How doestooh relateto vertical mandibular growth displacement

ORIGINAL ARTICLE

How does tooth eruption relate to vertical mandibular growth displacement?
Sean Shih-Yao Liua and Peter H. Buschangb Indianapolis, Ind, and Dallas, Tex

Introduction: Our objectives were to investigate the eruptive patterns of the mandibular teeth and assess their associations with mandibular growth displacements. Methods: Cephalograms for a mixed-longitudinal sample of 124French-Canadian girls were evaluated between 10 and 15 years of age. Vertical mandibular displacement and mandibular eruption were evaluated by using cranial and mandibular superimpositions, respectively. Multilevel modeling procedures were used to estimate each subject’s growth change over time. Stepwise multiple regressions were used to determine the amount and relative magnitudes of variationsin mandibular eruption explained by mandibular growth displacement, controlling for vertical maxillary tooth movements. Results: Cubic polynomial models explained between 91% and 98% of the variations in eruption and vertical growth displacement. All curves showed acceleration of eruption until approximately 12 years of age, after which eruption decelerated. The eruption of the mandibular teethdemonstrated greater relative variability than did vertical mandibular growth displacements. Independent of the overall movements of the maxillary molars, inferior mandibular growth displacement explained approximately 54% of the variation in mandibular molar eruption between 10.5 and 14.5 years of age. Conclusions: Inferior mandibular growth displacement and dental eruption followed similarpatterns of change during adolescence. Based on their associations and the differences in variability identified, mandibular eruption appears to compensate for or adapt to growth displacements. (Am J Orthod Dentofacial Orthop 2011;139:745-51)

he vertical positions of the teeth are thought to be maintained in a state of equilibrium between the forces of eruption and those that oppose it. Because themandible undergoes greater vertical changes than the maxilla, equilibrium is constantly disrupted during growth.1 Superimpositions of the patients presented by Bj€rk and Skieller1 suggest that those undero going the greatest eruption also have the greatest vertical growth. Subjects with short and long faces show smaller and larger dentoalveolar heights, respectively; this further substantiates arelationship between growth and eruption.2,3 Clinically, compensatory eruptions of the molars and incisors have been associated with inferior mandibular displacement
a Assistant professor, Department of Orthodontics and Oral Facial Genetics, School of Dentistry, Indiana University, Indianapolis. b Professor, Department of Orthodontics, Baylor College of Dentistry, Texas A&M University Health ScienceCenter, Dallas. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Partially supported by Medical Research Council grant MA-8917 and by Fonds des Rescherche en Sante du Quebec grant 850043. Reprint requests to: Sean Shih-Yao Liu, Department of Orthodontics and Oral Facial Genetics, Indiana University, School of Dentistry,1121 W Michigan St, Indianapolis, IN 46202; e-mail, SSLiu@iupui.edu. Submitted, April 2009; revised and accepted, March 2010. 0889-5406/$36.00 Copyright Ó 2011 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2010.03.029

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produced by functional appliances.4 Supraeruption has also been produced experimentally with bite-opening appliances, suggesting a direct relationshipbetween mandibular displacement and eruption.5,6 Although there is indirect and experimental evidence supporting the association, there are currently no large-scale longitudinal studies available that were designed specifically to evaluate the association of mandibular tooth eruption and vertical mandibular displacement. To fully understand this relationship, the potentially confounding effects of...