What Are The Treatment Options in Patients with Unilateral Congenitally Missing Second Mandibular Premolars?

by Gerassimos Angelopoulos, DDS, Dipl. Ortho, MSc, Dr. Dent; Afroditi Kouli, DDS

Four case presentations are utilized to review the treatment options in patients with unilateral congenitally missing second mandibular premolars. Once diagnosed, the dentist can either preserve or remove the respective primary molar. Preservation will lead to a tooth-size discrepancy. To limit the size of the second primary molar to the dimension of the contralateral premolar, and to allow the preservation of alveolar bone, reproximation of its mesio-distal aspect should be undertaken. Later on, the primary molar may become infraoccluded or lost, necessitating coronal built-up or a prosthetic replacement, respectively. In the latest case, autotransplantation, replacement by an implant after the completion of growth or orthodontic closure of the space are well-accepted solutions.

Second primary molar removal may be performed by:

A) Immediate removal to allow adjacent teeth to close the space and deal with the orthodontic aspects later on.

B) Extraction and closure of the space by means which will prevent the deviation of the lower midline and the lingualization of the lower anteriors.

C) Controlled slicing of the second primary molar and subsequent bisection and removal of the distal part utilizing the mesial root as bookend, while the first molar freely moves mesially. To permit the unimpeded movement of the molar, the premature contacts of the upper second molar should be removed.

In conclusion, aiming the ideal occlusion and profile, the clinician should take into account other orthodontic problems, the possible agenesis of the third molar, as well as pre-existing disparities in lower midline, and accordingly propose the most appropriate treatment plan for each patient.

Congenitally missing second mandibular premolars are the second most frequent type of agenesis, after the third molar, with an incidence of 2.5% to 5% of the population in the USA and Europe.1–5 Unilateral versus bilateral lower second premolar agenesis has been reported to consist up to 60% of the agenesis cases.5–9

The objectives of this review are to direct the clinician through a diagnostic sequence of recognition and decision-making in planning treatment for a unilaterally congenitally missing second mandibular premolar in the most appropriate time and cost effective way.

The first step to formulate a treatment plan is to confirm a definitive diagnosis of the agenesis.

The time of eruption of the second mandibular premolar may vary from the normal values established for different sexes and races. A permanent tooth should not erupt later than 6 months to 1 year after the natural exfoliation of its predecessor. The congenital absence of teeth in the primary dentition is almost always associated with congenitally missing permanent teeth. According to Haavikko, the calcification of the second mandibular premolar starts at around 3.6 years of age for both sexes10.

In the literature, several cases of delayed mineralization and slow development of second mandibular premolar have been reported. Alexander- Abt (1999)11 reported a case of a 12-year old girl whose panoramic radiographs revealed an apparent agenesis of the left second mandibular premolar, whereas 13 months later (at the age of 13 years), the progress radiograph showed initial crown formation. Daugaard et al.12 showed that delayed development of the second mandibular premolar is observed in women but not in men. Nevertheless, Rölling (1980)3 and Bergström (1977)4 advised that a reliable diagnosis of a congenitally missing second mandibular premolar is possible in most cases around 9 years of age, although radiographic evidence of their mineralization is visible as early as 5 years of age. To diminish the chance of misdiagnosis, radiographs that indicate developmental absence should be examined carefully by magnifying glass for the presence of a tooth germ. The spontaneous absorption and disappearance of the follicle may occur in the initial stages of tooth development but always prior to mineralization. The definite diagnosis of a tooth as congenitally missing is based upon the presence of various radiographic signs, including the significant delay compared to the contralateral side, the involution of the corticated border with bone infill and the absence of cusp tip calcification.13

Upon the diagnosis of agenesis two main treatment options may be considered, namely, the extraction of the primary second mandibular molar or its maintenance in the arch. In most cases of extraction in patients with normal occlusion, our goal is to mesialize the first permanent molar in conjunction with orthodontic treatment, possible extractions of the other 3 premolars, as well as autotransplantation. With the introduction in the recent years of Temporary Anchorage Devices (TADs) and therefore the reduction of anchorage requirements, the unilateral space closure with- out other extractions has become increasingly popular.

In the case of tooth maintenance, our goal is to maintain the tooth with the alveolar bone for future implant and prosthetic reconstruction.

