267

Crown formation times of the permanent dentition and root extension rate in humans

H.M. Liversidge

Crown formation times of permanent teeth are important growth markers in the study of growth and develop­ment of humans as well as non human primates. However, the defined stage of "crown completion" is particularly difficult to see from radiographs and published standards vary considerably. New data on crown formation times from direct observation of dry dissected specimens of the Spitalfields and Tomes' Collections of known age individuals are presented, including observations on permanent incisors, canines and first molars. One important finding is that few permanent incisors and canine crowns are complete before 5 years of age in these populations contrary to findings in radiographic studies. Other data from this sample on the rate of root formation of deciduous teeth and the permanent first molar suggest major differences in rates of root growth between different tooth types. The range of root extension was 20Jlm (11) to 9Jlm (m2) per day with initial root growth rate of MI at 5Jlm per day.

Key words: Crown completion, rate of formation, developing tooth length.

Introduction

Tooth fonnation is widely used as a growth marker, allowing comparisons between indi­viduals, populations, primates and fossil hominids. Archaeology and forensic science also rely on standards of dental fonnation to assess developmental age. The mineralization of a developing tooth can be conveniently divided into stages of crown and root formation. The stages most easily identified are initial mineralization, the end of crown growth and the end of root growth with closure of the apex. The choice and definition of other stages of fonnation is particularly impor­tant as many rely on estimated fractions of the crown and root length. In the absence of longitudi­nal radiographs, these estimates are entirely subjective. The radiographic assessment of the stage "crown complete" (Cc) of anterior pennanent teeth is difficult due to the contour of the enamel margin which extends several millimeters on the buccal and lingual surfaces. Initial root forma­tion occurs on the approximal surfaces of the tooth before the last enamel is fonned on the buccal and lingual surfaces. The enamel cementum margin in these last areas of enamel fonnation is not clearly visible from radiographs and thus true enamel completion of these teeth may be some time later than the age suggested from radiographic studies. Histological evidence suggests that the rate

Aspects ofdental biology: palaeontology, anthropology and evolution. J. Moggi-Cecchi, ed. Florence: International Institute for the Study of Man. 1995.

268 H.M. LIVERSIDGE

of growth of enamel and dentine is slow around this stage of formation (Beynon and Reid, 1987·. increasing the margin of error when assessment of crown completion is inaccurate.

The daily growth rate of enamel and dentine is thought to be slow in permanent teet!. (Shellis, 1984; Dean and Beynon, 1991), in contrast to evidence of rapid daily rate of tooth lengt:-, in deciduous teeth (Deutsch, Tam and Stack, 1985). The two aims of this study were to investi, gate the age of true crown completion of permanent anterior teeth and to compare the rate c~

growth in tooth length of deciduous and early forming permanent teeth.

Materials

The material studied is made up largely of an 18th Century coffin buried population reeej.~:

excavated from the crypt of Christ Church, Spitalfields, London (Adams and Reeve, 1986: C:' 1989). Names and exact ages of 63 individuals from 0 to 5.4 years were available from the eo~:~:

plates or parish records. Preservation varied considerably; for some individuals only a few t~:·_·

remain, while others consist of well preserved complete skeletons. Data on crown comp:~~:: : from 7 partly dissected jaws, aged between 4.5 and 6.4 years, were collected from the Ie:.:: Collection housed at the Odontological Museum at the Royal College of Surgeons, London ~.. : age and sex distribution of the material is shown in Figure 1.

15 ,,---------------------,

N • 63 + 7

10

N

I­

,.• - -I

I o _

_

unknown male

female

sex

I K@

5

o 2 3 4 5 6

AGE IN YEARS

Figure 1. The age and sex distribution of the material studied.

Methods

Initial mineralization and crown completion was assessed by direct observation c' . developing teeth, dissected from the maxillary and mandibular bone. The stage "ere:­pleted" (Cc) was defmed as all the enamel completed i.e. the enamel cementum junction .". entirety on the root surface.

Tooth length of developing teeth was measured directly with sliding callipers ane ";:

o

I 1

I 1

2 I

I 2

C

M1

CROWN FORMAnON AND ROOT EXTENSION RATES 269

.:. : 987), regressed against tooth length for prediction (Liversidge, Dean and Molleson, 1993). The mean rate of increase in tooth length is indicated by the slope of the regression line.

::~.: teeth ::. ~ength

::::esti­ Results = ~2.:e of

The age of the earliest observed mineralization and crown completion of some permanent teeth is depicted in Figure 2.

