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Atypical retention of infraoccluded primary molars with permanent successor teeth.


Background: Infraocclusion of primary molar teeth is relatively common. The majority of infraoccluded primary molars with permanent successors exfoliate naturally. There are currently no evidence based guidelines for the treatment of infraoccluded primary molars with permanent successor teeth. Case Series: The three cases presented demonstrate atypical retention of infraoccluded primary molars, following a conservative approach. In case 1 taking a conservative approach over 5 years, the infraocclusion became gradually more severe. Tilting of the adjacent teeth and the centre-line shift caused by leaving the affected tooth in place during dental and alveolar development was significant. In Case 2 the severely infraoccluded 55 required surgical removal and exposure of the underlying permanent successor (15). Case 3 showed a maxillary premolar (14) and first permanent molar (16) tilted toward the partially erupted, ectopic, rotated 15. Surgical removal of the impacted maxillary primary molar was required. Conclusion: Although there is evidence available to support the conservative treatment of such cases, it does not always lead to a favourable outcome. Detrimental effects on the adjacent teeth and occlusion were observed and surgical intervention was required.

Key words: Infraocclusion, Permanent successor, Primary Molar


Infraocclusion (IO) may be defined in many ways, perhaps most simply by Andlaw and Rock [1996] as: "A tooth that has failed to maintain its position relative to the adjacent teeth in the developing dentition and is, therefore submerged below the occlusal level". The prevalence of IO has been variously reported as ranging between 1.3% [Via, 1964] and 38.5% [Steigman et al., 1973] with most reports in the region of 1.3% to 8.9% and a peak prevalence in 8-9 year olds [Kurol, 1981]. IO is more common in Caucasian subjects with no sex predilection noted [Krakowiak, 1978]. Mandibular first primary molars are the teeth most frequently affected [Brearley and McKibben, 1973]. and are more commonly than permanent molars [Biederman, 1956] and mandibular molars more than maxillary molars [Messer and Cline, 1980; Kurol, 1981].

Diagnosis is usually by clinical presentation with severity classified as mild, moderate or severe, according to the position of the occlusal surface of the infraoccluded tooth relative to the adjacent teeth [Brearley and McKibben, 1973]. The IO may become progressively worse with age [Darling and Levers, 1973; Krakowiak, 1978] and continuing adjacent vertical alveolar growth.

The mechanism for IO is not fully understood but trauma to the primary dentition may cause disturbance of eruption, due to abnormal tissue changes overlying the tooth germ [Andreasen, 1994]. Deficient eruptive force [Dixon, 1963], disturbed metabolism of the periodontal ligament [Biederman, 1953], local inflammation, and disturbance in interaction between normal resorption and hard tissue repair [Kronfield, 1953], have all been postulated as possible causes of infraocclusion. Defects in the periodontal membrane [Biederman, 1962] and localized infection [Adamson, 1952] have also been suggested [Kurol and Thilander, 1984]. There are three main, generally accepted factors in the aetiology of IO.

Ankylosis: Dental ankylosis is thought to be the major aetiological mechanism of IO, [Darling and Levers, 1973; Kurol and Magnusson, 1984], although ankylosis may be a secondary, rather than an initiating factor in the process. It has been postulated that ankylosis can develop during the intermittent processes of root resorption and bone deposition, which occur in the physiological resorption of the primary tooth root [Kurol and Magnusson, 1984]. Ankylosis occurs if there is a break in the continuity of the periodontal membrane and direct contact of cementum or dentine and bone occurs [Krakowiak, 1978]. There is an increased degree of osteoblastic and osteoclastic activity with ankylosed teeth, as compared to normal teeth; and in favourable circumstances, the attachment of the affected tooth to the underlying tissues may be resolved and the tooth shed normally [Dixon, 1963; Thornton and Zimmerman, 1964].

Genetic basis: It has been proposed that IO is an hereditary condition, inherited on a multi-factorial basis, either with polygenic inheritance or controlled by an environmentally-sensitive single gene [Kurol, 1981]. A familial tendency has been noted, with an increased incidence amongst siblings of 18.1% [Kurol, 1981] and 44% [Via, 1964] also suggesting a genetic component to the aetiology. IO of primary molars also shows significant reciprocal associations with genetically related anomalies: ectopic eruption of first permanent molars (FPM); diminutive maxillary lateral incisors; enamel hypoplasia; and palatal displacement of maxillary canines [Baccetti, 1998].

Absence of a permanent successor tooth: This has been cited as a major aetiological factor [Biederman, 1962; Bjerklin et al., 1992; Baccetti, 1998]. In a retrospective study 65.7% of patients with developmentally missing teeth showed IO of primary molars [Lai and Seow, 1989].

It is generally accepted that IO of the primary molar may cause delayed eruption of the permanent successor [Biederman, 1962]. A 6 month delay, relative to the contra-lateral tooth, has been suggested as an acceptable exfoliation schedule [Kurol and Thilander, 1984]. The delay in exfoliation is not related to the degree of IO [Kurol and Thilander, 1984].

