Proffit WR, Vig KW Primary failure of eruption: a possible cause of posterior open-bite. Am J Orthod. 1981; 80:173-190
Raghoebar GM, Boering G, Vissink A, Stegenga B Eruption disturbances of permanent molars: a review. J Oral Pathol Med. 1991; 20:159-166
Decker E, Stellzig-Eisenhauer A, Fiebig BS, Rau C, Kress W, Saar K PTHR1 loss-of-function mutations in familial, non-syndromic primary failure of tooth eruption. Am J Hum Genet. 2008; 83:781-786
Frazier-Bowers SA, Koehler KE, Ackerman JL, Proffit WR Primary failure of eruption: further characterization of a rare eruption disorder. Am J Orthod Dentofacial Orthop. 2007; 131
Cahill DR Eruption pathway formation in the presence of experimental tooth impaction in puppies. Anat Rec. 1969; 164:67-77
Cahill DR, Marks SC Tooth eruption: evidence for the central role of the dental follicle. J Oral Pathol. 1980; 9:(4)189-200
Yao S, Pan F, Wise GE Chronological gene expression of parathyroid hormone-related protein (PTHrP) in the stellate reticulum of the rat: implications for tooth eruption. Arch Oral Biol. 2007; 52:(3)228-232
Wise GE, Yao S, Henk WG Bone formation as a potential motive force of tooth eruption in the rat molar. Clin Anat. 2007; 20:(6)632-639
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Failure of eruption of posterior teeth is rare but has significant clinical implications. There has been a recent re-classification of failure of eruption based on aetiology and presentation. Primary failure of eruption (PFE) affects all teeth distal to the affected tooth and can result in a significant posterior open bite. Mechanical failure of eruption (MFE) is due to ankylosis and the teeth distal to the affected tooth are not affected. Early diagnosis and differentiation between PFE and MFE is essential to ensure that the correct treatment is provided. Two cases are shown that demonstrate MFE.
Clinical Relevance: This article reviews the aetiology for non-eruption and identifies the differences between PFE and MFE.
Article
Claire Dunbar
Proffit and Vig originally used the term primary failure of eruption (PFE) for the failure of a tooth to erupt or cessation of initial eruption with no obvious local or systemic cause.1 Raghoebar et al further subdivided PFE into primary and secondary retention;2 primary if the tooth failed to erupt and secondary if there was cessation of initial eruption.
More recent genetic studies have found a genetic basis for PFE3 and, as a result, different mechanisms have been suggested for the aetiology of failure of eruption of posterior teeth.4 These are PFE, mechanical failure of eruption (MFE) and intermediate failure of eruption (IFE).4 This article will review the literature and present two cases of MFE.
The mechanism of eruption
An eruption path is cleared by resorption of overlying bone, deciduous tooth roots and alveolar mucosa.5 Experiments in dogs have shown that the tooth moves through this eruption path and the tooth does not ‘force’ its way through overlying tissue.5
The dental follicle has emerged as a central mediator of tooth eruption.6 Molecular studies have shown that there are a tightly regulated series of signalling events between the dental follicle and the osteoblast and osteoclast cells found in the alveolar bone.7,8 The stellate reticulum cells found in the dental follicle release parathyroid hormone-related peptide, resulting in an overexpression of colony stimulating factor-1 (CSF-1) and receptor activator of NF-kappaB ligand (RANKL) stimulating osteoclasts to resorb the overlying bone.7 The critical role of the follicle has been demonstrated by substituting a metal object for a tooth in the follicle and the metal object erupted successfully.6
Overexpression of bone morphogenetic protein 2 has been found at the apical part of the dental follicle.7 This stimulates osteogenesis, suggesting bone growth apical to the tooth is necessary to propel the tooth into the oral cavity.
It is also unclear if root development or crown mineralization is primarily involved in the eruption process. Genes involved with mineralization (eg ameloblastin and amelogenin) may interact with those associated with osteogenesis (eg RANKL and CSF-1).9
Aetiology of failure of eruption
A disruption of this eruption process can be local or systemic and can range from a delay in eruption to a complete failure of eruption. Table 1 shows the local, systemic and idiopathic factors that may prevent normal eruption.
