вход по аккаунту


Cercopithecoid canine tooth honing mechanisms.

код для вставкиСкачать
Cercopithecoid Canine Tooth Honing Mechanisms
Oregon Regional Primate Research Center, Beauerton, Oregon 97005
The form of the unworn male Cercopithecoid maxillary canine tooth
(C’) is effectively adapted for stabbing and slashing. Its essential features are maintained by wear against the mandibular canine ( C , ) and first premolar (Pa) teeth. The
cusp tip of Ci is sharpened by reciprocal wear against C’. The distribution of apposing wear facets indicates that functional attrition results from honing activity largely
distinct from mastication. Functional attrition also occurs in reduced form in fcmales
and is produced within the masticatory excursive range. The significance of the “sectorial” form of Ps is analvzed. Its elongated mesiobuccal surface serves the dual purpose of honing the distal cutting edge of C’ and functioning as a cutting block against
which vegetation is stabilized and shredded by the cervical third of the distal cutting
edge of C’. Behavioral aspects of honing are coyrelated with field observations linking
tooth grinding with aggression, tension releasc, and communication. Parallel human
behavior is cited and the suggestion is made that human tooth grinding with its
highly charged emotional overtones is largely relict behavior that once had high survival value i n a canine tooth honing context.
Reciprocal tooth wear serves to sharpen
teeth in rodents, lagomorphs, ruminants,
and certain other mammals. In the broadest sense, such dental mechanisms are
comparable to a wide variety of animal
devices and activities directed toward maintaining horns, claws, beaks, etc., i n good
working order.
Primatologists tend to dismiss primate
dental attrition as an incidental by-product
of aging. But contrary evidence shows that
functionally useful dental attrition occurs
in a wide spectrum of this order. In these
animals, as i n others, teeth are sharpened
by reciprocal action between occluding
parts. Although such mechanisms operate
in other teeth, they find their fullest morphological expression in the canines.
This paper,’ the first of a series exploring
primate dental honing mechanisms, elucidates these characteristics in the Cercopithecidne. This group, assigned family rank
in Simpson’s classification (’45). is divided
into two subfamilies: the Cercopithecinae
and the Colobinne. Despite differences
stemming from divergent feeding adaptations in these two groups, a common cercopithecoid dento-occlusal pattern permits
valid generalizations. Subfamilial traits
are noted when relevant.
Tooth form, occlusal relationships, and
occlusal function (insofar as this could
AM. J. PHYs. ANTHROP.,3 1 : 205-214.
be deduced from dry skulls) were noted in
specimens belonging to the Oregon Regional Primate Research Center. These observations were supplemented by a study
of material housed in the Primate Section
of the United States National Museum.
Table 1 summarizes the distributive nature of the material.
The specimens were examined for sex
related differences in canine tooth morphology and in the structure of the teeth
occluding with the canines. In each case,
wear facets and direction of abrasion lines
(where evident) were determined. The
mandible was articulated with the teeth in
centric occlusion. Starting from centric,
the excursive range of the functioning
dentition was ascertained by approximating
wear facets in opposing teeth (Butler, ’52;
Mills, ’55, ’64; Zingeser, ’68a).
Representative Cercopithecoid specimens
were selected for graphic representation.
Figures 1 to 3 illustrate salient occlusal
characteristics including consistent wear
patterns and associated excursive attributes.
Canine tooth sexual dimorphism is
marked in the Cercopithecidae. Males are
1 Publication No. 389 of the Oregon Regional Primate Rescarch Center. supported i& part-by Grant
FFR 00163 of the National Institutes of Health, and
by Grant 6618 of the MedicaI Research Foundation
of Oregon.
characterized by large maxillary canine
tooth fangs that function primarily as
stabbing and slashing weapons. Masticatory function is confined to a relatively
small area of the total tooth surface
(Zingeser, ’68b). The crown of the tooth
is tipped by a sharp cusp point, and a distal
cutting edge extends from cusp tip to
crown base. The thick mesial aspect of
the crown thins to the distal to form a
blade-like structure terminating in a cutting
edge. The labial aspect of the “blade” is
convex whereas the lingual surface is concave. The crown resembles a single-edged,
hollow-ground knife or dagger (figs. 1, 2).
