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The effect of extraction of infraoccluded deciduous molars: A longitudinal study
The effect of extraction of infraoccluded deciduous molars: A longitudinal study
Dr. Kurol
Jiiri Kurol, D.D.S., Odont. Dr., and G&an Koch, D.D.S., Odont. Dr. JiinkCping
and
Giiteborg,
Sweden
lnfraocclusion of deciduous molars is often associated with ankylosis. Such teeth are believed to be potential sites of malocclusion, with a risk of tipping of neighboring teeth and loss of space. Extraction has therefore been the most widely recommended treatment. The aim of this study was to follow longitudinally the effect of extraction versus nonextraction treatment in twenty-three homologous pairs of mandibular deciduous molars with infraocclusion when unilateral extraction was performed. The study comprised fifteen children with a mean age at the start of 10.1 years. Recordings were made at the start of the study and every 6 months thereafter until eruption of permanent successors. Periodic identical periapical radiographs and study models were taken every 6 months. Ten of the twenty-three mandibular deciduous molars on the nonextraction side showed progression of the degree of infraocclusion. All infraoccluded deciduous molars exfoliated within the normal time. There was a normal alveolar bone height on both sides after eruption of the successors. Extraction resulted in a gradually increasing space loss in fourteen of the fifteen children. In two cases a definite space deficiency at the time of eruption of the successors was registered. It has been possible to confirm very few of the previously reported negative effects following nontreatment of infraoccluded deciduous molars on exfoliation, eruption, and occlusal development in this study. The results favor a more conservative approach to extraction therapy of infraoccluded deciduous molars. Key words: Ankylosis,
infraocclusion,
malocclusion,
I
nfraocclusion of a deciduous molar means that the tooth loses its vertical position relative to the adjacent teeth and assumes a position below the occlusal plane. The tooth is often believed to be ankylosed, which means that a bony union exists between the bone and the tooth. Infraocclusion in deciduous molars usually develops during the early mixed dentition, and the prevalence has been reported to be 8% to 14% of the children 6 to 11 years of age.’ The infraoccluded teeth are believed to be in a fixed position, and the condition has been reported to be progressive.2-4 It has also been claimed that ankylosed deciduous molars interfere with exfoliation and eruption of permanent successors.4’ 5 There is no general agreement as to the treatment of infraoccluded deciduous molars, but extraction is recommended by many authors, preferably as early as possible.4, 6-E Several authors have reported complications when the condition has remained untreated. Such consequences are listed in Table I. On the other hand, other From the Department of Orthodontics, University for Postgraduate Dental Education, Jiinktiping.
46
of Giiteborg
and The Institute
molar, tooth (deciduous),
tooth diseases, therapy
authors have emphasized the risks and complications of early removal of the infraoccluded deciduous molars. The removal of the infraoccluded and ankylosed tooth may entail technical difficulties and often means fracture of the roots, which sometimes have to be left in the bone. Early extraction and insertion of space maintainers may also mean a risk of development of carious lesions. There is evidence that infraoccluded deciduous molars in the upper jaw show fusion with the bone wall of the maxillary sinus. In these cases extraction may create a pathway into the sinus and lead to further complications .g It is thus clear that opinions differ as to the treatment itself as well as to the treatment effects. However, most of the above-cited findings and opinions are based on case reports, and few longitudinal studies of the effect of treatment of infraoccluded deciduous molars have been published. 4, l6 Systematized knowledge concerning the indications, contraindications, and possible sequelae of different methods of treatment is largely lacking. It is therefore important to elucidate these aspects further in order to develop a rational basis for treatment. In a series of studies, different clinical approaches
Effect of
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extraction
of
infraoccluded
deciduous
molars
47
Table I. Reported consequences of long-standing and untreated infraocclusion of deciduous molars Feature Deciduous molars infraocclusion
Permanent
successor
Reference
Consequence in
Delayed exfoliation Increased difficulties in extraction Surgical removal often necessary Progressive development of ir.fraocclusion Prevention or obstruction of eruption of permanent successor Delayed eruption or impaction of permanent successor Abnormal eruption path of successor Disturbed root development Rotated premolars when erupted Potential sites of developing malocclusion Risk of damaging neighboring teeth by caries and periodontal disease Denuding of proximal root surface by deficient alveolar bone growth Reduced alveolar bone support for premolar Adjacent teeth tipping toward tooth in infraocclusion Loss of arch length Opposing teeth elongate Leads to tongue habits and ofen bite Impaired masticatory efficiency
to the problem of infraoccluded deciduous molars will be studied. AIM The aim of this study was to follow the effect of unilateral extraction of infraoccluded mandibular deciduous molars longitudinally with special reference to the development on the nonextracted, infraoccluded side in the same patient. Special attention was paid to eruption of permanent successors, marginal alveolar bone, and development of the dental arch.
Messer & Cline4 Krakowiak,8 Lamb and Reed’ Vorhies, Gregory, and McDonald,9 Biederman” Rygh and Reitan,2 Messer and Cline4 Andlaw, Silling, Keller, and Feingold” Biederman’” Krakowiak,’ Messer and Cline4 Adams, Mabee, and Browman” Messer and Cline” Biederman,13 Krakowiak* Steyn, ” Krakowiak’ Biederman”’ Messer and ClineJ Vorhies, Gregory, and McDonald9 Messer and Cline4 Konstat and White” Rygh and Reitan,* Silling, Keller, Silling, Keller, and Feingold”
and Feingold”
Table II. Distribution of bilaterally infraoccluded deciduous molars (homologous pairs) in the mandible, unilateral extraction Pairs of infraoccluded teeth First deciduous molars Second deciduous molars First and second deciduous molars Total
No. of individuals 2 5 8 Is
No. of extracted deciduous molars 2 5 16 23
MATERIAL At the start of a series of clinical studies on infraoccluded deciduous molars, dentists in the Public Dental Service in the town of Jonkoping were requested to refer children with infraoccluded deciduous molars to the Orthodontic Department of The Institute for Postgraduate Dental Education in Jonkoping for supervision and/or treatment. Out of this material, fifteen children with bilateral infraocclusion and no aplasia of successors were randomly chosen for inclusian in this study. This enabled us to study the treatment effect of unilateral extractions in cases with bilateral infraocclusion within the same jaw. These fifteen children (twelve boys and three girls) had a mean age at the start of the study of 10.1 years (SD, 1.40 years; range, 8.1 to 13.0 years). Altogether, fifty-five deciduous molars were in infraocclusion. Half of these infraoccluded teeth were caries-free and with-
out restorations. Twenty-three pairs of infraoccluded mandibular deciduous molars were located in the mandible (Table II). The rest of the infraoccluded teeth were single. The twenty-three homologous pairs constituted the material of this study. METHODS Recordings At the start of the study the fifteen children were subjected to a clinical and radiographic examination. In addition, models of the jaws were prepared and intraoral color photographs were taken. The medical and dental history of the child and mother was taken. No pertinent data, relating to this study, were obtained from medical/dental histories of child and mother. Longitudinally, the children were examined clinically every 6 months until permanent successors to the
Table IV. Age at exfoliation of mandibular infraoccluded deciduous molars on nonextraction side Age (in years) Teeth
No.
x
SD
Range
First molar Second molar
10 13
11.0 12.6
0.91 1.10
9.7-11.8 10.8-14.5
Table V. Difference in eruption time between extraction side and nonextraction side in relation to age at extraction Eruption time on extraction side1 versu.7 nonextraction side
Fig. 1. Degree of infraocclusion measured as the shortest distance from the infraoccluded deciduous molar to a plane from the mesiobuccal cusp of the permanent molar to the central incisor edge.
