Tony Ngan-Fat To* Alfred Chee-Ching Tsang
*

BDS, PDipGDS

DENTAL PRACTICE

Hong Kong Dent J 2009;6:46-8

DDS, FFDRCS, FHKAM (Dental Surgery), FCDSHK

Localization of impacted maxillary anterior tooth with tangential radiograph

* Department of Health, Hong Kong

ABSTRACT
An occlusal film placed parallel to the midsagittal plane of the head can be used to locate the bucco-palatal position of the supernumerary teeth. The same principle can also be applied with the central ray directed tangentially to the impacted canine for location of bucco-palatal position. This approach requires minor modification of the radiographic film-holding device and can be employed in all dental office settings. Two cases regarding this technique were also presented. Key words: Radiography, dental; Tooth, supernumerary

Introduction
The position of the supernumerary teeth in relation to the root of the maxillary anterior teeth is important for determining the surgical approach used for their removal. The prevalence of supernumerary teeth is 1 to 3% 1. Also, determining the bucco-palatal position of an unerupted and impacted canine (which has a prevalence rate of 2.56% 2) is essential to enable the orthodontist to formulate the treatment plan.

Principle of parallax
Traditionally, two radiographs of the same region with different angulations are used to localize the position of the unerupted supernumerary teeth or canine. The difference in angulations can be in the horizontal or vertical direction. Clark 3 described a technique where the position of the buried tooth is compared in three periapical radiographs, one central, one mesial, and one distal to the buried tooth. This approach is commonly referred as Clark’s rule and applies the principle of parallax to delineate the spatial relationships of an object. The parallax technique utilizes the apparent displacement of the image of an object relative to the image of a reference object caused by changing the angulation