Peck 2004.4


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In the last issue of Dental Anthropology, Edgar and 
Sciulli (2004) highlighted an interesting abnormality 
of human mandibular premolar (MnP) shape in their 
report, “Elongated mandibular premolar: a new 
morphological variant.”  They noted that the affected 
premolar is characterized by “either compressed…
buccolingual dimension or longer … mesiodistal 
dimension.”

We show here that these observations have greater 
depth in the literature.  For example. we identified and 
illustrated the same morphological crown anomaly in 
1975 (Peck and Peck) in two North American white 
orthodontic patients, describing the occurrence as a 
tooth shape deviation (TSD) of MnP.  One case was a 
female with bilateral MnP1-TSD (Fig. 1) and the other 
was a case of a male with bilateral MnP2-TSD (Fig. 2).  
In fact, this variation had previously been recognized 
by Dahlberg (1951) in a white female (bilateral MnP2) 
and by Suzuki and Sakai (1960) in a Japanese male 
(bilateral MnP2), each referring to the condition as 
“buccolingually compressed” mandibular premolars.  
To our knowledge, occurrences of this anomaly have 
not been demonstrated for the maxillary premolars.

We applied an MD/FL crown index ([mesiodistal 

Brief report:

Tooth Shape Deviations of Mandibular Premolars

Sheldon Peck*

Department of Oral and Developmental Biology, Harvard School of Dental Medicine
Boston, MA 02115

diameter in mm ÷ faciolingual diameter in mm] X 100) 
to quantify the extent of this tooth shape anomaly in 
our two subjects: deviant MnP1 teeth, with widened 
mesiodistal dimension and narrowed faciolingal 
dimension, had an MD/FL index of 122; deviant 
MnP2 teeth showed an MD/FL index of 120-127.  This 
compares with MD/FL indices for unaffected MnP1 in 
whites of 90 ± 5 and for unaffected MnP2, 85 ± 5.

We also found an association between MnP-TSD and 
a similar TSD of the mandibular incisors, commonly 
associated with the tendency for dental crowding (Peck 
and Peck, 1972a,b).

Here I report another case, a European white female 
showing unilateral expression of MnP1-TSD (Fig. 3).

From these several reported cases, I conclude that 
these peculiar deviations in mandibular premolar 
shape may derive from a developmental pinching 
of the faciolingual tooth mass with an associated 
enlargement of the mesiodistal tooth diameter.  MnP-
TSD is usually the product of reduced FL and increased 

Fig 1. Tooth shape deviations of both mandibular first 
premolars (MnP1-TSD) in a white female (reproduced 
courtesy of The Angle Orthodontist).

Fig 2. Tooth shape deviations of both mandibular second 
premolars (MnP2-TSD) in a white male (reproduced 
courtesy of The Angle Orthodontist).

Address for correspondence:  Sheldon Peck, 1615 
Beacon Street, Newton, MA 02468
Email: peckslam@att.net



64

MD dimensions.  All elements of occlusal morphology 
of the affected teeth seem to be intact, just dimensionally 
shifted and distorted.  The anomaly occurs in either 
sex, in either the first or second mandibular premolars 
independently, expressed mostly bilaterally and 
occasionally unilaterally.  The MnP-TSD anomaly is 
found occurring in whites, blacks and Asians.

My co-workers and I are undertaking further 
studies of various phenotypes of this unusual dento-
morphological condition.

ACKNOWLEDGMENT

The author thanks Dr. Daniela Garib for her 
contributions to this report.

LITERATURE CITED

Dahlberg AA. 1951. The dentition of the American 
Indian. In: Laughlin WS, editor. Papers on the 
physical anthropology of the American Indian. New 
York: The Viking Fund, p 138-176.

Edgar HJH, Scuilli PW. 2004. Elongated mandibular 
premolar: a new morphological variant. Dental 
Anthropology 17:24-27. 

Peck S, Peck H. 1972a. Crown dimensions and 
mandibular incisor  alignment. Angle Orthod 
42148-153.

Peck H, Peck S. 1972b. An index for assessing tooth 
shape deviations, as applied to the mandibular 
incisors. Am J Orthod 61:385-401.

Peck S, Peck H. 1975. Orthodontic aspects of dental 
anthropology. Angle Orthod 45:95-102. 

Suzuki M, Sakai T. 1960. A case of buccolingually 
compressed mandibular second premolar in the 
Japanese.  J Anthropol Soc Nippon (Zinruigaku 
Zassi) 68:119-123.

Fig 3. Tooth shape deviation of the mandibular left first 
premolar (MnP1-TSD) in a white female. 

S. PECK