Diagnosis and management of Class II malocclusion

Introduction

To diagnose malocclusions in our patients, we must first understand what is a normal occlusion. Evaluation of a patient’s dental occlusion should be performed at the first puppy or kitten visit and documented in the medical record. This should start with identification of the skull type (brachycephalic, mesocephalic, dolichocephalic), as this will give indications of common abnormalities seen with various skull types (1). Next, the veterinarian should evaluate facial symmetry and the maxillomandibular relationship. Cats and dogs have anisognathic jaws, which means that the maxillae are wider and longer in relation to the mandibles. Dental interlock is assessed and normal occlusion includes the mandibular incisors occluding upon the cingulum of the maxillary incisors. Additionally, there should be a triad interlock involving the maxillary 3rd incisors, the mandibular canines, and the maxillary canines. The mandibular canine teeth should rest in the diastema between the maxillary 3rd incisors and the maxillary canine teeth, with the incisive tip of the mandibular canine completely visible when the patient is placed in a closed bite (1) (Figure 1). A normal relationship between the maxillary and mandibular premolars should appear as interdigitation with the maxillary premolars occluding distal to the mandibular counterpart and without contact, as the maxillary premolars should be buccal to the mandibular teeth due to the anisognathic nature of the jaw relationship. Finally, the molars form a contact of occlusal tables for crushing of food. The mesial and main cusp of the mandibular 1st molar is the exception, which occludes on the palatal aspect of the maxillary 4th premolar to form a shear for cutting of food (Figure 2).

Figure 1.

Normal occlusion in a dog — Rostral view. Copyright AVDC used with permission.

Figure 2.

Normal occlusion in a dog — Buccal view. Copyright AVDC used with permission.

Class II malocclusion

The American Veterinary Dental College defines Class II malocclusion as mandibular distocclusion, when there is an abnormal rostro-caudal relationship between the dental arches in which the mandibular arch occludes caudal to its normal position relative to the maxillary arch (1) (Figure 3). Terms that have commonly been associated with class II malocclusions include overbite and overjet. It should be noted that overbite and overjet are seen in normal occlusion; however, the measurement of both overbite and overjet typically increases with increasing severity of mandibular distocclusion. Overbite is the measure of the vertical overlap of the incisors (2). In a mesaticephalic skull with normal anisognathism, the incisal edges of the mandibular incisors should rest on the cingulum of the maxillary incisors, resulting in a measurable overbite. Overjet is defined as the measure of horizontal overlap between the incisal edges of the mandibular and maxillary incisors (2). Since there is contact between the maxillary and mandibular incisors in normal occlusion, this measurement increases proportionally with the degree of mandibular distocclusion. Mandibular distocclusion is considered to be a heritable trait unless it is a result of trauma, and affected animals should not be used for breeding (1–3). Mandibular distocclusion has been diagnosed in many breeds including mixed breed dogs and cats. Anecdotally, this traumatic malocclusion is overrepresented in the following breeds: golden retriever, Labrador retriever, standard poodle, bull terrier, German shepherd, and more recently mixed breeds involving poodles.

Figure 3.

Mandibular distocclusion. Copyright AVDC used with permission.

Clinical relevance

There can be significant variability in the severity of mandibular distocclusion. The most significant clinical feature relates to the position of the mandibular canine teeth relative to their normal atraumatic retention in the diastema between the maxillary 3rd incisors and the maxillary canine teeth (1). For the purposes of this clinical review, we will include a commonly seen Class I malocclusion described as base narrow canines but more correctly identified as linguoversion of the mandibular canine teeth. Class I malocclusions have a normal relationship between maxillae and mandibular jaw length with malpositioned individual teeth within their arches (1). Resultant trauma and treatment options for linguoversed mandibular canine teeth are similar to those seen with mandibular distocclusion. The most common concern with mandibular distocclusion is the traumatic contact of the incisive tips of the mandibular canine teeth. These sharp teeth can be in contact with the gingiva mesial or distal to the maxillary canine teeth, the palatal mucosa and/or the palatal aspect, of the maxillary canine teeth. This traumatic contact not only results in oral pain and head-shy behaviors of the patients, but can result in non-vital teeth, dental attrition, periodontal diseases, and oronasal fistula (Figure 4). All of these problems can and should be addressed in an effort to improve the oral health, comfort, and overall quality of life of the patient.

Figure 4.

Penetrating oral trauma resulting from mandibular distocclusion.

Management

When considering the treatment options for dogs with any traumatic malocclusion, the main goal should be removing the trauma to provide the animal with a comfortable occlusion. Esthetics should not be a consideration during treatment planning. The purpose of the patient should also be considered and treatment should result in a functional occlusion. Prior to performing any orthodontic treatments, ethical considerations must be made. These malocclusions are heritable traits and the owners of these patients must be counselled as to the importance of removing these pets from the breeding population (1,3,4).

