Mental foramen

The mental foramen is the opening in the body of the mandible that carries the mental nerves and vessels [16]. On a radiograph it reads as a small round or oval radiolucency in the apical region of the mandibular premolars [11, 10]. Projected over a premolar apex, it can mimic periapical inflammatory disease [14, 11, 13].

Synonyms: foramen mentale

What is the mental foramen?

The mental foramen is a passage for the mental nerves and vessels, and a landmark in the body of the mandible [16]. To find it, follow the mandibular premolar roots to their apices and look around them for a small round or oval radiolucency [11, 10].

Where is the mental foramen on a periapical and a panoramic radiograph?

It usually lies apical to the mandibular second premolar, or between the apices of the two premolars [10].

On paralleling periapical radiographs of 75 dry adult mandibles, it usually lay mesial to the second premolar's radiographic apex and apical to it [6].

On a panoramic radiograph of the same kind of dry mandibles, the foramen looked slightly larger than on periapicals, and the panoramic projection may shift it distally [7]. A 2025 study of 500 digital panoramic radiographs from a Yemeni sample found round to be the most frequent shape (46.3%) [4]. In 72%, the foramen showed a continuous relationship with the mandibular canal [4].

The foramen doesn't always look the same on a panoramic radiograph. A 1989 study of panoramic radiographs from 297 patients sorted its appearance into four types: separated in 43%, diffuse in 24%, continuous in 21% and unidentified in 12% [8]. The authors suspected that the landmark taken for the foramen is sometimes the reappearance of the mental canal [8].

How much does its position vary between people and populations?

Enough that one rule won't place it for every patient. Its position ranges from the mandibular canine to the first molar [10].

Population is one source of that spread. A 2012 anthropometric study of dry skulls from three populations found the most common position in line with the second premolar in Chinese skulls, and between the first and second premolars in European and Indian skulls [2]. Its authors conclude that the notion of the foramen lying between the first and second premolars can no longer be accepted [2].

Radiographic studies of single populations report different shares:

The figures for "between the premolars" run from 30% to 70% across these samples [1, 3, 4]. The samples differ in population and projection, and the studies report position in different categories [1, 3, 4]. The Moroccan study also found the foramen symmetrical between sides in 79% [1].

Vertical position splits the same way. On the 1976 intraoral series, the largest share of foramina lay coronal to the level of the premolar apices [3]. On the Yemeni panoramic radiographs, most lay apical to the apices [4], and on the dry-mandible periapicals it usually lay apical to the second premolar apex [6].

Exposure conditions alone can change it [9]. In a 1989 experiment on four dry skulls, any change in exposure conditions changed the foramen's appearance and its apparent vertical position [9]. Its radiographic position matched its actual position less than half the time, whatever the technique, while its apparent diameter stayed close to the true diameter [9].

How do you tell the mental foramen from a periapical radiolucency on a mandibular premolar?

Check three things on the image: whether a lamina dura runs around the apex, whether the mandibular canal runs into the radiolucency, and whether the radiolucency moves on a second view taken at a different horizontal angle. These checks rest on case reports and expert commentary [11, 12, 13].

The problem is superimposition. Intraoral and panoramic radiographs are two-dimensional, so overlapping structures can confuse the reader [17]. When the foramen projects over a premolar apex, it can mimic periapical inflammatory disease [14, 11, 13].

Start at the apex. A 2014 case report describes a lamina dura traceable around the root apex, or the mandibular canal extending to the radiolucency, as pointing to the foramen [11]. The same report notes that where the foramen overlies the apex, the lamina dura can be too faint to see, and that a second view from another angle is likely to show it clearly [11].

On a second periapical radiograph at a different horizontal angle, a tube shift, the foramen is likely to show some shift relative to the apex [11, 13, 12]. A radiolucency that moves away from the apex is consistent with the foramen superimposed on the root [13, 11]. In the 2014 case, the radiolucency moved mesially on the second view, and the lamina dura around the tooth was intact [11]. A 2015 case report describes the radiolucency separating from the apex on mesial and distal shifts, with a periodontal ligament space that showed no widening [12].

An oral and maxillofacial radiologist, writing in a trade journal, adds that the tooth should respond positively to vitality testing when the radiolucency is the foramen superimposed on the apex [13].

What is the mental foramen confused with?

The mental foramen is one of the normal structures mistaken for pathology that can mimic periapical inflammatory disease [14].

What is an accessory mental foramen?

An accessory mental foramen is a small additional foramen near the mental foramen, mainly posterior to it [16].

A 2025 study of 114 Greek dry adult mandibles measured accessory foramina at a mean diameter of 0.96 ± 0.43 mm, at a mean distance of 4.12 ± 2.15 mm from the mental foramen [16]. On cone-beam CT (CBCT), accessory foramina were unilateral in 90.15% (95% CI 82.98-94.49) of cases and most often posterior and inferior to the mental foramen [15]. Accessory foramina superior to the mental foramen still appeared in 47.43% (95% CI 38.45-56.58) of cases [15].

Reported figures come from different modalities and samples, and they do not all count the same unit:

• CBCT: 7.87% of subjects (95% CI 6.69-9.24) and 4.75% of hemimandibles (95% CI 3.79-5.95), pooled across 46 articles and 21,761 subjects in a 2021 meta-analysis [15].
• Dry mandibles: 6.1% (95% CI 4.8-7.6), pooled across 27 publications in a 2025 meta-analysis [16].
• Panoramic radiographs: 3.8% of cases in one study of 500 radiographs (1,000 sides) from a Yemeni sample [4].

Read each figure with its modality attached.

Why is the mental foramen sometimes not visible on a radiograph?

The foramen usually opens in a posterior-superior direction [5]. The usual view of the premolars isn't projected through the long axis of that opening, which makes its image variable [11].

On a periapical radiograph, it can also fall outside the image. On paralleling periapical radiographs of 75 dry adult mandibles, the foramen was seen on 75% [6]. When it wasn't seen, it usually lay beyond the edge of the radiograph on the apical side [6].

On panoramic radiographs of 297 patients, the foramen's appearance was the unidentified type in 12% [8]. In a dry-skull experiment, any change in exposure conditions changed how the foramen appeared [9].

The foramen may not appear on conventional radiographs at all, and CT is more accurate for detecting it [10].

Common errors

• Calling periapical disease on one radiograph. Projected over a premolar apex, the foramen can mimic periapical inflammatory disease [14, 11]. A 2014 case report points to the lamina dura around the apex and a second view [11].
• Placing the foramen by the between-the-premolars rule. Its position ranges from the mandibular canine to the first molar [10], and its most common position differs between populations [2].
• Reading the image position as the true position. In a dry-skull experiment, radiographic position matched actual position less than half the time [9].