Caries-removal effectiveness and minimal-invasivenesspotential of caries-excavation techniques: A micro-CTinvestigation

Aline de A. Neves, Eduardo Coutinho, Jan De Munck, Bart Van Meerbeek *

Leuven BIOMAT Research Cluster, Department of Conservative Dentistry, School of Dentistry, Oral Pathology and Maxillo-Facial Surgery,

Catholic University of Leuven, Kapucijnenvoer 7, B-3000 Leuven, Belgium

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2

a r t i c l e i n f o

Article history:

Received 12 July 2010

Received in revised form

16 November 2010

Accepted 17 November 2010

Keywords:

Caries-excavation

Caries-removal techniques

Minimal-invasive dentistry

Micro-CT

Er:YAG laser

Carisolv

Caries Detector

CeraBur

Cariex

Tungsten-carbide bur

a b s t r a c t

Objectives: To determine the caries-removal effectiveness (CRE) and minimal-invasiveness

potential (MIP) of contemporary caries-removal techniques.

Methods: Carious molars were scanned using micro-CT, after which dentine caries was

removed by 9 contemporary caries-removal techniques. The micro-CT was repeated and

CRE was determined on basis of the relative volume of residual caries and the mineral

density (MD) at the cavity floor. MIP was determined by measuring the cavity size relative to

the initial size of the caries lesion.

Results: CRE and MIP varied most for the Er:YAG laser (Kavo) despite its laser-induced

fluorescence (LIF) feedback system. Whilst some specimens revealed much residual caries,

others showed over-excavation into sound dentine. With the highest Relative Cavity Size, the

Er:YAG laser presented the lowest MIP. Rotary/oscillating instruments revealed a more favour-

able CRE with some tendency towards over-excavation, except for CeraBur (Komet-Brasseler)

and Cariex (Kavo) that typically left caries at the cavity floor and cavity walls, respectively.

Chemo-mechanical excavation aided by conventional metal excavators (Carisolv, MediTeam;

exp. SFC-V and SFC-VIII, 3M-ESPE) combined best CRE with MIP. When however a plastic

excavator was used along with exp. SFC-VIII, caries was less completely removed.

Significance: Er:YAG-laser aided by LIF resulted in non-selective caries removal. Rotary/

oscillating caries removal may lead to over-excavation, especially when burs are combined

with Caries Detector (Kuraray). This risk for over-excavation is reduced when a tungsten-

carbide bur is solely used. On the contrary, Cariex (Kavo) and CeraBur showed a tendency for

under-preparation. Chemo-mechanical methods were most selective in removing caries,

whilst preserving sound tissue.

# 2010 Elsevier Ltd. All rights reserved.

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1. Introduction

The widespread concept of ‘‘minimal-invasive dentistry’’

implies that heavily infected and irreversibly denatured

dentine should be removed selectively in order to preserve

as much as possible sound or potentially remineralisable tooth

* Corresponding author. Tel.: +32 16 337587; fax: +32 16 332752.E-mail address: bart.vanmeerbeek@med.kuleuven.be (B. Van Meer

0300-5712/$ – see front matter # 2010 Elsevier Ltd. All rights reservedoi:10.1016/j.jdent.2010.11.006

tissue.1 As soft and wet carious dentine lesions harbour

significantly more bacteria than hard and/or dry lesions,2

clinicians are commonly advised to remove carious dentine to

the level where it is ‘firm’.3 Doing so, they may possibly leave

at the cavity floor demineralised dentine that is judged to still

possess some remineralisation/healing potential.4

beek).

d.

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2 155

Nevertheless, the exact endpoint of caries removal can

clinically not easily be defined. This may be explained by the

fact that dentists have mainly been trained in relying on the

hardness of dentine as felt with a dental probe, whilst other

more subjective characteristics, such as the colour and

moisture of the excavated dentine, are often neglected.

