a)
MOLAR EXTRACTION IN HORSES
Josep Subirana,
MRCVS.
INTRODUCTION
Oral
extraction of equine teeth on standing horses under sedation and using local anaesthesia
avoids the risks associated with general anaesthesia and repulsion
techniques. The procedure allows the
horse to recover faster and post operative complications are less common and of
minor importance. This compares favourably to the repulsion technique that can
compromise the integrity and function of structures associated with the teeth
as well as having a poor cosmetic result.
Due
to the nature of horse’s teeth, young horses normally require major diagnostical and therapeutical
intervention, their problems normally being linked to apical abscess, although
other abnormalities may be found.
INDICATIONS
Extraction of any diseased, loose or infected molar
that causes problems to the horse’s health. Oral extraction should be the first option
and attempted under the right conditions. Before undertaking the procedure,
different factors must be considered such as horse’s health, age, behaviour,
accessibility, other mouth problems, position of the molar in the arcade, size
of the exposed crown, possible osteitis, or sagital fractures affecting the molar.
DIAGNOSIS
Horses may show bone tumefaction, nasal discharge, fistula, halitosis, disphagia, intraoral evidences, pain related signs. When the affected
molar is not intraorally obvious (normally in young horses), the diagnosis must be established radiologicaly.
The most significant views are the lateral 30º dorso-lateral
view for the maxilla and the lateral 45º ventro-lateral
for the mandible, although all standard views must be taken to identify the
affected tooth satisfactorily. X-ray must compare both arcades to identify
differences. In case of bone tumefaction or fistula, a metallic guide may be
useful.
Other diagnostic methods that may be indicated are endoscopy,
CT and MRI scan and visual observation after exploratory trepanation.
PATOGENY
Food
impaction, periodontal disease, cavities, pulp exposure, diastemas,
molar fractures and endogenous infections may lead to a decayed molar or to an
apical abscess.
All
the affections present primary or secondary bacterial implication. Apical
Abscesses show preponderance
of anaerobic gram-negative where the most common are Fusobacterium
spp. And Prevotella
spp.
Once the infection is established and
depending on the age of the horse which affects interaction between the teeth, bone,
sinuses and other structures, the horse will be prompt to show different signs.
Young horses, due to the length and nature
of the teeth, will tend to suffer more
severe clinical signs such as osteitis, fistulas or
sinusitis, where root abscess and pulp cavity infection are common and
periodontal diseases more rare, except when diastemas
or molar fractures are found .
Older horses tend to show intraoral evidences with important periodontal implications.
TECHNIQUE
FOR ORAL EXTRACTION ON STANDING HORSES
Horses
must be properly restrained in a safe environment. Horses are sedated with
alpha-2 agonist in combination with opioids followed
by the pertinent nerve block; nonsteroidal anti-inflamatory drugs are indicated before and after the
procedure.
In
order to perform an optimal molar extraction, it is necessary to block the
Trigeminal Nerve (5th Cranial Nerve) in its mandibular
or maxillary branch. The maxillary branch is blocked in the maxillary foramen
using two possible approaches.
The
first possible access to the maxillary foramens is between the mandible and the
zygomatic bone; a 19-22 gauge spinal needle is
inserted perpendicularly 5-7 cm in depth and between 20 and 30 ml of lidocaine 2% injected.
The second possible approach is through
the supraobital foramen; a 19-22 gauge spinal needle
is introduced into the highest point of the zigomatic
arch, in the direction of the round foramen.
The
anaesthesia takes at least 10 minutes to work well and the effects last for 2-4
hours, the eye normally protrudes for several hours due to the relaxation of
the muscles of the orbit. Epiphora may be present for
few days.
An infraorbital
foramen block can be used when dealing with premolars. A 22 gauge spinal needle
is introduced following the infraorbital canal and 10
ml of lidocaine 2% injected. The technique can be
very painful and traumatic. It is not useful for molars as the needle must be
introduced too deeply.
The mandibular
foramen block is performed inserting a 19-22 gauge spinal needle in the back
edge of the mandible, running parallel to the medial surface of the mandible
towards the mandibular foramen where 20 ml. of lidocaine 2% are
injected accomplishing a 1-3 hours lasting block after 10 minutes
A mental foramen block can be attempted
but with similar problems presented in the infraorbital
foramen approach. Because it is impossible to advance the needle to any extent,
the procedure is only useful to block the incisors.
The gingiva surrounding the affected tooth must be elevated and
a dental pick is forced and then slid between the tooth and the adjacent bone, breaking
as much periodontal ligament as possible. Different sizes and lengths of picks
are used for this purpose being easier to accomplish in the lower arcade molars
due to its morphology.
Molar
spreaders are used
alternately in the caudal and rostral interdental space. Once positioned, they may be rotated or
left in position in order to increase the destruction of the periodontal
ligament and slightly increase the alveolus tolerance.
If
the molar for extraction is a 107, 207, 307 or 407, the spreaders must not be
placed between this and the 6´s, otherwise iatrogenic
damage of the 6’s could be caused.
The
most suitable molar forceps are placed on the crown and moved in a lingual to bucal direction as well as in a semicircular direction.
It
is important not to force the movements excessively as the root may brake or
the crown deteriorate making impossible to continue with the procedure.
In
the event of a root or sagital fracture, long picks
are used to remove remnants and if necessary the alveolus is curated. Once the socket is free of any dental structure,
it is necessary to clean and irrigate it and subsequently pack it in all young
horses.
Old
horses with a shallow alveolus are normally not packed. Special attention must
be given if the maxillary sinuses have been affected in order to prevent
communication between the sinus and the oral cavity. The alveolus are
packed with dental wax or with cold curing polymethymethacrylate,
especially when the sinuses have been compromised.
Packing
material is generally pushed out for the granulation tissue, in very deep
sockets it may be necessary to use roll
gauze as a temporally pack for the
mandible alveolus that tends to accumulate food.
When
sinusitis is involved, lavage of the sinus and
placement of the packing material are indicated. The horse may require a
trepanation in the affected sinus and a drip set connected to it in order to
irrigate the sinus until the sinusitis is resolved.
POST-OPERATIVE CARE
Nonsteroidal anti-inflammatory drugs are administered
IV before the tooth is removed and for a few days after. Antimicrobial drugs
are required depending on the depth of the alveolus and on the degree of
infection and structures affected. Antibiotherapy is
indicated before starting the procedure. Trimethoprim-sulfadiazine
and metronidazole are used as first election
antibiotics.
The horse’s mouth must be examined
post-operatively as appropriate. The alveolus or plug and adjacent structures
must be checked and signs of sinusitis or infection detected.
COMPLICATIONS
Damage
of the oral cavity is normally a minor problem. When osteitis
is been established for a long period, it may affect the resistance of the bone
to possible fractures, especially in young horses.
The
inability to remove the affected tooth is the main problem; it can be caused by
a tooth fracture or due to erosion and wearing on the external crown, making a
correct grip impossible. Some teeth conditions, especially cementomas,
where the root is wider than the crown, can interfere in the extraction.
Alveolar
plugs may become loose and the alveolus may be packed with food. Sinusitis may
be present due to fistulas, to remaining dental sequestrum
or to food and other infected or necrotic material.
REFERENCES
Baker
G.J, Easley J. A. Equine dentistry. Saunders 2005.
Lumb and Jones,
Williams and Wilkins, Veterinary Anaesthesia, 1996
Fin S.
T, Park R. D. Radiology of the nasal cavity and paranasal
sinuses in the horse, proceedings