rASUDAS:

A New Web-Based Application for Estimating Ancestry from Tooth Morphology


G. Richard Scott, Marin A. Pilloud, David Navega, João d'Oliveira Coelho, Eugénia Cunha, Joel Irish


Abstract

The use of crown and root morphology to estimate population relationships has a long history in dental anthropology. Over the past two decades, methods employing dental morphology within forensic anthropology have been formalized with the incorporation of statistical models. This paper presents a new web-based application (rASUDAS) that estimates the ancestry of unknown individuals based on their suite of tooth crown and root traits. The application utilizes 21 independent traits that were scored following the Arizona State University Dental Anthropology System (ASUDAS). The reference sample represents approximately 30,000 individuals from seven biogeographic regions. A naive Bayes classifier algorithm was created in the R open source programming language to assign posterior probabilities for individual group assignment. To test the application, 150 individuals were selected from the C. G. Turner II database with the proviso that an individual had to be scored for a minimum of 12 of the 21 traits. In a seven-group analysis, the model correctly assigned individuals to groups 51.8% of the time. In a four-group analysis, classification accuracy improved to 66.7%. With three groups, accuracy was at 72.7%. It is still necessary to validate the program using forensic cases and to augment the reference sample with modern skeletal data. However, results from the beta version of rASUDAS are presented as proof of concept on the potential of dental morphology in ancestry estimation in forensic contexts.

Forensic Anthropology, Volume 1, Number 1, 18 - 31

Disclaimer

This decision support system is freely provided as an aid for profiling skeletal material. The authors hold no responsibility for its ultimate use or misuse. As creators we try to ensure that the software is theoretically grounded and statically accurate, we provide no warranty and make no specific claims as to its performance or its appropriateness for use in any particular situation. Please read any research paper regarding this tool before applying it. Always keep in mind: you are the expert, this is just a decision support system.

Developed by David Senhora Navega, João d'Oliveira Coelho, G. Richard Scott and Marin A. Pilloud

1) Winging

Focal Tooth: Central Upper Incisor (UI1)

Trait Type: Crown

Rotated maxillary central incisors.

Grade | Description

0) If the line is parallel to the labial surfaces or if the distal margins fall below the line, winging is absent. Angle >= 180 degrees.
1) Mesial margins of the upper incisors fall slightly below the line. Angle 160-180 degrees.
2) Mesial margins are more removed from the line. Angle 135-150 degrees.
3) There is a distinct distance between the line and the mesial margins. Angle < 135 degrees.

Following Scott and Irish (2017)

Note: Grade of 1 or greater counts as presence in the rASUDAS application.

2) Shovelling

Focal Tooth: Central Upper Incisor (UI1)

Trait Type: Crown

The presence of lingual marginal ridges.

Grade | Description

0) None. Lingual surface is essentially flat. Rare to find a complete lack of marginal ridges.
1) Trace. Marginal ridges can be discerned, but expression is slight, with mesial marginal ridge not extending to the basal eminence.
2) Low moderate. Ridges more pronounced, with mesial marginal ridge extending further down on basal eminence.
3) High moderate. Ridges more pronounced, almost coalescing at basal eminence.
4) Low pronounced. Well-developed ridges that converge at the basal eminence.
5) Medium pronounced. More pronounced ridges that meeting at basal eminence.
6) High pronounced. Pronounced ridges that meet a basal eminence, almost folding around on themselves.
7) Extreme pronounced. Any expression that exceeds grade 6 can be placed in grade 7. It is a rare expression. This grade would involve marginal ridges that folded around on themselves, similar to grade 6 on the UI2 shoveling plaque.

3) Interruption grooves

Focal Tooth: Upper Lateral Incisor (UI2)

Trait Type: Crown

Distinct grooves that interrupt the normal course of the mesial or distal marginal ridges or even the basal cingulum.

Grade | Description

0) Absence of grooves on lingual marginal ridges and basal cingula.
1) [M] Groove on mesiolingual marginal ridge.
2) [D] Groove on distolingual marginal ridge.
3) [MD] Grooves on both mesiolingual and distolingual marginal ridges.
4) [med] Groove on medial aspect of basal cingulum, sometimes extending onto root.

*Note: Any presence is counted in rASUDAS – regardless of location. *

4) Carabelli’s Trait (or Cusp)

Focal Tooth: Upper First Molar (UM1)

Trait Type: Crown

A cingular derivative expressed on the lingual surface of the protocone (mesiolingual cusp of upper molars).

