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The International Journal of Periodontics & Restorative Dentistry
Sufficient alveolar bone volume and
favorable architecture of the alveo-
lar ridge are essential to obtain ideal
functional and esthetic prosthetic
reconstruction following implant
therapy.
1
Knowledge about the heal-
ing process at extraction sites,
including contour changes caused
by bone resorption and remodeling,
is essential. Loss of alveolar bone
may occur prior to tooth extraction
because of periodontal disease,
periapical pathology, or trauma to
teeth and bone. Damage of the
bone tissues during tooth extraction
procedures may also result in bone
loss. Finally, alveolar bone atrophy
after tooth extraction is a well-known
phenomenon.
2,3
Histologic investigations in ani-
mals
4
and humans
5,6
have described
the healing of extraction sockets.
The gross morphologic changes of
the alveolar processes after loss of
teeth have been evaluated by
cephalometric analyses
2,7,8
and
measurements on study casts.
9,10
The resorption of the alveolar
process after tooth extraction in the
maxilla or mandible is significantly
larger at the buccal aspect than at
Bone Healing and Soft Tissue Contour
Changes Following Single-Tooth
Extraction: A Clinical and Radiographic
12-Month Prospective Study
Lars Schropp, DDS*
Ann Wenzel, DDS, PhD, Dr Odont**
Lambros Kostopoulos, MS, DDS, PhD***
Thorkild Karring, DDS, Dr Odont****
Preservation of alveolar bone volume following tooth extraction facilitates subse-
quent placement of dental implants and leads to an improved esthetic and func-
tional prosthodontic result. The aim of the present study was to assess bone for-
mation in the alveolus and the contour changes of the alveolar process following
tooth extraction. The tissue changes after removal of a premolar or molar in 46
patients were evaluated in a 12-month period by means of measurements on
study casts, linear radiographic analyses, and subtraction radiography. The results
demonstrated that major changes of an extraction site occurred during 1 year
after tooth extraction. (Int J Periodontics Restorative Dent 2003;23:313–323.)
****PhD Student, Department of Oral Radiology, University of Aarhus,
Denmark.
****Professor, Department of Oral Radiology, University of Aarhus, Denmark.
****Assistant Professor, Department of Oral and Maxillofacial Surgery,
University of Aarhus, Denmark.
****Professor, Department of Periodontology and Oral Gerodontology,
University of Aarhus, Denmark.
****Reprint requests: Dr Lars Schropp, Department of Oral Radiology,
University of Aarhus, Vennelyst Boulevard 9, 8000 Århus C, Denmark.
Fax: + 0045 86 19 60 29. e-mail: lschropp@odont.au.dk
313
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the oral aspect of the jaws
9
; the
reduction in width of the maxillary
alveolar ridge is greater than the loss
in height.
10
This was supported by
Lekovic et al,
11
who studied bone
changes at extraction sites using clin-
ical measurements during operation
and measurements on models
poured from silicone impressions of
the exposed sockets. The maximum
loss of tissue contour takes place
during the first month following
tooth extraction.
12
Subtraction radiography is a
well-established method for the
detection of subtle bone changes.
The technique was introduced in
the 1930s and has been applied to
several diagnostic tasks within den-
tal research.
13
Different subtraction
systems, from photographic to dig-
ital, have been developed, either
operated manually or by more
advanced automated systems (for
review, see Lehmann et al
13
). In sev-
eral reports, subtraction radiogra-
phy has been evaluated regarding
technical facilities and diagnostic
effectiveness for the estimation
and interpretation of bone mass
changes.
14–17
However, healing of
the extraction socket and changes
of the alveolar process following
tooth extraction have not yet been
evaluated by means of subtraction
radiography. Therefore, the aim of
the present study was to assess
bone formation in the alveolus and
changes of the contour of the alve-
olar process following single-tooth
extraction.
