Most premolars have one root, but the answer depends heavily on which premolar you are talking about and, surprisingly, on your ethnic background. Upper first premolars are the most variable of the group, with anywhere from roughly half to over 80 percent having a single root depending on the population studied. Lower premolars are almost always single-rooted. And complicating things further, a premolar with one root can still hide two or even three separate canals inside it, which is the detail that matters most if you are sitting in a dentist’s chair.
Upper First Premolars Are the Wild Cards
Of all eight premolars in your mouth, the upper (maxillary) first premolars show the widest range of root configurations. A cone-beam computed tomography (CBCT) study found that about 72 percent of maxillary first premolars had a single root and roughly 29 percent had two roots.1PubMed Central. Analysis of root number and canal morphology of maxillary premolars using cone-beam computed tomography But those numbers shift dramatically across populations. A large comparative study using CBCT found that in Asian patients, about 83 percent of maxillary first premolars were single-rooted, while in white patients that figure dropped to just under 49 percent, meaning more than half had two distinct roots.2PubMed. Differences on the Root and Root Canal Morphologies between Asian and White Ethnic Groups Analyzed by Cone-beam Computed Tomography That is a massive difference for the same tooth in the same position.
Even when the maxillary first premolar looks like it has one root on the outside, the internal canal system is often split. A classic study that decalcified and cleared 400 of these teeth found that 69 percent had two canals at the tip and another 5 percent had three, leaving only about a quarter with a truly single canal from top to bottom.3PubMed. Root canal morphology of the maxillary first premolar So a dentist treating this tooth needs to be prepared for hidden plumbing even when the root count seems straightforward.
Upper Second Premolars Are Simpler, Usually
The maxillary second premolar sits just behind the first and tends to be more predictable. Multiple CBCT studies put the single-root rate somewhere between 88 and 98 percent, with two-rooted forms making up most of the remainder.1PubMed Central. Analysis of root number and canal morphology of maxillary premolars using cone-beam computed tomography4PubMed Central. Roots Form and Canals Morphology of Maxillary Second Premolar in a Sample of Yemeni Population Three roots pop up in under 1 percent of cases.
That said, internal canal anatomy can still be complex. A study of a Jordanian population found that while about 55 percent of maxillary second premolars had one root, over 85 percent had two canals when the internal system was mapped.5PubMed Central. The Number of Roots and Canals in the Maxillary Second Premolars in a Group of Jordanian Population The one-root rate in that sample was also noticeably lower than in East Asian studies, which again underscores how population background shifts the numbers. If you only looked at one study, you could come away with a very different picture of what “typical” means.
Lower Premolars Are Nearly Always Single-Rooted
Both mandibular (lower) premolars are far more consistent. A literature review covering thousands of mandibular first premolars found that roughly 98 percent had a single root, about 1.8 percent had two roots, and three- or four-rooted versions existed only as rare case reports.6PubMed. The root and root canal morphology of the human mandibular first premolar: a literature review The mandibular second premolar is even more uniform, with extra roots showing up in only about 0.4 percent of teeth.7PubMed. The root and root canal morphology of the human mandibular second premolar: a literature review
Still, lower premolars have earned a reputation among endodontists for “aberrant anatomy” inside that single root.8PubMed Central. Endodontic management of four rooted mandibular first premolar About a quarter of mandibular first premolars have more than one canal system despite having just one root, and roughly a tenth of mandibular second premolars do the same.7PubMed. The root and root canal morphology of the human mandibular second premolar: a literature review So from the outside, the tooth looks simple. Inside, it can be anything but.
Why Population Background Changes the Numbers So Much
Root morphology is one of those traits where global averages can be genuinely misleading. The CBCT comparison between Asian and white populations mentioned earlier is just one example. A study comparing Jamaican and Portuguese patients found that Jamaican premolars tended to have more roots and more root canals overall, with three-rooted maxillary first premolars appearing in about 5.5 percent of Jamaican patients versus roughly 3 percent of Portuguese ones.9PubMed Central. Population-Specific Anatomical Variations in Premolar Root Canal Systems: A Cross-Sectional Cone-Beam Computed Tomography Study of Jamaican and Portuguese Subpopulations
Anthropological research has shown that the size of the developing tooth germ influences whether a root divides during formation. Larger primordia are more likely to develop additional roots, and tooth-germ size varies systematically between populations. A study of over 1,600 modern humans found a direct correlation between single-rooted premolar size and the tendency toward multirootedness, helping explain why some populations consistently show higher rates of extra roots.10PubMed. Mandibular premolar and second molar root morphological variation in modern humans: What root number can tell us about tooth morphogenesis This also explains a longstanding observation in physical anthropology: men, who tend to have slightly larger teeth, are somewhat more likely to have multirooted premolars than women.
