, English, Pages 1349

Coll. Antropol. 33 (2009) 4: 1349–1352
Original scientific paper
Changes of Alveolar Bone Density Around the
Abutment Teeth in Patients Wearing Removable
Partial Dentures Depending on Kennedy
Classification
Daniela Kova~evi} Pavi~i}1, Zdravko Deli}1, Vlatka Lajnert1, Vesna Fugo{i}1, Sun~ana Simoni}
Kocijan1 and Dino Bukovi}2
1
2
Department of Prosthodontics, School of Dental Medicine, University of Rijeka, Rijeka, Croatia
Department of Prosthodontics, School of Dental Medicine, University of Zagreb, Zagreb, Croatia
ABSTRACT
The aim was to study the influence of Kennedy classification on alveolar bone density changes around the abutment
teeth of removable partial denture (RPD) clasp and rests. A total of 50 examinees of both gender wearing RPDs were included in the study. Changes of bone density around the abutment teeth were determined by an intraoral microdensitometry method. Standard retroalveolar radiographs were obtained twice: the first one at the RPD delivery and the second one after a period of 3 month of denture wearing. The copper stepwedge consisting of 5 steps (0.1–0.1 mm) was
attached to the radiograph prior to exposure in order to calibrate it. Seven regions of interest (ROI) in different position
close to the root of the abutment tooth were selected on each radiograph, all 10 pixels in size. Grey levels of each ROI were
measured and were converted into equivalents of the copper stepwedge thickness using the third degree polynomial in order to compare the difference of bone density between the two radiographs. The results indicated that Kennedy classification had no significant influence on the change of bone density in RPD patients during first 3 month of RPD wearing
(ANOVA: p>0.05).
Key words: alveolar bone, intraoral microdensitometry, retroalveolar radiography, removable partial denture, Kennedy classification
Introduction
The reduction of alveolar bone density is an individual process that depends on many sistemic (age, gender,
hormonal disturbancies, osteoporosis, etc.)1–8 and local
factors (oral hygiene, masticatory stress, well planned
construction of RPD, etc.)9,10. All the examined subjects
wearing a RPD have a greater possibility of alveolar bone
resorption due to a greater stress to the abutment teeth
and the denture bearing area. It is well known that
occlusal rests distribute masticatory forces on the abutment teeth and further through the periodontal apparatus to the alveolar bone11. During mouth opening, clasps
prevent RPD to dislodge from the denture bearing area
thus transmitting forces to tha abutment teeth in oblique directions. The forces that affect the abutment teeth
in RPDs are different than in eugnatic natural dentition.
It is to be expected that bone apposition would occur
in cases of higher forces directed axially to the tooth
rooth12. In that case apposition of cement and alveolar
bone, i.e. greater bone density and specific bone trabecules are to be expected13. On the contrary, other forces
(such as the action of the retentive clasp) lead to the
stress of periodontal ligament. Such forces may exceed
the individual tolerance level leading to the reduction of
alveolar bone density. Literature suggests that some nonphisiological components of any of the RPDs can not be
completely avoided14–16. It has also been proven that every overload of the abutment tooth and surrounding alveolar bone, as well as poor retention and stability of the
RPD lead to an increase in alveolar bone resorption10. In
different Kennedy classification of the edentulous areas
Received for publication May 20, 2009.
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D. Kova~evi} Pavi~i} et al.: Bone Density Depending on Kennedy Classification, Coll. Antropol. 33 (2009) 4: 1349–1352
the position of RPD clasp and RPD rests are planned in
different manner. We expected that Kennedy classes I
and II (distal extensions) would show bone density reduction due to a greater representation of unfavourable
forces than in Kennedy classes III and IV17. In Kennedy
classes III and IV normally two abutment teeth receive
masticatory force loads and therefore there is a lower
possibility of exceeding the adaption capacity of abutment teeth.
Changes in alveolar bone density can be easily determined by comparing series of radiographs. The difference of intesity of X-radiation, different voltage and current intesity during exposure, difference in developing
procedure and sensitivity of film have to be overcome18.
Therefore stepwedges of different materials and of different tickness have been used19–24. Bone mineral density
values are transformed into the equivalents of a stepwedge
thicknes by using different mathematical methods25,26.
The registered errors are minimal and occasional27.
The aim of the study was to measure changes of alveolar bone density around the abutment tooth of RPDs in
patents of different Kennedy classification.
