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AN ASSESSMENT OF MANDIBULAR APICAL BASE AND CURVE OF SPEE FROM A DEVELOPMENTAL PERSPECTIVE Anas Athar, B.D.S. M.S. 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 2011 Abstract Introduction: The difference between the mesio-distal width of teeth and the perimeter of apical base is defined as dental crowding. It is thought that a relationship of teeth to the apical base is essential for diagnosis and long term stability of orthodontic treatment. Unfortunately there is no reliable definition of apical base in literature. Researchers have defined apical base using various methods, but none of the definitions have taken development into consideration, Purpose: This study will investigate if there is a relationship between the apical base measured at inferior alveolar nerve level, arch perimeter and crowding as measured on the plaster model. An attempt will also be made to determine if there is a relationship between the curve of Spee and the curve fOlmed by the inferior alveolar nerve when viewed sagitally. Method: A sample of 27 randomly selected untreated patients with pre~treatment cone beam computed tomography (CBCT) scans and available pre-treatment plaster models were utilized. Patients were selected based on eruption of full pennanent dentition. Data collected by CBCT included measurements of basal bone perimeter at the level of inferior alveolar nerve canal, and tracing of the curve of Spee and curve of the inferior alveolar nerve canaL Model analysis included measures of the arch pedmeter and dental crowding, Results: The apical base perimeter and arch perimeter measured on dental cast are significantly different. A statistically significant difference was also observed between the two curves (curve of Spee and curve of the inferior alveolar canal). 1 Conclusions: No relationship was established between the apical base measured at inferior alveolar nerve canal, crowding, and the arch perimeter as measured on model. Similarly, the curve of Spee was significantly different from the curve formed by the inferior alveolar canal. 2 COMMITTEE IN CHARGE OF CANDIDACY Assistant Professor Ki Beom Kim, Chairperson and Advisor Professor Eustaquio Araujo Professor Rolf G. Behrents DEDICATION I dedicate this project to the Saint Louis Fire Department and to the doctors and staff of Saint Louis Children's Hospital for their efforts and knowledge in saving my daughter's life. r would also like to dedicate this work to the people and leaders of the U.S.A. for providing me and my family an environment of success, peace and care. ii ACKNOWLEDGEMENTS I would like to acknowledge the following individuals: • Dr. Ki Beom Kim for his support • Dr. Behrents for his advice and guidance throughout this project • Dr. Araujo for being the most supportive teacher and being there, whenever needed. • Dr. Condoor for his help with data collection • Dr. Israel for assistance with statistics I specially want to thank my wife Samia for her unconditional love and support. My daughter, Amna for all her hugs and kisses. My son, Mustafa for being a special gift for me. iii TABLE OF CONTENTS List of Tables ....................................................................................................................... v List of Figures .................................................................................................................... vi CHAPTER 1: INTRODUCTION ........................................................................................ 1 CHAPTER 2: REVIEW OF THE LITERATURE .............................................. 4 Methods of Measuring Apical Base ......................................................................... 6 Basal Bone and Tooth Size-Arch Length Discrepancy ........................................... 8 Role of Inferior Alveolar Nerve in Development of Mandible ............................. 12 13 Role of Inferior Alveolar Nerve and Dental Development. ......... Inferior Alveolar Nerve and CBCT ....................................................................... 15 Curve of Spee ............................... :......................................................................... 18 Pllrpose of the Study .............................................................................................. 20 References .......... 21 0 ......................... o ................................................................................................... CHAPTER 3: JOURNAL ARTICLE 25 Abstract .................................................................................................... Introduction ............................................................................................................ 27 Materials and Methods .t ••••• 29 Measuring Basal Bone from CBCT at the Inferior Alveolar Nerve .......... 29 Model Analysis .......................................................................................... 33 Tracing Curve of Spee ............................................................................... 34 Tracing Curve of Inferior Alveolar Nerve ................................................. 36 Intra-rater reliability ................................................................................... 36 Comparison of Curves ............................................................................... 38 Statistical Analysis ..................................................................................... 40 Results .................................................................................................................... 41 Inferior Alveolar Nerve Perimeter ............................................................. 41 Comparison of Curves ............................................................................... 43 Discussion .............................................................................................................. 45 Inferior Alveolar Nerve as Apical Base ..................................................... 45 Curve of Spee and Inferior Alveolar Nerve .............................................. .47 Conclusions ............................................................................................................ 49 t ............. o . . . . . oo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . to . . . . . . . . . . . . . . . . . . Literature Cited ...................................................................................................... 50 Vita Auctoris ...................................................................................................................... 52 IV LIST OF TABLES Table 3.1: Descriptive statistics of27 patients' model analysis ................................ .41 Table 3.2: Cronbach's Alpha for intra-rater reliability .............................................. .42 Table 3.3: Pearson's correlation for the nerve perimeter and methods of crowding ................................................................................................... 42 Table 3.4: Comparison of inferior alveolar nerve pedmeter and arch perimeter by Proffit's method; analyzed by paired sample t-test. .................................. .42 Table 3.5: Descriptive Statistics; Measurement of sections in the curve of Spee ...... 43 Table 3.6: Descriptive Statistics; Measurements of section of the curve of the inferior alveolar nerve ................................................................................ 43 Table 3.7: Comparison of Left and Right side curves by paired sample t-test .......... .44 Table 3.8: Comparison of the curve of Spee and the inferior alveolar nerve at each section by independent sample t-test ........................................................ .44 v LIST OF FIGURES Figure 3.1: Panoramic radiographs refolTIlatted from CBCT: visibility of inferior alveolar nerve canal ............................................................... 31 Figure 3.2: 3-Dimensional volumetric image: axial view showing measurement of inferior alveolar nerve .................................... 32 Ie . . . . . . . . . . . . . . . . . . . . . . . . Ie . . . . . . . . . . . . . . . . Figure 3.3: Quadrant diagram for straight line approximations of mandibular arch perimeter .................................................................................................... 33 Figure 3.4: Lateral cephalogram reformatted from CBCT ................................. 35 Figure 3.5: Curve of the inferior alveolar nerve traced on sagittal view of 3dimensional volumetric image ................................................................... 36 Figure 3.6: Comparison of curves by dividing each curve into five equal segments ... 39 Vi CHAPTER 1: INTRODUCTION The most common reason that patients seek orthodontic treattnent is dental crowding. For treatment of dental crowding it is essential to identify the cause of crowding. The characteristic features of dental crowding are malaligned teeth, deep curve of Spee and protrusion or retrusion of teeth. 1 Dental crowding is determined by comparing the mesio~distal width of the teeth to the perimeter of apical base. If the total width of teeth is greater than the perimeter of apical base, dental crowding is observed~ whereas, if the total width of teeth is less than perimeter of apical base, spacing between the teeth is usually noticed. In order to have optimum arrangement of teeth in the arch, a balance between the measurements of tooth structure and apical base is essential. 