02 - Primary Tooth Eruption and Exfoliation

Timing and Variability of Eruption

Purpose of This Module

The purpose of this module is to review normal eruption and exfoliation of primary teeth and to identify common abnormalities associated with each process. In addition to viewing the module, be sure to read pages 86-91 (5th ed) or 97-103 (4th ed) in Contemporary Orthodontics. After viewing the teaching program and doing the reading, be sure that you are able to:

• describe the sequence and timing of the eruption of the primary teeth
• describe the pathways from the primary to permanent dentition, especially early to late mesial shift routes
• use the chronology tables to assess the dental developmental status of a child and determine the age at which dental development was affected if a problem is present
• describe the etiology, prevalence and treatment implications of the most commonly encountered disturbances of primary tooth eruption

Variability of Primary Tooth Eruption

The eruption of the primary teeth is relatively variable from child to child. Variation of 6 months of acceleration or delay is well within the range of normal.

However, the sequence of eruption of primary teeth is constant. Eruption of antimeres (i.e., left and right teeth) in the same arch usually occurs very close to the same time, so eruption can be described as symmetric in that sense. A lengthy delay in eruption between antimeres in the same arch may signal underlying pathology, such as a congenitally missing tooth or a supernumerary tooth that is blocking the path of eruption.

Eruption Sequence of Primary Teeth

Usually the first primary teeth to erupt are the mandibular lower incisors at 6-9 months of age. The maxillary central incisors then erupt and they are followed by the mandibular and maxillary lateral incisors. (Image 1) After 3-4 months, the first molars erupt.

Some anxious parents may be concerned that there is a space between the newly erupted first molars and the lateral incisors. The dentist must explain that the primary canines will erupt into the space in a further 3-4 months and the space and sequence is part of the normal eruption sequence. (Image 2)

The primary dentition is completed at 24 – 30 months with the eruption of the mandibular, then the maxillary second molars. (Image 3)

Image 1, Newly erupted primary incisors: Erupted mandibular central incisors, maxillary central and maxillary lateral incisors in an infant of approximately 11 months of age	Image 2, Eruption of first primary molars: The first primary molars erupt before the primary canines, at around 1 year of age.
Image 3, Complete primary dental arch: Eruption of all 20 primary teeth, as seen in this 2-year-old child, is completed at approximately 24 months of age.

Eruption Trends

Both gender and race affect the timing of eruption of the primary teeth. Eruption of primary teeth usually occurs earlier in girls than boys, and earlier in African-American children than in Caucasian children.

The eruption and development of the primary teeth serves as a template for the development of the permanent dentition. Tooth buds of the permanent teeth develop through a budding process off of the primary teeth. The succedaneous permanent teeth are intimately related to the overlying primary teeth.

Eruption Problems

Common Clinical Problems: “Teething”

A common problem related to the primary teeth is the complex of symptoms often summarized as “teething”. Eruption of primary teeth in infants is associated with drooling, increased salivation, restlessness and irritability.

In the past, systemic conditions such as croup, diarrhea and fever were also attributed to the eruption of primary teeth and dismissed as teething problems. Research has shown no association between systemic conditions (increase in fever and white blood count) and primary tooth eruption, which is a normal physiological process. Any systemic conditions that may occur during the eruption of the primary teeth should be considered coincidental, and should be investigated by a physician rather than being dismissed as a symptom of teething.

Dental intervention is usually not required during primary tooth eruption, but eruption may be hastened or the symptoms relieved by allowing the infant to chew on an approved commercially available teething aid like the one shown here.

Common Clinical Problems: Eruption Hematomas

Eruption hematoma or cyst:

During eruption of a tooth, as the tooth nears the epithelial surface, blood or fluid can fill the tooth follicle to form an eruption hematoma (which is also called an eruption cyst). This appears as a raised bluish lesion usually in the region of a soon-to-erupt second primary molar. The lesion is self-limiting. Once the tooth breaks the mucosa, the cyst and contents are lost and it disappears.

This picture shows bilateral eruption hematomas in the areas of the maxillary first primary molars.