No less than 13 factors must be considered to decide whether to extract or maintain the second primary molar.

1. Dental and skeletal age of the patient: At the time of diagnosis, the skeletal and the dental age of the patient are important both for definite diagnosis of the agenesis and/or the presence of the ipsilateral third molar. Furthermore, vertical growth often continues past the pubertal growth spurt. Treatment initiations to close the space before or close to the peak of the pubertal growth spurt stimulate mesial dental drifting of the molars.14,15

2. The presence of the respective third molar: Agenesis of second mandibular premolars is associated with absence of other permanent teeth, especially the third molars of the same quadrant,7,9,10 which may be found in 48% of the cases. Usually, initial calcification of the third molars is observed at 9 years of age14 and third molars are considered to be missing only after 14 years of age.13

3. Additional aplasiae16 may influence the treatment decision.

4. Gender: Males and females have different maturation rates. Fudalej et al. (2007)14 showed that on average girls’ facial growth continues until about 17 years of age, whereas the average boys’ facial growth is complete at about 21 years of age.17,18

5. The distance of the second primary molar from the occlusal plane (possible presence of ankylosis): In ankylosis, vertical growth of the adjacent alveolar processes continues while the primary molar and its surrounding bone remain stable, a fact which leads to the submergence of the tooth relevant to the adjacent teeth, especially during adolescence. In adults, if submergence has not yet occurred, there is little or no chance of occurring during the rest of the life of the primary tooth, due to the fact that little growth of the alveolar ridges occurs19. However, crowns of primary molars are shorter than permanent molar crowns, therefore slight submergence might not be diagnosed as ankylosis.20,21 Certain methods for the detection of ankylosis, such as the tapping the tooth to detect a difference in sound are considered inaccurate. The most reliable indicator of primary molar ankylosis is to evaluate the interproximal alveolar bone le
vels on a bitewing radiograph. Flat bone levels between the primary molar and the adjacent permanent teeth indicate that the primary tooth erupted evenly with the adjacent tooth while angled or oblique bone levels between the second mandibular primary molar and the adjacent permanent first molar indicate that the primary tooth is ankylosed and the permanent tooth continued to erupt.17,22

6. The condition of the second primary molar, the degree of its root resorption, the presence of tooth decay, fillings and pulp pathology, the size difference between primary and permanent teeth, the condition of the bone after extraction of the primary tooth: Once the decision is made to extract the primary molar because of caries, resorbed roots or ankylosis, care should be taken to maintain the cortical plates intact during the extraction, especially in cases of ankylosis.

7. The stage of development of adjacent teeth: Peck et al. in 1996 had associated the agenesis of third molars and second mandibular premolars with the occurrence of peg-shaped laterals and palatally displaced canines.23 Two years later, Baccetti had also included the presence of submerged primary molars and enamel hypoplasia in the above findings.24 Contemporary data correlate agenesis of one or two second mandibular premolars with delayed tooth maturation. More specifically, in cases with unilateral congenitally missing second mandibular premolar, it can be expected that the canine and the first molar are delayed in development in men and women compared to dentitions without agenesis (canines, second premolars and first molars belong to the same developmental field).12 Furthermore, there seems to be an association between the agenesis of premolars and the reduction of the size of the remaining teeth, suggesting that in these cases extraction treatment may be often unnecessary.10

8. Lip prominence in relation to pronasale, pogonion and protrusion of the jaws: The extraction of the mandibular second primary molar is contraindicated in subjects with deep bite or hyperdivergent vertical skeletal pattern, mandibular retrusion or generalized spacing of the teeth. In addition, closing spaces may be detrimental to the facial profile of these patients.25

9. Lack of space for the permanent dentition and proclination of incisors may suggest extraction treatment.

10. The axial inclination of the teeth.16

11. The degree of interlocking intercuspation.16

12. The type of saggital occlusion.16

13. Parents and patients agreement in the treatment selection.

In contemporary democratic societies the clinician makes the treatment proposals and the patient with his/her parents make the decision taking in consideration their finances.

An 8-year old white Caucasian boy with Angle Class III dentoalveolar malocclusion has congenitally missing #45 and #38 (FDI numbers).

