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Brief communication Possible third molar impactions in the hominid fossil record.

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Brief Communication: Possible Third Molar Impactions in the
Horninid Fossil Record
Department of Anatomical Sciences, University of Texas Dental Branch,
Houston, Texas, 77225 (K.R.G.);Department of Sociology and
Anthropology, Loyola Uniuersity of Chicago, Chicago, Illinois 60626
Third molar impactions,
Australopithecus, Dental evolution
Impacted third molars affect 15%-20%of modern Americans
and Western Europeans. In contrast, third molar impactions have not been
reported in the early hominid fossil record. It is uncertain whether the lack of
reports reflects an absence of impactions or a failure to recognize them. This
communication is intended to raise awareness of the possibility of impactions
by describing the appearance of impacted teeth and by noting two possible
instances of impaction in early hominids. Specifically, the mandibular third
molars of the Sterkfontein specimen, STS52b (Australopithecus africanus),
and the left maxillary third molar of the Lake Turkana specimen, KNM-WT
17400 (Australopithecus boisei), are positioned in a manner which suggests
that they would not have erupted normally. Both specimens also exhibit
strong crowding of the anterior dentition, providing further support for the
view that these individuals lacked sufficient space for normal eruption of the
third molars. Other published reports of dental crowding in the hominid fossil
record are noted, and it is suggested that more attention be paid to dental
impaction and dental crowding in hominid evolution. o 1993 Wiley-Liss, Inc.
Approximately 15-20% of the modern
population of Western Europe and the
United States experiences impacted “wisdom t e e t h (Kramer and Williams, 1970). In
many other individuals, the third molars
erupt only partially or in a manner which
causes them to abut against the second molars. Little data exist, however, pertaining
to the antiquity of hominid third molar impactions except for a few reports of impactions among the Krapina Neandertals and
European Upper Paleolithic peoples (Wolpoff, 1979; Skinner and Sperber, 1982;
Frayer and Russell, 1987). These sparse reports of third molar impaction may reflect
an extreme rarity of impaction and crowding
in ancient hominids. Alternately, perhaps,
the incidence of third molar impaction has
been underreported in the literature, because it is difficult to recognize impactions
in the skeletal record except in cases of extreme displacement.
The purpose of this brief communication
is to raise the level of awareness, not to provide the final word, of possible third molar
impactions in the fossil record. Hopefully,
this will result in increased interest in the
phenomenon and in better methods of recognition.
Impacted or partially erupted third molars may assume one of several positions:
mesioangular, horizontal, vertical, inverted,
or distoangular (Archer, 1966; Kruger,
Received March 15,1990; accepted January 31,1993.
Classification of mandibular impacted teeth. A, Mesioangular; B, horizontal; C, vertical; D,
distoangular; E, buccoversion; F, linguoversion; G, low-level; H, high-level.
Fig. 1. Types of third molar impactions. (Reprinted from Kruger, 1984, with permission from the
1984; Fig. 1).In a mesioangular impaction,
the long axis of the tooth inclines in a mesial
direction; in a distoangular impaction, the
long axis of the tooth inclines distally, and so
on. Impacted teeth may also be displaced to
the buccal (buccoversion) or lingual (linguoversion) sides or rotated in position, and
they may assume several vertical levels.
Thus, the highest portion of an impacted
third molar may be on a level above the occlusal line of the second molar, below the
occlusal line but above the cervical line, or
below the cervical line of the second molar.
As a result of the many positions an impacted third molar might assume, a variety
of complications arise when attempting to
assess third molar impaction in a fossil specimen. For instance, most fossil hominids
died young. Many australopithecines, in
particular, died during late adolescence
(Mann, 1975). Thus, age, rather than pathology, might account for the lack of eruption of some third molars. The examples
given below are instances in which we believe that the molar is seriously malpositioned and would not have erupted normally.
An examination of fossil casts distributed
among anthropology and anatomy departments throughout the world indicates that
the third molars of one well-known fossil is
positioned in a manner typical of third molar impaction. Yet, to our knowledge no one
has suggested the possibility of impaction in
this specimen. Specifically, the Sterkfontein
specimen STS-52b (Australopithecus africanus) shows signs of possible impaction of
Fig. 2. Cast of STS-52b. Notice anterior crowding and
the displacement of the right M3 which appears to be in
both mandibular third molars. In addition,
observations of the original Lake Turkana
KNM-WT 17400 specimen dating from approximately 2,500,000 years ago and classified as Australopithecus boisei by Leakey
and Walker (1988) suggest the presence of
an impacted left maxillary third molar.