A first attempt to more objectively define the caries-removal

endpoint involvedthe use ofa staining agent consisting ofan1%

acid-red solution in a propylene glycol base (Caries Detector,

Kuraray, Osaka, Japan).5 It was first recommended to remove all

the red-stained dentine because the staining solution was

considered to stain the irreversibly denaturated and thus not

remineralisable collagen.6 After more recent research showed

that removal of all red-stained dentine led invariably to over-

excavation,7 one nowadays instruct to retain the ‘pink’ or ‘light-

pink’ stained tissue, because this usually contains only slightly

demineralised dentine that potentially can remineralise.8

Unfortunately, objective interpretation of what is tissue stained

‘red’, ‘pink’ or even ‘light pink’ is still a major issue of dispute.

Moreover, the tendency of Caries Detector to over-stain sound

tissue cannot be ignored.9

In light of minimal-invasive tooth preparation and with the

intention to simplify and standardise caries-removal proce-

dures, so-called ‘self-limiting’ caries-excavation techniques

have more recently been introduced. For instance, new rotary

cutting instruments include round burs made of an alumina-

based ceramic material intended for slow-speed caries

excavation (CeraBur K1SM, Komet-Brasseler, Lemgo,

Germany),10 or oscillating sono-abrasion tungsten-carbide

tips (Cariex system, Kavo, Biberach, Germany).11 Other self-

limiting alternatives include dentine solubilising agents used

to selectively dissolve carious dentine, such as the sodium-

hypochlorite-based Carisolv (MediTeam, Goteborg, Sweden)12

or the new experimental enzyme-based caries-removal gels

(exp. SFC-V and VIII, 3M-ESPE, Seefeld, Germany).13 The latter

consist of pepsin in a phosphoric acid/sodium biphosphate

buffer that is claimed to more selectively remove carious

tissue.14 According to the manufacturer, phosphoric acid

dissolves the inorganic component of carious dentine, allow-

ing pepsin to access the organic part of the caries biomass,

thereby selectively dissolving the denatured dentine collagen

that lost the triple-helix structure. The chemically softened

tissue can then be removed mechanically using either a metal

or plastic hand instrument.

An Er:YAG laser equipped with a laser-induced fluores-

cence (LIF) feedback system (Key III, Kavo, Biberach, Germany)

also claims to possess self-limiting caries-removal potential.

The fluorescence emitted by the bacterial metabolites present

in the carious tissue is continuously measured during the

caries-removal process, and if a pre-selected threshold is

exceeded, the laser device is activated and the carious tissue

ablated.15 The clinical use of a LIF threshold level of 7 has been

shown to result in an endpoint of cavity preparation where the

bacterial viability within the remaining tissue was very low,15

or where histologically bacteria at the cavity floor could no

longer be detected.16 Moreover, this technique was demon-

strated to be more minimally invasive (smaller cavity size)

than a conventional tungsten-carbide bur.17

Micro-CT is a non-destructive research technique that

allows hard tissues to be measured volumetrically and

evaluated on their mineral density.18 This technique is

increasingly becoming popular in dental research, as it

enables to collect detailed full-quantitative data of the

substrate before and after a specific substrate treat-

ment.13,19–22 Its application to study caries-excavation tech-

niques has recently been demonstrated.20 Following that

approach, the aim of this study is to determine, using micro-

CT, the caries-removal effectiveness (CRE) and minimal-

invasiveness potential (MIP) of 9 contemporary caries-exca-

vation techniques.

2. Materials and methods

2.1. Selection of teeth and micro-CT scanning procedures

From a bulk of extracted molars, stored in aqueous chloramine

for less than 6 months, those presenting occlusal carious

lesions were selected. After ultrasonic cleaning of plaque,

calculus and other debris, a radiograph was taken (MiniRay,

Soredex, Tuusula, Finland) with the aid of a CCD-detector

(Vista Ray CCD Systems, Durr Dental, Bietigheim-Bissingen,

Germany), so that teeth without dentine-caries involvement

and those, of which the carious lesion was less than 1 mm

remote from the pulp chamber, were excluded. The teeth were

mounted by the roots in gypsum for ease of manipulation

(n = 63).

A first micro-CT scan of the occlusal part of each tooth was

performed using a Skyscan 1172 desktop micro-CT (Skyscan,

Kontich, Belgium) and the resulting 3D volume was assigned

to the ‘Baseline’ stack (Fig. 1a1). The acquisition settings

employed were 100 mA, 100 kV, 14.6 mm pixel size and a

rotation step of 0.78. A flat-field reference was taken before the

first scan and the random-movement amplitude was set to 30

lines to reduce ring artefacts. To improve signal-to-noise ratio,

32-frame averaging was applied during the acquisition phase.