Method and materials
Forty-six patients (31 women, 15
men), referred for extraction of a
maxillary or mandibular premolar or
molar and subsequent single-tooth
implant treatment, were included in
this study. The study teeth com-
prised 11 maxillary and 10 mandibu-
lar premolars and 9 maxillary and 16
mandibular molars. Mean patient
age was 45 years (range 20 to 73
years). The reasons for extraction
included root fractures, periodon-
tally compromised teeth, endodon-
tic treatment failures, and advanced
caries lesions. The patients were
given oral and written information
regarding the study, and their
informed consent was obtained. The
research protocol was approved by
the Danish Committee for Scientific
Ethics as being in accordance with
the Helsinki Declaration II.
Following local anesthesia, the
teeth were gently luxated with an
elevator and carefully extracted with
an extraction forceps, attempting to
produce as little trauma as possible
to the bone circumscribing the alve-
olus. The patients, except for two,
agreed not to wear any prostheses
during the 12-month healing period.
Clinical and radiographic evaluation
of the extraction site was carried out
at baseline (immediately after tooth
extraction) and 3, 6, and 12 months
following tooth extraction.
Clinical evaluation
The soft tissue and bone contour
changes were assessed on study
models. Casts were prepared from
irreversible hydrocolloid impressions
taken immediately after tooth extrac-
tion and at the follow-up visits. The
distance from the midpoint of the
extraction site perpendicular to the
line connecting the occlusal surfaces
of the adjacent teeth was recorded at
the most occlusally situated point
both buccally and orally (Fig 1). In
addition, the width of the alveolar
ridge was measured perpendicular
to the tangent of the dental arch at
the midpoint of the extraction site as
the distance between the most
prominent points buccally and orally.
All measurements were carried out
twice by one investigator using a dig-
ital caliper. The reproducibility of the
measuring method was evaluated by
means of a nonparametric test based
on Spearman’s rho. Using the mean
value of the first and the second mea-
sure, the changes over time were cal-
culated and tested by the Wilcoxon
matched pairs signed rank test.
The periodontal conditions of
the teeth adjacent to the extraction
314
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Fig 1 Measurements of alveolar height
buccally (B) and orally (O), and width on
study casts.
site were assessed by measuring
probing pocket depths and clinical
attachment levels at the tooth sur-
faces mesial and distal to the extrac-
tion site using a periodontal probe
(Hu-Friedy). The measurements were
performed buccally, in the center,
and orally at each surface.
Radiographic procedure
Standardized intraoral radiographs
(Ektaspeed Plus film, Eastman
Kodak) were obtained at the time
points described above. To achieve
reproducible periapical images, the
paralleling technique was used with
an occlusal bite index prepared from
silicone material (President putty,
Coltène) and fixed to a Trollbiten film
holder (Trollhatteplast). After place-
ment in the patient’s mouth, the bite
block was attached to the cone of
the radiographic unit by means of a
metal muff fitting the outer contour
of the cone. This recording device
alveolar bone crest at the mesial
(M
x
) and distal (D
x
) aspects of the
socket of the extracted tooth was
measured. The recordings were car-
ried out in the images taken at base-
line (I
Base
) and in those taken 12
months following tooth extraction
(I
12
). In image I
12
, the most apically
situated point between M
x
and D
x
was recorded (C) (Fig 2c). For assess-
ing the bone levels at the extraction
site in these images, the position of
the extracted tooth was determined
by drawing a contour of the tooth in
the image taken before extraction
(I
BX
) (Fig 2a). The “tooth contour”
was then transferred to images I
Base
and I
12
using the computer program
for subtraction radiography. The ref-
erence line was drawn in I
BX
and
transferred in a similar manner. All
linear measurements were per-
formed twice by the same investi-
gator, and the correlation between
the first and second recordings was
evaluated by means of Spearman’s
rho test.
has been described in more detail
elsewhere.
18
The bite index was
saved for use at all visits. All radi-
ographs were digitized with a reso-
lution of 300 dpi by a flatbed scan-
ner with a transparency module
(Hewlett Packard).
