Assessment of Initial Reaction of Nasomaxillary Complex to Maxillary Protraction using Electronic Speckle Pattern Interferometry

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1 /jp-journals ORIGINAL ARTICLE Poornima Raghuraman Jnaneshwar et al Assessment of Initial Reaction of Nasomaxillary Complex to Maxillary Protraction using Electronic Speckle Pattern Interferometry 1 Poornima Raghuraman Jnaneshwar, 2 Prem Kumar Sridhar, 3 WS Manjula, 4 Basanta Bhaduri ABSTRACT Objective: The aim of this study was to evaluate the initial reaction of nasomaxillary complex to protraction force using electronic speckle pattern interferometry (ESPI). Materials and methods: The experiment was done on a dry human skull. Orthopedic protraction forces were applied bilaterally at two different levels; one at the occlusal level and the other at about 15 mm above the occlusal plane and the bone response was studied at two different parameters for each point of force application, namely reactions at 0 angulation and 20 downward to the occlusal plane and to two different force magnitudes of 10 ounces (280 gm) and 16 ounces (453.6 gm). The tests were repeated after expansion and the bone response patterns were compared with preexpansion patterns. Results: The results showed that when a protraction force was applied at the occlusal level, maxilla underwent anterior displacement and counterclockwise rotation. Maxilla underwent pure translation without rotational component when the protraction force was applied at 15 mm above the occlusal plane at an angle of 20 downward to the occlusal plane with activation of the rapid expansion screw by quarter turn. The image obtained during translation was used to locate the center of resistance of nasomaxillary complex. Conclusion: The study highlighted the importance of expanding the maxilla prior to or during the application of protraction force. ESPI is a valuable tool in the evaluation of initial bone response following orthopedic traction in orthodontics. Keywords: Maxillary protraction, Electronic speckle pattern interferometry, Fringe pattern. How to cite this article: Jnaneshwar PR, Sridhar PK, Manjula WS, Bhaduri B. Assessment of Initial Reaction of Nasomaxillary Complex to Maxillary Protraction using Electronic Speckle Pattern Interferometry. J Ind Orthod Soc 2013;47(1): INTRODUCTION Skeletal Class III malocclusion due to maxillary retrognathism warrants early treatment as maxillary growth closely follows the neural growth. Orthopedic traction to protract the maxilla using facemask forms the mainstay of treatment modality in such cases. The forces of protraction are not applied just to the maxillae but are transmitted to many bones namely zygomatic, sphenoid, frontal and ethmoidal bones. 1,2 Rapid maxillary expansion (RME) is required to loosen the circum maxillary sutures, which will ease the process of protraction. The methods used for studying bone changes to applied forces vary from strain gauges 2 to photoelasticity, 3 to 1 Reader, 2 Professor, 3 Professor and Director of PG Education 4 Postdoctoral Associate 1 Department of Orthodontics, SRM Dental College, Ramapuram Chennai, Tamil Nadu, India 2 Department of Orthodontics, Tamil Nadu Government Dental College and Hospital, Chennai, Tamil Nadu, India 3 Department of Orthodontics, Sree Balaji Dental College, Pallikaranai Chennai, Tamil Nadu, India 4 Department of Applied Optics, Indian Institute of Technology, Chennai Tamil Nadu, India Corresponding Author: Poornima Raghuraman Jnaneshwar, Reader Department of Orthodontics, SRM Dental College, Ramapuram Chennai, Tamil Nadu, India, poorni01@gmail.com Received on: 31/3/12 Accepted after Revision: 9/7/12 10 holograms 4 and finite element method. The use of strain gauges is an invasive procedure, which might alter the surface characteristic of the bone. In the photoelastic studies, the models of skull are constructed using epoxy resins that have elastic moduli grossly different form that of bone. Instruments like dial indicators and other electronic devices give only linear value of displacement and do not give a qualitative account of the displacement pattern. Finite element method views structures as isotrophic and homogenous but bone cannot be considered a homogenous structure. Moreover, finite element method produces only a computer simulation of the skull that may not be accurate. Techniques utilizing laser for measuring bone displacement have the following advantages, they are noninvasive and nondestructive; the object under study is not in contact with the measuring device. Electronic speckle pattern interferometry (ESPI), a recent advancement in the field of holographic interferometry has the following advantages over holography. The images in ESPI are viewed in real time so that the experiment can be repeated immediately if it is felt that the image is not proper due to movement of the object. There is no need for chemical development of the photographic/ holographic plate. Viewing the images in real time gives us the advantage of recording it immediately so that there is no interference/obstacle due to other vibrations (micro- JAYPEE

