Iowa City, Iowa
Am J Orthodo Dentofac Orthop (1992) 101: 159-171
Incidence of Canine Impaction:
Incidence of max canine impaction sited between 0.92-2.2%. Of all pts w/ max imp canines, 8% are bilateral. Imp 2X as common in females as males. Md. canine imp is 0.35%.
Developmental Considerations:
Mx canines have the longest period of development, as well as the longest and most tortuous course to travel from point of formation, lateral to the piriform fossa, until they reach full occlusion. Crowns of permanent canines are intimately related to the roots of the lateral incisors. Broadbent cautioned against early correction of the flared and distally tipped lateral incisors for fear of either impacting the canines or resorbing the roots of the laterals.
Etiology of Maxillary Canine Impaction:
Generalized--endocrine deficiencies, febrile diseases, and irradiation.
Localized (most common)-- (a) tooth size/arch length discrep (b) prolonged retention of deciduous canine (c) abnormal position of the tooth bud, (d) the presence of an alveolar cleft, (e) ankylosis, (f) cystic or neoplastic formation, (g) dilaceration of the root, (h) iatrogenic origin, (i) idiopathic condition.
The presence of the lateral incisor root with the right length, formed at the right time, is an important variable needed to guide the mesially erupting canine in a more favorable distal and incisal direction. 2.4X higher incidence of palatally impacted canines adjacent to the sites of missing lateral incisors as compared with the general population.
Sequelae of Impaction:
(a) labial or lingual malpositioning of the impacted tooth, (b) migration of the neighboring teeth and loss of arch length, (c) internal resorption (d) dentigerous cyst formation (e) external root resorption of the impacted tooth as well as the neighboring teeth, (f) infection particularly with partial eruption (g) referred pain, (h) combinations of the above.
In the 10-13 yr age group, ~0.71% have resorbing permanent incisors due to ectopic eruption of max canines. 80% of the teeth of the teeth resorbed by an ectopic canine are laterals.
Diagnosis of Impaction:
Clinical Eval-- (a) delayed eruption of the permanent canine or prolonged retention of deciduous canine beyond 14-15 years of age, (b) absence of normal (present in 95% of kids age 11) labial canine bulge (non-palpable or asymmetric), (c) presence of palatal bulge, (d) delayed eruption, distal tipping, or migration (splaying) of the lateral.
Radiographic Eval-- PA films reliable for assessment. Single PA to determine mesiodistal and superoinferior position. Use second film to to evaluate the buccolingual position (Use Tube-shift technique or SLOB rule). Occlusal films, frontal and lateral cephs, panoramic films can act as adjuncts.
Proper localization of the impacted tooth needed to determine the feasibility of, as well as proper access for, the surgical approach, and the proper direction for the application of orthodontic forces. Use of PA's to localize canines accurate in 92% of cases, but only 37% of cases were able to project the lateral incisor image away from that of the canine.
Estimates are that 0.7% of the children in the 10-13 year age group have resorbed permanent incisors because of ectopic eruption of the max canines. With tomography, that estimate doubles, with apx half of the teeth showing resorption extending into the pulp. Furthermore, 50% of the resorption occurred on the labial or lingual of the teeth, and would not be detectable with routine PA's.
Prevention of Maxillary Canine Impaction:
Selective EXT of deciduous canines as early as 8 or 9 years of age as interceptive approach to canine impation in Class I uncrowded cases. This done before 11 yrs may normalize the position of the ectopically erupting permanent canines in 91% of the cases if the canine crown is distal to the midline of the lateral incisor. Only 64% if the canine crown is mesial to the midline of the lateral incisor.
Treatment Alternatives:
Consider including the following with treatment planning: (a) No tx if pt does not desire it. If so, the clinician should periodically evaluate the impacted tooth for any pathologic changes. It should be remembered that the long-term prognosis for retaining the deciduous canine is poor, regardless of its present root length and the aesthetic acceptability of its crown. (b) Auto transplantation of the canine (c) EXT of the impacted canine and movement of a 1st premolar in its position (d) EXT of the canine and posterior segmental osteotomy to move the buccal segment mesially to close the residual space (e) Prosthetic replacement of the canine (f) surgical exposure of the canine and orthodontic treatment to bring the tooth into the line of occlusion. This is most desirable approach.
