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Titre: Long‐term follow up of 103 ankylosed permanent incisors surgically treated with decoronation – a retrospective cohort study

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Dental Traumatology 2015; 31: 184–189; doi: 10.1111/edt.12166

Long-term follow up of 103 ankylosed
permanent incisors surgically treated with
decoronation – a retrospective cohort study
Barbro Malmgren1, Georgios
Tsilingaridis1,2, Olle Malmgren3
1
Department of Dental Medicine, Division of
Pediatric Dentistry, Karolinska Institutet,
Huddinge; 2Department of Paediatric Dentistry,
Eastmaninstitutet, Stockholm; 3Orthodontic
Clinic Tandregleringen, Huddinge, Sweden

Key words: decoronation; alveolar ridge;
implants
Correspondence to: Barbro Malmgren,
Department of Dental Medicine, Division of
Pediatric Dentistry, Karolinska Institutet, POB
4064, SE-14104 Huddinge, Sweden
Tel.: +46 73 9851788
Fax: +46 8 7743395
e-mail: barbro.malmgren@ki.se
Accepted 4 January, 2015

Abstract – Background/Aim: Decoronation is a technique developed in
1984 to remove ankylosed teeth and increase marginal bone levels in
young, growing individuals. This retrospective cohort study evaluates marginal bone development after decoronation in relation to gender and age at
treatment. Materials and methods: The study evaluated all 95 patients
with 103 ankylosed permanent incisors treated with decoronation at the
Eastmaninstitutet Department of Pediatric Dentistry during 1978–1999.
Mean age of the patients was 10.7 years (6.8–17.8) at the time of trauma
and 14.9 years (9.3–22.0) at decoronation. The mean follow-up period was
4.6 years (1.0–19.3 years). The study evaluated development of the marginal alveolar bone level with a three-point scoring system: 1 = Unchanged
or reduced alveolar bone level, 2 = A moderate increase in alveolar bone
level, and 3 = A considerable increase in alveolar bone level. The final
group for statistical evaluation comprised 75 patients: 56 boys and 19 girls
who had only one tooth decoronated. Kappa statistics showed almost complete agreement between the two observers (j = 0.90). Results: Bone level
changes were significantly correlated (P < 0.05) to gender and age at treatment. In decoronations performed after the age of 16, bone levels were
unchanged or reduced, while decoronations performed at a mean age of
14.6 years in boys and 13 years in girls yielded a considerable increase in
bone levels. Conclusion: This study indicates that age at decoronation is
an important factor for favorable development of the alveolar ridge and
that decoronation should be performed earlier in girls.

Traumatic injuries to the permanent dentition are
most common in children 8–12 years of age, with a prevalence of 22% (1). Of these, 0.5–3.0% (2, 3) are avulsions
and 0.5%–1.9% are intrusive luxations (4, 5).
A common complication after avulsion and intrusion
injuries is dentoalveolar ankylosis, in which the alveolar bone fuses to the root substance. An ankylosed root
is continually resorbed and replaced by bone, eventually resorbing the entire root. The condition is progressive, and the rate of this resorption seems to vary with
age (6). To date, there is no means of arresting or
reversing the process. If no other changes intervene,
the patient can retain the ankylosed tooth until the
crown falls off or is removed by forceps (7).
By the 1970s, experiments had shown that new
marginal bone might form over the coronal surface of
submerged roots covered with a mucoperiosteal flap (8–
10). When vital roots were submerged, very few inflammatory changes were found, whereas inflammatory
changes occurred consistently, both periapically and
pericoronally, in submerged, endodontically filled roots.
Based on these findings, a technique to remove ankylosed teeth was developed. This technique is now known
as decoronation, in which the goal is to remove the
184

crown and the root filling while maintaining the resorbing root as a matrix for new bone development. This will
preserve the volume of the marginal alveolar ridge, creating better conditions for a future prosthetic solution.
Our research group published the first description of
decoronation treatment in 1984. The study examined the
material of 24 ankylosed permanent incisors (11). We
demonstrated an increase of marginal bone, particularly
in patients treated before their pubertal growth. Several
case reports, as well as a recent study by Lin et al. (12),
support this finding, demonstrating that decoronation
might preserve alveolar bone width and height (12–17).
The aim of this retrospective cohort study was to evaluate marginal bone development after decoronation in
relation to gender and age at treatment.
Materials and methods

