Equine Dental Disorders

BEVA Continuing Professional

Development and Client

Education

Prof P M Dixon

The University of Edinburgh

Copyright The University of Edinburgh and The British Equine Veterinary

Association

The horse evolved in the Americas circa 55
million
years ago. Dawn horse (hyracotherium) was a
rabbit
sized animal that browsed on soft leaves had
short
teeth (brachydont) similar to human or canine
teeth

Large intestine of equidae

•

Climatic Changes 55 million
years ago

•

Change of vegetation

•

Development of caecal & colon
microbial digestion of cellulose

•

Enlargement of caecum and
colon

Brachydont teeth of Dawn horse changed
to
Hypsodont (long crowned) teeth to cope
with eating an abrasive grass diet
(contains high levels of silica) for up 18
hours/day

Evolution and migrations of horses

Drawings of wild horses:

Lascaux Caves in France -15,000 years

BC

Horses were only a food source then

First evidence of equine
domestication

Bit-induced cheek teeth damage in a fossil
equine skull dated circa 4000 BC found
near the Black Sea

Signs of Dental Disease in

Horses

•

Many horses will suffer dental disease without showing any

obvious signs of disease

Affected Horses may:

•

Drop partially chewed food (quid)

•

Pack food into cheeks

•

Have poorly digested food present in faeces

•

Have bitting or head carriage problems

•

Suffer weight Loss – only in extreme cases

Quidding food is sign of painful

dental disease

Feeding forage to assess mastication

•

Assess if normal loud crunching sounds are made during
chewing

•

Assess if horse chews with both sides of mouth

•

Assess if quidding or food packing in cheeks occur

“Hamster Like”

Food packing in
cheeks with
painful dental
disease

Painful dental disease

•

Large quantities of undigested grain in
faeces

•

Long and large fibrous particles in faeces

•

Much nourishment not obtained from food

Weight Loss only Occurs with

Longstanding & Severe Dental

Disease

Bitting and Head Carriage

Disorders

•

Disorders around contact areas of Bit, Bridle and
Noseband

•

Large Cheek Teeth Overgrowths that Restrict Jaw Movement

•

Other sharp overgrowths that contact the Cheeks and Tongue

Dental Examination

•

Equine dental examination and treatment cannot be
performed without use of a full mouth speculum (gag)

•

Some horses will need to be sedated for dental
examination

Deciduous Incisors (milk teeth)

Deciduous Incisors (milk teeth)

Erupt at circa

•

01s (Central) 1 week of age

•

02s (Middle) 6 weeks

•

03s (Corner) 6 -9 months

•

(Rule of thumb - 6 days, 6 weeks & 6 months)

Permanent Incisors

Permanent Incisors

Erupt at circa:

•

Central (01s) 2½Years

•

Middle (02s) 3½ Years

•

Corner (03s) 4½ Years

Age-related changes in 301 or

401

incisor appearance

24 years

18 years

12 years

6-7 years

4
years

Labial Aspect

Infundibulum

Secondary dentine (‘star’)

Why ageing

Why ageing

cannot

cannot

be accurate

be accurate

Pulp directly beneath
occlusal surface

Pulp deep beneath
occlusal surface

Deep

infundibulum

Shallow

infundibulum

Aged horse -very worn incisors

Anisognathia

Anisognathia

Maxillary CT Rows are 20-25% (median 23%)

Maxillary CT Rows are 20-25% (median 23%)

further apart than Mandibular CT Rows

further apart than Mandibular CT Rows

Note also the angulated surface of the CT

Note also the angulated surface of the CT

Lateral excursion test

•

Close the jaws and force the lower jaw sideway

•

After 1 cm or so the jaws will be forced apart

•

This is caused by the angulated surface of the upper and lower
cheek teeth coming into contact

OVERJET (upper incisors

rostral)

•

‘Parrot mouth’
‘Overshot jaw’ ‘
Overbite’

•

Rarely causes a problem
grazing

•

Inherited defect ?

