The mandibular molar pit-tubercle (MMPT) dental nonmetric trait: Comprehensive analysis of a large sample

Abstract

Dental nonmetric traits are quasicontinous variables, mostly of genetic origin. Thus, sets of such traits allow biological distance estimation between samples. Mandibular molar pit-tubercle (MMPT) is a buccal trait defined by Weets (2009) in Irish samples. This study aims to analyze (a) trait frequencies, (b) grade definitions, (c) intraobserver error, (d) sexual dimorphism, (e) asymmetry, and (f) trait associations for MMPT in a Portuguese sample. The first (LM1), second (LM2) and third (LM3) lower molars of 600 identified individuals from the Coimbra collections were scored for MMPT in three scoring sessions. Intraobserver error, bilateral asymmetry and trait correlations were tested using Kendall's τ-b, while sexual dimorphism was verified using Pearson's χ. Frequencies (LM1: 2.1%; LM2: 3.5%; LM3: 30.3%) were similar to previous reports. However, a new free apex cusp form (grade 3+) was detected. Considering three scoring sessions, intraobserver precision was above 85%, and correlation coefficients between observations were positive and moderate to very strong (0.291<τ-b<0.835). Intrasample variation was low, since only LM3 showed sexual dimorphism (female: 30.2%; males: 16.2%; χ=15.512; p<0.001; df=1; n=556) and large asymmetry (27.1%). There were no strong (τ-b>0.3) intertrait associations involving MMPT. MMPT shows low trait presence, sexual dimorphism and asymmetry in stable teeth (LM1 and LM2). Intraobserver precision is high, so scoring should be reliable, although a plaque and better threshold grade definition is needed. After further research on non-European samples, MMPT can be useful in biodistance research.

Expression of two near absent dental traits, mesial cuspule and paraconid, on one Archaic period modern human from the Ohio Valley

“…An example of what here is called the lingual cuspule may also be present on the lower left third molar of a female individual but is recorded there as an expression of the MMTP (Marado, 2014: 236). The MMTP is expressed as an ident, pit, or fully developed cusp high on the buccal surface of the protocone (Weets, 2009;Marado and Silva, 2016) whereas the lingual cuspule has been identified as a fully developed cusp found on the lingual surface of the crown. The examples presented here suggest this trait's expression is consistently found on first and third mandibular molars from both the left and right sides.…”

“…Tooth traits for all individuals were recorded using the Arizona State University Dental Anthropology System (ASUDAS;Turner et al 1991). Reference manuals, recent publications (Scott and Turner, 1997;Weets, 2009;Marado and Silva, 2016;Scott et al, 2016;Scott and Irish, 2017), and consultation with Joel Irish were used to identify these traits as neither the lingual cuspule nor paraconid are included in the ASUDAS. Based on information from available sources, the descriptions presented below were used to identify the two cusps.…”

“…Lack of reporting on the lingual cuspule may be because the trait is being conflated with other paramolar structures, such as the MMTP. Although the MMTP is described as occurring on the buccal surface of mandibular molars (Weets, 2009;Marado and Silva, 2016), it is possible that similar expressions on the lingual surface are being lumped together during observation and recording since no formal scoring is in place for lingual expressions.…”

Dental and oral nonmetric traits in a Coimbra reference sample: testing intrasample chronological and spatial variation

“…In actuality, a total of 52 tooth-trait combinations were scored using the ASUDAS, since many of these traits were scored in more than one tooth each. Correlations between all pairs of traits were tested (results not shown; see Marado and Silva 2016 for correlations between the mandibular molar pittubercle (MMPT) and protostylid), and only UP3 and UP4 odontomes were correlated. Since this is a very rare trait and pooled results for all premolars are commonly reported (e.g., Scott and Turner 1997;Irish 1998), this correlation was disregarded.…”

“…Some discrete traits were scored using different methods, because they were not included in ASUDAS: (1) midline diastema, as per Irish (1998); (2) upper premolar accessory crests and mesial marginal accessory tubercles, scored according to Scott and Turner (1997) 1 ; (3) the MMPT, scored according to Marado and Silva (2016) (using methodology adapted from Weets 2004Weets , 2009; and (4) Hauser and De Stefano's (1989) method, used to score the foramina mentales and mylohyoid bridges.…”