L. BIRK et al.: CONTEMPORARY TECHNOLOGIES FOR THE MEASUREMENT OF PULPAL BLOOD PERFUSION IN TEETH
437–441
CONTEMPORARY TECHNOLOGIES FOR THE MEASUREMENT
OF PULPAL BLOOD PERFUSION IN TEETH
SODOBNE TEHNOLOGIJE ZA MERJENJE PREKRVLJENOSTI
ZOBNE PULPE
Leja Birk
1*
, Lidija Nemeth
2,3
, Ksenija Cankar
4
, Luka Birk
5
1
Department of Orthodontics and Dentofacial orthopaedics, Faculty of Medicine, University of Ljubljana, Hrvatski trg 6,
1000 Ljubljana, Slovenia
2
Department of Dental Diseases and Normal Dental Morphology, Faculty of Medicine, University of Ljubljana, Hrvatski trg 6,
1000 Ljubljana, Slovenia
3
Division of Stomatology, University Medical Centre Ljubljana, Hrvatski trg 6, 1000 Ljubljana, Slovenia
4
Institute of Physiology, Faculty of Medicine, University of Ljubljana, Zalo{ka cesta 4, 1000 Ljubljana, Slovenia
5
Department of Prosthodontics, Faculty of Medicine, University of Ljubljana, Hrvatski trg 6, 1000 Ljubljana, Slovenia
Prejem rokopisa – received: 2022-06-28; sprejem za objavo – accepted for publication: 2022-07-18
doi:10.17222/mit.2022.536
Pulse oximetry (PO) and laser-Doppler fluxmetry (LDF) can be used for a determination of tooth vitality by measuring the
pulpal blood perfusion. They offer an alternative to conventional pulpal sensibility tests, which evaluate only the pulpal sensory
function. The aim of the study was to conduct vitality and sensibility tests on permanent caries-free and carious teeth with dif-
ferent degrees of caries progression and compare the results. In the clinical study, 230 permanent teeth from 25 adult subjects
were tested with two conventional pulpal sensibility tests (electric, cold) and two novel pulpal vitality tests (PO, LDF). Carious
lesions were detected and assessed using the criteria of the International Caries Detection and Assessment System (ICDAS). In
the further statistical analyses, pulpal oxygenation levels and LD flux values were compared between the carious and caries-free
teeth. The degree of agreement between the sensibility and vitality tests was also evaluated. Both methods proved reliable for a
determination of pulpal vitality with their consistent readings on the teeth. Carious teeth had significantly lower PO values than
non-carious teeth (p < 0.05). The degree of agreement between the tests of vitality and sensibility was fair to poor (!k < 0.40),
which confirmed the thesis that further clarification of their relations is needed. PO and LDF proved useful in the evaluation of
the pulpal tissue function by enabling the assessment of pulpal blood supply.
Keywords: pulse oximetry, laser-Doppler fluxmetry, dental technologies, dental biomaterials
Pulzna oksimetrija (PO) in lasersko doplersko merjenje pretoka krvi (LDF) omogo~ata merjenje prekrvljenosti zobne pulpe in
se lahko uporabljata za ovrednotenje vitalnosti zob. Predstavljata alternativo klasi~nim testom ob~utljivosti, ki vrednotijo zgolj
senzori~no funkcijo zobne pulpe. Namen raziskave je bil izvesti teste prekrvljenosti in ob~utljivosti pulpe na nekarioznih in
karioznih stalnih zobeh z razli~nimi stopnjami napredovalosti zobnega kariesa ter primerjati njihove rezultate. V klini~ni
raziskavi smo opravili preizkus ob~utljivosti pulpe z dvema klasi~nima testoma (z elektri~nim dra`ljajem, s hladnim dra`ljajem)
in preizkus vitalnosti z novej{ima testoma prekrvljenosti pulpe (PO, LDF) na 230 stalnih zobeh 25 odraslih preiskovancev. Za
zaznavo in ovrednotenje karioznih lezij smo uporabili kriterije Mednarodnega kazalnika za zaznavo in ovrednotenje karioznih
lezij (ICDAS). V nadaljnjih statisti~nih analizah smo primerjali izmerjene vrednosti pretoka krvi v pulpi in zasi~enosti pulpe s
kisikom med karioznimi in nekarioznimi zobmi. Ocenili smo tudi stopnjo ujemanja med testi ob~utljivosti in testi prekrvljenosti
zobne pulpe. Obe metodi sta imeli dosledne od~itke na zobeh in sta zanesljivi pri dolo~anju vitalnosti zob. Kariozni zobje so
imeli zna~ilno ni`je PO vrednosti kot nekariozni zobje (p < 0.05). Stopnja ujemanja med testi prekrvljenosti in testi ob~utljivosti
zobne pulpe je bila majhna ali slaba (!k < 0.40), kar potrjuje tezo, da je potrebna nadaljnja razjasnitev odnosa med vitalnostjo in
ob~utljivostjo zob. PO in LDF omogo~ata ovrednotenje prekrvljenosti zobne pulpe in s tem oceno funkcije pulpinega tkiva.