Earlier Same Later Total
Radiographic
Right Differences between left and right sides
First deciduous molar Second deciduous molar First deciduous molar Second deciduous molar First deciduous molar Second deciduous molar
3.3 3.1 3.5 3.2 -0.2 -0.1
No. of children 9 2 4 Is
x
SD
10.7 9.2 9.3 10.1
I .45 0.47 I .63 1.40
sound denoting ankylosis was recorded and distinguished from the dull sound of a normally vibrating tooth. During percussion the tip of a finger was held against the tooth and the presence or absence of vibrations upon percussion was registered. All infraoccluded deciduous molars were in ankylosis according to these criteria.
Table III. Degree of infraocclusoin at start of study with respect to side and tooth and differences between the two sides
Left
Age at extraction
0.72 0.69 0.77 0.56 0.62 0.72
infraoccluded deciduous molars in the lower jaw had erupted. The observation period ranged from 1.5 to 4.5 years, with a mean of 2.6 years. At each examination, intraoral radiographs and impressions for study models were taken. Orthopantomograms were obtained once a year. Clinical examination Percussion of infraoccluded molars was performed, and the sound was compared with that of normal deciduous molars and permanent molars. The sharp, clear
examination
Orthopantomograms and intraoral periapical radiographs of the studied infraoccluded teeth were taken. In order to obtain periodical identical intraoral radiographs, we used the following method. The film was attached to a film holder (Twix). By means of a thermoplastic material (Kerr), the film holder was individually adapted to the occlusal surface of the first permanent molar distal to the studied deciduous molar. The film holder could then be placed identically for each child at different radiographic examinations. A specially designed aluminum plate (weight 25 grams) was adapted to the film holder and extended out of the mouth and laterally at right angles to the film in order to orient the beam of the x-ray correctly in the paralleling technique used. In the orthopantomograms, the occurrence of aplasia and the eruption sequence were registered. In the intraoral radiographs, the marginal bone level, eruption progress of the permanent successor, and root resorp-
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Effect
of extraction
of infraoccluded
deciduous
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49
Number
Extraction
side
:ion extraction side
Me
8 years
6 months
10 years
0 month
10 years
6 months
11 years
6 months
12 years
0 month
13 years
0 month
Fig. 2A. Plaster casts of a boy with bilateral infraocclusion of the deciduous mandibular molars. Age at start, 8 years 6 months. The right side is the extraction side. Extraction resulted in no difference between the sides in eruption time for the first premolar. The second premolar erupted 1.5 years earlier on the extraction side than on the nonextraction side, where the second premolar erupted spontaneously within the normal time. Tootkl 75 showed progressive infraocclusion with time. There was no space deficiency and no tipping of permanent molars. At 13 years of age, there was complete normalization on both sides.
tion of the deciduous molars, tipping and displacement of the developing successor, and unresorbed deciduous roots were noted. Cast analysis Study models were used for measurement of the degree of infraocclusion and the available space in lateral segments and for diagnosis of tipping and rotation of teeth. The type of occlusion was also registered. The degree of infraocclusion was measured by placing a
steel ruler from the mesiobuccal cusp of the first permanent molar to the incisal edge of the central incisor in the same jaw and side. From this horizontal plane, the shortest vertical distance to the occlusal surface of the infraoccluded tooth was measured to the nearest 0.1 mm by means of sliding calipers (Fig. 1). The distance between the mesial surface of the first permanent molar and the distal surface of the permanent lateral incisor, representing the arch space for the canine and premolars, was measured with sliding calipers. The diagonal
50 Kurol and Koch
Extraction
side
Maa side
extractirxr
%le
years
months
Table VI. Distribution of residual deciduous root fragments in the twenty-three pairs of infraoccluded deciduous molars with respect to side and type of tooth
LW
years
years
months
years
months
years
months
month
Fig. 28. Periapical radiographs of the same boy as in Fig. 24. Note alveolar bone height at age of 9 years 6 months, root deviation of 45, retained deciduous root fragments on both sides and exfoliation of tooth 75.
distance, representing the lateral arch length, between the mesial surface of the first permanent mandibular molar and the mesial surface of the lower central incisors on both sides was also measured. Extraction procedures Immediately after the recordings, infraoccluded molars in one side of the lower jaw were extracted. The extraction side for each child was determined by tossing a coin. This resulted in nine left-sided and six right-sided extractions in the fifteen children. For the removal of a tooth under local anesthesia, a mucoperiosteal flap was raised, after which the tooth was loosened with an elevator and extracted with forceps. Small biopsy specimens were taken from the marginal bone for histologic analysis.” The flap was then sutured back and the child was given 0.1% chlorhexidine solution for rinsing the mouth twice a day for 1 week. No space-maintaining appliance was used. RESULTS Clinical findings at the start of the study The degree of infraocclusion ranged from 2.0 to 4.5 mm (X 3.1 mm, SD 0.70 mm). The mean degree of infraocclusion of the first decidu-
Extraction side Nonextraction side
3 -
7 10
ous molars on the left and right sides was 3.3 mm and 3.5 mm, respectively. The corresponding figures for the second deciduous molar were 3.1 mm and 3.2 mm, respectively. The mean difference in infraocclusion between left and right sides was small, less than 0.2 mm (Table III). In only two persons did the difference between sides exceed 1 mm (1.4, 1.5 mm). Ten of the twenty-three mandibular deciduous molars on the nonof the infraoccluextraction side showed progression sion during the observation period (Figs. 2 and 3), resulting in a total infraocclusion of 2 .O to 5.8 mm (X 3.6 mm, SD 1.09 mm). The increase in degree of infraocelusion was not correlated to the age of the child or the initial degree of infraocclusion. On the nonextraction side, the infraoccluded deciduous molars exfoliated normally within the normal time (Table IV) and without complications.‘* All successors, on both the extraction and the nonextraction sides, erupted spontaneously and reached normal positions. In all cases, there was a normal alveolar bone height on both sides after eruption of successors (Figs. 2 and 4). In two children no difference in eruption time between the two sides was noted. In four children there was a delay of 0.5 to 1 year on the extraction side (Figs. 3 and 5), while in nine children the successors erupted about 1 year earlier on the extraction side than on the nonextraction side (Figs. 2 and 4). There was a tendency toward earlier eruption in the older children (Table V). However, the eruption time for all teeth was within normal range. It) Radiographic
findings
The radiographs also showed that earlier eruption occurred in all cases but one in which the successor was not covered with alveolar bone at the 6-month followup after extraction. There was no difference in root development of successors on the extraction side as compared to the nonextraction side.
