HUMAN PREMOLAR CROWN SIZES ARE VARIABLE EVEN IN THE SAME MOUTH, WITH LOW TO HIGH POSITIVE CROWN SIZE CORRELATIONS AMONG PREMOLARS AND ALL MOLARS.
Date
2023-10-02
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Introduction: The Inhibitory Cascade Model (ICM) predicts in mice that a larger permanent first molar (M1) results in a smaller second molar (M2) and even smaller third molar (M3). Building on the ICM, other work in primates reported a Premolar Molar Module (PMM) where sizes of the fourth premolar (P4) and all three molars were highly positively correlated. Counter to the ICM, our lab previously found in contemporary humans that instead of M1 size, only M2 size estimates M3 size. Our lab also identified in humans 13 different molar size ratio patterns instead of only one classic ICM pattern (M1>M2>M3). However, premolar:molar size correlation in contemporary humans is yet to be explored in-depth to help test whether the development of these two classes of teeth influence each other’s sizes. Here I explored variation in premolar size ratio pattern in contemporary humans by testing whether all three mathematically possible patterns (P3=P4, P3>P4, P3<P4) were observed in my sample. Next, I tested whether premolar crown sizes and size ratios estimated molar absolute sizes and size ratio patterns (e.g., M1>M2>M3). I also tested whether absolute sizes and size ratios of earlier initiating teeth estimate sizes and ratios of later initiating teeth.
Material and Methods: Maximum mesiodistal lengths of P3, P4, M1, M2, and M3 crowns were measured from retrospective Cone Beam Computed Tomography scans of 91 dental patients (54 female, 37 male) aged 13-23 years using Horos software.
Results: Using SPSS, a frequency analysis revealed all three premolar size ratio patterns (P3>P4: 49.83%, P3<P4: 34.13%, and P3=P4: 16.04%, n=293 oral quadrants). Also, 57% (n=49) of subjects with data collected from all quadrants showed all three premolar patterns within the same mouth. Pearson correlation test showed that crown sizes of P3 and P4 were positively correlated with a moderate to high magnitude throughout all four quadrants (p<0.001). Crown sizes of P4 and M1 showed moderate correlation in lower jaws and low correlation in upper jaws (p<0.001). Crown sizes of P3 and M1, showed low positive correlation in all four quadrants (p<0.001). Crown sizes of P4 and M2 showed moderate positive correlation in lower jaws, but low positive correlation in upper jaws. P3 and M2 crown size correlation was moderately positive in the upper left quadrant, but low positive in all other quadrants (p<0.001). For P3 and M3, and P4 and M3, correlation was negligible except for the lower right quadrant where the correlation of P3 and M3 was low positive (p<0.001). A linear mixed model analysis (95% confidence level, alpha = 0.05) showed that P3 crown size was significantly and positively predicted by the crown MDLs of P4 and M2. Also, P4 crown MDL was significantly and positively predicted by the crown MDLs of P3 and M2.
Conclusion: Variation in premolar size ratio patterns was similar to variability previously reported in molars. Study outcomes supported the PMM findings and reported significant low to high positive crown size correlations among premolars and all molars.
Description
Keywords
Premolar Molar Module (PMM), premolar:molar size correlation, CBCT, Contemporary Human
Citation
Degree
Master of Science (M.Sc.)
Department
Anatomy, Physiology, and Pharmacology
Program
Anatomy, Physiology, and Pharmacology