2 The significance of the apical base is repeatedly mentioned in orthodontic literature. Even so there is no satisfactory definition of the apical base. The telID 'apical base' was first mentioned by Lundstrom in 1923 3, he defined it as the section of bone upon which teeth rest. Since the introduction of this term several methods have been developed by investigators to define the apical base. Salzman,4 Downs,s Riedel6 and several others used lateral cephalogram. While Howes, 7 Sergt 8 Kanaan9 and others used dental casts to define the apical base. Bell took advantage of advancement in dental radiography and used cone beam computed tomography (CT) to define the apical baselO. It is commonly believed that orthodontic ally moved teeth that are placed in a 'nolmal' position in the arch may not be stable if the basal arch over which they are placed is not sufficiently large enough. Orthodontists believe that there is a strong relationship not only bet\veen dental crowding and the apical base, but stability of orthodontic treatment 1 result, the orthodontic literature fails to precisely define apical base. All the studies so far have attempted to define apical base from the anatomical position of the basal bone. None of the investigations have attempted to define apical base from a developmental perspective. A literature search demonstrated a strong association between inferior alveolar nerve (IAN) and development of mandible. It has been established that the first sttucture that is formed in the human mandible is inferior alveolar nerve. The ossification of the mandible starts at the mental foramen and progresses to fonn the mandible. The inferior alveolar nerve has been strongly associated with dental development and the bone sUl1'0unding the teeth. Il • 12. 13, 14 Previously it was difficult to identify the inferior alveolar nerve canal with conventional 2-dimensional radiographs. This was due to the distortion or superimposition of anatomic structures. With the advances in dental radiography Cone Beam CT (CBCT) is becoming popular. Images acquired by CBCT are not only free from any distortion and superimpositions effects, but they are also free from magnification. These advantages allow a clinician to accurately identify structures that were not readily visible on 2-dimensional images. IS It is evident from the literature that there is a developmental relationship between the inferior alveolar nerve and the mandible and the inferior alveolar nerve and teeth. With the introduction of CBCT and advancement in software, it is possible to accurately identify and trace the inferior alveolar nerve canal. The purpose of this study is to seek a reliable method of measuring the perimeter of the apical base from a developmental 2 perspective. There will be an assessment to see if a relationship exists between the curve of Spee and the curvature formed by the inferior alveolar nerve. 3 CHAPTER 2: REVIEW OF LITERATURE Orthodontics is the area of dentistry concelned with the supervision, guidance and correction of growing and mature dentofacial structures, including those conditions that require movement of teeth or conection of malre1ationships and malformations of related structures by the adjustment of relationships between and among teeth and facial bones by the application of forces and/or the stimulation and redirection of the functional forces within craniofacial complex. l In a report by United States Public Health Services 750/0 population has some noticeable deviation from ideal occlusion. 16 In this repol1 it was stated that crowded, mal aligned teeth are the most common single contributor to malocclusion. About 40% of children and 850/0 of youths had some degree of malalignmentlcrowding within dental arches. Dental crowding is considered the most conunon form of malocclusion. 17 In another survey, the National Health and Nutrition Examination Survey (NHANES-III) repol1ed that only 35% of adults have well aligned teeth. It is obvious from the previous reports that prevalence of malaligned teeth or dental crowding is high in the US population. Crowding is defined as the discrepancy between tooth size and jaw size that result 2 in a misalignment of the tooth position. Many factors such as evolutionary trends, heredity, environmental effects, lack of attrition, and tooth size have been implicated as causes of dental crowding. However, the most impo11ant detenninants of crowding and spacing in dental arches are the size of the teeth and the size of the bony bases. 17 4 Common features of dental crowding are malaligned teeth, a deep curve of Spee and proclinationlretroclination of teeth. The importance of the basal bone in determining dental arch crowding has been widely discussed in literature. A common belief is that when tooth mass is too small relative to basal bone, spacing or diastema is more likely to occur and when tooth mass is too big in relation to the basal bone the teeth will be 4 crowded out of normal arrangement. Salzmann recognized the importance of basal bone dimensions in dental crowding. Tweed 19 considered treatment to be successful when the mandibular incisors were positioned on basal bone; when this is not achieved, relapse of crowding may be evident. Several studies have suggested important interaction of basal bone/apical base and dental crowding. The terms basal bone and apical base are used interchangeably in literature. The apical base is defined most recently as the portion of the jawbone that gives support to the 3 teeth. 2 The term "apical base" was first mentioned by Axel Lundstrom in 1923 who defined it as the section of bone upon which teeth rest or are attached; this is very similar 4 to modern definition of apical base. Salzmann discussed apical base in more detail and according to him the alveolar processes hold the teeth and are not in stress concentrating areas of jaw. Such areas are located in the constricted portions of the jaw subjacent to the alveolar processes in mandible and supeljacent to the alveolar process in maxilla. This area is called the apical base. Although apical base is a widely used term in orthodontics, it has never been precisely defined. According to Brodie 2o the reason for this lack of definition of apical base is the limitation of available methods. He suggested that apical base may be determined by the limit of absorption of alveolar bone after the teeth are 5 lost. All the definitions of apical base in literature are determined by anatomical location. The literature search shows no definition of apical base from a developmental aspect of basal bone. In this study we attempted to define apical base from developmental point of vIew. Methods of Measuring Apical Base Since the advent of term "apical base" by Lundstrom,3 there has been a great deal of interest in the literature concerning the measurement of the apical base. As mentioned by Brodie,2o there is no satisfactory definition of apical base. However, several methods are reported that have attempted to locate and quantify basal bone. Traditionally, the apical base is assessed by means of palpation or on cephalogram. 8 Cephalometric methods utilizes point A and B (as described by Downs 5) denoting the apical base in the region of central incisors, to the anterior cranial base. Both methods have limitations, one being subjective and other being limited to one isolated relationship. Both these methods only assess the location of the apical base and not its size. 8 Downs5 (1948) searched for an accurate method to determine the limits of the basal bone. He introduced two cephalometric landmarks, point A and point B that represented what he called the denture base. He used these two points, along with other points, to study the skeletal patteln of the face as a part of his classical cephalometric analysis. To study the discrepancy in apical base relationships, Riedel6 adapted Downs' points A and B, and used them in two angular measurements, SNA and SNB. Ever since, 6 points A and B have been used extensively in cephalometric evaluations, and in many studies, to determine the apical base relationship. Howes' used dental casts to analyze the relationship between tooth size and the supporting bone. He found that the supporting bone was above the palatal shelf and over the apices of the teeth. By using a survey line above the apices of teeth without impinging on the muco-buccal fold and sectioning horizontally on this line, he was able to remove the alveolar process and expose the supporting bone. He found the basal arch to be at the apical pOl1ion of the alveolar bone. In the mandibular arch it is 8 mm below the gingival 21 margin. Falck defined the apical base as "the area resulting from peripheral connection of two reference points located 14 mm away from buccal cusps of the first primary molars/premolars." Miethke et. a1. 