Morfometria mandibular aplicada ao bloqueio anestésico para o Lobo Guará (Chrysocyon brachyurus).

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MANDIBULAR MORPHOMETRY APPLIED TO
ANESTHETIC BLOCKAGE IN THE MANED WOLF
(CHRYSOCYON BRACHYURUS)
Author(s): Paulo de Souza Junior, D.V.M., M.Sc., Flavio Machado de Moraes,
D.V.M., M.Sc., Natan da Cruz de Carvalho, D.V.M., Evandro Alves Canelo,
D.V.M., Roberto Thiesen, D.V.M., Ph.D., and André Luiz Quagliatto Santos,
D.V.M., Ph.D.
Source: Journal of Zoo and Wildlife Medicine, 47(1):91-97.
Published By: American Association of Zoo Veterinarians
DOI: http://dx.doi.org/10.1638/2015-0092.1
URL: http://www.bioone.org/doi/full/10.1638/2015-0092.1
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Journal of Zoo and Wildlife Medicine 47(1): 91–97, 2016
Copyright 2016 by American Association of Zoo Veterinarians
MANDIBULAR MORPHOMETRYAPPLIED TO ANESTHETIC
BLOCKAGE IN THEMANEDWOLF (CHRYSOCYON BRACHYURUS)
Paulo de Souza Junior, D.V.M., M.Sc., Flavio Machado de Moraes, D.V.M., M.Sc., Natan da Cruz de
Carvalho, D.V.M., Evandro Alves Canelo, D.V.M., Roberto Thiesen, D.V.M., Ph.D., and Andre´ Luiz
Quagliatto Santos, D.V.M., Ph.D.
Abstract: Chrysocyon brachyurus (maned wolf) is the biggest South American canid and has a high frequency of
dental injuries, both in the wild and in captivity. Thus, veterinary procedures are necessary to preserve the feeding
capacity of hundreds of captive specimens worldwide. The aim of this study was to investigate the mandibular
morphometry of the maned wolf with emphasis on the establishment of anatomic references for anesthetic block
of the inferior alveolar and mental nerves. Therefore, 16 measurements in 22 mandibles of C. brachyurus adults
were taken. For extraoral block of the inferior alveolar nerve at the level of the mandibular foramen, the needle
should be advanced close to the medial face of the mandibular ramus for 11.4 mm perpendicular to the palpable
concavity. In another extraoral approach, the needle may be introduced for 30.4 mm from the angular process at a
20–258 angle to the ventral margin. For blocking only the mental nerve, the needle should be inserted for 10 mm
from ventral border, close to the labial surface of the mandibular body, at the level of the lower first premolar. The
mandibular foramen showed similar position, size, and symmetry in the maned wolf specimens examined.
Comparison of the data observed here with those available for other carnivores indicates the need to determine
these anatomic references specifically for each species.
Key words: Chrysocyon brachyurus, mandible, maned wolf, morphometry.