These settings were standardised following a methodological

study done before,20 during which a polychromatic source

micro-CT technique was validated to study dentine caries-

excavation methods. During the scanning procedure, desic-

cation of the tooth was prevented by wrapping the specimen

in Parafilm (Pechiney Plastic Packaging, Menasha, WI, USA),

together with a cotton pellet soaked in chloramine enclosed.

After caries excavation, each tooth was scanned again

using micro-CT following the same acquisition settings

described above. The resulting 3D volume obtained from the

cross-section images was assigned to the ‘Excavated Caries’

stack (Fig. 1b1). The micro-CT projections obtained for both the

‘Baseline’ and ‘Excavated Caries’ stacks were reconstructed

(NRecon, Skyscan, Kontich, Belgium) based on a modified

Feldkamp algorithm. Specific reconstruction settings included

a 5th order polynomial beam-hardening correction and input

of optimal contrast limits, as described previously.20

2.2. Caries-excavation procedures

The teeth were then randomly assigned to 9 different

contemporary caries-excavation techniques, including 6

commercially available and 3 experimental methodologies.

All caries-removal techniques were employed by one experi-

[()TD$FIG]

Fig. 1 – 3D-volume renderings obtained from micro-CT cross-section slices of a tooth before and after caries excavation,

based on a previously defined cut-off point for dentine caries.23 (a1) 3D volume of a tooth before caries removal (‘Baseline’).

(b1) 3D volume of the same tooth after caries removal (‘Excavated Caries’). (c1) Result of the subtraction of the ‘Excavated

Caries’ (b1) from ‘Baseline’ (a1). (a2) 3D volume of initial caries (IC) after application of the cut-off point (1.11 g/cm3 HAp) at

‘Baseline’. (b2) 3D volume of residual caries (RC) after application of the cut-off point (1.11 g/cm3 HAp) at ‘Excavated Caries’.

(c2) Resulting 3D-volume of the prepared cavity (PC) after subtracting ‘Excavated Caries’ (b1) from ‘Baseline’ (a1).

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2156

enced operator (AAN). If a certain degree of subjectivity was

expected during assessment of the caries-removal endpoint,

some guidelines were used. The relative hardness of the cavity

floor, felt upon gentle pressure with a blunt explorer, was

considered as the caries-removal endpoint for tungsten-

carbide bur excavation and the Cariex system, whilst a visible

residual pink staining was considered the endpoint of caries

removal after application of the Caries Detector solution

followed by thorough rinsing with water.

Regarding the cavity preparation, first, all enamel overhangs

from each carious lesion were minimal invasively removed

with a cylinder diamond bur (Komet-Brasseler, Lemgo,

Germany) in a high-speed air turbine under water cooling until

the underlying dentine lesion was exposed. Five teeth were

excluded due to a too small dentinal caries lesion and five other

teeth because of pulp exposure after caries-excavation. The

caries-removal techniques employed are described below:

(a) Tungsten-carbide round bur (Komet-Brasseler, Lemgo,

Germany): Different bur sizes (n.10–23) were used, depend-

ing on the size of the carious lesion, along with a low-speed

contra-angle with an approximate speed of 1500 rpm,

without water-cooling. The caries-removal endpoint was

reached when a ‘hard’ cavity floor was felt upon gentle

pressure with a blunt dental explorer (n = 7).

(b) Tungsten-carbide round bur aided by Caries Detector

(Kuraray, Osaka, Japan): Dentine stained with Caries

Detector was removed with a tungsten-carbide bur, as

described above. The caries-removal endpoint was reached

when the residual dentine stained ‘light-pink’ (n = 6).

(c) CeraBur (K1SM, Komet-Brasseler, Lemgo, Germany): Dif-

ferent bur sizes (n.10–23) were used, depending on the size

of the carious lesion, along with a low-speed contra-angle

with an approximate speed of 1500 rpm, without water-

cooling. The caries-removal endpoint was established by

the self-cutting ability of the instrument (n = 6).