Linear measurements on
radiographs
Linear measurements in the digitized
radiographs (Fig 2) were performed
by means of a computer program
designed for linear and angular
analyses (PorDiosW, Institute of
Orthodontic Computer Sciences).
19
Bone levels at the mesial aspect
of the tooth distal (D
t
) as well as at
the distal aspect of the tooth mesial
(M
t
) to the extraction site—in cases
where these teeth were present—
were determined by measuring the
distance from a reference line to the
bone level at these sites (Figs 2b
and 2c). Further, the level of the
315
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Fig 2a Linear radiographic measurements
from reference line (#2) to crestal bone lev-
els: image taken before tooth extraction
(I
BX
). The contour of the tooth (#3) has been
drawn in this image. #1 = ROC.
Fig 2b Image taken immediately after
tooth extraction (I
Base
). The tooth contour
has been transferred to this image. D
t
=
mesial aspect of tooth distal to extraction
site; M
t
= distal aspect of tooth mesial to
extraction site; M
x
= level of alveolar bone
crest at mesial aspect of extraction socket;
D
x
= level of alveolar bone crest at distal
aspect of extraction socket.
Fig 2c Image taken 12 months after
tooth extraction (I
12
). C = most apically sit-
uated point between M
x
and D
x
.
To assess the level of bone heal-
ing at the extraction site, the
changes of the bone level at the
mesial and distal aspects of the
socket from baseline to 12 months
after tooth extraction were calcu-
lated. In addition, the bone level at
the mesial and distal aspects of the
extraction socket was compared
with that of the adjacent teeth. For
these calculations, the mean of the
first and the second measures was
used. The Wilcoxon matched pairs
signed rank test was used to evalu-
ate differences between bone level
changes over time, and between
bone levels at the extraction site and
adjacent teeth.
Subtraction radiography
The scanned radiographs were
imported into a semiautomated sub-
traction program, X-PoseIt (version
3.01, Torben Jørgensen), and the
subtraction process was performed
on an IBM-compatible Pentium PC.
For alignment of the images, four to
nine reference points were defined
in each image (Figs 3a and 3b),
allowing geometric differences to
be corrected to some extent using
algorithms for scaling, translation,
and rotation. The program operates
with a dynamic range of 256 gray
shades. By definition, all pixels in a
perfect subtraction image of a site
without bone changes would have a
mean gray level of 128. Bone gain is
defined as pixels with a gray level of
more than 128 and appears bright in
the subtraction image, whereas
bone loss is defined as pixels with a
gray level of less than 128 and
appears dark. This definition is based
on similar radiographic density and
geometry in the images to be sub-
tracted, and on the absence of phys-
ical background noise.
In the clinical situation, however,
thresholds for the pixel values must
be determined to compensate for
differences in the recording and pro-
cessing of the radiographs, and to
take physical noise into account.
20
These thresholds were related to the
mean pixel value and the standard
deviation (SD) of the histogram dis-
tribution of the pixels in a “region of
control” (ROC), thereby defining
when pixel changes should be
regarded as bone gain and loss,
respectively, in the “region of inter-
est” (ROI).
• ROI corresponded to the alveo-
lus of the extracted tooth. It was
determined by drawing a con-
tour of the root(s) in the image
taken before extraction (Fig 3a).
The ROI could then be trans-
ferred to the baseline image (Fig
3b). The area was subsequently
extended so that lamina dura
and the septum in cases of mul-
tirooted teeth were included in
ROI.
• ROC was an area expected not
to be involved in bone changes.
The area was drawn as large as
possible in I
BX
in a region of tra-
becular bone and transferred to
I
Base
.
Both regions were automatically
transferred to the subtraction image
by the program. Pixels with a gray
value within the interval mean value
±2 SD for the ROC were defined
as unchanged. Pixel values above
this level corresponded to bone
gain, and values below corre-
sponded to bone loss. For better
visualization, bone gain in the ROI
was colored blue, and bone loss was
colored red.
