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At what point during the process of dentaldevelopment can a definitive diagnosis of developmen-

tal hypodontia be made? A knowledge of average min-

eralization times can be helpful in determining whether

a developing tooth, not visible on radiographs, can beconsidered developmentally absent.1 A differential

diagnosis should include the possibility of delayed

mineralization, given the significant individual varia-

tion in the timing of dental development.2 Although

radiographic evidence of second premolar mineraliza-

tion is usually visible by 5 years of age, these teeth can

be very late in developing, especially in the maxilla.3

When a second premolar is diagnosed as missing, 1

solution is timely interceptive extraction of the overly-

ing deciduous second molar to allow space closure by

drift of the adjacent teeth.4 Alternatively, where

planned extraction of the deciduous molar to provide

space for relief of crowding is not anticipated, the toothcan be retained on the understanding that later it may

become infraoccluded, necessitating coronal build-up.5

If retained, the tooth may later become lost through

exfoliation or forced extraction, necessitating replace-

ment prosthetically, by autotransplantation or an

implant.6 Therefore, the unexpected late development

of a second premolar may complicate the initial treat-

ment plan or even go undiagnosed if appropriate fol-

lowup radiographs are not taken.

CASE REPORT

A girl (aged 11 years 11 months) received treatment

for a Class I malocclusion with a crossbite associated

with a functional shift. The panoral radiograph (Fig 1)

showed agenesis of /3, /5 and5/ ;

/5 was erupting

ectopically,E/

E were infraerupted by 2mm, and E/CE

was retained. Both developing 5/ and

/5 had not yet

developed roots (suggesting slow development com-

pared with the rest of the dentition) and appeared

asymmetric in the stages of their development. In allother respects, the dental age corresponded to the

chronologic age. All third molars showed signs of ini-

tial tooth formation.

Treatment began with the extraction of all remain-

ing deciduous teeth to encourage earlier establish-

ment of the permanent dentition.7 Removable appli-

ances were provided to correct the crossbite and

maintain space for the ectopically erupting

/5 while

allowing spontaneous closure of theE/E extraction

spaces. Thirteen months later (at the age of 13 years),

the progress panoral radiograph (Fig 2) showed ini-

tial crown formation of5/, which was impacting

between 6/ and 4/. The patient was referred for surgi-cal extraction of 5/,

/5, and 5/ before space closure

with fixed appliances.

DISCUSSION

This case illustrates a group of features hypothe-

sized to arise from a common cause, namely delayed

mineralization of a second premolar, slow development

and asymmetry in the stages of formation of the con-

tralateral second premolars, and developmental

hypodontia.8 The cause of developmental hypodontia

is largely genetic,9 transmitted most commonly in an

autosomal dominant pattern with incomplete pene-

trance and variable expressivity.10 It is hypothesized

that delayed formation of the second premolars might

be a milder expression of developmental hypodontia.8

The frequency of occurrence of some or all of these

features is reported to range from 0.1%8 to 9%11 in

children with no cleft palate and as much as 30% in

children with cleft palate.12 The delay in mineraliza-

tion and development of second premolars has been

shown to be constant throughout subsequent tooth for-

321

CASE REPORT

Apparent hypodontia: A case of misdiagnosis

Jonathan Alexander-Abt, BDS, FDS RCS(Eng)a

Hitchin, Herts, UK

The case of a 12-year-old girl is reported, whose pretreatment radiograph demonstrated agenesis of two

premolars and a canine and slow development of the contralateral premolars. A follow-up radiograph taken

1 year later showed initial mineralization of a tooth germ in the site of one of the apparently missing

premolars. The cause, diagnosis, and treatment planning implications of delayed mineralization and slow

development of second premolars are discussed with reference to the literature. (Am J Orthod Dentofacial

Orthop 1999;116:321-3)

aIn Private Practice

Reprint requests to: Jonathan Alexander-Abt, 47 Bancroft, Hitchin, Herts SG5

1LA, United Kingdom.

Copyright 1999 by the American Association of Orthodontists.

0889-5406/99/$8.00 + 0 8/4/95061

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322 Alexander-Abt American Journal of Orthodontics and Dentofacial OrthopedicsSeptember 1999

mation so that their ultimate size and shape are within

normal limits.12 Although a link between developmen-

tal absence of third molars and delayed mineralization

of posterior teeth has been demonstrated,13 such a link

is not evident in this nor in other reported cases,14,15

because all 4 third molars were developing.

To reduce the chance of misdiagnosis, radiographs

that indicate developmental absence of a second pre-

molar should be scrutinized with a magnifying glass to

screen for the presence of an unmineralized tooth

germ.2 The radiographic appearance of a circumscribed

homogenous area in the usual site of second premolar

odontogenesis is indicative of a tooth germ before min-

eralization; (bony) trabeculation indicates developmen-

tal absence.2 A retrospective examination of the pre-

treatment radiograph in this case does reveal a circum-

scribed homogenous area in the bone directly beneath

the bifurcation area of

E/, providing evidence of veryearly

/5 odontogenesis (Fig 3).

