The ratio of the lengths for the root and crown of a permanent tooth reflects on its development. A disturbance in tooth development is often manifested by a decrease in the ratio.


Method: The landmarks for each tooth type is shown in Figure 1, page 492, Hollta et al (2004).


root-crown ratio =

= (vertical length of root in mm) / (vertical length of crown in mm)



• Another ratio to consider would be the ratio of root to total tooth length (root + crown).

• The longest root is used when measuring a multi-rooted tooth.



• Normal teeth show ratios that range from 1.78 to 2.46 depending on the specific tooth (Table 2, page 494, Hollta et al, 2004).


R/C Ratio

Disturbance in Root Development

> 1.6

no disturbance

1.2 - 1.6


0.9 - 1.1

moderate to severe

< 0.9

very severe disturbance or arrested root development

from page 123 Holtta et al (2002)


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