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Introduction â€˘ Two dimensional cephalometry was introduced to the orthodontic field in 1931, simultaneously and independently by Broadbent in the United States and Hofrath in Germany. â€˘ Since then it has become one of the most important clinical and research tools for evaluating craniofacial growth and dentofacial deformities.
Some uses of Cephalometry 1. 2.
Predicting growth Evaluating dentofacial disproportion and determining the basis of malocclusion. 3. Making comparisons during active orthodontic treatment 4. During surgical planning for individuals with complex dentofacial abnormalities. www.indiandentalacademy.com
Limiting Factors in Cephalometry 1. A head film is only a 2-D representation of a 3-D object. 2. Assumption of a perfect superimposition of the right and left sides about the mid sagittal plane. 3. Significant amount of radiographic projection error including magnification and distortion, errors in positioning, and projective distortion. www.indiandentalacademy.com
4. Ambiguity in locating anatomical landmarks ( Baumrind and Frantz, AJO 1971) 5. Cannot be used in patients suffering from marked craniofacial asymmetries.
In recent years, as orthodontists have become craniofacial orthopaedists, it has become clear that 3 dimensional imaging is the need of the hour in orthodontics.
History of 3 D Imaging: Earliest 3 D measurements of the skull were made by anatomists and physical anthropologists in the late 19th century. In the beginning of the 20th century, Calvin Case advocated the use of plaster facial moulages to record the facial changes before and after treatment. During the 1920â€™s, Van Loon and Simon attempted to relate the location of the dento-alveolar structures with respect to thewww.indiandentalacademy.com skull.
In 1931 Broadbent and Bolton stressed the need for coordinating lateral with postero-anterior films using an Orientator. In the 1960â€™s and 1970â€™s a number of investigators such as Rune, Sarnas and Sevik, attempted to implement the use of stereophotogrammetric methods, originally developed for aerial mapping to measure the skull. In the late 1970â€™s, computerized axial tomography became available, followed by magnetic resonance imaging. www.indiandentalacademy.com
Moss et al in the 1980â€™s introduced laser surface scanning technique for measurement of facial surface morphology Recently, more sophisticated technologies such as Moire topography, structured light techniques, computerized stereophotogrammmetry, stereolithography, as well 3-D facial morphometry have found application in the study of the cranial morphology. www.indiandentalacademy.com
General 3 D concepts: â€˘ Unlike 2D photographs and radiographs where there are two axes, (vertical and horizontal), 3 D imaging utilizes 3 Cartesian co-ordinates: the x, y and z axes. These co-ordinates define a space in which multidimensional data are represented and this space is called the 3D space www.indiandentalacademy.com
Basic steps in creating a 3 D model Modelling: The use of mathematics to describe the physical properties of the object. Shading and lighting: This adds realism to the 3D object. Rendering: Data collected from the patient is converted by the computer intowww.indiandentalacademy.com a lifelike 3D object
Geometric strategies used to measure objects in 3D Orthogonal measurement: The object is optically sliced into layers and the x,y dimensions measured directly, while the z dimension is measured by tallying in the area of interest. E.g. the ordinary CT scan.
Analogous to geometry of mammalian stereoscopic vision, requires two images of the object to be captured from two different views, simultaneously or in rapid succession. E.g. stereophotogrammetry. www.indiandentalacademy.com
Techniques in 3D imaging: •
CT- assisted 3D imaging
3D Laser Scanning
• Moiré topography and contour photography • 3D Facial Morphometry • 3D ultrasonography www.indiandentalacademy.com
3D Cephalometry: Based on manual techniques for abstracting 3D co-ordinate data from 2 biorthogonal head films. E.g. lateral and antero-posterior radiographs. Grayson etal ( AJO-DO 1988) described a technique in which two landmark locations, one derived from the lateral cephalogram and one from the postero-anterior cephalogram were combined into a 3 D point. The two views were precisely registered using the Frankfort Horizontal Plane.www.indiandentalacademy.com
Mori et al (JO 2001) described a 3D cephalometric system which calculates the 3 D co-ordinates of landmarks from lateral and frontal cephalograms, while correcting for the magnification of the image as well as cephalic malposition. In a study on 7 dry human skulls they reported that precise cephalometric measurements were possible with this system and that it could be clinically applied. www.indiandentalacademy.com
Recently, a methodology for identifying landmarks in calibrated and digitized X-rays and optical images (Acuscape and Sculptor, Glendora, Calif.) has been under development and will soon be commercially available. Adams et al ( AJO-DO 2004) compared this new 3D program with traditional 2D evaluation on 9 dry skulls. It utilizes three views: standard lateral (90)ยบ, frontal (0ยบ) and oblique (45ยบ) to obtain the 3D landmark co-ordinates. They reported much more precise evaluation of linear measures as www.indiandentalacademy.com compared to the conventional 2D system.