Severe Overbite (upper incisors
rostral to and overlying lower
incisors)

Severe 06 and 11 overgrowths

along with “parrot mouth”

Orthodontic Treatment of Foal

with Overjet

Drilling between cheek teeth to fit steel wires
for orthodontic brace

Brace fitted between cheek teeth and
incisors to slow down growth of upper
jaw

Orthodontic treatment of

marked overbite using a wire

brace and acrylic biteplate

Before and after 3 months bracing

– overjet almost fully corrected

Successful Bracing of Overbite in Foal

Underjet

(“Sow Mouth”, “Monkey

Mouth”)

•

‘

Sow mouth’

‘Undershot jaw’ ‘Underbite’

•

Uncommon

•

Incisors clinically
insignificant

•

CT overgrowths occur

•

Surgical correction is
difficult

Retained Deciduous Incisors

•

Usually lie in front of
permanent tooth (arrow)

•

Cause displacement
(caudal) of permanent
tooth

•

If loose, remove with
forceps

•

If firmly attached,
remove with dental
elevators

Full length retained incisor

•

Local anaesthesia of mental nerve

•

Alveolar wall being removed for
extraction

Alveolar Wall Removed on Labial

Aspect of a 5 cm Long, Retained

702

Supernumerary Incisors

•

Develop in addition to the 6
normal permanent adult
incisors

•

Have long ( up to 7cm)
reserve crowns

•

Lie close to reserve crowns
& roots of normal
permanent incisor

•

Usually cause little problem

•

Often best not to remove

Supernumerary Incisor (SI)

causing palatal displacement of

101 and 201 and diastemata

SI

Traumatic complicated (pulp exposed)

fractures of permanent incisors

Fractured 103 (corner incisor)

with exposure of pulp in a

young horse

•

Good candidate for
endodontic treatment

•

a) Remove dead pulp
(arrow)

•

b) Seal off healthy
underlying pulp

•

c) Tooth will continue to
erupt and should come
into wear eventually

Fractured Incisors Receiving

Endodontic (root canal)

Treatment

Different stages of Endodontic

Treatment of a Fractured

Incisor

Traumatic Damage to Upper Incisors

with Overgrowths on Opposing Incisors

Old lower incisor fractures with secondary

overgrowths in opposing incisors

This horse can only chew in one

This horse can only chew in one

direction

direction

Incisor fractures in a “Crib Biter”

Abnormal Incisor Wear in a

Young “Crib Biter”

Young horse with caries of incisor
(210)

•

Dental Caries is uncommon
in Horses

•

May be associated with high
molasses levels in diets

•

Caries is most common in
infundibula of upper cheek
teeth

Must not mistake the normal brown chalky
covering (cement) of many equine teeth as caries

Treatment of incisor caries

Clockwise: Removal of caries, apply acid etching soln, apply
bonding agent & defect filled with a modern composite filling

“Slope” or “Slant” Mouth

•

Indicates the horse has
been chewing in just
one direction

•

Often is sign of a
severe problem with

cheek teeth

•

Diagnose and treat the
cheek teeth problems
first

Reducing sloping incisor overgrowths

after correcting the underlying CT

problems

Reducing incisor overgrowths with

power and manual instruments

Slight “Wry Nose” can cause

abnormal incisor misalignment &

wear

Severe Wry Nose in Foal

•

Wry nose can be corrected in some foals

•

May need extensive nasal surgery also

•

Ethical considerations if foal severely
deformed

Incisor Diastema in an Aged Horse

Causing Food Impaction and Gingivitis

•

There should be no
spaces between the
occlusal surface of
adjacent teeth

•

Narrow spaces can be
most problematic as
they can act like valves
i.e. diastema(ta)
trapping food

Incisor diastemata can be treated by

widening space with diamond coated

disc or a saw blade

Canine Teeth (“Tushes”)

•

Present in male horses

•

Erupt at circa 5 years of
age

Calculus accumulation on

canine (and adjacent incisor)

•

The lower canines are
predisposed to
accumulating calculus

•

Calculus can cause
severe gingivitis of
adjacent gums

•

Remove calculus and
brush canines weekly to
prevent recurrence

Extraction of an infected canine tooth

long reserve crown and roots

(<7.5cm)

“Wolf” Teeth (05s ; 1

st

Premolar)

•

No deciduous precursors

•

Erupt at circa 1 year of age

•

Many lost when 1st upper
deciduous cheek tooth
(“cap”) is shed

•

If of normal small size and in
normal position – can they
cause bitting problems?

