The populational frequencies of dental discrete traits can be compared to determine relatedness. Twin studies and animal breeding research have proven high heredity for non-metric traits though the precise genetic mechanism is not well understood. The evidence for relatedness must be corroborated by convergent evidence from metric traits, analysis of skeletal traits, other genetic and/or serological evidence, archaeological, geographical and historical evidence as well as linguistic phylogenetics. This study will supplement research on the metric trait analysis and act as a foil to the historical record. The traits used in this study are outlined in Hillson (1996) and they were scored based on a system developed at ASU be Christie Turner, et al. (1991). The Turner system includes standardized reference plaques, terminology, and scoring charts to minimise the effects of observer error. The following is a written summary of the dental discrete traits and I am developing a link to photographs of some of the reference plaques. The plaques reflect the fact that the traits are really quasi-continuous and are divided into grades of expression.
Shovelling
Shovelling is most commonly found in maxillary incisors but can also be present in the mandibular incisors and sometimes in canine teeth. The ASU system has defined six grades of shovelling in the central incisors, seven in the lateral incisors, and six grades of double shovelling. The term "shovel-shaped" was coined by Hrdlicka (1920) to describe anterior teeth with a deep fossa on the lingual surface created by large marginal ridges, a normal morphological feature which has been exagerated in cases of shovelling. Double shovelling refers to a ridge on the labial surface of the tooth which may or may not occur in addition to the lingual ridge. Populations from Asia and Native America generally have the highest frequencies of shovelling with occurances in up to 90 % of the population.
Carabelli's Cusp
The maxillary first molar (and occasionally the second, rarely the third) can have an accessory cusp on the mesiolingual surface. This feature has grades from a small pit or ridge to a full sized cusp. The trait can effect up to 85 % of some European populations.
Anterior Cingulum
A cingulum is a projection or ridge of enamel which in it's most extreme expression, can form an accessory cusp. The maxillary incisors and canines are scored for the presence and severity of this trait on the lingual surface. Grooves on the root of the maxillary incisors are also scored.
Maxillary Molar Cusp Variation
These traits involve reduction or absence of the generally large distobuccal cusp on the third maxillary molar. The scoring system is based on whether all four cusps are present and to what size thay have developed.
Maxillary Molar Metaconule, Metacone, and Hypocone
There is a five stage scoring system for the development of the metaconule cusp (or Max Cusp 5) on the distal surface of the maxillary molars. The cusp grades from absent to very pronounced and often includes two vertical ridges. There are also five stage scoring systems for the presence and size of the metacone and hypocone cusps. Photographs of the reference plaques will be especially helpful in describing these cusp variants.
Maxillary Molar Parastyle
This feature is found on the mesiobuccal surface of the maxillary molars and again ranges from a small pit to a full sized cusp. The parastyle is most common on the third molar and least common on the first.
Mandibular Premolar Cusps
There is a lot of variability in the number of lingual cusps on the mandibular premolars. Most commonly there is one cusp but two or three can also be present in different size grades. This trait is subject to error due to occlusal wear, however most researchers leave out of the sample teeth that are very worn.
Mandibular Molar Cusps
The mandibular first molar generally has five cusps, this trait describes the presence of only three or four cusps. The four cusp variant occurs with the absence of the distobuccal cusp, the three cusp variant is missing the distolingual cusp as well. If the five common cusps are present other variations exist in the presence of a sixth or seventh cusp at the distobuccal and distolingual surfaces. These latter two traits are rare in humans but can be more common among some of our hominid ancestors.
Mandibular Molar Protostylid
On the buccal surface of the lower molars there can be a protostylid ranging from a small fissure to a prominant cusp. This trait can be present on any of the lower molars, with higher frequencies in the first and third, and on the deciduous second molar.
Occlusal Patterns
Fissures in the occlusal, or biting surface of the first mandibular molars are generally in a "Y-5" pattern, meaning that there are usually five cusps and a Y-shaped groove separating them. Variations in the shape of this groove include the “+” pattern and the “x” pattern. The second mandibular molars typically have four cusps and a “+” pattern of grooves. The ASU system has divided the variants into five grades and again teeth with occlusal wear should be eliminated from the sample.
Deflecting Wrinkle and/or Trigonid Crest
The term ‘deflecting wrinkle’ describes the occurance in first molars of an "L"shaped wrinkle in the distal side of the mesiolingual cusp. This trait can effect up to 80 % of a given population. The trigonid crest is a high ridge which can develop between the mesiobuccal and the mesiolingual cusps.
Enamel Pearls
The maxillary posterior teeth can have pearls of enamel at the cervical margin or on the root surface. These size and number of these enamel pearls are recorded.
Molar Root Number Variations
Maxillary premolars can have one to three roots with the first premolar being the most variable. The degree of bifuraction, or separation, between the roots is also scored.
Uto-Aztecan Maxillary Premolar
The anterior maxillary premolar may have an especially prominant buccal cusp and an associated furrow on this cusp. The expression of this trait is generally restricted to Native American groups from the Arizona area (Uto-Aztecan refers to the linguistic category for the area).
Distal Accessory Ridge
This trait is a measure of the size of the mesial marginal ridge on the maxillary canines. The mesial ridge is generally larger than the lateral ridge but in certain populations, such as the San, it is generally particularly large with an accessory ridge on the lingual surface of the crown.
Taurodontism This trait refers to teeth which have short roots and tall crowns enclosing high pulp cavities. This trait is generally found in molar teeth and is best seen in x-ray images. The trait is uncommon in humans and is usually seen in Neanderthals.