INTRODUCTION
The maned wolf (Chrysocyon brachyurus) is the
largest wild canid in South America, with Brazil
accounting for 90% of the population.4 Despite
this wide dispersion, it is one of the least-studied
canids.15 In recent years there has been a drastic
reduction of the population in the southern
Brazilian state of Rio Grande do Sul while the
species range has expanded because the Atlantic
Forest areas have been cleared for agriculture.4
The maned wolf measures between 95 and 115 cm
in length (plus tail length of 38–50 cm) and weighs
between 20–30 kg.4 This wolf stands out from
other canids for its peculiar reddish-orange coat,
long ears, and long and slender legs.15 Despite its
relatively large size, its eating habits are omnivo-
rous, with a diet based on fruits and small
vertebrates.5,21
Oral lesions have a variable impact on wild
populations and some investigations suggest this
limits wolves’ lifetime.12,13,24 Dental treatment is
frequently given to carnivores maintained in
captivity as part of routine preventive care.28
Traumas with exposure of the pulp and conse-
quent mandibular fistulas are common, resulting
from fights with other animals, collisions with
fences and concrete obstacles, or stress from
capture.28 Therefore, procedures to preserve the
dentition and occlusion are important to assure
integrity of the chewing ability and adequate food
intake.18
In the particular case of the maned wolf,
Furtado et al. (2007)10 found that 63% of wild
animals captured had dental injuries. A more
comprehensive study determined that stomato-
gnathic lesions are very frequent in maned wolves
both in the wild and captivity, with dental wear
and fractures causing pulp exposure being the
main injuries.17
The mandibular foramen of carnivores is locat-
ed on the medial face of the mandibular ramus
and corresponds to the caudal opening of the
mandibular canal. The inferior alveolar artery,
vein, and nerve pass through this canal. The
inferior alveolar nerve supplies sensory nerves
to the molars, caudal premolars, and surrounding
gingiva, also called the inferior dental plexus. On
the labial face of the rostral region of the
mandibular body, the nerves leave the canal
From the Animal Anatomy Laboratory, Federal Univer-
sity of Pampa (UNIPAMPA), BR 472, Km 592, 97500-970,
Uruguaiana, RS, Brazil (Souza Junior, Carvalho); the
Presidente Antoˆnio Carlos University (UNIPAC), Bara˜o
de Camargo Street, 695, 38400-000, Uberlaˆndia, MG, Brazil
(Moraes); the Federal University of Uberlaˆndia (UFU),
Amazonas Avenue, 2245, 38405-302, Uberlaˆndia, MG,
Brazil (Canelo, Santos); and the Veterinary Teaching
Hospital, UNIPAMPA, BR 472, Km 592, 97500-970,
Uruguaiana, RS, Brazil (Thiesen). Correspondence should be
directed to Dr. Souza Junior (paulosouza@unipampa.edu.br).
91
through the mental foramina and give rise to the
mental nerves, which provide sensorial branches
to the lower lip and rostral intermandibular
region.6,9
A regional block of the inferior alveolar nerve is
efficient to anesthetize all the lower teeth and
ipsilateral soft tissues and can be done by an
extraoral or intraoral technique in domestic
dogs.8,11 Mental nerve block generally provides
analgesia to the rostral premolar, canine, and
incisor teeth, and to the rostral area of the lower
lip.3 The area anesthetized depends on local
anesthetic caudal diffusion within the canal.3 Both
block types have several advantages such as
providing local analgesia, enhancing the effect of
systemic narcotics, and reducing inhalation anes-
thetic requirement, besides being inexpensive and
easy to execute.2
Because of the relevance of the species and the
high occurrence of dental injuries, the aim of this
study was to investigate the mandibular mor-
phometry of C. brachyurus with emphasis on
determining the anatomic references for anesthet-
ic block of the inferior alveolar and mental nerves.
MATERIALS AND METHODS
Mandibles from 11 adult male specimens of C.
brachyurus were used. The cadavers had been
collected on highways in the ‘‘Triaˆngulo Mineiro’’
region of the state of Minas Gerias, Brazil (under
cooperation agreement 002/2011 between Uber-
laˆndia Federal University [UFU] and the national
environmental agency Instituto Brasileiro do
Meio Ambiente E DosRecursos Naturais Reno-
va´veis [IBAMA]). The specimens were main-
tained in the collection of the Wild Animal
Education and Research Laboratory (LAPAS) of
UFU. The mandibles were prepared for analysis
with detachment of the temporal bone followed
by scraping of surrounding soft tissues. Then the
mandibles were soaked in hot water (1008C) for 1
hr to clean the bones. Finally, the bones were
whitened by immersion in a 130 volume solution
of hydrogen peroxide for 3 hr.
