Tooth substitutions in orthodontic treatment

Dr. Ricky E. Harrell discusses how to manage space for teeth that are either congenitally missing or lost due to disease or trauma

One of the significant decisions facing an orthodontic practitioner is the management of missing teeth in orthodontic therapy. For the purpose of this article, the discussion of those missing teeth will exclude third molars as they are the most commonly missing teeth (9%-50% of patients)^1,2 and rather examine substitution patterns for missing maxillary lateral incisors, mandibular second premolars, mandibular molars, and mandibular incisors. Teeth may be congenitally missing, with 3%-8% of the population missing one or more teeth exclusive of third molars,³ or teeth may be lost for any number of reasons, including dental disease and trauma.

Substitution of maxillary canine for maxillary lateral incisor

The maxillary canine for a congenitally missing maxillary lateral incisor is a substitution frequently encountered in orthodontic practice. The incidence of congenitally missing maxillary lateral incisors varies between different racial groups and genders, with an incidence reported to be 1%-3% of females demonstrating a greater incidence than males.⁴ The decision to open space or to close space for a missing maxillary permanent lateral incisor is predicted on a number of issues:

• posterior occlusal pattern
• shape and color of the maxillary permanent canine
• residual bone in the lateral space
• tooth display at rest and smiling
• patients’ needs

Figures 1-3 show the dentition of an adolescent female who is congenitally missing tooth No. 10 and has a malformed tooth No. 7. The patient also demonstrated absence of teeth Nos. 1, 17, 18, 31, and 32, which influenced the decision on whether to open space for the maxillary lateral incisors or to close space as it affects the final occlusion of the maxillary and mandibular molars. The occlusion presents with normal overbite and overjet with the buccal occlusion presenting as a half-step Class II relationship. The profile is slightly full with normal vertical facial thirds. After consultation with parents and the patient, the decision was reached to extract tooth No. 7, to close the spaces while centering the maxillary midline onto the lower midline and mid-sagittal plane of the patient, and to reshape the canines to look more like lateral incisors with the possible long-term solution being either porcelain veneers or full coverage porcelain restorations.

Figure 1: Frontal occlusal

Figure 2: Right buccal

Figure 3: Left buccal

The 24-month treatment regimen consisted of fixed orthodontic appliances with Class III elastic support. The extraction space for tooth No. 7 and space in the area of tooth No. 10 were closed with posterior protraction (Figures 4 and 5), and an acceptable functional and esthetic result was achieved. Molar relationship at the completion of treatment was Class II, and the maxillary canines were substituted for the lateral incisors and the maxillary first bicuspids substituted for the maxillary canines (Figures 6 and 7).

Figure 4: Right buccal progress

Figure 5: Left buccal progress

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Figure 6: Right buccal final

Figure 7: Left buccal final

Substitution of a mandibular first permanent molar for a congenitally missing mandibular second premolar

A first permanent molar for a congenitally missing second premolar is the second most commonly encountered tooth substitution in orthodontics, although the incidence of missing mandibular second premolars is higher than that of maxillary lateral incisors (1.6%-9.0% according to the population and study).⁵ Dental disease, ankylosis, and idiopathic root resorption — all are reasons that non-replaced second deciduous molars are removed, often at a young age. The orthodontic practitioner and restorative dentist face the dilemma of a long-term restoration or tooth substitution by closing the space via resolution of dental crowding or protraction of the mandibular first and second permanent molars.

Before the advent of TADs (temporary anchorage devices or miniscrews), two problems were frequently encountered:
1. Closing this 9 mm-10 mm of space remaining in the arch after loss of the second deciduous molar was deviation of the mandibular midline toward the side of the lost second premolar as a result of the space closure, especially in a unilateral loss situation.
2. Over-retraction of the mandibular incisors and canines resulted in an adverse outcome on the occlusion and, in certain situations, the facial profile.

Figure 8 shows the right buccal occlusion of an adolescent patient who had lost the contralateral non-replaced second deciduous molars. #A was ankylosed and had allowed mesial tipping of tooth No. 3. Because two of the three non-replaced second deciduous molars were either missing or scheduled for extraction, it was decided to extract both #A and #T and close the residual spaces. A TAD (Ormco™ VectorTAS™ 6 mm TAD 1.4 mm diameter) was utilized for direct anchorage to protract tooth No. 30 into the space left from the extraction of tooth No. 7. An Ormco power arm was utilized for attachment of the coil spring to place the point of force application close to the center of resistance of tooth No. 30 (Figure 9). A lingual attachment was placed for elastic traction to counteract the tendency of the molar to rotate mesio-lingually as the protraction occurred (Figure 10). Tooth No. 31 was allowed to passively follow tooth No. 30 as the first molar translated mesially and bonded toward the later stage of treatment to close residual space.
Figure 8: Right buccal

Figure 9: Right buccal TAD
Figure 10: Occlusal

Figure 11: Right buccal final

Figure 12: Radiograph

The resulting occlusion exhibited a Class I molar relationship with good control of molar tip (Figures 11 and 12). Tooth No. 3 was also moved into the space of ankylosed A during the treatment. One could argue that #T should have been left in place and a Class II molar relationship accepted as the final result for the right side occlusion. However, should #T exhibit later resorption and eventual loss, either an implant-supported restoration or a fixed prosthesis would be necessary, or a second orthodontic treatment regimen could resolve the lost primary first molar.