Clinical (fig. 1a,b,c,e,f,g) and radiographic (fig. 1d) examination revealed the following: a) Incomplete formation of #44 b) #47 has not erupted at all c) #48’s sperm was present d) #85 was present.

At that stage, a 3-month inclined plane treatment for the anterior crossbite correction was performed. The above findings in combination with the patient’s age and facial profile led to the decision of extracting # 85. Glassionomer cement was positioned on the mesial of # 55 (fig. 2a,b) and occlusal grinding of the distal cusps followed. Movement of both # 44 and # 46 (fig. 2c) was then noticed until age 12,1. This space reduction occurred without any orthodontic action and was followed by sectional orthodontics at age 14,8 (fig.3) for 11 months and by full-banded orthodontic treatment for 18 months, finishing with a Class III molar and Class I cuspid relationship (fig. 4a,b,c,d,e,f,g). Total treatment time with appliances was 32 months.

A 12 year 3-month-old white Caucasian boy, presented an Angle class II div. 1 dentoskeletal malocclusion and a congenitally missing second mandibular premolar (# 45). Clinical and radiographic (fig. 5a,b,c) examination revealed the following: a) eruption of the teeth proximal to # 85 b) slight crowding c) increased overbite d) lack of # 85’s root resorption and mild infra-occlusion of its clinical crown.

The above findings in combination with the patient’s age and facial profile led us to decide the maintenance of #85 in addition to interproximal reduction of the mesiodistal width to the width of the #35 to improve interocclusal relation- ship.

To estimate the correct amount of reduction, without causing any pulpal damage, the mesiodistal width of the primary molar was measured at the level of the cementoenamel junction on a bitewing radiograph. The estimate was marked on the occlusal surface of the primary molar and subsequently the bur (fig.16a,b) was positioned to cut toward the gingiva following the marked line on both mesial and distal surfaces. The average mesiodistal width of the primary molar was 9,5 mm and 2mm were removed from both surfaces. This procedure had left the crown 7,5 mm wide, which corresponds to the width of the contralateral second mandibular premolar (7,5 mm) (fig. 6c). Despite the root proximity of the adjacent permanent molar the enamel removal was asymptomatic and this is further discussed in the discussion section chapter 5. In order to prevent decay from interproximal surfaces where dentin is exposed, a layer of light cured restorative composite resin was applied to the proximal lateral and the occlusal surfaces of the typically short primary molar, so that it can function with the teeth in the opposing dental arch preventing supraeruption17,26 (fig.7). The total treatment length was 22 months and the class II correction was achieved thoroughly.

A 12 year 9 months old white Caucasian boy presented an Angle class II div. 1 dentoskeletal malocclusion with congenitally missing teeth # 25, # 35 and impacted # 43. Clinical (fig. 8a,c,e) and radiographic (fig. 8b,d) examination revealed the following: a) incomplete formation of # 34 b) # 37 had not yet erupted c) # 38’s sperm was present. d) significant restoration of #75.

The above findings in combination with the patient’s facial profile (fig. 8c) led us to decide the extraction of # 65, 75 and 83 (fig. 9), along with a Delaire face mask, as anchorage to facilitate the anterior movement of the posterior teeth anteriorly (fig. 10a,b). Alternatively TADs could have been used. The impacted # 43 was guided in transposition with the # 42. Mesial movement of # 26 and # 36 with improved occlusion and facial profile was noticed (fig. 11a,b,c,d). The total treatment length was 34 months.

A 9 year 1 month white Caucasian girl presented an Angle class II div. 1 dentoalveolar malocclusion with CM #45. Clinical (fig. 12a,c,d) and radiographic (fig. 12b) examination revealed the following: a) incomplete formation of # 44, b) # 47 has not yet erupted, c) # 48’s sperm was present, d) # 85 was intact.

The above findings in combination with the patient’s facial profile led us to decide the hemisection of # 85 (fig. 13a,b) and removal of its distal part to facilitate # 46’s mesial movement. The pulp was extirpitated from the pulp chamber and calcium hydroxide was placed to seal it off from contamination. There was no need to provide endodontic extirpitation to the mesial half. Once the mesial movement of the first permanent molar had slowed, due to its approximation to the mesial half of the hemisected tooth (fig. 14a,b), the mesial half of the # 85 was removed and space closure was completed by applying orthodontic forces27 (fig. 15a,b,c,d,e). At this point, an anchorage protection appliance was used (Class II elastics) to hold the lower anterior teeth forward. Such appliances may alter
natively be an activator, a Jasper Jumper, a Herbst, a Forsus, a protraction face mask, or a Hickham chincap.2,27 The total treatment length was 33 months.