I
Base
was subtracted from the fol-
low-up images taken 3, 6, and 12
months following extraction (I
3
, I
6
,
I
12
), resulting in the subtraction
images I
3
– I
Base
, I
6
– I
Base
, and I
12
–
I
Base
(Figs 3c to 3e). The statistics of
the ROI in these images were
exported to the statistical program
(SPSS, version 10.0, SPSS), includ-
ing the mean gray value and the size
(using number of pixels as the unit)
of the gain, loss, and unchanged
areas. The significance of the differ-
ences of the mean gray values and
the size of the areas over time was
tested by the Wilcoxon matched
pairs signed rank test. For all statis-
tical tests (both clinical and radi-
ographic data), the level of signifi-
cance was set to = .05.
316
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Results
Clinical evaluation
Two patients withdrew from the
study after the 6-month visit. For
assessments on models, high repro-
ducibility of the measuring method
was found (Spearman’s rho > .88; P
< .0001). Immediately after tooth
extraction, the mean width of the
alveolar ridge was 12.0 mm (range
8.6 to 16.5 mm). The most occlu-
sobuccal point was located on aver-
age 1.3 mm more apically than the
occlusooral point. After 12 months of
healing, this difference was reduced
to 0.2 mm as a result of a tissue gain
of 0.3 mm buccally and a loss of 0.8
mm orally (Table 1). Most of the gain
reduction of approximately 1 mm
was obtained. Hereafter, the pocket
depths were almost unchanged. A
mean recession of the gingiva
amounting to 0.7 mm occurred
gradually during the 12-month heal-
ing period. A mean attachment gain
of 0.3 mm at the tooth surfaces adja-
cent to the extraction site was found,
with no appreciable difference
between the changes at the mesial
and distal aspects of the teeth next
to the extraction site.
Linear measurements on
radiographs
The linear measurements recorded
twice correlated well (Spearman’s
was achieved from 3 to 12 months
following extraction, whereas almost
the entire loss of height took place
during the first 3 months. With
regard to the width of the ridge, a
reduction of approximately 50% was
found, ie, from 12.0 to 5.9 mm (6.1
mm; range 2.7 to 12.2 mm), of which
two thirds occurred during the first 3
months of healing. The percentage
reduction was somewhat larger in
the molar regions than in the pre-
molar regions, and in the mandible
compared with the maxilla.
Changes in pocket depth, gin-
gival recession, and attachment level
at the tooth surfaces mesial and dis-
tal to the extraction site are shown in
Table 2. During the first 3 months fol-
lowing tooth extraction, a pocket
317
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Fig 3a Subtraction radiography: image
taken before tooth extraction (I
BX
). The
contour of the tooth (#2, ROI) has been
drawn in this image. #1 = ROC.
Fig 3b Image taken immediately after
tooth extraction (I
Base
). The ROI has been
transferred to this image.
Fig 3d (left) I
6
– I
Base
.
Fig 3e (right) I
12
– I
Base
.
Fig 3c Resulting subtraction images.
Blue and red areas in the ROI illustrate
bone gain and loss, respectively: I
3
– I
Base
.
rho > .90; P < .0001). The bone lev-
els at the tooth surfaces mesial as
well as distal to the extraction site
were almost unchanged from extrac-
tion to the 12-month visit (a loss of
approximately 0.1 mm). At baseline,
the mean bone levels corresponding
to the mesial (M
x
) and distal sites
(D
x
) of the extracted tooth were
located 0.7 mm and 0.3 mm more
apically than the level at the mesial
and distal teeth, respectively. After
12- month healing of the extraction
socket, the difference in bone levels
mesially and distally had increased
from 0.7 to 0.9 mm and from 0.3 to
0.5 mm, respectively. The bone level
at M
x
and D
x
after 12 months was sit-
uated 0.3 mm more apical than at
baseline. This difference was statis-
tically significant (P < .04). Further-
more, the bone level at the most
apically situated point between M
x
and D
x
was located 1.2 mm more
apical than at these two sites (P <
.0001).
