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Impacted maxillary first molars

Published: February 2014

Bulletin #30 February 2014

Impacted maxillary first molars

Maxillary first permanent molars normally erupt at the age of 6-7 years and they take up a position in contact with the bulbous distal surface of the maxillary second deciduous molar, to establish a tight interproximal juxtaposition, initially with a slight distal orientation of their long axis. In time and as the occlusion develops into its full permanent stage with the shedding of the second deciduous molars, the teeth adopt a slight mesial orientation.

CCC.fig._1

Fig. 1. A bilateral case of impacted first permanent molars, with complete disappearance of the distal root of each second deciduous molar. The crowding tendency is already established. Note the mesial angulation of the permanent molars.

It is not often that anything goes wrong with this pattern of occlusal development but, just occasionally, the permanent molar appears to get stuck in a partially erupted state in the depression which is the distal surface of the deciduous molar, between the CEJ and the distal crown convexity (Fig. 1). This phenomenon has been attributed to a shortness of the maxilla and consequent crowding. Characteristically, the affected permanent molar will have developed a marked mesial inclination which, at this stage, is abnormal and which will also have initiated premature resorption of the distal root of the deciduous second molar. By doing so, it leaves a sharp edge of enamel at the dentino-enamel junction between crown and root and, because enamel is not resorbable, the permanent molar becomes trapped. In more advanced cases, the entire distal root of the deciduous tooth becomes resorbed and the resorbed root area on the underside of the distal part of its crown is sitting on gingival soft tissue. The pulp chamber of the tooth loses its distal wall to the resorption process and the pulp becomes exposed to the surrounding tissues, with which it becomes contiguous. Metaplasia then slowly converts the pulpal tissue into the same connective tissue of the surrounding area. Most often, this is a symptomless process and there is no inflammatory tissue reaction. The immediate area of gingival tissue may well be edematous and it may bleed easily, but this is most probably due to irritation and trauma from the sharp edge of the undermined enamel of the crown, rather than pulp pathology.

In the more severe cases, therefore, it is sometimes possible to probe horizontally for some distance under the sharp distal edge of the crown of the deciduous molar, without causing pain or discomfort. The dentist may then wrongly assume that the pulp is exposed and that this is, therefore, a potentially emergency situation. This is not so, since the mesial and palatal roots are often unresorbed and will maintain the tooth firmly in place for many months with no symptoms and no pathology per se.

CCC.fig._2

Fig. 2. Although this appears to be a unilateral case of molar impaction, careful examination of the intact side will reveal that the distal root of the deciduous molar has been resorbed away, suggesting a spontaneously resolved mild impaction. Note the contrasting angulation of the first molars.

Clinically, it seems that the condition is more frequently unilateral than bilateral. However, when studying a panoramic radiograph of the normally erupted permanent molar in a unilaterally affected very young patient, it is common to see considerable dystrophic resorption of the distal root of the second deciduous molar  (Fig. 2). This suggests a subclinical or spontaneously corrected, milder variation of the same condition.1

Treatment

Orthodontic treatment in the very young in the early and middle mixed dentition stages, is very much discouraged for most malocclusions. There is certainly a place for initiating orthodontic treatment in the later mixed dentition, when the millimeter or two of leeway space may be critical but, for the most part, treatment should be started only when the permanent teeth are erupted.

Nevertheless, there are situations in which an early treatment is justified, such as in the present context, or in a patient with a unilateral crossbite with functional shift, or an impacted central incisor. These conditions should be treated to alleviate the immediate problem as simply and in as short a time as possible and without aiming for alignment or occlusal perfection at this time.

Active treatment is necessary to resolve the impaction of the molar. It should be treated as soon as it is diagnosed, since non-treatment will make the impacted tooth vulnerable to caries and endanger the future of the deciduous second molar which, at the age of 6-7 years, is an important pillar in maintaining a physiologic occlusion.

Without question, the simplest and quickest solution is to extract the deciduous second molar and permit the permanent molar to erupt unimpeded – but that will collaterally initiate a chain of deleterious effects. Mesial drift will occur very quickly and, in combination with a mesio-lingual rotation around the palatal root, will exaggerate the mesial inclination as the tooth races to close off the extraction space. Coming from fairly high up in the alveolus, the tooth also translates mesially as it develops vertically, to end up with its developing root apices too far mesially. Thus, when space regaining becomes necessary, the molar needs to be moved back a considerable distance and tipping alone will be insufficient. Distal root uprighting and the need to establish appropriate anchorage to achieve this, become serious practical problems.