2 JIOS Assessment of Initial Reaction of Nasomaxillary Complex to Maxillary Protraction using Electronic Speckle Pattern Interferometry vibrations). The aim of the study was to analyze using ESPI: (i) the initial changes in the nasomaxillary complex to the protraction force before and after expansion; (ii) the effect of changing the direction of force application on protraction; (iii) the effect of changing the point of application of force on protraction and (iv) to locate the center of resistance of nasomaxillary complex and compare with previous studies. MATERIALS AND METHODS A dry human adult skull with a complete set of well aligned permanent teeth, symmetric maxillary arch and no physical damage was used for the study. A splint with Hyrax screw was fabricated for assisting in protraction and expansion 5 (Fig. 1A). Two hooks soldered distal to first premolar roots bilaterally, one at the level of occlusal plane and the second 15 mm above the occlusal plane. A stainless steel framework was fabricated to fix the skull rigidly as even microvibration of the specimen would give erroneous results. The framework had a platform, one and a half inches in height, for placement of the skull (Fig. 1B). The skull was immobilized using four screws (two at temporal Fig. 1A: Appliance fabricated for applying protraction force fossae, one at sagittal suture, one at occipital region) with an intermediary agent (impression compound) to prevent damage to the skull. The skull was made to rest on the platform in such a way that the contact of the appliance with the platform was in the second molar region and the rest of the maxilla was suspended without touching the platform. The occlusal surface was parallel to the floor and the framework with the skull was placed on a vibration resistant table with rubber tubing which buffered minor vibrations. PRINCIPLE OF ELECTRONIC SPECKLE PATTERN INTERFEROMETRY ESPI is an advancement of holographic interferometry, both working on the common principle of coherent interference of laser beam. An expanded laser beam is used to illuminate both the object and a mirror called reference mirror. The reference beam falls on the holographic plate and the object beam from the object carries information about the object at that instant/time. The deformations of the object are carried by the object beam and when it interferes with the reference beam, the fringe pattern is obtained which is recorded in the holographic plate. The basic ESPI system consists of an optical head, charged couple device (CCD) camera, host computer, image processing system and a TV monitor (Fig. 1C). Helium Neon (He-Ne) laser of wavelength nm, generating an expanded laser beam, was used to illuminate the object and reference mirror (RM) simultaneously. It is mandatory to keep both the object and reference mirror in the same plane. A Michelson interferometer in the setup received the scattered light from the object and imaged it via the mirror M2 and imaging lens L onto a CCD camera. In the experiment, the mirror M1 was mounted on a precision rotational stage. The mirror was rotated such that it received the scattered light from the mirror (RM) and neutral density (ND) filter and transmitted the same to the CCD camera via a cube beam splitter (BS). The CCD camera was interfaced to a personal computer (PC) with the frame grabber chord. Image acquisition with phase stepping was carried out with the support of software LabVIEW. Smooth reference wave was provided by the ND filter. Fig. 1B: Experimental specimen: The skull with the framework Fig. 1C: ESPI set-up: Schematic diagram of ESPI apparatus The Journal of Indian Orthodontic Society, January-March 2013;47(1):

3 Poornima Raghuraman Jnaneshwar et al Temporary photograph Fig. 2A: Force application at the level of occlusal plane and parallel to it. Arrow showing the apex of the inverted V Fig. 1D: Arrows showing the direction of protraction force. Red arrows showing parallel and 20 downward direction at occlusal level and yellow arrows indicating same directions at a level 15 mm above the occlusal plane. Movable mount to which the other end of elastic was attached is also seen in the picture PROCEDURE The anterior traction force was applied by means of orthopedic elastics attached to the hooks on the appliance at one end, and to a movable mount on the other end so that the chosen magnitude of force could be accurately applied. A dynamometer (Captain Ortho, USA) was used for measuring force. Two different force magnitudes of 10 (283.5 gm) and 16 ounces (453.6 gm) were applied bilaterally at two levels: At the level of occlusal plane and 15 mm above the occlusal plane. The direction of the elastic traction also had variables; one parallel to the occlusal plane and the other 20 downward from the occlusal plane (Fig. 1D). So, for each level of force application, the magnitude of force was of two variables (10 