Roots vs. Canals and Why the Difference Matters
If you are reading this because you are about to have a root canal, the number of roots is less important to your treatment than the number of canals. A root is the part of the tooth embedded in bone. A canal is the hollow channel running through that root that contains nerve tissue and blood vessels. One root can house one, two, or occasionally three canals. The canals can split, merge, loop, and reconnect in complex patterns that dental researchers have catalogued into classification systems with types numbered I through VIII and beyond.
This distinction matters because during root canal treatment your dentist needs to locate, clean, and seal every canal. Miss one and bacteria can survive, leading to reinfection. A retrospective study of failed root canal treatments in maxillary premolars found that missed canals were one of the top four reasons for failure, identified in about 11 percent of failed first premolars and nearly 22 percent of failed second premolars.11PubMed. A retrospective study of initial root canal treatment failure in maxillary premolars via using cone-beam computed tomography The second premolar’s higher miss rate is somewhat ironic given that it usually has fewer roots than the first premolar; the problem is that its canals split in less predictable ways, and clinicians may not expect the complexity.
Three-Rooted Premolars and Other Oddities
Premolars occasionally develop three fully separate roots, mimicking the anatomy of a molar. These have been nicknamed “ridiculous premolars” or “small molars” in dental literature because they look like a molar that got lost in the wrong part of the arch.12Journal of Dental Sciences. Root canal treatment of a three-rooted maxillary second premolar The typical layout is two buccal roots (toward the cheek) and one palatal root (toward the palate), each housing its own separate canal. Reported rates sit around 1.8 percent for maxillary first premolars and 0.4 percent for second premolars.13Frontiers in Oral Health. Endodontic management of maxillary premolars with three roots: a case series
At the other extreme, mandibular first premolars with four roots have been documented, though they are vanishingly rare, occurring in fewer than 0.1 percent of cases.6PubMed. The root and root canal morphology of the human mandibular first premolar: a literature review These anomalies almost never cause problems on their own, but they can turn a routine root canal into a much longer procedure if the extra roots are not detected beforehand.
Tomes’ Root and C-Shaped Canals
Mandibular first premolars have a specific anatomical quirk called the Tomes’ root, where a deep developmental groove on the root surface partially divides it, creating a bifurcated or kidney-shaped cross section without producing two fully separate roots. A study of a Chinese population found that about 13 percent of mandibular first premolars met the criteria for this trait, and every single one of those teeth had two or more canals. About two-thirds of them also had C-shaped canal configurations, a ribbon-like canal shape that is especially tricky to clean during treatment.14PubMed Central. Root anatomy and canal morphology of mandibular first premolars in a Chinese population A separate study confirmed that deeper grooves strongly predicted more complicated canal systems: teeth with deep grooves had complex canals 90 percent of the time, compared with about 16 percent in teeth with no groove at all.15PubMed. Root and canal morphology of mandibular first premolars with radicular grooves
The prevalence of C-shaped canals in mandibular premolars varies widely by study and population. In a large Eastern Chinese sample, about 10 percent of mandibular first premolars had C-shaped root canals, with men showing higher rates than women.16Scientific Reports. Prevalence and correlation of C-shaped root canals of mandibular premolars and molars in Eastern Chinese individuals An Australian cross-sectional study reported a lower overall rate of about 3.3 percent for mandibular first premolars and 1 percent for second premolars.17PubMed. Prevalence and morphology of different root canal systems in mandibular premolars: a cross-sectional observational study A Thai study landed in between, at about 3.7 percent for first premolars and 0.5 percent for second premolars.18Journal of Dental Sciences. Prevalence and morphology of multiple roots, root canals and C-shaped canals in mandibular premolars from cone-beam computed tomography images in a Thai population The spread reflects both genuine population differences and the difficulty of standardizing how you define a C-shape on imaging.
How Dentists Figure Out What They Are Dealing With
Traditional dental X-rays flatten a three-dimensional tooth into a two-dimensional image, which makes it easy to miss extra roots hiding behind one another and nearly impossible to identify unusual canal configurations. A study comparing standard periapical radiographs to CBCT scans found that conventional X-rays correctly identified the canal configuration only about 55 percent of the time, while CBCT achieved roughly 89 percent accuracy.19Journal of Endodontics. Diagnostic Accuracy of Periapical Radiography and Cone-beam Computed Tomographic Imaging in the Detection of Root Canal Configuration of Human Premolars Some rarer canal types were almost invisible on regular X-rays.