Intervention is usually not required or indicated. The bluish lesion may cause some concern to untrained professionals or parents who suspect a more serious malignant pigmented lesion.

Common Clinical Problems: Natal Teeth

Natal and neonatal teeth:

Natal teeth are teeth that are present at birth, while neonatal teeth erupt during the first 30 days after birth. The prevalence of natal teeth is approximately 1/3000 births and neonatal teeth is about 1/2000 births. In the majority of cases these teeth occur in the mandibular incisor region and are the true primary teeth and not supernumerary teeth.

These teeth can be very mobile due to incomplete root development. If there is a risk of aspiration due to displacement, extraction is indicated.

Sharp incisal edges can also cause ulceration and irritation of sublingual tissues in affected infants. In these cases extraction may also be indicated if the lesions are significant. The teeth may also cause discomfort for the mother during breast feeding.

Delayed Eruption

If there are no primary teeth by 18 months, one should suspect an underlying cause and order a thorough dental and medical evaluation. A number of systemic conditions have found to be associated with delayed eruption of primary and permanent teeth. Some of these conditions include:

1. Trisomy 21 (Down Syndrome) An extra chromosome 21 is found in individuals with Down syndrome. Delayed eruption of the primary and permanent teeth are common, as is an abnormal eruption sequence. Exfoliation of primary teeth is delayed and over-retained primary teeth are common in adolescents and adults with the condition (Image 1).
2. Cleidocranial dysplasia In this condition the clavicles are either absent or rudimentary (Image 2). The primary teeth erupt without problems on the normal schedule, and since the permanent molars are formed from an extension of the primary dental lamina, they also erupt without major problems. The succedaneous teeth, however, develop normally initially but are blocked from eruption by three things: a) lack of resorption of the primary teeth, b) multiple supernumerary teeth, and c) heavy fibrotic gingiva that is difficult for the succedaneous teeth to penetrate if they do get that far. Over-retained primary teeth are common (Image 3.) In these children, extraction of the supernumerary teeth is a necessary part of treatment but by itself does not usually lead to eruption. Removal of overlying bone and incision of the gingiva also is needed. Even then, orthodontic treatment to bring the permanent teeth into the mouth usually is needed.

Image 1, Down syndrome: Children with Down syndrome have over-retained primary teeth and an abnormal eruption pattern.	Image 2, Cleidocranial dysplasia –clavicles: Missing clavicles in a patient with cleidocranial dysplasia.
Image 3, Cleidocranial dysplasia – dentition: Multiple unerupted supernumerary teeth and over-retained primary teeth in a patient with cleidocranial dysplasia.

Delayed Eruption (cont.)

1. Hypothyroidism This condition results from a deficiency in thyroid hormone production. A congenital form is seen if affected infants are not treated with thyroid hormone replacement medications. In these individuals delayed eruption of primary teeth and delayed exfoliation of primary teeth can result. In the juvenile form of the condition that develops in childhood, delayed exfoliation of primary teeth and eruption of permanent teeth also often occurs.
2. Hypopituitarism This condition develops due to a deficiency in growth hormone or an abnormality in the pituitary gland. Patients have deficient physical growth along with delayed eruption of primary teeth and delayed exfoliation of primary teeth.
3. Acondroplastic Dwarfism
4. Osteopetrosis (dense alveolar bone)
5. Ectodermal dysplasia (congenital absence and retained primary teeth)

Early Eruption of Primary Teeth

Systemic conditions have also been associated with the early eruption of primary teeth. These are usually hormonal in nature and can include:

1. Hyperpituitarism Hyperpituitarism is due to an abnormality in the pituitary gland and excessive production of growth hormone. In these patients, increased growth is accompanied by early eruption of primary teeth.
2. Hyperthyroidism Excessive production of thyroid hormone also can be associated with early eruption of primary teeth.

Ankylosis of Primary Teeth

Ankylosis occurs when a tooth becomes fused to the adjacent bone, instead of being separated from the bone by an intact periodontal ligament. Once ankylosis occurs, the affected tooth can no longer erupt.