Here are two options:
1. An implant-supported restoration or fixed prosthesis would be necessary.
2. A second orthodontic treatment regimen would need to be initiated to resolve the issue of the lost primary first molar.

Substitution of second and third molars for first and second molars

Figures 13-16 show an adult female patient who presented with non-restorable teeth Nos. 19 and 30. She also exhibited an impacted malformed maxillary left second bicuspid with an over-retained #J, and an endodontically treated tooth No. 4 with a full coverage restoration.

Figure 13: Right buccal

Figure 14: Radiograph right buccal

Figure 15: Left buccal

Figure 16: Radiograph left buccal

Figure 17: Radiograph TAD

The chosen plan of treatment included these steps:

• Remove tooth No. 4, J, and impacted tooth No. 13, root tips No. 19, and the failing tooth No. 30.
• Protract and substitute the mandibular second molars for the first molars, and the third molars for the second molars. Use TADs to assist in the protraction of the mandibular molars (Figure 17).

As a result of the treatment, a Class I canine relationship and Class II molar relationship (with mandibular second molars substituted for first molars and third molars substituted for second molars) were to be established.

After 36 months of fixed appliance wear, the spaces left by the extraction of the mandibular first molars were closed with second molar protraction and substitution, and the mandibular third molars were substituted for mandibular second molars (Figures 18, 19, and 20). Treatment time was within the normal range in adults, i.e., 2 to 4 years, according to bone density, bone availability, turnover rate, and hyalinization of the perio-dontal ligament. The treatment established the Class I canine and Class II molar relationships, and the patient does not have to seek any prosthetic replacements for the missing mandibular first molars.
Figure 18: Right buccal

Figure 19: Left buccal

Figure 20: Mandibular occlusal

Substitution of mandibular canine for mandibular lateral incisor

One or more mandibular incisors are congenitally missing in approximately 0.5%-3.4% according to the population studied, with Asian populations demonstrating the higher range of incidence. Due to their early emergence in the eruption scheme of the permanent dentition, the space is often diminished by drifting of the adjacent teeth. This poses a problem for both the orthodontist and restorative dentist with the decision to reopen space and to place a restoration or to close the space and either accept a compromise in overbite/overjet and midline coincidence. One solution in this arena is substitution of a mandibular canine for a lateral incisor, provided certain parameters are met. There is a significant size discrepancy between the canines and the lateral incisors with the mandibular canines averaging 6.7 mm in width with the mandibular lateral incisors averaging 5.9 mm in width.Root anatomy and size are also different, and the task of moving a large canine root into the portion of the alveolus normally occupied by the lateral incisor can pose problems as well.

In this final patient, a late adolescent female, the clinical presentation was that of a full-step Class II molar relationship on the left side, end-to-end Class II relationship on the right side, small maxillary lateral incisors, and a missing mandibular right lateral incisor with generalized spacing in the mandibular arch. The mandibular right buccal dentition had drifted significantly in a mesial direction, diminishing the severity of the Class II molar relationship. The mandibular canines were not particularly large, which aided in the treatment decision. Neither overbite nor overjet were excessive (Figures 21, 22, 23).

Figure 21: Right buccal initial

Figure 22: Left buccal initial

Figure 23: Lower occlusal initial

Figure 24: Right buccal final

Figure 25: Lower occlusal final

The decision was made to take the following steps:

• Extract maxillary first bicuspids.
• Restore teeth Nos. 7 and 10 to a normal size and shape.
• Finish the left side with a Class II molar relationship.
• Substitute tooth No. 27 for teeth Nos. 26, 28, and 27.
• Establish a Class I molar relationship on the right side as a part of the treatment objectives.

Tooth No. 27 was slenderized to make the fit more compatible with that of a mandibular lateral incisor. The final results are shown in Figures 24 and 25.

Summary

For a significant number of patients, orthodontists must decide how to manage space for teeth that are either congenitally missing or lost due to disease or trauma. Often patients are young at the time of presentation so that placement of a restoration or prosthesis is a lifelong maintenance issue and should be considered carefully before embarking upon orthodontic treatment. With thoughtful treatment planning, patient cooperation, and excellent biomechanical control of the teeth during treatment, orthodontists can attain satisfactory results by thoughtful substitution of teeth with the elimination of prosthetic restoration that requires maintenance for the remainder of the patient’s life.