Introduction

Orthodontics is concerned with the study and treatment of dento-skeletal anomalies associated with growth and function of the dento-facial tissues.

The key to success in clinical veterinary orthodontics is case selection.  There is no substitute for a thorough diagnosis and treatment planning.  There are many cases of malocclusion where correction to a normal scissors bite is neither possible nor necessary. Always look for an underlying skeletal base problem.  Don’t let your clinical judgement be swayed by a dog owner. It’s not your fault that the dog has a malocclusion; it’s not your responsibility to correct bites to fool judges.

Orthodontic Treatment Planning

The ultimate goal of orthodontic treatment is an occlusion that functions normally, maintains oral health and is pain-free. 
Orthodontic treatment involves thorough assessment of the malocclusion including the aetiology of the malocclusion.
Malocclusions can be described as being genetic or environmental (local/systemic) in origin or both.
Genetic or hereditary factors will affect the shape and size of the jaws and teeth. There may also be variations in the no. of teeth present. A genetic defect such as cleft lip/palate is often assoc. with altered tooth morphology and number of teeth.
Environmental factors may include systemic influences such as infections, nutritional imbalances, and endocrine disorders.
Local factors include trauma- jaw or tooth fracture, early loss of primary or permanent teeth, damage to permanent tooth buds, and altered tooth/root shape.
Habits such as cage biting, rock chewing may also cause malocclusions in the developing animal. 
Jaw length, jaw width and height, tooth bud position and tooth size are inherited.
The development of the maxilla, mandible and teeth are independently regulated genetically.
Disharmony in the regulation of these 3 structures results in a malocclusion. 
As a general rule, tooth crowding and rotation in the premolar/molar area indicates a jaw that is shorter than normal.
Treatment planning for malocclusions will include the taking of impressions for study models, radiographs of the affected teeth, and the use of a dental laboratory for the manufacturing of customised intraoral appliances.

Malocclusions causing

• Crowding leading to periodontitis
• Oral trauma i.e. Base narrow canines
• Anterior crossbite –ethical dilemma!

Terminology

• Scissor bite: Maxillary incisors overlap Mandibular incisors, whose incisal edges rest on the lingual cingulum of the Maxillary incisors.
• Level bite: when incisor teeth meet edge to edge.
• Open bite: When a part or all of the teeth are prevented from closing into their normal occlusal relationship.
• Wry bite: The result of unequal arch development. There is a centre line displacement and the midline is not confluent between the upper and lower arch. May occur to trauma and slowed growth on one side of the face.
• Anterior crossbite: cusps of 1 or more anterior teeth (Incisors) are positioned labially or lingually to their normal cuspal relationship (undershot)
• Posterior crossbite: cusps of 1 or more posterior teeth (Premolars/Molars) are positioned bucally/lingually to their normal cuspal relationship.
• Overbite: is the overlap of the lower incisor crown height by the upper incisor.
• Overjet: the horizontal distance between the upper and lower incisors measured parallel to the occlusal plane.   

Types of tooth movement

Tooth movement requires sufficient space, an applied force, sufficient anchorage and retention.
The lip, tongue, cheeks also apply forces to teeth and these forces should be in harmony post orthodontic movement. (Shar-Pei: lower tight-lip syndrome)
The application of a continuous or intermittent force to a tooth results in areas of pressure and tension in the periodontal ligament (PDL). (Acrylic bite plane=intermittent force)
Pressure causes osteoclast activity and tension causes osteoblast activity.
Correct level of force results in frontal surface resorption of the lamina dura.
A slow continuous force is best to match bone lysis with bone formation.
Excessive force leads to undermining resorption of bone due to occlusion of blood vessels in the PDL. Extreme force may lead to hyalinisation of the PDL, cemental damage, and tooth resorption.
A retention phase post movement is required to allow for bone formation on the tension side as well as allowing for gingival fibres to re-organise in the new position.

• Tipping: is the movement of the crown without changing the position of the root apex. Tipping usually requires minimal force.
• Translation: involves the bodily movement of the tooth without any tipping or rotation.
• Rotation, extrusion and intrusion: involve rotation around the apico-incisal axis, or the movement of the tooth coronally or apically.

Most tooth movements in veterinary orthodontics involve a combination of tipping and translation.
All tooth movements cause some degree of short term pain to the animal.

Treatment options

Orthodontic treatment can be divided into 3 areas

• Preventive: owners are given advice on correct chew toys, oral exercises to prevent fractured, avulsed teeth in the young animal. Counselling for genetic faults also.
• Interceptive: action taken to intercept a potential problem. Usually done in the deciduous or mixed dentition
• Corrective: Treatment of a existing malocclusion in the permanent dentition 

 A reasonable approach as to whether a malocclusion is inherited would be:

Skeletal malocclusions are inherited unless a developmental cause can be reliably identified
Retained deciduous teeth may be inherited or environmental in origin.
Pure dental malocclusions, unless known to have a breed or family predisposition, are judged to be not inherited. (Hennet, 1995) 

Summary

Veterinary Orthodontics is a science that is based on making a diagnosis and then formulating a thorough treatment plan to correct the malocclusion.
The use of study models, radiographs and a dental laboratory is imperative to have a successful treatment outcome. Orthodontic management should be reserved for those animals that have a malocclusion that will not allow for normal masticatory function or cause pain to the animal. Orthodontic treatment should not be contemplated in those cases where a genetic fault is considered the cause of the malocclusion.

- Dr Tony Caiafa