In both the primary and mixed dentition, primary teeth may become ankylosed. The affected teeth are sometimes errantly referred to as submerged teeth because they appear to be submerging into the alveolar bone (Image 1.) This term is not acceptable. In reality, the ankylosed tooth remains static while the adjacent teeth continue to erupt and bring bone with them as jaw growth creates space between the upper and lower jaws (Image 2).

Primary teeth are more commonly affected than permanent teeth. The prevalence in Caucasian children is approximately 4%. It is lower in African-American children at approximately 1%. Mandibular teeth are more commonly affected than maxillary teeth, and the most commonly ankylosed tooth is the mandibular first primary molar. Ankylosis commonly occurs bilaterally and can affect multiple teeth in a single quadrant.

Image 1, Ankylosed primary second molars: The maxillary and mandibular second primary molars are ankylosed and significantly below the plane of occlusion, especially the first permanent molars.	Image 2, Multiple ankylosed primary teeth: Multiple ankylosed primary teeth that are below the plane of occlusion. Coincidentally four permanent premolars appear to be congenitally missing.

Ankylosis of Primary Teeth (cont.)

Pathophysiology of Ankylosis: Resorption of primary teeth is a normal physiologic process that includes osteoclastic and osteoblastic activity near the root surfaces of teeth. In areas of recent osteoclastic resorption, osseous bridging may develop that results in fusion between the alveolar bone and root surface in the periodontal ligament space.

Diagnosis of Ankylosis: The best diagnostic criterion is evaluation of tooth position relative to the occlusal plane. If the primary tooth is below the occlusal plane and sufficient mesio-distal space exists for it to be positioned more superiorly, the tooth is diagnosed as ankylosed. An additional indication of ankylosis is the sound produced by tapping on the affected tooth. Ankylosis usually produces a sharp higher pitched sound that resonates through the alveolar bone. Normal teeth produce a more cushioned sound. Radiographs may reveal a reduced periodontal ligament space if the area of fusion occurs in a plane perpendicular to the central X-ray beam, but in the majority of cases, such radiographic evidence is not found.

Sequelae and Treatment of Ankylosis

Sequelae of Ankylosis: Ankylosis of primary teeth leads to a posterior open bite in that area, and can significantly disrupt normal vertical development of the alveolar process. As the vertical discrepancy increases, the normal interproximal contacts are lost between adjacent teeth, and the adjacent teeth can tip mesially or distally over top of the ankylosed primary tooth, which reduces arch length (image 1).

The majority of ankylosed primary teeth eventually exfoliate without intervention, but exfoliation may be delayed. In some cases succedaneous permanent teeth may be absent underneath ankylosed primary teeth. Research has shown that this is coincidental and not a cause and effect relationship.

Treatment of Ankylosis: Usually no treatment is indicated. However in cases with loss of arch length and tipping of adjacent teeth, which typically occurs with significant submergence of the primary tooth, extraction of the tooth along with space maintenance or space regaining may be required (image 2). Even without space loss, if the ankylosed tooth is not exfoliated before it would be completely submerged, it should be extracted.

Image 1: Ankylosed second primary molars eventually allow the first permanent molars to tip mesially above the ankylosed primary tooth as normal interproximal contact is lost.	Image 2, Space maintainer: This patient had ankylosed primary molars extracted and a lingual arch space maintainer placed to prevent further mesial tipping of the lower permanent first molars.

Resorption and Exfoliation

Root Resorption and Exfoliation of Primary Teeth

The process by which primary teeth are lost and replaced by the succedaneous permanent teeth is called exfoliation. Exfoliation, of course, occurs when the remaining root structure of the primary tooth is no longer sufficient to retain it in the dental arch. This panoramic radiograph of a nine year old boy shows erupting mandibular canines and first premolars and resorption of the overlying primary teeth.

Two processes occur during exfoliation: resorption of the overlying alveolar bone and primary tooth roots, and eruption of the permanent teeth. The degree of resorption of the primary teeth and the amount of root development of the permanent tooth can be valuable in estimating when the eruption of a permanent tooth is likely to occur, and this is the best way to determine dental age in children. The resorption of the primary roots and alveolar bone occurs due to the action of osteoclastic cells.