Grade | Description

0) Mesiolingual cusp does not exhibit any grooves or pits on the lingual surface.
1) A vertical groove separates the protocone from the mesial marginal ridge complex; grade 1 expression occurs when there is a slight eminence that deflects distally from this groove.
2) When expression goes beyond a slight groove or eminence and takes the form of a pit.
3) Expression is still slight but takes on a more distinct form than shown by grades 1 and 2.
4) The most pronounced Carabelli’s trait that does not involve a tubercle with a free apex; grade 4 takes the classic bird-wing form.
5) Small tubercle with a free apex.
6) Moderate tubercle with a free apex.
7) Pronounced tubercle with a free apex.

5) Cusp 5

Focal Tooth: Upper First Molar (UM1)

Trait Type: Crown

Also called the **Metaconule. A fifth cusp that occasionally may be present in the distal fovea of the upper molars between the metacone and hypocone (distobuccal and distolingual cusps). This cuspule is much smaller than the other cusps of the upper molars.

Grade | Description

0) Site of cusp 5 is smooth, there being only a single distal groove present separating cusps 3 and 4.
1) Faint cuspule is present.
2) Trace cuspule is present.
3) Small cuspule present.
4) Small cusp present.
5) Medium-sized cusp present.

6) Enamel extensions

Focal Tooth: Upper First Molar (UM1)

Trait Type: Crown

Enamel extends beyond the cementum-enamel junction towards the apex of the roots – typically in the bifurcation of the two buccal roots of either the upper or lower molars.

Grade | Description

0) Cervical enamel is straight.
1) Enamel line extends ~1 mm toward root apex.
2) Enamel line extends ~2 mm toward root apex.
3) Enamel line extends 4 mm or more toward root apex.

7) Hypocone

Focal Tooth: Upper Second Molar (UM2)

Trait Type: Crown

The distolingual cusp (cusp 4) on maxillary molars. Plaque #10.

Grade | Description

0) No hypocone.
1) Faint ridging present at site.
2) Faint cuspule present.
3) Small cusp present.
4) Moderate-sized cusp present (not shown on plaque - interpolation necessary).
5) Large cusp present.
6) Very large cusp present.

8) Pegged, reduced or missing (PRM) upper third molar

Focal Tooth: Upper Third Molar (UM3)

Trait Type: Root

A reduced in size to missing third molar.

0) Third molar present and normal.
1) Third molar significantly reduced in size (½ normal size with two or more cusps).
2) Third molar peg-shaped (only a single cusp evident).
3) Third molar congenitally absent.

9) Premolar multiple lingual cusps

Focal Tooth: Lower Second Premolar (LP2)

Trait Type: Crown

Lingual cusp variation of the lower premolars.

Grade | Description

0) Lingual cusp has no free apex.
1) Single lingual cusp (Grades 0 - 1).
2) Two lingual cusps (Grades 2 - 7).
3) Three lingual cusps (Grades 8 - 9).

Following Scott and Irish (2017), simplification of Turner et al. (1991)

10) Cusp 6

Focal Tooth: Lower First Molar (LM1)

Trait Type: Crown

Cusp 6 or **tuberculum sextum* is only present if there is also a cusp 5. It is expressed on the distal portion of the lower molars – cusp 6 is distal to cusp 5 (it is more associated with the entoconid (distolingual cusp).*

Grade | Description

0) Absence of cusp 6.
1) Cusp 5 is more than twice the size of cusp 6.
2) Cusp 5 is about twice as large as cusp 6.
3) Cusps 5 and 6 are about equal in size.
4) Cusp 6 is slightly larger than cusp 5.
5) Cusp 6 is markedly larger than cusp 5.

11) Cusp 7

Focal Tooth: Lower First Molar (LM1)

Trait Type: Crown

Cusp 7 occurs in the lingual groove between cusps 2 and 4 (the 2 lingual cusps). It has no relation to cusps 5 or 6.

Grade | Description

0) No occurrence of cusp 7.
1) Faint cusp is present.
1A) Faint tipless cusp occurs displaced as a bulge on the lingual surface of cusp 2 (the mesiolingual cusp).
2) Cusp 7 is small.
3) Cusp 7 is medium sized.
4) Cusp 7 is large.

12) Protostylid

Focal Tooth: Lower First Molar (LM1)

Trait Type: Crown

An extra cusp found on the buccal surface of cusp 1. It is normally associated with the buccal groove separating cusps 1 and 3 (the two buccal cusps).

Grade | Description

0) No expression of any sort. Buccal surface is smooth.
1) A pit occurs in the buccal groove.
2) Buccal groove is curved distally.
3) A faint secondary groove extends mesially from the buccal groove. 4) Secondary groove is slightly more pronounced.
5) Secondary groove is stronger and can be easily seen.
6) Secondary groove extends across most of the buccal surface of cusp 1. This is considered aweak or small cusp.
7) A cusp with a free apex occurs.