As IO becomes more severe, the vertical component in the configuration of the transseptal fibres between the adjacent teeth increases. This leads to a associated reduction in height of adjacent teeth and a tilting effect [Becker and Karnei R'em, 1992]. The infraoccluded tooth can become a centre to which all teeth mesial to it, including those across the midline become drawn, leading in unilateral IO cases to a centre line shift [Becker et al., 1992].

IO may lead to food packing, over-eruption of teeth in the opposing arch and subsequent occlusal disharmony and restorative problems. It has been proposed that IO of primary molars can initiate periodontal problems for adjacent teeth [Marechaux, 1986] and that restriction in vertical growth of the infraoccluded tooth and associated alveolar bone can lead to an extensive alveolar ridge defect [Steiner, 1997]. However it has been shown that IO and ankylosis of primary molars does not constitute a general risk of future alveolar bone loss mesial to the first permanent molars. After exfoliation of infraoccluded primary molars, even a marked loss in vertical position of the bone level normalises as the successor erupts [Kurol, 1981; Kurol and Thilander, 1984; Kurol and Koch, 1985].

Case Series:

Case 1: A 7 year old Caucasian boy, with no relevant medical history and normal development for his age was referred to Paediatric Dentistry at Leeds Dental Institute, in May 1997, regarding his infraoccluded mandibular left second primary molar (75).

Intra-oral examination showed the patient to be in the early mixed dentition and caries free. The mandibular left second primary molar (75) was found to be severely infra-occluded and teeth 74 and 36 had tilted toward the infraoccluded tooth. Radiographic examination by means of a panoramic radiographic (Fig 1a) showed that all permanent successor teeth to be developing. The underlying second premolar tooth (35) was in a normal relationship to the roots of the primary molar and tooth 45 to be comparable, with regard to both root development and relationship to the primary molar.

Treatment. The favourable position of the mandibular left second premolar (35) allowed a conservative approach to be taken, with annual review over the next five years. During this period the roots of 75 continued to resorb, adjacent teeth tilted further toward the infraoccluded tooth and a centre-line shift developed. Four months after the exfoliation of the contra-lateral primary molar (85), the decision was made to extract the infraoccluded 75, due to the poor position of 36 (Fig 1b).

Follow-up. At the age of 13, having previously declined orthodontic assessment, the patient expressed an interest in orthodontic correction of his Class II division 2 malocclusion and was referred accordingly. Orthodontic treatment was carried out on a non-extraction basis, with a twin-block functional appliance, followed by upper and lower fixed appliances and retention.

Case 2: A 13 year old Caucasian girl, medically fit and well, with normal development for her age was referred to Orthodontics at Leeds Dental Institute, in December 2003, regarding her Class II division 2 malocclusion, complicated by her retained infraoccluded maxillary left and right second primary molar teeth (55 and 65). Intra-oral examination showed the patient to be in the permanent dentition with maxillary left and right second primary molar teeth (55 and 65) were found to be severely infra-occluded. The maxillary FPMs and first premolars had tilted toward the infraoccluded teeth. Radiographic examination by means of a panoramic radiographic (Fig 2) and bitewing radiographs showed that all permanent teeth to be present or developing. Caries was present in permanent molars 37, 46 and 47.

Treatment. Three months following referral the infraoccluded 65 had exfoliated naturally and the permanent successor (25) began to erupt. Conversely, the severely infraoccluded 55 required surgical removal and exposure of the underlying permanent successor (15). Orthodontic treatment was carried out on a non-extraction basis with a modified twinblock functional appliance, followed by upper and lower fixed appliances and retention.

Case 3: A 14 year old Caucasian female, medically fit and well, with normal development for her age was referred to Orthodontics at Leeds Dental Institute, in January 2005, regarding her partially erupted maxillary right second premolar (15). Intra-oral examination showed the patient to be in the permanent dentition and caries free. The maxillary premolar (14) and FPM (16) had tilted toward the partially erupted, ectopic, rotated 15. Radiographic examination, by means of a panoramic radiograph (Fig 3) showed all permanent teeth to be present or developing and the retained, severely infraoccluded 55.

Treatment. Surgical removal of the impacted maxillary primary molar was carried out to allow up-righting of the maxillary right second premolar.



There is little argument that the major goal of treatment of infraoccluded molars with a permanent successor is to allow the normal eruption of the successor. The decision whether or not to instigate treatment is based on the age of the patient, the degree and extent of the IO, the amount of root resorption, the severity of tilting of neighbouring teeth and the presence and location of the permanent successor. There is no general agreement as to the treatment of infraoccluded primary molars and it is often difficult to decide at exactly what point treatment should be instigated. Treatment options for infraoccluded teeth with permanent successors include:

Monitoring the infraoccluded tooth. Continuous supervision of occlusal development and periodic radiographic observation of normal root resorption to allow assessment of the rate of the condition [Kurol and Olson, 1991]. The advice not to extract infraoccluded teeth, as they almost invariably shed normally in their due time, appears justified [Kurol and Thilander, 1984]. However this approach does not take into account the disturbance of development that is to be expected by leaving the affected tooth in place during the formative years of the dental and alveolar development of the child [Becker et al., 1992].