5. DISCUSSION (Table 1)
5.a. Maintain the second primary molar:
According to Ten Cate, as the subjects grow older, the upcoming increase in masticory muscle force applied to the immature periodontal ligament could lead to occlusal trauma, initiation of resorption of the primary roots and surrounding bone and ankylosis. Therefore, probable causes for extraction of primary molars without permanent successors are pulpal pathology, large restorations, carious lesions close to the pulp, normal or pathological root resorption, ankylosis, differences in tooth sizes between primary and permanent teeth as well as clearly crowded cases. Judging from the above, it is difficult to say that the aforementioned changes rather support an extended life for the primary tooth than condemn it to its loss.12,19

In contrast to the above, if the patient has an ideal or acceptable occlusion, the preservation of primary second molars is a reasonable plan; since many can be retained at least until the patient reaches the early twenties.17

Bjerklin et al. (2008)25 reported survival rates of primary molar without permanent successors greater than 90 per cent. In their study in the 99 subjects with retained primary molars (mean age 24 years and 7 months) only 7 primary molars were lost because of root resorption, caries or infraocclusion.

Bjerklin and Bennett (2000)26 noted a 60 percent resorption of the mesial and 46 percent resorption of the distal roots of retained second primary molar between 11 and 20 years of age. Ith- Hansen and Kjaer (2000)27 had found that from 16 years of age 64.5 percent of patients with retained second primary molar showed no signs of severe root resorption or significant infraocclusion. The rate of root resorption of primary teeth diminishes with age.28

There are many reports of primary posterior teeth surviving until the patient attains 40-60 years of age,19,29,39 although none of these teeth had been slenderized. However, there is lack of a long-term study of teeth retained from childhood to late adulthood to establish the actual primary molar survival, especially when these teeth are slenderized.

Maintaining the second primary molar equals maintaining the alveolar bone both vertically and buccolingually.

On the other hand, maintenance can create an anteroposterior arch-length discrepancy. The second primary molar can be 2 to 3 mm wider than their permanent premolar successors, and a Class II or “end-on” molar relationship will typically be found with a maintained second primary molar. Therefore, it is favorable to reduce the width of the primary second molar to the size of the second mandibular premolar of the other side and make it function like the absent premolar by establishing an ideal Class I molar relationship. If the decision to reshape the tooth is made, radiographs need to be examined to detect the divergent roots that limit the extent of reduction. This procedure can be initiated from age 8 to 9 and can be performed until age 14 to 15.30 The onset or acceleration of the progress of root resorption of the primary tooth is likely to be an adverse side effect as the adjacent teeth converge on the often divergent, bell shaped roots of the second primary molar during space closure. Depending on the malocclusion, it is quite possible that second primary molar need to be moved orthodontically. Unfortunately, common sense suggests that severe root resorption may occur when primary molars are moved. In this direction, existing data are insufficient so further research is required in order to clarify the risks of severe root resorption during primary tooth movement.19 The conclusion, the decision lies on the orthodontist either to compromise with an “end-on” molar relationship by leaving the second primary molar intact or to risk potential root resorption by slenderizing it.17,19

According to the prognosis of the second primary molar the following options are proposed:

5.a.1. The second primary molar remains until late adult­hood.
It is widely accepted that a retained intact second primary molar with a decent crown, roots and supporting alveolar process bone can offer an adult patient many years of service. It has been found that once these teeth survive into adulthood, they can function. Even for second primary molars that are eventually lost, the average “life- time” rivals the lifespan of some prosthetic appliances.19

5.a.2. The second primary molar remains until early adulthood.
Once the patient reaches adulthood, osseointegrated implants are currently becoming the most biologically conservative and the mostly indicated option for replacing congenitally missing single teeth, provided that the patient can afford the expense. Alternatively, prosthetic reconstruction or in some cases autotransplantation of a maxillary third molar may be the treatment of choice. (See 5.a.3)