Early Exfoliation and Systemic Conditions

Early exfoliation or loss of primary teeth can be associated with a number of systemic conditions, some of which can be very serious in nature. Early loss of multiple primary teeth in an atypical sequence is especially a concern as it may be a sign of a serious medical condition. For patients with abnormalities in loss of primary teeth or eruption of permanent teeth, a review of family history and genetic testing may be appropriate.

An astute dentist may be the first health care provider who suspects a systemic condition. Some of these conditions include:

1. Cherubism (images 1 and 2)
2. Acrodynia
3. Hypophosphatasia
4. Familial hypophosphatemic vitamin D-resistant rickets
5. Cyclic neutropenia (image3)
6. Progeria
7. Leukemia
8. Langerhan’s cell histiocytosis
9. Congential agranulocytosis

Image 1, Cherubism: teeth: Panoramic radiograph of a patient with cherubism. The significant feature is bilateral multilocular cystic lesions of the mandible that result in expansion of the mandibular borders.	Image 2, Cherubism: face: Patients with cherubism appear to have a round face form due to expansion of the mandibular borders, which produces a cherub-like appearance.
Image 3, Neutropenia: These radiographs show extensive alveolar bone loss in the primary dentition in a patient with neutropenia. The primary teeth seem to floating in air and will be lost prematurely.

Lingual Eruption of Permanent Incisors

The mandibular permanent incisors develop lingual to the primary incisors, and in some cases they erupt behind the primary teeth without loss of the primary incisors. First-time parents may be alarmed by this and seek treatment for the “two rows of teeth”.

In most cases intervention is not required. As the permanent teeth erupt further, the tongue will exert a forward force on the newly erupted permanent incisors that moves them forward; this forward movement stimulates resorption of the primary incisors and leads to their eventual loss. But, if there is not good spacing between the primary incisors, crowding of the permanent incisors is likely.

Ectopic Eruption

The eruption of permanent teeth along a deviated path is called ectopic eruption. This is relatively common with the eruption of mandibular lateral incisors, occurs sometimes with maxillary first molars, and can occur in the eruption of any permanent tooth.

Mandibular permanent lateral incisors may erupt distally, causing resorption and early loss of the primary canine (image 1.) This usually is a sign of a crowding problem in the mandibular arch. Early unilateral loss of a primary mandibular canine results in a shifting of the dental midline and retroclining of the mandibular incisors (image 2), which usually requires intervention.

Image 1, radiograph showing ectopic eruption: The eruption of the permanent right lateral incisor resulted in the unilateral loss of the right primary canine. As a result the permanent incisors have shifted to the right.	Image 2, dental cast showing ectopic eruption: This mandibular cast of the same patient shows the shifting of the lower midline to the right after early loss of the right primary canine.

Ectopic Eruption: Maxillary Molars

The second most frequently affected teeth for ectopic eruption are the maxillary first permanent molars.

In approximately 3% of children, mesial eruption of the maxillary first permanent molars causes significant resorption of the second primary molars. It is not uncommon to discover the ectopic eruption on routine bitewing radiographs (image 1.) Even though the resorption can be extensive, in the majority of cases the teeth are asymptomatic. Clinically, ectopically erupting maxillary first molars can appear partially erupted with only the distal portion of the occlusal surface visible (image 2). The primary molars can become mobile and can be lost prematurely due to the resorption (image 3).

Image 1, Radiograph of ectopic molars: The ectopically erupting maxillary first permanent molarst are resorbing the distal surfaces of the second primary molars bilaterally.	Image 2, Clinical presentation of ectopic molars: On clinical exam, an ectopically erupting maxillary may look partially or incompletely erupted. A bitewing radiograph would confirm the diagnosis and reveal any resorption of the adjacent primary molar.
Image 3, Severe resorption: An ectopically erupting first permanent molar has caused severe resorption of the upper right primary second molar. On the left side, the maxillary primary second molar has been lost prematurely.

Ectopic Eruption: Treatment

In approximately 2/3rds of the children with an ectopic maxillary first molar, the affected permanent molar is able to jump the area of resorption, which allows eruption to occur (image 1) so the problem self-corrects.

