Steve, from high school to residency, you have been with me every step of the way. Your love, support, and unwavering patience have made this journey possible. To my parents, your inspiration, guidance, and willingness to put your children first have made me the person I am today. ii

7 ACKNOWLEDGEMENTS I would like to acknowledge a number of individuals for their contributions to this thesis. Dr. Araujo for his thesis topic inspiration, patience, and support. Dr. Behrents for his guidance and wisdom. Dr. Oliver for his analytical eye and attention to detail. Heidi Israel for her help in statistical analysis. Dr. Andrew Haas and his assistant, Irene Williams, for allowing the use of the treated records and for going above and beyond in the records collection process. Dr. Carla Evans, Dr. Budi Kusnoto, and UIC dental assistant, Ayas Abood, for also allowing the use of treated records and aiding in the records collection process. iii

8 TABLE OF CONTENTS List of Tables...v List of Figures...vi CHAPTER 1: INTRODUCTION...1 CHAPTER 2: REVIEW OF THE LITERATURE History of Maxillary Expansion...2 Biology of Expansion...3 Indications for Expansion...5 Skeletal Effects Accompanying RPE...8 Dental Effects Accompanying RPE...11 Treatment Timing...16 Long-term Stability...17 Normal Occlusal Development...21 Data Acquisition with the R Summary and Statement of Thesis...24 References...26 CHAPTER 3: JOURNAL ARTICLE Abstract...30 Introduction...32 Materials and Methods...33 Subjects...33 Data Collection...34 Landmark Acquisition...35 Measurements...37 Error of Method...38 Statistical Analysis...38 Results...39 Maxillary Arch...39 Mandibular Arch...43 Discussion...44 Conclusions...48 References...49 Vita Auctoris...50 iv

9 LIST OF TABLES Table 2.1: Table 3.1: Table 3.2: Table 3.3: Reported long-term arch width changes...18 Maxillary and mandibular arch width (lingual and centroid) changes...41 Age- and sex-specific z scores based on established reference data...42 Arch width measurement comparison...45 v

10 LIST OF FIGURES Figure 2.1: Figure 2.2: Figure 2.3: Figure 2.4: Figure 3.1: Figure 3.2: Figure 3.3: Figure 3.4: Reaction of central incisors to RPE...12 Dental Effects of RPE...14 Box-plots of Lima s Variables...20 Location of the centroid D dental models displayed by OrthoAnalyzer software...35 Location of digitized points...36 Location of the centroid...36 Computation of arch width (from lingual point)...37 Figure 3.5: Computation of tooth centroid...37 Figure 3.6: Treatment and posttreatment changes in maxillary and mandibular arches...42 vi

11 CHAPTER 1: INTRODUCTION Transverse maxillary deficiency is a common problem among adolescents and rapid palatal expansion (RPE) is one of the most common procedures used by orthodontists to correct this discrepancy. 1 While the likelihood of upper arch expansion with a RPE appliance is not questioned in an adolescent, the amount of long-term expansion remaining after treatment is very important. Many studies have evaluated the stability of RPE by using various techniques ranging from manual measurement of dental casts 2 to plane film radiographic techniques 3,4 to digital imaging. 5 However, more sophisticated techniques for evaluating morphological changes in the dentofacial complex have been developed. The advent of the surface laser scanner and companion software has made it possible to capture 3D images of plaster casts and thus offer greater control and accuracy in measurement. The purpose of this study is to use the R700 in-office laser model scanner and OrthoAnalyzer software (3Shape, Copenhagen, Denmark) to assess the long-term stability of the maxillary and mandibular arch dimensions following rapid palatal expansion and edgewise mechanotherapy. 1

12 CHAPTER 2: REVIEW OF THE LITERATURE History of Maxillary Expansion The dawn of rapid palatal expansion dates back to 1860 with Angell cited as the founding father. In an article published by the prestigious Dental Cosmos, Angell demonstrated palatal expansion with a double action jack screw on a 14 year old female patient. Angell s treatment observations led him to claim that he had indeed separated the maxilla along the midpalatal suture. His claim, however, was perceived with much resistance as many disputed the validity and ability of maxillary separation. Because of this disagreement, the use of rapid palatal expansion was all but abandoned by the early 1900s. 6 It was not until the advent of radiology that RPE reemerged in the United States. In 1956, a German scientist by the name of Korkhaus visited the department of orthodontics at the University of Illinois. It was his cephalometric records of cases treated with RPE that provoked the curiosity of colleagues such as, Brodie and Haas, and ultimately reintroduced RPE to the country. 7 Haas popularized the RPE procedure with his 1958 animal study. The study reported that: (1) The procedure 2