We examined the decoronation of permanent ankylosed incisors performed in 102 patients at the Eastmaninstitutet Department of Pediatric Dentistry during
the period 1978–1999. Seven patients were excluded
from the study due to incomplete records, or because
they moved away or did not show up for their dental
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Ankylosed incisors treated with decoronation
appointments. The study group thus comprised 95
patients with 103 decoronated permanent incisors.
Their age at trauma ranged from 6.8 to 17.8 years
(mean 10.7; median 10.4), and their age at decoronation from 9.3 to 22.0 years (mean 14.9; median 15.0).
The average follow-up period was 4.6 years (range
1.0–19.3). Four patients received auto-transplantation
of a premolar to the incisor region, while ongoing
orthodontic treatment in nine patients made correct
evaluation of radiographs difficult. Furthermore, seven
patients had more than one tooth decoronated. We
evaluated this group of 20 patients, but did not include
them in the statistical analysis. The final group for statistical evaluation comprised 75 patients, the 56 boys
and 19 girls who had only one tooth decoronated. Of
the 75 teeth evaluated, 21 had been included in our
earlier study (11).
In the 1984 study, we followed up 14 of the 24 teeth
radiographically; exposures of the alveolar ridge were
made at predefined time points using a device that
ensured the same position was used each time. The
device consisted of the radiographic cone and a film
holder, adjusted parallel to the long axis of the tooth
in a fixed position (11). We traced the apical or coronal
surface of the postoperative bone level in a digitizer
connected to a Nord-10 computer and calculated the
surface area according to Grenn’s formula. These
radiographs became templates for measuring alveolar
ridge changes. A standardized long-cone radiographic
technique was used to evaluate the remaining 81 teeth.
We used a three-point scoring system to assess the
vertical shift in alveolar bone level on radiographs
taken with the standardized long-cone radiographic
technique: 1 = Unchanged or reduced alveolar bone
level, 2 = A moderate increase in alveolar bone level,
and 3 = A considerable increase in alveolar bone level
(Fig. 1). Differences in bone level were evaluated in
relation to the cementum–enamel junction of the
homolog on the most reliable radiographs.

185

determined by two of the authors (BM and OM) had
near perfect agreement (j = 0.90). All data were analyzed with STATISTICA v. 12 (StatSoft, Scandinavia AB,
Uppsala, Sweden).
Results

Considerable increases in alveolar bone level (score 3)
occurred in 20 boys and nine girls, moderate increases
(score 2) in 20 boys and seven girls, and unchanged or
reduced bone levels (score 1) in 16 boys and three girls.
Boys with a considerable increase in bone level were
significantly younger (mean age 14.6 years, SD 2.6)
than those with a moderate (mean age 15.1 years,
SD 2.3), P = 0.03, or unchanged bone level (mean age
16.8 years, SD 2.2), P = 0.01. Girls with a considerable
increase in bone level were significantly younger (mean
age 13.0 years, SD 2.6) than those with an unchanged
bone level (mean age 17.3 years, SD 1.2), P = 0.02
(Table 1). Furthermore, a gamma correlation (G) also
demonstrated that patient age at decoronation has a
significant effect on alveolar bone level for boys
(G = 0.34, P < 0.05) and for girls (G = 0.55,
P < 0.05). This indicates more favorable outcomes in
younger boys and girls, but particularly in girls.
Four patients had both central incisors decoronated;
resorption of the sharp edges of the bone at the suture
had occurred, with no vertical bone growth, but there
was a successive formation of new marginal bone at the
mesial surfaces of the laterals (Fig. 2). In the three
patients where a central incisor and a lateral incisor were
decoronated, no such resorption could be seen (Fig. 3).
At the last follow up, 29 patients had reached the
age of 20 years. Eighteen of these had received
implants. In six patients, root remnants were still present at the time of insertion. In four of these, the
implants were inserted in contact with the roots. This
did not impede insertion of the implants or the healing
process (Fig. 4a–b). Fourteen of the 18 implant
patients received no ridge augmentation.

