The first molar has been reported to be the most caries prone tooth in the permanent dentition. Orthodontists are treating more adult patients who are more likely to have missing and severely decayed first molars. This article will show the various orthodontic and restorative options for first molars that are already extracted or have to be extracted. The following clinical situations will be addressed: molar uprighting and its advantages for the future restoration vs orthodontic space closure, strategic extraction of salvable first molars, impacted molars, and early extraction of compromised permanent first molars in young children.
Orthodontists are treating more adult patients who have extracted and decayed first molars.
Molar uprighting after old first molar extractions vs orthodontic space closure.
Strategic extractions of compromised first molars instead of sound premolars.
Management of impacted and ankylosed first molars.
Early extraction of first permanent molars with enamel hypoplasia in young children.
Early extraction of permanent first molars has been advocated in the literature for over a century. Considered to be most prone to caries, the removal of such teeth was believed to reduce the decay incidence in the remaining teeth. , After World War II, first molar extraction became a standard procedure. Hence, the term “extraction for prevention” was presented as a way for solving the “spread” of caries. The importance of the permanent first molar in the development of the dentition and the occlusion was controversial. Edward Angle, the father of modern orthodontics, described it as the keystone of the dental arch, whereas others advocated permanent first molar extraction on a routine basis. Many studies tried to counteract the uncontrolled extraction of first molars by showing its detrimental effect on occlusion. ,
Despite all the preventive and prophylaxis measures available today, we still have to deal with extracted and severely decayed permanent first molars in our daily practices. , , For patients referred by restorative dentists for migrated teeth after first molar extractions, orthodontic treatment should be aimed at facilitating the restorative process rather than correcting an existing malocclusion when it is not the patient’s chief complaint. In long-standing extractions not compensated prosthetically, the edentulous space is partially closed by mesiolingual tipping of the second molar. First molar extraction in the late mixed dentition or early permanent dentition can also lead to residual spaces because of distal tipping of the premolars. Spaces can be redistributed for restorative replacement of the extracted first molar or closed orthodontically. The main advantage of space closure is that the whole treatment is finished right after completion of the orthodontic treatment without patient dependence on a permanent restoration and less treatment cost. Space closure can be difficult in atrophic extraction sites, which require remodeling of cortical bone. Adults can have less bone apposition when moving second molars into the narrowed space of first molars extraction sites, greater likelihood of loss of alveolar bone crest height on the mesial of the second molar roots, and in some patients gingival recessions and root resorption. , Efficient orthodontic mechanics must be used to ensure delivery of light forces and increase the interval between activations so that the tissues involved have time to recover and avoid the development of soft-tissue clefts, which have a tendency to reopen spaces. Space closure can also be difficult in the maxillary posterior area with low sinus because tooth movement through the maxillary sinus is limited. Pneumatization can extend to the alveolar ridge making implant placement difficult. , Space closure of recent first molar extraction sites have better predictable results than ancient extraction sites. Although technically more demanding, it is sometimes advisable to extract a compromised first molar rather than a healthy premolar. Compromised permanent first molars, mostly because of enamel hypoplasia, can also be seen in young patients in the mixed dentition stage. Consideration should be given to extraction at the ideal developmental age, which corresponds to a chronological mean age of 8-10 years, to achieve spontaneous space closure with a mesial eruption of second molars.
This article will describe the orthodontic and restorative approaches with common clinical situations of long-standing and recent extractions of first molars, “strategic” extraction of compromised first molars rather than healthy premolars, impacted molars, and early extraction of first permanent molars with enamel hypoplasia in young children.