Lower Wolf Tooth

•

Lower wolf teeth are uncommon (arrows)

•

They often interfere with bit and are best
extracted

Displaced (rostro-laterally) Wolf tooth
Protruding Towards the Cheeks and
Causing Bitting Problems

Palpating a rostrally displaced
“wolf tooth”

Local anaesthesia and/or Infraorbital

nerve

block for “wolf tooth” extraction

in sedated horses

•

Can involve extensive
elevation of the tooth

•

Considerable injury
can be caused by
unqualified personnel

•

Horses should be
vaccinated against
Tetanus

Wolf tooth extraction

Complete Extraction of Wolf

Teeth with Musgrave-type

Elevator

Fractured Wolf tooth

Attempted extraction can lead to fracture of wolf
tooth
Development of bitting problems not present
previously

Pre and post extraction images of a fractured wolf

tooth

Developmental cheek teeth disorders

•

Retention of deciduous cheek teeth
(“caps”)

•

Diastema(ta)

•

Displacement of cheek teeth rows

•

Supernumerary cheek teeth

Retained ‘Caps’

•

‘Caps’ - the remnants of
deciduous (milk) teeth

•

Normally shed during
eruption of the
underlying permanent
tooth

•

Loose, retained caps can
cause oral pain

Use of Cap extractors to

remove loose retained cap

•

There is

much

variation between horses in the

age at which caps are shed

•

Premature cap removal can damage the

underlying tooth

“Elephants don’t get diastema”

One large tooth in wear - lasts 10 years (x 7
teeth)

Diastema

•

Occlusal surfaces of Cheek Teeth (CT) should be tightly
compressed together

•

Act as one functional grinding surface

•

Angulation of 1st, against 5th & 6th CT compresses CT
row

Cheek Teeth Diastema(ta)

•

Food trapped between CT

•

Will eventually get packed
into periodontal spaces

•

Is the most painful equine
dental disease

•

Difficult to diagnose
– usually caudal, lower CT affected

•

A small diastema can be more
problematic than a large diastema

Open-Mouth
radiography

X-Ray showing 2
diastemata between
Upper cheek teeth

Diastema between 106 and 107

•

Diastemata present between all of lower CT

•

Severe periodontal disease

•

Teeth are angulated reasonably

•

Dental buds developed too far apart

•

This horse was euthanased on humane
grounds

Cheek Teeth Diastemata

Standing sinus surgery to treat
diastema that is allowing food into
sinus

Treatment of Diastema

•

Removal of overgrowths
that develop opposite
diastemata is essential

•

Replace long fibre food e.g. hay with grass, or
short chopped foods e.g. grass or alfalfa cubes can
be successful – also need 2-3 times annual rasping

Removal of impacted food

•

Long handled dental pick

•

High pressure water or air
picks

•

Transient improvement only

Widening a Diastema to prevent
food pocketing

A specialised veterinary
procedure

Widening Diastemata

Danger of opening into pulp of tooth

Danger of overheating adjacent pulp

Careful evaluation of cases and training of personnel
required

Severe 06 and 11 overgrowths

along with “parrot mouth”

Reducing tall overgrowths of (206)
1

st

cheek tooth with power

instrument

Sharp Overgrowths (“Beaks”) of upper
06s causing bitting problems
206 overgrowth has been removed

Caudal lower cheek
teeth overgrowths
(11s) (arrows) are
also common in
parrot mouthed
horses and are
often missed

Cheek Teeth Displacements

•

Developmental

•

Overcrowding of arcades during eruption
–

often bilateral

- Usually 4th and 5th cheek teeth (09s & 10s)
- Medial or lateral displacement
-Rotation of tooth may also be present

•

Acquired

More common

•

Usually lower 10s and 11s

in older horses

Developmental
cheek teeth
displacements
of 409 and 310

Horse with displaced cheek tooth
growing into its cheeks

This horse had a history of being “difficult” on bit and
had “routine treatment” by an unqualified EDT for many
years without detection of this very painful problem

Slight Medial displacement of 310 &
311 with high occlusal angulation
Diastema (D) between 309-310

311

310

D

309

Widespread
dental
displacement in
a geriatric horse
with secondary
diastemata and
overgrowths

Neglected mouth

Cheek Teeth

Displacements

•

Will result in malocclusion and thus
overgrowths and also diastemata and
periodontal disease

TREATMENT

•

Removal of overgrowths every 6 months
with mild displacements and widening of
diastemata

