Depressed Primary Molars

What is infraocclusion?

in 1981 Kurol defined infraocclusion as tooth occlusal surface being lower than the occlusal surface of the adjacent teeth.

nfraoccluded teeth
infraoccluded tooth
Ankylosis of teeth
infraoccluded teeth
Ankylosed tooth
Ankylosis of teeth

Ankylosis of teeth

While infra-occlusion is the favoured term used to describe the position of a tooth that has failed to achieve, or maintain its occlusal relationship to the adjacent and opposing teeth, several other terms such as, submergence, ankylosis, secondary retention, and incomplete eruption have been used in the litrature. ‘submerged tooth’’ is probably the most commonly used. The term ‘‘submerged tooth’’ is a misnomer, as these teeth fail to respond to the vertical growth of the alveolus and the eruption of the adjacent teeth. other terms include:

  • submerged 
  • unken 
  • ankylosed 
  • infra-erupted
  • infra-occluded 
infra-erupted teeth
Ankylosis of teeth in xray

Prevalance of submerged teeth

The prevalence has been estimated to be an average of 14% affecting males and females equally. There seems to be a higher incidence of infraocclusion amongst siblings.


Infraocclusion is 10 times more common in the mandible than the maxilla.

  • 2% to 38.5% according to  Moyers and  Riolo 1988 & Andlaw 1974
  • Common in Siblings according to Kurol 2002
  • 10 times > in the mandible than the maxilla according to Brearley & McKibben 1973

Consequences of infraoccluded teeth

Infraocclusion can cause lateral open bite, lack of normal mesial shift and supra eruption of opposing tooth. Infra occluded teeth do not respond to orthodontic movements.

  • lateral open bite
  • lack of normal mesial drift
  • supra eruption of opposing tooth
  • non-response to orthodontic forces

 Due to the position of the tooth and difficulty in maintaining adequate hygiene, there is a risk of caries affecting infra occluded teeth. Untreated caries can further progress to involve the pulp and cause pain, infection, abscess and emergency attendance to the dentist. If an infection does develop around the infra occluded tooth, the enamel forming on the successor's tooth may be defective. We call this condition a turner tooth. 

As you can see in this image the teeth adjacent to the infra occluded tooth may tilt making extraction of the infra occluded tooth difficult. In some cases, orthodontic uprighting may be required to be able to extract the infra occluded tooth and then maintain the space for the eruption of the permanent successor. 

Sometimes due to over retention of the primary infra occluded molar the permanent successor may erupt ectopically requiring orthodontic intervention.

In some cases the alveolar process does not completely develop as a consequence of the infra occluded tooth. 

  • caries
  • tipping of adjacent teeth
  • over-retained primary tooth
  • incomplete alveolar process development

The patient is a 4-year-old fit and healthy girl who was referred to a specialist paediatric dentist in Brisbane due to facial swelling of the left-hand side and a missing 35. Although rare, infraocclusion can lead to the formation of an abscess. Tooth 75 is severely infra occluded. The tooth bud of 35 is displaced to the distal of the 75. Super eruption of tooth 65 is evident on this radiograph.

infraocclusion and abscess
infraocclusion can lead to formation of an abscess
Abscess in sunken teeth
infraocclusion and abscess

Dental treatment under general anaesthesia (sleep dentistry for children) was provided for this child and tooth 75 was surgically removed. This panoramic radiograph was taken 12 months following surgery.

Tooth bud of 35 has developed further. Its path of eruption seems to be correcting, now that the infra occluded 75 has been removed.

Due to the infection in the 75 region, there is a high risk of 35 having developmental defects of the forming enamel.

Early diagnosis and management of infraoccluded tooth  75 have prevented further damage to the tooth bud of  35.

Another complication that may arise from an infra occluded primary molar is space loss and space management. This is usually best managed with an orthodontic consult.

How do you manage ankylosed teeth?
How is Infraocclusion treated

Diagnosis of infraocclusion

Diagnosis is usually based on clinical presentation. Infra occlusion is usually bilateral. There is a high pitched sound upon percussion. There might be an incomplete alveolar process development and there is usually tilting of the adjacent teeth. 

Diagnoss is usually by clinical presentation: 

  • ankylosis 
  • high pitched sound
  • tilting of adjacent teeth

According to Brearley and McKibben 1973,  radiographic presentation has limitations:

  • 2D
  • ankylosis can be microscopial

studies comparing radiographic diagnosis by obliteration of the periodontal ligament space with histological confirmation, have reported poor results. This may be due to the two-dimensionality of radiographs and that ankylosis can be microscopical. Histological studies have uncovered patterns that can be clinically useful during radiographic interpretation.