The mesiobuccal aspect of the distally
angulated mesiobuccal cusp of the mandibular first premolar (P, in paleontological
terms) together with the distal surface and
cingulum or talonid of the mandibular
canine (C,),forms a “ V shaped notch-like
embrasure that accommodates the maxil-
Fig. 1 Crown anatomy of male and female maxillary canine teeth of Macaca mulattU.
Mesiolingual view of male and lingual view of female showing homologous parts and regions of attrition. Crown details: a, mesial marginal ridge; b, anterior vertical groove or
fovea anterior; c, lingual paracone ridge. Numbered regions of attrition keyed to text..
lary canine (C’) in centric occlusion and away the lingual paracone ridge (C of fig.
against which this tooth differentially 1 ) . This contact relationship results in a
wears to sharpen blade and cusp-tip during double bevelled facet of variable length exhoning activities (fig. 2).
tending from cusp tip apically (wear reBecause of the extreme length of the gions 2 and 11). The mesial component of
male cercopithecoid C’ relative to the occlu- this double bevel is occasionally obscured
sal plane, honing activity is largely inde- by merging with the extensive wear region
pendent of masticatory function. A s the produced on the mesial surface by its conmandible moves laterally from centric (fig. tact with C, (see above), When C‘ is
3A) into the buccal phase of occlusion, it is viewed from the mesial aspect, especially
guided by the cusp inclines of the posterior in younger males, the pointing function of
teeth working in harmony with the tem- this relationship is evident in the acute
poromandibular joint. However, as the angle the lingual contour of the tooth takes
limits of the buccal phase are reached, fur- at the cusp-tip third of the crown (fig. 3 C ) .
ther lateral movement results in the sepa( 3 ) The distolingual surface of C wears
ration of apposing posterior teeth with against the mesiobuccal surface of P3.
progressive jaw opening as the excursive Because of the concave shape of the “blade”
movement is then guided by contact rela- of C’ on the lingual surface and because
tionships between C‘ and the apposing the lingual plate of enamel is thin, it soon
honing notch components of P3 and C1. wears through, exposing dentine and leavThus C’, P, and C1 form a sort of tongue- ing a hard, sharp rim of labial enamel
in-groove guiding and honing triad. The along the distal edge extending to and inresulting attrition serves primarily to cluding the cusp tip. P3 acts primarily as
sharpen C‘. This honing maneuver appears a whet stone in this differential wear proto constitute an extension of the buccal cess (reciprocal wear regions 3 and 111).
A second sort of honing activity funcmasticatory phase in the sense that a
smooth transition can be envisioned. With tions to sharpen the cusp tip of the mandiextreme jaw opening the tip of C’ slides bulur canine. The distal aspect of the cusp
over the mesiobuccal region of P 3 and tip of C1 is abraded against the middle
through the notch-like embrasure to lodge third of the grooved mesial surface of C’ by
upon the cingulum and against the su- opening and closing jaw movements (fig.
perior adjacent distal surface of the man- 3B) perhaps in association with “yawning”
threat behavior. This results in an oval
dibular canine tooth (fig. 3C).
Three functionally significant regions of facet on the distal surface of the cusp tip
attrition are distinguishable on the crown of C 1 . A discrete counterfacet is not often
surface of the male C’ as a result of this discernible because the mesial grooved
honing activity. They are identified in surface also wears against much of the
figures 1 and 2 by Arabic numerals, and distal surface of C, from cingulum to CUSP
their counterfacets on the crowns of Pa tip in the course of previously described
and CI are designated by corresponding honing activity.
A third attritional relationship is uniRoman numerals in figure 2. These reciprocal wear regions are produced by the formly present in Colobinae but generally
absent in mature male Cercopithecinae.
following relationships and activities.
(1) The mesial face of the maxillary During lateral excursions, the distal of the
canine wears against the distal surface of maxillary lateral incisor (I“) on the balancthe mandibular canine to sharpen the cusp ing side of the bite is seen to wear against
tip of C’ by a recontouring process (wear the mesial slope of C1.This occlusal contact relationship is described by Butler and
regions 1 and I).
