Eruption Rates of Human Upper Third Molars B. K. B. BERKOVITZ and T. P. BASS* Department of Anatomy and Department of Dental Surgery, University of Bristol, Bristol BS8 ITD, England
Eruption rates of human maxillary third molars varied from 1 mm/2 mo to rates of less than 1 mm/6 mo. More rapid rates were associated with spaced dentitions. Gingival recession was invariably associated with crown exposure. Though considerable data are available concerning the eruption rates of continuously growing incisors,1 there is little information about such rates for teeth of noncontinuous growth. In human teeth, Burke and Newell2 recorded the daily eruption rate of both upper central incisors of a patient by means of a photographic technique. The rate of clinical eruption of these teeth was maximal at the time of crown emergence and decreased thereafter; during the first month, the tooth erupted just more than 1 mm. Burke3 also recorded the eruptive movements of 22 maxillary central incisors, in which eruption had been delayed, by means of a series of study casts taken at intervals after the surgical exposure of the teeth. The findings suggested that the rate of movement on emergence of the crowns was between I and 2 mm per month. Because of the young age of these participants, it is to be assumed that the occlusal plane, the datum used for all measurements, is less stable than in an older age group. Because of the obvious lack of data concerning eruption rates of human teeth, it was decided to measure such rates for the upper third molar.
Materials and Methods The teeth chosen for the present study were the upper third molars of a group of dental students, participants readily availReceived for publication January 30, 1975. Accepted for publication November 25, 1975. 0 Present address: Department of Oral Surgery and Orthodontics, Royal Devon and Exeter Hospital, Barrack Road, Exeter, Eng.
able for the investigation. An added advantage of using this age group (18 to 21 years old) is that the occlusal plane is likely to be more stable in this age group than in younger people. A total of 90 students were examined both clinically and radiographically on entry to the University. In about 20% of the group, the third molars were congenitally absent and in a further 30%, these teeth were fully erupted. In only 14 of the remaining 45 students was there an erupting third molar or one that appeared clinically during the three-year study. Alginate impressionsa of the dentitions were obtained and cast immediately in artificial stone with the use of standardized techniques. The maximum error in dimension produced by this technique is + 0.1 %4 and has been confirmed in our laboratories.5 It had been our intention to take impressions regularly at four weekly intervals, but this aim could not always be realized because of university vacations. In some instances, too, the eruption rate was so slow that a longer interval between recordings was acceptable. In this manner, the eruption of the maxillary third molar was followed from its initial appearance in the mouth for intervals of between three months and two years. Three models from such a series are seen in Figure 1. The method used for measuring tooth movement is seen in Figure 2 and is a modification of the method used by Burke.3 When placed on a sheet of glass, a model will make contact at three specific points, namely the tips of cusps or incisal edges or both. These three points are recorded and it can be observed that these same three points will contact the glass plate for subsequent models in the series. With a datum plane for each series thus established, the a
Zalgan, Amalgamated Dental, London, Eng.
460 Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
HUMAN UPPER THIRD MOLARS
Vol 55 No. 3
461
.0 -
JU
.....7...1...
._ ._.
>
~19.3.71
FIG 2.-Method used for measuring tooth movement.
1.-Three
FLu. stages
in
rnoxrement leteiminled
thle
series
third1
illusirating
molar.
by
t ips
cusp
from
upper
thle maxillary thlird molar was measurinlg thle distance from
of
to
the
plane
(ieadting.
depth gauge
throulgh
models
eruption of
with
0).01
to
mm)
a hole cut in the glass.
a
xenier lowered
To establish
measulremlent, five successixe readings were made on eachl of four models. Anlalysis of the data by the F ratio t:echnriquee sulggests thalt the .5% conlfidence limit for the the
error
method
of
is
0.06
mm.
The
mean
of
three
separate meastirements was then used to proxide was
each
(latum
discardled
vanced
l)oint.
since
conserv atixe
course of the
study.
One
series
of
ca£st ad-
the student required
treatment
during
the
which altered the datum
p)lane. Results The distance
through
which the maxillary
third molar moved in each of six students is shown in Figure 3. The measurements were taken to the tip of thle first cusp to appear clinically. Figure 4 shows similar movement in an additional tlhree stuLdents recorded durinig a loniger period. The maximum rate of movement of the teetlh as seen in Figure 3 was about I mm/3 mo, whereas the mean rate of movement for the remainder of the students was approximately I mm/6 mo. In Figure 4, a linear relationship between eruption rate andI time is seen for two teeth and a curvilinear relationship for the third. The maximum rates of eruption for these tlhree teetlh were between 1 mm/2 mo and 1 mm/3 uio. The eruption rates slowed considerably as the three teeth came into occlusion. A common feature of the dentitions seen in Figure 4 and that in Figure 3 witlh the highest eruption rate was an absence of crowding resultiing from premature extraction of the miaxillary first molars. A comparison of the rates of movement of all cuisps of a tooth will indicate any tilting occurring during eruption. This is seen in Figure 5 which records the movements of the three cusps of a tooth from the series shown in Figure 4. In the remaining students, little or no
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462
j Dent Res May-June 1976
BERKOVITZ AND BASS
E E C
u
CZa. 0)
Time in days
FIG 3.-Graph showing amount of movement of first cusp of upper third molar to penetrate oral mucosa in six different students.