Effect of extraction of infraoccluded
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Extraction
side
deciduous molars
51
Non extraction side
9 years
0 month
11 years
0 month
12 years
6 months
Fig. 3A. Plaster casts of a boy with bilateral infraocclusion of the mandibular deciduous molars. Age at start of study, 9 years. The right side s the extraction side. On the nonextraction side, note progression of infraocclusion from 3.7 mm at the age of 9 years to 5.4 mm at the age of 11 years. Eruption of premolars on extraction side was delayed until the age of 13.0 to 13.6 years. There was no tipping of permanent molars.
Non extraction side
Extraction
side
Age
Fig. 36. Periapical radiographs of the same boy as in Fig. 34. Note lower right second premolar covered with bone occlusally at 11 years of age and root fragment distal to lower left second premolar.
The marginal bone generally had a concave contour on the nonextraction side, but after exfoliation no differences could be seen between the two sides at the end of the observation period (Figs. 4 and 5). No difference between the two sides with respect to development of carious lesions, periodontal disease, or reduced alveolar bone support for the premolars was recorded. Removal of the infraoccluded teeth was normally not associated with complications, but in eight chil-
Fig. 4. Periapical radiographs of a boy followed from 11 years 7 months to 14 years 2 months of age. The left side is the extraction side. Extraction resulted in eruption of successor 1 year earlier than on nonextraction side. Normal marginal alveolar bone height at end of observational period.
dren ten residual deciduous root fragments had to be left in the bone because of ankylosis (Figs. 2 and 4, Table VI). In six of those eight children, root rests were also found on the nonextraction side after exfoliation of the
52
Kurol
and
Koch
Fig. 5A.
Plaster casts of a boy with bilateral infraocclusion of mandibular start, 8 years 10 months. The extraction side is the left side. No progression Note normalization of alveolar bone height. There were minor differences quence between leff and right sides.
Extraction
side
Agl
8 years
10 months
9 years
4 months
IO years
4 months
10 years
70 months
11 years
4 months
deciduous molars. Age at in degree of infraocclusion. in eruption time and se-
infraoccluded deciduous molars. Of the ten deciduous root rests observed on the extraction side, seven were totally resorbed during the observation period while three were still visible in the radiographs at the end of the observation period. However, all root fragments on the nonextraction side were present at the end of the observation period. Occlusal development
Fig. 56. Periapical radiographs from the same boy as in Fig. 5.4. Note development and growth of alveolar bone on extraction side
Available space in lateral segments ranged from 20.4 to 24.0 mm (X 22.9 mm, SD 0.79 mm) at the start of the study. This means that no space deficiency was registered at the start. The mean difference in available space between the right and left sides in the total material was 0.27 mm (SD 1.55 mm). No difference was found between the two sides in the patients. In fourteen of the fifteen children a gradually increasing space loss was registered on the extraction side; this was measured as arch space for premolars and canine as well as the diagonal distance representing
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Effect of extraction
Table VII. Change of space conditions (mm)
Extraction
of infraoccluded
side
deciduous molars
53
Age
after unilateral extraction of bilaterally infraoccluded deciduous molars in the mandible (fifteen children) ~~
Decrease (mm) After 6 months After 12 months Maximum change Increase (mm) After 6 months After 12 months Maximum change
(n = 14) - 1.4 - 1.6 -1.9 (n = 1) 0 +o.s +0.9
1.00 1.12 1.29 -
(n = 6) -0.3 -0.4 - 1.0 (n = 9) +0.3 +0.8 +1.2
0.24 0.55 0.77 0.38 0.58 0.89
lateral arch length. In one case a small increase in space was noted after extraction of a first deciduous molar. On the nonextraction side, an increase in space was registered in nine of the children. In six children only a minor decrease in space on the nonextraction side was found (Table VII). In two cases the loss of space on the extraction side resulted in a definite space deficiency at the time of eruption of the permanent successors (Fig. 6) Late or early eruption of premolar3 on the extraction side compared to the nonextraction side could not be correlated to changes in space conditions. No mesial tipping of the mandibular first permanent molars could be observed on either side during the observation period. DISCUSSION
In this study it has been possible to confirm very few of the previously reported negative effects of nontreatment of infraoccluded deciduous molars on exfoliation, eruption, and occlusal development. General extraction of all infraoccluded teeth based on the risk of increasing degree of infraocclusion and disturbances in exfoliation, eruption, and occlusal development thus does not seem to be justified. seems to be the only study so far This investigation analyzing the effect of unilateral extraction in patients with bilateral infraocclusion of deciduous molars showing a more pronounced degree of infraocclusion. This makes possible intraindividual comparison and evaluation of the treatment effect. In addition, the children were followed up until eruption of permanent successors to the infraoccluded deciduous molars, which makes it possible to analyze development in the region of infraocclusion.
10 years
5 months
11 years
5 months
12 years
5 months
13 years
5 months
Fig. 6. Periapical radiographs of a girl followed from 10 years 5 months to 13 years 5 months of age. The left side is the extraction side. Note the increasing space loss in the segment, resulting in space deficiency for erupting premolars.