Statistical analysis

Analysis evaluated bone levels in relation to age at decoronation and gender using nonparametric correlation,
gamma statistics, and a t-test, all with a significance
level of P < 0.05. We randomly selected 20 cases from
the material for double determination of the bone
level classification, using Kappa statistics. The scores
(a)

(b)

Discussion

The main finding in this study is that age at decoronation is an important factor for favorable development
of the alveolar ridge. Furthermore, the time when the
development of the alveolar ridge is most favorable
differs significantly between boys and girls.
(c)

Fig. 1. Estimation of changes in bone level in the vertical direction. (a) Score 1 = Unchanged or reduced alveolar bone level. (b)
Score 2 = A moderate increase in alveolar bone level. (c) Score 3 = A considerable increase in alveolar bone level.
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

186

Malmgren et al.

Table 1. Alveolar bone level after decoronation of 75 teeth in 56 boys and 19 girls in relation to age at operation
Age at decoronation

Boys
N = 56
Girls
N = 19

(a)

Alveolar bone level

Number of teeth

Mean

SD

1.
2.
3.
1.
2.
3.

16
20
20
3
7
9

16.8
15.1
14.6
17.3
14.2
13.0

2.2
2.3
2.6
4.6
1.8
1.2

Unchanged or reduced
Moderate
Considerable
Unchanged or reduced
Moderate
Considerable

(b)

Fig. 2. Decoronation of both central
incisors. (a) A 15-year-old girl
immediately after decoronation. (b)
Result after 2 years. Note resorption of
the sharp edges of the bone at the
suture.

(a)

(b)

Fig. 3. Decoronation of right upper
lateral and central incisors. (a) A
16-year-old boy immediately after
decoronation. (b) Result after 3 years.
Note increase of bone in vertical
direction and formation of lamina dura.

Earlier studies have established a relationship between
infraposition of an ankylosed tooth and growth of the
alveolar bone. Infraposition is caused by local arrest of
the dentoalveolar bone, and its severity depends on the
development of occlusion and facial growth. These factors vary individually. Thus, monitoring the patient is
important. In general, it is recommended to remove an
ankylosed tooth before severe infraocclusion and tilting
of neighboring teeth develop (18, 19).

Clinical experience shows that extraction of an ankylosed tooth may involve loss of attached bone, particularly the thin buccal plate of the maxilla, which
jeopardizes socket healing, causing bone defects in both
the horizontal and vertical dimensions (18). The ankylosed tooth should therefore be removed in time to prevent these adverse effects. Decoronation preserves the
alveolar width and rebuilds the lost vertical bone of the
alveolar ridge in growing individuals. The biological
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Ankylosed incisors treated with decoronation
(C)

187

(D)

(a)
(B)

(A)

(H)

(I)

(b)
(E)

(F)

(G)

Fig. 4. (a) A 16-year-old boy before and after decoronation. (b) Implant insertion 14 years after decoronation. Radiographs
before and after insertion. Note root remnants at the arrows and the marginal bone prominence.