13 was apparently pain free. (2) The midpalatal suture offered little resistance to spreading. Suture openings of 15mm in two weeks were recorded. (3) The mandibular teeth, without treatment, uprighted in response to altered forces of occlusion and change in muscle balance. (4) Internasal width was increased. 7 Over the years, extensive research and clinical results have further proven RPE to be an effective method for increasing the transverse dimension. It is a common treatment modality used in practice today. Biology of Expansion In 1956, Pritchard et al. were one of the first to give much needed attention to the underlying histological structure and development of the craniofacial sutures. They stated, It is surprising, in view of the controversy which has long raged about the functional role of the sutures in the growth of the skull, that so little attention has been paid to their histological structure and development. Looking at serial sections in six species, including humans, the authors obtained more accurate and detailed information on the morphogenesis and function of the craniofacial sutures. Previous workers such as Sicher, Moss, and Scott, had described the various layers but Pritchard et al. claimed to be the first to recognize them 3

14 all. They also further defined the suture as, the entire complex of cellular and fibrous tissues intervening between, and surrounding, the definitive bone edges. 8 Up until 1965, there was some evidence to suggest that rapid expansion of the maxilla caused an opening of the midpalatal suture. Korkhaus, 9 Derichsweiler, 10 and Haas 7 reported that rapid palatal expansion is possible, and that widening of the nasal cavity does indeed take place. Krebs 11 and Thorne 12 reported similar changes and also discussed the possibility of relapse. However, at that point there was little understanding of the underlying sutural reactions that took place. Cleall et al. examined the histological changes of the midpalatal suture in rhesus monkeys. They found that the suture was disrupted very soon after the application of pressure. This disruption ultimately left a bony defect filled with disorganized fibrous connective tissue and irregularly-positioned spicules of bone. While evidence of tissue damage to the suture was obvious, the cellular reaction was both reparatory as well as osteoclastic. Overall, he concluded that the midpalatal suture was indeed opened and the resultant bony defect was rapidly filled by new bone, eventually returning to its normal form. 13 4

15 Until Melsen s report in 1972, all of the histological analysis had been confined to animal studies. The lack of basic knowledge of human suture closure had cast doubt on the reliability of animal experiments for clinical guidance. Melsen, using biopsies and radiography on children ages 8 to 13, looked at the effects of rapid expansion of the midpalatal suture. In all subjects, radiographic examination postexpansion revealed a midline radiolucent area approximately 3-4mm wide. After six weeks of healing, the suture was radiographically indistinguishable from its pretreatment appearance. Looking at the histology, Melsen found the treated subjects to have increased activity in the midpalatal suture after expansion. Osteoblast activity was primarily found along the bone surfaces, sometimes, however, on processes and islands in the middle of the suture. 14 Indications for Expansion Transverse maxillary deficiency could arguably be one of the most persistent skeletal problems in the craniofacial complex. It manifests itself in many forms, the most obvious being a unilateral or bilateral posterior crossbite. However, transverse maxillary deficiency can be present in the absence of crossbite. This is often seen in 5

16 cases with dental crowding. If the position of the maxillary dentition reflects the skeletal discrepancy, crossbite persists. However, if the maxillary constriction is concealed by the dentition and both arches are constricted, crowding in the absence of crossbite results. Crossbite and dental crowding are thus recognizable signs that could be the result of maxillary deficiency. Other effects of maxillary deficiency are less obvious, such as laterally flared posterior teeth that camouflage a crossbite. In such cases, the maxilla is narrow with an accentuated curve of Wilson. The lingual cusps of the upper posterior teeth are tipped below the occlusal plane, often leading to balancing interferences during function. 15 Certain types of sagittal malocclusion are often associated with maxillary transverse deficiency. One of the major possible components of the Class III malocclusion is maxillary skeletal retrusion, a condition that occurs in nearly half of all Class III patients. 16 Many clinicians use a protraction facemask following or simultaneously with palatal expansion, because there is evidence that suggests that expansion disrupts the cirucumaxillary sutural system, thus, making sagittal skeletal change more likely. 1 McNamara has found that in some mixed dentition patients 6

17 with only mild skeletal discrepancies, palatal expansion may lead to a spontaneous correction of an anterior crossbite and resolution of the Class III molar relationship. 17 Many Class II malocclusions, when evaluated clinically, have no obvious maxillary transverse constriction. However, when the patient is asked to posture into a Class I relationship, an edge-to-edge or crossbite relation is observed. Tollaro et al. have shown that a Class II patient with what appears to be a normal buccolingual relationship of the posterior dentition usually has a three to five millimeter transverse discrepancy between the maxilla and mandible. 18 According to McNamara, Class II malocclusions have a strong transverse component. In growing children, he advocates orthopedic expansion of the maxilla as the first step followed by a removable palatal plate for further stabilization. His clinical observations have revealed a spontaneous Class II correction during the first six to twelve months of the post-rpe period. 15 According to McNamara, overexpansion of the maxilla followed by a removable palatal plate disrupts the dentition. The patient is thus more inclined to posture his or her 7

