Shovel-shaped incisors

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Shovel-shaped incisors (or, more simply, shovel incisors) are incisors whose lingual surfaces are scooped as a consequence of lingual marginal ridges, crown curvature or basal tubercles, either alone or in combination.[citation needed]

Shovel-shaped incisors are relatively common in Central, East and Southeast Asians; the Eskimo and Aleut peoples of Northeast Asian and North America (including but not limited to the Inuit peoples of eastern Alaska, arctic Canada and Greenland); and Aboriginal North and South Americans.[1][2][3] In Europeans and Africans, shovel-shaped upper incisors are uncommon or not present.[1] In some instances, incisors can present a more pronounced version of this called double shovel-shaped. The differences observed in tooth morphology is believed to be partly determined by genetics.[4] When present, shovel-shaped incisors can indicate correlation among populations and are considered to be one of the non-metric traits in osteology. The characteristic could also be attributed to hormones, duration of development, and the capacity of the maxillary dental arch.

The shovel-shaped dental characteristic can also be traced back to Homo erectus and in Neanderthals.[1] The morphology of Neanderthal's anterior teeth has been seen as an adaptation to the heavy use of their canines and incisors in processing and chewing food, and the use of their teeth for activities other than feeding.[5]

History[edit]

The first description of shovel-shaped incisors was in 1870.[6]

Racial diagnostic[edit]

Shovel-shaped incisors is a very noticeable trait that indicates a difference of race.[7] A 1964 text said that many anthropologists at the time used the trait of shovel-shaped incisors as a diagnostic for race.[7]

Data tables[edit]

Comparison of Frequency Distributions Classified by Metrical
and non-Metrical Methods (in %)
Population & Author No-Shovel
0 ~ 0.49 mm.
Trace & Moderate
0.5 ~ 0.99 mm.
Marked
1.00 mm. ~
Japanese
Hrdlicka (1920)1 4.0 18.0 77.9
Carbonell (1963)2 7.1 51.3 41.4
Hanihara, Tanaka & Tamada (1970) 4.6 40.5 54.9
American White
Hrdlicka (1920) 68.5 29.5 2.0
Lasker (1957)3 55.0 45.0 0
Hanihara, Tanaka & Tamada (1970) 65.5 29.8 4.8
Amerindians
Nelson (1937 ; Pecos Pueblos)4 2.2 23.7 74.1
Dahlberg & Snow (1949 ; Indian Knoll) 0 16.0 84.0
Dahlberg (1949 ; Pimas) 0 2.2 97.8
Hanihara, Tanaka & Tamada (1970) 1.7 27.5 70.8
1 Males only ; both sexes combined in other groups.
2 Combined data for Japanese, Chinese and Tibetan.
3 Cited by Carbonell (1963).
4 Cited by Dahlberg (1949).
Source: Hanihara, Tanaka & Tamada (1970) Page 95[8]
Classification of the Shovel-Shaped Incisors in Terms of Depth of the Lingual Fossa
Depth of
Lingual fossa
Class of
Classification
Method Suggested by Carbonell (1963) 1+ mm. Shovel
1 mm. Semi-Shovel
1- mm. Trace-Shovel
Method Used in Hanihara (1970) 1+ mm. Shovel
0.6-1.0 mm. Moderate-Shovel
0.0-0.5 mm. No-Shovel
Source: Hanihara (1970) Page 11[9]
Frequencies of Each Class of Shovel-Shaping in I1 (in %).
Population No. of
Individuals
Shovel
( 1+ mm )
Moderate-Shovel*
( 0.6 – 1.0 mm )
No-Shovel
( 0 – 0.5 mm )
Total of
Shovel
Male:
Ainu 31 22.6 58.1 19.4 80.6
Japanese 60 48.3 48.3 3.3 96.7
Female:
Ainu 13 30.8 61.6 7.7 92.3
Japanese 60 50.0 48.3 1.7 98.3
Romano-British** 100 0.0 4.0 96.0 4.0
East Greenland
Eskimo**
76 38.1 61.7 0.0 100.0
Japanese-Chinese-
Tibetan**
70 41.4 51.3 7.1 92.9
* Carbonell's Semi- and Trace-shovel are combined.
** Carbonell, 1963
Source: Hanihara (1970) Page 12[9]

See also[edit]

References[edit]

  1. ^ a b c Kimura, Ryosuke; Yamaguchi, Tetsutaro; Takeda, Mayako; Kondo, Osamu; Toma, Takashi; Haneji, Kuniaki; Hanihara, Tsunehiko; Matsukusa, Hirotaka; Kawamura, Shoji (2009-10-09). "A Common Variation in EDAR Is a Genetic Determinant of Shovel-Shaped Incisors". American Journal of Human Genetics. 85 (4): 528–535. doi:10.1016/j.ajhg.2009.09.006. ISSN 0002-9297. PMC 2756549Freely accessible. PMID 19804850. 
  2. ^ Acs, G., Pokala, P., & Cozzi E. (1992). Shovel incisors, three-rooted molars, talon cusp, and supernumerary tooth in one patient. In Pediatric Dentistry, 14(4). Page 264. Retrieved December 27, 2016, from link.
  3. ^ DeLong, L. & Burkhart, N.W. (2008). General and Oral Pathology for the Dental Hygienist. USA: Lippincott Williams & Wilkins. Page 494. Retrieved December 27, 2016, from link.
  4. ^ Hemphill, Brian E. (2002-10-01). "Review". Journal of Anthropological Research. 58 (3): 412–414. JSTOR 3631186. 
  5. ^ Clement, Anna F.; Hillson, Simon W.; Aiello, Leslie C. (2012-01-01). "Tooth wear, Neanderthal facial morphology and the anterior dental loading hypothesis". Journal of Human Evolution. 62 (3): 367–376. doi:10.1016/j.jhevol.2011.11.014. PMID 22341317. 
  6. ^ Saukko, P. & Knight, B. (2004). Knight's Forensic Pathology (3rd ed.). USA: Taylor & Francis Group. Page 533. Retrieved January 14, 2016, from link.
  7. ^ a b Suzuki, M. & Sakai, T. (1964). Shovel-shaped incisors among the living Polynesians. In American Journal of Physical Anthropology, 22(1). Page 65. Retrieved December 28, 2016, from link.
  8. ^ Hanihara K., Tanaka T., Tamada M. (1970). "Quantitative Analysis of the Shovel-Shaped Character in the Incisors". Journal of the Anthropological Society of Nippon. 78 (2): 95. 
  9. ^ a b Hanihara K (1970). "Mongoloid Dental Complex in the Deciduous Dentition with Special Reference to the Dentition of the Ainu". Journal of the Anthropological Society of Nippon. 78 (1): 11 & 12.