The single most common mistake I see on referred CBCT is a field of view that is too large for the question being asked. It is an understandable instinct. If a small volume is good, a big one must be safer, because you will not miss anything outside the box. In imaging that instinct is backwards. A larger field of view means more dose to more tissue, more anatomy you are now responsible for interpreting, and often lower resolution for the thing you actually care about.
The principle is simple to state and harder to hold to: match the view to the question.
The four sizes, and what each is for
Most dental cone beam units offer a range of volumes. The exact numbers vary by machine, but they fall into four practical tiers.
A single site, around 5 by 5 cm. One tooth, one implant, one localized question. An impacted premolar, a periapical lesion, a single planned implant. This is the smallest dose and the sharpest detail, because the machine concentrates its resolution on a small volume. If your question is about one location, this is almost always the right answer.
Both jaws, around 8 by 8 cm. Full dentition, third molars, multiple implant sites in the same arch or across arches. This is the workhorse volume for general dental planning where the question spans several teeth but does not need the skeleton around them.
Jaws plus the joints, around 11 by 10 cm. When the temporomandibular joints are part of the question, or when you need skeletal context, or when the pathology is larger than a few teeth. You accept more dose and more anatomy in exchange for seeing the joints and the wider skeletal relationships.
Full craniofacial, around 17 by 13.5 cm. Orthodontic and airway analysis, sinus disease, syndromic and surgical planning. This is the largest volume and it images a great deal of anatomy, including structures a dentist may not be trained to interpret. Justify every centimeter of it, and be prepared for what a large field of view obligates you to review.
The part people skip
A larger field of view is not just a dose decision. It is a responsibility decision. The moment your volume includes the cervical spine, the skull base, the sinuses, or the orbits, those structures are in your study and you are on the hook for findings in them. Incidental findings are not rare in these regions. If you image them, someone qualified has to look at them and account for them. Choosing a volume that captures anatomy you are not going to interpret is not caution. It is a liability you created for no clinical benefit.
This is one of the honest arguments for sending large or complex volumes to a radiologist. Not because the referring dentist cannot read teeth, but because a full craniofacial volume contains a lot that is outside the dental question and still needs a set of trained eyes.
A working rule
Before you select a volume, finish this sentence: I am ordering this scan to answer whether ___. Then choose the smallest field of view that fully contains the answer to that question, plus the margin you genuinely need to make the call. If you find yourself reaching for a larger volume “just in case,” that is usually a sign the question has not been defined tightly enough, not a sign you need more anatomy.
Bigger is not better. Match the view to the question, keep the dose as low as reasonably achievable, and only image what you are prepared to read.