After being cleaned and bleached, the mandi-
bles were inspected for shape (FMM). Emphasis
was given to comparison with the domestic dog
and the presence of anomalies. Then, 15 mea-
surements (Fig. 1) were performed by a single
person (PSJ), in duplicate, with an Amatoolst
precision digital pachymeter (Amatools Ltda.,
City of Piracicaba, State of Sa˜o Paulo, Brazil,
Postal Code 13420-835), resolution 0.01 mm,
accuracy 6 0.02 mm). The measures for total
length (TL), length of the alveolar processes from
the third molar to first premolar (LMP), length of
the molar row (LM), thickness of mandible body
below the first inferior molar (MT), and height of
the vertical ramus (HVR) were performed as
indicated by Von-Den-Driesch (1976),27 and the
distances between mandibular foramen and ven-
tral border (MFVB), mandibular foramen and
angular process (MFANG), mandibular foramen
and condylar process (MFCOND), mandibular
foramen and coronoid process (MFCOR), and
transversal axis of the mandibular body (TAM)
were adapted from the work of Barroso et al.
(2009).1 The following measures were conceived
for this study: diagonal distance between the
mandibular and mental foramina (DMM), dorso-
ventral diameter of the mandibular foramen
(DMDF), dorsoventral diameter of the principal
mental foramen (DMNF), distance between the
rostral border of the mandibular foramen and the
most rostral point of the intermandibular suture
(MFINF), and the distance between the mental
foramen and ventral border of the mandible
(MNFBV).
The data were tabulated in spreadsheets and the
following statistical analyses were performed with
the BioEstat 5.3t software (Mamiraua´ Institute,
City of Tefe´, State of Amazonas, Brazil, Postal
code 69553-225): calculation of descriptive statis-
tics (arithmetic mean, standard deviation, coeffi-
cient of variation); a student unpaired t-test for
antimeric comparison (P , 0.05); and a Pearson
pairwise linear correlation of the 17 metrics (P ,
0.05). The nomenclature adopted is in accordance
with the Nomina Anatomica Veterinaria.14
RESULTS
The mandibular foramen of C. brachyurus is
located on the medial surface of the ramus of the
mandible at distances of 11.4 6 0.8 mm from the
ventral border of the mandible, 30.4 6 1.8 mm
from the angular process, 33.5 6 2.1 mm from the
condyloid process, 54.6 6 2.8 mm from the caudal
end of the coronoid process, and 142.5 6 5.5 mm
from the intermandibular suture (Table 1); it has
diameter of 4.1 6 0.3 mm. The caudal third of the
ventral border of the mandibular body has a
nonarticular depression that coincides with the
mandibular foramen in the transversal plane.
All the mandibles presented a (small) rostral
mental foramen, another middle foramen (main,
larger), and a variable number of caudal mental
foramina (accessory, small). The most-rostral
mental foramen (near the intermandibular suture)
was located ventrally to the alveolus of I2 in 18
92 JOURNAL OF ZOO AND WILDLIFE MEDICINE
mandibles (81.9%), of I1 in 3 (13.6%), and of I3 in
1 mandible (4.5%).
In 16 mandibles (72.7%), the middle mental
foramen was ventrally located between the lower
premolar tooth (P1); in 5 (22.8%) it was located
ventrally between P1 and P2; and in only 1 (4.5%)
it was situated ventrally between the C1 and P1
(Fig. 2). That foramen had a diameter of 2.9 6 0.4
mm and was located 10.0 6 0.7 mm from the
ventral border of the mandible.
A total of 30 caudal mental foramens were
identified on the labial surface of the body of the
mandibles (mean of 1.4/ mandible): 1 (3.3%)
located ventrally to the interalveolar space be-
tween P1 and P2, 10 (33.3%) between P2 and P3, 5
(16.7%) ventrally to the alveolus of C1, 1 (3.3%) of
P1, 3 (10.0%) of P2, 8 (26.7%) of P3, and 2 (6.7%) of
P4.
The intermandibular articular surface was
mainly flat with only discrete rough spots. The
angular process was pointed. In four mandibles,
discrete proliferative irregularities were observed
at the ventral border, on the medial face, or both.
Two right mandibles (9.1%) did not have forma-
tion or eruption of the third lower molar (M3).