18 mandible forward to reduce the buccal crossbite tendency. The sagittal relationship is improved and later mandibular growth presumably makes the initial postural change permanent. 15 In addition to correcting maxillary alveolar constriction, some clinicians have supported the expansion procedure as a means of improving nasal airway function. Using an oropharyngeal catheter, Hershey et al. measured the change in nasal airway resistance in subjects that required rapid palatal expansion for constricted maxillary dental arches. They found RPE to be an effective method for reducing nasal resistance from levels associated with mouth breathing to levels of compatible with normal respiration. This reduction in nasal resistance was noted to be stable through a three month period of retention. 19 Skeletal Effects Accompanying RPE The primary goal of rapid palatal expansion is to maximize skeletal effects and minimize orthodontic movements of the teeth. Thus, it is necessary to understand the skeletal changes that occur when an expander is utilized. Palatal expansion ultimately occurs when the force applied to the teeth and the maxillary alveolar process exceeds the limits needed for orthodontic tooth 8

19 movement. Upon activation, the appliance compresses the periodontal ligament, bends the alveolar processes, tips the anchor teeth, and gradually opens the suture. 20 Wertz, in his study of skeletal alterations brought about by midpalatal suture opening, noted that from an occlusal view the suture demonstrated a nonparallel opening. The majority of his cases showed the opening to be wider anteriorly. In fact, the ratio was 3:2 and sometimes 2:1 when measured at ANS and again at PNS. 3 The resistance of the zygomatic arch to opening forces applied inferiorly prevents parallel opening of the maxillary segments upon frontal view. A pyramid-shaped parting of the maxillary halves with the apex located at the frontomaxillary suture results. According to Wertz, this is a fortunate circumstance as pure parallel opening would move the frontal process of the maxilla bodily into the orbital cavity. 3 Many investigators have investigated the effect of expansion on the maxillary halves. In 1958, Krebs showed that the two halves of the maxilla rotated in both the sagittal and frontal planes. 11 Haas documented that when the midpalatal suture opens, the maxilla always moves forward and downward. This is most likely due to the 9

20 disposition of the maxillocranial sutures as they are oriented in a manner that growth would produce a downward and forward vector of movement. Haas further theorized that since the maxillocranial sutures are disengaged by the palatal expansion procedure, an effect similar to immediate growth is manifested in a downward and forward displacement of the maxilla. This movement of the maxilla is thus a disadvantage in Class II cases and an aid in Class III cases. 7 Wertz, in his cephalometric case studies, found that downward displacement of the maxilla was rather routine, but forward displacement to any degree was limited to isolated cases. He also documented that the final position of the maxilla, after completion of expansion, is unpredictable as only fifty percent of his cases maintained the downward displacement. 3 Rapid palatal expansion has also been reported to influence changes in the palatal height. As early as 1909, McCurdy stated that, The spreading of the maxilla causes the arch to drop down. 21 Several investigators agree with McCurdy including Haas who reported that, When the midpalatal suture opens, the alveolar processes appear to bend laterally while the palatal shelves drop inferiorly. 22 In 1969, Davis and Kronman studied the changes in palatal 10

21 contour by sectioning maxillary casts through the first molars and canines of patients treated with RPE. Their data contradicted the reports of other investigators as they found the roof of the vault to remain at the same height. 23 It is generally agreed that with RPE there is a concomitant tendency for the mandible to swing downward and backward. There is some disagreement regarding the magnitude and the permanency of the change. The increased lower face height observed during RPE has been explained by the disruption of occlusion caused by extrusion and tipping of the maxillary posterior teeth along with alveolar bending. As a guideline, RPE should be cautiously used on persons with steep mandibular planes and/or open bite tendencies. 20 Dental Effects Accompanying RPE From a patient s perspective, one of the most memorable changes accompanying RPE is the opening of a diastema between the maxillary central incisors. In a clinical study involving 45 private practice patients, Haas found the explanation of the central incisor reaction to be the most challenging. It was observed that the gap created between the incisors was half as great as the distance the 11

22 jackscrew had been opened. As seen in Figure 2.1, tracings revealed that the roots diverged a greater distance than the crowns upon active treatment. After expansion had ceased, the roots continued to diverge while the crowns tipped toward the midline. After the crowns drifted together, the roots began to move medially, resuming the initial axial inclination. The entire cycle was completed in four to six months time even with incisors spaced as much as eight millimeters after appliance manipulation. 24 The central incisor phenomenon was hypothesized to be a result of the elastic recoil of the transseptal fibers, a theory that is widely accepted by investigators today. Figure 2.1: Reaction of central incisors to RPE (adapted from Haas) 24 In addition to the elastic recoil of the transseptal fibers, Wertz found that the maxillary central incisors tend to be extruded relative to the S-N plane and in 76% of 12

23 the cases they upright or tip lingually. This movement, thought to be caused by the circumoral musculature, helps to close the diastema and also to shorten arch length. Prior to Wertz findings the pull of the transseptal fibers was thought to be the sole reasoning behind the return of the central incisors. He reported a combination of interseptal fiber reaction and change in the muscular tension to be responsible for movement of the incisors. 3 Another side effect of maxillary expansion is posterior dental tipping during the expansion phase (Figure 2.2). Isaacson and Zimring showed that expansion resistance of the midpalatal suture and circum-maxillary articulations cause microfractures within the buccal cortical plate before breakage of the suture. These microfractures result in buccal tipping and extrusion of the maxillary posterior teeth. Such side effects have been reported even when expansion devices have been placed deeply into the palatal vault, closer to the center of resistance. While studies vary on the final angular position of the dentition, they all agree that buccal tipping and extrusion of the anchor teeth is involved in RPE. 25 Asanza et al. reported frequent asymmetrical tipping of the respective abutment teeth. He found that most patients demonstrated a wide variation of 13