When to Extract an Impacted Canine:
EXT of labially erupting and crowded canine is contraindicated b/c this may complicate and compromise the orthodontic tx results, including the ability to provide the patient with a functional occlusion. EXT may be workable in the following conditions: (a) if it is ankylosed and cannot be transplanted, (b) if it is undergoing external or internal root resorption (c) if its root is severely dilacerated (d) if the impaction is severe (e.g. the canine is lodged between the roots of the central and lateral incisors and orthodontic movement will jeopardize these teeth) (e) if the occlusion is acceptable, with the first premolar in the position of the canine and with an otherwise functional occlusion with well-aligned teeth. (f) if there are pathologic changes (e.g. cystic formation, infection) and the patient does not desire orthodontic treatment.
Palatal Versus Labial Impations:
Palatal imp: Labial imp + at least 2:1 or 3:1. Labial imp primarily caused by arch length deficiency, and may erupt on their own without surgical intervention. Palatally impacted canines are more often inclined in a horizontal/oblique direction, whereas labial impactions offer a more favorable vertical angulation. Yet they are still considered difficult because of the needed delicacy ion managing the associated hard and soft tissues.
Management of the Palatally Impacted Canine:
Surgical methods are: (1) surgical exposure, allowing natural eruption...Useful when the canine has a correct axial inclination and does not need to be uprighted during its eruption. Progress should be closely monitored. A polycarbonate crown may be placed over the impacted tooth after its surgical exposure and cemented. Often, 6 mos-1 yr may elapse before the impacted tooth has erupted sufficiently to permit removal of the crown and its replacement with an orthodontic attachment. If the tooth fails to erupt, removal of any cicatricial tissue surrounding the crown. Takes a long time and unable to influence the path of eruption. (2) surgical exp with placement of auxiliary attachment with applied ortho forces. Attachment can be bonded to enamel or attached to a cemented band or crown. Two methods proposed:
- Two-step approach: First canine is surgically uncovered and the area is packed with a surgical dressing to avoid the filling in of tissues around the tooth. 3-8 weeks of healing, pack removed, and attachment placed.
- One-step approach: Attachment placed at the time of exposure after excision of tissues and a periodontal pack placed to minimize discomfort and prevent granulation tissues from covering the attachment before the clinician is ready to apply traction forces on the impacted tooth. Good for palatally erupting teeth with the advantage that when the force is applied, the clinician is able to visualize the crown of the tooth and have better control over the direction of the tooth movement.
Methods of attachment:
Don't "lasso" a ligature wire around the canine b/c too much bone has to be removed to accomplish this. Heavy exposure increases external root resorption risk from 8% to 14%.
Management of Labially Impacted Canines:
Due to insufficient arch length, the canine may erupt high in the alveolar bone and into the mucosa. Surgical exposure without the application of a traction force is a viable option, particularly in younger patients. The absence of adequate attached gingiva may cause inflammation of perio. It is hazardous to move teeth in the presence of inflammation. Therefore, exposure surgery should simultaneously provide a band of attached gingiva to the exposed tooth. Otherwise, mucogingival recession could lead to bone loss. Prior to surgically exposing labially positioned canine, adequate arch width should be achieved . The created space will also provide an adequate zone of attached gingiva that can act as a donor site for a partial thickness apically or laterally repositioned flap. Keratinized tissue should be placed to cover the CEJ and 2-3 mm of the crown. 3 mm of attached gingiva is considered physiologically adequate.
Orthodontic Considerations:
Prognosis depends on position of tooth relative to neighboring teeth, its angulation, the distance the tooth has to be moved, and the possible presence of ankylosis. Horizontal and ankylosed canines = poorest prognosis.
Fixed appliances advocated in most cases. Hawley-type appliances may be useful in patients with multiple teeth missing.
When applying traction, the direction of the applied force should initially move the impacted tooth away from the roots of the neighboring teeth. Additional considerations: (a) use light forces...no more than 2 oz (60 grams) of force, (b) either availability or creation of sufficient space in the arch for the impacted tooth, (c) maintenance of the space by either continuous tying of the teeth mesial and distal to the canine or placement of a close-coiled spring on the arch wire, and (d) provision by the arch wire of sufficient stiffness (.018 X .022) to resist deformation by the forces. This will also reduce intrusion of the anchor teeth as a reaction to the deflection of a lighter and more flexible arch wire.
If the overall ortho tx plan involves the removal of premolars, it is advisable to postpone their extractions until the canine is surgically exposed and orthodontic forces are applied. This is done to ensure the feasibility of moving the impacted tooth before extracting a workable replacement.
When it is decided to close the canine space orthodontically, the posterior segment must be protracted and the case finished in a Class II molar relationship on the affected side.
Retention Considerations:
Rotations and spacings more prevalent in posttreatment impacted canine spaces. To minimize or prevent rotational relapse, a fiberotomy or bonded fixed retainer may need to be considered by the clinician after completion of the desired movements and sometimes before the appliances are removed.