Long-standing nonreplaced first molar extractions
The main sequelae of extracted mandibular permanent first molars not replaced prosthetically are mesiolingual tipping of second and third molars and overeruption of the antagonist as seen with this 27-year-old patient ( Fig 1 , A and B ). By uprighting the tipped molars, the tooth movement not only facilitates prosthetic rehabilitation but also enables better design, periodontal conditions, function, and stability of the restorative solution. The maxillary third molar had to be extracted to facilitate the alignment of the blocked out second molar. In addition, the mandibular third molar had to be extracted because it would have been without an antagonist after molar uprighting. A maxillary removable biteplane was used to enable tooth movement ( Fig 1 , C ). The conventional uprighting spring made of a 0.019 × 0.025-in stainless steel wire was used against a segmental 0.019 × 0.025-in archwire engaged passively in canine and premolars 0.022-in brackets ( Fig 1 , D ). This anchor unit was reinforced by a wire from canine to canine bonded on the lingual of the canines. A space maintainer made of a 0.019 × 0.025-in wire was secured after tooth movement and replaced by a temporary bridge during the restorative phase ( Fig 1 , E ). As both abutment teeth adjacent to the extraction site had large restorations, a conventional full-coverage crown bridge was indicated. This restoration allowed occlusal grinding on the second molar to compensate for the extrusion effect of the uprighting spring. This reduction of the clinical crown height yields a more favorable crown-to-root ratio. Correction of the angular osseous defect on the mesial aspect of the second molar with better access to oral hygiene can be seen on pretreatment and posttreatment periapical radiographs ( Fig 1 , F and G ). Molar uprighting has also favored parallel preparations with better insertion and retention of the restoration ( Fig 1 , H ). Treatment time was 8 months. The orthodontic treatment objective was not to correct the existing Class II Division 2 malocclusion but to facilitate a restorative solution that remained functional and stable at 20 years after the treatment ( Fig 1 , I and J ).
This 32-year-old patient had a long-standing mandibular first molar extractions not replaced prosthetically. Orthodontic space closure replacing the first molar with the second molar is an attractive solution that avoids patient dependence on a permanent restoration. Light forces with increased intervals between activations are recommended in space closure, which greatly increases treatment time compared with molar uprighting for a restorative solution, especially in the mandibular arch with a greater bone density. What needs to be considered is not the clinical crown space at the extraction site, which often appears small because of crown tipping but the root space between the second premolar and the second molar ( Fig 2 , A ). This distance between the apices also needs to be reduced until adequate root parallelism is achieved. Optimal root position in space closure is essential for the correction of the mesial angular osseous defect, good occlusion, and stability. Despite a large extent of root movement, root resorption of the second molars was shown to be minimal in space closure. There is also a tendency for the mesial bone height of the second molar to decrease an average of 1.3 mm with space closure, but this does not compromise the periodontal support. ,
A diagnostic setup for second molar uprighting has shown that mandibular third molars will end up without an antagonist ( Fig 2 , B and C ). The 2 treatment alternatives were to extract third molars and upright second molars for a prosthetic replacement of the extracted first molars or to close the extraction space by bringing second and third molars forward. Even though more challenging and time consuming, orthodontic space closure was selected rather than extracting 2 sound molars to replace them with 2 implant restorations.
Uprighting springs started to mesial drive the second molar roots. Tip-back bends to fully correct root position, and power chains with light forces were used for space closure ( Fig 2 , D ). Progress periapical radiographs helped monitor root parallelism. Occlusal equilibration on the molars was necessary to compensate for mild uncontrolled extrusion. Complete space closure with adequate root parallelism between second premolars, second, and third molars was achieved in 15 months ( Fig 2 , E ). A 0.0215-in twisted wire was bonded between second premolars and second molars ( Fig 2 , F ). Space reopening and the likelihood of a long-term open contact is a common problem in first molar space closure, even with parallel roots and a twist wire.
A 52-year-old patient had the mandibular first molars extracted at age 14 years, resulting in a spaced dentition ( Fig 3 , A-D ). Orthodontic redistribution of the spaces in the first molar sites would be complex and time-consuming. Instead, as shown in the diagnostic setup, minor tooth movement of the canines and left second molar has facilitated a 3 single-tooth implants restoration in the existing spaces ( Fig 3 , E and F ). Orthodontic treatment time was 20 months. Optimal and stable occlusion was seen in photographs taken 6 years after the treatment ( Fig 3 , G and H ).