22 argued that Falck's method of locating the apical base was inaccurate for comparing treatment outcomes, given that the primary molars have shorter cusps than the premolars. The difference in the crown height between these two tooth types would change reference points and thus change the apical base level. To overcome this limitation, Miethke' s group agreed with Howes 7 and Rees23 by using the gingival margins as a reference point. They defined the apical base as the area resulting from the peripheral connection of six reference points located 5 mm below the most apical points of the gingival margins of the lower lateral incisors, canines and second primary molars/premolars. In their opinion, the 5 mm distance from the gingival margins was not a hue reflection of the apical base. Although some authors have used the gingival margins as a reference to locate basal bone, SergI, Kerr and McCo1l8 used the most concave contour of the buccal surface of the casts to measure the basal bone area. 7 Not surprisingly, confusion still exists concerning the location of basal bone, largely because of the absence of agreement among authors who simply used their opinion and speculation to locate it. Basal Bone and Tooth Size-Arch Length Discrepancy It has been shown that, over a period of many years, there has been discussion of, and concern for, stability by placing teeth "over basal bone." Unfortunately, one of the difficulties in orthodontic treatment planning has been the estimation of the size and dimensions of the basal bone.9 Angle's "line of occlusion" \-vas readily accepted by early orthodontists. 24 It prompted a search for meaningful measurements of dental arch dimensions that could be utilized in diagnosis and treatment planning. It was not until 1923 that the potential relationship between Lundstorm's3 apical base and dental arch form began to be understood, as well as the realization that one of the most important diagnostic dental arch dimensions was dental arch perimeter. Lundstrom's theory was effectively translated into clinical practice by Nance in 1947. 25 In his classic work, Nance25 described a method for measuring the "outside" arch perimeter by using a piece of a .010 inch brass wire placed along the buccal surfaces of the teeth from the mesial of one side of pennanent molar to the mesial of the opposite side of pelmanent molar. Although most clinicians today do not measure the "outside perimeter" as advocated by Nance, the use of brass wire to determine the available dental arch perimeter is still a popular method. 8 Carey6with some modification adopted Nance's method. He used 0.020 inch soft brass wire bent to a symmetrical arch form that was placed over the contact point region of the posterior teeth and over the incisal edges of anterior teeth. He placed a mark where the wire crossed the mesial contact point of the first pelmanent molars; dental arch length could then be measured between these two marks. Even though he used the incisal edges of the anterior teeth to measure the dental arch perimeter) he suggested that in certain cases it was necessary to pass the wire over the incisal edges "at a point where we judge them to belong." Moorrees 21 presented a variation of the brass wire method for measuring dental arch perimeter. He used stainless steel tubes welded to a flange. The flange served as a mean of attaching a wire guide to a plaster model at the mesial aspect of the first permanent molar, and the tubes allowed the soft 0.15 mm stainless steel wire to be guided through them. Sticky wax was used to fix the flange to the cast, and the wire was bent along the buccal cusps of the incisal edges of the teeth, stabilized to the tube with hot wax, straightened and measured with a sliding caliper. Huckaba28 described a similar brass-wire approach to measure the dental arch length. He used 0.025 inch brass wire and centered the wire over the contact points in the posterior dentition. In the anterior region he positioned brass \vire depending on the anatomical position of anterior teeth. The wire is then cut and straightened with the fingers and measured with a boley gauge. Musich and Acketman29 used a catenometer to measure dental arch perimeter. Measurements were made based on a catenary curve. In addition to brass wire and chain techniques, Lundstolm30 suggested calculating the dental arch perimeter with a caliper by 9 measuring and adding straight line segments of the arch in six sections. Hew31 modified this method and calculated arch perimeter by dividing the basal bone into four segments and measuring the length of each segment individually. The total length of the four segments was believed to represent the perimeter of basal bone. He studied the conelation between tooth mass and available basal arch and found high correlation between relapse and basal arch deficiency. He fu11her indicated "the reduction of dental units improve the correlation between tooth mass and basal arch length in relapsed cases." Little proposed an irregularity index that would quantify the mandibular anterior teeth crowding. He used this index as a guide for treatment priorities. The scoring was done by measuring the linear distance of the displacement of two adjacent contact points. These measurements were made at five contact points; the sum of displacement of these five points represents the relative degree of incisor ilTegularity. Although, Little~s index is simple and clinically applicable this method does not measure arch length. BeGole32 took advantage of improvements in computer science and wrote the first program to perform dental model analyses, including calculating the tooth size larch length discrepancy. The program, MODELS, uses a set of 118 inputs to perform analyses. These inputs are dental landmarks digitized from a photocopy of study model. Arch perimeter is calculated as "the sum of various connecting line segments drawn around the dental arch;" the four segments start from mesial surface of lateral incisor, to the mesial surface of central incisor on the other side, to the distal surface of the lateral incisor, to the mesial surface of first molar. 10 Direct measurement of photocopied three-dimensional objects has a high potential for error in cases \vith severe tipping. Champagne33 reported that photocopies are an unreliable method for arch length measurements and space analysis detennination. On the other hand, Tran and colleagues 34 compared the manual measurement of the irregularity index to computer measurements based on photocopies of models. They concluded that the computer method is a valid and reliable alternative for assessing mandibular incisor alignment. Kanaan9 did a study to establish a reliable method of measuring length of basal bone. He used a mathematical fOlmula which he called "elliptical formula" and tested its validity. All above mentioned studies involved a 2 .. dimensional measurement of apical base. To overcome the um'eliability of2-dimensional measurements, 3-dimensional model analyses were introduced based on scanner-based 3-dimensional digitizers. 35 Yamamoto and associates described an optical method for creating 3-dimensional computerized models with a laser-beam scan of the dental casts. Later, other attempts were made to transfer the dental cast into 3-dimensional virtual nl0dels. Kuroda and colleagues36 introduced a three-dimensional dental cast analyzing system that employs laser scanning. This computerized model can be used to calculate distances and perimeters from the 3 -dimensional virtual model. BentO took advantage of advances in cone beam computerized tomography. He used cross-sections of 3-dimensional volumetric images at two different levels parallel to functional occlusal plane. The first cross-section was made at the level of B point, while the second cross-section was made at the inferior most point of the mental foramen. He then measured the perimeter using Kanaan's9 elliptical formula. In addition he also 11 measured the area of the basal bone at these two levels. He concluded that there is little justification for selecting a pruiicular basal bone measurement assessment over another. This literature review shows that there is no standard way of defining and measuring apical base. It was obvious from the literature that methods that have been developed to measure arch length, most do not measure arch length of the apical base. Therefore, crowding has been commonly measured relative to the perimeter of the dental arch, but not relative to the dental arch that houses the teeth. In addition to this, all the definitions of apical base in literature are based on individual perception. No definition of apical base is discussed on the basis of developmental aspect of apical base. Because hard and nerve tissues interact during early development, and the hard tissue bears traces of this interaction3? we will attempt to define basal bone at the level of inferior alveolar nerve. According to the literature seru'ch, no study has investigated apical base from this perspecti vet Role of Inferior Alveolar Nerve in Development of Mandible Embryologically, nerve tissue forms first and the bone tissue successively fOlms as a canal around the nerve path. If, for instance no nerve canal appears in the bone tissue regions where it should normally be present, there can be only two explanations: either the nervous tissue was never present, or it has been destroyed. The reason cannot be that nerve tissue has not yet penetrated the hard tissue, because nerve tissue never penetrates bony tissue. 31 12 The first bony tissue to form in the human mandible is seen about the i h_8 th fetal week on the external surface of Meckel) s cartilage in the lower border of the later foramen mentale. 11 ,12,13 This early bone tissue supports the mental nerve. Recent studies have shown that the mandibular canal in mid fetal life is not one hut three or more separate canals. 