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An atypical presentation of mechanical failure of eruption of a mandibular permanent molar: diagnosis and treatment case report.


Failure of eruption is rare but has significant clinical risks and implications. Early diagnosis and correct treatment are essential to its management [Raghoebar et al., 1991a]. Primary failure of eruption (PFE) was first described by Proffit and Vig [1981] and defined non-ankylosed teeth which fail to erupt. This eruption disorder was further classified by Frazier-Bowers et al. [2007]. In their study of 97 cases, almost 40% of the cases were PFE and 20% were mechanical failure of eruption (MFE). Both have similar presentations at their early stage. Differentiation between PFE and MFE is essential and often relies on progress radiographs, longitudinal clinical data and a therapeutic diagnosis.

PFE (Table 1, Fig 1a-b) can lead to severe posterior open bite. Affected teeth may erupt into occlusion and then cease erupting becoming relatively submerged without ankylosis or they may fail to erupt completely. PFE can be divided into two types depending on the timing of onset:

* Type I (classic form, Fig 1a) affects all susceptible teeth at a pre-determined chronological age i.e. all teeth fail to erupt at the same time, teeth posterior to the most mesially affected tooth may not erupt at all.

* Type II (Fig 1b) affects all susceptible teeth at a specific stage of root development i.e. teeth posterior to the most mesially affected tooth will develop, partially erupt and then gradually fail to erupt any further.

Involved teeth have an abnormal and limited response to orthodontic force and usually result in ankylosis following its application. An autosomal dominant inheritance pattern has been suggested, possibly linked to a mutation of the Parathyroid Hormone Receptor (PTHR1) [Frazier-Bowers et al., 2010].

Conversely, MFE (Table 1, Fig 1d) has a normal eruption mechanism. Radiographically there is appearance of relative submergence due to ankylosis. There is no clearance of the eruptive path. Mechanical failure is speculated to be secondary to a period of ankylosis [Brown, 1981] or a mechanical interference [Brady, 1990]. Successful treatment which combines a surgical and orthodontic approach [Raghoebar 1991a; Lim et al. 2008; Lygidakis et al., 2009] to erupt the affected tooth can resolve future dental problems [McCafferty et al., 2010].

This article reviews a case that was affected by atypical MFE. The patient presented with failure of eruption of her mandibular right first permanent molar, 46. This may have been attributed to either a failure of the eruption process (PFE) or as a result of a mechanical interference (MFE). Distinguishing between the two is crucial in determining the prognosis of the affected teeth.


Case Report

A 10-year-old girl was referred by her general dentist to the Dublin Dental University Hospital Orthodontic Department to investigate her partially erupted 46. Her medical and dental history was uneventful and there was no family history of tooth eruption failure. Her extra-oral features were normal. Intra-oral examination revealed a partially erupted 46 with only the occlusal surface evident. The remaining three first permanent molars were fully erupted. 46 gave a dull sound on percussion. An orthopantomograph (OPG) confirmed the presence of all permanent teeth, including third molars. In the mandibular right quadrant there was a submerged 46 relative to the occlusal plane of the teeth in the lower arch, an unerupted mandibular right second permanent molar, 47, and third permanent molar, 48 (Fig 2).


There appeared to be evidence of obliteration of the periodontal ligament of the mesial root of the 46. This obliteration and the dull sound of the affected tooth on percussion could indicate ankylosis [Andersson et al., 1984; Raghoebar et al., 1991b]. A follow-up appointment was made for 6 months to allow spontaneous eruption. At that second appointment, there was no evidence of eruption of 46 so treatment was commenced.







Treatment. All local, systemic and endocrine factors were eliminated. The initial treatment plan involved surgical luxation followed by orthodontic treatment. Surgical intervention requires significant force and carries a considerable risk to the infra-occluded tooth and the surrounding teeth, including root fracture and pulp necrosis, however it was the treatment of choice and consent was obtained.

Following mandibular block analgesia, the 46 was mobilised using a Coupland[R] elevator by surgical luxation. Orthodontic forces were immediately applied to the tooth in an effort to promote its eruption (Fig 3). This attempt was unsuccessful and no movement of the 46 was observed. This negative response to orthodontic force could indicate ankylosis of the 46 [Frazier-Bowers et al., 2007]. At this stage mechanical impaction was not suspected as there was no obvious obstruction as 46 was occlusal to 47. Subsequent radiographic examination revealed that the 47 had continued to develop thus eliminating the diagnosis of PFE type I (Fig 4). Clinically, 47 became partially erupted and then ceased erupting. This could indicate PFE type II. However, a subsequent OPG (Fig. 5) showed that the eruption failure was most likely mechanical in origin. 46 may have experienced a transient ankylosis which would be coincident with its failure to erupt and migrate mesially thus allowing 47 to over-erupt. The 47 then became impacted against the 46 and the 46 against the mandibular second premolar, 45.

Follow-up. An attempt was made to upright the partially erupted 47 to relieve crowding and its mechanical obstruction of 46. This was difficult and complicated by the unerupted 48 which acted as a physical barrier to the uprighting of 47. No eruptive movement of 47 was achieved and consequently no movement of 46. Any delay in treatment at this stage was significant and risked re-ankylosis of 46 [Frazier-Bowers et al., 2010].

Extraction of one unit would relieve the crowding and 46 and 47 were assessed for ankylosis and their radiographic position; 46 showed signs of mobility thus indicating that it was not ankylosed anymore. A decision was made to extract 47 due to its comparatively unfavourable alignment in order to salvage the non-ankylosed 46 (Fig 5). Therefore 47 was extracted surgically without complication. Orthodontic forces were applied to 46 (Fig 6) and the tooth began to erupt. With continued force it was up righted and brought into occlusion with no complication of ankylosis (Fig 7 and 8).