Klju~ne besede: pulzna oksimetrija, lasersko doplersko merjenje pretoka krvi, dentalne tehnologije, dentalni biomateriali
1 INTRODUCTION
Determining pulp vitality remains a slightly ambigu-
ous field of dentistry. To make the correct diagnosis,
anamnestic, clinical, and radiographic data should be in-
terpreted in conjunction with the results of pulpal diag-
nostic tests.
1
In current clinical practice, pulp vitality is
assessed indirectly by applying an external painful stim-
ulus to the surface of a tested tooth and recording the
presence or absence of a pulpal nociceptive response.
2
Conventional pulp sensibility tests have limited accuracy,
reproducibility, and reliability.
3
Therefore, laser-Doppler
fluxmetry (LDF) and pulse oximetry (PO) have been
adopted from the general field of medicine as alterna-
tives for the pulp vitality assessment.
4,5
Both methods al-
low an objective and non-invasive assessment of the
pulpal blood supply, which has been demonstrated as the
only true parameter of pulp vitality.
6
The light generated by a PO or LDF probe easily
passes through the translucent dental hard tissues and
reaches the pulp, where it is either absorbed or re-
flected.
4,7
The portion of the light that is reflected from
the moving red blood cells in the pulp tissue has a Dopp-
ler-shifted frequency, which is detected by the LDF
probe and the pulpal blood flux is calculated as a sum of
mean erythrocyte velocity and erythrocyte concentra-
Materiali in tehnologije / Materials and technology 56 (2022) 4, 437–441 437
UDK 616.314.18 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 56(4)437(2022)
*Corresponding author's e-mail:
leja.birk@gmail.com (Leja Birk)

tion.
8
Thus, LDF enables a real-time semi-quantitative
recording of the pulpal blood flux and its dynamic
changes.
5
On the other hand, PO uses the detected frac-
tion of light that remains unabsorbed when passing
through the pulp to measure the pulp-tissue haemoglobin
oxygen saturation (SpO
2
).
9
The reports on the application of these two methods
for the vitality assessment of carious teeth are sparse.
The aim of the present study was to measure the pulpal
blood perfusion of permanent teeth and compare the val-
ues between carious and caries-free teeth.
2 EXPERIMENTAL PART
The clinical cross-sectional study included 25 healthy
adult subjects (14 females, 11 males, mean age (40.88 ±
15.12) years). Each of them was presented with at least
one clinically evident carious lesion. At the first visit,
written informed consent was obtained, medical and den-
tal histories were taken, and a clinical examination was
performed. Carious lesions were detected and assessed
by one calibrated examiner using the criteria of the Inter-
national Caries Detection and Assessment System
(ICDAS).
10
Each tooth was ascribed an ICDAS score
(scores 0 to 6) according to the degree of caries progres-
sion: from caries-free teeth (score 0), which served as
negative controls, to the teeth with the most advanced le-
sions (score 6).
After the examination, the selected teeth were sub-
jected to SpO
2
measurement. The pulse oximeter
SpetrO2 (Smiths Medical, USA) was used with two dif-
ferent probe designs: the "Y" sensor and the "infant
wrap" sensor, which were small enough and adjustable to
allow placement on the teeth (Figure 1). After 45 s, the
SpO
2
value was recorded. A separate PO probe was
placed on the patient’s finger for simultaneous control of
systemic oxygenation alternations, which could affect
the pulpal PO readings.