Local
A supernumerary tooth
Mucosal barrier
Trauma to primary tooth (particularly intrusion that may result in dilaceration of the permanent successor)
Retained primary tooth
Early extraction or loss of primary tooth resulting in space loss
Crowding
Local pathology such as a cyst
Radiation damage
Ectopic position of tooth germ
Lateral tongue pressure
Systemic
Cleidocranial dysplasia
Cleft lip and palate
Gardners
Osteopetrosis
Hypothyroidism
Hypopituitarism
Hypoparathyroidism
Idiopathic
Primary failure of eruption
Mechanical failure of eruption
Intermediate failure of eruption
Failure of eruption
Frazier-Bowers et al suggest subdividing failure of eruption where there is no obvious cause into four categories based on different presentations and aetiologies:4
Primary failure of eruption (PFE);
Mechanical failure of eruption (MFE);
Intermediate failure of eruption (IFE);
Other.
The features of these four groups are described in Table 2.
Primary failure of eruption
Only affects posterior teeth
All teeth distal are affected
Frequently unilateral
Can affect a whole quadrant
Results in posterior openbite
Mechanical failure of eruption
Usually only first molars
Teeth distal are not affected
Radiographic appearance of infraocclusion due to ankylosis
Intermediate failure of eruption
Distinction between PFE and MFE is not clear
Too young to determine if the distal teeth are affected
Other
Affected teeth not in occlusion but not submerged as in PFE or MFE
Primary failure of eruption (PFE)
The main differential factor between PFE and MFE is whether the distal teeth are affected. In PFE all teeth distal to the affected teeth are also affected. This is an important aspect to identify for treatment planning. However, in a young child it is not possible to identify if the distal teeth are affected until the second molar is due to erupt. During this time the term IFE is used.
In PFE the eruption path is cleared but there is no movement along this path, suggesting failure of the eruptive mechanism. During surgery of these teeth it is often found that the teeth are movable within their crypt. However, they will respond abnormally to an orthodontic force and become anklyosed if a force is applied.
Only posterior teeth are affected resulting in a posterior openbite. PFE is commonly unilateral, however, all four quadrants may be affected.
PFE has been divided into three types, depending on the timing of onset:4
Type 1
All affected teeth have a similar lack of eruption potential and there is a progressive posterior openbite towards the distal. The loss of eruption appears to strike at a certain chronological time.
Type 2
The teeth distal to the affected tooth show more but still inadequate eruption. The timing may be related to the stage of root development.
Type 3
Type 1 and 2 are present in the same patient.
There is a strong genetic basis for PFE. In one study, 26% of cases were found to have a genetic link.4 Decker et al found mutations in parathyroid hormone 1 receptor (PTH1R), which explains several familial cases of PFE.3 The inheritance can be autosomal dominant with variable expressivity.10 It is not known if Type 1 and Type 2 are associated with specific mutations or if there is a broad spectrum associated with, for example, PTH1R.10 While the exact reason for this clinical variation is unknown, in light of the recent PTH1R finding, it has been speculated that the predominant ‘molar’ phenotype that is observed may be the result of a co-ordinated series of molecular events that act in a temporally-and spatially-specific manner, such that posterior rather than anterior alveolar bone is affected.11 It has been suggested that, once MFE has been ruled out, genetic testing of PTH1R could be a critical part of the diagnosis.10 By discovering one gene that is associated with PFE does not rule out that additional genes may also be associated with the condition.
Mechanical failure of eruption
This is due to ankylosis resulting in infraocclusion of the tooth. MFE can be differentiated from PFE as teeth distal to the affected tooth are unaffected. This may be thought of as a secondary form of failure of eruption as there is no failure of the eruption mechanism. The failure of eruption is due to ankylosis leading to infraocclusion. Ankylosis can be identified by:
Absence of a periodontal ligament radiographically;
Absence of physiological movement;
Infraocclusion; and
A cracked cusp sound on percussion.
The aetiology of MFE is unknown, however, a link with PFE has been suggested.
Intermediate failure of eruption
This term is used when a differentiation between PFE and MFE cannot be made, such as between the ages of 8 and 14 when the first molar has been identified as unerupted and the second molar has not yet erupted.
