Introduction Understand buccal object rule Assessment of the

大綱 Introduction Understand buccal object rule Assessment of the impacted maxillary canine tooth position Summaries References: 1. White & Pharoah: Oral radiology: principle & interpretation, 5 th edition, Chapter 5, p. 91 -93 2. Eric Whaites: Essentials of dental radiography & radiology, 3 rd edition, p. 7, 8, 113, 279 -283

Introduction * In 1909, Clark [1] reported a radiographic procedure for the localization of impacted teeth. * The Buccal Object Rule is a method for determining the relative location of objects hidden in the oral region. * The rule is: When two different radiographs are made of a pair of objects, the image of the buccal object moves, relative to the image of the lingual object, in the same direction that the X-ray beam is directed. * The initial concepts of the procedure were reported in 1952 & 1953 [2, 3] & since that time the procedure has been developed to its present state of refinement & usefulness. [1] CLARK C A. A method of ascertaining the relative position of unerupted teeth by means of film radiographs. Royal Society of Medicine Transactions 3: 87 -90, 1909 -1910. [2] RICHARDS AG. Roentgenographic localization of the mandibular canal. Journal of Oral Surgery 10: 325 -329, 1952. [3] RICHARDS AG. The Buccal object rule. Journal of the Tennessee State Dental Association 33: 263268, 1953.

Understand buccal object rule Buccal object rule Lingual Tube shift technique Mesial shift Clake’s rule (1910) 同方向移動 Zygomatic process X-ray beam Direct orientation Buccal Zygomatic process 往mesial方向移 (與X-ray beam相反方向移動) Mesial shift 相反方向移動 Ref. 1 X-ray beam Distal shift

Assessment of the impacted maxillary canine tooth position 1. Parallax in the horizontal plane 2. Parallax in the vertical plane 3. A vertex occlusal 4. A true PA and lateral skull views (two views at right angles) *Impacted maxillary canine teeth occur in about 2% of the population.

1. Parallax in the horizontal plane Principle of parallax: The apparent displacement of an object due to different positions of the observer Object moves in different direction Left Same Ref. 2 Right Front Lingual Opposite (遠方) Buccal (近方) SLOB

1. Parallax in the horizontal plane ion sit Po Position 2 distal shift 2 11 Position 1 centrally oriented Same Lingual (遠方-palatal side) Ref. 2 12

1. Parallax in the horizontal plane 12 12 11 21 22 Choice Same Ref. 2 Lingual (遠方) Opposite Buccal (近方)

1. Parallax in the horizontal plane Choice Ref. 2 Same Lingual (遠方) Apex Opposite Buccal (近方) Crown

2. Parallax in the vertical plane Unerupted mesiodens Upper occlusal Panorex Lingual Crown portion Same (遠方-palatal side) Apex portion Opposite Buccal (近方-labial side) Ref. 2 SLOB

3. A vertex occlusal Not recommended due to high radiation dose Vertex occlusal Ref. 2

4. A true PA and lateral skull views (two views at right angles) Similar images PA view Mass of head in a different position & different shape Similar images Ref. 2 Radiodense object Lateral view

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