JJOD-2354; No. of Pages 6
journal of dentistry xxx (2014) xxx–xxx
Available online at www.sciencedirect.com
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journal homepage: www.intl.elsevierhealth.com/journals/jden
Tactile sensitivity of vital and endodontically
treated teeth
Birte-Juliane Schneider a,1, Sandra Freitag-Wolf b,2, Matthias Kern a,*
a
Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts
University at Kiel, Arnold-Heller-Str.16, 24105 Kiel, Germany
b
Institute of Medical Informatics and Statistics, Christian-Albrechts University at Kiel, Brunswiker Str.10, 24105 Kiel,
Germany
article info
abstract
Article history:
Objectives: Endodontically treated teeth (ETT) used as abutments for removable partial
Received 20 June 2014
dental prostheses (RPDPs) have an increased fracture risk as compared to vital abutments.
Received in revised form
One suggested explanation is that ETT exhibit a lower threshold level for tactile sensitivity
7 August 2014
than vital teeth. Therefore, this study compared the threshold for tactile sensitivity of vital
Accepted 26 August 2014
teeth and ETT in the same individuals.
Available online xxx
Methods: Forty participants with double crown-retained RPDPs fixed to vital teeth and ETT
Keywords:
contralateral endodontically treated abutment tooth in the same jaw. After removal of the
Tactile sensitivity
RPDP, an increasing centric force (0 cN to max. 2000 cN) was separately applied axially to
were included in the study. Each subject had at least one vital and one corresponding
Endodontically treated teeth
both free-standing abutment teeth using a force gauge while the patient was asked to give
Tooth vitality
three acoustic signals: (1) when noticing the first contact, (2) when noticing pressure and (3)
Removable partial dental prostheses
when the pressure became displeasing. Afterwards, the same trial was performed with an
Humans
eccentric force applied parallel to the tooth axis.
Gender
Results: Statistical analysis revealed no significant differences in the threshold of tactile
sensitivity of vital teeth and ETT to either centric or eccentric loading ( p > 0.05). Eccentric
loading showed lower mean threshold values compared to centric loading. A large variability of tactile sensitivity between individuals was noted. However, there were no genderrelated significant differences in tactile sensitivity ( p > 0.05).
Conclusions: The tactile sensitivity of vital and non-vital teeth seems comparable.
Clinical significance: The assumption that a lower threshold level for tactile sensitivity in ETT
than in vital teeth is responsible for their increased fracture risk could not be confirmed.
Therefore, other reasons, e.g. loss of hard tissue due to root canal treatment, have to be
considered responsible for the increased fracture risk of ETT.
# 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC
BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
* Corresponding author. Tel.: +49 431 597 2874.
E-mail addresses: bi-u@gmx.de (B.-J. Schneider), freitag@medinfo.uni-kiel.de (S. Freitag-Wolf), mkern@proth.uni-kiel.de (M. Kern).
1
Tel.: +49 17621982383.
2
Tel.: +49 4315973180.
http://dx.doi.org/10.1016/j.jdent.2014.08.016
0300-5712/# 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/3.0/).
Please cite this article in press as: Schneider B-J, et al. Tactile sensitivity of vital and endodontically treated teeth. Journal of Dentistry (2014),
http://dx.doi.org/10.1016/j.jdent.2014.08.016
JJOD-2354; No. of Pages 6
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1.
Introduction
A healthy periodontium has various neural receptors with
distinct functions.1 One function of the receptors in the
periodontal ligament is the discriminatory ability of tactile and
nociceptive sensitivity and the regulation of muscular activity.2 The existence of intradental pressoreceptors has been
documented and a higher threshold for pressoreceptive
sensibility of ETT has been reported.3
Subjects with a removable partial or complete dental
prosthesis have shown a reduced discriminatory ability
compared to natural teeth.4 In addition, there are receptors
outside of the periodontium, for example, in the mucosa, the
periosteum of the jaw bone, in the joints and muscle spindles,
which seem to be important for mechanoreception and
discriminatory ability.1,5
Active and passive assessments of thresholds of oral tactile
sensitivity have been described. The passive threshold is
determined by applying an increasing mechanical force to the
tooth. The first sensation that is provoked with the minimal
force is called the absolute threshold of perception.6 The
required loading for the first sensation on teeth is 1–10 cN.7
Endodontically treated teeth (ETT) used as abutment teeth
for removable partial dental prostheses (RPDPs) have an
increased fracture risk as compared to vital abutments.8 One
suggested explanation is that ETT exhibit a lower threshold
level for tactile sensitivity than vital teeth.9 Randow et al.9
reported in 1986 that non-vital teeth have a reduced
discriminatory tactile function with lower nociceptive responsiveness than vital teeth. However, they investigated only
three subjects with one vital tooth and one ETT using
cantilever loading. Results showed that the mean pain
threshold level of non-vital teeth was twice as high
compared to the level of vital teeth. However, this small
clinical study seems to present a rather weak clinical evidence
as only three subjects have been evaluated, resulting in an
inadequate power of the study to draw reliable conclusions.