Treatment
1. Rule out any local or systemic factors that could be preventing eruption;
2. Monitor for 6–12 months to see if there has been any progress of eruption (depending on age of patient);
3. If eruption continues, no treatment is required;
4. If the first molar fails to erupt and the fate of the second molar is not known, extraction will allow the second molar to drift mesially, if it is normal, and does no harm if it is not.
5. Determine if distal teeth are affected and if there is a positive family history. Differentiation can then be made between PFE and MFE. Unfortunately, this differentiation cannot be made until 14 or 15 years of age, when the second molar completely fails to erupt or erupts partially.
Treatment is difficult as the posterior openbite tends to be severe. There is no orthodontic solution for PFE or MFE as the anklyosed tooth will not move and the remaining teeth will be intruded if a force is applied. In PFE the distal teeth cannot be moved orthodontically, however, in MFE the remaining teeth will respond normally. If the remaining dentition is crowded, the tooth affected by MFE can be used to create space for orthodontic alignment.
Options for treatment include:
Accepting the premolar occlusion, leaving or extracting the unerupted teeth;
If mild, the occlusal surface of the teeth can be brought up with onlays or crowns;
Extraction of the unerupted teeth and restoration with a removable partial denture or implants. If implants are the option of choice it is likely that bone grafting will be required;
A small, segmental osteotomy or distraction osteogenesis of the segment have been suggested.12
Case 1
A fit and healthy 15-year-old male presented with a Class II division 1 incisor relationship complicated by mechanical failure of eruption of UL6. On examination there was also a buccally impacted UL3, upper and lower crowding, bimaxillary proclination and buccal crossbites (Figure 1). As this patient was 15 years of age, the second molars had erupted and a diagnosis of MFE could be made once all other local and systemic factors had been ruled out. The radiograph (Figure 2) shows infraocclusion of the UL6 and tipping of the adjacent teeth. On examination, this tooth made a dull sound on percussion, indicative of anklyosis. Owing to the crowding and Class II division 1 incisor relationship, the space from the extraction of the UL6 could be used for orthodontic treatment.
Figure 1.
(a–c) Pre-treatment views showing infraocclusion of UL6 and normal eruption of the remaining dentition.Figure 2. Pre-treatment radiograph demonstrating MFE of UL6 and normal eruption of UL7.
The near end of treatment photographs (Figure 3) and radiograph (Figure 4) show successful orthodontic treatment and the UL7 has responded to the orthodontic force. There has been some tipping of the UL7 into the extraction spaces and further root uprighting is required.
Figure 3.
(a–c) Near end of treatment views showing successful orthodontic treatment.Figure 4. Near end of treatment radiograph.
Case 2
A fit and healthy 14-year-old female presented with a Class II division 1 incisor relationship complicated by mechanical failure of eruption of the LR6. As in Case 1, the LR7 had erupted and a diagnosis of MFE could therefore be made (Figures 5 and 6). Ideally, this patient should have been referred as soon as the LR6 had failed to erupt. This would have allowed the LR6 to be extracted at a younger age and the LR7 would have erupted into a better position.
Owing to the ankylosis, the LR6 was extracted and the LR7 was allowed to drift into the available space. The patient was also treated with a twin block functional appliance to reduce the overjet.
One year later, Figures 7 and 8 demonstrate successful overjet reduction with the twin block appliance. There has been some further eruption of the LR7, however, due to the patient being 14 at the time of extraction, little further spontaneous improvement can be expected. The lateral openbites seen in Figure 7 are due to twin block treatment and not failure of eruption. Treatment will now involve upper and lower fixed appliances to level and align the arches and attempt to close the space between LR5 and LR7. It is hoped the LR7 will respond normally to an orthodontic force due to the diagnosis of MFE.
Figure 7. Near end of treatment radiograph; there has been minimal further eruption of LR7.Figure 8. Post extraction views of LR6 and overjet reduction with functional appliance.
Conclusion
Failure of eruption of posterior teeth has significant clinical implications. It is important to differentiate between PFE and MFE to ensure that the correct treatment is provided for the patient.
