A comparison between bitewing radiographs taken with rectangular and circular collimators in UK military dental practices: a retrospective study

Abstract

Objectives: The aim of this study was to determine any increase in the incidence of cone cut errors that adversely affected diagnostic yield resulting in more retakes using rectangular collimation with film holders in bitewing radiography. Comparisons were also made with other positioning errors that occurred when bitewings were taken with circular collimation, with and without film holders.

Methods: A preliminary questionnaire was used to determine the year that rectangular collimation was adopted by military dental practice. 3 time-framed subsets, each of 1000 bitewing radiographs, were identified: subset 1, films taken with circular collimators without film holders; subset 2, films taken with circular collimators with film holders; and subset 3, films taken with rectangular collimators with film holders. Each subset was assessed for positioning errors of cone cut, horizontal overlap, vertical distortion and film centring. The χ(2) test was used to test significant differences amongst the three subsets.

Results: The use of film holders with circular collimation significantly reduced the incidence of cone cut errors from 21.7% to 3.3%. There was an increase in the incidence of cone cut errors from 3.3% to 20.9% when rectangular collimation was used, but the actual number considered "rejects" was very small, only 0.1% (1 in 1000 films) in subset 2 and 0.3% (3 of 1000 films) in subset 3, when assessed for diagnostic yield.

Conclusions: This study provides evidence that rectangular collimation did not significantly affect the diagnostic yield of bitewing radiographs despite the presence of cone cut. Therefore, all practitioners should adopt rectangular collimation.

Figure 1

An example of a complete set of film images from the same patient at different times. These show radiographs taken (a) without a film holder (subset 1) and (b) with a film holder (subset 2) using a circular collimator, and (c) with a film holder using a rectangular collimator (subset 3)

Figure 2

A complete positioning error analysis table (PEAT) for subset 1. Similar tables were devised for subsets 2 and 3

Figure 3

Data to show the year of adoption of rectangular collimation. 58 of the respondents had graduated and joined the Defence Dental Service (DDS) before 1998. They were asked to qualify the strength of their memory recall in one of three categories. (One outlier in 1980 and two in 1986 are not shown)