How do you diagnose an Ankylosed tooth?
Diagnosis of infraoccluded tooth

3D imaging can be used in severe cases to assess the exact position of the infraoccluded tooth and its relationship to the successor if present. CBCT in kids can be used to assess the exact position of the infra-occluded tooth and its relationship to the successor's tooth. This is a very good case that demonstrates how 3D imaging can help determine the exact position of the infra occluded tooth, its successor and its relationship with the adjacent structure. A better surgical plan can be formed and long term consequences can be better predicted. Due to the lingual position of tooth 45, it was decided both 85 and 45 be surgically removed with dental work under general anesthesia. After 12 months follows the 46 has tilted more mesially but the spaces mesial and distal to 44 will need to be managed orthodontically.

depressed primary molars;
Diagnosis of depressed primary molars in children

Classification of Infraocclusion

Infra occlusion can be classified as mild/moderate and severe according to Messer and Cline in 1981. However, there is a more recent classification by Ingear Kjaer in 2008 classifying infraoccluded teeth into 4 groups, mild, moderate-severe and extreme. Mild infra occlusion refers to the occlusal surface of the infra occluded tooth being above the interproximal  contact point of the adjacent teeth

  • Slight or mild
  • Moderate
  • Severe

 If the occlusal surface of the infroccluded tooth is within the occluso- gingival dimension on the interproximal contact area, it is classified at moderate infra occlusion.

Position of the occlusal surface of the infra occluded tooth being anywhere below the inter-proximal contact area Including teeth below the level of the alveolar crest is referred to as severe to extreme infra-occlusion. 


infraocclusion of primary molars
Slight Moderate Severe Infraocclusion
Eextraction, restoration, and luxation of Infraoccluded teeth

How do you manage ankylosed teeth?

The answer depends on the presence or absence of the permanent successor. A treatment decision-making model for infraoccluded primary molars by Ekim is a useful tool to guide paediatric dentists in treatment planning. When the successor's tooth is present we aim to keep the primary tooth as long as possible. Most of the infraoccluded teeth with a successor will exfoliate naturally. By keeping the primary molar we are maintaining the space for the eruption of the permanent successor. Management when a successor is present:

  • keep the tooth as long as possible
  • normal exfoliation
  • space maintainer

Management of slight to moderate infraoccluded teeth when the successor is present

If there is slight infra occlusion and the permanent successor is present we aim to keep the infra occluded tooth as long as possible. We can monitor the tooth for natural exfoliation. To prevent tilting of the adjacent teeth and over eruption of the opposing tooth we can build up the occlusal surface of the infra occluded primary molar.

It is important to note preparing the tooth for a zirconia crown is more aggressive compared to a stainless steel crown and sometimes an elective pulpotomy may be required.


 slight – moderate

  • monitor
  • build-up
    1. resin composite
    2. stainless steel crown
    3. zirconia crown

Management of severely infraoccluded teeth when the successor is present

  • extraction
  • space maintainer
  • eruption of a permanent successor

If infra occlusion is severe to an extreme we need to extract the primary molar and hold the space for the eruption of the permanent successor. If there has been tipping of the adjacent teeth, orthodontic uprighting may be required prior to placing the space maintainer.

Management of slight to moderate infraoccluded teeth when the successor is Absent

The chance of a missing premolar associated with an infra occluded primary molar has been reported to be 14%.

In case the permanent successor is not present, we aim to keep the tooth for as long as possible while the child is in the growth and development stage. To prevent tilting of the adjacent teeth and over eruption of the opposing tooth, we may need to build up the occlusal surface with resin composite, stainless steel crown or zirconia crown in mild to moderate cases of infraocclusion.

short term

  • mild-moderate
    • build-up
      • resin composite
      • SSC
      • zirconia crown

Management of severely infraoccluded teeth when the successor is absent

If the infra occlusion is severe we will need to extract the affected primary tooth. Depending on the patient's age and long term treatment plan, we may consider placing a space maintainer for future prosthesis or dental implants.

long term

  • severe-extreme
    • extraction
    • ortho consult
    • space maintainer?

Long term the missing tooth can be managed by orthodontic space closure, prostheses such as a resin-bonded dental bridge or an implant.

A report article by Valencia et al. described a simple method of allowing first molars to drift mesially in case of a missing second premolar facilitating future orthodontic treatment.