Nevertheless, this unique experiment has been widely cited
in the dental literature although these results have never
been confirmed.
Various other reasons for the increased fracture risk of
ETT have been discussed in the literature.10–17 One obvious
factor is the higher loss of tooth substance due to carious
destruction and endodontic access cavity preparation in ETT.
Additionally, the stress caused by endodontic procedures such
as instrumentation, irrigation and obturation as well as the
insertion of posts might introduce micro-cracks in non-vital
teeth.10–17 ETT with or without post-placement had a lower
fracture resistance than vital teeth serving as RPDP abutments.8,10,16,18,19 On average, 71% of fractured teeth were
endodontically treated.20,21 Often approximately 10 years after
endodontic treatment vertical root fractures occured.11,22
In order to reveal whether a difference in tactile sensitivity
of vital teeth and ETT might play a role in the increased
fracture risk of ETT when serving as RPDP abutments, this
study evaluated the passive threshold level for tactile
sensitivity of vital teeth and ETT using centric and eccentric
loading. The null hypothesis was that the tactile sensitivity of
ETT does not differ from that of vital teeth.
2.
Materials and methods
The study protocol has been approved by the Ethics Committee of the Christian-Albrechts University at Kiel, Germany.
Forty participants (24 males, 16 females) were recruited from
the Department of Prosthodontics, Propaedeutics and Dental
Materials, Christian-Albrechts University at Kiel. All recruited
participants gave their informed consent to participate in the
study and defined insurance policy was contracted for all
participants to cover possible risks for the loaded abutment
teeth, such as tooth fracture.
Each subject had at least one vital and one endodontically
treated abutment tooth supporting a double crown-retained
RPDP. Matched abutment teeth in the same jaw were
compared, i.e. incisor to incisor, canine to canine, premolar
to premolar and molar to molar.
Inclusion criteria for selected test teeth were a healthy
periodontium with a probing depth of maximum 3 mm, no
bleeding on probing, a mobility of 0–1,23 normal response of
vital teeth when tested with CO2 snow, stable bone level with a
maximum of one-third bone loss and a root canal filling of
sufficient quality. The quality of a root canal treatment was
deemed sufficient if there were no clinical symptoms such as
pain on bite or percussion and there was no evidence of
pathologic changes in the periodontal ligament. Also the root
canal filling had to be of appropriate density and extension
within 1 mm of the radiographic root length.
After removal of the double-crown retained RPDP for
reproductive eccentric loading an extension bar (CoCrMo,
10 9 2 mm) was individually adapted to each abutment
tooth in a right angle to its labial surface by underlining its
annular opening with autopolymerizing composite (Luxatemp, DMG Chemisch-Pharmazeutische Fabrik GmbH, Hamburg, Germany) while it was positioned over the abutment
(Fig. 1). A rounded notch for the application of the centric
loading was created manually in composite resin in the
vertical axis of the tooth, for eccentric loading a standardized
groove was present in the metal extension. So the threshold of
tactile sensitivity could be examined on the freestanding
abutment teeth without proximal contacts to adjacent teeth.
The threshold of tactile sensitivity was passively assessed
using two force gauges (Correx Force Gauge 25–250 and
200–2000 cN, Correx, Hahn + Kolb Werkzeuge GmbH, Stuttgart, Germany). Pressing slowly down the feeler arm of the
gauge with its rounded tip, a continuously increasing axial
force up to 2000 cN was applied first centrically and then
eccentrically parallel to the tooth axis. The reproducibility of
manual force application was evaluated using a modified
typodont in a universal testing machine (Zwick Z010; Zwick
GmbH, Ulm, Germany). The measured force application
varied between 2.4 and 4.3% for the 250 cN force gauge and
between 2.2 and 2.7% for the 2000 cN force gauge when
measurements were repeated 10 times.
The order of loading the teeth was randomized. Throughout the study, loading was applied blinded by the same
individual, who thus did not know whether the loaded tooth
was vital or endodontically treated. Every testing was
videotaped for a precise subsequent analysis. While the
loading force was increased continuously, the patient had
Please cite this article in press as: Schneider B-J, et al. Tactile sensitivity of vital and endodontically treated teeth. Journal of Dentistry (2014),
http://dx.doi.org/10.1016/j.jdent.2014.08.016
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journal of dentistry xxx (2014) xxx–xxx
Fig. 1 – Experimental design. (A) Vital and non-vital canines with inner copings. (B) Individualized extension. Arrows are
pointing to the metal groove and the composite resin notch as loading points for the tip of the feeler arm of the force gauge.