Materials and Methods
Fifty subjects wearing RPD participated in the study
(32 women, 18 men). Age mean was 62.1 years (women
61.4, men 63.4). The Kennedy class I was diagnosed in
54% of cases and Kennedy class II in 24% of the analysed
sample. Kennedy class III was present in 18% of patients
wearing RPD and Kennedy class IV in only 4%. The patients wearing RPD were chosen randomly at the Dental
Department of the School of Medicine, University of
Rijeka. Ethical Comittee of the Faculty of Medicine approved the study and all patients signed their informed
consent. All the examined teeth were radiographed twice
by a standard retroalveolar radiography, the first time
prior to receiving their new RPD (radiographs had been
obtained for diagnostic purposes) and the second time after wearing RPDs for three months. All radiographs
were recorded under same conditions using the same
X-ray apparatus »Ei Ni{« (Ni{, Yugoslavia) with 1st exposure and voltage X-ray apparatus of 70 kV with constant
current strenght of 15 mA/s. »Kodak ultraspeed« films
(Eastman Rochester, N.Y.) were used. The films were developed in an automatic dark chamber »Durr Dental XR
24 nova« (Germany). A stepwedge (SW) consisting of five
steps 0.1–0.5 mm thick were attached onto each film
prior to exposure. The SW was placed carefully not to
cover the soft or the hard tissues. The developed radiographs were scanned using the »Umax Astra 3450«
(Umax Technologies, Inc, USA) scanner with 8-bit resolution and 300 dpi. Seven ROIs were selected around the
tooth root, each 10 pixels in size, and the levels of greyness were measured by software »Scion image« (Beta
4.0.2., USA). The positions of the ROIs were as follows:
ROI 1 – 1 mm mesially from the periodontal ligament
at the level of the alveolar crest
ROI 2 – 1 mm distally from the periodontal ligament
at the level of the alveolar crest
ROI 3 – 1 mm mesially from the periodontal ligament
at the level of the apex of the tooth root
ROI 4 – 1 mm distally from the periodontal ligament
at the level of the apex of the tooth root
ROI 5 – 1 mm apically from the periodontal ligament
at the level of the apex of the tooth root
ROI 6 – 1 mm mesially from the midway between the
distances of ROI 1 and ROI 3
ROI 7 – 1 mm distally from the midway between the
distances of ROI 2 and ROI 4.
Figure 1 explains ROIs position.
In case of multi-rooted tooth, only one root (mesial
root) was selected. The same ROIs were selected on the
both radiographs. The measured grey levels were transformed into equivalents of the copper SW using the polynomials of the 3. degree, according to Knezovi}-Zlatari}28. The difference between the two radiographs was
calculated using the SW equivalents in each of the Kennedy classification.
Statistical analysis
Data were analysed using the Statistical Package for
Social Sciences (SPSS Inc, 10.0.1., Chicago, IL). The level
of reliability was set at 0.05. One-way analysis of variance was chosen for comparasion of 4 different Kennedy
classification.
Results
Fig. 1. Position of ROIs.
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The level of reliability was checked by coefficient variability. The results were found to have normal distribution (SD/x<0.44).The results indicated no statistically
significant difference of alveolar bone density changes
for any of the selected ROIs during the three month period of RPD wearing between different Kennedy classification (Table 1, Figure 2) (p>0.05). No statistically significant difference of alveolar bone density was found in
different Kennedy Classes.
D. Kova~evi} Pavi~i} et al.: Bone Density Depending on Kennedy Classification, Coll. Antropol. 33 (2009) 4: 1349–1352
TABLE 1
CHANGES OF ALVEOLAR BONE DENSITY DEPENDING ON KENNEDY CLASSIFICATION
Difference
ROI
ROI A
Sum of squares
df
F
p
ROI 1-1A
0.1947
0.1852
0.104
49
1.531
0.219
ROI 2-2A
0.1554
0.1499
0.151
49
0.822
0.488
ROI 3-3A
0.1380
0.1293
0.171
49
0.843
0.477
ROI 4-4A
0.1915
0.1749
0.385
49
0.053
0.984
ROI 5-5A
0.1486
0.1443
0.363
49
0.919
0.439
ROI 6-6A
0.1771
0.1717
0.374
49
0.188
0.904
ROI 7-7A
0.1431
0.1420
0.385
49
0.205
0.892
ROI – region of interest
ROI A – region of interest on the second picture
0,10
0,09
CLASS I
CLASS II
CLASS III
CLASS IV
0,08
0,07
0,06
0,05
0,04
0,03
0,02
0,01
0,00
ROI 1DIFF
ROI 2DIFF
ROI 3DIFF
ROI 4DIFF
ROI 5DIFF
ROI 6DIFF
ROI 7 DIFF
Fig. 2. Changes of alveolar bone density (expressed in equivalents of Cu stepwedge) depending on Kennedy classification.