CROWN FORMATION ~::: emly ~~. Cox to : :ffm :-;:. :eeth :;: .e::on . : ::les

0 2 3 4 5 6

AGE Figure 2. The age of the earliest observed mineralization and crown completion of some permanent teeth. Closed bar is the age range of Ci or Cc.

Initial mineralization of the incisal edge of the central incisors, the mandibular lateral incisor and the cusp tip of the canine were fIrst observed at 0.4 years of age. Initial mineralization of the F was fIrst noted at 1.1 years. Cusp tips of Ml were seen from birth to 0.4 years. Some of these early stages were not visible from good quality radiographs.

True crown completion of II and 12 was observed between the ages of 4.5 to 6 years. The crown of the II was complete in one individual nearly 6 years old. No individuals presented with the canine or j2 crowns complete. Crown completion of Ml ranged from 2.9 to 3.6 years. In several anterior teeth the assessment of this stage was difficult without magnifIcation due to a band of immature enamel on the buccal and lingual surfaces. Observation of these teeth revealed that this was only present where the enamel cementum junction was not yet formed.

Tooth length of Ml for age is illustrated in Figure 3. Each dot represents tooth length before crown completion, each cross indicates root growth; each is plotted against the age of the indi­vidual. The line represents the mean predicted age for tooth length.

270 H.M. L1VERSIDGE

M1 TOOTH LENGTH V8. AGE mm

15 r------------------------~

+10 .,-::P: + +

• • CROW"5 • ROOT.. , .

• ---­•

o 1-1,-----'---------'-----'-------'-------'-------'

o 234 5 6

AGE IN YEARS

Figure 3. Tooth length of Ml for age. Dots represent tooth length before crown completion, each cross inc:;; : root growth. The regression line indicates the mean predicted age for tooth length.

A comparison of regression curves of tooth length for age of deciduous and permanent ::-:-.­is depicted in Figure 4. Deciduous teeth all grow faster than permanent crowns. The mean ~=.::

daily growth in length ranges from 19 !J.m for i1 to 5 !J.m for Ml.

REGRESSION LINES

20 ,.--------------------,

i1 m1

m2 15

M1H E I G H T

o 1'-­ -'---­ ---1­ -'­ -----' -'-----'

o 02 3 4 5

AGE

Figure 4. A comparison of regression curves of tooth length for age of deciduous and permanent t:-:-;­

~ '.: ~l\'ERSIDGE CROWN FORMAnON AND ROOT EXTENSION RATES 271

Discussion

Results from this study, despite the very small sample size, reveal that the age of true crown completion of permanent anterior tee.th is considerably later than age of Cc from most radio­graphic studies. The mean age of radiographic Cc of the permanent incisors and canine in the literature shows considerable variation (Tab. I).

Table 1. Mean age of radiographic Cc [girlslboys] from the literature.

~

Radiographic study II II 12 12 C Ml • CROWN • ROOT Gleiser and Hunt 1955 3.3/3.5

Gam et at. 1958 3.7/4.0

Moorrees et at. 1963 4.9/5.3 5.6/5.8 4.0/4.0 2.2/2.2

Haavikko 1970 3.3/3.3 4.4/4.6 /3.3 4.1/4.3 3.5/3.5

. Fanning and Brown 1971 4.4/4.5 2.4/2.4

Anderson et at. 1976 3.6/3.7 3.6/3.6 3.8/4.0 3.7/4.0 4.114.8 /3.7

- ­- . : ~:~. :ro,s indicates Nielsen and Ravn 1976 4.8/4.2 4.5/4.7 4.2/4.4

Guerrero et al. 1980 5.5 5.4

~:: :::~:manent teeth Trodden (Inuit) 1982 4.2 3.5 5.0 4.4 4.8 3.3

, -=-.~e mean rate of Trodden(Indian) 1982 5.5 3.3 5.4 4.4 5.4 3.2

Diato et at. 1990 3.8/3.9 3.6/3.7 4.4/4.8 3.9/3.9 4.2/4.7 2.5/2.6

However, comparisons are complicated where studies differ in definition of stage, methodol­ogy and age structure (reviewed by Smith, 1991). Although many radiographic studies lack infants and young children, a more important reason for the wide variation for this stage is the difficulty defining this stage from radiographs. The consecutive formation stages of dental radio­graphic studies illustrate Cc schematically showing the beginning of root formation on the mesial and distal surfaces. Presumably this represents completion of enamel approximally with the presence of the enamel cementum junction in this area. The stage Cc is followed by initial root formation (Ri), representing some root growth after completion of the entire enamel cementum junction. It is clear that the curvature of the enamel cementum junction results in earlier age of radiographic Cc than that of direct observation. The curvature of the enamel cementum junction complicates the assessment of this stage from a two dimensional radiograph (Beynon, Dean and Reid, 1991). This curvature is more pronounced in permanent incisors and canines, between 2 to 4 mm on the buccal and lingual aspects (Black, 1902).

