Evaluation of Er:YAG and Er, Cr:YSGG Laser Irradiation For The Debonding of Prefabricated Zirconia Crowns
Evaluation of Er:YAG and Er, Cr:YSGG Laser Irradiation For The Debonding of Prefabricated Zirconia Crowns
Evaluation of Er:YAG and Er, Cr:YSGG Laser Irradiation For The Debonding of Prefabricated Zirconia Crowns
A – research concept and design; B – collection and/or assembly of data; C – data analysis and interpretation;
D – writing the article; E – critical revision of the article; F – final approval of the article
Advances in Clinical and Experimental Medicine, ISSN 1899–5276 (print), ISSN 2451–2680 (online) Adv Clin Exp Med. 2021;30(1):7–15
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8 J. Golob Deeb et al. Zirconia crown debonding using erbium lasers
Fig. 1. Prepared surfaces of teeth (A) and cameo surfaces of the crowns (B) were scanned to calculate tooth surface area and the tooth volume
pressure for approx. 20 s. The cement was polymerized for Each crown was debonded twice to determine whether
5–10 s with a curing light (800–1200 mW/cm2) on both the previous laser debonding process would affect adhe-
the facial and lingual sites. After gently removing any ex- sion properties or shorten the time needed to retrieve
cess cement, the crowns were polymerized for an additional the crowns.
20 s on the facial, lingual and occlusal surfaces, mimicking The laser settings in this study were chosen based on re-
the clinical situation where interproximal sites are not acces- ports from previous studies, manufacturers’ recommenda-
sible. All the teeth were stored in a humidor for 24–48 h be- tions and our observations. The goal was to achieve mini-
fore retrieval was initiated. Following cementation, a 2nd mal retrieval time at the lowest possible settings to avoid
scan of each tooth with a cemented crown was made. All potentially harmful temperature increases and irreversible
stereolithographic files (STL format) were imported into damage to the tooth substance. The laser irradiation was
Meshmixer© software (MeshMixer©; Autodesk, San Rafael, combined with light tapping forces and digital manipula-
USA) in order to calculate the prepared tooth surface area tion of the crowns for their retrieval.
[mm2] and cement volume [mm3]. Both scans were super-
imposed and sectioned at the marginal line of the crown Experiment 1
to determine the exact margin of the bonding surface area
on the prepared teeth. The volume of the bonded tooth The settings used for the Er:YAG laser were the same
preparation and the overall volume of the tooth, cement for both experiments (G1-FL1 or G1-FL2) and were based
and crown were measured. The cement volume was then on our observations from previous studies.17,18 The oper-
calculated from the difference between the overall volume ating parameters of the laser were 300 mJ, 15 Hz, 4.5 W,
and sum of the volumes of bonded tooth preparation and and 50-microsecond pulse duration (super-short pulse
prefabricated crown. The prefabricated crown volumes were (SSP) mode) with the non-contact H02 tip. The settings
provided by the manufacturer (Fig. 1B). for the Er,Cr:YSGG laser were closely matched in the
The teeth were divided into 2 groups according to the la- 1st experiment (G2-BL1): 4.5 W, 15 Hz, 20 water/20 air,
ser used for the debonding procedure. and 60-microsecond pulse duration with the Turbo
Group 1 (G1): debonding with Er:YAG laser (LightWalker; MX9 handpiece.
Fotona, Ljubljana, Slovenia). The 1st debonding experiment After the 1st debonding, the crowns were cleaned accord-
was labeled G1-FL1 (n = 12) and the 2nd debonding experi- ing to the manufacturer’s recommendations and checked
ment was labeled G1-FL2 (n =10). for cracks and damage. The remaining cement and debris
Group 2 (G2): debonding with Er,Cr:YSGG laser (Water- was removed from the tooth using a dental air polishing
lase; Biolase, Irvine, USA). The 1st debonding experiment and the crowns were re-cemented using the same cement
was labeled G2-BL1 (n = 13) and the 2nd debonding experi- and cementation procedure. All teeth were stored in a hu-
ment was labeled G2-BL2 (n = 13). midor for 24–48 h before the 2nd retrieval.
10 J. Golob Deeb et al. Zirconia crown debonding using erbium lasers
Fig. 2. To measure temperature changes inside the tooth during the laser irradiation, a channel was prepared through the furcation (A) to enable insertion
of the temperature probe (B) into the pulpal chamber (C)
Table 1. Pearson’s correlation coefficients for associations between crown metrics and irradiation time
Type of laser Group Outer surface area Inner surface area Space volume
G1-F1 (n = 12) −0.154 −0.241 0.758*
Er:YAG G1-F2 (n = 10) −0.113 −0.176 0.545**
overall −0.136 −0.211 0.667*
G2-BL1 (n = 13) 0.506** 0.586* 0.539**
Er,Cr:YSGG G2-BL2 (n = 13) 0.711* 0.801* 0.123
overall 0.515* 0.586* 0.287
*p < 0.05; **0.05 < p < 0.10; Er:YAG – erbium-doped yttrium, aluminum and garnet laser; Er,Cr:YSGG – erbium, chromium-doped yttrium, scandium, gallium
and garnet laser.
