Unusual role in occlusion and mastication of a horizontal positioned erupted mandibular third molar: a rare case

Abstract

Lower third molars are frequently extracted due to pathologies of the dental follicle, pericoronitis, advanced carious lesions, orthodontic reasons (risk of anterior tooth crowding) or causing periodontal or carious lesions in the distal area of the second molar. The case presented here is of a male patient that came to our Clinic experiencing pain in the distal area of one of his old bridges. The clinical examination revealed a malpositioned, but unusually functional third molar; it is a very rare situation for an initially impacted third molar to erupt in an almost horizontal position and not only to remain on the arch for a very long period of time, but also to contribute to mastication efficiency and occlusion, despite the fact that masticatory forces are distributed at a right angle on its long axis and that mastication takes place on the distal surface of the crown and root, and not on the usually occlusal cusped surface. The horizontal mandibular right third molar contributed to maintaining the vertical dimension of occlusion and the masticatory efficiency for a very long period of time; it also ensured a proper distribution of forces trough the long axis of the second premolar, since the distal contact of the third's molar crown with the second premolar helped it to resist masticatory forces and to remain on the arch, despite the prolonged absence of any mesial contact.

Keywords: lower third molar; malposition; mastication; occlusion.

Figure 1

Clinical situation at presentation: (A) Lower arch with the all-metallic old bridge, perforated on the lingual side of the distal abutment; (B) Upper metal-acrylic old bridge, making occlusal contact with the right third mandibular molar; (C) Upper arch image showing the normal morphology of the palatal cusp of the first molar and the accentuated attrition of the palatal cusp of the second molar; (D) Disparity between lower and upper arch dimensions and the subsequent reverse occlusion

Figure 2

Mirror image of the lower arch showing a high degree of attrition on the upper surface due to its intensive use in mastication.

Figure 3

Initial radiological investigation: (A) Panoramic X-ray showing the unusual, overerupted horizontal position of the third right molar, and its mesial contact with the second premolar; (B) Periapical X-ray showing the degree of bone resorption in the distal and mesial areas, and also the presence of alveolar bone between the roots. R: Right.

Figure 4

Occlusal view of the working cast for the three implant-supported crowns; the abraded area on the third molar’s crown and root is also highlighted

Figure 5

CBCT cross sections, showing the mesialized position of the third molar, in front of the retromolar triangle (slices 1–12), occupying the second and first molars’ place (images beginning with slice 13), and the horizontal position of its roots, which exclude a potential root canal treatment. The mesial root, which is the deepest, is situated in the bone, but always above the canal lumen, while the distal root is having contact with the bone only on its lower face; there is no root septum. CBCT: Cone-beam computed tomography; R: Right

Figure 6

CBCT three-dimensional model: (A) Lateral right view of bone resorption around the third molar and premolar’s roots; (B) Pronounced loss of the enamel and dentin at the level of third molar’s crown facing the occlusal plane; (C) Lingual view of bone resorption around the third molar and premolar’s roots. CBCT: Cone-beam computed tomography; R: Right; L: Left

Figure 7

CBCT axial sections parallel to the basilar border showing the main axis of the right mandibular third molar (4.8): (A) Crown of the third molar contacting the distal surface of the adjacent premolar; (B) Horizontal position of the third molar offering a wider, unusual occlusal area for mastication; (C) Alveolar bone separating the roots of 4.8 and the absence of cortical bone at that level. CBCT: Cone-beam computed tomography; R: Right; L: Left

Figure 8

Final oral rehabilitation: (A) Occlusal view of the fourth quadrant showing composite restoration of the third’s molar crown; (B) Frontal view in occlusion