• The mandibular torus is an exostosis manifesting (usually bilaterally) on the lingual side of the mandible (Sellevold, 1980). An extreme example is pictured, left (Figure A).

• Oral exostoses (including mandibular torus and palatal torus) are benign multifactorial threshold traits (Eggen, 1989) and of debated etiology (Eggen and Natvig, 1986).

• The presence of mandibular torus is correlated with greater occlusal force (Yoshinaka et al., 2012).

• A smaller gonial angle increases mechanical advantage, allowing for greater occlusal force to be applied more efficiently (Throckmorton et al., 1980).

• Another phenotypic indicator of the gene responsible for mandibular torus development, if strongly correlated, could increase the utility of the trait in osteological investigations.

Materials and Methods

• We analyzed 175 individuals from the Maxwell Museum of Anthropology’s Documented Skeletal Collection from modern forensic cases. Measurements were taken from all individuals within the collection possessing intact mandibles and maxillae. We excluded individuals under twenty-five years of age who may still have been undergoing craniofacial development. Information on age and sex was provided by the museum after all other data had been gathered.

• Mandibular torus measurements were taken using digital calipers and classified using the method first established by Eggen (1989), based on the maximal lingual width.

• We measured gonial angle using a mandibulometer (pictured right).

• We noted palatal tori, buccal exostoses and maxillary exostoses visually.

• Dental attrition was scored solely on the molars using the quadrant-system established by Scott (1979).

• We performed an unpaired t-test using GraphPad Prism software to test the means of the two populations, followed by an F-test to compare variances. Significance was set at p < 0.05. We then used a Pearson’s R test to test for correlation between gonial angle and ramus height, and gonial angle and maximal torus width. Graphs were created using the GraphPad Prism software as well as R.

Question: Do individuals with mandibular tori have a smaller gonial angle on average?

AcknowledgmentsWe wish to thank Ariel Gruenthal for her help with this project as well as the faculty at the Humboldt Center for Evolutionary Anthropology for their invaluable input. This project would not have been possible without support from the Department of Anthropology, the College of Arts, Humanities, and Social Sciences, and the Office of Research at Humboldt State University. Skeletal samples were part of the Documented Skeletal Collection from the Maxwell Museum of Anthropology. We also wish to thank their faculty, in particular, Ms. Carmen Mosley and Dr. Heather Edgar for their help with this study. Sincere thanks to Yoon Kim for his assistance and Humboldt State University for providing travel funds.

ReferencesAl Quran F a M, and Al-Dwairi ZN. 2006. Torus palatinus and torus mandibularis in edentulous patients. J Contemp Dent Pract 7:112–9. Eggen, S. Torus mandibularis: an estimation of the degree of genetic determination. Acta Odontol Scand 47: 409–15 (1989).Eggen S. & Natvig B. Relationship between torus mandibularis and number of present teeth. Scand J Dent 94, 233-240 (1986). Sellevold, B. 1980. Mandibular torus morphology. Am J Phys Anthropol 53:569–72. Scott GR, Halffman CM, and Pedersen PO. Dental conditions of Medieval Norsemen in the North Atlantic. Acta Archaeologica 62: 183–207 (1991). Throckmorton G, Finn R, and Bell W. 1980. Biomechanics of differences in lower facial height. Am J Orthod 77:410–420.Yoshinaka M, Ikebe K, Furuya-Yoshinaka M, and Maeda Y. 2012. Prevalence of torus mandibularis among a group of elderly Japanese and its relationship with occlusal force. Gerodontology:1–6.

Introduction

Gonial Angle and Mandibular TorusAdam Martinetti and Karina Coscuna

Humboldt Center for Evolutionary Anthropology, Department of Anthropology, Humboldt State University, Arcata, CaliforniaAmerican Association of Physical Anthropologists 82nd Annual Meeting, Tennessee, April 2013

Results

Discussion

• The lack of a standard method for measuring the mandibular torus can obfuscate results of torus size (Eggen 1989; Hassett 2006). In this study, considering all individuals with tori as part of the same population or separating them by size, as suggested by Eggen (1989), did not significantly alter our results.

• Although the mean gonial angle of the sample population without mandibular tori was larger to a statistically significant degree than the sample with mandibular tori, the difference in means was very small, and the variance of the two means was not considered significantly different. More data is needed to say whether mandibular torus is related to a smaller gonial angle.

• Edentulism has been observed to reduce the rate mandibular torus (Eggen and Natvig 1986) and affect the gonial angle (Huumonen et al., 2010). The high degree (52%) of individuals we recorded experiencing some degree of antemortem edentulism is skewed due to the over-representation of the elderly in our sample.

•Dental attrition and dental crowding were omitted from our analyses due to the high degree of edentulism in our sample.

• The number of edentulous samples in this study with mandibular torus (12.5%) is similar to the rate shown in previous studies (e.g. Al Quran et al., 2003).

Torus Class Frequency

<2mm 5

2-4mm 21

>4mm 7

Total 33

Sex With MT Total

Male 25 (23%) 109

Female 8 (12%) 66

Total 33 (19%) 175

Torus SizeTorus by Sex

Distribution of Gonial Angle in Sample

Without Exostoses With Mandibular Torus100

110

120

130

140

150

Go

nia

l A

ng

le

• Of the 175 individuals examined, 33 (18.64%) had perceptible mandibular tori. 24 crania showed a palatal torus but did not show mandibular tori, and these individuals were not used in the following statistics.

• 120 individuals with no perceptible palatine or mandibular torus were then compared to group with mandibular tori. The difference between the means of the two groups, while only three degrees (3.195° ± 1.509°), was statistically significant (p = 0.0359). Variance between the two groups was not quite statistically significant (p = 0.0832).

• Gonial angle was not significantly correlated to the maximal width of the torus (r2 = 0.09071, p = 0.0885). Gonial angle and ramus height were highly correlated (p < 0.0001).

Figure A

Figure B

Figure C Figure D

With MT Without

25-39 5 8

40-59 6 35

60-79 13 72

80-101 4 36

Age Distribution