Subtraction radiography
Because of lack of useful reference
points, the subtraction procedure
was not performed in three patients.
318
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Table 1 Model measurements of mean changes of width and height of alveolar process (mm)*
Region Baseline–3 mo 3–6 mo 6–12 mo Baseline–12 mo
All regions
Height buccally –0.1 [–0.3; –0.9/0.6] 0.2 [0.2; –0.2/0.5] 0.3 [0.3; 0.0/0.5]
†
0.4 [0.1; –0.6/1.0]
Height orally –0.8 [–0.8; –1.3/–0.5]
†
–0.1 [0.1; –0.4/0.4] 0.1 [–0.1; –0.3/0.4] –0.8 [–0.7; –1.4/–0.2]
†
Width –3.8 [–3.4; –5.2/–2.3]
†
–1.3 [–0.9; –2.2/–0.4]
†
–1.0 [–0.8; –1.3/–0.3]
†
–6.1 (12.0–5.9) [–5.9; –7.7/–4.7]
†
Premolar
Height buccally –0.3 [–0.4; –0.9/0.3] 0.2 [0.1; –0.2/0.6] 0.3 [0.3; 0.1/0.6]
†
0.2 [0.0; –0.6/0.9]
Height orally –0.9 [–1.0; –1.3/–0.5]
†
0.0 [0.1; –0.5/0.3] 0.1 [0.2; –0.1/0.5] –0.8 [–0.8; –1.4/–0.3]
†
Width –3.1 [–2.9; –3.9/–2.1]
†
–0.9 [–0.7; –1.3/–0.3]
†
–0.9 [–0.7; –1.2/–0.4]
†
–4.9 (10.9–6.0) [–4.9; –5.5/–4.3]
†
Molar
Height buccally 0.1 [0.3; –0.9/0.8] 0.1 [0.2; –0.2/0.5] 0.3 [0.1; –0.1;0.5] 0.5 [0.2; –0.6/0.9]
Height orally –0.7 [–0.7; –1.2/–0.4]
†
–0.1 [0.1; –0.4/0.4] 0.0 [–0.2; –0.4/0.2] –0.8 [–0.7; –1.5/–0.1]
†
Width –4.5 [–3.7; –6.2/–2.6]
†
–1.7 [–1.6; –2.8/–0.4]
†
–1.0 [–0.9; –1.5/–0.3]
†
–7.2 (13.0–5.8) [–7.6; –8.3/–6.3]
†
Maxilla
Height buccally –0.2 [–0.6; –1.0/0.4] 0.2 [0.4; 0.1/0.5]
†
0.5 [0.3; 0.0/0.6]
†
0.5 [0.1; –0.6/1.4]
Height orally –0.9 [–1.0; –1.2/–0.5]
†
0.0 [–0.1; –0.4/0.4] 0.2 [0.2; –0.2/0.5] –0.7 [–0.7; –1.3/–0.1]
†
Width –3.4 [–3.0; –4.6/–1.9]
†
–1.4 [–0.9; –1.4/–0.4]
†
–1.0 [–1.0; –1.2/–0.4]
†
–5.8 (12.7–6.9) [–6.2; –7.7/–4.4]
†
Mandible
Height buccally –0.1 [–0.1; –0.7/0.7] 0.1 [0.1; –0.3/0.5] 0.2 [0.1; 0.0/0.5]
†
0.2 [0.0; –0.7/0.4]
Height orally –0.8 [–0.7; –1.3/–0.4]
†
–0.1 [0.1; –0.4/0.2] 0.0 [–0.2; –0.3/0.2] –0.9 [–0.8; –1.6/–0.2]
†
Width –4.2 [–3.7; –5.1/–2.7]
†
–1.3 [–0.9; –2.3/–0.4]
†
–0.9 [–0.7; –1.4/–0.3]
†
–6.4 (11.5–5.1) [–5.8; –7.6/–5.0]
†
*Absolute width in parentheses; median and 25th/75th percentiles in brackets; positive values = tissue gain;negative values = tissue loss.