Disadvantages of 3D cephalometry: • •
Time consuming technique Patient exposure to radiation
Does not define soft tissues Difficulty in accurately relating the same landmarks in the two radiographs.
Morphoanalysis: Morphoanalysis is a method of obtaining 3D records using photographs, radiographs and study casts of a patient. Rabey claimed that the principal benefits of morphoanalysis in orthognathic surgery were
Analytic and Statistical validity Accuracy Superior communication. www.indiandentalacademy.com
The equipment however is extremely elaborate and expensive. The technique is time consuming and not very practical for every day use.
CT assisted 3 D imaging • Modern CT Scanners use an array of detectors mounted in a circle around the patient-positioning portal. • The X-ray tube produces a narrow fan shaped beam and rotates around the patient during an exposure. • The various views are integrated using mathematical algorithms to provide 3D data for visualization. www.indiandentalacademy.com
In the mid 1980â€™s CT assisted 3D imaging and modeling of the skull was introduced for use in maxillofacial surgery. In a majority of patients with congenital and acquired cranio-facial anomalies, the deformity is 3 dimensional in nature and many patients are asymmetric. In such cases, 2D diagnostic records are rendered inadequate and the benefits of CT may outweigh the risks. www.indiandentalacademy.com
Vannier and Marsh ( Plast Reconstr Surg 1983) developed the first method to reconstruct 3 dimensional models based on CT data for routine use. With the help of aluminium or plastic plates, milled by an electronically assisted cutting device, they constructed a life size individual skull model. Brix et al (1985) described a more sophisticated approach in which the CT data was transferred to a computer work station in which the craniofacial bony surface was reconstructed 3 dimensionally. The reconstruction data was then used for computer-aided control of the milling process. www.indiandentalacademy.com
Richtsmeier et al (Cleft Palate Craniofac J. 1995) evaluated the precision, repeatability, and validation of the localization of cranial landmarks using CT scans. The average error of landmark position was always less than 0.5 mm and for some landmarks error was negligible. Troulis et al ( Int J Oral Maxillofac Surg 2002) reported the development of a 3D treatment planning software called Osteoplan which uses CT data to to produce 3D images for visualization of the craniomaxillofacial skeleton. www.indiandentalacademy.com
When this software was retrospectively applied to a case of hemifacial microsomia treated with distraction osteogenesis, the authors found that this predicted the bony movements and motion limiting bone collision of the coronoid process far more accurately than the 2D method using a PA cephalogram.
Recent advances in CT technology Tomosynthesis and Tuned Aperture Computed Tomography (TACT) Mathematical reconstruction techniques that require multiple transmission type X ray projections acquired at different angles. May be achieved with one or more digital sensor and one X ray source that moves between exposures. Fiducial markers projected onto the image plane assist in reconstruction of the image www.indiandentalacademy.com
The future of TACT in orthodontics will lie in its ability to assist in evaluation of alveolar bone, detection of root resorption, and evaluation of the TMJâ€™s. The advantages of TACT or tomosynthesis when compared to CT include low dose, low cost and improved detail.
Cone Beam Computed Tomography:
Based on conventional CT technology but contain a number of enhancements to optimize them for imaging the head and neck. • Reduced chamber volume • Cone beam projection of X-rays which produces much less radiation scatter •Radiation exposure is only 20% that of CT. www.indiandentalacademy.com
Stereolithography: • Also known as 3D Layering and 3D Printing • Process of turning CAD designs into real 3D objects in a matter of hours • Manufacturing process uses a UV laser to create successive cross-sections of a 3D object within a vat of liquid photopolymer. www.indiandentalacademy.com
Shortcomings of the procedure: Need for experienced and skilled operators for accurate 3D modeling Expense of the method. Patient exposure to radiation for CT scans. No production of soft tissue in a machinereadable form. www.indiandentalacademy.com
3D Laser Scanning: • Provide a less invasive method for capturing the maxillofacial region in 3 dimensions. • Operates on the principle of structured lighting in which known patterns of light are projected on an object to infer its shape. • The geometry of the setup enables the calculation of the depth of the point on which the laser falls. www.indiandentalacademy.com
One of the first commercial applications of light stripe laser scanning was by Cyberware ( Calif ).