38 These canals contain the nerve supply to the incisors, premolars and molars, in that ordet.. The nerve branches to the incisors and deciduous molars/premolars develop before the innervations to the permanent molars, In the final stage of fetallife~ the mandible doubles in size by apposition of bone tissue on the posterior margin of the mandibular ramus and by resorption on its anterior border. During this process, the canal openings on the inside of the ramus gradually merge. In this way, by gl'owth and remodeling processes, the canal openings become one canal opening, corresponding to the mandibular foramen seen at birth. The nerve pathways to the different tooth groups thus become one nerve bundle, the inferior alveolar nerve. Role of Inferior Alveolar Nerve and Dental Development Nerve growth factor receptor (NGF-R) is expressed close to the developing tooth buds, and nerves seemingly participate as fine network in the developing dental follicle. 39 Nerve tissue does seem to be essential for tooth development from the moment the dental follicle forms. It is interesting that the teeth located closest to the nerve stems are the first ones to be formed. 37 Thereafter, they are formed in the patteln in which ossification occurs. There is a close relationship not only between tooth development and nerve development, but also between tooth development and development of stuiounding bone 13 tissue. Studies have shown that canines are the first teeth to be laid down in the primary dentition. In the anterior region, the upper central incisor form before the lateral incisor, while opposite is true of the lower jaw, \vhere the pattern of innervation is different. With regard to the primary molars and premolars the anterior teeth are formed before the posterior ones in a pattern that corresponds to the innervation sequence and bone formation. 37 In a report by Jakobsen4o a mandible with unilateral absence of mandibular canal has been described and agenesis of teeth has been found on the side where the mandibular canal was absent. The anterior teeth were present, however, and in these cases a canal opening lingual to the incisors, not normally found was evident. It was speculated that the innervation to the anterior region occurred via a lingual canal. In another study by Bang et. a1. 41 the role of inferior alveolar nerve and the development of teeth was discussed. In this study evidence was presented that the mumps vitus may destroy myelin sheaths and hence interrupt tooth development by disluption. This results in a shortening of root. When the myelin sheath grows out again, the temporarily arrested root development resumes and molar root can accordingly change form from its normal morphology to a taurodontic root fonn. Kjaer42 discussed various patterns of tooth agenesis. The traditional regions in which agenesis occur are: upper lateral incisors, upper second premolars, upper third molars, lower central incisors, lower second premolars and lower third molars. The regions in question are all those in which the innervation of the field involved occurs last. It is evident from the literature that there is a strong relationship between the inferior alveolar nerve and apical base development, also the inferior alveolar nerve and 14 tooth development. As the literature shows, no studies appear that discuss the relationship between the apical base and the inferior alveolar nerve. A possible reason for this omission in literature is that the canal that houses inferior alveolar nerve is not always readily visible in conventional two dimensional radiographs. However, with the introduction of more advanced imaging modalities like MDCT, CBCT etc. the inferior alveolar nerve canal can be readily visualized with precision. 15 Inferior Alveolar Nerve and CBCT A variety of imaging modalities are available~ including panoramic radiography (conventional and digital), tomography or computed tomography (CT) and these have been used for assessing the anatomy of various sttuctures including the inferior alveolar nerve canaL The contribution of panoramic radiography to maxillofacial diagnoses in the last 30 years has been significant. Over the last decade, digital panoramic radiography was introduced and it appears to demonstrate certain advantages compared with filmbased panoramic radiography (e.g., faster image acquisition, elimination of dark room, lower radiation exposure and availability of various imaging tools). 15 The recently introduced cone-beam computed tomography creates 3-dimensional image data by a single scan around the imaging volume of interest. Data produced can be displayed in any clinically meaningful way (e.g., panoramic and cross-sectional images of maxilla and mandible, or temporomandibular joint sagittal and coronal images). CBCT is well suited for imaging in the craniofacial area. It provides clear images of highly contrasted structures and is extremely useful for assessing bone. 43 Images produced are 15 corrected for magnification resulting in accurate measurements. All of these considerations, along with reduced radiation exposure to patient compared with medical CT make CBCT a very promising imaging modality for maxillofacial diagnosis. 15 Although CBCT and panoramic radiographs are two different imaging modalities they have been compared for their diagnostic accuracy. A few studies have compared these two modalities in evaluating the inferior alveolar canal. Tantanapornku144 evaluated the diagnostic accuracy of cone beam CT compared with panoramic radiographs in predicting neurovascular bundle exposure during third molar extraction. CBCT were superior to panoramic radiographs with sensitivity of93% and specificity of 77%. For panoramic radiographs similar values were 70% and 63%. Friedland and associates45 presented cases utilizing 3-dimensional reconstructions from CBCT data to evaluate the anatomic relationship of mandibular canal and impacted mandibular third molars. They concluded that clinicians should consider the use of CT in selected cases, chiefly when one or more of the telltale signs are present on panoramic image. Angelopoulos et.al. 15did a study to compare CBCT reformatted panoramic images and digital panoramic images for identification of the mandibular canal as part of peri-implant assessment. They concluded that CBCT reformatted panoramic images were superior to digital panoramic images for identification of the inferior alveolar canal. In addition to depicting inferior alveolar canal accurately these reformatted images were free of magnification and superimposition of neighboring sttuctures, which are inherent problems in panoramic images. Lofthag-Hansen46 evaluated the visibility of the inferior alveolar canal and the marginal bone crest and the agreement between observers in images from one CBCT technique. According to authol'S the visibility of the inferior alveolar canal and the 16 marginal crest, as well as the observer agreement of the location of these structures was high. Naitoh47 compared multislice computed tomography and cone beam computed tomography in detection of fine anatomical sttuctures in the mandible such as bifid mandibular canal, accessory mental and buccal foramina. They concluded that there is no difference in depiction of various fine anatomical structures between images obtained using the two modalities. The authors suggested use of CBCT for similar diagnostic tasks due to low radiation dose to the patients. It is evident from literature that cone beam computed tomogl'aphy is a reliable method for inferior alveolar nerve canal identification. Previously we discussed that one of the characteristic feature of crowding is a deep curve of Spee. Also we have discussed relationship of the inferior alveolar nerve and development of apical base and teeth. The o11hodontic literature shows only a few publications discuss the curve of Spee and no study discusses factors that establish the curve of Spee. 17 Curve of Spee The "curve of Spee" was first introduced by a German embryologist Ferdinand Grafvon Spee in 1890. 48 Spee connected the anterior surfaces of mandibular condyles to occlusal surfaces of the mandibular teeth with an arc of circle, tangent to the surface of a cylinder lying perpendicular to the sagittal plane. According to him this geometric arrangement is the optimum for maximum tooth contact during chewing and considered it an important tenet in denture construction. Nowadays, the curve of Spee is defined differently in different specialties of dentistry. In prosthodontics the curve of Spee starts from canine and extends back to the terminal molar. The curve then continues posteriorly to intersect the anterior surface of the condyle as originally proposed by Spee. In orthodontics, the curve of Spee commonly refers to the arc of a curved plane that is tangent to the incisal edges and the buccal cusp tips of the mandibular dentition viewed in the sagittal plane. The difference in definitions can be due to the difference in patient population served by two specialties. Orthodontists see mostly young patients, while prosthodontists usually deal with adult patients. It has been suggested that the deciduous dentition has a curve of Spee ranging from flat to mild, whereas the adult curve of Spee is more pronounced. 49 Andrews50 in describing the 6 characteristics of normal occlusion found that the curve of Spee in subjects with good occlusion ranged from flat to mild, noting that best static intercuspation OCCUlTed when the occlusal plane was relatively flat. He proposed that flattening the occlusal plane should be a treatment goal in orthodontics. 