†
P < .05.
Table 2 Changes at tooth surfaces adjacent to extraction sites (mm)*
Baseline–3 mo 3–6 mo 6–12 mo Baseline–12 mo
Mesial Distal Mesial Distal Mesial Distal Mesial Distal
Pocket depth–1.1–1.0 –0.1 0.2 0.1 –0.1 –1.1 –0.9
Gingival recession 0.4 0.3 0.3 0.2 0.1 0.1 0.8 0.6
Attachment level 0.7 0.7 –0.2 –0.4 –0.2 0.0 0.3 0.3
*Mean values for the three sites measured at each tooth;positive values = tissue gain; negative values = tissue loss.
In addition, eight patients were
excluded from the statistical analysis
of the subtraction data because of
poor recording reproducibility. The
results of the subtraction analysis are
described for the remaining 35
patients.
The general observation of
bone changes in the extraction sites
was that bone formation took place
in the extraction alveoli simultane-
ously with a loss of height of the
alveolar crest (Figs 3c to 3e). Most of
this bone gain and loss occurred
within the first 3 months. In contrast,
remodeling of the lamina dura—
including the septum in cases of mul-
tirooted teeth—was more pro-
nounced in the period from 6 to 12
months after tooth extraction. In
approximately one third of the cases,
and I
6
– I
Base
was significantly differ-
ent (P < .005). For the unchanged
area, the mean gray value in images
I
3
– I
Base
and I
12
– I
Base
differed sig-
nificantly (P < .05).
Comparing the results of sub-
traction radiography and the linear
radiographic measurements, of the
34 patients who were analyzed by
subtraction radiography and fol-
lowed for 12 months, a reduction of
the crest was seen in 26. Crestal
bone loss was found in 25 of these
also when using linear measure-
ments. In five of the remaining eight
patients, agreement between the
two methods was found.
the area showing bone gain was
larger after 6 months than after 12
months of healing. The area of gain
was larger after 6 months than after
3 and 12 months (Table 3), and it
was larger than the area of loss after
3, 6, and 12 months. The size of the
latter area was approximately the
same at 3, 6, and 12 months. The
mean gray value of both the gain
and loss areas increased during the
12 months of healing; the bone
became more dense over this
period. Using a nonparametric test,
it was found that for areas of gain,
the mean gray value in images I
3
–
I
Base
and I
6
– I
Base
(P < .05), as well as
the mean gray value in images I
3
–
I
Base
and I
12
– I
Base
(P < .02), differed
significantly. Furthermore, the size
of the gain area in images I
3
– I
Base
319
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Table 3 Descriptives for mean gray values in areas of gain,loss, and no change as defined by
thresholds,and size of these areas in pixels
I
3
– I
Base
I
6
– I
Base
I
12
– I
Base
Region Mean gray value Area size Mean gray value Area size Mean gray value Area size
Area of gain
Median 151.4*
†
1,644
‡
158.0* 2,640
‡
161.8
†
1,602
25th/75th percentiles 138.2/165.3 492/3,188 146.4/169.1 1,374/3,958 151.5/174.5 689/3,916
Mean 147.4 2,053 154.5 2,812 159.3 2,224
Standard deviation 32.1 1,917 32.4 2,067 33.9 1,690
Area of loss
Median 101.2 845 107.4 911 114.6 704
25th/75th percentiles 96.4/121.0 148/2,299 97.8/123.7 155/1,610 103.4/128.0 193/1,662
Mean 104.5 1,508 104.0 1,127 109.3 1,537
Standard deviation 27.1 1,770 31.5 1,288 32.3 1,964
Area of no change
Median 131.1* 5,438 135.2 4,987 139.7* 4,639
25th/75th percentiles 122.9/147.2 4,830/7,022 127.5/148.6 3,663/6,692 126.7/151.9 4,069/7,002
Mean 133.2 6,027 136.7 5,649 140.5 5,778
Standard deviation 19.3 2,319 20.0 2,679 17.7 2,706
*P < .05;
†
P < .02;
‡
P < .005.
