Developmental Abnormalities of the Mouth and Dentition in Small Animals

I. Core Principles and Etiology

• Normal Development: Proper growth relies on a series of events occurring normally and in the proper sequence.

• Causes of Abnormalities:

    ◦ Genetic abnormalities.

    ◦ Trauma affecting developing tissues or the timing of development.

• Treatment Necessity: Treatment is required for defects that decrease comfort, health, or function; those resulting only in an aesthetic problem do not require intervention.

• Breeding Recommendations: Pets with genetically caused problems (like persistent deciduous teeth, unerupted teeth, or malocclusions) should not be bred unless the condition is known to have been caused by trauma.

II. Persistent Deciduous Teeth

• Function: Deciduous teeth are smaller, fewer in number, and temporary.

• Causes of Persistence:

    ◦ The subjacent permanent tooth does not erupt in the correct position.

    ◦ Absence of a permanent successor tooth (hypodontia).

    ◦ Genetically malpositioned permanent tooth bud.

    ◦ Traumatic displacement of the permanent tooth bud.

• Clinical Presentation:

    ◦ Persistence in areas of wide tooth spacing may not cause a clinical problem.

    ◦ Canine Teeth: Most commonly, one deciduous and one permanent canine are present simultaneously.

        ▪ Maxillary permanent canine erupts mesial (rostral) to the deciduous one.

        ▪ Mandibular permanent canine erupts lingual (medial) to the deciduous one.

• Consequences:

    ◦ Crowding (especially canine teeth) predisposes the area to periodontitis.

    ◦ Displaced permanent teeth can result in traumatic occlusion.

• Treatment/Management:

    ◦ A deciduous tooth should be extracted once its successor permanent tooth has begun eruption to encourage proper eruption.

    ◦ If no permanent replacement exists, the deciduous tooth may be left if there is no clinical or radiographic evidence of disease or crowding.

    ◦ If no permanent eruption is evident, radiographs are necessary to verify the absence of embedded/impacted teeth, root resorption, or cysts.

III. Unerupted Teeth

• Etiology: Tooth eruption is genetically programmed.

    ◦ Predisposed breeds: Small breeds (e.g., Maltese) and some brachycephalic breeds (due to malpositioned first premolars).

    ◦ Trauma can move a tooth bud, leading to impaction against another structure.

• Diagnosis: Radiography is required for any edentulous area.

    ◦ Mandibular first premolars and canine teeth are most frequently observed to be clinically absent but radiographically present. Missing mandibular first premolars in brachycephalic breeds should always be radiographed.

• Terminology:

    ◦ Embedded: An unerupted tooth covered in bone; eruption compromised by a lack of eruptive force.

    ◦ Impacted: An unerupted or partially erupted tooth prevented from eruption by contact with a physical barrier (tooth, bone, or soft tissue).

• Consequences: Unerupted teeth can form dentigerous cysts that destroy large areas of the jaws.

• Treatment:

    ◦ Accepted Best Practice: Extraction of any unerupted teeth identified.

    ◦ Operculectomy: Treating incompletely erupted teeth with persistent gingival covering by sculpting the tissue to normal architecture.

    ◦ Conservative Monitoring: Only considered for mature/senior patients without radiographic or clinical evidence of cyst formation, who have comorbidities, and whose owners are committed to annual radiographs.

IV. Malformed Teeth

• Etiology: Interruption during tooth formation, which can be traumatic, metabolic, infectious (e.g., parvovirus, distemper), or rarely genetic.

• Enamel Abnormalities (Hypoplasia/Hypomineralization): Caused by insults to epitheliogenesis during amelogenesis.

    ◦ Appearance: Circumferential lines of missing enamel (rough, stained surface) or generalized loss of enamel.

    ◦ Treatment: Early dentin sealants to prevent bacterial ingress; composite resin veneers can protect the dentin.

• Root Abnormalities: Insults to dentin formation can cause deformed or missing roots.

    ◦ Radicular Dysgenesis (Missing Roots): Crowns may appear normal but are mobile. Prognosis is poor long-term, but teeth can be maintained with strict oral care.

    ◦ Convergent Roots (Mandibular First Molar): Appears genetic. Roots converge apically, and the crown may appear too large. Frequently results in endodontic disease due to communication between the pulp chamber and periodontal ligament.

• Other Individual Anomalies: Supernumerary teeth, twinning and fusion of teeth, supernumerary roots, and “peg” teeth (short cylindrical teeth).

    ◦ Supernumerary Teeth/Roots: Treatment may not be necessary if teeth are periodontally and endodontically healthy and space is adequate.

V. Malocclusion and Malformed Jaws

• Etiology: Nearly always genetic; trauma during development can interfere with growth.

    ◦ Timing of tooth eruption is critical, as abnormal jaw relationships at eruption time can lock the dentition into the abnormal position.

• Skeletal Malocclusions (Horizontal Symmetric):

    ◦ Mandibular Distoclusion (Class 2 / Overbite): Maxillary length greater than mandibular length. Often causes traumatic occlusion when mandibular canine teeth impact the rostral hard palate.

    ◦ Mandibular Mesioclusion (Class 3 / Underbite): Mandibular length greater than maxillary length. Considered normal for many brachycephalic breeds unless it results in traumatic occlusion.

    ◦ Asymmetric Skeletal Malocclusion (Class 4 / Wry Bite): Mismatch of midlines resulting from continued growth on one side and arrested growth on the other.

• Dental Malocclusion (Class 1): Individual tooth malposition.

• Treatment for Deciduous Dentition (Interceptive Orthodontics): Selective extraction is used to relieve dental interlock and allow jaws to grow to genetic potential.

    ◦ Class 2 deciduous: Extraction of mandibular canine/incisor teeth.

    ◦ Class 3 (rostral crossbite) deciduous: Extraction of maxillary incisors.

    ◦ Note: Avoid trauma to the permanent successive tooth bud during extraction.

• Treatment for Permanent Dentition (Traumatic Occlusion):

    ◦ Orthodontic Movement: Moving affected canine teeth into a nontraumatic position (requires at least two anesthetic events).

    ◦ Crown Reduction and Endodontic Therapy (Vital Pulp Therapy): Shortening the tooth to maintain form and function while treating the pulp; requires long-term follow-up radiographs.

    ◦ Extraction: A viable and frequently least expensive option, requiring the least amount of follow-up. (Extraction of associated maxillary incisors may resolve Class 3 trauma).