A total of 34 patients with 52 missing premolars were included in this study. Diagnosis of missing premolars was made between the ages of 8-11 years.

Valencia 2004

  • 34 patients
  • 8-11 years
  • missing 2nd premolar

In group I, controlled slicing was performed on 28 mandibular deciduous second molars. In group II, 14 mandibular deciduous second molars were extracted,
followed by physiologic mesial migration of the mandibular permanent first molar. In group III, 10 maxillary deciduous second molars were extracted, followed by
physiologic mesial migration of the maxillary permanent first molar. The groups were subdivided into 2 age groups: 8 to 9 years, and 10 to 11 years or older. The patients were seen monthly, and the results were evaluated for space closure, molar rotation and inclination, timing, and midline shift.

  • group I controlled slicing
  • group II extraction of mandibular 2nd primary molar
  • group III extraction of maxillary 2nd primary molar

The results were defined as good, average, or poor. Good results meant 80% or greater space closure, without or with only slight mesial rotation or inclination with no midline shift, achieved in less than 12 months

  • good results
  • ≥ 80 % space closure
  • without or with only slight mesial rotation or inclination
  • no midline shift

Average results meant 60% to 80% space closure with slight mesial rotation, inclination, or midline loss; treatment results were observed from 12 to 18 months.

  • 60% - 80 % space closure
  • with slight mesial rotation or inclination or midline loss

Poor results had less than 60% space closure, with major mesial rotation, inclination, or midline loss; treatment results were assessed with more than 18 months of follow-up.

poor result

  • < 60% space closure
  • major mesial rotation or inclination or midline loss

When considering the 3 clinical responses in the 2 treatment modalities, disregarding age, they found the best results with controlled slicing, with 71.4% having good results and 21.4% average results. The extraction group showed a greater tendency toward average to poor results


  • best results → controlled slicing
  • 71.4% good results
  • 21.4% average results

What causes infraocclusion?

We don’t really know. There have been a few extrinsic factors such as trauma, metabolic disturbance and infection.
Genetics has also been associated with infraocclusion.

  • not well understood
  • extrinsic factors
    • trauma
    • disturbed metabolism
    • infection
  • intrinsic factors
    • genetics

Infraocclusion or Primary Failure of Eruption

“non-ankylosed tooth fails to erupt, completely or partially due to disturbance in the eruption mechanism”, Proffit and Vig 1981

Primary failure of eruption refers to the condition in which a non-ankylosed tooth fails to erupt either, completely or, partially due to a disturbance in the eruption mechanism. in some cases, despite the resorption of the alveolar bone overlying the crown, the tooth still fails to erupt. Both, primary and permanent teeth can be affected. The clinical presentation is usually asymmetric with the posterior teeth being more commonly affected.
There are minimal data available for PFE affecting primary dentition.

There is limited data about the primary failure of eruption in primary teeth. In permanent teeth, it has been reported to have a prevalence of 0.06% and is more common in females.

  • prevalence in permanent dentition
  • 0.06%
  • F>M
  • limited data →PFE in primary dentition

Baccetti 2000

The diagnosis of this case can vary from primary failure of eruption to severe infra-occlusion based solely on the time of diagnosis.
For example, a radiograph (dated 2005) can represent a primary failure of the eruption of tooth 75. While in the subsequent radiograph (dated 2007) tooth 75 is in severe infraocclusion. Therefore, it would be logical to state that the age of the patient at the time of diagnosis was critical to categorising the clinical entity.

Primary Failure of eruption
Why do teeth not erupt

Associated dental abnormalities: hypodontia

Let's look at other anomalies that may be associated with an infraoccluded tooth.

Baccetti 1997: Here we can see teeth 75 and 85 are infraoccluded. Teeth 35, 45, 12 and the third molars are missing. Hypodontia is one of the anomalies associated with infra occlusion.

Associated dental abnormalities: Microdontia

Baccetti 1997: Another anomaly associated with infra occlusion is microdontia as seen here. Tooth 22 is micorodnt.

Associated dental abnormalities: Ectopic eruption of the canine 

Baccetti 1997 Ectopic eruption of the canine has also been associated with infra occlusion

Associated dental abnormalities: Ectopic eruption of first permanent molar 

Baccetti 1997 Another anomaly associated with infraoccluded primary molars is ectopic eruption of the first permanent molar. In tis radiograph  it is evident that the first permanent molar has jumped it’s ectopic path of eruption which we know it occurs in 70% of time.

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