(d) Cariex (Kavo, Biberach, Germany): An airscaler (Sonicflex

2003L, Kavo) to which tungsten-carbide oscillating tips (TC

tips n.71 and n.72) were coupled, was employed with an

oscillation of >6.5 kHz under water cooling. The caries-

removal endpoint was reached when a ‘hard’ cavity floor

was felt upon gentle pressure with a blunt dental explorer

(n = 6).

(e) Carisolv (MediTeam, Goteborg, Sweden): After dispensing

the gel with the auto-mix syringe system, a drop of the

solution was placed in the cavity. After 30 s, the mace-tips

Carisolv instruments (n.2–5) were used to scrape off the

carious tissue. This procedure was repeated until the

caries-removal endpoint based on the self-limiting capac-

ity of the solution was reached (n = 7).

[()TD$FIG]

Fig. 2 – Correlation between IC volume (volume of ‘carious’

tissue, segmented in ‘Baseline’) and RC volume (volume of

‘sound’ tissue, segmented in ‘Excavated Caries’). Pearson

moment correlation coefficient (PMCC) was statistically

significant (0.68, p < 0.05), indicating a positive correlation

between the two variables.

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2 157

(f) Experimental SFC-V (3M-ESPE, Seefeld, Germany) aided by

a conventional metal excavator: After mixing the two

separate gels according to the manufacturer’s instruction,

a drop of the mixture was placed in the cavity. After 30 s, a

metal spoon excavator was used to remove the caries. This

procedure was repeated until the caries-removal endpoint

based on the self-limiting capacity of the solution was

reached (n = 5).

(g) Experimental SFC-VIII (3M-ESPE, Seefeld, Germany) aided

by a conventional metal excavator: Same procedure as

under (f) (n = 5).

(h) Experimental SFC-VIII (3M-ESPE, Seefeld, Germany) aided

by a prototype plastic excavator (Star v.1.3, 3M-ESPE):

Same procedure as under (f) and (g), but instead of a metal

excavator, a prototype, disposable, star-shaped plastic

excavator was used to remove the carious tissue. The

plastic instrument was replaced during the caries-removal

procedure if it became blunt (n = 6).

(i) Er:YAG laser (Kavo): The substrate was irradiated using a

non-contact handpiece (n.2060, Kavo) at a working

distance of approximately 15 mm, whilst the irradiated

area was continuously cooled by a water spray (1 ml/min)

(n = 5). The output settings for dentine ablation were

250 mJ/pulse and 4 pulses/s repetition. The laser was

equipped with a LIF-feedback system, which emitted light

with a wavelength of 655 nm (red light). When the

measured LIF value of dentine was above a pre-selected

threshold, the laser was activated. For the present study,

the LIF threshold level was set to 7, thereby following

previous studies.16,17

2.3. Caries-removal effectiveness (CRE)

The effectiveness of caries removal was evaluated by means of

two parameters measured after caries excavation: (1) the

(mean) relative volume of residual caries and (2) the mean

mineral density (MD) at the bottom of the cavity. First, two 8-

mm diameter HAp phantoms made of fine calcium hydroxy-

apatite powder embedded in epoxy resin, resulting in two

different mineral densities (0.25 g/cm3 and 0.75 g/cm3), were

obtained from the micro-CT manufacturer (Skyscan, Kontich,

Belgium). A third phantom was produced by cutting a sintered

HAp block with a higher mineral density (3.14 g/cm3; Pentax

Lifecare Division, Tokyo, Japan) into a circular 8-mm cross-

section slab. Grey values obtained by micro-CT were converted

into MD of hydroxyapatite (HAp) by scanning and reconstruct-

ing the HAp phantoms using the same micro-CT acquisition

parameters as for the teeth, and eventually by defining a

calibration curve.20 Second, a cut-off point corresponding to a

MD value of 1.11 g/cm3 HAp (as determined previously by

correlating micro-CT grey values with hardness values of

carious dentine23) was used as a cut-off point to segment each

tooth into a ‘sound’ and ‘carious’ volume, this both in the

‘Baseline’ and ‘Excavated Caries’ stacks. Next, the two CRE

parameters were calculated as follows:

(1) The mean relative residual caries volume or RC/IC ratio

was obtained as the ratio of the volume of ‘carious’ tissue

segmented in the ‘Excavated Caries’ stack (residual caries

or RC, Fig. 1b2), over the volume of ‘carious’ tissue

segmented in the ‘Baseline’ stack (initial caries or IC,

Fig. 1a1). Consequently, the lower the RC/IC ratio is, the

more effective the carious lesion was excavated. This

normalisation procedure by dividing RC by IC was needed

for two reasons: (a) to exclude the probability of larger

lesions having larger areas of residual caries, and (b) to

correct/compensate the volume of residual ‘carious’ tissue

in the ‘Excavated Caries’ stack for a partial volume effect

(PVE). PVE is an artefact inherent to the micro-CT

technique24; in this case it accounts for low grey-value

pixels (and thus low MD values, similar to that of the

carious lesion) at the edge between the air (background)

and tooth tissue. In this study, the higher the IC was, the

higher the inner cavity area was and the higher the PVE

was. In fact, a statistically significant correlation was found

between RC and IC (Pearson’s coefficient = 0.68, p < 0.05),

as seen in Fig. 2.

(2) The MD at the cavity floor was calculated from a selected

volume of interest (VOI) with a thickness of 70 mm at the

deepest dentine part of the cavity in the ‘Excavated Caries’

volumes, as depicted in Fig. 3. This VOI was obtained by

first defining the deepest point of the prepared cavity.

Further, the VOI was expanded sideways towards the

cavity walls and next to a depth of 70 mm underneath the

cavity floor. Besides registering the absolute mean MD,

each caries-excavated tooth was further classified as

‘sound’ if the mean MD at the cavity floor was above the

dentine-caries cut-off point (1.11 g/cm3 HAp), or as ‘cari-

ous’ if the mean MD was lower than the cut-off point.

2.4. Minimal-invasiveness potential (MIP)

The minimal-invasiveness potential of the different caries-

excavation techniques was evaluated by means of the

[()TD$FIG]

Fig. 3 – (a) Occlusal view of a 3D-volume rendering obtained

from micro-CT cross-section slices of a tooth after caries

removal (‘Excavated Caries’), showing the selected volume

of interest (VOI), where MD was measured (rendered in red

colour). (b) Micro-CT mesio-distal cut view from the same

tooth in (a) showing the depth of the VOI used for MD

measurement. (For interpretation of the references to

colour in this figure legend, the reader is referred to the

web version of this article.)

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2158

‘Relative Cavity Size’ or PC/IC ratio.25 From each tooth,

the ‘Excavated Caries’ stack was subtracted from the

‘Baseline’ volume (Fig. 1c1), by which the volume of the

prepared cavity (PC, Fig. 1c2) was obtained. This PC was

divided by IC to provide the ‘Relative Cavity Size’. Conse-

quently, a ‘Relative Cavity Size’ near ‘1’ indicated a perfect

MIP, since the volume of the removed tissue (PC) then

corresponded to the volume of the initial carious lesion (IC

volume).

2.5. Statistical analysis

The two CRE parameters and the MIP parameter measured for

the 9 caries-excavation techniques were compared by one-

way analysis of variance with Fisher’s least significant

difference (LSD). The difference in percentage of ‘sound’

versus ‘carious’ teeth for the 9 caries-excavation techniques

was statistically assessed by the Fisher’s exact test. The

significance level was set to 5% for all analyses.

3. Results

The CRE in terms of both the RC/IC ratio and MD parameter is

shown for the 9 caries-excavation methods investigated in

Fig. 4a and b. The percentage of teeth exhibiting ‘sound’ versus

‘carious’ dentine according to MD is depicted in Fig. 4c. The

MIP of the different caries-excavation techniques investigated

is depicted in Fig. 5.