( 2 ) The juncture of the cingulum or Mills (’59) as characteristic of short-faced
talonid with the adjacent superior distal Anthropoidea. A similar occlusal relationsurface of C1 constitutes an important sec- ship was described in the howler monkey
ondary notched honing region nested with- (Zingeser, ’68a) and appears to be typical
in the first (fig. 2). It functions to point of the Ceboidea where it functions in henthe cusp tip of C’ by differentially wearing ing. It is variably present in females and
Fig. 2 Left canine and premolar occlusal segments of male Presbytis entellus showing
homologous crown parts as described in figure 1. Reciprocal wear regions are identified
by Arabic (maxilla) or corresponding Roman (mandible) numerals.
juvenile male Cercopithecinae before
growth at the premaxillary suture widens
the diastema to eliminate functional contact between P and C1.
Functional attrition is evident in the
wear patterns of the female canine-premolar complex (fig. 1). The honing triad
consisting of C’, P3, and C1, although
smaller and different in component proportions than the male, nevertheless operates
in a similar manner. The female C’, although much smaller than its male counterpart, still extends appreciably below the
occlusal plane and is instrumental in postbuccal phase lateral occlusal guidance associated with honing maneuvers similar to
but far less extreme than those of the male
(fig. 3C). The great length disparity be-
Fig. 3 Honing maneuvers i n the male Macaca mulatta. A, centric occlusicn. B, mandibular canine tip honing. C, left maxillary canine tip honing..
tween C’ and CI seen i n the male is not
present, and all honing is accomplished
either within the masticatory range or the
minimal post-buccal phase.
Homologies of male and female C’ parts
are obscured by form differences. A comparison of these parts examined in the context of their occlusal relationships and
associated wear facets is helpful in this
regard. The mesial edge of the mesial
marginal ridge of the female C’ (anterior
paracone cusp rim ridge) wears against
the distolingual of CL (distolingual slope
of the protoconid). This mesial marginal
ridge corresponds with the mesiolabial
ridge bordering the anterior vertical groove
in the male C’ (item a of fig. 1). The
mesial portion of the lingual paracone
ridge of the female (item c of fig. 1) corresponds with the massive mesiolingual
ridge bordering the lingual side of the
anterior vertical groove in the male. Thus
the male anterior vertical groove can be
regarded as a n elongated, laterally compressed fovea anterior (item b of fig. 1 ) .
The double bevelled facet (region No. 2 )
that results from attrition against the
talonid region of C1 in the male has its fema1 counterpart in a small oval facet on
the lingual paracone ridge at the cusp tip
(fig. 1 ) . Wear at the distolingual surface
of C’ (region No. 3 ) is easily homologized
in male and female teeth.
References to canine tooth attrition in a
functional context are rare. Reed (’65)
makes an acute observation when he describes the baboon C’ as functioning
“against the mandibular canine on the
mesial surface and on the distal surface
against the long sloping mesial surface of
the mandibular first premolar. It wears to
a sharp point and is apparently kept sharp
by the above described functional contacts.”
In essence, canine tooth honing is primarily directed toward preserving the functionally significant features of the unworn
crown of the maxillary canine tooth (e.g.,
a distal edge and a sharp cusp tip point).
All other premolar-canine wear, including
mandibular canine honing, assumes a secondary role, especially in the male. Maxillary canine tooth honing is accomplished
by a process analogous to sharpening a
pencil with a knife. Instead of cutting the
peripheral wood away at random, the
whittling is confined to definite regions.
In the juvenile, honing begins as C’
erupts into contact with CI and P3 and as
this tooth continues to erupt, the faceted
areas are widened and extended rootward.
As the original tip of the crown wears
down, the crown contour becomes relatively broader. However, its essential functional piercing and cutting properties
remain unimpaired because of the differential honing process.