Comprehensive orthodontic treatment was then commenced to align the maxillary and mandibular arches. This included a maxillary removable appliance and lower fixed sectional appliance. The treatment was completed using an upper and lower fixed appliance. The final result left the patient with an upright 46 in occlusion and a bilateral functioning posterior bite. No retention was needed to maintain the position of this tooth as 48 continued to erupt and migrate mesially thus increasing posterior occlusion and support.


Disturbance in eruption of first and second molars is rare with an incidence in the normal population of around 0.6% [Prece, 1985]. It can occur as a result of systemic factors or local factors as described by O'Connell and Torske [1999] or by failure of the eruption process.

Disorders of tooth eruption can be difficult to categorise so diagnosis must be based on a combination of longitudinal clinical and radiographic findings, and the tooth's response to treatment. In this case, initial treatment options were extraction, orthodontic treatment or prosthetic build up. Raghoebar et al. [1990], showed that timely extraction of a first molar tooth before a patient's growth spurt could result in spontaneous closure of the space, especially in the maxilla.

Extraction of the 46 was not recommended as it could have resulted in jaw fracture and the root formation of the 47 had developed beyond its bifurcation thus limiting its potential for space closure. In the absence of treatment or with extraction of the affected tooth, adjacent teeth could drift and opposing teeth over-erupt. There would also be a risk of decreased growth of the alveolar process which is dependent on tooth eruption which would complicate future orthodontic treatment with difficult space closure and unfavourable tooth angulation. Prosthetic build-up would be unpredictable at this age and best carried out after the patient's growth spurt if needed. A combined orthodontic and surgical approach to erupt the permanent molar has been suggested by [Geiger and Bronsky, 1994; Raghoebar 1991a; Lim et al. 2008].

The initial failed attempt at surgical luxation and orthodontic movement may have been due to transient ankylosis. Ankylosis can occur as a result of trauma, infection, disturbed local metabolism and genetic factors [Raghoebar, 1991a]. It can initially start as transient inflammatory resorption where damaged areas of the periodontal ligament are colonised by tissue-resorbing cells. This can progress to replacement resorption where bone forms on to the denuded areas of the root surface and the periodontal ligament is obliterated [Tronstad, 1988]. The outcome of these sequelae depends on the amount of root surface affected. Tronstad has suggested that if less than 20% of the root surface is affected then reversal of the ankylosis can occur and normal eruption can resume. This was most likely the case for tooth 46, where the tooth was transiently ankylosed but regained its potential to erupt.

The second failed attempt to erupt 46 was due to a mechanical obstruction. This transient ankylosis between 46 and the surrounding alveolar bone allowed MFE to ensue. From clinical and radiographic monitoring, 47 continued to develop thus ruling out PFE, type II. Subsequently, 47's eruption mechanically obstructed the 46 and simultaneously resulted in its own impaction against 46. The developing 48 may also have been a contributing factor to the spontaneous up righting of the 47. Following removal of the mechanical obstruction (47) the submerged 46 began to erupt. This confirmed that the periodontal ligament and eruption mechanism were normal. From all these clinical characteristics we can eliminate the diagnosis of PFE and diagnose MFE. Subsequent orthodontic treatment was carried out successfully.


MFE is a rare condition. It has a similar presentation to PFE, especially PFE type II in its early stages. If diagnosed early and the appropriate treatment initiated, it can be treated successfully. PFE and MFE have significantly different outcomes and their diagnosis should not be confused. Treatment should include:

1. Elimination of any local and systemic, including endocrine factors

2. Elimination of all mechanical factors which may cause mechanical obstructions

3. Repeated surgical luxation and orthodontic traction thus eliminating any transient ankylosis

Only after multiple failed attempts should PFE be considered as the eruption disturbance.

Significant risks are associated with the eruption of infraoccluded teeth affected by MFE, treatment is complicated and excellent patient cooperation is necessary. However, if the treatment is successful the patient will be left with a functional tooth in occlusion and classical alveolar bone which are invaluable for future dental health and facial aesthetics.


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Table 1. Comparison of primary failure of eruption (PFE)
and mechanical failure of eruption (MFE)

Classification    PFE Type I        PFE Type II       MFE

Number of teeth   All teeth         All teeth         Usually affects
affected          distal to the     distal to the     one tooth
                  most mesially     most mesially
                  affected tooth    affected tooth
                  in one or all     in one or all
                  four quadrants    four quadrants

Influence on      Distal teeth      Distal teeth      Tilting or
adjacent teeth    affected          affected          over-eruption
                                                      of teeth

Timing of onset   At a specific     At a specific     When a
                  chronological     stage of root     mechanical
                  time              development       obstruction
                                                      ceases eruption
                                                      of a tooth by
                                                      blocking its
                                                      path of

Immediacy of      Simultaneous      Gradual failure   Immediate
onset             failure of        of eruption of    failure of
                  eruption of       affected teeth    eruption of
                  affected teeth                      affected

Eruption          Abnormal          Abnormal          Normal

Ankylosis         No                No                Yes

Suggested         Failure of the    Failure of the    Transient
aetiology of      eruption          eruption          ankylosis,
failure           mechanism         mechanism         mechanical

Typical           Abnormal          Abnormal          May respond to
response to       response to       response to       luxation and
orthodontic       orthodontic       orthodontic       orthodontic
treatment         forces            forces            forces

Possible risks    Ankylosis         Ankylosis         Ankylosis
of orthodontic
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Article Details
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Author:Smith, C.P.; Al-Awadhi, E.A.; Garvey, M.T.
Publication:European Archives of Paediatric Dentistry
Article Type:Clinical report
Geographic Code:4EUUK
Date:Jun 1, 2012
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