18 The curve of Spee is usually measured as the maximum of the perpendicular distances between the buccal cusp tips of the mandibular teeth and a measurement plane described by the central incisors and the distal cusp tip of the most posterior tooth in mandi bular arch. 48 A significant curve of Spee is often evident in malocclusions with deep overbites. This curve is frequently leveled as pro1 of overbite reduction. The curve of Spee has been associated with size of the jaw. In retrognathic mandibles a deeper curve of Spee is observed while in Class III patients a flat curve of Spee is usually observed. 51 Marshall et. a1. 48 did a study to examine the development of the curve of Spee longitudinally in a sample of untreated subjects with nOlmal occlusion from the deciduous dentition to adulthood. They found that the curve of Spee develops as the result of the mandibular permanent first molal' and incisor eruption. The curve maintains its depth until the mandibular permanent second molars erupt above the occlusal plane, when it deepens again. During the adolescent dentition stage, the curve depth decreases slightly and then remains relatively stable into early adulthood. The literature does not explore the formation of the curve of Spee from a developmental point of view. 19 Purpose of the Study With the advent of Cone Beam Computed Tomography (CBCT), it is possible to identify and trace anatomical structures which were considered challenging with conventional 2-dimensional radiography. The literature shows that inferior alveolar canal can be accurately identified on images produced by CBCT. As we know embryologically the inferior alveolar nerve is the first sttucture to be formed in the human mandible and this nerve has been strongly associated with bone and dental development in human mandible. Also it has been commonly observed that the residual ridge resorption does not continue beyond the inferior alveolar canal. We attempted to define the apical base at the level of inferior alveolar canal. As this canal is not a straight canal and forms a curve when viewed from sagittal view we also studied whether or not the curve formed by the inferior alveolar canal is related to curve of Spee, as this has never been studied before. The purposes of the study are:: 1. To establish a method to measure the apical base at the level of inferior alveolar nerve from a developmental perspective. 2. To assess whether the curve ofSpee is similar to the curve formed by inferior alveolar nerve when observed from the sagittal view. 20 Reference: 1. Proffit WR. Malocclusion and dentofacial defonnity in Contemporary Society. In: Proffit, Fields editors. Contemporary Orthodontics. Saint Louis: Mosby 1986 2. Van der Linden EM, McNamara JA. Glossary of Orthodontic Terms. In: Jude, Daskalogiannkis J, editors. Leipzig, Germany: Quintessence; 2000 3. Lundstrom A. Malocclusion of the teeth regarded as a problem in correction with the apical base. Int J Orthod Oral Surg Radiogr 1923; 11 :591-602 4. Salzmann JA. Orthodontic therapy as limited by ontogenetic growth and the basal arches. Am J Orthod 1948 Apr;34:297-319 5. Downs WB. Variations in facial relationships: Their significance in treatment and prognosis. Am J Orthod 1948;34:812-840 6. Reidel RA. The relation of maxillary structure to the cranium in malocclusion and in nonnal occlusion. Angle Orthod 1952;22: 140-145 7. Howes AE. Case analysis and treatment planning based upon the relationship of the tooth material to its supporting bone. Am J Orthod and Oral Surg 1947;33:499-533 8. SergI HG, Kerr WJ, McColl JH. A method of measuring apical base. Eur J Orthod 1996; 18:479.. 483 9. Kanaan W. The correlation between tooth size, basal bone size discl'epancy and long term stability of the lo\vel' arch in Class II Division 1 patients. Masters Thesis. Orthodontics. Saint Louis: Saint Louis Univel'sity; 2006. 10. Bell DG. Three-dimensional cone beam computed tomography assessment of basal bone parameters and crowding. Masters Thesis. Orthdontics. Sain Louis: Saint Louis University; 2008. 11. Kjaer 1. Histochemical investigations on the symphysis menti in the human fetus related to the fetal skeletal maturation in the hand and foot. Acta Anat 1975; 93:607-633. 12. Bollobas E. Embryonic development of the mandibular canal. Acta Morphol Acad Sci Hung 1982; 30(3-4): 233-9. 13. Radlanski RJ, Renz H, Reulen A. Prenatal development of the human mandible 3D reconstructions, morphometry and bone remodeling pattern, sizes 12-117 mm CRL. Anat Embyol (Bed.) 2003 Oct; 207(3):221-32. 21 14. Smartt JM Jr) Low DW, Battlett SPa The pediatric mandible: 1. A primer on growth and development. Plast Reconstr Surg. 2005 Jul; 16(4):563-71 15. Angelopoulos C, Thomas SL, Hechler S) Pal'issis N, Hlavacek M. Comparison between digital panoramic radiography and cone-beam computed tomography for the identification of the mandibular canal as part of presurgical dental implant assessment. J Oral Maxillofac Surg. 2008 Oct;66(10):2130-5. 16. Kelly JE, Harvey CR. An assessment of the occlusion of the teeth of youths 12-17 years. Vital Health Stat 11. 1977Feb;(162):1-65 17. Puri N, Pradhan KL, Chandna A, Sehgal V, Gupta R. Biometric study of tooth size in normal, crowded and spaced permanent dentitions. Am J Orthod Dentofacial Orthop. 2007 Sep;132(3):279.e7-17 18. Sarver DM, Proffit WR. Special considerations in diagnosis and treatment planning. In: Grabel', Vanarsdall, Vig, editors. Orthodontics Current Principles and Techniques. St. Louis: Mosby 2005. 19. Tweed CH. Indications for the extraction of teeth in orthodontic procedure. Am J Otthod Oral Surg. 1944-45;42:22-45 20. Brodie AG. Appraisal of present concepts in Orthodontia. Angle Otthod 1950~20:24-38. 21. Falck F. Comparative studies on the development of the tooth root following orthodontic treatment with the active plate and function regulator. Fortschr Kieferorthop. 1969;30(2):225-9 22. Miethke RR, Lindenau S, Dietrich K. The effect of Frankel's function regulator type IlIon the apical base. Eur J Otthod 2003;25:311-8. 23. Rees DJ. A method for assessing the propottional relation of apical bases and contact diameters of the teeth. Am J Orthod 1953;39:695 .. 707 24. Angle E. Treatment of malocclusion of the teeth and fractures of the maxilla. Philadelphia: The S.S.White Dental manufacturing company; 1900. 25. Nance HN. Limitations of Orthodontic diagnosis and treatment. Am J Orthod 1947;33:177-223,253-301 26. Carey CWo Treatment planning and the technical program in the four fundamental treatment forms. Am J Orthod 1958;44:887-98 22 27. MOn'ees CF. The dentition of growing child. A longitudinal study of dental development between 3 and 18 years of age. Boston: Harvard University Press; 1959. 28. Huckaba OW. Arch size analysis and tooth size prediction. Dent. Clin North Am 1964:431·40. 29. Musich DR, Ackelman JL. The catenometer: a reliable device for estimating dental arch perimeter. Am J Orthod 1973; 63:366~ 75. 30. Lundstrom A. The significance of early loss of deciduous teeth in the etiology of malocclusion. Am J Orthod 1955 ;41 :819-26 31. Hew SKM. Basal bone contour as related to dental arch form (Thesis). Saint Louis: Saint Louis University; 1966 32. BeGole EA. A computer progl'am for the analysis of dental arch form using cubic spline function. Comput Programs Biomed 1979;10:136-42 33. Champagne M. Reliability of measurements from photocopies of study models. J Clin Orthod 1992;26:648-50 34. Tran AM, Rugh JD, Chacon JA, Hatch JP. Reliability and validity of a computer based Little irregularity index. Am J Orthod Dentofacial Orthop 1997; 111 :543-53 35. Yamanl0to K, Toshimitsu A, Mikami T, Hayashi S, Harada R, Nakamura S. Optical measurement of dental cast profile and application to analysis of threedimensional tooth movement in orthodontics. Front Med BioI Eng 1989; 1: 119-30 36. Kuroda T, Motohashi N, Tominaga R, Iwata K. Three-dimensional dental cast analyzing system using laser seaMing. Am J 011hod Dentofacial 011hop 2004; 125 :716-25 37. Kjaer I. Neuro-osteolgy. Cdt Rev Oral BioI Med. 1998;9:224-44 38. Chavez-Lomeli ME, Mansilla Lory J, Pompa JA, Kjaer I. The human mandibular canal arises from three separate canals iMervating different tooth groups. J Dent Res. 1996 Aug; 75:1540-4 39. Christensen LR, Mollgal'd K, Kjaer I, Janas MS. Immunocytochemical demonstration of nerve growth factor receptor (NGF-R) in developing human fetal teeth. Anat Embryol. 1993 Sep; 188:247-55 40. Jakobsen J, Jorgensen JB, Kjaer 1. Tooth and bone development in a Danish medieval mandible with unilateral absence of mandibular canal. Am J Phys Anthl'0p0l. 1991 May;85:15-23 23 41. Bang E, Christensen LR, Kjaer 1. Etiologic aspects and 011hodontic treatment of unilateral localized arrested tooth development combined with hearing loss. Am J Orthod Dentofacial 011hop. 1995 Aug; 108: 154-61 42. Kjaer I, Kocsis G, Nodal M, Christensen LR. Aetiological aspects of mandibular tooth agenesis-focusing on role of nerve, oral mucosa and supporting tissues. Eur J Orthod 1994 Oct;16:371-5. 43. Sukovic P. Cone beam computed tomography in craniofacial imaging. Orthod Craniofac Res. 2003;6 Suppl 1:31-6 44. Tantanapornkul W, Okouchi K, Fujiwara Y, Yamashiro M, Manlola Y, Ohbayashi N, Kurabayashi T. A comparative study of cone-beam computed tomography and conventional panoramic radiography in assessing the topographic relationship between the mandibular canal and impacted third molars. Oral Sur Oral Med Oral Pathol Oral Radiol Endod. 