The anatomy of the mandibular second
premolars reflects subfamilial dietary specializations (Hornbeck and Swindler, ’67)
in a manner that elucidates the functional
significance of the peculiar “sectorial” form
of the Cercopithecoid P3. P3 is commonly
described as sectorial, meaning shearing,
probably because it superficially resembles
such true shearing teeth as carnivorous
carnassials (Remane, ’60). Colobine mandibular second premolars tend to resemble
P3 in their elongated mesiobuccal components (cf. P3 and P4in fig. 2). This form
similarity has a functional basis, for the
mesiobuccal of the Colobine P4 hones
against the distolingual of the paracone
blade of P3 to sharpen this edge in a manner similar to the action of homologous
parts of Ps and C’ (regions 3 and I11 in
fig. 2). The mesiobuccal surface of P4
also acts as a cutting-block against which
vegetation is wedged and shredded by the
action of the sharpened distal edge of the
buccal cusp (paracone) of P3. Thus the
functionally relevant part of the “sectorial”
premolar form is seen to be the elongated
mesiobuccal aspect, which serves the dual
purpose of honing the distal cutting edge
of C’ (and P3 in Colobinae) while simultaneously providing a cutting-block against
which these edges can operate. The honing
aspect is dominant in the Ps-C’ Cercopithecoid relationship, mastication being confined to a relatively small area of the cervical crown region of C’. These functions
are co-equal in the Colobine P4--P3relationship.
Such form-functional merismic homologies (Butler, ’67) suggest that the capacity
for honing may have been intrinsic to the
ancestral Cercopithecoid dentition, and
hence may have constituted a preadaptive
factor favoring the dimorphic evolution of
large, necessarily self-sharpening male
canine teeth. This view complements a
previously stated hypothesis on the origins
of canine tooth sexual dimorphism in the
Cercopithecidae (Zingeser, ’68b).
Canine teeth are interesting because
their relative simplicity can clarify occlusal characteristics otherwise obscure. Their
single-cusped form is prototypic within
both evolutionary and ontogenetic frames
of reference. The crown cusp of C1 is a
protoconid, the primal Therian mandibular
cusp (Osborn, ’07). The crown cusp C’ js
a paracone now generally recognized as
the primal cusp in the maxillary dentition
(Gregory, ’16, ’22; Patterson, ’56, Vandebroek, ’61). In addition, numerous embryological studies confirm that these cusps
and their serial homologues in the posterior teeth are the first to develop (Butler,
’56; Kraus and Jordan, ’65; Swindler, ’64;
Turner, ’62).
The occlusal relationships of C’ and CI
parallel the primal condition. For example,
Mills (’64, ’67) concludes that in Jurassic
and Cretaceous Dryolestidae, a dominant
Pantotheriaii family, the paracone sheared
on the buccal of the vestigial talonid. This
arrangement, subsequently lost in the posterior teeth with the development of the
protocone, is seen as an important functional relationship in the canine teeth of
Cercopithecidae and other Anthropoidea.
The behavioral aspects of honing warrant consideration. Tooth wear facet relationships, like the articulation of skeletal
parts, afford insight into what Simpson
and Roe (’63) term elemental behavior.
This implies activity intrinsic to and
limited by morphology without reference
to such physiological factors as sequence,
timing, and higher associative correlations.
Obviously, more elaborate behavior can be
evaluated only in living animals.
What observations in living animals
elucidate the nature of honing behavior?
Both field studies and well-known human
traits supply information that can provide a
working hypothesis. In reporting observations made in the course of studying baboon
troop ethology, Hall and DeVore (’65) state
that “Grinding of teeth, the functional significance of which is not clear, has been
observed in adult males of the Kenya group
when closely threatening each other, as
in harassment sequences.” In another
field study, Jay (’65) designates canine
grinding as an indication of post-aggression subsidence in male langurs. She considers such sounds as meaningful signals
equivalent to other forms of vocalization. A
comparison of these two reports reveals
several differences in substance and interpretation. Jay’s designation of canine
grinding as the agent responsible for the
sounds is supported by the evidence of
dental attrition as set forth above. The
association of these sounds with males is
also consistent with tooth anatomy and
associated wear patterns. Such honing as
does occur in females is not notably associated with grinding noises or aggressive behavior. Hall and DeVore see this activity
as concomitant with aggression in male
baboons, although confessing ignorance as
to its functional significance. Jay associates canine grinding in male langurs with
tension resolution and signaling. To these
can be added a third set of observations by
Grand and Shininger (’68) who filmed the
locomotor behavior in the sizable colony of
Japanese macaques (M. fuscata) at the
Oregon Regional Primate Research Center.