Discussion
The resorption of alveolar bone around the RPD abutment teeth is a complex process depending on many factors. Retroalveolar radiograph is one of the most simple,
low-cost and non-invasive methods to evaluate bone quality. Since the loss of alveolar bone can be visually noticed
only when it exceeds the 30% between the 2 different radiographs, it was decided to use calibrated stepwedge29,30.
The ROI grey level changes (converted into SW equivalents) are percetable when bone loss (reduction of bone
density) exceedes 10%31. In this study copper SW was
used due to copper’s atomic number in order to assure
thin layers (steps)32,33. Too thick calibrated steps is not
possible to apply due to a small size of retroalveolar radiographs. The method described by Knezovi}-Zlatari}
method28 was used, as it was proved to be the accurate
method. The literature data suggest that the posterior
extensions RPD saddles (Kennedy classes I or II) exert
greater loadings to booth, the alveolar ridge and the
abutment tooth compared to Kennedy classes III and IV.
The RPD also acts as a lever, wich may overload the abutment tooth. Therefore a decrease of bone density can be
expected in Kennedy classes I or II. The results of the
present study did not prove the hypothesis. There was no
statistically significant difference of alveolar bone density around the abutment tooth considering Kennedy
classification. This can be explained by an intermitent
activity of masticatory forces and a well planned construction of the RPD, i.e. enlargement of the prosthesis
base. The masticatory forces are transfered to the abutment tooth via occlusal rests only during the mastication, mostly in axial direction. Imaia and Sato34,35 studied
the influence of constant pressure on changes of alveolar
bone density on experimental rat model. The constant
pressure is not phisiological and can lead to circulation
disturbances, damaging of periodontal apparatus of the
tooth and to the bone resorption.
Our RPD design was well planned according to the accepted rules, moreover distal saddles have been extended
as much as possible. The masticatory forces are thus distributed on a wide surface and remain within the limits
of tissue tolerance, what was in accordance with findings
of Tallgren36. However, we found a positive trend in the
reduction of alveolar bone density in examined ROIs (between first and second radiographs) although there was
no statistical siginificance. It can be concluded that RPDs,
if well planned, do not cause any significant bone loss in
any class of Kennedy classification. Still, a slight reduction of density has been noticed during a three month period. The study included only patients with new RPDs
with excellent occlusion, articulation, retention and stability. Over time, the plunge of distally extended saddles
is much higher in Kennedy classes I and II than in
classes III and IV, so unfavourable loading of the abutment tooth increases with time37. Longitudinal measurements should be therefore considered to find possible
bone density changes.
Conclusion
During the inital period of RPD wearing (a three-month period) no alveolar bone density changes have
been observed depending on Kennedy classification.
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D. Kova~evi} Pavi~i} et al.: Bone Density Depending on Kennedy Classification, Coll. Antropol. 33 (2009) 4: 1349–1352
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D. Kova~evi} Pavi~i}
School of Dental Medicine, School of Medicine, University of Rijeka, Kre{imirova 40, 51 000 Rijeka, Croatia
e-mail: daniela.kovacevic@medri.hr
PROMJENE GUSTO]E ALVEOLARNE KOSTI OKO RETENCIJSKOG ZUBA KOD NOSITELJA
DJELOMI^NIH PROTEZA OVISNO O KLASIFIKACIJI PO KENNEDY-U
SA@ETAK
Svrha ove studije bila je utvrditi utjecaj klasifikacije po Kennedy-u (produ`ena ili umetnuta sedla) na promjeneu
gusto}e alveolarne kosti oko zuba nosa~a kva~ica i upira~a tijekom 3 mjeseca no{enja proteza. U istra`ivanju je sudjelovalo 50 ispitanika obaju spolova, nositelja djelomi~nih proteza (DP). Metodom intraoralne mikrodenzitometrije procijenila se promjena gusto}e kosti oko retencijskih zuba. Svi ispitivani zubi su dva puta snimani standardnim retroalveolarnim rendgenskim snimkama u razdoblju od 3 mjeseca. Na svaki rendgenski film nalijepljen je bakreni kalibracijski
klin debljine 0,1–0,5 mm. Na svakom rendgenogramu odabrano je 7 podru~ja interesa (eng. region of interest ROI) oko
korijena zuba veli~ine 10 pixela. Izmjereni su nivoi sivila u ROI i pretvoreni u ekvivalent debljine bakrenog klina te je
izra~unata razlika u gusto}i kosti izme|u dvije snimke. Rezultati su pokazali da klasifikacija po Kennedy-u ne dovodi
do statisti~ki zna~ajnih promjena gusto}e kosti kod protetskih pacijenata tijekom razdoblja od tri mjeseca (ANOVA:
p>0,05).
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