Imaging Sci Dent.  2019 Mar;49(1):27-34. 10.5624/isd.2019.49.1.27.

Fourth molar: A retrospective study and literature review of a rare clinical entity

• Bamgbose B
• Okada S
• Hisatomi M
• Yanagi Y
• Takeshita
• Abdu ZS
• Ekuase EJ
• Asaumi JI

• KMID: 2442106
• DOI: http://doi.org/10.5624/isd.2019.49.1.27

Abstract

PURPOSE
The prevalence of supernumerary teeth has been reported to be between 0.1% and 3.8%. The aim of this study was to determine the prevalence, clinical significance, and associated pathologies of fourth molars based on a retrospective study and a literature review.
MATERIALS AND METHODS
A 5-year retrospective prevalence study was conducted at the Department of Oral Diagnosis and Dentomaxillofacial Radiology of Okayama University Hospital, Okayama, Japan. The study involved extracting data from the digital records of patients from January 1, 2013 through December 31, 2017. The sampling frame included all patients who had panoramic radiographs, cone-beam computed tomography (CT), and multislice CT images during the period under review.
RESULTS
A total of 26,721 cases were reviewed and 87 fourth molars were identified. The prevalence of fourth molars in the 5-year study at Okayama was calculated as 0.32%. The mean age of patients with a fourth molar was 30.43 years, and the male-to-female ratio was 1:0.98. The vast majority of cases were in the maxilla (92%) and had normal shapes (89.7%); furthermore, 82.8% of cases were unerupted.
CONCLUSION
The prevalence of fourth molars in the study population was found to be 0.32%, and fourth molars occurred with approximately equal frequency in males and females. Fourth molars were more common in the maxilla and were predominantly unerupted and small.

Keyword

Tooth, Supernumerary; Odontoma; Odontogenic Cyst

MeSH Terms

Cone-Beam Computed Tomography
Cross-Sectional Studies
Diagnosis, Oral
Female
Humans
Japan
Male
Maxilla
Odontogenic Cysts
Odontoma
Pathology
Prevalence
Retrospective Studies*
Tooth, Supernumerary*

Figure

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  Fig. 1 A. Panoramic radiograph shows a borderline case classified as “cannot decide,” portraying a toothlike radiopacity in posterior maxillary left region that cannot be classified as a third or fourth molar because of the absence of both maxillary third molars. B and C. Conebeam computed tomographic images demonstrate an abnormally shaped tooth-like entity with 2 distinct crowns and fused roots with an associated mucus retention cyst in the posterior wall of the maxillary sinus.

• 

  Fig. 2 A. Panoramic radiograph shows a fourth molar distal to the maxillary left third molar. There is also a fourth molar associated with a suspected odontoma in the region of the maxillary right third molar. Both fourth molars are in the maxillary tuberosity. B and C. Conebeam computed tomographic (CBCT) images demonstrate the maxillary left fourth molar as a normal-shaped microdont. D and E. Sagittal CBCT images show a complex odontoma superior to the maxillary right fourth molar (arrow head). D–G. The complex odontoma consists of a horizontally impacted microdont at its inferior segment (arrow), and the upper segment consists of various component tissues of the teeth.

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  Fig. 3 A. Panoramic radiograph shows a fourth molar overlapping the maxillary right third molar. Cone-beam computed tomographic images demonstrate a fourth molar distopalatal to the maxillary right third molar (B) and a fused tooth connecting with the third molar by the dental pulp (C and D).

• 

  Fig. 4 Fully-formed fourth molar associated with the distal surface of the maxillary right third molar in a patient with cleidocranial dysostosis.

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