The three-part plan

The alternative to extraction calls for a plan made up of three elements. The first part is to tip the permanent molar distally, to free it from its entanglement with the disto-cervical edge of the crown of the deciduous molar. The second is to guide it to erupt vertically downwards to the occlusal plane while preventing it from relapsing back into the resorption defect of its deciduous neighbor. The third part of the plan requires that the deciduous molar should remain in its place and, thereby, re-establish the integrity of the arch and maintain space for a further few years until the permanent teeth are due to erupt.

Many orthodontists will attempt to place an elastomeric separating ring around the contact area.2 However, unless the permanent molar contacts the deciduous tooth slightly apical to its normal contact area, insertion of the elastomeric separation ring will be virtually impossible, since the mesial part of the permanent molar crown will have burrowed into the resorbed area of the root in the area of the CEJ. Even in those cases where the ring may be placed, it is likely to be accompanied by considerable bleeding, as noted above, but it will have the effect of creating a minor separation between the teeth. At the same time, it will also prevent eruption of the permanent tooth and it will therefore have to be removed after a week or two, in the hope that a degree of eruption will occur before the tooth re-impacts in or close to its initial position – the tendency for this kind of relapse is common. Success can sometimes be achieved by repetition of placement and removal intermittently, although it may take a long time and many visits.

A second method uses a brass wire ligature, tightly encircling the area of contact between the two teeth, thereby forcing the two molars apart in much the same way as with the elastomeric ring. This is repeated several times and, again, short spells of respite may permit vertical eruption of the tooth, but the competition between vertical eruption and the tendency for mesial relapse is keen.3

Placement of an orthodontic band on the deciduous molar with a rectangular wire spring slotted into the tube or bracket on the buccal side has also been suggested. A good range of spring action is difficult to achieve unless the spring loops into the buccal sulcus as it approaches the impacted tooth. However reactivation, slotting the wire back into the attachment on the band and engaging the impacted tooth are difficult to perform successfully. Pain, discomfort and ulceration of the oral mucosa are difficult to avoid.

In each of these methods a force is applied to the impacted permanent molar and the reactive force is directed solely at the adjacent second deciduous molar, whose continued existence in the mouth rests on roots which are resorbing. As a consequence, the resorption process of the roots is likely to be aggravated by these forces and this deciduous anchor tooth may be lost very prematurely, sometimes before the first aim of the procedure has been secured. Accordingly, the second and third elements of the three-part plan referred to above cannot be realized and a separate space maintainer needs to be placed.

Of course, an appliance may be constructed to include more dental units, with orthodontic brackets on the erupted permanent teeth and the other deciduous teeth, in order to spread the load and minimize the reactive force on the weakened second deciduous molar. However, this would involve unnecessary widening of the scope and cost of treatment, when the aim of early treatment in these cases should be strictly interceptive in nature, leaving the overall treatment until the patient reaches the permanent dentition stage, 5 or 6 years later.

A removable appliance

A removable orthodontic appliance comprises an acrylic base which is held in place on the teeth by strategically placed clasps of one sort or another. In essence it is a standard Hawley retainer with the addition of active elements. Unlike a fixed appliance which is capable of applying force in different directions and on many teeth simultaneously, the removable appliance divides the teeth into those used for retention of the plate in the mouth and those that are to be moved. The movement of teeth must be limited to employing 2 or 3 active elements, otherwise the retentive elements will not be adequate to stabilize the plate in place. Proper adaptation of the acrylic base in the palatal vault and snug contact with the teeth provide adequate anchorage potential for the application of force from a spring which is cured into the acrylic base. CCC.fig._3

Fig. 3a. an 8 year old child with a crowded dentition and the maxillary right first molar impacted beneath the distal of the second deciduous molar (arrow).

Fig. 3b. a simple removable acrylic appliance with 5 retention clasps and a finger spring (arrow). The free end of the spring traverses the occlusal surface of the first molar and is adapted to lie flat across its undulating surface. A blob of acrylic was added to perform more closely to the occlusal pattern of the cusps.