Er:YAG laser guided by the LIF-feedback system resulted in

the most varying results and this for all parameters evaluated

(high confidence intervals). Whilst some specimens showed a

high RC/IC ratio (Fig. 4a), others did not and in fact exhibited

over-excavation into sound dentine (0.22 � 0.26). This high

variability is confirmed by the also highly varying MD

parameter (1.05 � 0.57) for the Er:YAG laser (Fig. 4b). The

mean Relative Cavity Size of the Er:YAG laser was statistically

significantly higher than that of all other caries-excavation

techniques, thereby having resulted in a statistically signifi-

cant lower MIP (19.16 � 28.58), except for the tungsten-carbide

bur when used along with Caries Detector (Fig. 5, ANOVA with

Fisher’s LSD test, p < 0.05).

CRE improved when rotary/oscillating caries-excavation

techniques were employed, with the tungsten-carbide bur, in

combination with Caries Detector or not, scoring the lowest

RC/IC ratio (0.05 � 0.05 and 0.06 � 0.06, respectively; Fig. 4a).

Although not statistically significant, a clear tendency

towards over-excavation was, however, noted especially

when Caries Detector was used to guide caries excavation

(with 1.34 � 0.14 as the highest MD in Fig. 4b, and 8.5 � 8.45 as

the lowest but one MIP in Fig. 5). Regarding CRE (in terms of

‘Mean Relative Residual Caries Volume’), Cariex and CeraBur

presented relatively high mean RC/IC ratios (0.16 � 0.15 and

0.15 � 0.08, respectively; Fig. 4a). For CeraBur, as depicted in

Fig. 4b, a statistically significantly lower MD at the cavity floor

was measured (0.89 � 0.19, ANOVA with Fisher’s LSD test,

p < 0.05), as compared to that of the other rotary/oscillating

caries-excavation techniques (1.34 � 0.14, 1.2 � 0.22,

1.2 � 0.22 for tungsten-carbide bur with or without Caries

Detector, and Cariex, respectively). All specimens prepared

with CeraBurs still revealed residual caries at the cavity floor

(Fig. 4c). On the contrary, for Cariex the mean MD at the cavity

floor remained above the threshold (1.2 � 0.22), indicating

that dentine caries was mostly completely removed (Fig. 4b).

Regarding MIP of rotary/oscillating instruments, both

CeraBur and Cariex showed a tendency towards more

conservative cavity preparation (1.85 � 1.43 and 2.11 � 1.46,

respectively; Fig. 5), although as mentioned above this cannot

be interpreted as favourable for CeraBurs that always left

caries at the cavity floor (Fig. 6).

Chemo-mechanical caries-removal techniques combined

best CRE with MIP. In terms of MD at the cavity floor, caries was

removed up to a level most closely approximating the micro-

CT determined dentine-caries cut-off point (Fig. 4b), when the

exp. SFC-VIII and Carisolv were employed (1.13 � 0.09 and

1.13 � 0.28, respectively). The exp. SFC-V revealed a slight

tendency for over-excavation (1.26 � 0.21). The MIP of chemo-

mechanical caries-removal techniques was statistically sig-

nificantly better than that of the Er:YAG laser (ANOVA with

Fisher’s LSD test, p < 0.05, Fig. 5). However when a plastic

excavator was used in conjunction with exp. SFC-VIII, the CRE

[()TD$FIG]

Fig. 4 – The parameter caries-removal effectiveness (CRE) measured in terms of the ‘Mean Relative Residual Caries Volume’

or RC/IC ratio in (a) and in terms of the ‘Mean MD at the cavity floor’ in (b). (a) Means (*) and confidence intervals (vertical

whiskers) for the ‘Mean Relative Residual Caries Volume’. The dotted line indicates the most optimal RC/IC (best score = 0),

indicating that all carious tissue was effectively removed. Horizontal bars connect groups without statistical significance,

as disclosed by ANOVA followed by Fisher’s LSD test. (b) Means (*) and confidence intervals (vertical whiskers) for MD at

the cavity floor. The dotted line indicates the cut-off point for residual caries. Horizontal bars connect groups without

statistical significance, as disclosed by ANOVA followed by Fisher’s LSD test. (c) Percentage of teeth exhibiting ‘sound’

versus ‘carious’ dentine, as determined on basis of MD. Horizontal bars connect groups without statistical significance, as

disclosed by Fisher’s exact test.

