Do visible nutrient canals on a radiograph mean high blood pressure?

Studies from 1976 to 2022 tested whether visible nutrient canals go with hypertension, and they split. Several report canals more often in patients with hypertension, and two found no significant difference. Two of the studies, from 2014 and 2019, list in their introductions the conditions the canals have been linked to: periodontal disease, hypertension, diabetes, tuberculosis, rickets, calcium deficiency, disuse atrophy and coarctation of the aorta [1, 2]. This article sets those studies side by side, shows where their designs part, and says what a visible canal should change at the chairside.

What counts as a visible nutrient canal on a radiograph?

Look at the bone between the mandibular incisors on a periapical radiograph. A nutrient canal shows as a radiolucent line running vertically between the roots or apical to them. The 2019 study of 600 patients scored exactly that: a vertical radiolucent line in the interdental or periapical bone between the mandibular right canine (43) and the mandibular left canine (33) [2]. The canals vary in size, number and prominence, and in how they sit against the roots [2].

A 2001 case report traced the mandibular canals on radiographs from the incisive branch of the inferior alveolar neurovascular bundle to the interdental area of the anterior teeth [3]. The nutrient canals reference entry covers how to tell one from the structures it resembles. This article is about one question: does seeing one tell you anything about blood pressure?

What have studies found about nutrient canals and high blood pressure?

The studies disagree. Each looked at whether canals appear more often in patients with hypertension. The table gives what each abstract or paper reports.

The authors read their own results in different directions. Yilmaz and colleagues concluded that canals are not indicative of hypertension [9]. Kumar and colleagues wrote that a canal should raise suspicion of hypertension and lead to further investigation, and added that it is not entirely indicative [10]. Hasan and colleagues suggested canals as ancillary screening support for systemic disorders [11].

Why do the studies disagree?

The designs differ in five places.

Age and bone loss. Canals appear more often with advancing age, periodontal disease and tooth loss. A study of 1,586 patients found the incidence very high with periodontal disease and advanced age, and especially in edentulous patients [12]. On cone beam CT, canals were seen in 55% of controls and 86% of patients with periodontitis [13]. In the 2014 Iranian study, patients with canals were older on average, 47.1 years against 42.6 (P = 0.002) [1]. A study that does not account for age and bone loss cannot separate their effect from any effect of hypertension.

How the groups were built. The 1989 Greek study compared patients with both hypertension and alveolar bone loss against patients with neither, so two variables changed at once [6]. The 2003 Turkish study used only edentulous patients [9]. The 2014 Iranian study excluded periodontal disease, took its hypertensive patients from a cardiovascular research centre and its normotensive patients from a dental school, and blinded the radiologists [1]. The 2019 study excluded edentulous patients and severe bone loss [2]. The 1985 study compared groups of the same age group and similar oral status [5]. The 2022 study took periapicals of patients who came with pain in the mandibular anterior teeth, deep caries, abrasion or attrition [11].

What counted as hypertension. The 2014 Iranian study set the line at 140/90 mmHg [1]. The 2019 study selected patients above 120/80 mmHg as hypertensive [2]. The ADA summarises the 2017 ACC/AHA definition as a systolic pressure of 130 mmHg or greater or a diastolic pressure of 80 mmHg or greater [14]. The same patient can land in different groups depending on which study enrolled them.

How the radiograph was taken. Some studies used the bisecting angle technique and others the paralleling technique [2]. The 2014 Indian and Iranian studies both used bisecting angle [10, 1].

Severity and duration. The 2019 study found no correlation with severity [2]. The 2014 Iranian study found no association with duration or with whether the hypertension was controlled [1]. The 2022 study reported an association with duration [11].

Two more things keep the question open.

The explanation offered for a link is vascular. The 2019 paper repeats the explanation that dilated vessel walls or extra collateral vessels in hypertension may be responsible for more canals [2]. That study scored canals on radiographs and did not examine the vessels, so the mechanism remains a proposal.

Some papers describe earlier studies the opposite way to those studies' own abstracts. The 2014 Iranian paper describes the 1985 study as showing no association with hypertension, and two sentences later lists it among studies with a positive correlation [1]. The 1985 abstract reports an increased incidence in hypertensive patients [5]. The 2019 paper lists the 2003 study as agreeing with a positive association [2]. The 2003 abstract reports no statistical difference [9]. If you follow the claim through citations alone, you can arrive at either answer.

Should a visible nutrient canal change what you do at the chairside?

The studies compare how often canals appear in groups with and without hypertension. Even the authors who report a link describe the canal as an adjunct or a prompt for further investigation [2, 10].

Hypertension is diagnosed from blood pressure readings. The ADA states that diagnosis is generally based on an average of two or more elevated readings obtained on two or more occasions [14]. It also lists blood pressure measurement as an important screening vital sign at dental visits [14].

Radiographs follow the history and the examination. The ADA and the American Academy of Oral and Maxillofacial Radiology recommend that a thorough evaluation of the patient history and clinical findings precede any radiographic examination [15]. They advise clinicians to base imaging decisions on the medical and dental histories, clinical findings, disease risk and specific clinical conditions [15].

The blood pressure question is answered by the blood pressure reading.