explanation for this is that the decoronated root serves
as a matrix for new bone development during resorption
of the root and that the lost vertical alveolar bone is
rebuilt during eruption of adjacent teeth. A new periosteum is first formed over the decoronated root, allowing
vertical alveolar growth. The interdental fibers severed
by the decoronation procedure are then reorganized
between adjacent teeth. The continued eruption of these
teeth mediates marginal bone apposition via the dentalperiosteal fiber complex. The erupting teeth are linked
with the periosteum covering the top of the alveolar
socket and indirectly via the alveolar gingival fibers,
which are inserted in the alveolar crest and in the lamina
propria of the interdental papilla. Both structures can
generate a traction force resulting in bone apposition on
top of the alveolar crest. This theoretical biological
explanation is based on known anatomical features,
known eruption processes, and clinical observations
(18). In the present study, we found considerable marginal bone development when decoronation was performed at an average age of 14.6 years in boys and
13 years in girls. This corresponds well with studies of
the craniofacial complex, agreeing with both Thilander’s
(19) description of an age difference of 2 years between
boys and girls in this age interval and the growth velocity
curves presented by Taranger and H€
agg (20). The age
distribution within the groups was large. As shown earlier, different changes in bone level can also be explained
by varying growth patterns, such as vertical vs horizontal growers, as well as growth intensity (21).
When two central maxillary incisors were decoronated, we found no increase in bone at the suture, but
instead found a resorption and rounding of the suture
edges. A possible explanation for this may be a split of
the uniting periosteum layer covering the suture. The
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

periosteum consists of two layers, an outer fibrous
layer containing blood vessels and an inner cellular
osteogenic layer (22). During decoronation of the two
central incisors, the fibers of the outer layer are cut off
and extend into the suture, so that no uniting periosteum layer is formed. Thus, stimulation for new bone
formation is lost. When a central incisor and a lateral
incisor are decoronated, however, new marginal bone
is formed and bone level increases (Fig. 5).
It is well known that the resorption of the alveolar
process after tooth extraction in both jaws is significantly greater on the buccal aspect than on the lingual
or palatal (23–26). The decoronation technique minimizes bone loss, and the ankylosed root is successively
resorbed and replaced with bone. An important part of
this treatment is that the root canal fills with a blood
clot; as the blood clot is organized from the surrounding bone tissue, bone will be created in the canal. It is
therefore important to remove a root filling. A recent
case study did not perform root filling removal, and
favorable alveolar bone development failed (27). Lin
et al. measured the bucco-palatal alveolar dimensions
of the alveolar ridge at the mid-mesio-distal distance
after decoronation on study casts (12). They found a
reduction of only 1 mm in the bucco-palatal dimension
at the mid-decoronation area compared with the
contralateral homologous tooth. This reduction is
significantly less than in the findings by Lam who measured alveolar change in the same way after extractions
and found a reduction of 3–5.5 mm (28).
Four cases received implants with contact to the
root remnants. The remnants did not impede insertion
of the implants or the healing process (Fig. 5). Earlier
studies have demonstrated implant integration in root
substances without ridge augmentation (17, 29, 30).

188

Malmgren et al.

(a)

(b)

(c)

Fig. 5. Schematic drawing showing the two layers of the periosteum. (a) The suture is bridged over by the outer united layer. (b)
The outer layer is cut off during the decoronation procedure. (c) The two parts extend from both sides down into the suture.

Furthermore, we demonstrate that 14 of 18 implant
patients did not receive ridge augmentation, indicating
a preserved bone volume suitable for dental implants.
This finding is supported by Lin et al. (12), who followed up avulsed teeth that had received implants after
decoronation without ridge augmentation using CBCT.
Like ankylosed teeth, osseointegrated implants do not
erupt or displace neighboring teeth during jaw growth
to create esthetic problems due to infraposition of the
implant with time (31–34). A recent study demonstrated that implant submersion continues through
adulthood, especially between the ages of 20–30 (35).
So for future studies, a long-term follow up on bone
development in patients receiving implants after decoronation in the central maxillary region would be interesting.
Furthermore, after decoronation, significant alterations occur in the alveolar ridge. Our study found considerable
marginal
bone
development
after
decoronation, although we cannot assess bone quality
at the time of implant placement. Thus, assessment of
the bone quality and the combinations of decoronation
and bone grafting prior to implant insertion are interesting subjects for future research (36).
In conclusion, this study indicates that age at the time
of decoronation is an important factor for favorable
development of the alveolar ridge and that decoronation
should be performed earlier in girls than in boys.
Acknowledgements

The enthusiastic and skillful assistance of dental nurse
Eva Jansson is gratefully acknowledged.
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