Early extraction and space maintenance. Wherever possible, extraction should be deferred until the FPM erupts, to allow space maintenance. Extraction is recommended by many authors, preferably as early as possible [Krakowiak, 1978; Messer and Cline, 1980]. Other authors recommend early treatment only when there is a severely affected primary molar and where there is evidence of possible future crowding [Winter et al.,1997]. However, early extraction is only necessary when there is a combination of occlusal disturbance, with severe tipping of neighbouring teeth, space loss, malposition of the permanent successor with irregular primary root resorption, combined with severe IO according to Kurol and Thilander, [1984]. Early extraction may, however, be technically difficult and may result in fracture of the roots, or possible disturbance of the succedaneous tooth bud [Raghoebar et al., 1989].



Restoration of occlusal height. The tooth may be restored with composite resin, or a preformed metal crown to reestablish occlusal and proximal contacts, to maintain the occlusion and prevent further tipping and over-eruption [Krakowiak, 1978]. This can be technically difficult and is not without long term management problems.

Luxation. The theory behind luxation of infraoccluded primary molars is that the bony union between the affected tooth and the alveolus can be broken, permitting the tooth to resume eruption. Luxation to free ankylosed permanent teeth has been attempted with limited success [Krakowiak, 1978] and as such is not generally recommended.

Later extraction. It has been suggested that if exfoliation is not achieved within the accepted delayed time of 6 months, extraction should follow [Ekim and Hatibovic-Kofman, 2001]. Other authors propose that only when it becomes obvious that resorption is not proceeding normally or that adverse occlusal changes are taking place, should extraction be considered [Kurol and Koch, 1985].

In case 1, over a monitored period of 5 years, the infraocclusion became gradually more severe. Tilting of the adjacent teeth and the centre-line shift caused by leaving the affected tooth in place during dental and alveolar development [Becker et al., 1992], was significant. Although earlier extraction of the infraoccluded primary molar was discussed, the patient and parent preferred a conservative approach. Resorption of 75 continued and it is unlikely that the primary molar would have exfoliated naturally, due to the severe IO and tilting of the adjacent teeth. Surgical extraction of the infraoccluded primary molar was eventually carried out. Orthodontic alignment of 35 was achieved, however, correction of the 6 mm centre-line shift was challenging and ultimately not fully achieved.

In case 2, the disturbance of normal development of the occlusion was again significant. This case demonstrates well, the difference in response of the moderately infraoccluded 65 which shed naturally and the severely infraoccluded 55 which required surgical removal, with the added complication of an iatrogenic oro-antral communication. Orthodontic alignment of the maxillary 15 and 25 was achieved.

Case 3 is unusual in that the severely infraoccluded maxillary right second primary molar had not prevented the eruption of the permanent successor. The premolar successor remained partially erupted, rotated and palatally positioned. Alignment of the premolar was not possible without surgical removal of the infraoccluded primary molar.

The cases described illustrate that the presence of a permanent successor does not ensure natural exfoliation of the primary tooth. In retrospect, all the cases may have benefited from earlier intervention and removal of the primary molar, rather than a conservative approach. These cases highlight the need for decision making on an individual basis, according the clinical presentation. Case 3 illustrates that persistence of a severely infraoccluded retained primary molar does not always prevent eruption of the successor. Neither restoration of the occlusal height, nor early extraction and long term space maintenance would have been simple solutions in these cases, but might have prevented the tilting, loss of space for the successor and the significant centreline shift (case 1) which can be difficult to correct. The tendency of ankylosed maxillary molars (case 2) to be severely infraoccluded usually indicates early extraction [Kurol and Koch, 1985].

Cases 1 and 2 demonstrate that once the obstruction is removed and space created, the permanent tooth will generally erupt normally.


Although the majority of infraoccluded teeth with permanent successors shed normally, the response in individual cases may vary. Early treatment to prevent adverse occlusal changes may be of benefit in some cases. Evidence-based clinical guidelines for the management of infraoccluded primary molars would be welcome, however decision making on an individual basis, according the clinical presentation is advised.


The advice and help in preparation of this case series by Dr S.A.Fayle, (Consultant Paediatric Dentist) at Leeds Dental Institute; and Dr J. Spencer, (Consultant Orthodontist, Pinderfields Hospital) is gratefully acknowledged.


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F.R. Jenkins, R.E. Nichol

Depts Paediatric Dentistry and Orthodontics, Leeds Dental Institute, Leeds, England.

Postal address: Dr. F R Jenkins, 28 Towngate, Huddersfield. HD4 6JS, England Email:
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Article Details
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Title Annotation:CASE SERIES
Author:Jenkins, F.R.; Nichol, R.E.
Publication:European Archives of Paediatric Dentistry
Article Type:Case study
Geographic Code:4EUUE
Date:Mar 1, 2008
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