Last month we covered the treatment of BNMCT in primary dentition.When treating BNMCT in permanent dentition, a variety of techniques may be utilized to correct the problem. Factors influencing the technique(s) selected include: how far the mandibular canines have erupted, if any eruptive potential for these teeth remains, if the mandible is too narrow to allow normal retention after correction, the owner’s desires, the potential need for multiple anesthetic episodes for some techniques, available equipment and the practitioners comfort with potential treatment modalities. Appropriate treatment planning requires a thorough understanding of the relative indications and contraindications of the different treatment options. Treatment modalities that may be utilized for permanent dentition will be presented this month and next. If primary canine teeth are present when the corresponding permanent canine teeth first erupt, they should be extracted, regardless of any other techniques utilized. Toy Ball Therapy: A therapeutic mode described in 1999 involves placement of some type of rubber toy in the mouth of the dog for 15 minutes, three times a day. The size of the toy (commonly a rubber ball) is selected so that the toy is cradled between the lower canine teeth without contacting the inter-dental soft tissues of the mandible. When the toy is sized correctly, it exerts a gentle lateral tipping force on the lower canine teeth. Advantages of this technique include the low cost and avoidance of anesthesia. The veterinary literature is unclear about how much time is required for a given force to affect movement of a target tooth. Human orthodontic texts indicate a need for a minimum of several hours per day of constant force to achieve orthodontic movement of teeth. Keep in mind that acrylic incline planes, which are sometimes employed to treat BNMCT teeth, exert non-stop tipping forces on the lower canine teeth 24 hours a day, yet still take 2-4 weeks to affect the desired movement. Could 15 minutes three times a day exert enough force? It seems unlikely that any owner could actually apply 15 minutes of constant pressure three times a day as recommended in the article. Toy ball therapy seems most appropriate in cases in which very small amounts of correction are required. Most of these cases would likely correct with no treatment at all. Attempting this treatment for too long may eliminate the window of opportunity to employ other treatment modalities. Extraction of permanent lower canine teeth: Extraction of the permanent canine teeth corrects the trauma to the palatal soft tissues, but the procedure is somewhat traumatic. Mandibular canine teeth comprise approximately 80% of the cross-sectional diameter of the mandible (Fig. 1 shows a cross-section of the mandible just distal to the crown of the canine tooth). Extraction of these teeth can be technically difficult, risks mandibular fracture and may leave the mandible weakened. Some patients will have the tongue protrude from the side of their mouths post-operatively due to the loss of the “cradling effect” of the lower canines on the tongue. Extraction of other permanent teeth: Occasionally, BNMCT may be corrected by selective extraction of permanent teeth that are preventing the lower canines from moving into a comfortable position. The most common example of this is patients that have the lower canines occluding palatally (caudal) to the maxillary third incisors. In these cases, extraction of the maxillary third incisors allows the lower canines to erupt and move into a comfortable position. Gingivectomy: When a small amount of correction is required, simply creating a gingival ramp (trough) in the diastema between the maxillary third incisors and canine teeth may free the cusp tip of the lower canine and allow it to erupt into a normal position. As the gingival tissues heal and fill the space back in, the mandibular canines usually stay labial to the soft tissues. This technique works best in patients whose BNMCT have some eruptive potential remaining, as evidenced by open apices on dental radiographs. Gingivectomies may also be performed as an ancillary technique in conjunction with other treatment options. The gingivectomy may be performed with an electrosurgical unit (the author’s preference), a laser (associated with delayed healing in the oral cavity) or with a cylindrical diamond bur in a high-speed handpiece. For the procedure to work, the cusp tips of the lower canine teeth must totally visible after treatment and be free to erupt further and tip labially. Figures 2 and 3 show the diastema before and after creation of a gingival ramp with an electrosurgical unit. Oral Acrylic Incline Planes: Incline planes are true orthodontic devices that can be utilized to treat BNMCT (fig. 4). These may be fabricated from acrylic or metal. Metallic incline planes require that dental impressions be obtained and submitted to a dental lab for fabrication of the appliance. The added lab expense and the need for an additional anesthetic episode makes metallic incline planes substantially more expensive than acrylic. Because of the aforementioned problems, incline planes are usually fabricated from acrylic materials in a single anesthetic episode. Strict restrictions against chewing or rough play must be adhered while the splint is in place. Normally, 3-5 weeks are required for the splint to affect the desired orthodontic movement. Once the desired movement is achieved, the mandibular canine teeth should be in normal occlusion and will be retained there by the maxillary soft tissues, canines and incisors. Problems with this technique include damage to the appliance due to incorrect bonding, fabrication errors, or overzealous oral behaviors by the patient. A minimum of two anesthetic episodes are required, with a third anesthetic episode commonly needed to adjust or repair the splint. Patients with a narrow mandible (compared to the maxilla) are not good candidates for incline planes. In patients with the lower canine teeth trapped inside the upper canine teeth, the maxillary canine teeth must first be moved distally (caudally) to make a space into which the mandibular canine may then be tipped. This entire process requires a two-stage orthodontic movement, requiring a minimum of three anesthetic episodes to complete.
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