If your dentist has mentioned needing an OPG or a CBCT — or you’ve been sent for one and you’re wondering what the difference actually is — this article is for you. These are the two most common dental x-rays used for wisdom teeth, implant planning, and surgical work, and the decision between them matters. Here’s how I explain it to patients in the chair.

The short version

  • OPG (orthopantomogram) — a 2D panoramic x-ray of your whole mouth. Low radiation dose, quick, excellent for a first look at wisdom teeth, fractures, cysts, or general overview.
  • CBCT (cone beam computed tomography) — a 3D scan of a targeted area. Higher radiation dose than an OPG (but much lower than a medical CT), used when we need to know exactly where a nerve, root, or bone structure sits in three dimensions.

For most questions, an OPG answers it. CBCT is reserved for the cases where 3D information changes the plan — particularly around nerves, implants, and complex surgical extractions.

What an OPG actually is

An OPG is the wide panoramic x-ray you’ve probably had at some point. You stand or sit in the machine, bite gently on a plastic post to keep your head still, and the tube rotates around your head while a sensor captures the image on the other side. It takes about 20 seconds. You don’t need to be injected with anything. The image comes out as a single flat picture of your upper and lower teeth, both jaws, the sinus floor, and the jaw joints.

What an OPG shows us well:

  • Wisdom tooth position, angle, and depth
  • Decay (especially between teeth, where the beam passes through both surfaces)
  • Cysts or unusual lesions in the jawbone
  • Jaw fractures
  • Bone loss from gum disease
  • Developing teeth in kids and teenagers
  • The general state of your roots, fillings, and crowns

What an OPG doesn’t show well:

  • Fine 3D relationships — two structures sitting side by side can overlap on a flat image and look like they’re touching when they’re not (or vice versa).
  • Bone width — the OPG shows bone height but not how thick the bone is from cheek to tongue. That matters for implants.
  • Exact nerve position — the inferior alveolar nerve runs through a canal in the lower jaw, and an OPG shows roughly where it is, not precisely.

Healthdirect’s general guidance on x-rays is that the dose is small and “unlikely to cause any serious problems” (Healthdirect — X-rays). An OPG sits at the low end of the dental x-ray range — well below the radiation dose of a medical CT scan.

What a CBCT actually is

CBCT stands for cone beam computed tomography. The machine looks a bit like an OPG — you sit or stand still while it rotates once around your head — but instead of producing a single flat image, it reconstructs a 3D volume you can slice through from any angle. We can scroll through the scan tooth by tooth, measure bone in millimetres, and see exactly where a nerve canal runs relative to a root tip.

Compared to a medical CT scan (the kind you’d get in a hospital for a head injury), a dental CBCT uses a tightly focused cone-shaped beam aimed at a small field of view — just the jaws and teeth. That’s a significantly lower radiation dose than a full medical CT. But it is higher than an OPG, which is why we don’t order it by default.

What a CBCT is genuinely useful for:

  • Deep wisdom tooth impactions near the inferior alveolar nerve. Before surgically removing a lower wisdom tooth that looks close to the nerve on an OPG, a CBCT tells us whether the roots actually touch the nerve canal, wrap around it, or sit safely above it. That changes how we plan the extraction and what we warn you about.
  • Implant planning. We need bone width, not just height. A CBCT tells us whether there’s enough bone for an implant, where the sinus floor sits, and whether we need a bone graft before we place the fixture.
  • Complex root anatomy. Extra roots, curved roots, or roots close to the sinus can complicate an otherwise routine extraction. CBCT shows us what we’re actually dealing with.
  • Cysts or lesions on an OPG. If something unusual shows up on a panoramic image, a CBCT helps us see its size, shape, and what structures it’s affecting.
  • Pathology around existing implants or root canals where we need to see bone loss in three dimensions.

What a CBCT is not for:

  • A routine check-up
  • A straightforward upper wisdom tooth with no nerves of concern
  • A patient who just wants “the best” scan — more imaging for its own sake isn’t better care

Radiation dose — put simply

Radiation is a reasonable thing to ask about. Here’s how I frame it for patients:

  • A dental OPG delivers a small radiation dose — comparable in order of magnitude to a few days of the natural background radiation you get just from living on Earth (cosmic rays, radon in soil, the potassium in your own body).
  • A dental CBCT delivers a higher dose than an OPG — typically several times higher, though the exact number depends on the machine settings and the size of the scan field.
  • Both are substantially lower than a medical CT scan of the head (Healthdirect notes that CT scans “use higher doses of radiation than plain x-rays” and that’s a meaningful jump).

I don’t quote precise microsievert numbers to patients because the values vary by machine, protocol, and scan size — and published ranges overlap. What matters clinically is the principle we follow: ALARA — As Low As Reasonably Achievable. We take the least imaging that answers the clinical question properly. For most wisdom tooth assessments, that’s an OPG. For the ones where 3D matters, we add a CBCT, because the risk of a nerve injury during surgery massively outweighs the marginal radiation dose of the extra scan.

If you’re weighing up imaging for wisdom teeth or an implant consult, you’re welcome to book a consult with me at Biltoft Dental and we can talk through what imaging (if any) your situation actually needs.