A high rate of increasing infraocclusion with time has been reported.‘, 4* l6 An increasing degree of infraocclusion has been considered a complicating factor. Against this background, it is easy to understand the general recommendation for early extraction of deciduous molars in infraocclusion.‘, g* 13* lg* 2o In this study, ten of twenty-three mandibular deciduous molars on the nonextraction side showed an increase in the degree of infraocclusion but still exfoliated normally. The choice of extraction therapy must therefore be based on factors other than increasing infraocclusion. However, a more extensive study also covering infraoccluded teeth in the upper jaw might make it necessary to modify this statement. In contrast with the findings of Messer and Cline,4 of the infraoccluded teeth and no delay in exfoliation eruption of permanent successors could be found with certainty. The fear of a delay in exfoliation, therefore, seems not to be a reasonable indication for extraction. There have been reports of extraction in older children causing an accelerated premolar eruption, while extraction in younger children causes retardation. In this study, those children with earlier eruption on the extraction side compared to the infraocclusion side also tended to be older. This is in agreement with findings
54 Ku-01 und Koch by Clinch21 and R6nnerman22 in children with early loss of deciduous molars but without infraocclusion. Some authors have argued that long-standing untreated intraoccluded deciduous molars may give growth disturbances of the alveolar bone.4, l3 We also found this, but during eruption of the successors there was a normalization of the alveolar bone height, irrespective of whether or not extractions had been performed. The residual root fragments did not seem to interfere with eruption. The often bilateral occurrence of residual root fragments indicates that the root morphology is of greater importance than the treatment for the presence of root fragments. In contrast to other reports, no tipping of the first permanent molars was observed, although there was seldom normal proximal contact with the second deciduous molar. However, it is an open question whether a more pronounced degree of infraocclusion might result in a higher incidence of tipping of the neighboring teeth and thus give space deficiency, as the mean degree of infraocclusion in this material was about 3 mm. Although there was a space loss in fourteen of the fifteen children on the extraction side, only two children showed definite space deficiency at the time of eruption of the successors. This might be explained by the fact that erupting premolars have the capacity to regain space and also use the available leeway space. However, the risk of development of a definite space deficiency indicates the necessity of careful analysis of the case prior to the decision as to whether or not to extract infraoccluded molars. In fact, infraoccluded deciduous molars may serve as excellent space maintainers, especially when compared to an extraction situation. When extraction of infraoccluded deciduous molars is necessary in such cases, the insertion of space maintainers must be considered. On the nonextraction side, no major space loss was recorded. On the contrary, the majority of segments showed an increase in space on the nonextraction side. This has also been observed by Rygh and Reitan2 who noted a space surplus in some patients with infraoceluded deciduous molars. This is in contrast to the findings of Lamb and Reed,’ who reported a loss of space in ten out of sixteen quadrants in a 2-year follow-up of ankylosed deciduous molars without extractions. The increase of space on the nonextraction side found in this study is difficult to explain. It seems, however, that the normal mesial drift may be reduced. If the ankylosed deciduous molar can be regarded as being in a fixed position, then the increase of space in
the dental arch may be due to sagittal growth mesial to the infraoccluded and ankylosed deciduous molar. However, the study was performed on a limited number of children with infraocclusion only in the mandible, and no tooth showed infraocclusion below the gingival margin. The findings should therefore be interpreted with caution. SUMMARY
The main findings concerning the effect of unilateral extraction of deciduous molars in children with bilateral infraocclusion were that there was no major difference in eruption time of successors between the extraction and nonextraction sides, eruption time of successors was within the normal range, there was no difference in marginal alveolar bone height between the extraction and nonextraction sides after eruption of the successors, the frequency of residual deciduous root remnants was the same on the extraction and nonextraction sides, and a risk of definite space loss in some cases after extraction means that the need of space maintainers must be carefully analyzed if extractions are necessary. Irz conclusion, the study warrants a more conservative approach to extraction therapy of infraoccluded deciduous molars. However, further studies in larger materials and including maxillary teeth, with comparison of infraoccluded and normal sides, are needed to analyze further the effect of infraoccluded deciduous molars on occlusal development.
REFERENCES 1. Km01 J: Infraocclusion of primary molars: an epidemiologic and familial study. Community Dent Oral Epidemiol 9: 94-l 02, 1981. 2. Rygh P, Reitan K: Changes in the supporting tissues of submerged deciduous molars with and without permanent successors. Trans Eur Orthod Sot 39: 171-184, 1963. 3. Darling AI, Levers BGH: Submerged human deciduous molars and ankylosis. Arch Oral Biol 18: 1021-1040, 1973. 4. Messer LB, Cline JT: Ankylosed primary molars: results and treatment recommendations from an eight-year longitudinal study. Pediatr Dent 2: 37-47, 1980. 5. Andlaw RJ: Submerged deciduous molars: a review, with special reference to the rationale of treatment. J Int Assoc Dent Child 5: 59-66, 1974. W: The incidence and etiology of tooth ankylosis. 6. Biederman AM J ORTHOD 42: 921-926, 1956. of space loss resulting from I. Lamb KA, Reed MW: Measurement tooth ankylosis. J Dent Child 35: 483-486, 1968. 8. Krakowiak FJ: Ankylosed primary molars. J Dent Child 45: 288-292, 1978. 9. Vorhies JM, Gregory GT, McDonald RE: Ankylosed deciduous molars. J Am Dent Assoc 44: 68-72, 1952.
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10. Biederman W: Etiology and treatment of tooth ankylosis. AM J ORTHOD 48: 670-684, 1962. 11. Silling G, Keller JG, Feingold M: Retained primary ~rnth: their effect on developing occlusions. J Dent Child 46: 296-299, 1979. 12. Adams TW, Mabee ME, Browman JR: Early onset aof primary molar ankylosis: report of a case. J Dent Child 48: 447-449, 1981. 13. Biederman W: Tooth ankylosis. Ann Dent 12: 1-15, 1953. tandwisselings problemc. J Dent 14. Steyn CL: Betekenisvolle Assoc S Afr 30: 549-552, 1975. teeth: a review 01‘ the litera15. Konstat MM, White GE: Ankylosed ture. J Mass Dent Sot 24: 74-78, 1975. 16. Sullivan B: Observations on submerged primary mola: teeth. NZ Dent J 72: 224-228, 1976. 17. Kurol J, Magnusson BC: Infraocclusion of primary molars: a histologic study. Stand J Dent Res (In press, 1984). 18. Gustafson G, Koch G: Age estimation up to 16 years of age based on dental development. Odontol Revy 25: 297-X)6, 1974.