None of the 15 measures showed variation
between antimers (Table 1) according to the t-test
(P, 0.05). The measures that presented moderate
to strong and significant linear correlation (P ,
0.05) are shown in Table 2.
Figure 1. Photomicrographs of the right hemimandible of an adult male C. brachyurus in (A) lateral, (B)
medial, and (C) dorsal views, depicting the measurement points used. Scale bar ¼ 1 cm.
SOUZA JUNIOR ET AL.—MANDIBULAR MORPHOMETRY IN CHRYSOCYON BRACHYURUS 93
DISCUSSION
Determination of anatomic references for an-
esthetic block of the inferior alveolar and mental
nerves is fundamental for the technique’s efficacy.
The benefits of this block are even more impor-
tant in wild canids due to the difficulty of
administering drugs, the high frequency of jaw
and tooth fractures, and the fact the animals are
often debilitated from their injuries.18,19 Injuries
suffered in zoo enclosures and by collisions with
vehicles on highways are the main reasons for
veterinary care of C. brachyurus.7
With respect to an extraoral anesthetic block of
the inferior alveolar nerve at the level of the
mandibular foramen, our findings indicate that
the needle should be introduced perpendicularly
and dorsally from the depression in the caudal
third of the mandibular body, close to the lingual
surface of the bone. It should be advanced about
11.4 mm from this point so that the anesthetic can
be applied in a region with greater probability of
blocking the nerve. Beckman (2002)2 also indicate
the depression of the ventral border of the
mandible should be used as a reference point to
introduce the needle for extraoral block of the
inferior alveolar nerve in domestic dogs, unlike
the observation of Souza Junior et al. (2013)23 for
Cerdocyon thous.
The distance that the needle needs to be
advanced (11.4 mm) is slightly less than that
indicated for C. thous (12.5 mm) by Souza Junior
et al. (2013).23 Paradoxically, C. brachyurus has
four times the body mass and twice the cranial
length of C. thous. In domestic cats, the needle
should be advanced 4.2 mm according to Barroso
et al. (2009).1 Those findings reveal that the
position in relation to the mandibular foramen
can vary widely between species of the same
order. Therefore, this should not be estimated just
by considering the size of the animal or its head.
Instead, it is necessary to obtain precise data for
each species.
Blocking the inferior alveolar nerve is the most-
frequent regional anesthetic technique in human
dentistry, but the failure rate is still high (15–
20%).20,25 These failures happen mainly due to
inaccuracy in the anatomic location of the man-
dibular foramen.16,25 Therefore, it is reasonable to
suppose that extrapolation of anatomic references
between different species (domestic and wild
dogs) leads to a high rate of failures in practice.
The angular process is also reported as a
reference point for insertion of the needle to
extraoral block of the inferior alveolar nerve in
domestic dogs by Eggerand Love (2009).8 On the
technique, the needle is inserted extraorally and
advanced toward the mandibular foramen.3 In the
case of C. brachyurus, the results of this study
allow us to suggest that the needle should be
introduced from the angular process, close to the
lingual surface and at an angle of 20–258 to the
ventral border of the mandibular body, and
advanced for 30 mm.
With respect to the morphometry of the man-
dibular foramen, it was possible to point out that:
1) its diameter and distances in relation to the
anatomic references had a very low coefficient of
variation (,10%); 2) there was no variation of its
diameter or distance between antimers; and 3) the
tests indicated moderate or strong positive and
significant correlations with various mandibular
metrics. These findings reflect the fact that the
Table 1. Morphometric results of the left and right
mandibles (n¼22) of Chrysocyon brachyurus. Arithmetic
mean X¯), standard deviation (r), coefficient of variation
(CV), and P-value of the t-test comparing the means
between antimers. r . 0.7 ¼ strong correlation; 0.3 , r
, 0.7 ¼moderate correlation.
