NEED FOR EVIDENCE-BASED TREATMENT PLANNING

Teeth are positioned exactly in the oral cavity for a reason. Even in a malocclusion, there is equilibrium between forces from the inside and from the outside of the dentition. If the orthodontist’s purpose is to change tooth positions significantly, the clinical problem is to estimate the amount of change that will remain stable over time.

Malocclusion of the teeth is caused by an interplay between inborn genetic factors and external environmental factors. Edward Angle believed that the environment could be modified by orthodontic treatment, that orthodontic treatment regenerated new bone, and that it would be possible to produce stable ideal occlusions without tooth extractions. However, we know now that bone yields to functional forces, and that premolar extractions are required in some cases. The percentage of extraction cases reflects a judgment as to the importance of how much the equilibrium of environmental forces around the dentition can be modified permanently. There is ample evidence in the literature that expansion in the lower arch, particularly in the canine region, is unstable, with little or no evidence to the contrary. Transverse expansion across the canines is almost never maintained, probably because of lip pressures at the corners of the mouth. It is important, therefore, to avoid an increase in the normal mandibular intercanine width (25-26 mm) during orthodontic treatment. Some excellent clinical long-term studies have demonstrated that not only the mandibular intercanine distance, but also the patient’s pretreatment mandibular arch form, should constitute a guide to arch shape.

The lower incisor position in space is also controlled by a balance of muscle forces, which may lie within a narrow zone of stability. Moving lower incisors forward more than 2 mm is problematic for stability, probably because lip pressure seems to increase sharply at that point. Further research is needed before evidence-based clinical guidelines on lower incisor proclinations can be established.

NEED FOR ARCHWIRE BENDING

Individualized archwire bends should be used to secure early and full correction of all rotations in the original malocclusion. The main reason is that even slightly broken contacts ( Fig. 8-1, A ) in both untreated cases and treated cases are the predictable starting points for relapse and later increased crowding.

Full correction of the crowded mandibular right central incisor (A) required marked archwire bends (B). C, Mesiodistal enamel reduction (stripping) was used to avoid incisor proclination and converted the contact points to small contact areas. The distal contact areas of the lateral incisors are purposely placed slightly labial to the mesial contact points of the canines and retained in these positions.

Slight undercorrection of previously rotated teeth is not easy to detect clinically. The size of the archwire bends necessary to produce full-rotation correction is often remarkably large ( Fig. 8-1, B ). This results from the slack between the archwire slot and the wire. Fine details must be checked toward the end of treatment by careful comparison with the pretreatment plaster models. In the maxilla, a mouth mirror is necessary to check the incisor region. If these steps are not taken, an undercorrected case may look good or even excellent on clinical examination in the orthodontist’s chair.

Small, meticulous archwire bends will also help ensure that the distal contact areas of the mandibular lateral incisors are placed slightly labial to the mesial contact points of the mandibular canines, and that the teeth are retained in these positions ( Fig. 8-1, C ). This is particularly important when the distal aspects of one or both lateral incisors are lingually displaced at the start of treatment. The mandibular anterior region is the most common area for increased crowding and relapse after treatment. Moderate crowding can be masked if the four incisors are positioned as a block outside the mesial contacts of the mandibular canines.

Careful archwire bends are also necessary to provide the desired and symmetrical axial inclinations (crown torque) of the maxillary and mandibular canines and premolars before appliance removal, to provide a full and radiant smile ( Fig. 8-2 ). No straight-wire approach or “fully programmed preadjusted appliance” used by an orthodontist without wire bending can place every tooth in correct position in all three planes of space.

Adult female patient with marked lingual tilt of all maxillary and mandibular teeth (A) and constricted smile with excessive gingiva-to-lip distance on the right side (B). C, Increased lingual root torque was provided by third-order bends in rectangular stainless steel archwires. Electrosurgery was performed from right second premolar to left lateral incisor. D, Posttreatment smile is radiant with symmetrical gingival exposure.

NEED FOR ARCHWIRE BENDING

Individualized archwire bends should be used to secure early and full correction of all rotations in the original malocclusion. The main reason is that even slightly broken contacts ( Fig. 8-1, A ) in both untreated cases and treated cases are the predictable starting points for relapse and later increased crowding.

Full correction of the crowded mandibular right central incisor (A) required marked archwire bends (B). C, Mesiodistal enamel reduction (stripping) was used to avoid incisor proclination and converted the contact points to small contact areas. The distal contact areas of the lateral incisors are purposely placed slightly labial to the mesial contact points of the canines and retained in these positions.

Slight undercorrection of previously rotated teeth is not easy to detect clinically. The size of the archwire bends necessary to produce full-rotation correction is often remarkably large ( Fig. 8-1, B ). This results from the slack between the archwire slot and the wire. Fine details must be checked toward the end of treatment by careful comparison with the pretreatment plaster models. In the maxilla, a mouth mirror is necessary to check the incisor region. If these steps are not taken, an undercorrected case may look good or even excellent on clinical examination in the orthodontist’s chair.

Small, meticulous archwire bends will also help ensure that the distal contact areas of the mandibular lateral incisors are placed slightly labial to the mesial contact points of the mandibular canines, and that the teeth are retained in these positions ( Fig. 8-1, C ). This is particularly important when the distal aspects of one or both lateral incisors are lingually displaced at the start of treatment. The mandibular anterior region is the most common area for increased crowding and relapse after treatment. Moderate crowding can be masked if the four incisors are positioned as a block outside the mesial contacts of the mandibular canines.

Careful archwire bends are also necessary to provide the desired and symmetrical axial inclinations (crown torque) of the maxillary and mandibular canines and premolars before appliance removal, to provide a full and radiant smile ( Fig. 8-2 ). No straight-wire approach or “fully programmed preadjusted appliance” used by an orthodontist without wire bending can place every tooth in correct position in all three planes of space.

Adult female patient with marked lingual tilt of all maxillary and mandibular teeth (A) and constricted smile with excessive gingiva-to-lip distance on the right side (B). C, Increased lingual root torque was provided by third-order bends in rectangular stainless steel archwires. Electrosurgery was performed from right second premolar to left lateral incisor. D, Posttreatment smile is radiant with symmetrical gingival exposure.

NEED TO INTRUDE MANDIBULAR RATHER THAN MAXILLARY INCISORS

Analogous with recent concepts of treatment planning in general and esthetic dentistry, the mechanical intrusion of maxillary incisors in orthodontics should be made with the utmost care to avoid “hiding” these teeth behind the upper lip. In most deep-bite cases, intrusion of the mandibular teeth should be done.