Infraocclusion or impaction of the maxillary first permanent molar

Published: January 2015

Bulletin #40 – January 2015

Infraocclusion or impaction of the maxillary first permanent molar

Unilateral impaction or arrested eruption of a maxillary first permanent molar is a condition which occurs from time to time and appears to be unrelated to other phenomena. There are no published figures in the literature of the prevalence of the phenomenon in the general population and neither are there known etiologic factors concerned with its occurrence.

For the most part, the molar begins normal eruption in its due time and then, for no apparent reason, its further vertical development becomes arrested. It seems never to reach the occlusal plane and, in time, its occlusal surface forms a step with that of the deciduous molar immediately mesial to it, as the latter continues to develop vertically. Often, too, a space develops between the impacted tooth and the second deciduous molar. As the dentition develops and matures with the shedding of the deciduous molars, the premolars erupt with interproximal spaces between themselves and between them and the infraoccluded permanent molar.

Normally developing maxillary first permanent molars erupt and very rapidly come into interproximal contact with the second deciduous molar, even in a generally spaced dentition. Thus, the existence of a space between these two teeth in the very young (7-8 years of age) patient is a very significant finding in the present context and bodes ill for the future, since it signifies a unilateral lack of the normal process of mesial drift on the affected side. In common, therefore, with infraocclusion of other deciduous and permanent teeth1-3 the arrangement of teeth mesial to the affected tooth will be disturbed in two possible ways. In the first place, they will become “strung out” with spaces between them forward to the canine and incisor region, often drawing the dental midline to that side, due to the integrity of the transseptal fiber band. The second effect is in the vertical plane, also due to the transseptal fiber band, where the immediate mesial neighboring tooth is out of occlusion, but to a lesser degree than the affected tooth.

Is the tooth ankylosed? Well, that depends on what you mean by ankylosed.

Strictly, according to Orphanet Journal of Rare Diseases, ankylosis is ….. a rare disorder characterized by the fusion of the tooth to the bone, preventing both eruption and orthodontic movement” and “…… the periodontal ligament is obliterated by a 'bony bridge' and the tooth root is fused to the alveolar bone.”

We orthodontists permit ourselves to use a broader definition of ankylosis, which is influenced to a degree by the lawyers whom we might suspect are watching us, when we look over our shoulders! For us, ankylosis is an all-inclusive term we like to employ when a particular impacted tooth has resisted our efforts to erupt it. Ankylosis is bandied about willy-nilly, to avoid the admission of failure and its possible legal consequences. This broader definition conveniently encompasses an array of errors of clinical judgment, which include imprecise positional diagnosis, inappropriate directional traction, poorly designed or impotent biomechanics and inadequate anchorage preparation4– after all, nobody can prove that the tooth was not truly ankylosed without doing the histology! Radiographs are singularly unreliable diagnostic aids in this respect and the use of CBCT in the determination of ankylosis has yet to be documented.

Yes, the tooth might be ankylosed, although this is by no means certain. Unfortunately, there are no published studies involving histologic examination of a large sample of cases affected by arrested eruption/impaction of a single maxillary first permanent molar. My own experience is relatively limited, since it is only over the past 3 decades that I have made a preoccupation or obsession of the treatment of impacted teeth. Because we have no evidence-based information to permit us to issue definitive treatment prognostications, only clinical aspects, diagnosis and treatment on an empirical basis will be offered here, highlighting features that have been seen in 3 of the few anecdotal cases that have recently come my way.

Case 1


Fig. 1a. Case 1. Panoramic film showing the infraoccluded maxillary right first permanent molar. There are interproximal spaces between all the teeth mesial to the molar and a deviation of the dental midline to that side.

Fig 1b. Case 1. A periapical view of the infraoccluded tooth. Note the marked radio-opacity of the roots of the tooth, indicating ankylosis.

To begin, I refer my readers to an article we published 4 years ago5 in which the infraocclusion of the maxillary right first molar had occurred during a 2 year period following the successful treatment of the patient’s malocclusion at age 14 years. It should be remembered that the period of 14 to 16 years is the critical growth period of the young female patient. The tooth had become ankylosed at some indeterminate point in time, probably close to the completion of the orthodontic treatment. As the result, 5mms of infraocclusion (a.k.a. 5mms of intermaxillary molar open bite) was seen 2 years later. The tooth was assumed to be ankylosed because of “….a sharp, solid sound on percussion” and “….the occlusion showed marked disturbances that could be attributed to the influence of the ankylosed molar ”. These included a distal tipping of the adjacent teeth towards the affected tooth (typically the second premolar more than the first), the presence of small spaces mesial to the molar and between the premolars themselves, a minimal maxillary dental midline discrepancy to the affected side and a degree of over-eruption of the opposing molar. It was noted that the second molar and second premolar had also become secondarily infraoccluded, to a lesser degree than the first molar, as has been reported elsewhere in relation to the teeth immediately adjacent to infraoccluded deciduous molars1-3. A panoramic view of the entire dentition (Fig. 1a) and a periapical view of the immediate area (Fig. 1b) were available, but a cone beam CT had been considered superfluous.