Animals, identified as juvenile males, disturbed by the presence of these observers
reacted with the usual threat manifestations and much loud canine grinding.
The association of tooth grinding with
aggression (Hall and DeVore, ’65); with
fear, anger, and anxiety (Grand and
Shininger, ’68); and with tension resolution (Jay, ’65) parallels human reactions
to a significant degree. It is a matter of
common experience that people respond to
a variety of unpleasant, stressful situations gnathically. Gnashing of the teeth
accompanies feelings of aggression, fear,
pain, and sorrow. Excessive grinding
(bruxism) is associated with severe anxiety
(Nadler, ’57; Thaller, ’60). The chewing
of gum, betel, tobacco, etc., and nail biting
are expediencies for relieving tension. Nor
is the communicative function of tooth
grinding with its aggressive overtones absent in human situations, although much
repressed in Western culture. A moment’s
reflection will confirm the psychological
perspicaciousness of that observer who,
viewing the scene from another time and
place, noted that “The wicked plotteth
against the just, and gnasheth upon him
with his teeth” (Psalm 37, verse 12).
Based upon human and Cercopithecoid
observations, a cause and effect relationship emerges. Granting that the degree
of overt gnathic activity varies in different
species at any one behavioral stage, an
overall cohesive picture emerges. Under
the stimulus of threat, men and monkeys
react psychically by manifesting fear,
anger, and anxiety. These disquieting
emotions are expressed gnathically by tooth
grinding in both groups and by nail biting
and chewing in men. The gnathic expression of tension functions to relieve the
tension in both groups. In Cercopithecidae,
it also functions to hone canine teeth and
the sounds thus produced probably have
a communicative significance. The need
for final resolution of tension may result
in active aggression in both groups. In this
event, canine teeth play a prime role in
Cercopithecoid combat. The efficiency of
canine teeth as weapons and the ability to
maintain these teeth in top condition by
honing are elements that relate directly to
combat performance and as such are probably influenced by rigid selection.
Small canine teeth are characteristic of
both fossil and recent hominids, and it is
doubtful that canine honing has taken
place in these groups since the emergence
of the Hominidae. Hominid attrition as
a concomitant of mastication has other
functions. It serves in the process of occlusal adjustment and in the preservation of
the aging peridontium (Beggs, ’54).
The widely held belief that prehominid
canines were considerably larger than hominid canines is supported by the presence
of primitive traits in recent and fossil
deciduous dentitions and in the permanent dentition of Homo erectus (Von
Koenigswald, ’67). Assuming that this evidence is valid, we can view human tooth
grinding with its highly charged emotional
content as relict behavioral activity that
at one time and for a very long period of
time, had high survival value.
Gregory, W. K. 1916 Studies on the evolution
of the primates. 1. The Cope-Osborn “Theory
of Tritubercyly” and the ancestral molar patterns of the primates. Bull. Mus. Nat. Hist.,
35: 239-257.
1922 The Origin and Evolution of the
Human Dentition. Williams and Wilkins, Baltimore.
Hall, K. R. L., and I. DeVore 1965 Baboon
social behavior. In: Primate Behavior. I. DeVore, ed., Holt, Rinehart and Winston, New
Hornbeck, P. V., and D. R. Swindler 1967
Morphology of the lower fourth premolar of
certain Cercopithecidae. In: Proc. Int. Symp.
Dent. Morph., A. A. Dahlberg, ed. Suppl. J.
Dent. Res., 46: 979-983.
Jay, P. 1965 The common Langur of India.
In: Primate Behavior, I. DeVore, ed. Holt, Rinehart and Winston, New York.
Koenigswald, G. H. R. Von 1967 Evolutionary
trends i n the deciduous molars of the Hominidea. In: Proc. Int. Syrnp. Dent. Morph. A. A.
Dahlberg, ed. Suppl. J. Dent. Res., 46: 779-786.
Kraus, B. S. 1959 Differential calcification rates
i n the human primary dentition. Arch. Oral
Biol., 1 133-144.