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2 159

(in terms of RC/IC ratio) was clearly less favourable (0.23 � 0.22

compared to 0.11 � 0.05, 0.08 � 0.06 and 0.11 � 0.09 obtained

for Carisolv, SFC-V and SFC-VIII, respectively), and even in

range with that of the Er:YAG laser (Fig. 4a).

4. Discussion

The ideal caries-excavation technique would be the one that

selectively removes the irreversibly destroyed tissue, but

leaves the potentially remineralisable tissue at the cavity

floor. This is however hardly achievable clinically, because

even when the currently available caries-excavation tech-

niques were specific enough to remove solely the irrevers-

ibly destroyed carious tissue, some ‘sound’ or at least

potentially remineralisable tissue is still sacrificed in order

to provide instrumental access to the internal dentine caries

lesion.

In this study, Er:YAG-laser excavation resulted in both a

highly variable CRE and MIP, by which it cannot be considered

[()TD$FIG]

Fig. 5 – The minimal-invasiveness potential parameter (MIP). Means (*) and confidence intervals (vertical whiskers) for the

Relative Cavity Size for the 9 caries-excavation methods investigated. The green dotted line represents the most optimal

MIP (best score = 1), indicating that the volume of removed tissue was equal to the volume of the initial carious tissue.

Horizontal bars connect groups without statistical significance, as disclosed by ANOVA followed by Fisher’s LSD test. (For

interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2160

as a selective caries-removal technique. This is confirmed by

the fact that the Er:YAG laser presented with the lowest MIP,

which is in contrast with what is often claimed by laser

manufacturers and users. These unfavourable results were

recorded despite the laser investigated in this study was

equipped with a LIF-feedback system. Previous research23,26

has shown that the staining status of residual dentine to a

large extent affected LIF. As we used a clinically representative

pool of carious lesions, including both active and inactive

lesions, we therefore hypothesise that excessive dentine may

have been removed in inactive, stained lesions, having thus

increased the ‘Relative Cavity Size’ and even lead to over-

excavation into sound dentine in some specimens. On the

[()TD$FIG]

Fig. 6 – Summary of results obtained for caries-removal effective

caries-removal techniques tested.

other hand, active, less stained carious lesions were most

likely not appropriately (completely) excavated, and thus

more residual caries was left at the cavity floor (lower MD) in

other specimens.

A low coincidence between the size of the actual carious

lesion and that of the prepared cavity for the Er:YAG laser

excavation was also previously reported, typically combining

deep areas of over-excavation together with widely underpre-

pared zones.27 The results of this study are, however, not in

agreement with the study from Eberhard et al.17 They also

used an Er:YAG laser equipped with a LIF-feedback system at

the same threshold of ‘7’, as was used in our study. A smaller

‘Relative Cavity Size’, indicating better minimal-invasiveness

ness (CRE) and minimal-invasiveness potential (MIP) for the

j o u r n a l o f d e n t i s t r y 3 9 ( 2 0 1 1 ) 1 5 4 – 1 6 2 161

potential, was found for a non-contact Er:YAG laser than for a

conventional tungsten-carbide bur excavation.

When tungsten-carbide bur excavation was guided by

Caries Detector, caries was removed until dentine solely

stained ‘light-pink’, which is definitely more tissue-preserving

than the original ‘red’ staining threshold.8 Both this technique

and the solely use of a tungsten-carbide-bur resulted in the

best CRE in terms of ‘Mean Relative Residual Caries Volume’

(Fig. 4a). However, Caries Detector involves a non-negligible

risk on over-excavation into sound dentine, as was confirmed

by the highest MD of residual dentine measured at the cavity

floor and the lower MIP (or higher mean ‘Relative Cavity Size’).