and 16 ounces) and direction of traction also had two variables. After recording the deformations for all the variables, the Hyrax screw in the splint was activated by turning it one-quarter turn and the experiment was repeated for all the previous different parameters. The idea of activating the screw after recording the initial deformation was to capture the displacement images of the skull in their original form, without the effect of expansion masking them. The skull was exposed to laser initially for 15 seconds and the traction applied for a period of 5 minutes. The deformation was then registered for a period of 15 seconds. Between every force application, there was a time gap of 5 minutes, which ensured that the previous strain gets dissipated. Interferometric images were recorded in the frontal view. The images were stored in the PC. A qualitative and quantitative analysis of the fringe pattern was done with the help of the images obtained during the experiment. RESULTS Qualitative Evaluation of Fringe Pattern When 280 gm of force was applied, optimal fringe pattern was not obtained; hence, fringe pattern obtained with 16 ounces 12 Temporary photograph Fig. 2B: Force application at the level of occlusal plane with 20 downward to occlusal plane. Arrow showing the change in direction of fringe at sutures Fig. 2C: Force application at 15 mm above occlusal plane and parallel to occlusal plane. Arrow pointing to the apex of the inverted V Temporary photograph Fig. 2D: Force application at 15 mm above occlusal plane and 20 downward to the occlusal plane. Arrow showing the apex of the inverted V skewed to one side Figs 2A to D: Fringe pattern obtained when 450 gm was applied prior to expansion JAYPEE

4 JIOS Assessment of Initial Reaction of Nasomaxillary Complex to Maxillary Protraction using Electronic Speckle Pattern Interferometry (453.6 gm) were considered for analysis. Fringe pattern obtained with 16 ounces (453.6 gm) before activation of expansion screw were as follows (Figs 2A to D): 1. When force was applied parallel to and at the level of occlusal plane, the predominant fringe pattern was horizontal in the area of teeth and alveolar bone. The fringe pattern became more vertical in the region of nasal bridge. Thus, during maxillary protraction, the direction of displacement of maxilla is forward with upward or anterior counterclockwise rotation. 2. When force was applied at the level of occlusal plane but at 20º downward to the occlusal plane, fringes obtained were more vertical and in inverted V pattern. 3. Fringe pattern varied when the point of application of force was shifted to about 15 mm above the occlusal plane. The direction of the fringes became more vertical (like an inverted V) than horizontal in the area of zygoma whereas in the maxilla they remained horizontal. 4. When direction of force was altered to 20 downward to occlusal plane at about 15 mm above the occlusal plane, the fringes obtained were more vertical and inverted V shaped. With the same magnitude of force, two points of force application and the two different direction of force application, protraction force was applied after the screw was expanded one-quarter turn (0.25 mm; Figs 3A to D). The changes were: 1. The inverted V changed into V pattern showing that with the application of expansion, protraction no longer had a constrictive effect on the anterior maxilla. The V fringes were not the same and symmetrical in all the images. There was variation in the number of fringes and also direction of V. In some images the V was smooth while in others the arms of the V had a steep slope. 2. With the force application at the level of occlusal plane and parallel to the occlusal plane, the fringe pattern obtained was almost horizontal with a sloping V in the region of maxilla and zygoma. Fig. 3A: Force application at the level of occlusal plane and parallel to it. Arrow showing the inversion in the direction of the fringes after expansion Fig. 3C: Force application at 15 mm above the occlusal plane and parallel to the occlusal plane. Apex of the V fringe skewed to one side Fig. 3B: Force application at the level of occlusal plane and at a direction of 20 downward to it. Note that the apex of the V is at a much lower level. This shows that the constrictive effect of anterior maxilla is nullified after expansion Fig. 3D: Force application at 15 mm above the occlusal plane and about 20 downward to the occlusal plane. Circular fringes on either side of pyriform aperture are highlighted. V-shaped fringed are steep with the apex centered Figs 3A to D: Fringe pattern obtained when 450 gm of force was applied after expansion of the hyrax screw by 1/4 turn The Journal of Indian Orthodontic Society, January-March 2013;47(1):

