Date of Award


Document Type


Degree Name

Master of Dental Science (MDS)



Research Advisor

Edward F. Harris, PhD


William Parris, DDS, MS Quinton Robinson, DDS, MS Richard Williams, DDS, MS


Demirjian system, dental age, root formation, secular trend, tooth eruption, tooth mineralization


Introduction: Improved environments in the U.S. have resulted in taller, larger, and heavier children and adults compared to past generations. Studies of other skeletal-dental dimensions have shown increases across generations, and our perception is that teeth now are forming faster. The purpose of this study is to test for a secular trend towards faster tempos of tooth mineralization in a sample of U.S. white adolescents over the past quarter century (1980-85 to 2005-10).

Materials: Two cohorts of 200 children each were identified, each with an age range of 10-to- 15 years, one group from 1980-85 and the more recent group from 2005-10. Children all were phenotypically normal American whites from the same dental clinic. Stages of tooth mineralization were scored for the lower 8 permanent tooth types using the 8-grade Demirjian system (Demirjian A, Goldstein H, Tanner JM. A new system of dental age assessment. Hum Biol 1973;45:211-27). Proportional hazards analysis was used to test for cohort differences while controlling for sexual dimorphism in tooth formation tempos.

Results: In the age interval studied, 10 tooth-stage combinations could be analyzed statistically. Median ages of the stages were characteristically younger in the recent (2005-10) cohort, and 5 of these 10 comparisons achieved statistical significance (P < 0.05). The difference between the cohorts is larger in girls than in boys. Faster tempos of development are on the order of ½ year.

Conclusion: Faster growth tempos mean that age-sensitive procedures—such a serial extraction or harnessing adolescent growth—occur at younger ages and that published standards for tooth formation and emergence probably now are biased. Faster maturation also suggests that children of the same chronological age are biologically more mature than in the past. It remains to be seen how widespread these secular quickenings are, both geographically and across segments of the population.