Mandibular distocclusion should be identified at the first puppy visit when the occlusion is assessed. If there is inappropriate contact of deciduous mandibular canine teeth with gingiva and/or palatal tissues, this should be addressed immediately not only for comfort and prevention of behavioral abnormalities but also to address the resultant interlock of the sharp incisive edges (1,4). This interlock can prevent rostral growth of the mandibles in the case that the patient has genetic potential for normal occlusion (Figure 5). Treatment at this stage typically involves extraction of the mandibular canine teeth causing the trauma. If the degree of mandibular distocclusion is severe enough that the mandibular incisors are trapped palatal to the incisive papilla, it is advisable to remove these teeth as well. When extracting deciduous teeth, knowledge of the anatomical position of the developing permanent tooth bud is imperative as iatrogenic trauma can cause developmental abnormalities in those successive teeth. Intra-oral radiography is absolutely necessary before and after the deciduous dentition has been removed. Prior to performing this procedure, the risks of iatrogenic trauma to the permanent teeth should be discussed in addition to presenting the option for referral to a Board-certified veterinary dentist in an effort to minimize the risks. An alternative to extraction of the deciduous canine teeth is orthodontic movement, which can be achieved with strategically positioned crown extensions applied by a veterinary dentist (Figure 6). This may be favorable to extraction, as it can encourage growth of the mandibles to parallel that of the maxillae and it may provide a path to eruption of the permanent mandibular canine teeth into a normal occlusion. Whether treatment of the deciduous teeth involves extraction or orthodontic correction, the owner must be made aware that there is a high likelihood that the permanent teeth will also erupt into a traumatic malocclusion.

Figure 5.

Mandibular distocclusion in a kitten treated with extraction of deciduous canine teeth.

Figure 6.

Crown extensions (incline plane) for orthodontic movement of deciduous canine teeth in a puppy with linguoversed 704 and 804.

There are several options for management of traumatic mandibular distocclusion. With the goals of removing painful contact of the mandibular canine teeth and return to normal function, orthodontic movement is the treatment of choice. Client education for these cases must be thorough and owners should be aware that there may be several orthodontic adjustments needed throughout the period of tooth movement, which often requires multiple general anesthesia events. Tipping movement is required for mandibular distocclusion and linguoversed mandibular canine teeth, which is a light force applied to the incisive tip of the tooth. This force causes the crown and the root to move in opposite directions about a fulcrum (1). Additionally, there may be a period of retention needed after the teeth have been moved into atraumatic occlusion. In general, a retention period is not needed after mandibular canine teeth have been moved, as they are placed into the diastema between the maxillary 3rd incisor and the maxillary canine teeth or they are moved distal to the maxillary canine teeth with more severe mandibular distocclusion (1). Both of these positions provide a natural retention of the mandibular canine teeth in atraumatic occlusion if the cusps are long enough. In the case in which the mandibular canine cusps are not sufficiently long to form an interlock mesiobuccal or distobuccal to the maxillary canine teeth, a retention period of 2 months is recommended.

The incline plane is a common passive force method of directing mandibular canine teeth into atraumatic occlusion with mandibular distocclusion. Several materials have been described to create direct incline planes, many of which produced exothermic reactions during the curing process (5). The incline plane is now designed and applied directly to the maxillary arches using self-curing temporary crown material (bisacryl composite). This can be used to guide the mandibular canine teeth into their normal position mesial to the maxillary canine teeth or distal to the maxillary canine teeth if the mandibular distocclusion is more severe and the shorter distance to an atraumatic occlusion is distal to the maxillary canine teeth (1) (Figures 7,8). These composite based appliances are bonded to the maxillary canine teeth, incisors, and/or the premolars and carefully shaped with acrylic burrs. The incline plane is custom formed to provide a trough in which the mandibular canine tooth will be guided into an atraumatic position (1). It is common to require adjustments throughout the tooth movement process and this will require anesthesia. An alternative to the bisacryl composite incline plane is a cast metal telescoping incline plane that is fabricated by a dental laboratory and known as a Mann incline plane (1,6). The telescoping bridge between the maxillary arches is designed to allow for unimpeded growth of the maxillae. Manufacturing of a Mann incline plane requires detailed dental impressions to produce articulating stone models, which increases costs. Additionally, adjustments cannot easily be made to a fixed metal incline plane if the inclination angle needs to be changed.

Figure 7.

Severe mandibular distocclusion with a shorter distance to tip the mandibular canine tooth distal to the maxillary canine tooth.

Figure 8.

Bisacryl direct incline plane directing the mandibular canine tooth into an atraumatic occlusion, distal to the maxillary canine tooth.