Implants and bone preservation
If implant therapy is the treatment of choice, the implant should be placed soon after extraction, close in time to extraction or exfoliation of the primary tooth, to achieve maximal preservation of alveolar bone. Extracting the primary teeth is sometimes difficult, requiring a flap and bone removal that could narrow the buccolingual alveolar ridge. Even an uncomplicated extraction will reduce the alveolar bone volume. This reduction has been estimated to be 18–25 percent of the bone mass and might jeopardize future implant therapy31,32. Ostler and Kokich (1994)33 estimated the long-term changes in the width of the alveolar ridge after the extraction of lower primary second molars and revealed a 25 percent reduction during the first 4 years, another 5 percent after 7 years, for a total reduction of 30 percent over 7 years. Nevertheless, the ridges could still receive a dental implant without a bone graft, even though the facial side was more resorbed than the lingual. Therefore the implant position should be more lingual, which suggests that the restorative dentist is about to alter the loading of the buccal and lingual cusps of the crown on the implant in order to prevent fracture of the abutment or the implant crown.17

Although implants seem to be the first choice, an obvious drawback is that they cannot be inserted until growth has been completed and they cannot be moved orthodontically since they behave as ankylosed teeth. The appropriate age for implant insertion is determined by the cessation of vertical facial growth. Cephalometric superimpositions practically show the cessation of vertical growth as they determine when the ramus stopped growing. Maintaining the primary tooth could be a semi-permanent solution, until the patient is old enough for the implant. It is the opinion of many authors that implants should be placed not immediately but close to exfoliation or extraction of persisting primary teeth in order to preserve alveolar bone34. If an implant is placed in this site, a bone graft might be necessary to provide adequate ridge width and height. Vertical bone grafting is usually an added expense for the patient and has variable results of success.

When implants are placed in young individuals in their late teens or early 20s, the time perspective is different, often 60–70 years with the life expectancy of today. Very little is known about the risks for complications and adverse effects in this elongated long-term perspective. Wear and degradation of the dental materials of the superstructure will necessitate revisions for functional and, most probably, aesthetical reasons. Therefore, a viable strategy is to place implants as late in life as possible and to use the different biological treatment modalities first.35

5.a.3. The second primary molar is lost early.
In case a second primary molar without a
permanent successor needs to be extracted early (caries, root resorption, infraocclusion), the choices are either to proceed to autotransplantation or to close the space. Another widely accepted treatment modality (known as orthodontic implant-site development) is to modify the eruption of the permanent first molar and first premolar, in a manner that they erupt adjacent one to the other, without maintaining the edentulous space. Despite the fact that such a plan requires longer orthodontic treatment to reposition the teeth apart to create the implant space, bone deposited equal to the width of the premolar and the molar is producing a more vigorous alveolar ridge, excellent for an implant placement.

The first premolar can be pushed into the position of second mandibular premolar, creating space for a single-tooth implant in the first premolar location, usually resulting in a much better ridge in which to place the implant.17,36 The alternative to implant replacement of the missing second mandibular premolar is the prosthetic reconstruction. This treatment modality, though financially attractive to the patient, requires tooth preparation, which advertently requires the sacrifice of the enamel of the adjacent teeth to the missing second mandibular premolar. Additionally, prosthetic replacements have a greater tendency to accumulate plaque and develop gingivitis. Keeping the tooth clean is more difficult in the molar region and can jeopardize not only the periodontal health but also the prosthetic result and the functional status.35 Eckert and Wollan (1998) had reported a 10-year implant survival rate of 95% while Näpängankas et al. (2002) showed an 84% success of conventional fixed restorations for the same period.

In general, biological methods i.e. growth-adapted measures, orthodontic treatment and autotransplantation are preferable to prosthetic replacement.

5.a.3.i. Autotransplantation
In an uncrowded arch in which the second primary molar is at risk of progressive root resorption or pronounced infraocclusion and the mesial movement of the first permanent molar is considered difficult or undesirable, autotransplantation may be the treatment of choice. Transplantation preserves alveolar bone volume and replaces a missing tooth without involvement of adjacent teeth, as, e.g. in tooth-supported prosthetic treatment. The tooth that can be used for such transplantation is a maxillary third molar, which has approximately the same crown size as a mandibular second primary molar. The success rates for autotransplantation range from 79 to 94 per cent for up to 26 years.30,37

Autotransplantation of a maxillary third molar, typically around age 18-19 years, is a viable option. Autotransplantation of maxillary premolars combined with orthodontic treatment should be the first treatment alternative in cases of missing second mandibular premolars, when a suitable donor tooth is available, as it reduces the severity of some orthodontic cases without compromising the dental status or interfering with conventional procedures in case of failure.