After the initial diagnosis in a child age 7-9, a period of observation (3-4 months) is usually recommended to allow self-correction to occur. If it doesn’t occur, intervention will be required to actively disengage the two teeth to facilitate eruption of the permanent molar. Techniques such as a brass separating wire, orthodontic separator, or an active appliance may be indicated. (image 2).

Image 1, Self-correction: Serial bitewing radiographs taken 3-4 months apart show the self-correction of an ectopically erupting maxillary molar.	Image 2, Treatment: Appliance with a band cemented on the second primary molar and an adjustable spring used to correct an ectopically erupting maxillary molar.
Image 3, Correction of an ectopically erupting maxillary molars: Bitewings showing the correction of bilateral ectopically erupting maxillary molars

Normal vs Pathologic Root Resorption

It is important for a dentist to be able to differentiate normal physiologic root resorption from pathologic inflammatory resorption. As with permanent teeth, pathologic resorption can occur either externally or internally on a primary tooth.

Internal (image 1) or external resorption (image 2) occurs due to inflammatory changes in the pulpal tissue or periapical tissues. The inflammation usually is a sequel to carious involvement of the pulp or trauma to the tooth.

Image 1, Internal resorption: Pathological internal resorption occurring from inside the mesial root canal of the first primary molar, tooth S.	Image 2, External Resorption: Pathological external resorption occurring on the distal root of the second primary molar, tooth K. Very little of the distal root is still visible.

Summary

This module reviewed normal eruption and exfoliation of primary teeth and identified common abnormalities associated with each process. A number of these conditions have serious medical prognoses and may initially be diagnosed through dental findings.

You should now be prepared to describe and discuss:

a). Timing and variability of primary tooth eruption

b). Eruption problems in the primary dentition

c). Resorption and exfoliation of primary teeth

d). Ankylosis of primary teeth

e). Ectopic eruption

Be sure you have read pages 86-91 (5th ed) or 97-103 (4th ed) in *Contemporary Orthodontic**s.*Then take the self-test to be sure you have mastered this material.

Self-Test

Question 1

Which of the following is the most common eruption sequence in the mandibular arch in the primary dentition?

1. Central incisor, lateral incisor, canine, first molar, second molar.
2. Central incisor, lateral incisor, first molar, second molar, canine.
3. Central incisor, lateral incisor, first molar, canine, second molar. ✓
4. Lateral incisor, central incisor, canine, first molar, second molar.

Correct

That’s right; in the mandibular arch the central incisor erupts first and is followed by the lateral incisor. The next tooth to erupt is the first primary molar which appears to be out of sequence skipping the canine. The canine then erupts and is followed by the second molar.

Incorrect

No, that’s incorrect. The correct answer is central incisor, lateral incisor, first molar, canine and second molar. The first primary molar erupts after the lateral incisor which appears to be out of sequence skipping the canine. The canine erupts after the first primary molar and the second primary molar follows the canine completing the primary mandibular arch.

Question 2

The eruption of the primary dentition is usually complete by:

1. 12-18 months of age.
2. 18-24 months of age.
3. 24-30 months of age. ✓
4. 30-36 months of age.

Correct

That’s right; the eruption of the primary dentition is usually complete by 24-30 months of age with the eruption of the maxillary second primary molar.

Incorrect

No, that’s incorrect. The correct answer is 24-30 months of age. The last primary tooth to erupt is usually the maxillary second primary molar.

Question 3

A mother has brought her 2 year old daughter in for a new patient dental examination. During the health history the mother states that her daughter has a fever, diarrhea and been irritable for the last two days. Your examination reveals that the mandibular first primary molars are erupting. Which of the following should you recommend to the mother?

1. Seek medical care to investigate the fever and diarrhea. ✓
2. Reassure her that the symptoms are due to teething and not serious
3. Have her apply topical anesthetic gel to the soft tissue around the erupting teeth.
4. Prescribe a systemic antibiotic.

