Notable developmental defects of the mandibular first molar in dogs

Look for molar malformations that may be harboring current or future endodontic problems

Tooth 309 (A) and tooth 409 (B) exhibit an enamel fissure in the furcational enamel which is a hallmark sign of a developmental abnormality often referred to as dens invaginatus. Photos courtesy John Lewis
Tooth 309 (A) and tooth 409 (B) exhibit an enamel fissure in the furcational enamel which is a hallmark sign of a developmental abnormality often referred to as dens invaginatus.
Photos courtesy John Lewis

Chelsey, a seven-year-old spayed cockapoo, recently presented for extraction of her left mandibular first molar tooth (tooth 309) that was diagnosed with endodontic disease on dental radiographs that were taken by her primary care veterinarian.

On inspection of tooth 309, there was no evidence of tooth fracture or discoloration of the tooth, but there was a subtle abnormality of the crown that revealed the cause of the endodontic disease.

I noticed a slight notch in the crown dorsal to the furcation of tooth 309, sometimes referred to as an enamel fissure. Inspection of tooth 409 showed a similar enamel fissure (Figures 1 A, B).

The patient was placed under general anesthesia, and dental radiographs were obtained. Abnormalities of tooth 309 included increased radiodensity in the furcation area of the pulp chamber, and large periapical lucencies of both the mesial and distal roots (Figure 2). Tooth 409 showed increased radiodensity in the furcation pulp chamber and periapical lucency of the mesial root.

Dens invaginatus

These clinical and radiographic findings are consistent with what the literature has described in a handful of case reports and case series as “dens invaginatus,” also referred to as “dens in dente.” Dens invaginatus is a malformation of teeth likely resulting from an infolding of the dental papilla during tooth development. Teeth affected by dens invaginatus show a deep infolding of enamel and dentin.

The tooth most affected in people is the maxillary lateral incisor, which may occur bilaterally. The malformation shows a broad spectrum of morphologic variations and frequently results in early pulp necrosis. Root canal therapy may be difficult or impossible in some cases due to the abnormal anatomy of the teeth.1

In dogs, dens invaginatus has been described in a Doberman pinscher,2 mixed breed dogs,3,8 Jack Russell terrier,4 Rottweiler,5 German shepherd,6 Irish setter,7 Cavalier King Charles spaniel,8 miniature pinscher,8 and other breeds. The mandibular first molar is the most commonly affected tooth, but it has been described in a maxillary first molar5 and the maxillary canine tooth.6

Clinically, I see the disease most commonly in the mandibular first molar of little white fluffy dogs, such as Maltese and Havanese breeds. This is not an uncommon finding: I likely see 10 cases in some years.

A developmental abnormality

Now that I may have introduced what may be a new disease to you, it is worth mentioning a recent publication suggests this developmental abnormality in mandibular first molars is not due to dens invaginatus, but rather due to some other developmental abnormality.8

Assessment of mandibular first molar malformations in six dogs did not definitively determine the cause of disease, but micro-CT and histopathology suggest the abnormalities seen more closely resemble a condition documented in humans called molar-incisor malformation.

Similar to what we see in our veterinary patients, molar-incisor malformation, also referred to as molar-incisor hypomineralization, a hypoplastic enamel notch is seen near the cervical third of the clinical crown.9

Based on this recently obtained information, the authors suggested veterinarians refer to these affected teeth as having “carnassial tooth malformations.”8

Regardless of what you call it, look for molar malformations that may be harboring current or future endodontic problems, particularly in the little white fluffy dogs!

Figure 2A (left): Tooth 309 in a seven-year-old cockapoo. Note the increased radiodensity within the pulp chamber and periapical lucencies of both the mesial and distal roots.
Figure 2B (right): A more severely affected tooth 309 in a different dog. Note the convergence of the normally divergent roots.

John Lewis, VMD, DAVDC, FF-AVDC OMFS, practices and teaches veterinary dentistry and oral surgery at Veterinary Dentistry Specialists and Silo Academy Education Center, both located in Chadds Ford, Pa.


  1. Hülsmann M. Dens invaginatus: aetiology, classification, prevalence, diagnosis, and treatment considerations. Int Endod J. 1997;30(2):79-90.
  2. DeForge DH. Dens in dente in a six-year-old Doberman pinscher. J Vet Dent. 1992;9(3):9,12. 
  3. Duncan HL. Diagnostic imaging in veterinary dental practice. Dens invaginatus leading to arrested maturation of the right and left mandibular first molar teeth. J Am Vet Med Assoc. 2010;237(11):1251-3.
  4. Stein KE, Marretta SM, Eurell JA. Dens invaginatus of the mandibular first molars in a dog. J Vet Dent. 2005;22(1):21-25.
  5. Assunção GSM, Ocarino NM, Sofal LC, Serakides R. A Rare Case of Radicular Dens invaginatus (dens in dente) in a dog. J Comp Pathol. 2020;178:46-49.
  6. Coffman CR, Visser CJ, Visser L. Endodontic treatment of dens invaginatus in a dog. J Vet Dent. 2009;26(4):220-225. 
  7. Pavlica Z, Erjavec V, Petelin M. Teeth abnormalities in the dog. Acta Vet Brno. (2001) 70:65–72.
  8. Ng KK, Rine S, Choi E, Fiani N, Porter I, Fink L, Peralta S. Mandibular Carnassial Tooth Malformations in 6 Dogs-Micro-Computed Tomography and Histology Findings. Front Vet Sci. 2019;6:464.
  9. Lee HS, Kim SH, Kim SO, Lee JH, Choi HJ, Jung HS, Song JS. A new type of dental anomaly: molar-incisor malformation (MIM). Oral Surg Oral Med Oral Pathol Oral Radiol. 2014;118(1):101-109.

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