At this stage donor teeth that have not completed their root formation continue their root development. The manipulation of extractions applies great forces on teeth and the resistance of periodontal ligament fibers affects not only the healing process but the prognosis of transplants as well. The trauma produced during re-implantation can cause undesirable periodontal reactions and pulp damage, which have the potential to heal through various pulpodental processes. Success rates are higher in teeth with wide open root apices compared to teeth with complete root formation, as their pulp easily “recovers” vitality. Andreasen et al. (1990) claimed that “immature” teeth have a periodontal healing that reaches the 90%, while teeth with closed apices only 60%. The most serious complications of transplantations are ankylosis (usually “replacement ankylosis”), persistent external root resorption (surface resorption and inflammatory resorption) and micro trauma to the periodontal membrane during removal of the donor tooth.1,37,38

Despite the fact that autotransplantation in children may have a successful outcome decades later, this treatment modality suffers from 3 main disadvantages: First, it is subject to time constraints and can only be performed when the root has reached but not exceeded a specific developmental stage, which means that radiographic monitoring is required. Secondly, a suitable donor tooth such as a premolar or a third molar must be available, which is not always the case. Thirdly and finally, it involves surgical intervention.29

5.a.4. The second primary molar becomes ankylosed.
In case of an ankylosed and submerged second primary molar depending on the age may result in a narrow alveolar ridge with a vertical defect. Two possibilities exist in these cases:

(a) In early ankylosis two options have been proposed, decoronation or extraction. Decoronation has been presented to be a simple and safe surgical procedure for preservation of alveolar bone prior to implant placement.39 Tooth eruption continues even after active growth of the jaws (usually 1/10 of a millimeter per year).40,41 It has been clinically shown (mostly in single rooted teeth) that decoronation preserves the alveolar width and rebuilds lost vertical bone of the alveolar ridge in growing individuals. The biological explanation is that the decoronated root serves as a matrix for new bone development during resorption of the root and that the lost vertical alveolar bone is rebuilt during eruption of adjacent teeth.42 More evidence though, needs to be presented whether, decoronation can be equally successful in ankylosed second deciduous molars. Fines et al.1 showed that the mean increase of infraocclusion in retained primary molars was 1.0mm from the ages of 11 to 20.

(b) If the ankylosis occurs in early adulthood, then the submergence is slow. This creates the necessity of reestablishing crown height, in some cases to avoid supraeruption of the antagonistic tooth and reduce the possibility of mesial inclination of the adjacent permanent first molar, which could compromise the finished orthodontic and prosthetic result.13,15,20,22

5.b. Extract the second primary molar
It has been suggested that early treatment may allow spontaneous space closure by guiding tooth eruption.43 Svedmyr (1983)44 suggested extracting the second primary molar prior to eruption of the first molar in order to stimulate mesial eruption of the first molars. However, a definite diagnosis of aplasia of the second mandibular premolar in patients under 9 years of age can rarely be made.4,5,44 Other proposals have included extraction of a premolar in the opposing arch with, or without, active orthodontic treatment26 or extraction of three premolars in the fully dentate quadrants.46

In subjects with agenesis of the second mandibular premolar, extraction of the second primary molar before the eruption of the permanent first molar is believed to create favorable conditions for spontaneous space closure and to cause minimum tipping of the molars.36 However the diagnosis of agenesis at this age is not reliable. If the decision to extract the second primary molar is made early, for instance at 11 years of age, before the eruption of the second permanent molar, spontaneous improvement is often expected. Joondeph and McNeill (1971)46 suggested that in subjects with hypodontia, the second primary molar should be extracted early, before 11 years of age, to allow spontaneous space closure. In a 4 year follow-up after the extraction of the primary molar in subjects with agenesis of the second mandibular premolar, Mamopoulou et al. (1996)36 showed that 80 per cent of the resultant space was closed, leaving a mean residual space of 2 mm. Lindqvist (1980)43 reported similar findings. In 84 per cent of selected cases, the space was closed by mesial drift and tipping of the first molar and distal drift and tip
ping of the first premolar. Ex traction of the primary molar after completed root development of the second molar and first premolar often leads to more tipping of these teeth. Lindqvist (1980) also reported a significant mandibular dental midline shift towards the extraction site. Follow up studies demonstrate that early extraction is likely to produce inclination in 46% of patients with mesial rotation of the permanent first molars and distal drift of the first premolar and the canine in 80% of these closures.37 Furthermore, extraction of the primary molar after completed root development of the adjacent teeth often leads to more tipping of these teeth.