(C) Metal extension. (D) Correx force gauge. (E) Applying centric loading axially with the rounded tip of the force gauge’s
feeler arm. (F) Applying eccentric loading parallel to the tooth axis.
been instructed to give acoustic signals with a beeper for both
teeth for the following events:
(1) when noticing first contact—absolute threshold of perception,
(2) when noticing pressure, and
(3) when the pressure became displeasing.
Since data were not normally distributed, statistical
analysis was performed by the Wilcoxon’s signed rank and
rank sum tests using SPSS, Version 17.0 with a level of
significance of a = 5%. Unexpectedly, a large number of ties
occurred, which reduces the value of the applied nonparametric statistical tests. For a sensitivity analysis of our results,
we also analyzed the data with a log-rank test assuming that
observations were independent and values above 2000 cN
were regarded as censored. The power calculation of the study
using BiAS for Windows, Version 8.03, revealed that with our
sample size of 40 participants, a log-rank test with a
significance level of 5% would be able to detect a difference
of 30% in the tactile sensitivity between the groups with a
power of more than 90%.
3.
Results
The study group consisted of 24 male and 16 female
participants with an average age of 68.2 years (min. 47.4—
max. 88.3 years). The dental prostheses had been in function
for an average time of 5.0 years (min. 0.5–max. 17.2 years).
Twenty-one participants had maxillary teeth and 19 participants had mandibular teeth tested, respectively. The groupings for the subjects and teeth tested are anterior; 24
participants with 48 teeth (14 incisors and 34 canines), and
posterior; 16 participants with 32 teeth (28 premolars and 4
molars). No abutment tooth fractured during testing.
The median values for the threshold of tactile sensitivity at
centric and eccentric loading for vital teeth and ETT at three
response levels did not differ significantly ( p > 0.05) and are
presented in Table 1 and Fig. 2. Eccentric loading provoked a
displeasing feeling earlier than centric loading.
The response of vital teeth and ETT to loading varied
greatly between individuals. A high subjectivity in detecting
pressure or pain was apparent. No general reaction pattern of
vital teeth and ETT to loading could be detected. Participant
gender did not influence the tactile sensitivity of the loaded
teeth, but women presented somewhat lower medians at all
three response levels. The second statistical approach with
the log rank test yielded similar results with no significant
differences between groups ( p > 0.05).
4.
Discussion
To the best knowledge of the authors, this is the first clinical
study comparing the tactile sensitivity of a larger number of
Table 1 – Median loading forces in cN for the three
particular time points (1) when noticing the first contact,
(2) when noticing pressure and (3) when the pressure
became displeasing did not differ significantly between
vital and non-vital teeth ( p > 0.05).
Centric loading
Eccentric loading
Vital
Non-vital
Vital
Non-vital
1
2
3
140
180
150
125
450
500
400
450
1800
1500
1150
1100
Please cite this article in press as: Schneider B-J, et al. Tactile sensitivity of vital and endodontically treated teeth. Journal of Dentistry (2014),
http://dx.doi.org/10.1016/j.jdent.2014.08.016
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2000
Values in [cN]
1500
1000
500
0
vital
non vital
1
vital
non vital
2
vital
non vital
3
Centric loading
vital
non vital
1
vital
non vital
2
vital
non vital
3
Eccentric loading
Fig. 2 – Loading forces in cN for the three particular time points. (1) When noticing the first contact, (2) when noticing
pressure and (3) when the pressure became displeasing. No statistically significant differences between vital and non-vital
teeth were found ( p > 0.05). The boxplot depicts the distribution of recorded loading forces. The horizontal lines that
intersect the colored boxes present the medians, the top of each box is the 75th percentile (Q3); the bottom is the 25th
percentile (Q1) and horizontal lines above and below the boxes, called whiskers, represent maximum and minimum
loading values. Values over 2000 cN were not evaluated for ethical reasons.
vital teeth and ETT serving as RPDP abutments. Proximal
contacts with adjacent teeth were eliminated by the use of
participants with double crown RPDPs. After removal of the
RPDPs, the inner copings of the abutments could be loaded
individually without any interference. Only one measurement
per tooth in centric and eccentric position was performed to
avoid the possibility of receptor adaption and a possible
training effect of participants. In order to eliminate variations
in sensitivity between individuals, only similar vital teeth and
ETT of the same subject in the same jaw were compared. With
the sample size of 40 participants, a difference of 30% in the
tactile sensitivity of groups could be detected with a power of
more than 90%, which was considered appropriate.
Neither load application (centric versus eccentric) nor
gender of the participants influenced the tactile sensitivity of
the tested teeth and no difference in tactile sensitivity
between vital teeth and ETT could be detected. Therefore,
the null hypothesis that the tactile sensitivity of ETT does not
differ from vital teeth has to be approved.