2007 Feb; 103 :253-9 45. Friedland B, DonoffB, Dodson TB. The use of3-Dimensional reconstructions to evaluate the anatomic relationship of the mandibular canal and impacted third molars. J Oral Maxillofac Surg. 2008 Aug;66: 1678.. 85 46. Lofthag Hansen S, Grondahl K, Ekestubbe A. Cone-beam CT for preoperative implant planning in the posterior mandible: visibility of anatomic landmarks. Clin Implant Dent Relat Res. 2009 Sep; 11 :246-55 4 47. Naitoh M, Nakahara K, Suenaga Y, Gotoh K, Kondo S, Ariji E. Oral Surg Oral med Oral Pathol Oral Radiol Endod. 2010 jan;109:e25-31 48. Marshall SD, Caspersen M, Hardinger RR, Franciscus RG, Aquilino SA, Southard TE. Development of curve of Spee. Am J Orthod Dentofacial Orthop. 2008 Sep;134:344-52 49. Ash M. Wheeler's dental anatomy, physiology and occlusion. W.B.Saunders; 1993. i h ed. Philadelphia: 50. Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972 Sep;62:296309 51. Lynch CD, McConnell RJ. Prosthodontic management of the curve ofSpee: use of Broadrick flag. J Prsothet Dent 2002;87:593-7 52. Little RM. The Irregularity Index: A quantitative score of mandibular anterior alignment. Am J 011hod 1975;68:554-563 24 CHAPTER 3: JOURNAL ARTICLE Abstract Introduction: The difference between the mesio-distal width of teeth and the perimeter of apical base is defined as dental crowding. It is thought that a relationship of teeth to the apical base is essential for diagnosis and long term stability of orthodontic treatment. Unfortunately there is no reliable definition of apical base in literature. Researchers, have defined apical base using various methods, but none of the definitions have taken development into consideration. Purpose: This study will investigate if there is a relationship between the apical base measured at inferior alveolar nerve level, arch perimeter and crowding as measured on the plaster model. An attempt will also be made to detelmine if there is a relationship between the curve of Spee and the curve formed by the inferior alveolar nerve when viewed sagitally. Method: A sample of 27 randomly selected untreated patients with pre-treatment cone beam computed tomography (CBCT) scans and available pre-treatment plaster models were utilized. Patients were selected based on eruption of full permanent dentition in mandible. Data collected by CBCT included measurements of basal bone perimeter at the level of inferior alveolar nerve canal, and tracing of the curve of Spee and curve of the inferior alveolar nerve canal. Model analysis included meaSU1'es of the arch perimeter and dental crowding. 25 Results: The apical bas perimeter and arch perimeter measured on dental are significantly different A statistically significant difference was also observed between the two curves (curve of Spee and curve of the inferior alveolar canal). Conclusions: No relationship was established between the apical base measured at inferior alveolar nerve canal, crowding, and the arch perimeter as measured on modeL Similarly, the curve of Spee was significantly different from the curve formed by the inferior alveolar canal. 26 Introduction Cone Beam CT (CBCT) was introduced in USA in 2001. Since that time it has become clear that this imaging modality allows the clinician to identify anatomical structures which were not readily visible in conventional 2-dimensional radiographs. CBCT has application in all fields of dentistry, particularly in oral surgery and 011hodontics. Due to various advantages, CBCT is used for diagnosis and treatment planning, which is critical for establishing a foundation for successful orthodontic treatment. l The most common cause to seek orthodontic treatment is dental crowding . Van der Linden and McNamara2 define crowding as the discrepancy between tooth size and jaw size (apical base) that results in the misalignment of teeth. It is generally believed that when the tooth mass is too small relative to apical base, interdental spacing or diastemas will likely occur. Conversely, if the apical base in the body of the mandible is constricted or too small relative to tooth mass, the teeth will be crowded out of nOlmal anangement, or if normal arrangement is maintained, they will show a procumbent relationship to the mandibular plane. 3 4 The term apical base was first introduced by Lundstrom in 1923 and, since then, several attempts have been made to define the apical base. Techniques for measuring basal bone have varied as have its definition and location. Some of these methods to measure apical base are complicated and time consuming and result in variable estimations. An the methods reported to measure basal bone are based on anatomic location or personal perspective of basal bone. 5-1l 27 It's been shown that there is a strong relationship between the inferior alveolar nerve and development of mandible, 12·15 This relationship has never been studied to explain the location of apical base. The relationship between crowding and apical base is one that has been extensively investigated in the literature. There is a long standing belief that a strong relationship exists between basal bone~ the teeth and related alveolar bone. Now with advancements in dental radiography, CBCT can be used to identify inferior alveolar canal and the apical base can be measured at this level. 16·20 By utilizing CBCT, we will explore the relationship between inferior alveolar nerve and different aspects of dental crowding. 28 Materials & Methods Randomly selected 30 pre-treatment records of patients were retrieved from Orthodontic Department of Center for Advanced Dental Education at Saint Louis University. Records included pre-treatment images by iCAT Cone Beam Computed Tomography (Imaging Sciences International, Hatfield, P A) and pre-treatment plaster models. Inclusion criteria were patients of any age or gender with all teeth erupted except for third molars. Patients with signs of clinical or radiographic pathology that will interfere with the visualization of inferior alveolar canal were excluded. Any patient with impacted teeth in the mandibular arch was also excluded. If any image had an artifact that would interfere with visualization of inferior alveolar canal} it was not utilized in this study. 27 recol'ds met the inclusion criteria. Each patient was identified with a number to eliminate the possibility of patient identification. Image data was retrieved from the server of orthodontic dep8.liment at Saint Louis University. All the images were analyzed at Saint Louis University Center for Advanced Dental Education using Dolphin Imaging version 11.0 (Chatswolih, CA). For comparison of the curve ofSpee and curve formed by the inferior alveolar nerve canal Corel DESIGNER X4 version 14.1 (Corel Inc. Mountain view, CA) was employed. Measuring Basal Bone from Cone Beam CT at the Inferior Alveolar Nerve: Cone Beam CT images were assessed using Dolphin Imaging version 11.0. All the images were formatted using the "nerve canal" too]. With this tool the focal trough is 29 constructed by visualizing the inferior alveolar nerve canal on a sequence of the axial views. The focal trough was traced from the mandibular foramen in the ramus of mandible of one side to the mandibular foramen on the contralateral side by principal investigator (who is also a certified oral and maxillofacial radiologist). These tracings result in the production of a panoramic radiograph clearly depicting the inferior alveolar nerve canal (Figure 3.1). Using this panoramic radiograph the inferior alveolar canal was traced. Because the inferior alveolar canal stops at mental foramen, the nerve anterior to mental foramen was traced by joining the mental foramen of one side to the mental foramen of the contralateral side following the curvature of the anterior part of the mandible. This information can be transfen-ed to the multiplanar images including the 3dimensional volumetric image. As the nerve is not a straight linear stlucture, it is measured in very small segments (less than 5 mm) to compensate for curvatures in the nerve. These measurements were made placing points using "Landmark" tool in the Dolphin Imaging software. Landmarks were placed from the apex of distal root of second permanent molar of one side to the apex of distal root of second pennanent molar of the contra-lateral side. The landmark tool calculates the orientation of each point in x, y and z coordinates and produces accurate measurements between two landmarks (Figure 3.2). These distances were then added to produce the perimeter of nerve from distal root of one second molar to the distal root of contralateral second molar. This measurement was considered the perimeter of the apical base. 30 A) Refonnatted panoramic radiograph clearly depicting inferior alveolar canal. B) Inferior alveolar canal traced Figure 3.1: Panoramic radiographs reformatted from CBCT. 31 Figure 3.2: 3-Dimensional volumetric image: axial view showing measurement of inferior alveolar nerve made at very short intervals. 