This does not mean every patient getting a root canal needs a CBCT scan. Most straightforward cases can be managed with a standard X-ray and careful clinical technique. But when initial treatment fails, or when the X-ray hints at something unusual, three-dimensional imaging can reveal canals and roots that would otherwise go undetected. Given that missed canals are a leading cause of retreatment in premolars, the technology has proven especially valuable for these teeth.
How Age Affects What Is Inside the Root
Root number is set during development and does not change over a person’s lifetime. But what happens inside the root does change. As you age, your teeth lay down secondary dentin along the inner walls of the canals, gradually narrowing them. In some cases this process can make a canal so thin that it effectively disappears on imaging, or it can cause two canals to appear to merge into one. A clinical CBCT study noted that age-related changes in canal morphology were statistically significant in maxillary first premolars.20PubMed Central. Exploring age and gender variations in root canal morphology of maxillary premolars in Saudi sub population: a cross-sectional CBCT study In practical terms this means an older patient’s premolar may look like it has a simpler canal system than it actually had decades earlier, creating a risk that a calcified but still present canal gets overlooked during treatment.
Another study pointed out that research conducted on extracted teeth from anatomy labs, which tend to come from older donors, may systematically underestimate the complexity of canal systems that younger patients actually have.21PubMed Central. Gender difference and root canal morphology in mandibular premolars: A cone-beam computed tomography study in an Iranian population So the textbook numbers you see quoted for canal prevalence can depend on the age of the teeth that were studied.
Upper Premolar Roots and the Sinus Floor
Your maxillary premolars sit directly below the maxillary sinus, the air-filled cavity in your cheekbone. In some people, the roots of the upper premolars poke into or press tightly against the floor of that sinus. This is mostly relevant during extractions, root canal surgery, or implant placement, where accidentally breaching the sinus lining can cause a communication between the mouth and the sinus cavity.
A radiographic survey found that only a small proportion of premolars actually present a real risk of sinus violation, and when they do, it is more often the second premolar than the first.22PubMed. Proximity of premolar roots to maxillary sinus: a radiographic survey using cone-beam computed tomography A study of an Egyptian population confirmed this pattern, finding that most maxillary first premolars had no close relationship to the sinus floor, while second premolars were much more likely to contact it, especially the palatal root in two-rooted teeth.23Journal of International Oral Health. Assessment of Proximity of the Maxillary Premolars Roots to the Maxillary Sinus Floor in a Sample of Egyptian Population Using CBCT If your dentist orders a CBCT before extracting an upper premolar, this is one of the things they are checking.
Extraction Complications and Root Morphology
Premolars are the teeth most commonly extracted for orthodontic purposes, usually to create space for crowding correction. The morphology of the roots directly affects how smoothly that extraction goes. A study of 334 premolars removed for orthodontic reasons found that over 93 percent of patients had normal root and bone morphology, but about 36 percent had some variation in root form or bone texture. The intraoperative complication rate was about 7 percent, including root fracture, and the postoperative complication rate was under 2 percent.24PubMed Central. Incidence of Risk and Complications Associated with Orthodontic Therapeutic Extraction Root fracture during extraction is more of a concern with teeth that have thin, curved, or divergent roots, which is why the two-rooted upper first premolar can occasionally be trickier to pull than its single-rooted neighbors.
Premolar Roots in Evolutionary Perspective
The trend in human evolution has been toward simpler premolar roots. Our distant hominin ancestors had premolars with larger, more complex root systems, often with multiple well-separated roots. Over millions of years, as jaw size and tooth size shrank, premolar roots simplified. A study of the subocclusal dental morphology of Sahelanthropus tchadensis, one of the earliest known hominins, described this trajectory as a reduction in both root size and root number, transitioning from an ape-like configuration toward the simpler forms seen in modern humans.25PubMed. Subocclusal dental morphology of sahelanthropus tchadensis and the evolution of teeth in hominins The anthropological research on modern premolar root variation also supports this picture: tooth-germ size during development predicts root complexity, and the evolutionary reduction in tooth size has carried root simplification along with it.10PubMed. Mandibular premolar and second molar root morphological variation in modern humans: What root number can tell us about tooth morphogenesis
What this means in practical terms is that the occasional premolar with three or four roots is not a freak mutation but an echo of an ancestral pattern. The developmental machinery for building extra roots still exists; it just gets activated less often in modern human jaws. When it does activate, often because of a slightly larger tooth germ, you get one of those “ridiculous premolars” that looks more like something a great ape would carry.