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.