Treatment was carried out under supervision by a resident in the graduate orthodontic program and an oral surgeon at Hadassah School of Dental Medicine, in Jerusalem. The first molar was slowly and carefully luxated under local anesthetic cover. Initially it was completely immovable but, little by little, it was loosened until is reached a class 3 mobility of 1mm amplitude. It then successfully responded to the extrusive orthodontic force applied to it from attachments placed on the adjacent teeth, supported by a midpalatal implant.

Case 2


Fig. 2. Case 2. A CBCT transaxial series in the coronal plane through the infraoccluded maxillary right molar showing the root apices protruding though the floor of the maxillary sinus. The entire furca area of the tooth shows the “woolly” appearance typical of root resorption, with a thin wall apparently separating it from the pulp (arrows) and an absence of the lamina dura.

The second case involved a 17 year old male whose maxillary right first molar was partially erupted, with no erupted tooth distal to it. The overall malocclusion was class 1 with a fairly well aligned lower dentition incorporating only slight anterior crowding. Apart from the right posterior area, the upper dentition was well aligned. The dental midlines were coincident but both were 2mm to the right side. It was judged that the lower dental midline discrepancy was due to the pattern of crowding. The teeth in the left side of the two jaws were ideally related with excellent interdigitation. The canine and premolars of the right side were spaced, leading to occlusal relation that reached a half cusp class 3 relation of the premolars.

Minimal conservative treatment had been attempted by the orthodontist, aimed only at resolving the impacted molar. The anchor unit used in this case was a sectional mandibular bracketed appliance based only on the right canine-second molar teeth, with a sectional archwire in place. The patient was instructed to place vertical elastics from the mandibular anchor unit to an attachment on the molar. When the tooth did not respond after a reasonable period of time, the tooth was luxated by an oral and maxillofacial surgeon and the vertical forces were reapplied. Again the treatment failed to produce a response on the part of the infraoccluded molar. After a repeat luxation still failed to erupt the tooth, a second oral and maxillofacial surgeon was consulted. His advice was to extract the unerupted second and third molars, in the hope that this would alleviate the situation!

This case was referred to me for a second (maybe third or fourth) opinion and he attended with his father (a lawyer!) bringing with him cone beam CT records. At that meeting, the patient admitted to having been less than diligent in the placement of his rubber bands! This admission was later borne out by the original orthodontist.

There is much to be learned in this case from studying the cone beam CT. In Fig.2 consecutive transaxial cuts of the affected molar show the “woolly” appearance of the furca area of the molar caused by resorption of the kind seen in invasive cervical root resorption (ICRR)6. Even the presence of a thin layer of unresorbed dentine, closest to the pulp chamber, is reminiscent of that typically seen in ICRR, illustrating where the resorptive process fails to penetrate the predentine layer.7-9 On the basis of this analogy, it was concluded that this was the cause of the non-eruption and the subsequent resistance of the tooth to orthodontic forced eruption attempts. Since there was no way to reach this lesion in its inaccessible location, in order to seal it off, extraction of the tooth was deemed the only appropriate line of treatment. It is expected that the second and third molars will erupt in due time and will hopefully take the place of the extracted tooth.

The tooth was subsequently extracted in several pieces and, as the result, any visual evidence of the resorptive lesion was obscured due to difficulty in proper examination.

The obvious question arises that perhaps the lack of patient compliance was the reason the tooth did not move. However, it is more logical to assume that the ICRR-like lesion was the reason that the tooth did not erupt in the first place. It is then more pertinent to comment that the lack of compliance was the reason the opposing anchor teeth did not super-erupt to wreck the occlusion!

Case 3


Fig. 3a. Case 3. A CBCT transaxial series in the coronal plane through the infraoccluded maxillary left molar showing the resorbed furca area, its “woolly” appearance of root resorption (arrows) and an absence of the lamina dura.

So let’s look at another case which was almost identical except that, in this instance, the child was extremely cooperative with the placement and regular changing of the vertical elastics. The treatment failed to engender a positive response from the arrested maxillary right first permanent molar and the patient was referred to an oral and maxillofacial surgeon with the tentative diagnosis of ankylosis, for a deliberate luxation procedure. Under local anesthetic cover, the surgeon seized the tooth in extraction forceps but, instead of finding the expected “rock solid” ankylosed tooth, he discovered that the tooth displayed a good degree of mobility as seen in a normal tooth. Notwithstanding the subsequent efforts of the orthodontist, active eruption mechanics failed to move the tooth..

