The study examined the relationship between the presence of mandibular tori and gonial angle in 175 individuals. It found that individuals with mandibular tori had a statistically significant but small (3 degrees) smaller average gonial angle. The variance in gonial angle between those with and without tori was not quite statistically significant. Gonial angle did not significantly correlate with torus size but did correlate with ramus height. The results provide limited evidence that mandibular tori may be related to a smaller gonial angle.

1. Gonial Angle and Mandibular Torus
Adam Martinetti and Karina Coscuna
Humboldt Center for Evolutionary Anthropology, Department of Anthropology, Humboldt State University, Arcata, California
American Association of Physical Anthropologists 82nd Annual Meeting, Tennessee, April 2013
Introduction Results
• The mandibular torus is an exostosis manifesting (usually bilaterally)
on the lingual side of the mandible (Sellevold, 1980). An extreme • Of the 175 individuals examined, 33 (18.64%) had perceptible mandibular tori. 24 crania
example is pictured, left (Figure A). showed a palatal torus but did not show mandibular tori, and these individuals were not used
in the following statistics.
• Oral exostoses (including mandibular torus and palatal torus) are
benign multifactorial threshold traits (Eggen, 1989) and of debated • 120 individuals with no perceptible palatine or mandibular torus were then compared to group
etiology (Eggen and Natvig, 1986). 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
• The presence of mandibular torus is correlated with greater occlusal groups was not quite statistically significant (p = 0.0832).
force (Yoshinaka et al., 2012).
• Gonial angle was not significantly correlated to the maximal width of the torus (r2 = 0.09071, p
• A smaller gonial angle increases mechanical advantage, allowing for = 0.0885). Gonial angle and ramus height were highly correlated (p < 0.0001).
greater occlusal force to be applied more efficiently (Throckmorton et Distribution of Gonial Angle in Sample
al., 1980). 150
Figure A
140
Gonial Angle
• Another phenotypic indicator of the gene responsible for mandibular 130
torus development, if strongly correlated, could increase the utility of 120
the trait in osteological investigations. 110
Question: Do individuals with mandibular tori have a smaller gonial angle on average? 100
Without Exostoses With Mandibular Torus
Figure C Figure D
Materials and Methods Torus by Sex Age Distribution Torus Size
With MT Without Torus Class Frequency
• We analyzed 175 individuals from the Maxwell Museum of Anthropology’s Documented Skeletal Collection Sex With MT Total
25-39 5 8 <2mm 5
from modern forensic cases. Measurements were taken from all individuals within the collection possessing Male 25 (23%) 109
40-59 6 35 2-4mm 21
intact mandibles and maxillae. We excluded individuals under twenty-five years of age who may still have been Female 8 (12%) 66
undergoing craniofacial development. Information on age and sex was provided by the museum after all other 60-79 13 72 >4mm 7
Total 33 (19%) 175
data had been gathered. 80-101 4 36 Total 33
• Mandibular torus measurements were taken using digital calipers and classified using the method first Discussion
established by Eggen (1989), based on the maximal lingual width.
• The lack of a standard method for measuring the mandibular torus can obfuscate results of torus size
• We measured gonial angle using a mandibulometer (pictured right). (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
• We noted palatal tori, buccal exostoses and maxillary exostoses visually. results.
• Dental attrition was scored solely on the molars using the quadrant-system established by Figure B • Although the mean gonial angle of the sample population without mandibular tori was larger to a
Scott (1979). 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
• We performed an unpaired t-test using GraphPad Prism software to test the means of the two populations, needed to say whether mandibular torus is related to a smaller gonial angle.
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 • Edentulism has been observed to reduce the rate mandibular torus (Eggen and Natvig 1986) and
were created using the GraphPad Prism software as well as R. 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
Acknowledgments
We 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 the elderly in our sample.
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. • Dental attrition and dental crowding were omitted from our analyses due to the high degree of
References edentulism in our sample.
Al 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).
• The number of edentulous samples in this study with mandibular torus (12.5%) is similar to the rate
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.
shown in previous studies (e.g. Al Quran et al., 2003).