The radiographic diagnosis of the developmental

absence of second premolars can be assumed to be cor-

rect when the patient is 8 to 9 years of age4,16 because

relatively few second premolars develop after this age.3

This case, in which a lower second premolar showed

unambiguous radiographic evidence of initial mineral-

ization after 12 years of age, should therefore be con-

sidered unusual. The optimal timing (to encourage

maximum space closure by bodily drift of the adjacent

teeth) for interceptive extraction of the retained

mandibular deciduous second molar is the period

between 8 years of age and the completion of rootdevelopment of the first permanent molar and first pre-

molar.4 It is probable that only in a few cases, such as

the one reported, does a conflict arise between the age-

related demands of correct diagnosis of the develop-

mental absence of the mandibular second premolar and

optimal timing for interceptive extraction of the over-

lying deciduous tooth.

It is not routine practice to screen for the late

development of teeth during orthodontic treatment.17

However, the presence of developmental hypodontia

coupled with slow and asymmetric development of

second premolars should alert the clinician to the pos-

sible presence of a not yet visible unmineralized tooth

germ. In these circumstances, consideration should be

given to taking follow-up radiographs, especially

after interceptive extractions or before orthodontic

space closure.

SUMMARY

Second premolar mineralization and development

can be delayed by as much as 7 years (or more).

Fig 1. Pretreatment panoral radiograph of patient aged

11 years 11 months shows agenesis of 13, 15, and5/;

/5

erupting ectopically.

Fig 2. Progress panoral radiograph 13 months into treat-

ment; initial crown fromation of5/is now apparent.

Fig 3. Magnified retrospective examination of the devel-

oping5/ area (arrowed).

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American Journal of Orthodontics and Dentofacial Orthopedics Alexander-Abt 323Volume 116, Number 3

Delayed mineralization results in the radiographic phe-

nomenon of apparent hypodontia. Published evidence

suggests an etiologic relationship between delayed

mineralization, slow and asymmetric development of

the contralateral second premolars, and developmental

hypodontia. Therefore, developmental hypodontia cou-pled with slow and asymmetric development of con-

tralateral premolars should alert the clinician to the

possible presence of a not yet visible, unmineralized

tooth germ. To reduce the chance of misdiagnosis, cor-

rectly taken radiographs should be scrutinized for early

indications of a tooth germ before mineralization. The

possibility of delayed tooth development should be

considered when deciding on the need for follow-up

radiographs, especially after interceptive extractions or

before orthodontic space closure.

REFERENCES

1. Mitchell L. An introduction to orthodontics. Oxford: Oxford University Press; 1996.

2. Moyers RE, Riolo ML. Early treatment. In: Moyers RE, editor. Handbook of ortho-dontics. 4th ed. Chicago: Year Book Medical Publishers Inc; 1988. p. 343-431.

3. Ravn JJ, Nielsen, HG. A longitudinal radiographic study of the mineralization of 2nd

premolars. Scan J Dent Res 1977;85:232-6.

4. Lindqvist B. Extraction of the deciduous second molar in hypodontia. Eur J Orthod

1980;2:173-81.

5. Evans RD, Briggs PFA. Restoration of an infra-occluded primary molar with an

indirect composite onlay: a case report and literature review. Dental Update

1996;23:52-4.

6. Fields HW. Treatment of nonskeletal problems in preadolescent children. In: Profitt

WR, editor. Contemporary orthodontics. 2nd ed. St Louis (MO): Mosby Year Book;

1993. p. 376-422.

7. Ronnerman A. The effect of early loss of primary molars on tooth eruption and spaceconditions: a longitudinal study. Acta Odont Scand 1977;35:229-39.

8. Ranta R. Hypodontia and delayed development of the second premolars in cleft palate

children. Eur J Orthod 1983;5:145-8.

9. Kirdelan JD, Rysieck;G, Childs WP. Hypodontia: Genotype or environment? A case

report of monozygotic twins. Br J Orthod 1998;25:175-8.

10. Graber LW. Congenital absence of teeth: a review with emphasis on inheritance pat-

terns. J Am Dent Assoc 1978;96:266-75.

11. Kahl B, Schwarze CW. Late mineralization of premolars in relation to orthodontic

diagnosis and therapy [German]. Fortschritte der Kieferorthopadie 1986;47:234-44.

12. Ranta R. Developmental course of 27 late-developing second premolars. Proc Finn

Dent Soc 1983;79:9-12.

13. Garn SM, Lewis AB, Vicinus JH. Third molar polymorphism and its significance to

dental genetics. J Dent Res 1963;42:1344-63.

14. Coupland MA. Apparent hypodontia. Br Dent J 1982;152: 388.

15. Uner O, Yucel-Eroglu E, Karaca I. Delayed calcification and congenitally missing

teeth: case report. Aust Dent J 1994;39:168-71.

16. Rolling S. Hypodontia of permanent teeth in Danish school children. Scand J Dent

Res 1980;88:365-9.

17. Wisth PJ, Thunold K, Boe OE. Frequency of hypodontia in relation to tooth size anddental arch width. Acta Odont Scand 1974;32:201-6.

18. Cochrane SM, Clark JR, Hunt NP. Late developing supernumerary teeth in the

mandible. Br J Orthod 1997;24:293-6.

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