55
19. Bhaskar SN (editor): Orban’s oral histology and embryology, ed. 9, St Louis, 1980, The C. V. Mosby Company, pp. 4M403. 20. Proffit WR, Vig KWL: Primary failure of eruption: a possible cause of posterior open-bite. AM J ORTHOD 80: 173-190, 1981. 21. Clinch L: A longitudinal study of the results of premature extraction of deciduous teeth between 3-4 and 13-14 years of age. Dent Pratt Dent Ret 9: 109-128, 1959. 22. Rb;nnerman A: The effect of early loss of primary molars on tooth eruption and space conditions: a longitudinal study. Acta Odontol Stand 35: 229-239, 1977. Reprint requests to: Dr. Jiiri Kurol Department of Orthodontics The Institute for Postgraduate J&nvigsgatan 9 S-552 55 J&kaping, Sweden
Dental
Education
Dr. Kurol
Jiiri Kurol, D.D.S., Odont. Dr., and G&an Koch, D.D.S., Odont. Dr. JiinkCping
and
Giiteborg,
Sweden
lnfraocclusion of deciduous molars is often associated with ankylosis. Such teeth are believed to be potential sites of malocclusion, with a risk of tipping of neighboring teeth and loss of space. Extraction has therefore been the most widely recommended treatment. The aim of this study was to follow longitudinally the effect of extraction versus nonextraction treatment in twenty-three homologous pairs of mandibular deciduous molars with infraocclusion when unilateral extraction was performed. The study comprised fifteen children with a mean age at the start of 10.1 years. Recordings were made at the start of the study and every 6 months thereafter until eruption of permanent successors. Periodic identical periapical radiographs and study models were taken every 6 months. Ten of the twenty-three mandibular deciduous molars on the nonextraction side showed progression of the degree of infraocclusion. All infraoccluded deciduous molars exfoliated within the normal time. There was a normal alveolar bone height on both sides after eruption of the successors. Extraction resulted in a gradually increasing space loss in fourteen of the fifteen children. In two cases a definite space deficiency at the time of eruption of the successors was registered. It has been possible to confirm very few of the previously reported negative effects following nontreatment of infraoccluded deciduous molars on exfoliation, eruption, and occlusal development in this study. The results favor a more conservative approach to extraction therapy of infraoccluded deciduous molars. Key words: Ankylosis,
infraocclusion,
malocclusion,
I
nfraocclusion of a deciduous molar means that the tooth loses its vertical position relative to the adjacent teeth and assumes a position below the occlusal plane. The tooth is often believed to be ankylosed, which means that a bony union exists between the bone and the tooth. Infraocclusion in deciduous molars usually develops during the early mixed dentition, and the prevalence has been reported to be 8% to 14% of the children 6 to 11 years of age.’ The infraoccluded teeth are believed to be in a fixed position, and the condition has been reported to be progressive.2-4 It has also been claimed that ankylosed deciduous molars interfere with exfoliation and eruption of permanent successors.4’ 5 There is no general agreement as to the treatment of infraoccluded deciduous molars, but extraction is recommended by many authors, preferably as early as possible.4, 6-E Several authors have reported complications when the condition has remained untreated. Such consequences are listed in Table I. On the other hand, other From the Department of Orthodontics, University for Postgraduate Dental Education, Jiinktiping.
46
of Giiteborg
and The Institute
molar, tooth (deciduous),
tooth diseases, therapy
authors have emphasized the risks and complications of early removal of the infraoccluded deciduous molars. The removal of the infraoccluded and ankylosed tooth may entail technical difficulties and often means fracture of the roots, which sometimes have to be left in the bone. Early extraction and insertion of space maintainers may also mean a risk of development of carious lesions. There is evidence that infraoccluded deciduous molars in the upper jaw show fusion with the bone wall of the maxillary sinus. In these cases extraction may create a pathway into the sinus and lead to further complications .g It is thus clear that opinions differ as to the treatment itself as well as to the treatment effects. However, most of the above-cited findings and opinions are based on case reports, and few longitudinal studies of the effect of treatment of infraoccluded deciduous molars have been published. 4, l6 Systematized knowledge concerning the indications, contraindications, and possible sequelae of different methods of treatment is largely lacking. It is therefore important to elucidate these aspects further in order to develop a rational basis for treatment. In a series of studies, different clinical approaches
Effect of
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extraction
of
infraoccluded
deciduous
molars
47
Table I. Reported consequences of long-standing and untreated infraocclusion of deciduous molars Feature Deciduous molars infraocclusion
Permanent
successor
Reference
Consequence in
Delayed exfoliation Increased difficulties in extraction Surgical removal often necessary Progressive development of ir.fraocclusion Prevention or obstruction of eruption of permanent successor Delayed eruption or impaction of permanent successor Abnormal eruption path of successor Disturbed root development Rotated premolars when erupted Potential sites of developing malocclusion Risk of damaging neighboring teeth by caries and periodontal disease Denuding of proximal root surface by deficient alveolar bone growth Reduced alveolar bone support for premolar Adjacent teeth tipping toward tooth in infraocclusion Loss of arch length Opposing teeth elongate Leads to tongue habits and ofen bite Impaired masticatory efficiency
to the problem of infraoccluded deciduous molars will be studied. AIM The aim of this study was to follow the effect of unilateral extraction of infraoccluded mandibular deciduous molars longitudinally with special reference to the development on the nonextracted, infraoccluded side in the same patient. Special attention was paid to eruption of permanent successors, marginal alveolar bone, and development of the dental arch.
Messer & Cline4 Krakowiak,8 Lamb and Reed’ Vorhies, Gregory, and McDonald,9 Biederman” Rygh and Reitan,2 Messer and Cline4 Andlaw, Silling, Keller, and Feingold” Biederman’” Krakowiak,’ Messer and Cline4 Adams, Mabee, and Browman” Messer and Cline” Biederman,13 Krakowiak* Steyn, ” Krakowiak’ Biederman”’ Messer and ClineJ Vorhies, Gregory, and McDonald9 Messer and Cline4 Konstat and White” Rygh and Reitan,* Silling, Keller, Silling, Keller, and Feingold”
and Feingold”
Table II. Distribution of bilaterally infraoccluded deciduous molars (homologous pairs) in the mandible, unilateral extraction Pairs of infraoccluded teeth First deciduous molars Second deciduous molars First and second deciduous molars Total
No. of individuals 2 5 8 Is
No. of extracted deciduous molars 2 5 16 23
MATERIAL At the start of a series of clinical studies on infraoccluded deciduous molars, dentists in the Public Dental Service in the town of Jonkoping were requested to refer children with infraoccluded deciduous molars to the Orthodontic Department of The Institute for Postgraduate Dental Education in Jonkoping for supervision and/or treatment. Out of this material, fifteen children with bilateral infraocclusion and no aplasia of successors were randomly chosen for inclusian in this study. This enabled us to study the treatment effect of unilateral extractions in cases with bilateral infraocclusion within the same jaw. These fifteen children (twelve boys and three girls) had a mean age at the start of the study of 10.1 years (SD, 1.40 years; range, 8.1 to 13.0 years). Altogether, fifty-five deciduous molars were in infraocclusion. Half of these infraoccluded teeth were caries-free and with-
out restorations. Twenty-three pairs of infraoccluded mandibular deciduous molars were located in the mandible (Table II). The rest of the infraoccluded teeth were single. The twenty-three homologous pairs constituted the material of this study. METHODS Recordings At the start of the study the fifteen children were subjected to a clinical and radiographic examination. In addition, models of the jaws were prepared and intraoral color photographs were taken. The medical and dental history of the child and mother was taken. No pertinent data, relating to this study, were obtained from medical/dental histories of child and mother. Longitudinally, the children were examined clinically every 6 months until permanent successors to the
Table IV. Age at exfoliation of mandibular infraoccluded deciduous molars on nonextraction side Age (in years) Teeth
No.
x
SD
Range
First molar Second molar
10 13
11.0 12.6
0.91 1.10
9.7-11.8 10.8-14.5
Table V. Difference in eruption time between extraction side and nonextraction side in relation to age at extraction Eruption time on extraction side1 versu.7 nonextraction side
Fig. 1. Degree of infraocclusion measured as the shortest distance from the infraoccluded deciduous molar to a plane from the mesiobuccal cusp of the permanent molar to the central incisor edge.