Correct

That’s right; you should counsel the mother to seek medical care to investigate the cause of the fever and diarrhea. One should not dismiss the symptoms as being related to teething. The use of topical anesthetics around the erupting teeth may provide some relief of local symptoms, but this ignores the potentially serious systemic symptoms. The prescription of antibiotics is unwarranted, however, because a diagnosis of the systemic problem has not been made and the cause of the fever and diarrhea are not known. Unless there is a specific indication for antibiotics, their use may also lead to the development of antibiotic resistance.

Incorrect

No, that’s incorrect. You should counsel the mother to seek medical care to investigate the cause of the fever and diarrhea. One should not dismiss the symptoms as being related to teething. The use of topical anesthetics around the erupting teeth may provide some relief of local symptoms, but this ignores the potentially serious systemic symptoms. The prescription of antibiotics is unwarranted, however, because a diagnosis of the systemic problem has not been made and the cause of the fever and diarrhea are not known. Unless there is a specific indication for antibiotics, their use may also lead to the development of antibiotic resistance.

Question 4

Which of the following conditions are associated with delayed eruption of primary teeth?

1. Hypophosphatasia
2. Hyperpituitarism
3. Cherubism
4. Hypothyroidism ✓

Correct

That’s right; the congenital and juvenile forms of hypothyroidism are associated with the delayed eruption of primary and permanent teeth, and the delayed exfoliation of primary teeth. The other three conditions are associated with early loss of primary teeth.

Incorrect

No, that’s incorrect. The congenital and juvenile forms of hypothyroidism are associated with the delayed eruption of primary and permanent teeth, and the delayed exfoliation of primary teeth. The other three conditions are associated with early loss of primary teeth.

Question 5

A mother brings in her 13-month-old son to see you because no primary teeth have erupted at this time. What would be your advice to the mother concerning the eruption of the teeth?

1. No current intervention, this is within acceptable normal limits ✓
2. Suspect an underlying condition inhibiting eruption
3. Obtain radiographs to investigate whether the teeth are present
4. Both 2 and 3

Correct

That’s right; at the age of 13 months the eruption of the primary teeth is delayed but still within acceptable normal limits. However by 18 months of age the majority of children have some erupted primary teeth. In an 18-month-old with no erupted primary teeth options 2 and 3 would be appropriate.

Incorrect

No, that’s incorrect. At the age of 13 months the eruption of the primary teeth is delayed but still within acceptable normal limits. At this time no intervention would be required. However by 18months of age the majority of children have some erupted primary teeth. In an 18-month-old with no erupted primary teeth options 2 and 3 would be appropriate.

Question 6

Which of the following is correct with respect to ankylosed primary teeth?

1. Diagnosis is confirmed radiographically in the majority of cases
2. The mandibular first molar is the most commonly affected tooth ✓
3. A single tooth is most commonly involved
4. Maxillary teeth are more commonly involved than mandibular teeth

Correct

That’s right; the mandibular first primary molar is the most commonly involved primary tooth. Mandibular teeth are more often involved than the maxillary teeth and it is not uncommon to have multiple ankylosed primary teeth in the same patient. In the majority of cases no evidence of fusion between the root and the alveolar bone is apparent on radiographs.

Incorrect

No, that’s incorrect. The mandibular first primary molar is the most commonly involved primary tooth. Mandibular teeth are more often involved than the maxillary teeth and it is not uncommon to have multiple ankylosed primary teeth in the same patient. In the majority of cases no evidence of fusion between the root and the alveolar bone is apparent on radiographs.

Question 7

A mother brings her daughter (5 yr 10 months old) to see you. The mother is concerned about the eruption of the lower incisors, as she now has “two rows of teeth”. On examination you see that the lower central incisors are erupting lingual to the primary central incisors, which have not exfoliated. What would be your advice to the mother?

1. The primary central incisors should be extracted at this appointment.
2. Consider a removable appliance to move the permanent teeth labially.
3. 1 and 2
4. No intervention required at this time, the primary centrals should exfoliate in time and the permanent centrals should move facially. ✓

Correct

That’s right; no intervention is required at this time. As the permanent central incisors erupt further, tongue forces usually will move them forward and stimulate the exfoliation of the primary teeth. Extraction of the primary central incisors or the use of an active appliance is not required at this time.

