All teeth are viable candidates for extraction under the appropriate clinical circumstances. The clinical considerations regarding each type of tooth as a potential candidate for extraction will be discussed. Considerations include aesthetics, the ability of the patient to engage in interdisciplinary therapy, function, anatomic and skeletal limitations, compromised status, the mechanotherapy to be employed, the characteristics of the malocclusion being treated, the availability of specific types of anchorage, and the relative support of the hard and soft tissues. The decision to extract teeth and which ones, should support the orthodontic trilogy of function, stability and esthetics.
Once extraction therapy has been accepted as a viable treatment alternative for a given case, the next step is to determine which teeth are the most suitable for sacrifice under the particulars of the clinical situation presented. It must be noted at the outset that every tooth may be a candidate for extraction under the appropriate circumstances.
There are a number of generally accepted guidelines when considering extraction therapy. The first is to extract teeth that are nearest to the site of the deformity, crowding, or desired change. Another is to consider how the choice of dental units to be extracted, may affect the contacts, occlusion, and/or function? In other words, might extraction therapy deepen the bite, result in group function as opposed to canine guidance during lateral excursions, create food impaction areas interdentally, etc.? One might also want to consider in what way the choice of extraction units might affect anchorage considerations? Will the choice result in a greater dependence on differential as opposed to reciprocal anchorage?
One should also consider how the choice of which teeth to extract might affect the skeletal pattern? In other words, could there be a closing effect of the vertical dimension? How will the antero-posterior relationship be affected? For example, will the extraction of four first premolars in a Cl II Div II still leave the same relative maxillo-mandibular discrepancy; or would upper 4′s and lower 5′s, or just upper 4′s yield a better A-P correction? Another consideration might be whether the extraction pattern has the potential to result in a midline asymmetry.
The choice of which teeth to be extracted and the impact on the patient’s periodontal support should be balanced against those teeth scheduled to remain. Tangential to this consideration is if an atypical extraction pattern is selected based on periodontal considerations, will this result in compromised anchorage considerations and secondary occlusal disharmony? Another related consideration is whether implants should be used to create or enhance a compromised anchorage situation?
One must also be cognizant of the esthetic considerations relative to the teeth to be extracted, viz a viz the profile, the smile, and/or the midline. This often occurs in cases exhibiting a severely displaced upper lateral incisor or impacted canine with a poor prognosis for adequate retrieval. Finally, one needs to assess whether or not there is an asymmetry present? If so, is the asymmetry dental, functional, or skeletal? Is extraction therapy indicated for resolution of the asymmetry? Conversely, will extraction therapy, in conjunction with the other planned intra arch or inter arch mechanics, create an asymmetry where none previously existed?
Considerations regarding the extraction of individual teeth
Every tooth is a candidate for extraction under the appropriate clinical circumstances. Mascarenhas, et al. noted that “The selection of teeth for orthodontic extraction is an important decision [that is] modified according to the individual patient”. The extraction of premolars has been accepted and utilized for approximately 75 years. Every tooth in the arch has been extracted in conjunction with orthodontic therapy for a variety of reasons including space requirements; their longevity or usefulness has been compromised by caries, periodontal considerations, endodontic concerns, restorative issues, or surgical considerations; and patient choice stemming from financial constrains regarding attempts to save a particular tooth. What follows are the most common deliberations one should examine and evaluate when considering which teeth to extract.
Premolar teeth have always been considered the sacrificial lambs insofar as orthodontic extractions are concerned. Situated between the canines and molars, they function to aid in both incising and grinding while they guide boluses of food posteriorly for enhanced mastication. From an evolutionary perspective, early hominids had 4 premolars per quadrant and over time these teeth have become vestigial resulting in our having lost the first 2 from anterior to posterior.