•

Extraction of tooth if severe displacement
and periodontal disease present

Supernumerary CT (Polyodontia)

•

Means more than 6 permanent cheek teeth in a row

•

A caudal (7th) upper CT is most common

•

Supernumerary tooth may be connated (i.e. a double
tooth)

5

5

th

th

6

6

th

th

7

7

th

th

8

8

th

th

Supernumerary CT

•

Malocclusion, overgrowths and periodontal disease can occur

TREATMENT

•

Remove overgrowths

•

If severe periodontal disease present
- extract tooth

Oligodontia

•

Means absence of normal
tooth / teeth

•

True equine oligodontia is rare

•

Absence of teeth in older
horses – (see figure) is
common

•

Results in overgrowths on
opposing CT and drifting of
adjacent CT into vacant space

Oligiodontia – absence of

permanent lower 09s and

11s

Dental overgrowths

(Stepmouth) due to loss of

opposite teeth

Anisognathia

Anisognathia

Maxillary Arcades are spaced 20-25%

Maxillary Arcades are spaced 20-25%

(median 23%) wider apart than Mandibular

(median 23%) wider apart than Mandibular

Arcades

Arcades

Are:

- primarily composed of
enamel

Have:

- minimal dentine

Transverse section of young
equine skull

Young Teeth have:

- large pulp cavities

10

o

35

o

Normal Angulation of CT

CT occlusal angles are usually 10-15 degrees

but can be up to 35 degrees in normal

horses

(Brown 2005)

Initial crushing stroke during

mastication

Crushing
stroke

Resting

Power stroke of mastication

Hay or Grass

Hard Food

Lateral Jaw Movements are

Reduced when Eating Hard Feed

Sites of enamel overgrowths and

Sites of enamel overgrowths and

subsequent trauma from enamel

subsequent trauma from enamel

overgrowths

overgrowths

Enamel overgrowths on mandibular
cheek teeth – can cause
ulceration of the tongue and bitting
problems

Large vertical ridges on lateral edges of
upper cheek teeth are a common site of
enamel overgrowths

Ulcerated cheeks caused by

maxillary CT overgrowths

Sharp enamel ridges causing cheek
ulceration at areas of bridle and
noseband contact - subsequent
bitting problems

Shearmouth

If dental overgrowths are not treated they will eventually

involve all of the occlusal surface- causing abnormal
angulation of over 45 degrees

Wavemouth and Shearmouth

•

Multiple overgrowth disorders are common

•

This horse mainly chews with its normal left side

Smooth Mouth – Old Horse

•

Cheek teeth enamel largely worn away

•

Some teeth worn down to individual roots

•

Softer dentine & cementum become smooth -no good for grinding

•

These horses will need young grass or chopped forage to

maintain weight

Frequency of routine dental
examination and floating (if
necessary) can vary

Age

– Young horse shedding

caps & older horse with some
missing teeth need frequent care

Work

- e.g. dressage

horse check 6 monthly
vs. retired horse,
brood mare
examine >12 monthly

Frequency of routine dental
examination and floating (if
necessary)

Predisposing
abnormalities?

e.g. slight parrot mouth,
neglected overgrowths or a
displaced tooth? Will need
more frequent rasping

Level of concentrates
feeding

e.g. fully outdoors
permanently – may have
little enamel overgrowths
vs. horse fed 5kg of hard
food per day

A variety of shapes and sizes of
rasps are required to float teeth properly

Different rasps – different sites

Motorised dental instruments

Speeds up work
– especially in removing large overgrowths

Dental floating should remove enamel
overgrowths but leave an effective
( i.e. irregular) occlusal surface

Inappropriate power instrument
floating

•

Soft tissue damage and

haemorrhage

•

Excessive removal of

occlusal surface including
dentine

•

Deep exposure of

odontoblast processes –
painful chewing for weeks

•

May expose pulp – apical

infection

Normal Transverse Ridges

Normal Transverse Ridges

Tall (“exaggerated”;

“accentuated”) Transverse

Ridges

•

Will cause abnormal wear of opposite tooth

•

May restrict rostro-caudal mandibular movement

•

Should be reduced to level of other transverse ridges

Fractures of Cheek Teeth and

Supporting Bones

•

Trauma – e.g. kicks from other horses

•

Unskilled operators using dental shears

•

Bit damage

•

“Spontaneous Fractures” - upper cheek

teeth

a) Lateral Slab Fractures
b) Midline infundibular fractures

Trauma – Fracture of Mandible

and Invariably of Cheek Teeth

Severe oro-facial
infection following
iatrogenic damage to
6

th

mandibular C.T.