Incorrect

No, that’s incorrect. No intervention is required at this time. As the permanent central incisors erupt further, tongue forces usually will move them forward and stimulate the exfoliation of the primary teeth. Extraction of the primary central incisors or the use of an active appliance is not required at this time.

Question 8

Which of the following is not commonly associated with the ectopic eruption of a mandibular permanent lateral incisor?

1. Impaction of the central incisor ✓
2. Shifting of the mandibular dental midline
3. Incisor crowding
4. Early loss of the ipsilateral primary canine

Correct

That’s right; impaction of the permanent central incisor does not commonly occur in these situations but the other things do. As you recall the central incisors erupt before the lateral incisors and would not become impacted if the lateral incisor erupts ectopically. Ectopic eruption of a mandibular permanent lateral incisor commonly results in early loss of the primary canine on the same or ipsilateral side. Once the primary canine is lost, the incisors are free to move laterally resulting in a shift of the mandibular dental midline. This scenario is usually a sign of an underlying crowding problem in the mandibular arch.

Incorrect

No, that’s incorrect. Ectopic eruption of a mandibular permanent lateral incisor commonly results in early loss of the primary canine on the same or ipsilateral side. Once the primary canine is lost, the incisors are free to move laterally resulting in a shift of the mandibular dental midline. This scenario is usually a sign of an underlying crowding problem in the mandibular arch. Impaction of the permanent central incisor does not commonly occur in these situations. As you recall the central incisors erupt before the lateral incisors and would not become impacted if the lateral incisor erupts ectopically.

Question 9

Which permanent tooth is most likely to erupt ectopically?

1. Maxillary lateral incisor
2. Mandibular canine
3. Mandibular second premolar
4. Maxillary first molar ✓

Correct

That’s right; although ectopic eruption of all these teeth can occur, the maxillary first molar is the tooth most likely to do so. When it erupts ectopically the maxillary first molar usually resorbs the distal surface of the primary second molar.

Incorrect

No, that’s incorrect. Although ectopic eruption of all these teeth can occur, the maxillary first molar is the tooth most likely to do so. When it erupts ectopically the maxillary first molar usually resorbs the distal surface of the primary second molar.

Question 10

Approximately what percentage of ectopically erupting maxillary first permanent molars self-correct and do not require intervention?

1. 1/3
2. 1/2
3. 2/3 ✓
4. 3/4

Correct

That’s right; approximately 2/3 of ectopically erupting maxillary first permanent molars will self correct and do not require intervention. This would imply that in an age appropriate child, after the initial diagnosis, a period of observation of 3-4 months is recommended to see if self correction occurs.

Incorrect

No, that’s incorrect. Approximately 2/3 of ectopically erupting maxillary first permanent molars will self correct and do not require intervention. This would imply that in an age appropriate child, after the initial diagnosis, a period of observation of 3-4 months is recommended to allow self correction to occur.

Question 11

(A) The apparent submergence of an ankylosed primary tooth is misleading because (B) what really happens is that the ankylosed molar stops erupting while the adjacent teeth continue to erupt.

1. A true, B true, A and B related ✓
2. A true, B true, A and B not related
3. A true, B false
4. A false, B true
5. A and B false

Correct

That’s right; both statements are true and related. Submergence is a misleading term since the ankylosed tooth stops erupting while the adjacent teeth continue to erupt.

Incorrect

No, that’s incorrect. Both statements are true and related. Submergence is a misleading term since the ankylosed tooth stops erupting while the adjacent teeth continue to erupt.

Question 12

Which of the following is most likely to indicate underlying pathology affecting the eruption process?

1. Eruption of the maxillary right but not the left central incisor ✓
2. Accelerated eruption (3 months) of both maxillary central incisors
3. Delayed eruption (3 months) of both maxillary central incisors
4. All are equally important signs of potential pathology

Correct

That’s right; a deviation of sequence or symmetry in eruption may indicate underlying pathology and is a more important sign than symmetric acceleration or delay.

Incorrect

No, that’s incorrect. A deviation of sequence or symmetry in eruption may indicate underlying pathology and is a more important sign than symmetric acceleration or delay.