Discussion
This prospective clinical trial demon-
strated that major changes of an
extraction site take place during the
12 months following tooth extrac-
tion. The width of the alveolar ridge
was reduced by 50% during the
observation period. This loss, corre-
sponding to 5 to 7 mm, is in agree-
ment with earlier studies.
9,10,21
The
finding that approximately two thirds
of this reduction occurred within the
first 3 months after tooth extraction
also corresponds to earlier find-
ings.
10,12,21
When analyzing the ex-
traction sites separately according
to region and jaw, there was no ma-
jor diversity between the sites.
Only slight changes, less than 1
mm, in soft tissue height took place
in both jaws during the 12 months of
healing. A small increase buccally
and a reduction orally were found
within the first 3 months. This dis-
agrees with other studies,
10,12
which,
although demonstrating a greater
width than height reduction of the
alveolar process, reported a height
reduction of 2.0 to 4.5 mm. This dis-
agreement may be explained by the
fact that those studies involved mul-
tiple extractions. Furthermore, the
few patients (n = 3) examined in one
study
12
received an immediate
removable partial denture after ex-
traction of the teeth; in the present
study, 44 of 46 patients wore no
prosthesis in the healing period.
In addition to the analysis of
study casts, possible changes in
attachment levels at the teeth adja-
cent to the extraction site were
examined clinically. Gingival reces-
sion was less than probing pocket
depth reduction 12 months after
tooth extraction at the surfaces
mesial and distal to the extraction
site, showing that a 0.3-mm gain of
attachment level was achieved
during the 12 months of healing.
Despite the minor magnitude of
these changes, the results indicate
that periodontal health tends to
improve at teeth adjacent to an
extraction site during the healing
period.
In the present material, linear
measurements on radiographs
showed that the level of the bone
generated into the extraction socket
never reached the levels at the tooth
surfaces distal and mesial to the ex-
traction site. Furthermore, the bone
levels at the mesial and distal sites of
the extraction socket almost corre-
sponded to the level of the bone
generated into the socket 12 months
following tooth extraction. These
observations suggest that the bone
level at the extraction site, rather
than the bone level of the adjacent
teeth, dictates the level to which the
bone crest heals after extraction.
Between the mesial (M
x
) and distal
(D
x
) sites of the extraction socket,
the morphology of the alveolar crest
became curved, with the “lowest”
point situated 1.2 mm apical to M
x
and D
x
.
Despite the fact that the intra-
oral radiographs were standard-
ized, some degree of magnifica-
tion is inevitable, and therefore it
must be emphasized that the mea-
surements are approximated and
not “real size.” However, the com-
puter-assisted analysis method was
320
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associated with high reproducibil-
ity, since a high correlation was
found between the first and second
measurements.
This study introduced subtrac-
tion radiography as a new method
for assessing morphologic changes
and remodeling processes of extrac-
tion sites during the healing period.
The image analysis demonstrated
that a large amount of bone gener-
ation, bone loss as well as remodel-
ing, takes place within 12 months
after tooth extraction. Bone forma-
tion in the alveoli and loss of height
of the alveolar bone crest occurred
simultaneously during the first 3
months. Formation of bone contin-
ued during the next 3 months. From
6 to 12 months, some of this new
bone underwent remodeling. Fur-
thermore, the size of the loss was
almost unchanged from 3 to 12
months. When studying the sub-
traction images, loss of crestal bone
height mainly occurred within the
first 3-month period after tooth
extraction, while reorganization of
lamina dura took place during the
entire healing period.
The digital subtraction tech-
nique is associated with several
problems that should be considered
when interpreting the resulting
images. In this study, 11 patients
were excluded from the image
analysis because of limitations of the
technique. In three patients, it was
not possible to define a sufficient
number of reference points.