The 13.5 year old male patient was referred to me for an opinion and he attended with both parents, armed with a cone beam CT series. As with the previous case, above, the transaxial slices from the CBCT series showed the same “woolly” appearance of resorption of the root in the trifurcation area, similar to that seen in case 2 above and in almost any other patient afflicted with an advanced ICRR lesion. My advice was to extract the tooth and I also requested that the surgeon send the extracted tooth to me in formalin solution. The surgeon reported that the extraction was very easy with little resistance from the socket walls and clearly no clinically evident direct bony attachment.


Fig. 3b. Case 3. A view of the roots of the affected molar, showing the lesion in the furca area (arrow). Fig. 3c. Case 3. An explorer has been gently inserted deep into the lesion and reaches the pulp without hard tissue resistance.

Fig. 3b show views of the roots, together with the circumscribed ICRR-type resorption defect in the trifurcation between the roots. Inserting an explorer into the defect revealed considerable depth and its tip was judged to have entered the pulp chamber with no resistance (Fig. 3c).


Whether the etiology for impaction/infraocclusion of the molar is ankylosis or this ICRR-type of resorption, the affected tooth has very little bone to support it between the alveolar crest and the floor of the maxillary sinus. Usually, the root apices raise the mucous membrane of the sinus floor as seen in the cases presented here. Accordingly, there are several treatment options to consider, but a careful differential diagnosis is essential in order to make the appropriate choice.

The options are:

1. No treatment

2. Prosthetic build-up to compensate for the height loss

3. Surgical luxation and orthodontic extrusion

4. Extraction

5. Localized ostectomy

6. Intra-alveolar segmental osteotomy

While each of these options should be considered, the following are to be preferred.

If the tooth has been diagnosed as ankylosed, its extraction is fraught with several complications. In the presence of an extensive ankylosis, heavy handed attempts at extraction are likely to cause root fracture or even the establishment of an oro-antral fistula. For the most part, however, careful, slow and deliberate luxation to mobilize the tooth, followed by high levels of extrusive force maintained over a several weeks period, will often achieve positive results. For this to happen, the mobilization must achieve class 2 mobility (severe mobility of up to 1-mm amplitude) on the tooth mobility scale.10 Secondly, the extrusive force must be continuous and of broad range, to prevent re-ankylosis.

If, on the other hand, the diagnosis is ICRR-type of resorption, then extraction may be the only way out, because the location of the lesion makes it inaccessible to any attempt to eliminate or isolate it. Obviously in these cases extreme care must be exercised in removing the tooth, but there is reason to believe that the extraction should not be difficult and the likelihood of surgical complications consequently reduced.


1. Becker A, Karnei-R'em RM. The effects of infraocclusion: part 1 - tilting of the adjacent teeth and space loss. American Journal of Orthodontics, 1992;102: 257-264.

2. Becker A, Karnei-R'em RM. The effects of infraocclusion: part 2 - the type of movement of the adjacent teeth and their vertical development. American Journal of Orthodontics,1992; 102:302-309.

3. Becker A, Karnei-R'em RM, Steigman S.The effects of infraocclusion: part 3 - dental arch length and the midline. American Journal of Orthodontics ,1992;201:427-433.

4. Becker A, Chaushu G, Chaushu A. An analysis of failure in the treatment of impacted maxillary canines. American Journal of Orthodontics & Dentofacial Orthopedics 2010;137:743-54.

5. Rosner D, Becker A, Casap N, Chaushu S. Orthosurgical treatment including anchorage from a palatal implant to correct an infraoccluded maxillary first molar in a young adult. American Journal of Orthodontics & Dentofacial Orthopedics 2010;138:804-809.

6. Becker A, Abramovitz I, Chaushu S. Failure of treatment of impacted canines associated with invasive cervical root resorption. Angle Orthodontist, 2013, 83:870-876.

7. Heithersay GS. Invasive cervical resorption: an analysis of potential predisposing factors. Quintessence International, 1999;30:83-95.

8. Heithersay GS. Clinical, radiologic, and histopathologic features of invasive cervical resorption. Quintessence International, 1999;30:27-37.

9. Brosjo M, Anderssen K, Berg JO, Lindskog S. An experimental model for cervical resorption in monkeys. Endodontics and Dental Traumatology, 1990;6:118-120.Miller PD. A classification of marginal tissue recession. International Journal of Periodontics and Restorative Dentistry, 1985;5:9-13

10. Miller PD. A classification of marginal tissue recession. International Journal of Periodontics and Restorative Dentistry, 1985;5:9-13