Given that the patient is a 6-7 year old child, with relatively little or no appreciation of the importance of the intended treatment, no motivation and often with management issues, the removable appliance has several advantages. The sole intra-oral procedure that is needed is taking an alginate impression of the teeth. No other dental procedures need to be performed in the mouth apart from teaching the child and the parent how to place and remove the appliance, together with oral hygiene instruction. Adjustments, tightening of the clasps and activation of the springs are all performed outside the mouth, at the chairside. Pain is not a factor and the entire process is an excellent way in which to overcome fear of the dental unknown and to introduce and encourage a very young child into becoming an exemplary patient. Children adapt to these appliances extremely well and the whole treatment regimen can be eminently positive.

CCC.fig._4

Fig. 4a. The removable appliance is placed and engaged on the left side, leaving the right side a few millimeters away from its final location, to illustrate the degree of deflection of the spring after activation (arrow).

Fig. 4b. The spring was brought mesially to its place before fully engaging the right side of the appliance (arrow).

Ideally in these cases, it is recommended to use several retention elements on the plate (Figs. 3-5). An Adams’ clasp on the deciduous second molar of the affected side and another on the erupted first molar or second deciduous molar of the opposite side are essential. A ¾ circumferential clasp should be constructed to engage the buccal bulge of each deciduous first molar or the deciduous canines. A labial arch or a single clasp on the two central incisors is often a good stabilizing unit. A useful addition is to extend the acrylic base to cover the occlusal of the posterior teeth. This enhances the retention of the plate and also separates the teeth to provide better access to the occlusal surface of the tooth and to simplify its movement.

A palatal finger spring should be extended from the middle of the palatal acrylic base and over the occlusal surface of the impacted tooth, terminating on the buccal side of the tooth, to provide the means of controlling its placement in the active mode. The activated spring has a strong displacement component which will destabilize the plate unless the above retentive elements are adequate. The anchorage for this simple movement is shared by all the teeth that come in contact with the plate.

CCC.fig.5

Fig.5. A view of the right side after completion of the distal movement and subsequent eruption of the permanent molar, which took 4 months to achieve.

The plate should be worn full time, including during meals and taken out only for tooth brushing. Within days, the initial difficulties with speech and eating are overcome and the appliance is very comfortable and easy to accommodate to.

CCC.fig._6

Fig. 6a. A pre-treatment lateral jaw view of the right side to show the degree of impaction of the permanent molar and resorption of the distal root of the deciduous second molar.

Fig. 6b. A post-treatment lateral jaw view of the disimpacted molar.

Movement of the tooth is usually rapid and, once a small gap has appeared (Fig. 6) and has revealed the unencumbered mesial surface of the permanent molar, the shape of the spring should be altered so that it rests between the permanent and deciduous molars in its passive position. This will prevent the tooth from relapsing and, at the same time permit its vertical eruption towards the occlusal plane.

The force required to move the molar is ideally around 25-30 grams and, on the removable appliance, its delivery can be easily measured and controlled with the aid of a Dontrix or other form of force gauge instrument. Sir Isaac Newton’s “equal-and-opposite” counter force is distributed to all the other teeth in the upper jaw that come into contact with the removable appliance, including the area of the palatal vault. Thus, there is virtually no reactive force pitted against the second deciduous molar and this tooth will usually last considerably longer before it sheds naturally. Nevertheless, in the event that it exfoliates before its due time, the same plate may be modified very quickly, easily and cheaply by adding an Adams’ clasp to the previously impacted permanent molar and, thereby, maintaining the vacated ridge space until premolar eruption.

The clear advantages exhibited by the removable plate make it particularly suited for all three essential elements needed for the treatment of an impacted maxillary permanent first molar.

References

1. Barberia-Leache E, Suarez-Clúa MC, Saavedra-Ontiveros D. Ectopic eruption of the maxillary first permanent molar: characteristics and occurrence in growing children. Angle Orthod. 2005;75:610-5.

2. Seehra J, Winchester L, DiBiase AT, Cobourne MT. Orthodontic management of ectopic maxillary first permanent molars: a case report. Aust Orthod J. 2011;27:57-62.

3. Kupietzky A. Correction of ectopic eruption of permanent molars utilizing the brass wire technique. Pediatr Dent. 2000;22:408-12.