Subtraction radiographs of eight
patients were excluded from the sta-
tistical analysis because of poor
agreement between presubtraction
evaluation of the radiographs and
the resulting subtraction images. In
some cases, this disagreement may
have biologic explanations. In two of
these cases, the maxillary sinus was
superimposed on the extraction site,
and changes of this anatomic struc-
ture might have interfered with the
results. In other cases, the unex-
pected results of the subtraction
procedure may be explained by
problems with alignment of the radi-
ographs because of differences in
projection geometry.
For the subtraction procedure
in this study, changes in bone den-
sity were defined as a divergence
from the mean gray value of an area
expected to be unchanged. The
threshold value for this divergence
was set to the mean gray value of the
ROC ± 2 SD. This factor 2 is arbi-
trary, but was chosen after perform-
ing the subtraction procedure with
different factors in 10% of the mate-
rial. The “optimal” resulting image,
an image with maximum detection
of changes in the ROI and as small a
change as possible in the image out-
side the ROI, could best be achieved
by a factor of 2. Obviously, changes
shown as red or blue areas might be
a result of difference in physical noise
of the images within the same
patient rather than a biologic change
in bone density. However, the noise
in the images of the same patient dif-
fered only slightly. Another limita-
tion of subtraction radiography is
that the visualization depends on
the buccooral width of the defect.
For example, total bone fill with uni-
form density in a cone-shaped
defect like an extraction socket may
321
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be visualized only in the coronal part
because the alveolus makes up a
larger fraction of the total width of
the alveolar bone in the coronal
compared with the apical part.
Different methods have been
employed in the present study
to evaluate changes of the alveolar
bone following tooth extraction.
Strong agreement was found be-
tween the linear radiographic mea-
surements and subtraction analysis
when studying the bone changes of
the alveolar crest. Subtraction radi-
ography is a supplementary radi-
ographic method for evaluation of
crestal changes of the alveolar bone.
By means of linear radiographic
measurements, a bone loss of less
than 0.1 mm at the teeth adjacent to
the extraction site was found. This
does not contradict the finding that
the attachment level was almost
unchanged during the healing
period. Finally, the model analysis
revealing a loss of height of approx-
imately 1 mm corresponded very
well with the linear radiographic
measurements.
The reduction of alveolar bone
volume following tooth extraction
may interfere with placement of
implants and influence the treatment
success of fixed or removable den-
tures with regard to function and
esthetics. Therefore, it would be
advantageous to avoid this loss of
tissue. Procedures have been sug-
gested to facilitate bone formation
in extraction sockets and minimize
loss of bone height and buccolin-
gual width. Placement of grafting
materials in extraction alveoli has
been used with contradictory
results.
22–24
Guided tissue regener-
ation, with or without grafting mate-
rial, can be applied to preserve bone
volume.
11,25
Immediate implant
placement in fresh extraction sockets
has been shown to be a successful
alternative to the original treatment
protocol.
26–30
In addition to the
advantages of reduced treatment
time and costs, preservation of the
osseous structures could be pro-
vided by this concept.
31–34
However,
in some cases, it is preferable to
defer the time of implant placement,
eg, to minimize the risk of compli-
cations caused by infected recipient
sites. This study indicates that con-
cerning the optimal dimensions of
the alveolar bone, it would be favor-
able to place the implant as soon as
possible following tooth extraction.
Because preservation of alveolar
bone following tooth extraction has
a major impact on the functional and
esthetic outcome of subsequent
prosthetic treatment, further re-
search should be conducted on this
topic.
Acknowledgments
The authors wish to thank the staff at the
Department of Oral Radiology, and the
Department of Periodontology & Oral
Gerodontology, Royal Dental College,
University of Aarhus, Denmark, for their assis-
tance. In addition, we appreciate Torben
Jørgensen’s help with the program for digi-
tal subtraction radiography.
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