24 angular change from one side to another. 4 Hicks evaluated slow expansion appliances in young children and also found asymmetrical angular changes in the frontal plane. He attributed some of this tipping to the maxillary segments themselves and variation in rigidity of the skeletal architecture. 26 Figure 2.2: Dental Effects of RPE. Dental tipping and extrusion of lingual cusps of maxillary posterior teeth during RPE. Before bony movement, expansion forces create microfractures within the buccal cortical plate, leading to buccal tipping. The net result of RPE is (1) the opening of the midpalatal suture, (2) the buccal tipping of the two halves of the maxilla and posterior teeth, and (3)the extrusion of the lingual cusps. (Adapted from Majourau and Nanda) 27 While there is an abundance of material related to maxillary dental reactions, fewer studies to date have looked at the response of the mandibular teeth to RPE. Haas, in both animal and human studies, reported that the mandibular dental arch expanded in response to altered functional forces resulting from maxillary expansion. He stated that, The thickness of the expansion appliance 14

25 caused the tongue to be displaced totally into the confines of the mandibular arch; concurrently as the maxillae separated, the attached buccinator muscles also moved laterally away from the mandibular buccal teeth, hence the uprighting and expansion of the buccal teeth. 24,28 Wertz also investigated changes associated with RPE. He examined 48 patients that were followed over a three month period. Contrary to Haas 24,28 findings, his results showed that the mandibular intermolar width had the potential to expand, remain the same, or even constrict following RPE. The study advocated a longer observation period by stating, Although the majority of cases failed to demonstrate lower arch width gain, a longer study might be expected to disclose such a gain, as function of the overexpanded maxillary buccal segments would tend to upright the mandibular antagonists. 3 Gryson took note of the results and recommendations made in Wertz s 3 study. He attempted a longer term study which evaluated preexpansion, postexpansion and stabilization periods to assess mandibular arch dimension over the course of seven months. Gryson s results showed no correlation between the change in mandibular intercanine and intermolar distances with respect to the increase in maxillary intercanine and intermolar distances. From Gryson s study, it was 15

26 concluded that RPE could influence the mandibular dentition, but the concurrent changes are neither pronounced nor predictable. 29 Treatment Timing When evaluating the efficacy of rapid palatal expansion, age has been indicated as a contributing factor in treatment outcome. Available information related to the ideal time for treatment by means of an orthopedic device mainly consists of studies of the growth and maturation of the intermaxillary sutural system. Melsen used autopsy material to histologically examine the maturation of the midpalatal suture at different developmental stages. In the infantile stage (up to 10 years of age), the suture was broad and smooth, whereas in the juvenile stage (from 10 to 13 years) it had developed into a more typical squamous suture with overlapping sections. Finally, during the adolescent stage (13 to 14 years of age) the suture was wavier with increased interdigitation. 30 In their 1982 study, Melsen and Melsen also included observations of the adult stage of the suture that noted synostoses and numerous bony bridge formations across the suture. Their histological data implied that patients who show an advanced stage of skeletal maturation at the midpalatal 16

27 suture may have difficulty undergoing orthopedic maxillary expansion. 31 Wertz and Dreskin provided clinical support to Melsen s 30 histological data in their study of 56 cases from private practice members of the Foundation for Orthodontic Research. The ages within the sample ranged from 8 to 29 years which permitted observation of the orthopedic effect on adults. While maxillary expansion was observed in all 56 cases, the older patients (over 18) with more rigid skeletal components experienced little orthopedic change. Greater and more stable orthopedic changes were noted in the group of patients under the age of Long Term Stability Although the possibility of adolescent upper arch expansion with an RPE appliance is not questioned, the amount of long-term expansion remaining is very important for borderline extraction cases (Table 2.1). Moussa et al. analyzed the long-term stability of RPE and edgewise therapy. Arch width measurements were made directly on dental casts obtained at three time intervals: before treatment, after treatment, and after retention. Patients had been out of retention for approximately 8-10 years at a mean age of 30 years. Their findings suggested good stability for upper intercanine and upper/lower intermolar 17

28 widths. Lower intercanine widths presented with poor stability as retention measurements closely approximated those of pretreatment. 2 Table 2.1: Reported long-term arch width changes Canine width change Premolar width change Molar width change References Measurement T 2-T 1 T 3-T 2 T 3-T 1 T 2-T 1 T 3-T 2 T 3-T 1 T 2-T 1 T 3-T 2 T 3-T 1 Maxilla McNamara 5 Centroid Lingual Moussa 2 Cusp Tip Lima 33 Cusp Tip Lingual Mandible McNamara 5 Centroid Lingual Moussa 2 Cusp Tip Lima 33 Cusp Tip Lingual McNamara et al. conducted a similar study and they included an untreated control group that was matched in age, sex distribution, and duration of observation to compare dental arch changes. In the short term, after RPE and fixed appliance therapy, the treated group presented with significant changes in arch dimensions when compared to the control group. During the postretention period, some relapse was noted compared to the initial gain in arch dimension. However, when comparing the overall changes of the treated group to those of the untreated group, the 18