4,9
After PO, the pulpal sensibility
of the included teeth was tested with two conventional
methods: with a cold stimulus – liquid CO
2
sprayed on a
cotton pellet and applied to the tooth (Pluradent Plurasol
Kältespray, Pluradent AG&Co KG, Germany) and weak
electric current (Gentle Pulse Analog Pulp Vitality
Tester, Parkell, USA) for a comparative analysis.
The pulpal LD flux of the included teeth was mea-
sured at the second visit with the Periflux P4001 Mas-
ter/4002 Satellite device (Perimed, Sweden) (Figure 2).
Before the visit, a custom-designed silicone probe holder
(Exaflex Putty, GC Europe) was fabricated for each pa-
tient on the working model. The holder allowed a stable,
reproducible, and accurate placement of the LDF probe.
The signal was recorded in five-second intervals and the
mean of at least eight consecutive recordings was used
for further statistical analyses. Afterwards, the patients
were treated according to the comprehensive caries-treat-
ment protocol.
A custom-designed metal forceps (Figure 1) were
used to hold the light-emitting diode and photodetector
of the PO sensor parallel to each other and in tight con-
tact with the tooth crown during the measurement. The
reflector of the dental chair was turned off and dry condi-
tions were maintained with cotton rolls to avoid signal
disruption.
The laser-Doppler probe (Figure 2) was retained in
place with a custom-made silicone holder, which was de-
signed individually for every patient on a plaster model
of his or her jaw. The holder prevented ambient light
passing and moist contamination of the probe tip and en-
sured a fixed position of the probe. The subject was re-
quested to lie still, refrain from body movement and
swallowing during the measurement.
The study was approved by the Republic of Slovenia
National Medical Ethics Committee (Nr.
0120-679/2017/7679/2017/7).
L. BIRK et al.: CONTEMPORARY TECHNOLOGIES FOR THE MEASUREMENT OF PULPAL BLOOD PERFUSION IN TEETH
438 Materiali in tehnologije / Materials and technology 56 (2022) 4, 437–441
Figure 2: Pulpal blood flux measurement in a carious upper incisor
with the laser-Doppler device
Figure 1: Measurement of pulpal oxygenation level in a carious upper
incisor with the pediatric "Y" sensor plugged into a conventional pulse
oximeter

3 RESULTS
Pulpal SpO
2
measurement was conducted on 230 per-
manent teeth, of which 60.0 % were carious (ICDAS
1–6) and 40.0 % were caries-free (ICDAS 0) (Table 1).
Signal was obtained in 84.3 % of the teeth (carious or
caries-free). The pulpal SpO
2
values of all carious teeth
combined were significantly lower than the values of car-
ies-free teeth ((78.95 ± 15.69) % vs. (82.93 ± 11.94) %,
p = 0.046, independent samples t-test).
Pulpal LD flux signal was obtained in 95.1 % of the
123 measured teeth (Table 2). No significant differences
in pulpal LD flux values were observed between carious
and caries-free teeth ((9.44 ± 4.05) PU vs. (8.99 ± 3.72) PU,
p = 0.56, independent samples t-test).
The results of the four pulpal diagnostic tests were
compared using the Cohen’s kappa analysis, which de-
termines the degree of agreement between two different
tests according to the calculated Cohen’s kappa quotient
(!
k
) as follows: < 0.20 poor, 0.21–0.40 fair, 0.41–0.60
moderate, 0.61–0.80 good, 0.81–1.00 very good. A result
of the vitality testing was considered positive when the
obtained SpO
2
value was greater than 20 % or when the
recorded pulpal LD flux value was equal or greater than
1 PU. The degrees of agreement for all the pairs were
fair or poor (Table 3). The highest !
k
value was present
within the pair electric test/cold test, whereas the lowest
degree of agreement was found within the pair PO/LDF.
The pulpal LD flux measurement confirmed the results
of conventional pulpal sensibility tests more frequently
than PO.
4 DISCUSSION
The consistent readings of both methods in the pres-
ent study prove that PO and LDF can be used for the vi-
tality assessment of carious teeth. In contrast to the re-
sults of sensibility testing, which are binary (i.e., the
presence or absence of a response) and provide very little
spare space for interpretation, PO and LDF enable a
quantitative evaluation of the pulpal blood supply. With
the method of LDF, the pulpal blood flux was recorded
in a semi-quantitative manner and even dynamic changes
of the blood flux could be observed (if the subject moved
or swallowed). The methods allowed the monitoring of
different pulpal oxygenation levels and LD flux values in
relation to the different histologic depths of carious de-
mineralization, which correlate with the ascribed ICDAS
codes.