The Minolta Vivid scanner (New Jersey) uses a horizontal stripe of laser to scan the object from top to bottom. A camera reads the laser light and the color texture of the object being scanned; the whole process takes less than 1 second Another scanner using the light stripe method is the handheld FastScan by Polthemus Co., which uses two cameras to detect the laser light as well as an electromagnetic sensor to detect its orientation and position relative to the object being scanned. www.indiandentalacademy.com
The Minolta Vivid 700 Scanner
Kusnoto and Evans ( AJO-DO 2002) assessed the reliability of the Minolta Vivid700 3D laser surface scanner for generating 3D object reconstructions by testing it on a geometric calibrated cylinder, on a dental study model as well as on a facial model. They found the laser surface scanner to generate accurate 3 D data and suggested that it could be used in orthodontics to analyze growth, soft tissue changes, treatment simulation, and treatment effects in 3D. www.indiandentalacademy.com
Morris, Illing and Lee ( EJO 1998) used 3D laser scanning to assess soft tissue changes in 47 patients treated with the Bass, Bionator and Twin Block functional appliances. They found statistically and clinically significant changes in the group treated with the Twin block appliance, and to a lesser extent in the group treated with the Bionator appliance. They reported the laser scanning system to be a sensitive and accurate method of quantitatively www.indiandentalacademy.com assessing small changes in the soft tissue form.
Twin Block Pretreatment
Twin Block Post treatment
Some important issues regarding lasers Safety: Scanning the face with the use of structured lighting methods may require closing the eyes if laser light is used. Speed: Cyberware (Calif.) reports a scanning time of 17 seconds for a complete head scan. This is too long for acquiring reliable data of facial expressions. www.indiandentalacademy.com
Accuracy: Head and face laser scanning is reported to have an accuracy of 0.5 mm which seems sufficient for such applications but would be inadequate for scanning dental casts. Holes in the scanned objects: These may occur because the laser light may be very feebly reflected by certain dark areas of the object, such as hair. Inability to capture soft tissue surface texture which may make it difficult to identify www.indiandentalacademy.com landmarks which are dependent on surface color.
MoirĂŠ topography and contour photography In 1970 Takasaki was the first to report on Moire topography, which uses interference of rays. In 1986 Segner reported on contour photography with a reflecting mirror to simplify the apparatus. These use grid projections during exposure, resulting in standardized contour lines on the face. Difficulties are encountered if a surface has sharp features, so these 2 methods are suitable to use on smoothly contoured faces. www.indiandentalacademy.com
3D Facial Morphometry: • This system comprises 2 charge-coupled device (CCD) cameras that capture the subject, real-time hardware for the recognition of markers placed on patients’ faces, and software for the 3D reconstruction of landmarks’ x,y,z coordinates relative to a reference system. • Ferrario et al (AJO-DO 1999) studied soft tissue facial growth and development using 3 D facial morphometry. They found the technique to be mathematically simple and that it provided an easy geometric representation of the craniofacial situation. www.indiandentalacademy.com
Some of the more sophisticated analytical methods in 3D geometric morphometry are: The Procrustes superimposition Euclidean Distance Matrix Analysis Thin Plate Spline Analysis.
Procrustes superimposition • One of the new geometric morphometric techniques, which assume that all landmarks carry equal information. • Treats size as a separate variable from shape, preventing it from over-determining the resulting shape analysis. • Translates 2D or 3D landmark co-ordinates of one form as a group to best fit those of a second form. www.indiandentalacademy.com
Differences in shape are shown by residual differences ( Procrustes distances) in the positions of the corresponding landmarks. Banu et al ( Int J Adult Orthod Orthognath Surg 2002) studied the outcome of orthognathic surgery using this technique and reported that it provided additional information on overall facial and craniodental shape change that traditional cephalometrics cannot provide.
Euclidean Distance Matrix Analysis (EDMA): â€˘ This is a co-ordinate free statistical program that takes into account the inequality of variance of samples, and indicates which inter landmark distances are contributing to form change. â€˘ It attempts to describe changes in form in terms of the entire shape and localizes areas of major shape change. www.indiandentalacademy.com
Singh and Hodge ( Angle Orthod 2002 ) used this method to assess changes in the bimaxillary morphology in Class II Division 1 patients treated with the Twin Block Appliance. Their results indicated that Twin Block Appliance treatment is associated with growth restriction of specific regions of the mid-face ( PNS-Pr), while permitting anterior advancement of the mandible. www.indiandentalacademy.com
Thin Plate Spline Analysis: Geometric morphometric technique that expresses the differences between two configurations as a continuous deformation, using regression functions in which homologous landmarks are matched exactly between the two forms, explicitly to minimize the bending energy. www.indiandentalacademy.com
Bending energy may be thought of as the energy that would be required to bend an infinitely thin metal plate over one set of landmarks so that the height over each landmark is equal to the co-ordinates of the corresponding point in the other form. Singh, McNamara and Lozanoff ( J Anat 1997) used the Thin Plate Spline analysis to analyze the deformations of the midface leading to Class III malocclusions. They found that decreased anteroposterior dimensions of the palatal complex as well as decreased mid face height posteriorly contributed to a Class III profile. www.indiandentalacademy.com
Franchi, Baccetti, McNamara (Angle Orthod 2001) also used the Thin Plate Spline Analysis to study mandibular growth changes during the pubertal growth spurt and found significant growth in the size of the mandible associated with it.