Measuresa X¯ 6 r (mm) CV (%) P-value
HVR 64.9 6 0.5 4.2 0.93
LM 41.2 6 2.2 5.3 0.89
LMP 89.6 6 2.4 2.7 0.96
TL 175.3 6 5.2 2.9 0.89
DMM 112.1 6 2.7 2.4 0.27
DMDF 4.1 6 0.3 8.4 0.48
DMNF 2.9 6 0.4 14.5 0.99
MT 10.0 6 0.5 5.2 0.95
TAM 23.6 6 1.3 5.7 0.67
MFANG 30.4 6 1.8 5.9 0.91
MFVB 11.4 6 0.8 7.2 0.30
MFCOND 33.5 6 2.1 6.2 0.37
MFCOR 54.6 6 2.8 5.2 0.95
MFINF 142.5 6 5.5 3.8 0.26
MNFBV 10.0 6 0.7 7.5 0.83
a HVR ¼ height of the vertical ramus; LM ¼ length of the
molar row; LMP ¼ length of the alveolar processes from the
third molar to first premolar; TL ¼ total length; DMM ¼
diagonal distance between the mandibular and mental foram-
ina; DMDF ¼ dorsoventral diameter of the mandibular
foramen; DMNF ¼ dorsoventral diameter of the principal
mental foramen; MT ¼ thickness of mandible body below the
first inferior molar; TAM¼ transversal axis of the mandibular
body; MFANG ¼ distance between mandibular foramen and
angular process; MFVB ¼ distance between mandibular
foramen and ventral border; MFCOND ¼ distance between
mandibular foramen and condilar process; MFCOR¼distance
between mandibular foramen and coronoid process; MFINF¼
distance between the rostral border of the mandibular foramen
and the most rostral point of the intermandibular suture;
MNFBV ¼ distance between the mental foramen and ventral
border of the mandible.
94 JOURNAL OF ZOO AND WILDLIFE MEDICINE
mandibular foramen showed constant position,
size, and symmetry in C. brachyurus, evidencing
that the measures reported here are reliable for
anesthetic block of the inferior alveolar nerve.
For block of the mental nerve of C. brachyurus,
we recommend that the needle be inserted 10 mm
from the ventral border of the mandible, close to
the labial surface, at the level of the first lower
premolar. For domestic dogs, Beckman (2002)2
indicates the reference for insertion of the needle
is at the level of the diastema between the first and
second lower premolars while Egger and Love
(2009)8 urge insertion of the needle ventrally at
the level of the canine tooth. These references for
the domestic dog are not suitable for the majority
of C. brachyurus specimens examined in this study,
corresponding to only 22.8 and 4.5% of the
mandibles analyzed, respectively. This strength-
ens the need for specific studies to provide
support for the technique of blocking the mental
nerve for each species. Furthermore, it is imper-
ative to palpate both foramina (mandibular and
mental) to better accomplish these two nerve
blocks effectively.
The diameter of the mental foramen was the
metric with highest coefficient of variation in this
study (14.5%). This can be explained by the
variation in the number, size, and position of the
caudal mental foramina.
According to Furtado et al. (2007),10 dental
traumas to the mandibular arch of free-living C.
brachyurus occur in the incisors (36.3%), canines
(45.5%), and premolars (18.2%). This proves the
potential benefit of anesthetic blockof the inferior
alveolar and mental nerves in this species because
Figure 2. Schematic representation of the lateral surface of the body of the right hemimandible of an adult C.
brachyurus showing the percentage distribution of the occurrence points of the medium mental foramens in (A)
and accessory caudal foramens in (B). c¼ canine; p1¼ first premolar; p2¼ second premolar; p3¼ third premolar;
p4 ¼ fourth premolar; m1 ¼ first molar; m2 ¼ second molar; m3 ¼ third molar.
SOUZA JUNIOR ET AL.—MANDIBULAR MORPHOMETRY IN CHRYSOCYON BRACHYURUS 95
these nerves provide sensitivity to the affected
teeth.
