a) BRIEF RESUME OF THE INTENDED WORK Need for the study Radiography is the only available noninvasive method for diagnosis and treatment planning of major surgical procedures of the mandible, also used for screening, diagnosis and selecting the best possible surgical approach.6 Panoramic radiographs, is a technique for producing a single tomographic image of the facial structures that includes both maxillary and mandibular dental arches and their supporting structures. This conventional tomography is based on principle of the reciprocal movement of the X ray source and an image receptor around a central plane, called the image layer (focal trough), in which the object of interest is located.
When the position of the object is changed in the image layer, it results in change in size and shape of the resultant image. The position of an object between the X ray source and the film is responsible for the magnification seen on a radiograph.
Measurement of vertical distance and gonial angle on panoramic radiographs have clinical significance viz. assessment of bone height before prosthetic treatment, assessment of position of mandibular foramen, ridge resorption, periodontal bone loss assessment etc. These widen the scope of panoramic radiographs in Implant dentistry, planning orthognathic surgery, assessing the severity of the disease, for planning effective mandibular nerve block and many more.
One major limiting factor in the clinical use of panoramic radiograph is its inability to confirm whether the dimensions of structures shown on radiographs correspond to the real dimensions of the structures.
Distortion, displacement, and in a special way, magnification cause changes in the dimensions of filmed structures on radiographic images in comparison with those of the actual structures.7
Dimensional measurements made on panoramic radiograph can involve considerable methodological error especially the oblique and horizontal distances.
Hence the study will be done for the dimensional precision of dry mandibles on the panoramic radiographs.
Review of Literature Dr.H Numata in 1933, proposed the use of panoramic radiographs for the first time, where he placed the curved film lingual to teeth and used a narrow X ray beam that rotated around the patients jaws to expose the film.4 In 1949, Paatero explained that the panoramic radiographs can be taken with the parabolographic technique by placing the film extraorally.4 A study found that the method variance should not exceed 3% of the total variance for appropriate measurements on panoramic radiographs.2 A study found that the horizontal assessment of linear dimensions are unreliable on panoramic radiographs but the vertical dimensions are reliable if patients are properly positioned.3 The study found the inconsistencies in correlation between the Panelipse II, Orthoralix SD Ceph, and reality may be the result of the different movement pattern, beam shape, location of focal trough, and shape of image layer of the machines.6 A Study has proved that characteristic distortion effects inherent in panoramic radiograph are due to magnification factor and methodological error.7
1-mm2 metal markers will be used as landmarks to denote the points at which distances will be measured.
The measurements will be first made on the dry mandibles by means of precise sliding ruler and similar measurements will be made on panoramic radiographs.
The mandibles will be placed in the PLANMECA PROSCANpantomographic machine, with 60kvp and 0.5mA.
The manufacturer lists the magnification factor for this machine as 1:1.4
A plastic holder will be fashioned so that the mandibles will be positioned in the cephalostat of the pantomographic machine in repeatable fashion
The holder will be designed in such a way that it will not absorb any X rays and superimpose itself on the radiographs
During exposure, each mandible will be centered in the midline of the pantomogram, horizontally perpendicular to the midline; the light cross of the pantomograph will be used as a guide.
The magnification index will be calculated for each variable through use of the following formula: magnification index = distance on the radiograph : distance on the dry mandible, or
Xmagnification = Xradiograph: Xmandible.
Following measurements will be made on dry mandible and panoramic radiographs:-
UBM-LBM(S) = distance between upper and lower border of mandible in sagittal line.
R UBM-LBM (FM) = distance between upper and lower border of mandible in line perpendicularly drawn at medial opening of right mental foramen.
L UBM-LBM (FM) = distance between upper and lower border of mandible in line perpendicularly drawn at medial opening of left mental foramen.
R UBM-LBM = distance between upper and lower border of mandible in line perpendicularly drawn at distal border of crown of right third molar or at mesial border of trigonum retromolar in edentulous mandible.
L UBM-LBM = distance between upper and lower border of mandible in line perpendicularly drawn at distal border of crown of left third molar or at mesial border of trigonum retromolar in edentulous mandible.
Co-Co = distance between highest points of left and right condylar processes.
PM-PM = distance between highest points of left and right coronoid processes.
Go-Go = distance between left and right gonion points.
R LBM(S)-Go = distance between lower border of mandible in sagittal line and gonion point of right side of mandible.
L LBM(S)-Go = distance between lower border of mandible in sagittal line and gonion point of left side of mandible.
RW = width of right ramus.
LW = width of left ramus.
R Co-PM = distance between highest point of right condylar process and highest point of right coronoid process.
L Co-PM = distance between highest point of left condylar process and highest point of left coronoid process.
R Co-S = distance between highest point of right condylar process and lower border of mandible in sagittal line.
L Co-S = distance between highest point of left condylar process and lower border of the mandible in the sagittal line.
R Go-angle = angle between tangents of right corpus and right ramus of mandible.
L Go-angle = angle between tangents of left corpus and left ramus of mandible.
To assess reliability, 3 different examiners will measure vertical, horizontal, oblique, and angular parameters on mandibles and their images twice during a 1-month period.
Descriptive statistics will be calculated, that is the arithmetic mean (x), standard deviation (SD), standard error (SE), and
t test will be used to compare the difference between the calculated magnification factors and the value of the magnification listed by the manufacturer for all measured variables.
Does the study require any investigations or interventions to be conducted on patients or other humans or animals? If so, please describe briefly.
Has ethical clearance been obtained from your institution?
Langland EO, Langlais PR, Morris CR. Principles and practice of panoramic radiology. W B Saunders company; 1982:p.1-30.
Habets LLMH, Bezuur JN, Van Ooji CP, Hansson TL. The orthopantomogram, an aid in diagnosis of temperomandibular joint problems, II: the vertical symmetry. J Oral Rehabil 1988;15:465-471.
Kaffe I, Ardekian L, Gelerenter I, Taicher S. Location of mandibular foramen in panoramic radiographs. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1994;78: 662 -669.
Catic A, Celebid A, Valentid-Peruzovid M, Catovid A, Vjekoslav J, Ivana M, Zagreb, Croatia. Evaluation of the precision of dimensional measurements of the mandible on panoramic radiographs. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;86: 242-248.