13) Deflecting wrinkle

Focal Tooth: Lower First Molar (LM1)

Trait Type: Crown

This trait occurs on the median occlusal ridge of the mesiolingual cusp (cusp 2). Cusp 4 is the distolingual cusp. No dentin involvement in trait, difficult to Grade on teeth with wear.

0) Deflecting wrinkle is absent – essential ridge of metaconid runs a straight course from cusp tip to central occlusal fossa.
1) Cusp 2 essential ridge is straight, but shows a midpoint constriction.
2) Essential ridge deflects at halfway point toward central occlusal fossa but does not contact hypoconid (cusp 4).
3) Essential ridge shows strong deflection at midpoint and does contact hypoconid (cusp 4).

14) Groove pattern

Focal Tooth: Lower Second Molar (LM2)

Trait Type: Crown

Pattern of contact of major cusps of lower molars.

Grade | Description

1) [X pattern] Contact between cusps 2 and 3 (mesiolingual and distobuccal).
2) [Y pattern] Contact between cusps 1 and 4 (mesiobuccal and distolingual).
3) [+ pattern] Contact between cusps 1, 2, 3, and 4 at central sulcus (all four cusps touch).

15) 4-cusped molar

Focal Tooth: Lower Second Molar (LM2)

Trait Type: Crown

This is also the scoring of Cusp 5 or Hypoconulid. Lower first molars generally have five cusps (though not always), there is much more geographic variation in this trait on the lower second and third molars. Both teeth are Graded the same way. Sometimes a molar can have 6 cusps – two in the area of cusp 5. If you see this, then you definitely have a cusp 5, the second, lingual cusp, is a cusp 6. Grade the cusp 5 according to the table below, still looking at its size relative to the other cusps.

Grade | Description

0) No occurrence of cusp 5. The molar has only 4 cusps.
1) Cusp 5 is present and very small.
2) Cusp 5 is small.
3) Cusp 5 is medium-sized.
4) Cusp 5 is large.
5) Cusp 5 is very large.

Note: For rASUDAS any presence of cusp five should be marked as a five-cusped molar. Absence of cusp 5 is a four-cusped molar.

16) Upper premolar root number

Focal Tooth: Upper First Premolar (UP1)

Trait Type: Root

Root number of the anterior upper premolar premolar

1) One rooted upper first premolar.
2) Two-rooted upper first premolar – inter-radicular groove separates buccal and lingual roots for ¼ to 1/3 of total root length.
3) Three-rooted upper first premolar – inter-radicular groove separates the buccal root into two distinct roots, and another projection separating the two buccal roots from a single lingual root.

17) Upper second molar root number

Focal Tooth: Upper Second Molar (UM2)

Trait Type: Root

The number of roots of the upper second molar. Upper molars typically have three roots, but can fused together, with a root sheath.

1) One-rooted UM2 – root cones separated by grooves but there are no interradicular projections.
2) Two-rooted UM2 – one inter-radicular projection spearates one root from two fused roots.
3) Three-rooted UM2 – three inter-radicular projections separate all three roots for at least ¼ to 1/3 of total root length.

19) Tome’s root

Focal Tooth: Lower First Premolar (LP1)

Trait Type: Root

Mesiolingual groove or separation of the roots of the lower first premolar.

0) Slight or no groove separating cones on mesial surface of LP1 root.
1) Slight V-shaped groove separating cones.
2) Deeper V-shaped groove separating cones.
3) Deep developmental groove separating root cones along at least 1/3 of root.
4) Deep grooving on both mesial and distal surfaces of root.
5) Inter-radicular projection present so LP1 has two roots, a large buccal rooth and a smaller mesial/lingual root.

Note: For rASUDAS 4 or greater is considered present.

20) 3-rooted lower first molar

Focal Tooth: Lower First Molar (LM1)

Trait Type: Root

Lower molars typically have two roots. But can have an accessory distolingual root.

1) One-rooted lower first molar (no inter-radicular projection separating roots).
2) Two-rooted lower first molar (distinct mesial and distal roots).
3) Three-rooted lower first molar (distinct distolingual accessory root).

21) 1-rooted lower second molar

Focal Tooth: Lower Second Molar (LM2)

Trait Type: Root

Two roots may fuse in one of three ways: buccal aspect of both roots fuses (lingual aspect open), lingual aspect fuses (buccal aspect open), or both buccal and lingual aspects fuse.

1) One-rooted lower molar (mesial and distal roots of lower molars can be fused on the buccal or lingual aspect, or both).
2) Inter-radicular structure produces clear separation of mesial and distal roots for at least ¼ to 1/3 of total root length.