The measures for MT (10.0 6 0.5 mm) and
TAM (23.6 6 1.3 mm) reveal that the mandible of
C. brachyurus has typical traits of the subfamily
Caninae, i.e., a smaller and narrower mandibular
body when compared to the family Canidae.
These measures fit a long and delicate row of
premolars,26 compatible with an omnivorous diet
based on fruits and small to medium vertebrates.21
The pointed angular process, in the shape of a
hook turned dorsally, was another synapomorphic
trait of the subfamily Caninae recognized in C.
brachyurus.26 This pointed shape can facilitate
palpation and use of the angular process as an
anatomic reference for anesthetic block of the
inferior alveolar nerve. This format differs from
that reported by Souza Junior et al. (2013)23 for
the canid C. thous. The subangular lobe, identified
by Huxley (1880)13 for broader insertion of the
digastric muscle in some canids, was not recog-
nized in C. brachyurus. The fibrous filling of the
intermandibular suture of the maned wolf should
allow some flexibility, which has also been report-
ed for the domestic dog.22
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Table 2. Measures of the left and right mandibles
of C. brachyurus (n ¼ 22) that presented significant
pairwise linear correlation (P , 0.05) according to the
Pearson correlation coefficient (r).
Correlated measuresa r P-value
HVR 3 MFCOR 0.89 ,0.0001
TL 3 HVR 0.79 ,0.0001
TL 3 TAM 0.77 ,0.0001
HVR 3 TAM 0.76 ,0.0001
TL 3MFCOR 0.69 0.0004
MFANG 3 MFCOR 0.68 0.0004
TL 3MFCOND 0.67 0.0006
TL 3MT 0.66 0.0007
LMP 3 DMM 0.66 0.0008
MFCOR 3 TAM 0.66 0.0009
HVR 3 MFANG 0.64 0.0014
TL 3 LMP 0.62 0.0020
TL 3MFANG 0.62 0.0022
MT 3 TAM0.60 0.0031
MFANG 3 TAM 0.59 0.0036
TL 3 DMM 0.59 0.0037
MFANG 3 MFCOND 0.58 0.0044
LMP 3 MFANG 0.58 0.0046
MT 3 MFANG 0.58 0.0049
MFCOND 3 TAM 0.57 0.0057
LMP 3 TAM 0.56 0.0067
MFCOND 3 MFCOR 0.54 0.0093
MT 3 MFCOND 0.53 0.0112
LMP 3 MT 0.53 0.0113
HVR 3 MFCOND 0.49 0.0198
LMP 3 MFVB 0.48 0.0228
MT 3 MFCOR 0.47 0.0261
MT 3 DMM 0.47 0.0270
LM 3MFVB 0.46 0.0302
LMP 3 LM 0.46 0.0323
MFINF 3MFVB 0.46 0.0325
MT 3 HVR 0.45 0.0350
LMP 3 HVR 0.44 0.0385
LM 3 DMM 0.44 0.0398
MT 3 MFVB 0.43 0.0439
a DMDF ¼ dorsoventral diameter of the mandibular fora-
men; DMM ¼ diagonal distance between the mandibular and
mental foramina; DMNF ¼ dorsoventral diameter of the
principal mental foramen; HVR¼height of the vertical ramus;
LM ¼ length of the molar row; LMP ¼ length of the alveolar
processes from the third molar to first premolar; MFANG ¼
distance between mandibular foramen and angular process;
MFCOND ¼ distance between mandibular foramen and
condilar process; MFCOR ¼ distance between mandibular
foramen and coronoid process; MFINF¼distance between the
rostral border of the mandibular foramen and the most rostral
point of the intermandibular suture; MFVB ¼ between
mandibular foramen and ventral border; MNFBV ¼ distance
between the mental foramen and ventral border of the
mandible; MT ¼ thickness of mandible body below the first
inferior molar; TAM ¼ transversal axis of the mandibular
body; TL ¼ total length.
96 JOURNAL OF ZOO AND WILDLIFE MEDICINE
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Received for publication 21 May 2015
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