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L3 Comparative dentition (Herbivores (hypsodont teeth ) (Rabbits (( 2 0 …

- - - - canines
        
        premolars
        
        molars
        
        AGEING OF ANIMALS
        USING DENTITION
        
        Factors affecting accuracy of ageing
        • Breed
        • Individual genetics
        • Age
        • Diet
        • Environment
        • Behaviour e.g. ‘crib biting’
        • Malocclusion
        • Filing or trimming
      - upper > the most rostral teeth
        in maxilla
- - - - tricuspid (loss of definition with age)
        sharp for holding and tearing
        single root
        
        weapons for attack and defence
        root much longer than crown
        
        (Premolars and molars)
        cutting food, crushing bones
        only occlude caudally ⇒ cannot grind
        
        Dog/cat > No teeth erupted at birth
        
        1 root > upper & lower P1 / lower P3
        2 roots > upper P2 & P3 / rest of lower cheek teeth
        3 roots > rest of upper teeth (i.e. P4, M1, M2) ⇒ need to divide crown before extractio
        
        carnassial teeth > upper P4 and lower M1
        • rostrally sharp for cutting
        • caudally flat, blunt for crushing
        • upper carnassial often infected due to crown damage
  - - - Structure and function of teeth similar to dog
      - exception >
        no blunt crushing surfaces
        no upper & lower P1
        no lower P2
      - Only one upper & one lower molar
- - - - Needle teeth
        born with 8 deciduous teeth
        ( 4 third incisors and 4 canines)
        farmers clip to reduce injuries
        
        Canines =’ tusks’
        
        Cheek teeth
        (Premolars and molars)
        
        Pig > a lot of variability between breeds
        
        • for crushing and grinding, have rounded cusps
        • brachydont teeth
        
        in males
        Hypsodont with much longer growth period
        (much later root formation)
        Used for fighting
        Larger > require regular trimming
        (embryotomy wire)
      - lower incisors
        project forward for digging
        brachydont teeth
- - - - Incisors
        
        Canines
        
        Cheek teeth
        (Premolars and molars)
        due to morphological similarity
        
        Horse
        main criteria used to age horses >
        • Eruption of incisors
        • Changes to the incisor occlusal surface
        • Shape of upper corner incisor
        • Curvature of dental arch of lower incisors
        • Angle of incisors
        • Hook on upper corner incisor
        • Galvayne’s Groove
        
        wolf tooth > P1
        vestigial brachydont tooth
        (13-32% present, possibly F>M,
        upper more common than lower )
        erupts at 6-12 months of age
        (no deciduous precursor)
        May require removal
        
        ‘table’ > hypsodont teeth together form a continuous grinding surface
        
        Enamel > not continuous over occlusal surface > abrasive enamel ridges ( due to different rates of wear)
        Some dentine > exposed
        Cementum > present around the enamel crown
        
        wide : Maxillary teeth > Mandibular teeth
        may result in formation of sharp points on buccal aspect of maxillary and lingual aspect of mandibular cheek teeth that require filing down (‘floating’) > an occlusal or grinding surface angled between 15 and 35°
        
        Most males (stallions and geldings)
        have four that erupt from 4-6 years of age
        
        Most mares > absent or rudimentary
        
        a long diastema
        ( normal feature in herbivores)
        
        Usually classified as brachydont
        but have features of hypsodont teeth
        (long reserve crown > difficult for extration)
        
        Function unclear – may be related to fighting
      - Hypsodont teeth
      - I1:‘central,’I2: ’middle’ and I3:‘corner’ incisors
      - enamel not continuous over occlusal (grinding) surface ⇒ exposure of dentine
      - infundibulum = ‘cup’ or ‘mark’ - disappears with age
      - pulp cavity - appears with age (protected by 2° and 3° dentine) = ‘star’
  - - - Incisors and canines
        
        Cheek teeth
        (Premolars and molars)
        
        Ox
        • Appearance of the incisors and eruption times of the permanent incisors are used
        • Some incisors may already be erupted at birth, eruption of all deciduous incisors complete by week 4
        • Deciduous incisors are smaller and narrower, with a more triangular shape (narrower base) than permanent incisors
        • Deciduous incisors are initially short and broad, but become longer and narrower as the animal approaches 15-18 months of age
        • Stages are ‘milk tooth’ (no permanents), ‘2 tooth’ (centrals erupted), ‘4 tooth’ (middles) ‘6 tooth’ (laterals) and ‘8 tooth’ or ‘full mouth’ (corners)
        • By 5 years all incisors are in wear and then the occlusal table is observed for ‘levelling’ (the ridges on the lingual surface disappear and the surface becomes smooth and convex): 6 years (centrals) 7 years (middles) 8 years (laterals) and 9 years old (all incisors levelled)
        
        • increase in size from rostral to caudal
        • similar to horse > hypsodont
        • arrangement of enamel ridges slightly different from horse, enamel stands out more
      - • no continuous eruption > brachydont
      - • grip food between incisors and dental pad and tear by head movement
        
        • no upper incisors or canines > replaced by hard fibrous dental pad
        
        • lower canines are incisor in form so dental formula may classify as incisor
        I1:‘central’, I2:‘middle’ I3:‘lateral’ and C:‘corner’ incisors
  - - - Sheep
        • Usually no teeth at birth
        • In Australia a ‘lamb’ has no erupted permanent incisors
        • Appearance of teeth similar to that of ox
        • After the eight tooth/full mouth stage the next stage is ‘broken mouth’ – rate of dental deterioration depends on dietary and environmental factors so ageing difficult from full mouth stage
        • After all teeth have fallen out the sheep is known as ‘gummy mouth’
  - - - Incisors and canines
        
        Cheek teeth
        
        • Brachydont
        
        • no folded enamel ridges > require ‘floating’ (filing down) if malocclusion > look for signs of condition loss as ability to grind food is affected
      - • Have a dental pad ( no upper incisors, but retain the upper third incisor that is canine in appearance )
      - • fighting teeth > Third upper incisor + upper and lower canines
        present in males(larger) and females > often trimmed (embryotomy wire or Dremel tool) > necessary in younger males up to about 7 years of age when tooth growth ceases
        **No Extraction > long roots and risk of injury to jaw or adjacent teeth
      - • Lower incisors in alpacas (not llamas) > hypsodont and may require trimming if overgrown > usually as a result of malocclusion between incisors and dental pad
  - - - Incisors
      - • 4 upper incisors – the smaller ’peg teeth’ lie immediately caudal to the first incisors in the upper arcade.
        • Two lower incisors
      - • function .> tear off vegetation, gnaw harder materials such as roots and bark
      - • enamel only rostrally ⇒ sharp, chisel-shaped incisors
      - • Pulp cavity > extends only approx 3mm distal to gingival margin –so incisors ‘can’ be clipped in conscious animal if overgrown– but possible underlying problem further caudal in mouth must be ruled out/treated. Must also use appropriate technique.