5 Poornima Raghuraman Jnaneshwar et al wavelength of the laser used. In the present study, He-Ne laser was used with wavelength of nm. For each image, displacement is calculated in nm by counting the number of fringes and multiplying the value by /2. The formula is: d = n The highest displacement as measured in microns was found to be (Table 1) and the least displacement was 2.5. On an average, the displacement was DISCUSSION Fig. 4: Location of center of resistance: Horizontal and vertical lines drawn to locate the center of the circular fringe. Horizontal reference lines are drawn touching midline of the skull, center of the circular fringe bilaterally and zygomaticomaxillary sutures bilaterally. The vertical reference lines are drawn touching the infraorbital margin, center of the circular fringe and inferior most part of the zygoma 3. Asymmetric V shaped fringes were obtained when force was applied at the occlusal plane with 20º downward angulation and similar results were obtained when force was applied at about 15 mm above the occusal plane with the direction of force application parallel to the occlusal plane. 4. When gm of force was applied at a distance of 15 mm above the occlusal plane, at an angle of 20º downward, circular fringes were seen along with the V fringes which were almost vertical (Fig. 3D). The circular fringes were located on either side of the piriform aperture bilaterally. The center of the circular fringe could be located exactly (Fig. 4). Quantitative Evaluation Fringes represent contours of constant displacement. Displacement is minimum around the periphery of the object under study due to boundary conditions, i.e. peripheral portions are rigidly fixed from getting displaced. Displacement of the object can be evaluated using the method of manual counting of the fringes which gives an approximate idea of displacement in nanometers (nm). Either the dark or light fringe is counted. The value for each fringe corresponds to /2 where is the Table 1: The quantitative evaluation of the displacement in microns Serial Image No. of Displacement Displacement no. fringes n /2 in microns ( = nm) 10 3 nm ( ) 1 2a b c d a b c d wavelength of He-Ne laser = nm, n number of fringes 14 Application of an orthodontic force results in primary and secondary displacement. 6 Similar reactions are observed when an orthopedic force is applied to bone to correct skeletal malocclusion; there is an initial mechanical reaction and the subsequent biological response. Knowledge about the initial reaction to the applied orthopedic force helps to differentiate the effects of applied force from the response to normal growth pattern of the individual. In the present study, ESPI has been used to study the initial reaction of maxillary complex to protraction on a dry human skull, as the safety of the He-Ne laser in live subjects is not guaranteed. 7 Application of protraction force (450 gm) at the level of occlusal plane and parallel to it resulted in horizontal fringe pattern. This correlated with the results of Lee et al. 4 Prior to expansion, fringe pattern were near horizontal at the level of the teeth and the alveolar process but at a higher level, i.e. near the infraorbital rim, the fringes changed into an inverted V pattern ( ) with the apex of V at the midline (Fig. 2A). Horizontal fringes indicate rotation of the object under study, about an axis perpendicular to the direction of fringes. In the study, protraction force was applied which causes a forward movement and rotation in the counterclockwise direction. Prior to expansion, protraction forces yielded inverted V fringes. This shows that there is a transverse component to the rotation of maxilla. The location of inverted V was at the level of the nasal bridge when force was applied at the occlusal level. This shows that there is a constrictive effect on maxilla. This constriction effect on anterior palate coincided with the results of Hata et al; 2 Itoh et al 3 and Lee et al. 4 With the change in the direction of force application, 20º downward to the occlusal plane, the fringes obtained were inverted V fringes and not horizontal. This denotes that there is a reduction in the rotational component but pure translation was not achieved (Fig. 2B). When the point of force application was shifted to 15 mm above the occlusal plane and parallel to it, maxilla underwent forward movement with counterclockwise rotation (Fig. 2C). When the direction of force application was changed to 20º downward to the occlusal plane at a distance of 15 mm, there was a reduction of rotation component, there was a visible change in the direction of the fringes from near horizontal to a more of vertical pattern (Fig. 2D) with the maintenance of inverted V pattern in contrast to circular fringe pattern obtained in the study of Lee et al. 4 Though the point of JAYPEE