Stereophotogrammetry Refers to the special case where 2 cameras, configured as a stereo-pair, are used to recover the 3D distance to features on the surface of the face by means of triangulation The incorporation of recent technology has given the ability to process complex algorithms to convert simple photographs to 3D measurements ofwww.indiandentalacademy.com facial changes.
C3D: A 3D non-contact visionbased imaging system â€˘ Developed for clinical applications in a collaboration between Glasgow University and the Turing Institute â€˘ Consists of 2 pods, and each pod consists of 3 cameras. Two monochrome cameras form a stereo baseline A third central color camera captures the natural photographic appearance of the subject www.indiandentalacademy.com
Facial Texture Mapping
The Facial Analysis Tool used for identifying landmarks
3D Meshes of a skeletal Class III case
“ The near future will be based on the actual biology of an individual’s own craniofacial growth and development and it will be determined by a 3 dimensional evaluation based on that person’s actual morphogenic characteristics, not simply developmentally irrelevant radiographic landmarks.” ( Enlow, D. AJO-DO 2000) www.indiandentalacademy.com
Hajeer M, Ayoub A, Millett D, Bock M, Siebert J. Three dimensional imaging in orthognathic surgery: The clinical application of a new method. Int J Adult Orthod Orthognath Surg 2002: 17:318-330. Baumrind S. Integrated Three Dimensional Craniofacial Mapping: Background, Principles, and Perspectives. Semin Orthod 2001:7:223-232. Adams, Gansky, Miller, Harrell, Hatcher. Comparison between traditional 2-dimensional cephalometry and a 3dimensional approach on human dry skulls. AJO-DO 2004;126:397-409. Mori Y, Miyajima, Minami, Sakuda. An accurate Three dimensional Cephalometric System : a solution for the www.indiandentalacademy.com correction of cephalic positioning. JO 2001;28: 143-149.
5. Grayson B, Cutting C, Bookstein F, Kim H, Mc Carthy J. The three dimensional cephalogram: Theory, technique, and clinical application. AJO-DO 1988;94:327-37. 6. Hajeer M, Millett, Ayoub A, Siebert J. Applications of 3 D imaging in orthodontics: Part I. JO 2004; 31: 62-70 7. Troulis M et al. Development of a three dimensional treatment planning system based on computed tomographic data. Int J Oral Maxillofac Surg. 2002;31:349-357. 8. Mah J, Bumann A. Technology to create the three dimensional patient record. Semin Orthod 2001;7:251-257. 9. Kusnoto B, Evans C. Reliability of a 3D surface laser scanner for orthodontic applications. AJO-DO 2002;122:342-348. 10. Halazonetis D. Acquisition of 3-D shapes from images. AJO-DO 2001; 119: 556-560. www.indiandentalacademy.com
11. Morris D, Illing H, Lee R. A prospective evaluation of the Bass, Bionator and Twin Block appliances. Part II- The soft tissues. EJO 1998;20:663-684. 12.Cakurer B, Dean D, Palomo J, Hans M. Orthognathic surgery outcome analysis: 3 dimensional landmark geometric morphometrics. Int J Adult Orthod Orthognath Surg 2002;17:116132. 13. Singh GD, Hodge MR. Bimaxillary morphometry of Patients with Class II Division 1 Malocclusion treated with Twin Block Appliance. Angle Orthod 2002;72 :402-409. 14. Ferrario V, Sforza G, Colombo A, Ciusa V. Soft tissue facial growth and development as assessed by the three-dimensional computerized mesh diagram analysis. AJO-DO 1999;116: 215-226. 15. Singh GD, Mc Namara JA, Lozanoff S. Localization of deformations of the midfacial complex in subjects with Class III malocclusions employing thin-plate spline analysis. J Anat 1997;191: 595-602 www.indiandentalacademy.com
16.Franchi L, Baccetti T, Mc Namara JA. Thin Plate Spline Analysis of Mandibular Growth. Angle Orthod 2001;71:83-92. 17.Harrell W, Hatcher D, Bolt R. In search of anatomic truth: 3 Dimensional digital modeling and the future of orthodontics. AJODO 2002;122: 325-330. â€˘
www.indiandentalacademy.com Leader in continuing dental education