Equis ISSN 2398-2977

Teeth: abnormal wear

Contributor(s): Gordon Baker, Jack Easley, Jill Richardson, Vetstream Ltd

Introduction

  • Abnormal wear results in irregularities to the occlusal surface of dental arcades.
  • Cause: missing teeth, enamel pathology, abnormal occlusal movements, malocclusion or malalignment of teeth , diet, behavioral problems.
  • Signs: depends on severity. Varies from asymptomatic to refusing food, quidding and weight loss.
  • Presentation: sharp enamel points, wave mouth, step mouth, hooks at the ends of the molar arcades, shear mouth, excessive transverse ridges.
  • Diagnosis: oral examination, radiography.
  • Treatment: dental care, diet change, management of behavioral vices.
  • Prognosis: good.

Pathogenesis

Etiology

  • Excessive concentrate portion of ration relative to forage, so that there is decreased daily 'chewing time', and increased vertical relative to lateral chewing motion.
  • Developmental disorders:
    • Rostral displacement of the maxillary arcade.
    • Unequal lengths of cheek teeth rows   →   areas without occlusal contact.
    • Dental displacement   →   eruption of cheek teeth in medial/lateral/rotated or abnormal positions.
    • Supernumerary cheek teeth, ie 7th cheek tooth   →   areas without occlusal contact.
    • Oligodontia (reduced number of teeth) - very rare.
    • Diastema   →   food compression in gaps plus transverse overgrowths.
  • Acquired dental disorders:
    • Lost cheek tooth.
    • Tooth fracture.
    • Unilateral oral discomfort, eg deep periodontal food pocketing, soft tissue trauma   →   horse favors opposite side for chewing.
    • Senility   →   total wear of reserve crown   →   smooth mouth.

Predisposing factors

General
  • Poor routine care (rasping) of teeth   Teeth: rasping (floating)  .
  • Increasing age.
  • Dental malocclusion (genetic, traumatic, developmental).
  • Diet.

Pathophysiology

  • Missing teeth:
  • Sharp enamel points:
    • Occurs in almost all horses at some stage.
    • Along lingual edges of lower arcades and buccal edges of upper arcades.
    • Hooks form on first maxillary cheek tooth (second premolar) and last mandibular cheek tooth (third premolar) due to slight caudal retraction of mandible during mastication.
    • Hooks (supra-eruptions) also due to age-related changes in length of upper and lower cheek teeth arcades, and developmental disorders, eg diastema, supernumary cheek teeth.
  • Wave mouth:
    • Changes in the shape and position of the normal transverse ridges across the occlusal surfaces. Seen most often in older horses when the upper 1st and 2nd molars begin to show excessive wear or infundibular decay and the opposite lower grinders elongate causing a hump in the center of the lower arcade.
    • Arcades take on a 'wave-like' pattern.
  • Step mouth:
    • Gross variation in the height of adjacent teeth, usually due to missing or damaged opposing teeth.
  • Shear mouth:
    • Steep bevel develops across the occlusal surface of cheek teeth.
    • Is caused by limited lateral jaw motion during mastication.
    • Prohibits normal lateral movement of mandible during mastication.
    • Resulting dorso-ventral movements of mandible cause a scissor (or shearing) action.
  • Abnormal incisor wear:
    • Behavioral problems, eg crib-biting   Behavior: crib-biting and wind-sucking    Teeth: uneven wear 01 - cribbiter    Teeth: uneven wear 02 - wallgrinder  wears the incisors excessively.
    • Rostral occlusal surfaces eventually fail to appose.
    • Incisor arcade may wear at an angle due to limited jaw motion during mastication.
    • Incisors may become elongated due to poor occlusion (parrot mouth, sow mouth).
    • Incisors can wear unevenly due to tooth damage or missing teeth.
    • May give false impression of old age   Teeth: aging by dentition  .
  • Smooth mouth:
    • Loss of dental crown   →   rapid wear of root (lacks enamel)   →   inevitable loss due to age.
    • Prolonged periods (years) of very poor grazing, or sand in diet, can smooth off the occlusal surfaces of incisors or cheek teeth.
    • The hypsodont equine teeth have less enamel in the dental crown as they get closer to the tooth apex or root (which contains no enamel).
    • Efficient mastication becomes impossible.
    • Weight loss and debilitation result.
  • Abnormal wear of teeth   →   trauma and ulceration to buccal and/or lingual mucosa   →   painful mastication   →   food dropped from mouth, ie quidding, or refusal to eat   →   loss of condition.
  • Sharp enamel points -> soft tissue injury or sensitivity -> biting problems -> poor athletic performance.

All abnormalities of wear will become worse with age, eg a hock   →   wave mouth if not rasped.

Timecourse

  • Several months to years.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Tremaine H & Pearce C (2012)A modern approach to equine dentistry 4. Routine treatments.In Pract34(6), 330-347 VetMedResource.
  • Tremaine H & Casey M (2012)A modern approach to equine dentistry 2. Identifying lesions.In Pract34(2), 78-89 VetMedResource.
  • Du Toit N, Bezensek B & Dixon P M (2008)Comparison of the microhardness of enamel, primary and regular secondary dentine of the incisors of donkeys and horses.Vet Rec162(9), 272-275 PubMed.
  • Weller R, Livesey Let al(2001)Comparison of radiography and scintigraphy in the diagnosis of dental disorders in the horse.Equine Vet J33(1), 49-58 PubMed.
  • Brigham E J & Duncanson G R (2000)An equine postmortem dental study - 50 cases.Equine Vet Educ12, 59-62 VetMedResource.
  • Brigham E J & Duncanson G R (2000)Case study of 100 horses presented to an equine dental technician in the UK.Equine Vet Educ12, 63-67 VetMedResource.
  • Dixon P M (2000)Removal of dental overgrowths.Equine Vet Educ12, 68-81 VetMedResource.
  • Dixon P M, Tremaine W H, Pickles K, Kuhns L, Hawe C, McCann J, McGorum B, Railton D I & Brammer S (1999)Equine dental disease Part 1 - a long-term study of 400 cases - disorders of incisor, canine and first premolar teeth.Equine Vet J31(5), 369-377 PubMed.
  • Dixon P Met al(1999)Equine dental disease Part 2 - a long-term study of 400 cases - disorders of development and eruption and variations in position of the cheek teeth.Equine Vet J31(6), 519-528 PubMed.
  • Muylle S, Simoens P, Verbeeck R, Ysebaert M T & Lauwers H (1999)Dental wear in horses in relation to the microhardness of enamel and dentine.Vet Rec144, 558-561 PubMed.
  • Lane J G (1994)A review of dental disorders of the horse, their treatment and possible fresh approaches to management.Equine Vet Educ6(1), 13-21 Wiley Online Library.

Other sources of information

  • Easley J (1998)Dental Care and Instrumentation.Vet Clin North Am Equine Pract.Philadelphia: W B Saunders14(2), 309-332. (Review)
  • Easley J (1998)Dental Corrective Procedures.Vet Clin North Am Equine Pract.Philadelphia: W B Saunders14(2), 411-432. (Review)


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