eruption was observed over a recording period of five months. An invariable finding was that the rate of exposure of the clinical crown exceeded the recorded rate of cusp movement, so it must be concluded that eruption is associated with a considerable degree of gingival retraction.
Discussion There is much debate as to what constitutes a "normal" dentition. Among its features coLlld be included an intact dentition with absence of crowding, which implies sufficient room to allow for the eruption of tthe third molars. Such a dentition is uncom-
3.5
3.0
E
2..
.o
=,2.0.-
*-
Q
~~~~~*****/'< S /
1.5
O
1.0
.
Time in days FIG 4.-Graph showing amount of movement of first cusp of upper third molar to penetrate oral mucosa in three different students.
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
HUMAN UPPER THIRD MOLARS
Vol 55 No. 3
E E
463
2.0/ 1.6 ~
~
.
C
e 1.0 a'
.*
0.
o /i 0
100
200
400 300 Time in days
500
600
700
FIG 5.-Graph showing movements of three primary cusps of upper third molar to occlusal plane, indicating tilting of distobuccal cusp. DB, distobuccal cusp; P, palatal cusp; MB, mesiobuccal cusp.
in the British population where the prevalence of dental crowding is well established.6,7 In our students, only 11 % had uncrowded, intact dentitions with sufficient space for the eventual eruption of the maxillary third molars, and none of these had erupting third molars during the study. Such material, of necessity, was from either dentitions in which space was available for the erupting third molars as a result of premature extraction of first molars or from intact dentitions that had varying degrees of crowding. However, this material is representative of the greater part of the population.8 Where space was available, the maximum rate of eruption was about 1 mm/3 mo whereas in crowded dentitions, the figure was less than 1 mm/6 mo. The maximum rates recorded for maxillary third molars were still less than half those recorded for two erupting human central incisors.2 Though further work needs to be done, our preliminary results indicate that crowding may retard eruption rates. It may be noted that rodent incisors when cut free of occlusion to produce the so-called unimpeded condition erupt at rates of I mon
mm/day.1 9 Apart from active eruption, our results indicate that exposure of the clinical crown is also due to gingival retraction, this being
especially obvious in third molars that had no eruption during the period of observation. Conclusions Human maxillary third molars have been observed to have maximum rates of eruption of approximately 1 mm/2 mo. Rates of less than 1 mm/6 mo have also been recorded. Maximum rates of eruption were associated with spacing of the dentition. Passive eruption in the form of gingival recession is an important factor resulting in the exposure of the clinical crown. The authors acknowledge Miss A. Featherstone for photographic assistance.
References 1. NESS, A.R.: Movement and Forces in Tooth Eruption, in STAPLE, P.H. (ed): Advances in Oral Biology, Vol 1, London: Academic Press, 1964, pp 33-75. 2. BURKE, P.H., and NEWELL, D.J.: A Photographic Method of Measuring Eruption of Certain Human Teeth, Am J Orthod 44: 590602, 1958. 3. BURKE, P.H.: Eruptive Movements of Permanent Maxillary Central Incisor Teeth, Proc R Soc Med 56: 513-515, 1963. 4. PHILLIPS, R.W.: Skinner's Science of Dental Materials, 7th ed, Philadelphia: W. B. Saun-
clers, 1973. 5. STEPHENS, C.D.: Unpublished results.
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
464
BERKOVITZ AND BASS
6. FOSTER, T.D., and WALPOLE DAY, A.J.:
J Dent Res May-June 1976 A
Survey of Malocclusion and the Need for Orthodontic Treatment in a Shropshire School Population, Br J Orthod 1: 73-78, 1974. 7. HARKNESS, E.M.: The Prevalence of Malocclusion in a Random Sample of 12 Year Old Cardiff Schoolgirls, Dent Practit (Bristol) 20: 77, 1969-1970.
8. TODD, J.E.: Children's Dental Health in England and Wales, 1973, London: Her Majesty's Stationery Office, 1975. 9. BERKOVITZ, B.K.B., and THOMAS, N.R.: Unimpeded Eruption in the Root-Resected Lower Incisor of the Rat with a Preliminary Note on Root Transection, Arch Oral Biol 14: 771-780, 1969.
