DEFINITION/OVERVIEW
- A malocclusion is any deviation from a normal occlusion due to skeletal influences (asymmetry or other deviation of bone that support the teeth) or an abnormal positioning of a tooth or teeth (dental malocclusion)
- Normal occlusion: perfect interdigitation of maxillary and mandibular teeth (see “Classification of Dental Occlusion in Dogs” section in Appendix B)
- Maxillary incisors are rostral to the mandibular incisors
- Crown cusps of mandibular incisors contact the cingulum of the maxillary incisors (“scissor bite”)
- Mandibular canines incline labially and are positioned equidistant between the maxillary third incisor and canine in the interdental space (diastema)
- Maxillary premolars do not contact the mandibular premolars
- Crown cusps of the mandibular premolars are lingual to the maxillary premolar arch
- Crown cusps of mandibular premolars bisect the interproximal spaces rostral to the corresponding maxillary premolars (“pinking shear configuration”)
- Crown cusps of the mandibular premolars are lingual to the maxillary premolar arch
- Maxillary fourth premolar’s mesial cusp is positioned lateral to the space between the mandibular fourth premolar and first molar
- Maxillary incisors are rostral to the mandibular incisors
- Terms of malocclusion
- Neutroclusion (Class 1)
- Normal rostral–caudal relationship of the maxillary and mandibular dental arches
- Malposition of one or more individual teeth (see “dental malocclusions” below)
- Dental malocclusion: tooth in anatomically correct position in the dental arch, but
- Distoversion: abnormally angled in a distal direction (“snake tooth”)
- Mesioversion: abnormally angled in a mesial direction (“lance tooth”)
- Linguoversion: abnormally angled in a lingual direction (“base-narrow mandibular canine”)
- Labioversion: abnormally angled in a labial direction
- Buccoversion: abnormally angled in a buccal direction
- Distoversion: abnormally angled in a distal direction (“snake tooth”)
- Crossbite: mandibular tooth/teeth have a more buccal or labial position than antagonist maxillary tooth
- Rostral crossbite: synonym: anterior crossbite—incisors
- Caudal crossbite: synonym: posterior crossbite—cheek teeth
- Rostral crossbite: synonym: anterior crossbite—incisors
- Dental malocclusion: tooth in anatomically correct position in the dental arch, but
- Normal rostral–caudal relationship of the maxillary and mandibular dental arches
- Mandibular distoclusion (Class 2):
- Mandibular arch occludes caudal to its normal position relative to the maxillary arch (“mandibular brachygnathism”; “overshot”)
- Mandibular mesioclusion (Class 3):
- Mandibular arch occludes rostral to its normal position relative to the maxillary arch (“mandibular prognathism,” “maxillary brachygnathism”; “undershot”)
- Incisors may still appear to be in scissor bite, but if the mandibular canine placement seems too far forward, there is mandibular mesioclusion (Fig. 23-1)
- Mandibular arch occludes rostral to its normal position relative to the maxillary arch (“mandibular prognathism,” “maxillary brachygnathism”; “undershot”)
- Asymmetrical skeletal malocclusion
- Mandibular–maxillary asymmetry
- Rostrocaudal direction: mandibular mesioclusion or distoclusion present on one side; contralateral side normal alignment
- Side-to-side direction: loss of midline alignment of maxilla and mandible
- Dorsoventral direction: abnormal vertical space between opposing dental arches when the mouth is closed (open bite)
- Rostrocaudal direction: mandibular mesioclusion or distoclusion present on one side; contralateral side normal alignment
- “Wry bite”: nonspecific term used to describe a wide variety of unilateral occlusal abnormalities
- Mandibular–maxillary asymmetry
- Neutroclusion (Class 1)
Figure 23-1 Mild to moderate mesioversion (rostroversion) of mandibular canine possibly due to rostral placement of mandibular canine, even though incisors still appear to be in a “scissor bite.” Simple extraction of the third incisor should provide this patient with a comfortable bite.
(Image courtesy of Larry Baker, DVM, DAVDC)
ETIOLOGY/PATHOPHYSIOLOGY
- Risk factors
- Congenital or hereditary factors: skeletal malocclusions (Class 1, 2, and asymmetry) and breed predilection
- Traumatic injury affecting the jaws or teeth, especially during developmental and growth phases
- Mechanical misdirection
- Tooth eruption contact impediment
- Delayed loss of deciduous teeth (see Chapter 12)
- Delayed eruption of deciduous or permanent teeth
- Tooth eruption contact impediment
- Congenital or hereditary factors: skeletal malocclusions (Class 1, 2, and asymmetry) and breed predilection
SIGNALMENT/HISTORY
- Can occur in dogs or cats with primary (deciduous, temporary, baby) or permanent dentition
- No sex predilections
- No age predilections, other than malocclusions are typically discernable at the time of or shortly following eruption of the deciduous or permanent teeth
- Significant jaw growth can occur up to 6–8 months (and longer in large breeds); full evaluation can only be done once growth is complete
CLINICAL FEATURES
- Vary greatly according to the type, extend, and collateral injuries caused by the malocclusion (see the description of malocclusions above)
- May be associated with open or closed bites, or overcrowding of the teeth
- Periodontal disease may result due to crowding or misalignment of teeth
- Soft tissue defects may be seen both in the floor or roof of the mouth from traumatic tooth contact
- In the roof of the mouth, the injuries may eventually extend in depth resulting in oronasal fistula formation
- Fractured (chipped or broken) or attrition (wear) teeth may result from improper tooth contact
- Common malocclusion presentations
- Rostral (anterior) crossbite: maxillary incisors positioned distal to mandibular incisors
- Level bite (cusp contact directly) or crossbite with abnormal contact and potential periodontal disease
- Note: many “rostral crossbites” may actually be due to a mild Class 3 malocclusion
- Level bite (cusp contact directly) or crossbite with abnormal contact and potential periodontal disease
- Base-narrow canines: linguoversion of mandibular canine(s)
- Common sequelae to narrow mandible or delayed exfoliation of deciduous mandibular canines (permanent tooth is deflected into a lingual position) (Fig. 23-2)
- Significant trauma to the palate can result
- Common sequelae to narrow mandible or delayed exfoliation of deciduous mandibular canines (permanent tooth is deflected into a lingual position) (Fig. 23-2)
- Lance teeth: rostroversion of maxillary canine(s)
- More common in dolichocephalic breeds (Shetland sheepdog); with significant rostral deviation—crown nearly horizontal
- Mild to moderate rostroversion due to persistent deciduous tooth—permanent tooth erupts further rostral than normal
- Rostroversion of canine obliterates the diastema between the canine and third incisor: this can result in malocclusion of the mandibular canine
- More common in dolichocephalic breeds (Shetland sheepdog); with significant rostral deviation—crown nearly horizontal
- Caudal (posterior) crossbite
- More common in dolichocephalic breeds (collie)
- Reversal of the relationship of maxillary fourth premolar and mandibular first molar; crown of fourth premolar buccal to molar
- More common in dolichocephalic breeds (collie)
- Rostral (anterior) crossbite: maxillary incisors positioned distal to mandibular incisors
Figure 23-2 Significant base-narrow canine in addition to/or as a result of a Class 2 malocclusion (mandible in distoversion). Even with an adequate diastema between the maxillary third incisor and canine, movement would be complicated.
(Image courtesy of Larry Baker, DVM, DAVDC)
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