This over-excavation risk corroborates other studies that even

suggested that the ‘light-pink’ threshold still leads to a too

invasive removal of tissue.5,7 Indeed, solely using a tungsten-

carbide bur appeared more conservative in our study, which is

also in agreement with another study.28

For the sono-abrasion Cariex, the mean MD at the cavity

floor was higher than the cut-off point for dentine caries

(Fig. 4b), indicating that sound dentine was exposed and no

carious tissue was left. However, CRE in terms of ‘Mean

Relative Residual Caries Volume’ (RC/IC) indicated that

residual caries was found, which thus must have remained

at areas different from the cavity floor. It is not unreasonable

that the sono-abrasion was effective at the cavity floor, but not

at the cavity walls, since indeed most residual caries was

found at the latter location. Although in literature no data is

available regarding tungsten-carbide sono-abrasion, also

diamond-coated sono-abrasion previously revealed a tenden-

cy towards underpreparation.28 Furthermore, sono-abrasion

was reported to induce a ‘compacting’ effect on carious

dentine,28 which may be an alternative explanation for the

increased MD at the cavity floor measured in this study.

For CeraBur, the lowest MD at the cavity floor was

measured (Fig. 4b). In addition, all specimens still presented

‘carious’ dentine (Fig. 4c). Different from Cariex, most carious

dentine was remained at the cavity floor itself. The only study

reporting on CeraBur showed that, although not statistically

significant, this ceramic bur tended to leave more caries at the

cavity floor as compared to a tungsten-carbide bur.10 Never-

theless, such a ceramic bur is not expected to become blunt as

easily as its precursor made of plastic material (SmartBurs,

SSWhite, Lakewood, NJ, USA). Possibly, a learning curve with

respect to the force applied during caries removal is involved

and thus may improve its CRE. Both CeraBur and Cariex

resulted, however, in the best MIP (lowest Relative Cavity Size),

meaning that these instruments most likely do not easily cut

into sound dentine tissue.

The chemo-mechanical excavation methods most closely

removed carious tissue up to the level of the actual MD cut-off

point for dentine caries (Fig. 4b). The exp. SFC-V, however,

resulted in the highest mean MD at the cavity floor, indicating

that it may remove caries less selectively. According to the

manufacturer, this difference could have been caused by some

instability of the thickening agent present in the exp. SFC-V at

room temperature; when the solution becomes more fluid, it

must penetrate deeper and dissolve more demineralised

dentine.

A previous micro-CT study has revealed MDs at the cavity

floor of 0.85 and 0.9 g/cm3, when caries was removed with

Carisolv or the exp. SFC-V, respectively.13 Both methods made

use of the same prototype plastic excavator, as used in this

study with the exp. SFC-VIII. Therefore, these relatively low

MDs probably resulted from the use of the plastic excavator,

which when employed along with the exp. SFC-VIII in this

study, also resulted in the highest ‘Mean Relative Residual

Caries Volume’ (Fig. 4a). In fact, during caries excavation, the

plastic instrument became easily blunt and had to be replaced

at least 3 times during treatment of one single specimen. The

use of a conventional metal spoon excavator with both

experimental SFC versions improved the CRE, as proven by

a lower ‘Mean Relative Residual Caries Volume’ compared to

that of the exp. SFC-VIII used along with the plastic excavator

(Fig. 4a). In general, chemo-mechanical methods resulted in

the best compromise, entailing a rather ‘complete’ caries

removal and adequate MIP.

5. Conclusion

The caries-removal effectiveness and minimal-invasiveness

potential varied amongst the contemporary caries-removal

techniques tested in this study.

Er:YAG-laser excavation guided by the LIF feedback system

resulted in low CRE and MIP, with highly variable results.

Whilst some specimens presented the highest volume of

residual caries, others excessively removed tissue into sound

dentine. Thus, the Er:YAG-laser excavation could not be

considered a selective caries-removal technique.

The use of rotary/oscillation caries-excavation techniques

resulted in a better CRE, with the exception of CeraBur and

Cariex, which although amongst the most conservative caries-

removing methods, showed a clear tendency to leave residual

caries at the cavity floor and walls, respectively. Tungsten-

carbide bur excavation guided by Caries Detector, resulted in

over-excavation into sound dentine, which was slightly less

the case when a tungsten-carbide bur was solely used.

Regarding chemo-mechanical methods, whilst the plastic

excavator associated with the exp. SFC-VIII resulted in a low

CRE, the other methods (exp. SFC-VIII, exp. SFC-V, and

Carisolv), when used along with a metal excavator, resulted

in the better compromise between effective and selective

caries removal.

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