11
L. BIRK et al.: CONTEMPORARY TECHNOLOGIES FOR THE MEASUREMENT OF PULPAL BLOOD PERFUSION IN TEETH
Materiali in tehnologije / Materials and technology 56 (2022) 4, 437–441 439
Table 1: Results of the pulpal oxygenation level measurement in carious and caries-free teeth
N
0
N
1
SpO
2
(%) 95 % CI SpO
2
range (%) p-value
Carious teeth (ICDAS 1–6) 138 113 78.95 ± 15.69 (76.06, 81.84) 20–99
0.046*
Caries-free teeth (ICDAS 0) 92 81 82.93 ± 11.94 (80.33, 85.53) 20–99
All teeth 230 194 80.61 ± 14.35 (78.59, 82.63) 20–99 /
Note: The absolute frequencies of positive PO readings (SpO
2
value of 20 % or more) are given in the N
1
column, whereas N
0
represents the ini-
tial sample size. The SpO
2
values are presented as means and standard deviations (independent samples t-test,  < 0.05, * – statistically signifi-
cant difference).
Table 2: Results of pulpal blood flux measurement in carious and caries-free teeth
N0 N1 LD flux (PU) 95 % CI LD flux range (PU) p-value
Carious teeth (ICDAS 1–6) 87 83 9.44 ± 4.05 (8.57, 10.31) 1.0–18.0
0.56
Caries-free teeth (ICDAS 0) 36 34 8.99 ± 3.72 (7.74, 10.24) 2.0–19.0
All teeth 123 117 9.31 ± 3.94 (8.59, 10.03) 1.0–19.0 /
Note: The absolute frequencies of positive LDF readings (LD flux value of 1 PU or more) are given in the N
1
column, whereas N
0
represents the
initial sample size. The LD flux values are expressed with relative units (PU – perfusion unit) and presented as means and standard deviations (in-
dependent samples t-test,  < 0.05).
Table 3: Comparison of results obtained with different pulpal diagnostic tests: electric test (ET), cold test (CT), laser-doppler fluxmetry (LDF),
and pulse oximetry (PO)
Comparative pair N
Agreement
(% of +/+ and -/-)
Disagreement
(% of +/- and -/+)
!k p-value
CT/LDF 123 87.8 12.2 0.232 0.004*
CT/PO 226 81.0 19.0 0.121 0.051
ET/LDF 118 89.8 10.2 0.354 0.000*
ET/PO 181 77.3 22.7 0.050 0.463
ET/CT 181 91.7 8.3 0.526 0.000*
PO/LDF 123 82.1 17.9 0.011 0.885
Note: The outcomes were compared within the listed pairs, which resulted either in agreement of both tests (e.g. a positive response yielded by
sensibility testing and positive pulpal vitality assessment) or in disagreement (contradictory results of the compared tests, e.g. when no pulpal
perfusion signal was recorded on a tooth deemed vital by pulpal sensibility testing). N – number of statistic units tested with both diagnostic tests,
!
k
– Cohen’s kappa quotient, Cohen’s kappa analysis,  < 0.05, * – statistically significant !
k
value.

In the present study, an innovative use of the biocom-
patible addition silicone (Exaflex Putty, GC America)
was proposed and successfully implemented. The high-
density vinyl polysiloxane (VPS) material enabled the
fabrication of rigid LD probe holders, which were cus-
tom-designed for each patient and improved measure-
ment quality by stabilizing the probe. The doughy con-
sistency of VPS and its relatively long setting time
provide easy handling and sufficient time for holder
shaping. The set material is still elastic and can be re-
moved from undercuts of the jaws. VPS is not translu-
cent and impedes the signal contamination with light, re-
flected from the soft tissues in the oral cavity and from
the nearby gingiva. At the same time, hydrophobicity of
the material and its tight adaptation to the crowns of
teeth prevented saliva and gingival crevicular fluid from
reaching the probe and affecting light detection. Thus,
we propose that apart from its conventional use for im-
pression making, VPS can also be used for the fabrica-
tion of probe holders in dental pulp vitality assessment.
Teeth with different degrees of caries progression
may have significantly different pulpal blood flux levels.