Another passive force modality of orthodontic movement that is gaining popularity within the veterinary dental community is composite crown extensions. Crown extensions are another form of incline plane that exerts tipping forces on the mandibular canine teeth (1). This is typically reserved for mild to moderate malocclusion and involves core build-up and shaping the mandibular canine teeth such that the incisive tip no longer impacts tissue. As the patient closes its mouth, forces are acted upon the teeth thereby causing them to tip into atraumatic position. The success of this modality depends on a strong bond between the composite crown extension and the enamel of the tooth. When the crown extensions are applied and the patient’s mouth is held in occlusion, the incisive tips of the extensions should be visible and not impacting tissue (Figure 9). Initially, the patient will not be able to fully close the mouth, as the crown extensions contact the diastema between the maxillary 3rd incisors and the maxillary canine teeth (Figure 10). This contact with the gingival diastema is what provides the tipping forces needed to move the mandibular canine teeth into atraumatic occlusion. This author uses a semi-translucent blue core build-up material as the operator can see the clinical crown inside the crown extension. This facilitates appropriate shaping of the crown extensions and also makes removal of the crown extensions safer, as the operator can see the difference between the blue composite material and the white enamel.

Figure 9.

Lateral view of coronal extension resting in the diastema between 203 and 204. This contact passively provides the tipping forces required to tip 304 buccally into an atraumatic occlusion.

Figure 10.

Photo demonstrating the inability to completely close the mouth immediately after application of crown extensions.

A treatment option that addresses the discomfort of the traumatic contact of the mandibular canine teeth is crown reduction with vital pulp therapy (7). This is an alternative to orthodontic movement of the malpositioned teeth that requires only 1 anesthetic procedure followed by radiographic evaluation of the treated teeth for assessment of success and failure. This procedure leaves the patient with short crowns that no longer have a sharp tapered incisive tip, and therefore the painful contact point is removed. This is a technically demanding procedure in which crown reduction is followed by sterile partial pulpectomy, a pulp dressing and a layered restoration of the surgical site (Figure 11). Vital pulp therapy has been shown to have a success rate above 90% when the appropriate techniques and materials are applied (8). This high success was seen in a study evaluating vital pulp therapy in 190 cases of complicated crown fractures in which the pulp had been exposed to saliva, plaque flora, and debris. It can be inferred that the success rate of vital pulp therapy in the controlled setting of crown reduction is even higher than those done on crown fractures with pulp exposure.

Figure 11.

Radiograph before and after crown reduction and vital pulp therapy and photo of reduced crown without contact on palatal mucosa.

The salvage procedure for management of traumatic mandibular distocclusion is extraction of the mandibular canine teeth. This can be a safe and successful option if the mandibular canine teeth are skillfully extracted. There is a risk of iatrogenic jaw fracture if the surgical technique is poor, as the tooth root of the mandibular canine tooth encompasses a very large volume of the rostral mandibular body. This risk of jaw fracture inherently increases with smaller dogs, as the percentage by volume of the mandibular space that is occupied by tooth root increases with decreasing body weight (9). One concern of note is the risk of wound dehiscence after mandibular canine tooth extraction. A large alveolus remains after mandibular canine tooth extraction and it is crucial that the closure is without tension and that the suture line is over healthy bone and not over the empty alveolus. Additionally, the labial frenulum should be left undisturbed or at very least secured in the natural position if elevating the frenulum is necessary for safe canine extraction.

A gingival wedge resection surgery can be considered if the malocclusion is minor, and the mandibular canine tooth is not in distocclusion but only slightly palatoversed. This should not be considered if any substantial orthodontic movement of the mandibular canine teeth is needed. The purpose of the gingival resection is to remove the tissue impression that is caused by the incisive tip of the mandibular canine tooth. This will allow unimpeded passage of the incisive tip buccal to the tissues of the diastema and if further eruption of the mandibular canine tooth occurs, it will be free to naturally displace labially (Figure 12). Another option for orthodontic correction with minor contact that can be started with deciduous dentition and/or at the time of eruption of the permanent mandibular canine teeth is ball therapy. This technique requires a cooperative pet that will carry a ball that has a slightly larger diameter than the distance between the incisive tips of the mandibular canine teeth. The recommendation is to have the patient carry the ball for a minimum of 10 minutes, 3 times per day (10). These patients must be regularly monitored by the veterinarian to ensure that intervention with additional therapy is performed in a timely manner in the event that this treatment is unsuccessful.

Figure 12.

Wedge gingivectomy performed to remove to interlock of the incisive tip of the mandibular canine tooth and to provide a tissue ramp to encourage buccal tipping movement.

In conclusion, Class II malocclusions and linguoversed mandibular canine teeth result in traumatic contact of maxillary teeth and tissues leading to pain, periodontitis, endodontic disease, oronasal fistula, and behavioral issues in dogs. These traumatic malocclusions should be diagnosed and treated with the goal of providing these patients with a healthy and functional occlusion. All options for management of traumatic malocclusions should be presented to the pet owners and referral to a dentist for advanced procedures such as orthodontic movement and crown reduction with vital pulp therapy should be offered.