In this study, only one individual of 5.8 years old was seen to have Cc of II. This is later than both data from Kronfeld (1935) and the mean age from radiographic studies. Two radiographic studies have a range (±2 standard deviations from the mean age) that exceeds this age: Moorrees et al. (1963) and Trodden (1982). Crown completion of II and 1

2 from this study occurred in two

individuals some time before 4.5 and 6 years respectively. This is outside the dispersion (10-90 percentile) given by Haavikko (1970) but just within the range from other radiographic studies (Anderson, Thompson and Popovich, 1976; Trodden, 1982; Diato, Kawahara, Tanaka, Nishihara and Hieda, 1990). Previous data based on direct observation are from the classic dissection and radiographic study of Logan and Kronfeld (1933), updated by Kronfeld (1935). However, scru­

G:'-'"

E.:.: le:.,_­

11 TO

2C

:.. -

...

272 H.M. L1VERSIDGE

tiny of the age structure of their original sample reveals that permanent crown formation ages are probably based on very few individuals (probably four individuals over the age of two: 2.5,3,4.5, 8 years). The age range for Cc of permanent incisors from Kronfeld (1935) is 4 to 5 years, while the age of canine Cc is 6 to 7 years. The absence of true crown completion from this study of either F and canine before six years of age contrasts to the mean age of radiographic Cc and highlights the difficulty assessing this stage radiographically. Even if allowance is made for individual variation, the age for P is later than the outer range from studies by both Haavikko (1970) and Anderson et aI. (1976) but within the dispersion of other studies where this is given. Trodden (1982, Inuits and North American Indians) and Diato et aI. (1990 Japanese boys) also give a later age range (+2 SD) than 6 years for Cc of the canine.

The age of crown completion of Ml from this study is similar to the mean age found in the numerous radiographic studies. This lends support to the assumption that individual dental growth in these Collections is not abnormal and that the numerous factors resulting in high infant mortality, including chronic childhood disease, do not adversely affect the rate or stage of dental formation. A detailed analysis of the dental formation of the SpitalfIelds children demonstrated few differences with contemporary standards (Liversidge, 1993).

The mean rate of growth in length of deciduous teeth during the first year is between 10/lm (c) and 20/lm (it) per day (Deutsch et aI., 1985). Other data from the same sample for deciduous molars is tabulated together with similar results from this study of the SpitalfIelds children (Tab. II).

Table II. Mean rate of deciduous root growth (in ~m per day). Deutsch= data from Deutsch. Tam and Stack (1985), Spitalfields= results from this study, Stack= unpublished data from MY Stack.

Deutsch Spitalfields

it 16 to 20 19 .. i2 17 to 18 18 c 10 to 12 13

Stack Spitalfields

ml 16 12 m2 13 9

The mean rate of tooth extension of some permanent teeth can be calculated from the few quantitative radiographic studies (Ledley, Huang and Pence, 1971; Israel and Lewis, 1971; Carels, Kuijpers-Jagtman, van der Linden and van't Hof, 1991). Two early longitudinal studies by Carlson (1944) and Gleiser and Hunt (1955) provide individual rate of growth in tooth length from an early age but for a few teeth only. These data together with an histological study (Dean and Beynon, 1991) are found in Table III.

The extra time taken for buccal and lingual enamel to complete following termination of secretion at the mesial and distal margins may be between 0.8 to 2.3 years calculated from the number of perikymata in this region (Beynon,. 1992). One unaged individual (specimen 2179) from Spitalfields has approximately 67 perikymata between the level of the fIrst and last cementum enamel margin suggesting 1.3 years (Dean, personal communication).

Results from any cross-sectional study combine data from early and late maturers and give little indication of individual growth rate over time. This problem is illustrated in the comparison of data from cross-sectional and longitudinal studies (Fig. 5).

:.: '.~. LIVERSJIX::

i.:.::.on ages ar" • =: 2.5, 3, 4.5. : years, while : ::-is study 0: "2.;:-uc Cc ane ~ :s made for '=::. Haavikko , ::"':s is given. :-So: joys) also

f :')und in the

273

-..: := :-.-.e mean rate of root growth of Ml (in Ilm per day). yr = years, Cc= crown complete, R'/,= root =:: ;".' . :::nplete, R1/2= root length '1

2 complete. .