The common considerations relating to the extractions of maxillary or mandibular first premolars are (1) they are usually closest to the crowding, proclination, and/or procumbency ; (2) they usually allow for more posterior anchorage to be available in order to maximize anterior retraction ; (3) the mesial concavity on their roots of maxillary first premolars often results in a predilection for periodontal sequelae; and (4), in cases of skeletal maxillary or mandibular prognathism, they may be extracted to camouflage the discrepancy if adjunctive surgical correction is not an option. Kravitz also notes that lower premolars may be viable alternatives to orthognathic surgery in the following circumstances:
no more than a full step Class III molar relationship,
less than 5 mm of reverse or negative overjet,
less than 3 mm of anterior open bite,
a mandibular dental protrusion,
mandibular anterior crowding,
acceptable facial esthetics, and
a thick tissue biotype with good dentoalveolar thickness and a healthy periodontium.
However, he goes on to note that thee challenge regarding the removal of lower premolars “…lies in avoiding excessive retroclination of the mandibular incisors, settling the posterior occlusion, and preventing supraeruption of the hanging maxillary second molars.”
The deliberations involving the extraction of second premolars are that they are (1) usually further from the site of the crowding, proclination and/or procumbency, thus there is the potential for less of an effect on the profile than if first premolars are removed; (2) there is less posterior tooth mass thus it is easier to protract posterior teeth due to enhanced anterior anchorage ; (3) it is often a smaller tooth thus enhancing the esthetic effect of the smile and a reduction in the visual perception of the buccal corridor; (4) depending upon the mechanics employed it may help decrease the patient’s vertical dimension; (5) it helps preserve the width/length ratio and zenith position ; (6) more rapid extraction space closure ; (7) it facilitates obtaining a Class I molar relationship. The negative considerations are the decreased ability to control first molar tipping and/or rotation, and that their extraction may result in a less than ideal contact point between the first molar and the first premolar.
Cotez and colleagues, noted that one of the key reasons to consider first molar extraction was that treating skeletal open bites in this manner “…provides functional results with more stability than [that] obtained in non-extraction treatment”. Aside from cases exhibiting high mandibular plane angles with or without an anterior open bite, first molars are also considered for extraction in cases where there is significant posterior crowding, extensive caries, hypoplastic lesions, periapical pathology, significant restorations, a high mandibular plane angle, and an open bite.
Maxillary first molars will often be identified for extraction when there is significant posterior crowding and there is a minimal need for any change in the anterior part of the mouth or soft tissue drape. If conventional protraction of the second and or third molars is to be undertaken, root structure of the anterior teeth must be of sufficient anchorage requirements to meet the demands of posterior dental unit protraction. Utilization of TADs often negates this consideration. The third molars should be in a viable position to erupt and become functional. All things being equal, these cases require more time as there is a greater amount of space that has to be closed. Extracting first molars has a greater potential to decrease the vertical dimension than the extraction of more anteriorly positioned dental units. Extracting mandibular first molars harbor similar considerations however greater attention needs to be paid to the potential for the third molars to erupt successfully.
Maxillary second molar extraction, aside from the introductory reasons for extracting molar teeth, is an underutilized alternative; reserved for those situations when the tooth “is severely damaged, ectopically erupted, severely rotated, or crowding in the tuberosity area ; or minimal first molar distalization is required and there is not enough space for 3 molars. Often called second molar replacement therapy it seeks to allow the third molar to replace the second molar while providing the required space for distal movement of the first molar. It also allows a full complement of teeth to occupy the esthetic zone and the buccal corridor. The only requisite for choosing this alternative is a good position of the third molar for acceptable future occupation in the arch; a trait that has been observed to occur 96–99% of the time. As noted by de Freitas and colleagues, the advantages associated with maxillary second molar extraction therapy are reduced treatment time, a lesser potential for extraction site re-opening, and easier distalization of the first molar. Mandibular second molar extraction is a much rarer called upon extraction pattern and is mostly reserved for those pre-prosthetic situations where first molar uprighting is required and the second molar may inhibit this treatment goal. The third molar must be closely watched as normal replacement for the second molar is far less predictable.