Earlier Same Later Total
Radiographic
Right Differences between left and right sides
First deciduous molar Second deciduous molar First deciduous molar Second deciduous molar First deciduous molar Second deciduous molar
3.3 3.1 3.5 3.2 -0.2 -0.1
No. of children 9 2 4 Is
x
SD
10.7 9.2 9.3 10.1
I .45 0.47 I .63 1.40
sound denoting ankylosis was recorded and distinguished from the dull sound of a normally vibrating tooth. During percussion the tip of a finger was held against the tooth and the presence or absence of vibrations upon percussion was registered. All infraoccluded deciduous molars were in ankylosis according to these criteria.
Table III. Degree of infraocclusoin at start of study with respect to side and tooth and differences between the two sides
Left
Age at extraction
0.72 0.69 0.77 0.56 0.62 0.72
infraoccluded deciduous molars in the lower jaw had erupted. The observation period ranged from 1.5 to 4.5 years, with a mean of 2.6 years. At each examination, intraoral radiographs and impressions for study models were taken. Orthopantomograms were obtained once a year. Clinical examination Percussion of infraoccluded molars was performed, and the sound was compared with that of normal deciduous molars and permanent molars. The sharp, clear
examination
Orthopantomograms and intraoral periapical radiographs of the studied infraoccluded teeth were taken. In order to obtain periodical identical intraoral radiographs, we used the following method. The film was attached to a film holder (Twix). By means of a thermoplastic material (Kerr), the film holder was individually adapted to the occlusal surface of the first permanent molar distal to the studied deciduous molar. The film holder could then be placed identically for each child at different radiographic examinations. A specially designed aluminum plate (weight 25 grams) was adapted to the film holder and extended out of the mouth and laterally at right angles to the film in order to orient the beam of the x-ray correctly in the paralleling technique used. In the orthopantomograms, the occurrence of aplasia and the eruption sequence were registered. In the intraoral radiographs, the marginal bone level, eruption progress of the permanent successor, and root resorp-
Volume 87 1
Effect
of extraction
of infraoccluded
deciduous
molars
49
Number
Extraction
side
:ion extraction side
Me
8 years
6 months
10 years
0 month
10 years
6 months
11 years
6 months
12 years
0 month
13 years
0 month
Fig. 2A. Plaster casts of a boy with bilateral infraocclusion of the deciduous mandibular molars. Age at start, 8 years 6 months. The right side is the extraction side. Extraction resulted in no difference between the sides in eruption time for the first premolar. The second premolar erupted 1.5 years earlier on the extraction side than on the nonextraction side, where the second premolar erupted spontaneously within the normal time. Tootkl 75 showed progressive infraocclusion with time. There was no space deficiency and no tipping of permanent molars. At 13 years of age, there was complete normalization on both sides.
tion of the deciduous molars, tipping and displacement of the developing successor, and unresorbed deciduous roots were noted. Cast analysis Study models were used for measurement of the degree of infraocclusion and the available space in lateral segments and for diagnosis of tipping and rotation of teeth. The type of occlusion was also registered. The degree of infraocclusion was measured by placing a
steel ruler from the mesiobuccal cusp of the first permanent molar to the incisal edge of the central incisor in the same jaw and side. From this horizontal plane, the shortest vertical distance to the occlusal surface of the infraoccluded tooth was measured to the nearest 0.1 mm by means of sliding calipers (Fig. 1). The distance between the mesial surface of the first permanent molar and the distal surface of the permanent lateral incisor, representing the arch space for the canine and premolars, was measured with sliding calipers. The diagonal
50 Kurol and Koch
Extraction
side
Maa side
extractirxr
%le
years
months
Table VI. Distribution of residual deciduous root fragments in the twenty-three pairs of infraoccluded deciduous molars with respect to side and type of tooth
LW
years
years
months
years
months
years
months
month
Fig. 28. Periapical radiographs of the same boy as in Fig. 24. Note alveolar bone height at age of 9 years 6 months, root deviation of 45, retained deciduous root fragments on both sides and exfoliation of tooth 75.
distance, representing the lateral arch length, between the mesial surface of the first permanent mandibular molar and the mesial surface of the lower central incisors on both sides was also measured. Extraction procedures Immediately after the recordings, infraoccluded molars in one side of the lower jaw were extracted. The extraction side for each child was determined by tossing a coin. This resulted in nine left-sided and six right-sided extractions in the fifteen children. For the removal of a tooth under local anesthesia, a mucoperiosteal flap was raised, after which the tooth was loosened with an elevator and extracted with forceps. Small biopsy specimens were taken from the marginal bone for histologic analysis.” The flap was then sutured back and the child was given 0.1% chlorhexidine solution for rinsing the mouth twice a day for 1 week. No space-maintaining appliance was used. RESULTS Clinical findings at the start of the study The degree of infraocclusion ranged from 2.0 to 4.5 mm (X 3.1 mm, SD 0.70 mm). The mean degree of infraocclusion of the first decidu-
Extraction side Nonextraction side
3 -
7 10
ous molars on the left and right sides was 3.3 mm and 3.5 mm, respectively. The corresponding figures for the second deciduous molar were 3.1 mm and 3.2 mm, respectively. The mean difference in infraocclusion between left and right sides was small, less than 0.2 mm (Table III). In only two persons did the difference between sides exceed 1 mm (1.4, 1.5 mm). Ten of the twenty-three mandibular deciduous molars on the nonof the infraoccluextraction side showed progression sion during the observation period (Figs. 2 and 3), resulting in a total infraocclusion of 2 .O to 5.8 mm (X 3.6 mm, SD 1.09 mm). The increase in degree of infraocelusion was not correlated to the age of the child or the initial degree of infraocclusion. On the nonextraction side, the infraoccluded deciduous molars exfoliated normally within the normal time (Table IV) and without complications.‘* All successors, on both the extraction and the nonextraction sides, erupted spontaneously and reached normal positions. In all cases, there was a normal alveolar bone height on both sides after eruption of successors (Figs. 2 and 4). In two children no difference in eruption time between the two sides was noted. In four children there was a delay of 0.5 to 1 year on the extraction side (Figs. 3 and 5), while in nine children the successors erupted about 1 year earlier on the extraction side than on the nonextraction side (Figs. 2 and 4). There was a tendency toward earlier eruption in the older children (Table V). However, the eruption time for all teeth was within normal range. It) Radiographic
findings
The radiographs also showed that earlier eruption occurred in all cases but one in which the successor was not covered with alveolar bone at the 6-month followup after extraction. There was no difference in root development of successors on the extraction side as compared to the nonextraction side.