These results are in contrast to an earlier study9 in which a
two-fold difference in the nociceptive responsiveness of ETT
compared to vital teeth was reported. However, because of the
rather low number of participants (n = 3) in that older study, an
inadequate statistical power has to be assumed. Loewenstein
and Rathkamp reported a 57% higher threshold for tactile
perception for ETT than for vital teeth evaluating 10
individuals, but they did not evaluate when pressure was
noticed or pressure became displeasing.3 In the present study,
the thresholds of tactile sensitivity of vital teeth and ETT were
compared in 40 participants. A 22.3% higher threshold was
found with ETT for the first sensation, which supports the
findings of Loewenstein and Rathkamp. However, a 10%
higher value for noticing pressure and a 20% lower value for
displeasing pressure was calculated for ETT in the current
study but these differences with no statistical significance for
any level of perception.
In general, a loading of 1–10 cN is considered adequate to
provoke the first sensation of teeth in a complete dentition
with proximal contacts to the adjacent teeth.3,7 In the current
study when testing freestanding abutment teeth of RPDPs, we
found much higher values for noticing the first contact with a
median value of 140 cN for vital and 180 cN for non-vital teeth.
A possible explanation for these differences might be a
reduced discriminatory ability in elderly patients with
removable dental prostheses.4 It can be assumed that the
higher loading forces on abutments of RPDPs will result in a
neurologic adaptation to these day-to-day loading conditions
during chewing with the RPDPs.
In general, the threshold values for vital teeth and ETT will
be greatly influenced by the level of discriminatory ability in
each individual. This was reflected in the substantial
individual variety for noticing; the first contact (ranging from
25 to 250 cN), pressure (100–2000 cN) and displeasing pressure
(250–2000 cN). Similar variations between individuals were
reported in previous studies.3,7 Forces higher than 2000 cN
were not applied to the abutment teeth for ethical reasons as
higher forces may damage the loaded teeth. Fortunately, no
abutment tooth fractured during the measurements, which
might be related to the low loading forces that were applied as
compared to possible masticatory forces.24–26 The latter
might involve maximum forces of 300–500 N with a great
individual variation.
Please cite this article in press as: Schneider B-J, et al. Tactile sensitivity of vital and endodontically treated teeth. Journal of Dentistry (2014),
http://dx.doi.org/10.1016/j.jdent.2014.08.016
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Besides the amount of force, the loading direction seems to
be important.7,27 Forces directed on the surface of the restoration are transmitted to the supporting tooth structure. Fractures
will occur at the weakest point or at the point of maximum
stress.28,29 Non-axial forces increase the risk for fatigue
fractures. Horizontal loading, in particular, generates much
higher levels of stress than vertical loading. Horizontal loading
should be avoided30,31 as it creates the greatest level of stress in
the cervical region and at the post-dentin interface. The present
study found lower threshold values for all sensations with
eccentric loading but without a statistically significance.
In regard to gender, no significant differences in tactile
sensitivity was detected, even though the females presented
lower median values. It might be assumed that these results
correlate to lower average masticatory forces of females.32 This
is supported by the literature where the mean threshold values
regarding teeth were not significantly different between women
and men. However, comparing teeth to implants, women had a
significant finer discriminatory ability than men.33
There is a broad consensus in the literature that ETT are
more susceptible to fracture than vital teeth.8,10,16,18,19 However,
our current results provide no evidence that the higher
fracture risk of ETT would be caused by a reduced discriminatory
ability in the periodontal ligament of ETT. Instead, we suggest
that loss of tooth substance due to carious destruction and
endodontic access cavity preparation is the major reason for the
increased risk of fracture of ETT.8,10,16,18,19 Furthermore, insertion of posts, instrumentation, irrigation and obturation during
endodontic treatment introduce stresses to the tooth.10–17
5.
Conclusions
The mean threshold values of freestanding vital teeth and
non-vital teeth were not statistically significant. Thus, the
tactile sensitivity seems comparable and the assumption that
a lower threshold level for tactile sensitivity in non-vital teeth
than in vital teeth is responsible for their increased fracture
risk could not be confirmed. Therefore other reasons, e.g. a
higher amount of substance loss, have to be considered to be
responsible for the increased fracture risk of non-vital teeth.
Acknowledgments
The study was conducted and funded by departmental
funding. The authors especially thank the dental assistant
for her help during the study and Sönke Harder, Munich, for
his input in the initial study design. In addition, the authors
thank Ove A Peters, San Francisco University of the Pacific, and
Van P Thompson, King’s College London Dental Institute for
their help in revising the original manuscript.
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Please cite this article in press as: Schneider B-J, et al. Tactile sensitivity of vital and endodontically treated teeth. Journal of Dentistry (2014),
http://dx.doi.org/10.1016/j.jdent.2014.08.016