29 conclusion was that the treatment did provide an overall gain in arch dimension that was greater than the control. 5 One of the most current and controlled studies on mandibular arch response and stability following RPE is by Lima et al. The authors looked at the dental casts of 30 patients obtained longitudinally at four assessment stages spanning approximately 12.5 years. What is unique about the investigation is that all subjects were treated with a Haas-type RPE only during the early and mid mixed dentition, with no subsequent orthodontic intervention. The bar graphs in Figure 2.3 depict the results of the longterm evaluation from A1 through A

30 Intermolar Occlusal Point Intercanine Occlusal Point Arch Perimeter Intermolar Lingual Point Intercanine Lingaul Point Arch Length Figure 2.3: Box-plots of Lima s Variables. Measurements at preexpansion(a1), short-term follow-up (A2), progress (A3), and long-term followup(a4). (Lima et al.) 33 Results of the study showed that mandibular intermolar arch width increased significantly after rapid expansion. The increase was followed by a slight decrease of the occlusal value, however, the lingual value was maintained. Intercanine width (occlusal value) remained stable throughout all assessment stages. Overall, there was remarkable stability in intermolar width (lingual value) and intercanine width (occlusal value), indicating that the increase in mandibular arch width dimension was in response to RPE and was maintained until adulthood

31 Normal Occlusal Development In evaluating the effectiveness of treatment modalities, it is important to understand that dental arches and the facial skeleton are in a dynamic state throughout most of life. Understanding the location, magnitude and timing of these changes provides a baseline of comparison when assessing treatment modalities. In the 1930s, the University of Michigan conducted an extensive longitudinal growth study on untreated children ranging from 3 to 18 years of age. Physical growth data included dental casts and cephalometric radiographs in addition to standard non-craniofacial anthropologic data. 34 This data ultimately provided a sound reference to analyze outcomes of future treated groups. In measuring arch widths, Moyers et al. used the centroids of respective antimeres (Figure 2.4). In the past, dental arch width dimensions were measured by using certain cusp tips or points at the lingual cervical margin of the teeth as reference points. However, cusp tips wear off, vary in location and provide misleading information during the transition from primary molars to succeeding premolars. Points at the lingual cervical margin are affected by the buccolingual width of the tooth and its 21

32 level of eruption. Thus, the authors chose to use the tooth centroid to represent the real position of the crown and be independent of the location and abrasion of cusp tips. They found the centroids, more so than other tooth landmarks, to be sensitive to translative movements but insensitive to simple tipping of the crown, thus providing a sufficient reference for comparison. 34 Figure 2.4: Location of the centroid was found first by determining midpoint (A) of the line connection the mesial and distal landmarks. Similar midpoint (B) was constructed midway between buccal and lingual landmarks of the tooth. The centroid (C) was located between points A and B. (Adapted from Moyers et al.) 34 Moyers et al. found that the intercanine width mildly increases up to age 6, at which point, with the eruption of the permanent incisors, the canines move distally and laterally, and an increase occurs until the permanent canines are erupted. Following eruption of all of the permanent teeth, the intercanine width slightly decreases. 34 The maxillary intermolar width at the first molar shows a consistent increase, reaching up to 5-6mm in both 22

33 males and females from age 6 to 17, with the largest increase occurring within the first year of first molar eruption. The mandibular first molar width also increases from ages 6 to 17, although not as significantly as the maxillary molars, with an average increase during that time of 3-4mm. 34 Data Acquisition with the R700 For about two decades, orthodontists have been able to choose among several companies to digitize plaster models or impressions. Software allows users to view their models, conduct diagnostic analyses and measurements, present cases to patients and colleagues, and retrieve the virtual models at the click of a button. More recently, in-office scanners have allowed practices to create their own digital study models. Three types of systems are available: intraoral scanners, model scanners, and impression scanners. It is also possible to extract digital study models from cone-beam computed-tomography scans, although the radiation dosage needed to achieve a suitable level of detail may be excessive for clinical use. 35 The R700 (3Shape, Copenhagen, Denmark) is an inoffice model scanner with the added ability to scan impressions. It projects a laser line onto the surface of 23