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
Eruption rates of human maxillary third molars varied from 1 mm/2 mo to rates of less than 1 mm/6 mo. More rapid rates were associated with spaced dentitions. Gingival recession was invariably associated with crown exposure. Though considerable data are available concerning the eruption rates of continuously growing incisors,1 there is little information about such rates for teeth of noncontinuous growth. In human teeth, Burke and Newell2 recorded the daily eruption rate of both upper central incisors of a patient by means of a photographic technique. The rate of clinical eruption of these teeth was maximal at the time of crown emergence and decreased thereafter; during the first month, the tooth erupted just more than 1 mm. Burke3 also recorded the eruptive movements of 22 maxillary central incisors, in which eruption had been delayed, by means of a series of study casts taken at intervals after the surgical exposure of the teeth. The findings suggested that the rate of movement on emergence of the crowns was between I and 2 mm per month. Because of the young age of these participants, it is to be assumed that the occlusal plane, the datum used for all measurements, is less stable than in an older age group. Because of the obvious lack of data concerning eruption rates of human teeth, it was decided to measure such rates for the upper third molar.
Materials and Methods The teeth chosen for the present study were the upper third molars of a group of dental students, participants readily availReceived for publication January 30, 1975. Accepted for publication November 25, 1975. 0 Present address: Department of Oral Surgery and Orthodontics, Royal Devon and Exeter Hospital, Barrack Road, Exeter, Eng.
able for the investigation. An added advantage of using this age group (18 to 21 years old) is that the occlusal plane is likely to be more stable in this age group than in younger people. A total of 90 students were examined both clinically and radiographically on entry to the University. In about 20% of the group, the third molars were congenitally absent and in a further 30%, these teeth were fully erupted. In only 14 of the remaining 45 students was there an erupting third molar or one that appeared clinically during the three-year study. Alginate impressionsa of the dentitions were obtained and cast immediately in artificial stone with the use of standardized techniques. The maximum error in dimension produced by this technique is + 0.1 %4 and has been confirmed in our laboratories.5 It had been our intention to take impressions regularly at four weekly intervals, but this aim could not always be realized because of university vacations. In some instances, too, the eruption rate was so slow that a longer interval between recordings was acceptable. In this manner, the eruption of the maxillary third molar was followed from its initial appearance in the mouth for intervals of between three months and two years. Three models from such a series are seen in Figure 1. The method used for measuring tooth movement is seen in Figure 2 and is a modification of the method used by Burke.3 When placed on a sheet of glass, a model will make contact at three specific points, namely the tips of cusps or incisal edges or both. These three points are recorded and it can be observed that these same three points will contact the glass plate for subsequent models in the series. With a datum plane for each series thus established, the a
Zalgan, Amalgamated Dental, London, Eng.
460 Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
HUMAN UPPER THIRD MOLARS
Vol 55 No. 3
461
.0 -
JU
.....7...1...
._ ._.
>
~19.3.71
FIG 2.-Method used for measuring tooth movement.
1.-Three
FLu. stages
in
rnoxrement leteiminled
thle
series
third1
illusirating
molar.
by
t ips
cusp
from
upper
thle maxillary thlird molar was measurinlg thle distance from
of
to
the
plane
(ieadting.
depth gauge
throulgh
models
eruption of
with
0).01
to
mm)
a hole cut in the glass.
a
xenier lowered
To establish
measulremlent, five successixe readings were made on eachl of four models. Anlalysis of the data by the F ratio t:echnriquee sulggests thalt the .5% conlfidence limit for the the
error
method
of
is
0.06
mm.
The
mean
of
three
separate meastirements was then used to proxide was
each
(latum
discardled
vanced
l)oint.
since
conserv atixe
course of the
study.
One
series
of
ca£st ad-
the student required
treatment
during
the
which altered the datum
p)lane. Results The distance
through
which the maxillary
third molar moved in each of six students is shown in Figure 3. The measurements were taken to the tip of thle first cusp to appear clinically. Figure 4 shows similar movement in an additional tlhree stuLdents recorded durinig a loniger period. The maximum rate of movement of the teetlh as seen in Figure 3 was about I mm/3 mo, whereas the mean rate of movement for the remainder of the students was approximately I mm/6 mo. In Figure 4, a linear relationship between eruption rate andI time is seen for two teeth and a curvilinear relationship for the third. The maximum rates of eruption for these tlhree teetlh were between 1 mm/2 mo and 1 mm/3 uio. The eruption rates slowed considerably as the three teeth came into occlusion. A common feature of the dentitions seen in Figure 4 and that in Figure 3 witlh the highest eruption rate was an absence of crowding resultiing from premature extraction of the miaxillary first molars. A comparison of the rates of movement of all cuisps of a tooth will indicate any tilting occurring during eruption. This is seen in Figure 5 which records the movements of the three cusps of a tooth from the series shown in Figure 4. In the remaining students, little or no
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
462
j Dent Res May-June 1976
BERKOVITZ AND BASS
E E C
u
CZa. 0)
Time in days
FIG 3.-Graph showing amount of movement of first cusp of upper third molar to penetrate oral mucosa in six different students.
eruption was observed over a recording period of five months. An invariable finding was that the rate of exposure of the clinical crown exceeded the recorded rate of cusp movement, so it must be concluded that eruption is associated with a considerable degree of gingival retraction.