(311) from dental shears
by untrained operator

Bitting injuries

•

Severe damage can be caused to gingiva,

cheeks, bones and teeth by rough use of bits

•

The bit is made of steel - the mouth of

sensitive tissues!

Bit injury – can lead to severe
damage (sequestration) of
mandible

Repeated Bit damage can eventually cause severe bony
damage to bars of mouth (“polo pony mouth”) and
even to 1

st

cheek teeth

Horses play with drop-down handles in boxes and
then trap their lower jaw
Repaired by wiring the incisors to canine or
cheek teeth

Displaced Fracture of Rostral
Mandible

Lateral “Slab” Fractures of Cheek

Teeth

•

These fractures develop spontaneously

•

Common in the upper cheek teeth especially

4

th

(09)

•

Fracture tends to displace into the cheeks -

painful

Advanced caries of infundibula of
upper cheek teeth

Coalescence of caries

(

Left

)

can lead to midline

fractures of these teeth

Right

- food impacted into fracture will spread out

the
fractured tooth into cheeks and hard
palate

Cheek Tooth extracted because of

midline sagittal fracture caused by

advanced infundibular caries

Severe caries of upper cheek teeth can

be cleaned out (“sandblaster system”)

and filled to help prevent fracture and
apical infection of tooth

Apical (tooth root) infections in
cheek teeth

•

Because of long reserve crowns of equine

cheek teeth – these infections will usually
cause deep infections of the supporting
bones

•

The signs will depend on which tooth and

so which supporting bones are infected

Exposure of the pulp causes
some apical infections

Ventral swelling and excoriation of

the mandible due to apical infection

of a mandibular cheek tooth

– usually develop soon after eruption of tooth

Sinus tract and swelling of ventral

mandible due to cheek teeth

apical infections in young horses

Diagnosis of apical infections requires

radiography of suspect teeth

Some dental
radiographs
can be
difficult to
interpret -
even by
“experts”

Transverse section through rostral skull of

young horse – Infection of 1

st

and 2

nd

maxillary cheek teeth (arrow) cause facial

swelling and possibly tracts externally or into

nasal cavity

Transverse Section through Caudal
Aspect of Young Equine Skull

The last 4 Cheek Teeth lie in the sinuses and
infection of these teeth will cause sinusitis –
difficult and expensive to treat

Dental examination in a horse
with sinusitis -to assess caudal
maxillary CT

Diagnosis of sinusitis may require

endoscopy, radiography,

sinoscopy and scintigraphy

Treatment of Apical Infection

•

Very early cases may respond to prolonged antibiotic
courses

•

Dental Extraction usually required by:
- Oral Extraction
- Repulsion
- Buccotomy

•

Endodontic (Root canal treatment)
– poor success to date

Repulsion of infected cheek tooth
under general anaesthesia

Intra-operative X-rays being taken to ensure
the right tooth is repulsed

Left

- infected tooth being punched into oral

cavity

Right

- mandibular wound being partly sutured

after tooth repulsed

Repulsion of cheek Teeth

•

Teeth are often fragmented
during repulsion

•

Many cases will need
further treatment

Dental wax or bone cement plugs
are placed into empty alveolus
following dental repulsion

Oro-mandibular fistula
following dental repulsion

An incision is made through the cheeks to gain
access to the teeth – risk of nerve and parotid
duct damage

Buccotomy dental extraction

•

An old-fashioned method recently re-introduced

Oral extraction of cheek
teeth

•

general anaesthesia not required

•

reduced level of post-operative problems

•

wide range of instruments and good technique

required

Use of “molar” Separators

During Oral Extraction of 107

Oral Extraction of 107 in 6 yo horse

– Fulcrum being used on a well–loosened tooth

Successful Oral Extraction in
Young Horses

Left:

Mandibular CT partly elevated prior to

extraction

Right:

10cm long upper cheek tooth orally extracted

in a 5yo

Endodontic Treatment of Apical
Infection – Limited Success to
Date

Over 500 BEVA Members have
attended postgraduate courses on
equine dentistry in the
last 8 years