32 Model Analysis Conventional plaster models were utilized to perfolID two well established method of estimating crowding. The first method is recommended by Proffit and Fields; 1 it utilizes a direct approach on the dental casts. To measure the arch perimeter (space available), the dental arch is divided into segments that can be measured as straight line approximations of the arch, Four quadrants are created: distal of the left second molar to distal of left canine, distal of left canine to the mesial of left central incisor, mesial of right centl'al incisor to the distal of l'ight canine and distal of right canine to the distal of right second molar (Figure 3.3). Each quadrant was measured to the nearest hundredth of a millimeter. Space required was measured as the sum of the individual tooth widths from the distal of the mandibular left second molar to the distal of the right second molar. Figure 3.3: Quadrant diagram for straight line approximations of mandibular arch perimeter (modified from Bell's thesis). 33 In addition, Little's irregularity index was measured on each mandibular arch. The scoring method involved measuring the linear displacement of the anatomic contact point of the anterior teeth (canine to canine). The sum of five displacement values represents the relative degree of incisor irregularity. Tracing Curve of Spee 3-dimensional volumetric data was refolmatied to generate lateral cephalometric view of the hemi-mandible. All the mandibles in the study were divided into left and right and a total of 54 hemi-mandibles were used to trace the curve of Spee. Lateral cephalometric images of the hemi-mandible \vere generated in a way that all the incisaVocclusal edges of mandibular teeth from lower central incisors to the second molar are clearly visualized (Figure 3.4). After lateral cephalometric of the hemi-mandible was generated, the images were saved and transfen'ed to Corel DESIGNER X4 for tracing the curve of Spee. Using the 3 point curve tool in Coral DESIGNER X4 a curve was consttucted to the best fit of cusp tips of all the mandibular teeth. 34 A) Reformatted lateral cephalogram B) Curve of Spee traced Figure 3.4: Lateral cephalogram refolmatted from CBCT: 35 Tracing Curve of the Inferior Alveolar Nerve Using the "Nerve Canal" tool in Dolphin Imaging software the panoramic image depicting the inferior alveolar canal was generated as described above. This time the nerve was traced from the mandibular foramen to the mental foramen on both sides. This nerve tracing was than transferred to 3~dimensional volumetric image. On 3-dimensional volumetric image a point \vas marked on the nerve cOll'esponding to the distal root apex of the second molar and another point was marked at the apex of the lower central incisor of the same side. These images were then saved and transferred to Corel DESIGNER X4. Using the same 3 point curve tool in this software a curve was constructed using points marked on the image and simultaneously fitting the curve to the curvature of the nerve (Figure 3.5). Intra-rater Reliability A reliability test was perfolmed to evaluate the measurement error. Four of the 27 cases were randomly selected and measurements of the nerve perimeter and comparison of the curve ofSpee and curve of the inferior alveolar nerve were duplicated. Intraclass Correlation Coefficient (ICC) was executed on the repeated measures. A perfect score equals 1.00; however, a Cronbach's Alpha ~ 0.8 is considered an indicator of a reliable technique. SPSS version 18 (SPSS Incorporated} Chicago, IL) was used to calculate intraclass correlation coefficient. 36 Figure 3.5: Curve of the inferior alveolar nerve traced on sagittal view of3-dimensional volumetric image 37 Comparison of Curves: The traced curve of Spee and the curve formed by the inferior alveolar nerve were isolated from the images using Corel DESIGNER X4. In order to quantitatively compare the two curves a plane was constlucted between the two ends of each curve. That plane was then divided into 6 equal segments21 from which perpendiculars were extended to the base of the curve at each segment (Figure 3.6). The two curves were then compared mathematically by similar ratios at each segment. Mathematically this comparison can be explained as: 38 A) Curve of Spee '" .1'/ ....................... _-----------. ........ -- ------- -- .------_¥ // ".,.,.,/ B) Curve formed by Inferior Alveolar Nerve Figure 3.6: Comparison of curves by dividing each curve into 6 equal segments a) Curve of Spee b) Curve formed by Inferior Alveolar Nerve 39 Statistical Analysis It is hypothesized that when comparing apical base at the level of inferior alveolar nerve and the perimeter of basal bone on plaster model a relationship will be observed. Also there is a correlation between the nerve perimeter and the crowding estimated by two established methods. The curve of Spee and curve formed by the inferior alveolar nerve are similar. In ordel' to test these hypotheses, descriptive statistics were computed for all the variables. Paired sample t-test was computed for apical base and perimeter of basal bone on plaster model comparison. Pearson's correlation was used to analyze whether relationship existed between variables. SPSS version 18 (SPSS Incorporated, Chicago, IL) was used to calculate all the statistics. 40 RESULTS Inferior Alveolar Nerve Perimeter: Descriptive statistics were calculated for the model analysis measures. The range, mean and standard deviations are reported in Table 3.1. The average space available (basal sum) by Proffit's method over the sample was 104.4 mm, while the average space available by measuring the inferior alveolar nerve perimeter was 113.5 mm. The average discrepancy was -1.7 mm by Pfoffi t' s method of cast analysis, while average value for Little's irregularity index was 4.4 mm. Intrac1ass Correlation Coefficient (ICC) was calculated from error measurements on four patients (Table 3.2). It was found that the measurements are highly repeatable. Table 3.1: Descriptive Statistics for 27 patients~ model analysis. Values repolied in millimeter Mesurement N Maximum 27 27 27 -8.2 118.9 119.2 9.2 104.4 106.1 -1.7 5.3 6.3 4.1 27 27 0.1 101.1 14.2 128.3 4.4 113.5 3.1 7.1 S.D. Proffit Cro\vdin Basal Sum Tooth size sum Discrepanc Little Crowdin Irregularit Index Nerve Perimeter 41 Table 3.2: Cronbach's Alpha for Intra-rater reliability Measurement Nerve Perimeter Curves Section 1 Section 2 Section 3 Section 4 Section 5 Cronbach's Alpha .96 Spee Nerve .90 .97 .91 .98 .97 .89 .94 .99 .98 .95 Pearson's correlation was used to analyze whether relationships existed between the nerve perimeter and Proffit's method of crowding and nerve perimeter and Little's irregularity index. It was also assessed if there is any relationship between nerve perimeter and tooth size sum (Table 3.3). Low values ofR indicate no correlation exists between the groups. Table 3.3: Pearson's correlation for the nerve perimeter and methods of crowding. Measurement Nerve Perimeter-Proffit Crowding Nerve Perimeter-Little's Crowding Nerve Perimeter-Sum of Teeth R 0.55 0.38 0.53 A paired sample t-test was done to compare the nerve perimeter to the apical base measured by Proffit's method. Table 3.4 show these two measurements are significantly different (Sig. (2-tailed) = .000) from each other. Table 3.4: Comparison of inferior alveolar nerve perimeter and arch perimeter by P1'0ffit' I d b>y patre . d sampe Itt ; analyze - est . 1 S me th 0 d S.D. Sig. (2-tailed) Mean Group N 27 113.5 7.18 .000 Nerve Length Arch Perimeter 27 104.4 .000 5.37 42 Comparison of Curves: Table 3.5 and 3.6 shows the descriptive statistics for each curve. Each curve was sectioned into five equal segments and these segments were than compared. Means and standard deviations were calculated for each segment of both the curves. Table 3.5: Descriptive Statistics; Measurement of sections in the Curve of Spee Sections 1 2 3 4 5 N 54 54 54 54 54 Mean(mm) 1.18 2.16 2.92 3.27 2.98 S.D. (rom) .52 .94 1.25 1.40 1.28 Table 3.6: Descriptive Statistics; Measurements of section of the curve of the Inferior Alveolar Nerve Sections 1 2 3 4 5 Mean(mm) 3.55 5.75 6.64 6.18 4.10 N 54 54 54 54 54 S.D. (mm) 0.67 1.08 1.34 1.46 1.23 Paired sample t-test was computed to compare the curves of the right side to the curves of the left side. Table 3.7 shows that the curves on two sides are similar at each section. 43 Table 3.7: Comparison of Left and Right side curves by paired sample t~test. Section l~L* 2-L 3~L 4~L 5~L I~R** 2-R 3~R 4-R 5-R N 54 54 54 54 54 54 54 54 54 54 Mean (mm) 2.41 4.00 4.81 4.73 3.54 2.33 3.91 4.75 4.72 3.53 S.D. (mm) 1.38 2.11 2.27 2.03 1.35 1.29 2.03 2.29 2.07 1.40 Sig (2~tai1ed) .74 .81 .90 .99 .97 .74 .81 .90 .99 .97 L*~Left R**- Right Independent sample t~test was computed to compare the curve of Spee and the curve of the inferior alveolar nerve. Data show that the two curves are significantly different and are not dependent on each other. Table 3.8: Comparison of the curve of Spee and the inferior alveolar nerve at each section b )y '1n dependent samp.1e tt - es t . Mean(mm) S.D. (mm) Sig (2-tailed) Section N 1.18 I-N* 0.00*** .52 54 2~N 54 2.16 .94 0.00 54 3-N 2.92 1.25 0.00 4-N 3.27 1.40 54 0.00 1.28 5-N 54 2.98 0.00 54 I-S** 3.55 .67 0.00 2-S 54 5.75 1.08 0.00 54 6.64 1.34 0.00 3-S 4-S 54 6.18 1.46 0.00 5-S 1.23 54 0.00 4.10 N*-Nerve S**~Curve of Spee *** no correlation 44 Discussion The purpose of this study was to attempt a new definition of basal bone based on the embryologic development of mandible. The study was designed to assess if there is a relationship between apical base measured at inferior alveolar nerve (IAN) and apical base measured on a plaster model. It was hypothesized that arch perimeter as measured by He~2 and recommended by Proffit and Fields l in their text book are dependent on the arch perimeter measured at the IAN (Le., a large basal hone at IAN) will result in a large perimeter in the cast; the results showed that there is no correlation between these two measurements. Inferior Alveolar Nerve as Apical Base In human craniofacial skeleton the mandible is seen by the ih_sth week of fetal life. The ossification of human mandible starts at the point of future mental foramen. The literature has shown that a single ossification center for each half of the mandible fOlms lateral to Meckel's cartilage at the bifurcation of the inferior alveolar nerve. 