Closure of the space is beneficial in cases of a protrusive facial profile or crowding in the opposite dental arch.35,43 The major advantage of orthodontic space closure is the permanence of the finished result.

5.b.i. Controlled slicing of the second primary molar

5.b.ii. Hemisection of second primary molar
Controlled slicing is a good option for treating patients with congenitally missing second mandibular premolar for several reasons. It preserves the buccolingual ridge and produces bodily controlled mesial movement of the permanent first molar with no or minor rotation and inclination. In addition, it abolishes the need for prosthetic replacement, which could compromise the final occlusion or create bony defects.

The success rate of controlled slicing is high. A 90% success may be achieved when the technique is applied at an early age (8 to 9 years); the success rate tends to decrease as age increased. Controlled slicing is advantageous at an early age as it controls the inclination of the permanent first molar. It allows the permanent tooth to move through the buccolingual bone plate, which is maintained by the residual crown-root portion of the second primary molar, thus avoiding undesirable mesial rotation. Sequential slicing followed by hemisection and extraction of second primary molars in cases of congenitally missing second mandibular premolars is reported to be more successful than extractions avoiding the flattening of the facial fullness. An obvious disadvantage of controlled slicing technique is that the patient must visit the pediatric dentist or surgeon’s office twice, for the hemisection and the extraction of the primary tooth. The initial slicing of the distal crown portion of the primary molar can be done in the orthodontic office and requires only topical anesthetic. Care must be taken to protect the permanent molar.35 In a hemisection study of Northway (2004),45 the hemisection groups demonstrated diminished distal movement of the upper incisors, as well as of the upper and lower lip, whereas the lower molar protraction and molar relation were significantly improved.2 Hemisection facilitates the preservation of upper premolars, a fact which further enhances the facial fullness.

5.b.iii. Push and Pull technique
One other way to close the space is the push-pull technique, which refers to localized space closure (push and pull mechanics- PPM). The application of conventional space closing mechanics, such as powerchain, closing coils and closing loops should be avoided in order to minimize intrusive forces on the anterior teeth while maximizing mesial movement of the lower molars (Zimmer et al.). Utilizing PPM traction to the anterior teeth may also be avoided, as well as dental restorations and surgical procedures. This treatment modality is indicated for the majority of patients affected with aplasia.29

5.b.iv. T.A.Ds and 5.b.v. Reverse Headgear
In patients with no dental crowding and a normal facial profile, closure of the edentulous space from a congenitally missing second mandibular premolar could alter undesirably way the facial profile by flattening it. In this case additional anchorage is needed, intraoral or extraoral; in order to prevent these unwanted changes. Intraoral methods of additional anchorage are mini orthodontic implants or other temporary anchorage devices (TADs). However, the application of TADs has been reported to fail frequently in younger patients.47 Extraoral appliances able to accomplish this type of movement are a protraction facemask and a chin cap and elastics.29 By utilizing these methods, the molars can be protracted without side-effects on the anterior teeth of the arch.