Kraus, B. S., and R. E. Jordan 1965 The Human Dentition Before Birth. Lea and Febiger,
Mills, J. R. E. 1955 The ideal dental occlusion
in the primates. Dent. Prctnr. Bristol, 6: 4761.
1964 The dentition of Paramus and
Amphiterium. Proc. Linn. SOC. London, 178,
I am grateful to staff members of the
2: 117-133.
Oregon Regional Primate Research Center
1967 Development of the protocone during the Mesozoic. In: Proc. Inter. Symp. Dent.
for their assistance in preparing the manuMorph., A. A, Dahlberg, ed. Suppl. J. Dent. Res.,
script. Mr. Joel Ito’s skillfully executed
46, 5: 787-791.
illustrations are a valued complement to Nadler,
S. C. 1957 Bruxism, a classification:
the text. I wish to thank Dr. Charles 0.
Critical Review. J. Am. Dent. Assoc., 54: 615622.
Handley, Jr., Curator in Charge, Division of
H. F. 1907 Evolution of Mammalian
Mammals, U. S. National Museum, for his Osborn,
Molar Teeth. W. K. Gregory, ed. The Macmillan
friendly and courteous cooperation. Dr.
Co., New York.
Ashima Valiathan’s able assistance in re- Patterson, B. 1956 Early cretaceous mammals
and the evolution of mammalian molar teeth.
cording observations is gratefully acknowlFieldiana: Geology 13: 1. Chicago Natural Hisedged.
tory Museum.
Reed, 0. M. 1965 Studies on the dentition and
eruption pattern i n the San Antonio baboon
colony. In: The Baboon in Medical Research,
Beggs, P. R. 1954 Stone age man’s dentition.
Vol. 1. H. Vagtborg, ed. University of Texas
Am. J. Orthod., 40: 293-312, 373-383, 462Press, Austin.
Butler, P. M. 1952 The milk molars of the
Remane, A. 1960 Zahne und gebiss. In: Primatologia, Vol. III/2. H. Hofer, A. H. Schultz,
Perissodactyla, with remarks on molar occluD. Starch, eds. S. Karger, Basel.
sion. Proc. Zool. SOC.London, 121: 77-817.
Simpson, G. G. 1945 The principles of classifi1956 The ontogeny of molar pattern.
cation and a classification of mammals. Bull.
Biol. Rev., 31: 30-70.
Am. Mus. Nat. Hist., 85: 66-67.
Butler, P. M., and J. R. E. Mills 1959 A contribution to the odontology of Oreopithecus.
Simpson, G. G., and A. R. Roe 1963 The evoluBull. Brit. Mus., 4, 1: 1-26.
tion of behavior. In: The Behavioral Sciences
Today. B. Berenson, ed., Basic books Inc., New
1967 Dental merism and tooth development. In: Proc. Int. Symp. Dent. Morph. A. A.
Swindler, D. R. 1964 Calcification of deciduous
Dahlberg, ed. Suppl. J. Dent. Res., 46: 845-850.
teeth i n rhesus monkeys. Science, 144, 3623:
Grand, T. I., and E. S. Shininger 1968 Personel
Thaller, J. L. 1960 Use of the Cornell Index
to determine the correlation between bruxism
and the anxiety state: a preliminary report. J.
Periodont., 31: 138-140.
Turner, E. P. 1962 Cusp development i n human deciduous molars: a preliminary report.
J. Dent. Res., 41: 1262.
Vanderbroek, G. 1961 The comparative anatomy of the teeth of lower and non-specialized
mammals. Intern. Colloq. on the evolution of
lower and non-specialized mammals. Kon VL,
Acad. Wetensch. Lett. Sch. Kunsten Belgie,
Zingeser, M. R. 196th Characteristics of the
masticatory system. In: Biology of the Howler
Monkey (Alouatta Caraya). M. R. Malinow, ed.
Bibl. Primat., 7: 141-150, Karger, Basel.
1968b Functional and phylogenetic significance of integrated growth and form in
occluding monkey canine teeth ( Alouatta caraya
and Macaca muhtta). Am. J. Phys. Anthrop.,
28: 263-5470,
Без категории
Размер файла
721 Кб
honing, mechanism, toots, cercopithecoid, canine
Пожаловаться на содержимое документа