.=:' ~·'_".:-IOS AND ROOT EXTENSION RATES

agelstage rate

3;::alfields 2.9 to 6.4 yr 5 :::eiser and Hunt 1955 Cc to R'/, 4 :::ieiser and Hunt 1955 R'/, to RI/2 8 Carlson 1944 3 to 6 yr 6 Lcdley et al. 1971 4 to 6 yr 7 Carels etal. 1991 5 to 6 yr 8 Dean and Beynon 1991 R'/, 4

-:::.~l growth :-igh infant

'~e of dental ~::::lonstrated

:-;;. een lOllm == :eciduous .' ::en (Tab.

_.. a.nd Stack

-= :..~e few -: :3.rels, ,=-::es by -: :"-. :ength

=:. ~ean

'..:.::.)n of -=:= the

:::' :179) =:.~:::lrum

, c.:.: give ==.; ;"lson

11 TOOTH LENGTH

mm 20,...-------------------,

15

10

5

.." . --l- LONGITUDINAL

CROSS-SECTIONAL 0'-----.1....-----'--------'--------'--'

o 2 4 6 8

AGE

Figure 5. The comparison of data from cross-sectional and longitudinal studies. Dots indicate individual tooth length from Spitalfields and Tomes, lines connect tooth length over time (Carlson, 1944).

Be' ~.::

Ca::~;:: :

Cex :.~

De'-.-. '. ~

De·~:;.:-

Di::: :.: _.':-':.

~~~:~'", G:e:;:: ~

G':::-:::: ~ - _,:"­

r-.:.:'. -'.' .

15:.:.:. :: ~ - -:

~:~.::.:

.: - ':",

", ~..:....=

.

':. .:" -.:.­ :..:

H.M. LlVERSlDGE c~.:·c··. =:'274

The dots represent individuals from Spitalfields; the lines connect tooth length of several -:>

individuals over time (data of indirect radiographic tooth length from Carlson, 1944). It is clear from Carlson's data that not only does the individual rate of growth in tooth length at any age vary but the timing of the growth spurt in root extension occurs at different ages, possibly associated with the stage of root formation and/or eruption. Recent histological studies have quantified for the fIrst time the individual root extention rate of some permanent teeth. The rate of cervical enamel development of upper incisors is about 2 mm per year or 51lm per day (Beynon, 1992), while initial root extension of lower incisors is 2.9 to 3.81lm per day (Dean and Beynon, 1991). The root extension rate of Ml during initial root growth from this cross-sectional study of SpitalfIelds is similar to individual rate of permanent incisors (Dean and Beynon, 1991).

The results of this study question the validity of using the age of crown completion of permanent anterior teeth from radiographic standards of dental growth. The slow rate of growth in tooth length during the end of the crown and the beginning of the root hampers the accuracy of this important developmental stage.

Conclusions

Crown completion, one of the most important stages of tooth formation is diffIcult to assess unequivocally from radiographs. This is particularly significant in the anterior permanent incisors and canine where a considerable amount of time occurs between cessation of enamel secretion at the mesial and distal margins (the radiographic stage of crown complete) and the fInal edge of the enamel on the buccal and lingual aspects of the tooth. The results from this study of an archaeo­logical population of known age at death reveal that the age of true crown completion is later than most data from previous radiographic studies. This is in agreement with recent histological evidence of individual tooth rate growth of enamel and dentine. The earliest permanent anterior tooth observed with true crown completion were 11 and 1

2 at 4.5 years. The latest age where only

initial root was formed was 6 years. One individual was noted with Cc of 11 at 5.8 year, while no 12 or C crown were observed as complete in this sample.

Differences in the mean rate of growth in length were noted between teeth. The range of deciduous root extension was 20llm (il) to 91lm (m2) per day. The mean initial root growth rate of Ml was about 51lm per day.

Acknowledgements

I am particularly grateful to T.!. Molleson (Natural History Museum, London) as well as C. Grigson (Odontological Museum, Royal College of Surgeons, London) for allowing me access to these Collections. I am grateful to M.V. Stack for kindly sending me data from his collection of autopsy specimens. The excava­tion of the crypt of Spitalfields was funded by English Heritage and the Nuffield Foundation.

S_-.=~~ _-__

,- -.- .._- _. _~-::..cReferences

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- --------------

275CROWN FORMATION AND ROOT EXTENSION RATES

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