The Honest Answer
Sometimes, and It Depends Entirely on the Crack
You have probably been told your tooth is cracked, or that it might be, and that nobody can quite tell. Perhaps your dentist has taken X-rays that look unremarkable while the tooth continues to hurt when you bite. That is a common and genuinely miserable situation, and it is one of the most frequent reasons patients are referred to us.
So here is the direct answer, without the marketing gloss. A cone beam CT scan, which produces a three-dimensional image of your tooth and the bone surrounding it, will sometimes show a fracture clearly. It will often not show the fracture line at all. A scan that does not show a crack is not proof that there is no crack. Any office that tells you otherwise is overstating what the technology does.
What CBCT does exceptionally well is something different, and arguably more useful. It shows us the bone. And the pattern of bone loss around a root is frequently what tells an experienced endodontist that a fracture is present, even when the fracture itself is invisible.
Not All Cracks Are Alike
The Word Covers a Whole Spectrum
Part of the confusion around this question is that “cracked tooth” describes at least five different conditions with five different outlooks. There are craze lines, which are superficial cracks in the enamel that almost everyone has by middle age and that mean nothing at all. There is the fractured cusp, where a corner of the tooth shears off, often leaving the tooth restorable. There is the cracked tooth proper, where a crack runs from the chewing surface downward toward the root, which may or may not be salvageable depending on how far it extends.
Then there is the split tooth, where the crack has progressed completely through and separated the segments, and the vertical root fracture, which begins in the root itself and travels upward. These last two generally mean the tooth cannot be saved.
CBCT performs very differently across that range. A split tooth with visibly separated segments, or a fracture that has opened enough to create a gap, will often appear on the scan. A hairline vertical root fracture in a tooth that already has a root filling, a metal post, or a crown is the hardest case of all, and that is unfortunately the case we are asked about most often.
Why the Line Hides
Two Physical Limits Working Against Us
The first is resolution. A CBCT scan is built from tiny three-dimensional units called voxels, and the scanner can only resolve detail down to roughly the size of one voxel. A hairline fracture can be narrower than that. When a crack is thinner than the smallest thing the machine can distinguish, the crack does not appear as a line, it simply blends into the surrounding tooth.
The second is artifact. Dense materials such as metal posts, root filling material, amalgam, and some crowns scatter the beam and create bright streaks and dark bands radiating across the image. This is the frustrating part: those streaks appear precisely in the region we are trying to examine, because the post and the root filling sit inside the very root we are inspecting. A dark artifact band can also mimic a fracture line convincingly enough to fool an inexperienced reader in the other direction.
There are things we can do to improve the odds, including using a small field of view focused tightly on the tooth in question and selecting a finer voxel size. These help. They do not make a sub-voxel crack appear.
Reading a CBCT scan of a possibly fractured root is as much about interpretation as acquisition. The scan is data. The diagnosis comes from the person reading it against the clinical picture in front of them.
What the Scan Does Show
The Fracture Leaves a Signature in the Bone
A fracture that communicates with the mouth becomes a pathway for bacteria along the entire length of the crack. The bone responds to that, and it responds in a shape that is recognizably different from the shape produced by a straightforward infected nerve.
When a nerve dies and the canal becomes infected, bone loss is usually concentrated at the tip of the root, where the canal exits. It appears as a rounded area centered on that point. A vertical root fracture produces something else: bone loss that follows the crack down the side of the root, often wrapping around it. On a scan this can appear as a J-shaped or halo pattern, or as a narrow, isolated defect running alongside a root while the bone on either side remains healthy. A deep, narrow pocket in an otherwise sound mouth is one of the most telling signs there is.
None of these findings is absolute proof, and each has occasional alternative explanations. But combined with your symptoms, with how the tooth responds to specific bite and percussion testing, and with careful probing around the tooth, this is often enough to reach a confident conclusion.
Ruling Things Out
Often the Most Valuable Thing the Scan Does
Several conditions produce the same complaint a fracture does: a treated tooth that still hurts, with a conventional X-ray that looks acceptable. Distinguishing among them matters enormously, because most of them are fixable and a root fracture is not.
The most common culprit is an untreated canal. Upper molars frequently carry a second canal in the front inner root that is narrow, easy to miss, and a well-known cause of persistent symptoms after otherwise sound treatment. CBCT finds these reliably, because an unfilled canal is a real space of meaningful size rather than a sub-voxel line. Other possibilities include a canal that was filled short of its full length, a separated instrument fragment, a perforation, or a lesion in the bone that has nothing to do with the tooth at all.
This is why we take the scan even knowing it may not image a crack. If it reveals a missed canal, your tooth is very likely saveable through retreatment or, in some cases, an apicoectomy. Ruling in a treatable cause is every bit as valuable as ruling out an untreatable one, and it is the difference between keeping the tooth and losing it.
Confirming the Crack
Two Instruments, Two Different Jobs
If the scan cannot see the crack, what does? Direct vision, under magnification, with the restoration out of the way.
Our operatories are equipped with dental operating microscopes providing up to 25× magnification with coaxial illumination, which means the light travels along the same axis as our line of sight and reaches to the bottom of the tooth rather than casting shadows into it. Under that magnification, with the filling or crown removed and the tooth dried, a crack that was completely invisible on every image becomes visible as a line running across the floor of the pulp chamber or down a canal wall.
Two additional techniques help. Transillumination, which involves shining a bright fiber optic light through the tooth from the side, causes a genuine crack to interrupt the light so that one side glows and the other stays dark. Staining with a dye allows the dye to seep into the crack and outline it. Neither works through a crown, which is why a definitive answer sometimes requires removing the existing restoration first.
So the two technologies do different work, and neither replaces the other. The CBCT scan tells us where to look and what the bone has already recorded. The microscope confirms what is actually there. A practice using only one of them is working with half the picture.
What This Means for You
Uncertainty Is Sometimes the Accurate Answer
Occasionally the honest conclusion after imaging and examination is that a fracture is likely but not confirmed, and that certainty would require opening the tooth. When that is where we land, we will tell you so plainly, explain what each option would involve, and let you decide with a clear picture of the odds. Being told a tooth is probably fractured is difficult news. Being told a tooth is definitely fine, and losing it four months later, is worse.
If you have been carrying a tooth that hurts when you bite while every image comes back clean, that is not something you have to accept indefinitely. It usually means the diagnosis needs a different set of tools, not that the pain is imaginary.
Both of our San Francisco locations are equipped with CBCT and dental operating microscopes, and we welcome patients seeking a second opinion before a tooth is extracted.
A Tooth That Hurts and Images That Look Normal
That combination has an explanation. Let us find it with 3D imaging and microscopic examination before any decision is made about the tooth.