How many retakes are too many?

John B. Ludlow jbl at EMAIL.UNC.EDU
Mon Apr 24 09:04:12 PDT 2000

on 4/21/00 3:22 PM, Sharon Brooks at slbrooks at UMICH.EDU wrote:

> We had a personnel issue come up recently in which one of our xray
> techs is accused of overexposing patients by needing an excessive
> number of retakes. I was asked what an acceptable number would be for
> an experienced person who has been taking oral radiographs for about
> 30 years.
> Obviously the best answer would be "none" but that may not be
> realistic since none of us is perfect. Does anyone have a reasonable
> answer to this? Apparently they checked the log of patient visits for
> a month and found that she retook at least one film on about 20-25%
> of patients in that month, which seems excessive to me, especially
> for someone experienced. (No, I am not her supervisor. It's a long
> story that has to do with how our school was reorganized several
> years ago.)
> Thanks for any help you can give me.
> Sharon
> --
> **************************************************************************
> Sharon L. Brooks, DDS, MS (slbrooks at
> University of Michigan, School of Dentistry, Ann Arbor, MI 48109-1078
> Phone: 734-764-1595     FAX: 734-764-2469 (UM)     FAX: 734-475-0122 (Home)

This is an excellent essay question. In our worst case scenario we have an
operator taking bitewing films (4) on recall patients. At a rate of 1 retake
for every 4-5 patients we have a repeat film rate of 1 in 8-10 (10-13%). Our
best case scenario is that we are making FMXs on new admissions patients. If
my memory serves, this is 22 films at Michigan. The repeat film rate is now
1 in 88-110 (about 1%). But the real trick in the question is not that it
depends on the magnitude of the math so much as the pattern in the numbers.
An intervention should de based on recognition of a pattern of repeated
error type. For instance, if systematic vertical collimator cuts are the
problem, we know that the operator is not taking time to view the cone
orientation from a lateral position where beam centering on the occlusal
plane may be judged with less parallax error. In the absence of review by an
experienced supervisor (radiographer), interpretation of the log book is
problematic and successful remedial intervention becomes highly unlikely.

I suspect you really wanted the short answer to this question. This is what
you get for not using a multiple choice format.

Best regards,

John B. Ludlow, DDS, MS
Associate Professor of Oral and Maxillofacial Radiology
University of North Carolina School of Dentistry
Diplomate ABOMR
jbl at

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