Effect of extraction of infraoccluded
Volume 87 Number I
Extraction
side
deciduous molars
51
Non extraction side
9 years
0 month
11 years
0 month
12 years
6 months
Fig. 3A. Plaster casts of a boy with bilateral infraocclusion of the mandibular deciduous molars. Age at start of study, 9 years. The right side s the extraction side. On the nonextraction side, note progression of infraocclusion from 3.7 mm at the age of 9 years to 5.4 mm at the age of 11 years. Eruption of premolars on extraction side was delayed until the age of 13.0 to 13.6 years. There was no tipping of permanent molars.
Non extraction side
Extraction
side
Age
Fig. 36. Periapical radiographs of the same boy as in Fig. 34. Note lower right second premolar covered with bone occlusally at 11 years of age and root fragment distal to lower left second premolar.
The marginal bone generally had a concave contour on the nonextraction side, but after exfoliation no differences could be seen between the two sides at the end of the observation period (Figs. 4 and 5). No difference between the two sides with respect to development of carious lesions, periodontal disease, or reduced alveolar bone support for the premolars was recorded. Removal of the infraoccluded teeth was normally not associated with complications, but in eight chil-
Fig. 4. Periapical radiographs of a boy followed from 11 years 7 months to 14 years 2 months of age. The left side is the extraction side. Extraction resulted in eruption of successor 1 year earlier than on nonextraction side. Normal marginal alveolar bone height at end of observational period.
dren ten residual deciduous root fragments had to be left in the bone because of ankylosis (Figs. 2 and 4, Table VI). In six of those eight children, root rests were also found on the nonextraction side after exfoliation of the
52
Kurol
and
Koch
Fig. 5A.
Plaster casts of a boy with bilateral infraocclusion of mandibular start, 8 years 10 months. The extraction side is the left side. No progression Note normalization of alveolar bone height. There were minor differences quence between leff and right sides.
Extraction
side
Agl
8 years
10 months
9 years
4 months
IO years
4 months
10 years
70 months
11 years
4 months
deciduous molars. Age at in degree of infraocclusion. in eruption time and se-
infraoccluded deciduous molars. Of the ten deciduous root rests observed on the extraction side, seven were totally resorbed during the observation period while three were still visible in the radiographs at the end of the observation period. However, all root fragments on the nonextraction side were present at the end of the observation period. Occlusal development
Fig. 56. Periapical radiographs from the same boy as in Fig. 5.4. Note development and growth of alveolar bone on extraction side
Available space in lateral segments ranged from 20.4 to 24.0 mm (X 22.9 mm, SD 0.79 mm) at the start of the study. This means that no space deficiency was registered at the start. The mean difference in available space between the right and left sides in the total material was 0.27 mm (SD 1.55 mm). No difference was found between the two sides in the patients. In fourteen of the fifteen children a gradually increasing space loss was registered on the extraction side; this was measured as arch space for premolars and canine as well as the diagonal distance representing
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Effect of extraction
Table VII. Change of space conditions (mm)
Extraction
of infraoccluded
side
deciduous molars
53
Age
after unilateral extraction of bilaterally infraoccluded deciduous molars in the mandible (fifteen children) ~~
Decrease (mm) After 6 months After 12 months Maximum change Increase (mm) After 6 months After 12 months Maximum change
(n = 14) - 1.4 - 1.6 -1.9 (n = 1) 0 +o.s +0.9
1.00 1.12 1.29 -
(n = 6) -0.3 -0.4 - 1.0 (n = 9) +0.3 +0.8 +1.2
0.24 0.55 0.77 0.38 0.58 0.89
lateral arch length. In one case a small increase in space was noted after extraction of a first deciduous molar. On the nonextraction side, an increase in space was registered in nine of the children. In six children only a minor decrease in space on the nonextraction side was found (Table VII). In two cases the loss of space on the extraction side resulted in a definite space deficiency at the time of eruption of the permanent successors (Fig. 6) Late or early eruption of premolar3 on the extraction side compared to the nonextraction side could not be correlated to changes in space conditions. No mesial tipping of the mandibular first permanent molars could be observed on either side during the observation period. DISCUSSION
In this study it has been possible to confirm very few of the previously reported negative effects of nontreatment of infraoccluded deciduous molars on exfoliation, eruption, and occlusal development. General extraction of all infraoccluded teeth based on the risk of increasing degree of infraocclusion and disturbances in exfoliation, eruption, and occlusal development thus does not seem to be justified. seems to be the only study so far This investigation analyzing the effect of unilateral extraction in patients with bilateral infraocclusion of deciduous molars showing a more pronounced degree of infraocclusion. This makes possible intraindividual comparison and evaluation of the treatment effect. In addition, the children were followed up until eruption of permanent successors to the infraoccluded deciduous molars, which makes it possible to analyze development in the region of infraocclusion.
10 years
5 months
11 years
5 months
12 years
5 months
13 years
5 months
Fig. 6. Periapical radiographs of a girl followed from 10 years 5 months to 13 years 5 months of age. The left side is the extraction side. Note the increasing space loss in the segment, resulting in space deficiency for erupting premolars.