6 JIOS Assessment of Initial Reaction of Nasomaxillary Complex to Maxillary Protraction using Electronic Speckle Pattern Interferometry application of force was shifted to a higher position at 15 mm above the occlusal plane, it had no effect on the constrictive effect of the protraction force, the inverted V fringes were still obtained. At the areas of sutures, the direction of fringe changed abruptly (Fig. 2B). This is in accordance with the results of Dermaut et al, 8 Kragt et al, 9,10 Lee et al. 4 The sutures act as hinge or adjustment areas of the bone. The change in the direction of the fringes was seen in frontonasal, frontomaxillary and zygomaticomaxillary sutures. The results of the experiment after expansion showed that the inverted V pattern seen with protraction before expansion changed to V pattern.when the force application was at the level of the occlusal plane, the fringes were V fringes with near horizontal pattern (Fig. 3A). As the point of application of force was altered to 15 mm above the occlusal plane, the V fringes obtained were more vertical and had steep slope (Fig. 3C). The rotation component was reduced. Apex of the V was at a much lower level, i.e. below the infraorbital rim and alveolus. The inversion of the apex of the V and descent of its location after expansion indicates that the transverse constriction obtained before expansion is nullified by expansion (Figs 3A to C). Anterior protraction of maxilla with rotation leads extrusion of posterior teeth, counterclockwise rotation of the occlusal plane and clockwise rotation of mandible. 3 When gm of force was applied at 15 mm above the occlusal plane at an angle of 20º downward to the occlusal plane after expansion, the V shaped fringe pattern was seen accompanied by circular fringes on both sides of the piriform aperture (Fig. 3D). The circular fringes denote that object under study undergoes pure translation, i.e. maxilla undergoes pure translation. The center of the circular fringe could be accurately located in the present study (Fig. 4). It was found that the center of the fringe was 64.5% of the distance from the midline to the zygomaticomaxillary sutures. This value correlated with the results of Lee et al. 4 In the horizontal axis, it was found that the center of the fringe was located at 40% of the distance from the infraorbital margin to the inferior border of zygoma. In the study by Lee et al, 4 the location of circular fringe is 13% of the distance from the zygomaticomaxillary axis to the infraorbital margin. The zygomaticomaxillary axis has not been defined clearly and in this study, the inferior border of zygoma is taken to mark the reference axis since it is seen better and clearer. Many studies have determined the center of resistance of nasomaxillary complex to be at the posterosuperior portion of zygomaticomaxillary suture. The location of the center of the circular fringe in the present study is more medial and at a higher level than the other studies. 4 When expansion is applied to maxilla during protraction, it not only helps in the disruption of the sutural system but also seems to nullify the constrictive effect of the protraction force on the anterior palate. This revelation of the constrictive effect on the anterior palate due to the protraction appliances is a significant aspect of the study and it throws light on the importance of giving expansion 2 weeks before the start of facemask therapy. CONCLUSION The application of protraction force without expansion at the level of occlusal plane without change in direction caused forward displacement and counterclockwise rotation of maxilla. Changing the direction of force application at the level of occlusal plane did not bring about translation. When the point of application of force was altered to 15 mm above the occlusal plane with 20 downward force along with expansion, translation of maxilla was observed. The center of resistance was located at 64.5% of the distance from the midline to the zygomaticomaxillary sutures. In the horizontal axis, the center of resistance of naosmaxillary complex was located at 40% of the distance from the infraorbital margin to the inferior border of zygoma. Expansion not only helps in disruption of the sutural system but also to nullify the constrictive effect of the protraction force. The study has highlighted the efficacy of ESPI as a tool in evaluation of bone reaction following application of protraction force. ACKNOWLEDGMENTS The author acknowledges Dr MP Kothiyal, Professor, Department of Physics Applied Optics, Indian Institute of Technology Madras, Chennai and Dr N Krishna Mohan, Senior Scientific Officer Gr 1, Department of Physics Applied Optics, Indian Institute of Technology Madras, Chennai. The study is the postgraduate thesis of the 1st author in TNGDC & H, Chennai-3. REFERENCES 1. Pavlin D, Vukicevic D. Mechanical reaction of facial skeleton to maxillary expansion determined by laser holography. Am J Orthod 1984;85: Hata S, Itoh T, Nakagawa M. Biomechanical effects of maxillary protraction on craniofacial complex. Am J Orthod Dentofacial Orthop 1987;91: Itoh T, Matyas J, Chaconas SJ, Caputo AA. Photoelastic effects of maxillary protraction on the craniofacial complex. Am J Orthod 1985;88: Lee KG, Kyukyu Y, Park YC, Rudolph DJ. A study of holographic interferometry on the initial reaction of maxillofacial complex during protraction. 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