13,14 From this center, ossification proceeds ventrally to the body and dorsally to contribute to the mandibular ramus. Bone deposition begins to proceed superiorly around the neurovascular bundles to provide a bony framework for developing teeth. I5 It is obvious from the literature that there is a strong association between nerve tissue and osseous development. Kjaer23 used the term Neuro-Osteology which emphasizes the biologic connection during development between nerve and hard tissues. In the orthodontic literature the significance of having teeth upright over the basal bone has been discussed numerous times. It is a strong belief in orthodontic community that the stability of the result depends on the relationship of the teeth to the basal bone. 3 45 To date there is no specific definition of apical base/basal bone. This issue was addressed by Brodie in 1950~ when talking about basal bone he said "upon critical questioning, however, the definition (of the apical base) become vague." Several attempts have been made to define the apical base, but none of the methods to define basal bone have satisfactorily addressed the issue. Previously, several attempts were made to identify the apical base, using traditional orthodontic records, including plaster models and cephalogram, surveyors and recently CBCT. s.11 The literature showed a strong association between nerve tissue and osseous and dental development. 12-15 We attempted to define apical base as the bone which is surrounding the inferior alveolar canal as this is the first osseous structure to be formed in mandible. Other than the concept ofNeuro-osteology another factor that leads us to this belief is that, when observed in an edentulous patient the resorption of residual ridge continues until it reaches the inferior alveolar canal, at this point the residual ridge usually stops resorbing. 26 Cone Beam CT is increasing in popularity and literature has shown that anatomical structures that were not easily identified on 2-dimensional radiographs can be easily identified by utilizing cone beam CT. 16 Utilizing CBCT, a new assessment of basal bone parameter was performed in 27 orthodontic patients. We attempted to assess whether the apical base defined at IAN level is related to arch perimeter measured on plaster modeL Our results indicated that there was no relationship observed and the null hypothesis was rejected. This could be due to the difference in the way the measurements were made. For the measurement of nerve perimeter, curvatures of nerve canal within the mandible were measured; however, for the perimeter of apical base according to Proffit's 46 method, lineal' measurements were made and curvatures of alveolar crest (apical base) were not taken into consideration. We chose to measure the perimeter on plaster model according Proffit's method, as this is the most common way of estimating apical base. Using CBCT, we can measure the perimeter at the level of cervical margins of teeth; this will allow us to accommodate curvatures of the alveolar crest. This may produce different results. A challenge in this method would be find patients with fully developed occlusion and healthy periodontium. We measured the inferior alveolar nerve at very small intervals; this was done to compensate for curved path of the inferior alveolar canal. We used Dolphin Imaging version 11 for making measurements and this software allowed us to mark points on the inferior alveolar canal at regular intervals. Orientation of each point was than calculated in x, y and z coordinates by the software and the exact distance between two points was calculated, this helped us in eliminating possible human errors. We used apex of distal root of second permanent molar in our study as the terminal point for measurement of the inferior alveolar canal, this was done because Bell il suggested that value of perimeter back to the mandibular foramen were found to be inconsistent, he suggested that this was the result of the inclination of mandibular ramus. Curve of Spee and Inferior Alveolar Nerve: The relationship between the inferior alveolar nerve and development of the teeth has been discussed in literature. This was the first study that evaluated the relationship of the curve of Spee to the inferior alveolar nerve. Our results indicate that inferior alveolar nerve is not related to the development of the curve of Spee. Since, no study has evaluated the curve ofSpee from developmental aspect; a number of factors may playa 47 role in development of the curve of Spee. We traced the curve of Spee from distal cusp of second molar to the incisal edge of the central incisor, but had we chosen the central groove of the second molar instead of the distal cusp, we may have seen different results. Another factor that may contribute to the development of the curve of Spee is the path of eruption of teeth. Studies have shown that a close relationship exist not only between tooth development and nerve development, but also between tooth development and development of surrounding bone tissue. 12 As bone forms around the teeth in its path of eruption, studies evaluating factors that determine the path of eruption of teeth may be helpful in understanding the curve of Spee from a developmental aspect. We compared the t\vo curves by using a mathematical formula to compare the curve of Spee. We chose this method because this method would allow us to compare the two curves in small segments. Both curves were divided into 6 equal segments and than each segment were compared to conesponding segment on the other curve. A similar method of comparing curves has been used previously.21 Another method of comparing curves would be to measure the radius of the arc formed by two curves. This would give one reading for each curve and it will not compare the curves in small segments. It is possible that if other methods of comparing two curves are applied, this may produce a different result. 48 Conclusions 1. A con-elation among the inferior alveolar nerve perimeter and the arch perimeter measured on plaster model was not observed. This suggests that there is no relationship between inferior alveolar nerve and dental arch perimeter. 2. A cOll'elation between the nerve perimeter and the Proffit's method of measuring crowding was slightly higher than the cOll'elation between the nerve perimeter and Little's in-egularity index. The con-elation for both these values was low. Such low correlations have almost no value in prediction. 3. Based on the results of this study, development of the curve ofSpee may not be associated with curve formed by the inferior alveolar nerve when viewed sagitally. 49 Literature Cited: 1. Proffit WR. Malocclusion and dentofacial deformity in Contemporary Society. In: Proffit, Fields, Editors. Contemporary 011hodontics. Saint Louis: Mosby 1986 2. Van der Linden EM, McNamara JA. Glossary of Orthodontic Terms. In: Jutte, Daskalogiannkis J, Editors. Leipzig, Germany: Quintessence; 2000 3. Tweed CH. Indications for the extraction of teeth in orthodontic procedure. Aln J Orthod Oral Surg. 1944-45;42:22-45 4. Lundstrom A. 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Br J Oral Maxillofac Surg. 1993 Dec;31 :370-5 51 VITA AUCTORIS Anas Athar was bOITI on 15th of October 1979 in Saudi Arabia. Dr. Athar is the youngest of four children. At the age of four years he moved to Karachi, Pakistan in 1983. In 1995 he graduated from B.V.S. Parsi High School, he then continued his education at D.J.Sind Government Science College for his pre-dental education. After graduating from college, Dr. Athar started his dental education from Baqai Medical University in 1998. He graduated from dental school and received his Bachelor of Dental Surgery degree in 2002. Dr. Athar then moved to U.S.A in 2003 and started his postgraduate training in Oral and Maxillofacial Radiology (OMFR) from UMKC School of Dentistry in Kansas City, MO. He completed his OMFR training in 2005 and joined UMKC School of Dentistry as an Assistant Professor. In 2006, he received his Master of Science in Oral Biology from UMKC School of Dentistry. During his time as faculty at UMKC School of Dentistry, he lectured on various topics in Oral and Maxillofacial Radiology, nationally and internationally. In 2008, Dr. Athar was accepted into the 011hodontics residency program at Saint Louis University. He has two publications and has presented research papers at various conferences. He ma11'ied his wife, Samia~ in December, 2006. They have two children, a two years old daughter, Amna and a five month old son, Mustafa, bOlTI during his residency in August, 2010. Dr. Athar and his family are planning to move to San Antonio, Texas after completing his Orthodontic residency. 52