A high rate of increasing infraocclusion with time has been reported.‘, 4* l6 An increasing degree of infraocclusion has been considered a complicating factor. Against this background, it is easy to understand the general recommendation for early extraction of deciduous molars in infraocclusion.‘, g* 13* lg* 2o In this study, ten of twenty-three mandibular deciduous molars on the nonextraction side showed an increase in the degree of infraocclusion but still exfoliated normally. The choice of extraction therapy must therefore be based on factors other than increasing infraocclusion. However, a more extensive study also covering infraoccluded teeth in the upper jaw might make it necessary to modify this statement. In contrast with the findings of Messer and Cline,4 of the infraoccluded teeth and no delay in exfoliation eruption of permanent successors could be found with certainty. The fear of a delay in exfoliation, therefore, seems not to be a reasonable indication for extraction. There have been reports of extraction in older children causing an accelerated premolar eruption, while extraction in younger children causes retardation. In this study, those children with earlier eruption on the extraction side compared to the infraocclusion side also tended to be older. This is in agreement with findings
54 Ku-01 und Koch by Clinch21 and R6nnerman22 in children with early loss of deciduous molars but without infraocclusion. Some authors have argued that long-standing untreated intraoccluded deciduous molars may give growth disturbances of the alveolar bone.4, l3 We also found this, but during eruption of the successors there was a normalization of the alveolar bone height, irrespective of whether or not extractions had been performed. The residual root fragments did not seem to interfere with eruption. The often bilateral occurrence of residual root fragments indicates that the root morphology is of greater importance than the treatment for the presence of root fragments. In contrast to other reports, no tipping of the first permanent molars was observed, although there was seldom normal proximal contact with the second deciduous molar. However, it is an open question whether a more pronounced degree of infraocclusion might result in a higher incidence of tipping of the neighboring teeth and thus give space deficiency, as the mean degree of infraocclusion in this material was about 3 mm. Although there was a space loss in fourteen of the fifteen children on the extraction side, only two children showed definite space deficiency at the time of eruption of the successors. This might be explained by the fact that erupting premolars have the capacity to regain space and also use the available leeway space. However, the risk of development of a definite space deficiency indicates the necessity of careful analysis of the case prior to the decision as to whether or not to extract infraoccluded molars. In fact, infraoccluded deciduous molars may serve as excellent space maintainers, especially when compared to an extraction situation. When extraction of infraoccluded deciduous molars is necessary in such cases, the insertion of space maintainers must be considered. On the nonextraction side, no major space loss was recorded. On the contrary, the majority of segments showed an increase in space on the nonextraction side. This has also been observed by Rygh and Reitan2 who noted a space surplus in some patients with infraoceluded deciduous molars. This is in contrast to the findings of Lamb and Reed,’ who reported a loss of space in ten out of sixteen quadrants in a 2-year follow-up of ankylosed deciduous molars without extractions. The increase of space on the nonextraction side found in this study is difficult to explain. It seems, however, that the normal mesial drift may be reduced. If the ankylosed deciduous molar can be regarded as being in a fixed position, then the increase of space in
the dental arch may be due to sagittal growth mesial to the infraoccluded and ankylosed deciduous molar. However, the study was performed on a limited number of children with infraocclusion only in the mandible, and no tooth showed infraocclusion below the gingival margin. The findings should therefore be interpreted with caution. SUMMARY
The main findings concerning the effect of unilateral extraction of deciduous molars in children with bilateral infraocclusion were that there was no major difference in eruption time of successors between the extraction and nonextraction sides, eruption time of successors was within the normal range, there was no difference in marginal alveolar bone height between the extraction and nonextraction sides after eruption of the successors, the frequency of residual deciduous root remnants was the same on the extraction and nonextraction sides, and a risk of definite space loss in some cases after extraction means that the need of space maintainers must be carefully analyzed if extractions are necessary. Irz conclusion, the study warrants a more conservative approach to extraction therapy of infraoccluded deciduous molars. However, further studies in larger materials and including maxillary teeth, with comparison of infraoccluded and normal sides, are needed to analyze further the effect of infraoccluded deciduous molars on occlusal development.
REFERENCES 1. Km01 J: Infraocclusion of primary molars: an epidemiologic and familial study. Community Dent Oral Epidemiol 9: 94-l 02, 1981. 2. Rygh P, Reitan K: Changes in the supporting tissues of submerged deciduous molars with and without permanent successors. Trans Eur Orthod Sot 39: 171-184, 1963. 3. Darling AI, Levers BGH: Submerged human deciduous molars and ankylosis. Arch Oral Biol 18: 1021-1040, 1973. 4. Messer LB, Cline JT: Ankylosed primary molars: results and treatment recommendations from an eight-year longitudinal study. Pediatr Dent 2: 37-47, 1980. 5. Andlaw RJ: Submerged deciduous molars: a review, with special reference to the rationale of treatment. J Int Assoc Dent Child 5: 59-66, 1974. W: The incidence and etiology of tooth ankylosis. 6. Biederman AM J ORTHOD 42: 921-926, 1956. of space loss resulting from I. Lamb KA, Reed MW: Measurement tooth ankylosis. J Dent Child 35: 483-486, 1968. 8. Krakowiak FJ: Ankylosed primary molars. J Dent Child 45: 288-292, 1978. 9. Vorhies JM, Gregory GT, McDonald RE: Ankylosed deciduous molars. J Am Dent Assoc 44: 68-72, 1952.
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10. Biederman W: Etiology and treatment of tooth ankylosis. AM J ORTHOD 48: 670-684, 1962. 11. Silling G, Keller JG, Feingold M: Retained primary ~rnth: their effect on developing occlusions. J Dent Child 46: 296-299, 1979. 12. Adams TW, Mabee ME, Browman JR: Early onset aof primary molar ankylosis: report of a case. J Dent Child 48: 447-449, 1981. 13. Biederman W: Tooth ankylosis. Ann Dent 12: 1-15, 1953. tandwisselings problemc. J Dent 14. Steyn CL: Betekenisvolle Assoc S Afr 30: 549-552, 1975. teeth: a review 01‘ the litera15. Konstat MM, White GE: Ankylosed ture. J Mass Dent Sot 24: 74-78, 1975. 16. Sullivan B: Observations on submerged primary mola: teeth. NZ Dent J 72: 224-228, 1976. 17. Kurol J, Magnusson BC: Infraocclusion of primary molars: a histologic study. Stand J Dent Res (In press, 1984). 18. Gustafson G, Koch G: Age estimation up to 16 years of age based on dental development. Odontol Revy 25: 297-X)6, 1974.
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19. Bhaskar SN (editor): Orban’s oral histology and embryology, ed. 9, St Louis, 1980, The C. V. Mosby Company, pp. 4M403. 20. Proffit WR, Vig KWL: Primary failure of eruption: a possible cause of posterior open-bite. AM J ORTHOD 80: 173-190, 1981. 21. Clinch L: A longitudinal study of the results of premature extraction of deciduous teeth between 3-4 and 13-14 years of age. Dent Pratt Dent Ret 9: 109-128, 1959. 22. Rb;nnerman A: The effect of early loss of primary molars on tooth eruption and space conditions: a longitudinal study. Acta Odontol Stand 35: 229-239, 1977. Reprint requests to: Dr. Jiiri Kurol Department of Orthodontics The Institute for Postgraduate J&nvigsgatan 9 S-552 55 J&kaping, Sweden
Dental
Education