Higher pulpal blood flux may be recorded not only in
teeth with incipient caries, as a reflection of the early
immuno-inflammatory response of the pulp due to the
early carious demineralization, but also in teeth sub-
jected to acid etching or an invasive dental procedure
that involves a removal of enamel and dentin.
12,13
On the
contrary, significantly lower blood flux values may be
obtained on teeth with extensive carious cavities due to
the neurovascular and metabolic events of late stages of
pulpal inflammation.
13–16
In a PO measurement, signifi-
cantly lower pulpal oxygenation levels of teeth with car-
ies were observed compared to caries-free teeth, which
could be attributed to the deoxygenation of haemoglobin
due to lower pH values and hyperaemia of the pulp.
17
As
dentists strive for a method that could successfully dif-
ferentiate between reversible and irreversible pulpal in-
flammation, PO and LDF could represent a step forward
towards this goal.
18
However, the determination of refer-
ence pulpal oxygenation and blood flux values on intact
teeth would be necessary.
18,19
The degree of agreement between the results of the
vitality and sensibility testing was relatively low (fair to
poor), which proves the thesis that further elucidation of
the difference between pulpal sensitivity and true vitality
is necessary. The teeth deemed non-vital according to PO
measurement often responded to electric current or a
cold stimulus. Within both of the sensibility/PO pairs,
the p-values were greater than 0.05, which means that
additional coincidental matching of the results should be
considered. In contrast, LDF signal was usually obtained
in the teeth that did not respond to sensibility testing.
Thus, LDF could be interpreted as a method with higher
sensitivity and lower positive predictive value, whereas
PO could be considered as a method with lower negative
predictive value. However, a golden standard for the de-
termination of tooth vitality should be included in the
study to allow the calculation of sensitivity, specificity,
and clinical relevance of the compared tests.
At present, none of the commercially accessible
pulse oximeters and laser-Doppler devices is completely
suitable for dental use. The probes are originally de-
signed to fit an earlobe or a finger or to be adapted to the
surface of the skin. Poor conformity with the crown of
the tooth leads to an unstable placement and a less than
optimal transillumination of the tooth. Therefore, the in-
terpretation of the results should be cautious and false re-
sults should always be considered because of the signal
of the nearby gingiva and other soft oral tissues.
20
To fa-
cilitate the use of PO and LDF in dentistry, the develop-
ment of custom-designed dental probes would be crucial.
A therapist should always apply a combination of diag-
nostic tests to improve the reliability of clinical deci-
sions.
5 CONCLUSIONS
In current dental clinical practice, pulp vitality is as-
sessed indirectly with the use of conventional pulp-sensi-
bility tests. These only evaluate the nociceptive function
of the dental pulp and may consequently yield false-posi-
tive or false-negative results, which can also lead to erro-
neous treatment decisions. Therefore, the use of methods
for a direct evaluation of pulpal blood supply, which is
the only reliable parameter of tooth vitality, has been
adopted in dentistry, especially in the field of dental
trauma. The present study represents one of the rare re-
ports on the use of two pulp-vitality assessment methods,
pulse oximetry and laser-Doppler fluxmetry, for the vi-
tality evaluation of carious teeth, which are routinely
tested for sensibility prior to any restorative procedure.
The study demonstrates that pulse oximetry and la-
ser-Doppler fluxmetry have consistent readings on cari-
ous teeth and thus their use is suitable and beneficial also
in clinical scenarios of dental caries with obscure
pulp-sensibility test results. The study also performed all
four pulpal diagnostic tests on carious and caries-free
teeth and compared their results. The latter prove the the-
sis that pulpal sensibility cannot simply be regarded as
pulpal vitality, because the level of agreement between
the sensibility and vitality testing was low. We can con-
clude that a further elucidation of the relations between
pulpal sensibility and pulpal vitality is essential and sug-
gest clinicians opt for a combination of different pulpal
diagnostic tests when assessing the vitality of teeth prior
to their treatment, rather than just relying on the ambigu-
ous results of pulpal-sensibility tests.
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L. BIRK et al.: CONTEMPORARY TECHNOLOGIES FOR THE MEASUREMENT OF PULPAL BLOOD PERFUSION IN TEETH
Materiali in tehnologije / Materials and technology 56 (2022) 4, 437–441 441