The right M3 of the Sterkfontein 52b mandible is buccally displaced and identical in
appearance to third molars impacted in buccoversion (Fig. 2). It is important to note
that even in young individuals whose molars have not yet erupted, the molars do not
occupy a position of buccoversion. On the left
side, the third mandibular molar is erupting
in an angulated fashion and the tip of its
crown nearly touches the cementoenamel
junction of the second molar (Fig. 3). In position, the tooth matches descriptions of mesioangulated midlevel impactions (Archer,
1966). We have shown this tooth to a number of orthodontists and oral surgeons, who,
based on their clinical experience, concluded
that the tooth would not have erupted normally.
It is true that this mandible, like much of
the Sterkfontein material, is badly fractured, but it is unlikely that the fracture has
distorted the relationship between the second and third molars because the fracture
runs anterior to the second molar on both
sides. In addition, this fracture is typical of
some which commonly occur in modern humans as a result of trauma. In the clinical
Fig. 3. Cast of STS-52b left mandibular second and
third molars. The left third molar exhibits a mesioangular orientation and its tip nearly touches the second
experience of oral surgeons who commonly
treat these problems, a fracture of this nature would not have altered the relationships between the second and third molars
(McFarland, personal communication). Nor,
given its position, is this fracture likely to
have altered the third molar position even if
the fracture occurred post-mortem.
Further indications that the mandibular
third molars of STS-52b may have lacked
sufficient room for eruption come from the
crowded condition of the anterior teeth (Robinson, 1956; Oppenheimer, 1964; Wallace,
1972). Thus, in STS-52b, “insufficient space
is available for the (right) canine to fit properly into the normal arch. This has resulted
in a buccalward protrusion of the canine”
(Robinson, 1956, p. 16). Judging from the
condition of the anterior alveoli, Robinson
concludes that the left canine, although
missing, was also likely to have been
crowded and displaced during life. Although
crowded anterior teeth may occur in the absence of third molar impactions, the two often coexist, as both conditions may indicate
overall dental crowding and insufficient
arch space. In fact, crowding of the anterior
dentition sometimes manifests itself at the
time of eruption of the third molars (Richardson, 1989).
The WT-17400 maxilla from Lake Turkana also exhibits signs of possible impaction. In this specimen, the mesiafiuccal corner of the left third molar is in contact with
Fig. 4. Cast of the WT-17400 maxilla from Lake Turkana. Note the contact between the left third molar and
the second molar. Also note the crowding of the anterior
the buccalldistal root of the second molar
(Fig. 4). Erosion around the roots of the second molar make this clear. Insufficient
space exists for the third molar to erupt into
the normal position. Indeed the occlusal surface of the tooth exhibits some distal tilting.
This specimen also exhibits extreme crowding of the anterior dentition (Leakey and
Walker, 1988). The lateral incisors have actually been displaced posteriorly behind the
incisal canine tooth row. In addition, the left
P4 has been displaced lineally.
Despite the paucity of reports of third molar impactions in the fossil record, it is unlikely that STS-52b and WT-17400 were the
only members of their populations to suffer
from this phenomenon. As stated previously, third molar impactions often coexist
with crowding in the remainder of the dentition. A number of authors report dental
crowding in Plio-Pleistocene hominids. Additional specimens exhibiting such crowding
include “Lucy”(Johanson et al., 1982), “Zinjanthropus” (Tobias, 1967), Swartkrans
specimens SK-23, SK-48, SK 838, and SK1590b, Makapansgat specimen MLD-18
(Oppenheimer, 1964; Robinson, 1956; Wallace, 19721, and the Galusi hominid
(Protsch, 1981). Similarly, dental crowding
and impaction have been reported in the
Krapina Neandertals (Wolpoff, 1979; Skinner and Sperber, 1982; Frayer and Russell,
A number of the australopithecine specimens also evidence heavy wear on the first
and second molars, but unerupted third molars. While this may reflect a lengthy period
of time between the eruption of the second
and third molars or heavy masticatory
stress on the anterior molars, it could also be
a sign of impacted teeth, a possibility which
appears to have escaped the attention of previous investigators. Finally, the dental arch
length of the australopithecines was relatively long in comparison to the length of the
cranial base and overall size of the skull
(Rak, 1983; Tobias, 19671, suggesting that
among the robust australopithecines tooth
size may have been approaching the maximum compatible with the size of the skull.
Given that dental crowding and impaction
can exert a major impact on health (Calcagno and Gibson, 1988, 1991), we believe
that it is time for a more serious examination of the incidence of dental crowding in
the fossil record.
We thank Paul McFarland, former Associate Dean for Research and Professor of Oral
Surgery, University of Texas Dental
Branch, and Dan West, Chairman of Orthodontics, University of Texas Dental
Branch, for expert consultation during the
preparation of this paper. We also thank
Meave Leakey for granting permission for
one of us (Calcagno)to examine the original
WT17400 cranium, and to Alice Maunda of
the National Museums of Kenya for her onsite assistance.
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molar, record, brief, communication, possible, third, fossil, hominis, impaction
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