Projection Geometry
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Transcript of Projection Geometry
PROJECTION GEOMETRY
Dr. Kristina Corazon L. Robles
Ideal results:Sharp imageTrue Shape & Size of the object
Principles of Image Formation
Terminologies
Sharpness- measures how well a boundary between two areas of differing density is revealed.
Spatial resolution- measures how well small objects that are close together can be seen
Terminologies
Image size distortion (magnification)1. film and object not parallel to each
other2. smaller focal - object distance. (short
cone)3. central beam not at 90 degrees to
object.
Image shape distortion is the result of unequal magnification of different parts of the same object.
5 Fundamental Principles
1. Small radiation source / focal spot2. Target-film-distance long as practical3. Object-film-distance short as possible4. Parallel film to long axis of teeth5. Perpendicular alignment of beam to
film & objects
STOPP!!!
INTRAORALRADIOGRAPHIC
TECHNIQUES
Types of Intraoral Radiographic Examination
1. Periapical ExaminationPurpose used to examine the entire tooth and
supporting bone Film type- periapical film Technique - paralleling technique and
bisecting angle technique
Types of Intraoral Radiographic Examination
1. Periapical Examination
Types of Intraoral Radiographic Examination
2. Interproximal ExaminationPurpose used to examine the crowns of
opposing teeth on a single film; used in examining adjacent tooth surfaces and crestal bone
Film type- bitewing film Technique-bitewing technique
Types of Intraoral Radiographic Examination
2. Interproximal Examination
Types of Intraoral Radiographic Examination
3. Occlusal ExaminationPurpose used to examine large areas of
maxilla and the mandible Film type- occlusal film Technique- occlusal technique
Types of Intraoral Radiographic Examination
3. Occlusal Examination
Paralleling Technique
Paralleling Technique
Film placed parallel to long axis of teeth
Beam directed perpendicular to film & long axis of teeth
Film holder used to keep film flat & unbent
Long PID or TFD to offset increased magnification due to great OFD
Paralleling Technique
Bisecting Angle Technique
Bisecting Angle Technique
Cieszynski ’ s Rule of Isometry
Rule of Isometry- 2 triangles are (=) if they have two (=) angles and share a common side
Film placement- Lingual surface
Bisecting Angle Technique
1. Horizontal Angulation
Correct- central ray is directed perpendicular to the curvature of the arch and through the contact areas leading to open contact areas
X Incorrect - results in and overlapped interproximal contact areas
Bisecting Angle Technique
2. Vertical Angulation
Bisecting Angle Technique
Video
Foreshortening
Elongation
Seatwork: (by group)
1. Draw the diagram of paralleling technique and bisecting angle technique
2.State the advantages and disadvantages of each.
3. Draw the components of a dental xray film. Label and describe the functions of each.
4.Indicate the uses of each size of the film. (size 0, 1, 2, 4)
5. Describe the uses of a developer and a fixer.