34 the model or impression, and two high resolution chargecoupled-device cameras, one on either side of the laser, observe the profile of the line as it falls on the object. The laser and cameras sweep over the object, and the cameras take snapshots of the laser profile at predetermined spatial increments. Since it is not possible for the cameras to see every detail on the object from a single position, the object is rotated and tilted through several orientations, and the data acquired during each scan are aligned to produce a 3D digital representation. Data-quality checks compare the accuracy of points that have been captured by both cameras and either ignore or average the data points, as appropriate, for better accuracy. 35 Summary and Statement of Thesis Rapid palatal expansion first appeared in the dental literature when Angell introduced it to the dental community in Since then, much has been learned about the biology of the midpalatal suture, the concomitant skeletal and dental effects, and the various indications of palatal expansion in correcting a malocclusion. However, as its popularity in correcting transverse maxillary deficiency began to rise, so did interest in the long-term 24

35 stability of the procedure. Many studies have evaluated the long-term stability of RPE by using various measurement modalities such as photographic imaging, 5 radiographic imaging, 3,4 and direct model analysis. 2 However, a more sophisticated measurement technique has been developed that may provided greater insight into the morphological changes that occurs with RPE. The advent of the surface laser scanner and companion software has made it possible to generate 3D images from plaster casts and, through various viewing functions, offer greater accuracy and precision in measurement. The purpose of this study is to use the R700 in-office laser model scanner and companion OrthoAnalyzer software to assess the long-term arch width stability of rapid palatal expansion followed by fixed edgewise appliances. 25

36 References 1. Proffit WR, Fields HW, Sarver DM. Contemporary Orthodontics. 4th ed. St. Louis, MO: Mosby Elsevier, Moussa R, O Reilly MT, Close JM. Long-term stability of rapid palatal expander treatment and edgewise mechanotherapy. Am J Orthod. 1995;108: Wertz, RA. Skeletal and dental changes accompanying rapid midpalatal suture opening. Am J Orthod. 1970;58: Asanza S, Cisneros GJ, Nieberg LG. Comparison of hyrax and bonded expansion appliances. Angle Orthod. 1997;67: McNamara JA Jr, Baccetti T, Franchi L, Herberger TA. Rapid maxillary expansion followed by fixed appliances: a long-term evaluation of changes in arch dimensions. Angle Orthod. 2003;73: Timms DJ. The dawn of rapid maxillary expansion. Angle Orthod. 1999:69: Haas AJ. The treatment of maxillary deficiency by opening the midpalatal suture. Angle Orthod. 1965;35: Pritchard JJ, Scott JH, Girgis FG. The structure and development of cranial and facial sutures. J Anat. 1956;90: Korkhaus G. Discussion of report: a review of orthodontic research ( ). Internat D J. 1953;3: Derichsweiler H. La disjonction de la suture palatine mediane. Tr European Orthodont. Soc. 1953: Krebs A. Expansion of the midpalatal suture studied by means of metallic implants. Tr European Orthodont. Soc. 1958:

37 12. Thorne NH. Experiences of the midpalatal suture studied by means of metallic implants. European Orthodont Society Report on 32nd Congress. 1956: Cleall JF, Bayne DI, Posen JM, Subtelney JD. Expansion of the midpalatal suture in the monkey. Angle Orthod. 1965;35: Melsen B. A histological study of the influence of sutural morphology and skeletal maturation on rapid palatal expansion in children. Trans Eur Orthod Soc. 1972: McNamara JA. Maxillary transverse deficiency. Am J Orthod Dentofacial Orthop. 2000;117: Guyer EC, Ellis EE 3rd, McNamara JA Jr, Behrents RG. Components of Class III malocclusion in juveniles and adolescents. Angle Orthod. 1986;56: McNamara JA Jr. An orthopedic approach to the treatment of Class III malocclusion in young patients. J Clin Orthod. 1987;21: Tollaro I, Baccetti T, Franchi L, Tanasescu CD. Role of posterior transverse interarch discrepancy in Class II, Division 1 malocclusion during the mixed dentition phase. Am J Orthod Dentofacial Orthop. 1996;110: Hershey HG, Stewart BL, Warren DW. Changes in nasal airway resistance associated with rapid maxillary expansion. Am J Orthod. 1976;69: Bishara SE, Staley RN. Maxillary expansion: clinical implications. Am J Orthod Dentofacial Orthop. 1987;91: McCurdy SL. Separation of the upper maxillae. J Am Med Assoc. 1909;52: Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. Angle Orthod. 1970;57:

38 23. Davis WM, Kronman JH. Anatomical changes induced by splitting of the midpalatal suture. Angle Orthod. 1969;39: Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening the midpalatal suture. Angle Orthod. 1961: Zimring JF, Isaacson RJ. Forces produced by rapid maxillary expansion. 3. Forces present during retention. Angle Orthod. 1965;35: Hicks EP. Slow maxillary expansion. A clinical study of the skeletal versus dental response to lowmagnitude force. Am J Orthod. 1978;73: Majourau A, Nanda R. Biomechanical basis of vertical dimension control during rapid palatal expansion therapy. Am J Orthod Dentofacial Orthop. 1994;106: Haas AJ. Gross reactions to the widening of the maxillary dental arch of the pig by splitting the hard palate. Am J Orthod. 1959;45: Gryson JA. Changes in mandibular interdental distance concurrent with rapid maxillary expansion. Angle Orthod. 1977;47: Melsen B. Palatal growth studied on human autopsy material. A histologic microradiographic study. Am J Orthod. 1975;68: Melsen B, Melsen, F. The postnatal development of the palatomaxillary region studied on human autopsy material. Am J Orthod. 1982;82: Wertz R, Dreskin, M. Midpalatal suture opening: a normative study. Am J Orthod. 1977;71: Lima AC, Lima AL, Filho RMAL, Oyen OJ. Spontaneous mandibular arch response after rapid palatal expansion: a long-term study on Class I malocclusion. Am J Orthod Dentofacial Orthop. 2004;126:

39 34. Moyers RE, Van Der Linden F, Riolo ML, McNamara JA Jr. Standards of Human Occlusal Development. Monograph 5. Craniofacial Growth Series. Ann Arbor: Center for Human Growth and Development; University of Michigan; Barry, M. In-office digital study models. J Clin Orthod. 2011;45:

40 CHAPTER 3: JOURNAL ARTICLE Abstract Introduction: While the likelihood of adolescent upper arch expansion with a RPE appliance is not questioned, the amount of long-term expansion remaining after treatment is very important. Recent technological advances have allowed the generation of digital dental models from plaster casts that can be saved and viewed three-dimensionally on a computer. With the advent of such technology, digital dental models of RPE treated cases can potentially be measured with greater control and accuracy to evaluate morphologic changes over time. Purpose: The purpose of this study is to use the R700 in-office laser model scanner and OrthoAnalyzer software (3Shape, Copenhagen, Denmark) to assess the long-term stability of rapid palatal expansion followed by fixed edgewise appliances. Materials and Methods: The sample consisted of 67 patients (53 females, 14 males) with an average pretreatment age of 12 years and 3 months. All patients were treated with a Haastype RPE and nonextraction edgewise appliance therapy in a single orthodontic practice. Serial dental casts were available at three different time points: pretreatment (T 1 ), after expansion and fixed appliance therapy (T 2 ), and at 30

41 long-term recall (T 3 ). The mean duration of the T 1 -T 2 and T 2 - T 3 periods was 4 years 10 months and 11 years 0 months, respectively. The dental casts were digitized with the R700 in-office model scanner and the computed measurements were compared with untreated reference data. Results: The majority of treatment increases in the maxillary and mandibular arches were statistically significant (P <.05) and greater than expected for untreated controls. Although many measurements decreased postretention (T 2 -T 3 ), net gains persisted for all of the measurements evaluated. Conclusions: Based on the long-term stability observed in this study, it was concluded that the use of RPE therapy followed by full fixed appliances is an effective method for increasing maxillary and mandibular arch width dimensions in the growing patient. 31

42 Introduction Transverse maxillary deficiencies are a common problem among adolescents and rapid palatal expansion (RPE) is one of the most common procedures used by orthodontists to correct this discrepancy. 1 While the likelihood of upper arch expansion with a RPE appliance is not questioned in an adolescent, the amount long-term expansion remaining after treatment is very important. Many studies of have evaluated the stability of RPE by using various techniques ranging from manual measurement of dental casts 2 to plane film radiographic techniques 3,4 to digital imaging. 5 However, more sophisticated techniques for evaluating morphological changes in the dentofacial complex have been developed. The advent of the surface laser scanner and companion software has made it possible to capture 3D images of plaster casts and thus offer greater accuracy and precision in measurement. The purpose of this study is to use the R700 in-office laser model scanner and OrthoAnalyzer software (3Shape, Copenhagen, Denmark) to assess the long-term stability of the maxillary and mandibular arch dimensions following rapid palatal expansion and edgewise mechanotherapy. 32

43 Materials and Methods Subjects The sample consisted of 197 paired dental casts obtained from 67 patients (53 females and 14 males) that were treated by a single practitioner. To be included in the study, dental casts at pretreatment and posttreatment had to be available, pretreatment dental casts had to be obtained under 18 years of age, and all cases had to be treated with a Haas-type RPE and subsequent nonextraction edgewise appliance therapy. The majority of all patients exhibited posterior crossbites and narrow maxillary arches. The patients underwent a standardized protocol of Haas-type RPE with two turns a day (~0.25 mm per turn) until the expansion screw reached 11mm to 14mm. The desired expansion was achieved when the mandibular arch was completely contained by the maxillary arch. The Haas expander was kept on the teeth as a passive retainer for an average of 3 months. After expansion, all patients received full maxillary and mandibular fixed standard edgewise appliances. The retention protocol after orthodontic treatment consisted of an upper removable appliance and a lower fixed lingual retainer from canine to canine worn for approximately 6.5 years. 33