Discussion There is much debate as to what constitutes a "normal" dentition. Among its features coLlld be included an intact dentition with absence of crowding, which implies sufficient room to allow for the eruption of tthe third molars. Such a dentition is uncom-
3.5
3.0
E
2..
.o
=,2.0.-
*-
Q
~~~~~*****/'< S /
1.5
O
1.0
.
Time in days FIG 4.-Graph showing amount of movement of first cusp of upper third molar to penetrate oral mucosa in three different students.
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
HUMAN UPPER THIRD MOLARS
Vol 55 No. 3
E E
463
2.0/ 1.6 ~
~
.
C
e 1.0 a'
.*
0.
o /i 0
100
200
400 300 Time in days
500
600
700
FIG 5.-Graph showing movements of three primary cusps of upper third molar to occlusal plane, indicating tilting of distobuccal cusp. DB, distobuccal cusp; P, palatal cusp; MB, mesiobuccal cusp.
in the British population where the prevalence of dental crowding is well established.6,7 In our students, only 11 % had uncrowded, intact dentitions with sufficient space for the eventual eruption of the maxillary third molars, and none of these had erupting third molars during the study. Such material, of necessity, was from either dentitions in which space was available for the erupting third molars as a result of premature extraction of first molars or from intact dentitions that had varying degrees of crowding. However, this material is representative of the greater part of the population.8 Where space was available, the maximum rate of eruption was about 1 mm/3 mo whereas in crowded dentitions, the figure was less than 1 mm/6 mo. The maximum rates recorded for maxillary third molars were still less than half those recorded for two erupting human central incisors.2 Though further work needs to be done, our preliminary results indicate that crowding may retard eruption rates. It may be noted that rodent incisors when cut free of occlusion to produce the so-called unimpeded condition erupt at rates of I mon
mm/day.1 9 Apart from active eruption, our results indicate that exposure of the clinical crown is also due to gingival retraction, this being
especially obvious in third molars that had no eruption during the period of observation. Conclusions Human maxillary third molars have been observed to have maximum rates of eruption of approximately 1 mm/2 mo. Rates of less than 1 mm/6 mo have also been recorded. Maximum rates of eruption were associated with spacing of the dentition. Passive eruption in the form of gingival recession is an important factor resulting in the exposure of the clinical crown. The authors acknowledge Miss A. Featherstone for photographic assistance.
References 1. NESS, A.R.: Movement and Forces in Tooth Eruption, in STAPLE, P.H. (ed): Advances in Oral Biology, Vol 1, London: Academic Press, 1964, pp 33-75. 2. BURKE, P.H., and NEWELL, D.J.: A Photographic Method of Measuring Eruption of Certain Human Teeth, Am J Orthod 44: 590602, 1958. 3. BURKE, P.H.: Eruptive Movements of Permanent Maxillary Central Incisor Teeth, Proc R Soc Med 56: 513-515, 1963. 4. PHILLIPS, R.W.: Skinner's Science of Dental Materials, 7th ed, Philadelphia: W. B. Saun-
clers, 1973. 5. STEPHENS, C.D.: Unpublished results.
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
464
BERKOVITZ AND BASS
6. FOSTER, T.D., and WALPOLE DAY, A.J.:
J Dent Res May-June 1976 A
Survey of Malocclusion and the Need for Orthodontic Treatment in a Shropshire School Population, Br J Orthod 1: 73-78, 1974. 7. HARKNESS, E.M.: The Prevalence of Malocclusion in a Random Sample of 12 Year Old Cardiff Schoolgirls, Dent Practit (Bristol) 20: 77, 1969-1970.
8. TODD, J.E.: Children's Dental Health in England and Wales, 1973, London: Her Majesty's Stationery Office, 1975. 9. BERKOVITZ, B.K.B., and THOMAS, N.R.: Unimpeded Eruption in the Root-Resected Lower Incisor of the Rat with a Preliminary Note on Root Transection, Arch Oral Biol 14: 771-780, 1969.
Downloaded from jdr.sagepub.com at Bibliothekssystem der Universitaet Giessen on May 24, 2015 For personal use only. No other uses without permission.