5.b.vi. Corticotomy
Corticotomy has long been used in orthodontic treatment to accelerate dental movement and improve its efficacy. In 2001, Wilcko et al.48 suggested that, based on computed tomographic studies, the rapid tooth movement associated with corticotomy-facilitated orthodontics was more likely the result of a demineralization/remineralization process consistent with the initial phase of regional acceleratory phenomenon, namely an increase in cortical bone porosity and a dramatic increase of trabecular bone surface turnover due to increased osteoclastic activity. In corticotomy-facilitated orthodontics, the optimal tooth movement seemingly occurs when only a thin layer of bone overlies the root prominences in the direction of the intended tooth movement, in close approximation to the osseous insult. This thin layer of bone will demineralize and the remaining soft tissue matrix and islands of osteoid will be transported with the root surfaces, where the bone matrix will remineralize at the completion of the orthodontic therapy. In adolescents, the demineralization/ remineralization of the alveolar housing is seemingly complete, without a net tissue loss. In the adult population, however, the remineralization is less complete, albeit to a clinically insignificant degree, due to the decreased vitality of adult tissues in comparison with adolescent tissues. The tooth movement in this treatment is merely the result of a physiologic process and not the repositioning of segments of bone. Conversely, the movement of the teeth in the traditional orthodontics treatment is accomplished through tipping and uprighting and thus the pretreatment angulations of the teeth weigh heavily on the amount of tooth movement.

Compared with traditional orthodontic treatment, this treatment has the obvious advantage of dramatically shorter treatment times, which represents an attractive alternative for many patients. This convenience, additionally, is claimed to possess the ability to move teeth farther and yet provide a greater alveolar volume for increased post-treatment stability with decreased side effects.49

•Recommendations on treatment in young individuals with tooth agenesis are based mainly on clinical experience. Establishing registries for monitoring of clinical outcomes in this group of individuals is strongly advocated.

•The second mandibular premolars have a tendency to form late and may be thought to be missing only to be discovered to be forming at a subsequent visit. Congenitally missing second mandibular premolars can be diagnosed with a very high degree of certainty, in the early mixed dentition at about 9 years of age. Good quality premolars seldom form after the child is 9 years of age. To reduce the chance of misdiagnosis, correctly taken radiographs should be scrutinized for early indications of a tooth germ before mineralization.11

•Early detection of congenitally missing second mandibular premolars is important to enable appropriate interceptive orthodontic treatment. After the age of 9 options become more limited. Spontaneous space closure might no longer be an option.1

•No less than 13 factors must be considered to decide whether to extract or maintain the primary molar. These include the dental and skeletal age of the patient, the presence of the respective third molar, an additional aplasia, gender, a possible ankylosis, the condition and morphology of the primary molar, the stage of development of adjacent teeth, a lip prominence, the skeletal pattern, space conditions and finally the agreement of parents and patients in
the treatment selection.

•In adults with missing second mandibular premolar and retained second primary molar in good condition, its long-term prognosis seems promising.9 There are cases of primary molar that are eventually lost, but whose average duration of functionality competes the lifespan of some prosthetic appliances. There are many reports of primary posterior teeth surviving until the patient is 40 to 60 years of age.9 In adults, the shortening of retained second primary molar roots and changes in their submergence usually go unnoticed.19 The introduction of TADs enables absolute anchorage making the choice of space closure more accessible even in adults.47

•Second primary molar maintainance serves as an excellent tool to preserve bone for future implant replacement. In the case of early lost primary molar, the adjacent teeth are left to drift and to occupy the space until orthodontic treatment opens the space, while maintaining the alveolar bone for future implant placement, autotransplantation or space closure.

•In adolescents, space closure is definitely a more appealing solution because the final result is more permanent, as there is no need of maintaining space and awaiting the completion of growth for a permanent restoration.

•Hemisection provides an excellent first step in the process of space closure. It diminishes the backward movement of the anterior teeth, as well as the flattening effect that space closure might generate on the facial profile.2

•In cases of primary mandibular molar ankylosis the treatment choice is influenced by the continuing growth. At early phases, decoronation or extraction are proposed. In adulthood, crown height is reestablished to avoid supraeruption of the antagonist teeth and inclination of the adjacent teeth.

In conclusion, the timely cooperation of dentists and orthodontists allows the occlusal assessment, as well as the detection of other orthodontic problems, such as the absence of third molars and possibly pre-existing disparities in lower midline. Bearing in mind the final result in regard to the occlusion and profile, the thorough assessment that we have described should point to the most appropriate solution for the individual patient case.OH

Dr. Gerassimos Angelopoulos is an orthodontic graduate from the University of Toronto and is an instructor in the Department of Orthodontics at the National and Kapodistrian University of Athens.

Dr Afroditi Kouli currently is a graduate orthodontic resident at the University of Athens, Greece.

Oral Health welcomes this original article.

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