When an OPG is enough (most of the time)

For the bulk of what we do, an OPG is plenty. Specifically:

  • Routine wisdom teeth assessment. You’re 17, your dentist wants to see if there’s room at the back of the jaw — OPG.
  • Upper wisdom teeth. Uppers are rarely close to nerves the same way lowers are. Unless there’s something unusual, an OPG is enough.
  • General check-up imaging. We don’t do OPGs at every visit — bitewings and periapicals do most of the routine work — but a wide-view panoramic every few years for an adult patient is sensible.
  • Monitoring an impacted tooth over time. If we’re watching a quiet impacted wisdom tooth to make sure nothing’s developing around it, periodic OPGs are the right tool.

For a broader read on when wisdom teeth imaging matters and what age range we start looking, when should a teenager get their wisdom teeth checked walks through the timing.

When a CBCT is justified

I’ll recommend a CBCT when the clinical question is genuinely a 3D one. In practice, that means:

  1. Lower wisdom tooth with roots close to the inferior alveolar nerve on OPG. This is the most common reason. The OPG flags a concern; the CBCT answers it. If the roots genuinely touch or wrap the nerve, we plan the extraction differently or refer to a specialist oral surgeon.
  2. Implant planning where bone quantity is borderline. We need to know width, height, and the position of vital structures like the sinus floor and the mental nerve.
  3. Surgical extraction with unusual anatomy on OPG — extra roots, curved roots, or a tooth sitting in an odd position.
  4. A cyst or unusual lesion seen on an OPG that needs proper characterisation.
  5. Pathology around an existing implant or large restoration where 2D imaging isn’t resolving what’s going on.

If your OPG shows a straightforward impaction well clear of the nerve, you don’t need a CBCT. We’d just be adding radiation dose without changing the plan.

For the full context on how imaging fits into wisdom tooth decision-making, read our full wisdom teeth guide, and for the specifics of what “impacted” means on these images, our article on impacted wisdom teeth walks through the categories.

How we handle imaging at Biltoft

A straight rundown of how it works at our practice in Murwillumbah:

  • OPG on-site. We take panoramic x-rays in-house. If you come in for a wisdom teeth consult and we decide we need one, we do it that visit — no second appointment, no extra trip.
  • CBCT referred out. We don’t run a CBCT machine in-house. When we need one, we refer to a specialist imaging centre. That isn’t a downside — CBCT reporting benefits from specialist radiology interpretation, and the centres we refer to do this work every day. You get the scan, the images come back to us, and we review them with you at your next visit.
  • We’ll use your existing imaging where we can. If you’ve had an OPG or CBCT taken elsewhere in the last year or two and it answers the question, we’ll use it rather than repeating the scan. Bring a copy (or a download link) to your consult.
  • We explain what we’re ordering and why. You shouldn’t have to guess why we want a scan. If we ask for one, we’ll tell you what we’re looking for, what we expect to find, and how it changes (or confirms) the plan.

The bottom line

OPG and CBCT aren’t competing — they’re different tools for different jobs. An OPG is the everyday workhorse: wide view, low dose, quick, and enough for most questions we need to answer. A CBCT is the specialist’s magnifying glass: higher dose, 3D, reserved for the situations where the extra detail genuinely changes what we do.

The honest principle we work to is ALARA — least imaging that properly answers the clinical question. If your dentist has recommended a CBCT, it should be because a 2D image isn’t enough, not because the scan is available. And if you’ve had imaging elsewhere, bring it in — we’d rather build on existing work than add unnecessary dose. Individual situations vary, and the right imaging depends on your teeth, your anatomy, and the specific question being asked.

If you’re in Murwillumbah or anywhere across the Tweed or Northern Rivers and you’d like an honest opinion on what imaging you actually need, you can book a consult at Biltoft Dental online or call us on (02) 6672 1980.

— Dr Daniel Johnston

Frequently asked questions

What's the difference between an OPG and a CBCT? +

An OPG (orthopantomogram) is a flat 2D panoramic x-ray that shows all your teeth, both jaws, and the joints in a single wide image. A CBCT (cone beam CT) is a 3D scan that lets us look at a specific area from any angle — depth, width, and height — so we can see exactly where nerves, roots, and bone sit relative to each other.

Is a CBCT safer than a medical CT scan? +

Yes. A dental CBCT delivers a considerably lower radiation dose than a conventional medical CT scan of the same region because the beam is shaped as a cone and targeted to a small field of view. It's still higher than an OPG, which is why we only order it when the 3D information will actually change our plan.

Why can't I just have a CBCT every time — wouldn't that be more accurate? +

More data isn't always better. A CBCT delivers a higher radiation dose than an OPG and the extra detail only helps when the clinical question is a 3D question — nerve proximity, bone volume for an implant, an unusual root shape. For most routine assessments an OPG gives us everything we need, so the CBCT isn't justified.

Do you take OPGs on-site at Biltoft Dental? +

Yes. We take OPGs in-house — so if you need one as part of your consult, we can do it the same visit. CBCT scans we generally refer out to a specialist imaging centre, because the scan itself is only part of the picture — reporting and interpretation matter too, and specialist radiologists do that work every day.

How long are dental x-rays valid for? +

It depends on what we're looking at. For a general check-up, an OPG every few years is usually plenty. For wisdom teeth under review, we re-image when symptoms change or roughly every 2–3 years to monitor for cysts or changes. Before any surgery, we'll want imaging that's recent enough to reflect the current situation.

Can I bring x-rays from another dentist? +

Absolutely — and please do. If you've had an OPG or CBCT taken recently elsewhere, bring the images (or a link to download them) to your consult. We'd rather review existing imaging than put you through another scan unnecessarily.