44 Dental casts were obtained at three observation times: pretreatment (T 1 ), after expansion and fixed appliance therapy (T 2 ), and at long-term recall (T 3 ). The mean age at T 1 was 12 years 3 months ± 2 years 5 months, 17 years 0 months ± 3 years 11 months at T 2, 27 years 11 months ± 6 years 2 months at T 3. The mean duration of the T 1 -T 2 and T 2 - T 3 periods was 4 years 10 months ± 3 years 6 months and 11 years 0 months ± 5 years 5 months, respectively. Data Collection The dental casts were digitized with the R700 inoffice model scanner. Three scans were performed by the R700 for each set of dental models: the full maxillary model, the full mandibular model, and the models together in occlusion (Figure 3.1). The software uses a best-fit algorithm to automatically fit the individual full scans with the occlusion scan to produce on-screen digital models with an accurate occlusion. 6 34

45 Figure 3.1: 3D dental models displayed by OrthoAnalyzer software Landmark Acquisition The R700 scanner software, OrthoAnalyzer, was used to compute midpoints and thus identify landmarks on the 3D model. A point was placed on the distal, facial, mesial and lingual surfaces of canines, premolars/primary molars and first permanent molars in the same arch (Figure 3.2). These points were selected in accordance with the guidelines established by Moyers et al. 7 to determine the geometric center of each tooth, the tooth centroid (Figure 3.3). This point provides a more valid measurement of arch width because it eliminates the effect of tooth rotation. 35

46 Midpoints and landmarks were not recorded if the teeth were in the process of eruption before the height of contours of the four outer surfaces (mesial, distal, facial and lingual) were visible. Figure 3.2: Location of digitized points (mesial, distal, lingual, buccal) to determine centroid landmark. Similar points and landmarks were located on the mandibular dental arch. Figure 3.3: Location of the centroid was found first by determining midpoint (A) of the line connection the mesial and distal landmarks. Similar midpoint (B) was constructed midway between buccal and lingual landmarks of the tooth. The centroid (C) was located between points A and B. (Adapted from Moyers et al.) 7 36

47 Measurements The OrthoAnalyzer software was also used to measure arch width at the following teeth: primary canines/permanent canines, first primary molars/first premolars, second primary molars/second premolars, and the first permanent molars (Figure 3.4). Arch width was evaluated by two sets of measurements: from the lingual point of a given tooth to the like on its antimere and between the centroid of a tooth (Figure 3.5) and its antimere as described by Moyers et al. 7 Figure 3.4: Computation of arch width (from lingual point) Figure 3.5: Computation of tooth centroid 37

48 Error of Method To test the reliability of the model measurements, a random number generator ( 8 was used to select 10% of the sample for re-evaluation. Intraclass correlation was estimated by Cronbach s α. Reliability is commonly considered adequate when the intra-class correlation coefficients are equal to or greater than For all variables, reliability coefficients were found to be greater than Therefore, all data was reliable. Statistical Analysis Maxillary pretreatment (T 1 ) comparisons between the treated subjects and corresponding reference data provided by Moyers et al. 7 were performed by Student s t-test for independent samples. Comparisons between treatment time points of the treated subjects were performed by Student s t-test for dependent samples. The following statistical comparisons were performed: evaluation of treatment changes (T 2 -T 1 ), evaluation of postretention changes (T 3 -T 2 ), and evaluation of overall changes (T 3 -T 1 ). For each subject, age and sex-specific z scores were calculated for arch width by using reference data reported 38

49 by Moyers et al. 7 Z scores provide the subjects deviations (in standard units) from values expected for untreated subjects and obviate dimensional adjustments due to arch changes that normally occur between the mixed and permanent dentitions. Z scores were then compared by Student s t-test for dependent samples. The following statistical comparisons were performed: z score evaluation of treatment changes (T 2 -T 1 ), z score evaluation of postretention changes (T 3 -T 2 ), and z score evaluation of overall changes (T 3 -T 1 ). Results Maxillary Arch At T 1, the maxillary arch widths of the treated patients were significantly narrower than the corresponding dental arches of the established reference data. Maxillary arch widths increased significantly (P<0.05) during treatment (T 2 -T 1 ) (Table 3.1, Figure 3.6). At the centroid level, intercanine widths increased the least (3.18 ± 2.47mm) and inter-second premolar widths increased the most (7.40 ± 2.56mm). Lingual arch widths followed a similar suit, increasing most at the second premolars (7.10 ± 2.43mm) and least at the canines (1.56 ± 2.60mm). The ratio of the centroid width increase to the corresponding lingual width increase, which provides a rough measure of 39

50 tipping, was greatest for the canines (2.0:1) and least for the second premolars (1.0:1). Z scores, adjusted for age and sex, showed significant treatment increases in arch width at the centroid (Table 3.2). With the exception of intermolar width, maxillary arch widths decreased significantly postretention (T 3 -T 2 ) (Table 3.1). Width decreases ranged from 9% of the treatment increase at the second premolars to 27% of the treatment increase at the canines. Compared with untreated reference data (Table 3.2), arch width decreased more than expected posttreatment. Arch width at the first molar decreased more than expected, however the difference was not statistically significant. When looking at the net change of treatment (T 3 -T 1 ), maxillary arch widths at both the centroid and lingual levels increased significantly. At the centroid level, the intercanine widths increased the least and inter-second premolar widths increased the most. Z scores were greater than expected and significant for the overall observation period. 40