SD – standard deviation; Er:YAG – erbium-doped yttrium, aluminum and garnet laser; Er,Cr:YSGG – erbium, chromium-doped yttrium, scandium, gallium
and garnet laser.
250
The average time for crown removal using the Er,Cr:YSGG
200
laser in group 2 was 2 min 34.7 s (SD = 67.9 s) for the 1st
time [s]
Comparison: Er:YAG vs Er,Cr:YSGG All pulpal temperatures remained within a safe range,
with the highest recorded temperature change of 5°C
The 1st debonding was, on average, 60.9 s faster (stan- for Er:YAG and 4°C for Er,Cr:YSGG. These temperatures
dard error (SE) = 20.2) for the Er:YAG laser than for should be interpreted with caution, as they reflect vari-
the Er,Cr:YSGG laser, which was a statistically sig- ous other factors such as the temperatures of the room
nificant difference (p = 0.0076). For the 2nd debonding, and water. The temperature range during the irradiation
the Er:YAG laser was 2 min 21.6 s faster, on average, than is shown in Table 2.
the Er,Cr:YSGG laser, which was also statistically signifi-
cant (p < 0.0001) (Fig. 3). Scanning electron microscopy analysis
Pulpal temperature After irradiation, none of the teeth or crowns appeared
damaged on visual inspection or under an optical micro-
The mean temperature changes were 1.40 ±1.36°C for scope using a ×40 magnification lens.
the Er:YAG laser and 2.2 ±0.99°C for the Er,Cr:YSGG la- The SEM examination did not reveal any damages or ma-
ser (p = 0.0321). For both erbium lasers, the differences jor structural changes suggesting photoablation or ther-
in temperature change between the 2 debonds were not mal ablation of the abutment teeth caused by irradiation
statistically significant (p = 0.23 and 0.76, respectively). of either laser (Fig. 4). The decrease in adhesion strength
12 J. Golob Deeb et al. Zirconia crown debonding using erbium lasers
Fig. 4. Residual cement and undamaged surface is observed on SEM images of the teeth following irradiation with Er:YAG laser (A) and Er,Cr:YSGG laser (B)
and intaglio surface of the crowns following Er:YAG (C) and Er,Cr:YSGG laser (D) lase
appeared either between the cement and the tooth surface, using high-powered erbium lasers such as Er:YAG and
leaving the cement attached mostly inside the crown, or be- Er,Cr:YSGG.30 Both erbium lasers are selectively absorbed
tween the cement and the intaglio surface of the crown, by water molecules25 and residual monomers of cements,
leaving cement attached to the surface of the tooth. No leading to a decrease in adhesion strength between the ce-
carbonization, cracks or fractures in the macro- or micro- ment and the crown or a tooth due to photothermal ablation.
structure were observed on the tooth or on the zirconia A dentin–crown interface can be debonded with thermal
prefabricated crown. Slight, partial ablation of the cement softening, thermal ablation or photoablation, resulting
caused by Er,Cr:YSGG laser irradiation was occasionally in cracks in the cement layer and the breakage of material
observed. The intaglio surfaces appeared to be simi- bonds.5,17,20
lar in roughness for both lasers. The teeth treated with Closer study of the absorption peak between the 2 la-
the Er:YAG laser showed less cement remaining on the sur- sers shows three-fold higher absorption coefficients for
faces than those treated with the Er,Cr:YSGG laser (Fig. 4). the Er:YAG laser in comparison to the Er,Cr:YSGG laser.
The Er,Cr:YSGG laser wavelength thus penetrates deeper
into the tissue and requires more time to heat up the irradi-
Discussion ated volume to the evaporation temperature, while the sub-
stance heated by the Er:YAG laser will reach ablation tem-
The development of prefabricated all-ceramic crowns peratures faster and progress deeper into the targeted
and modern adhesive systems has improved the restor- substance.25,31 Our findings are in alignment with these
ative options for severely damaged teeth in the pediatric observations, since the time required to debond the crowns
and adolescent population. The removal of these tempo- was shorter for the Er:YAG laser than the Er,Cr:YSGG laser
rary restorations can be challenging and is usually accom- after the 1st debonding using similar settings. Both lasers
plished with rotary instruments. Alternatively, atraumatic showed clinically acceptable debonding times, proving
removal can be predictably and reproducibly accomplished them to be an efficient tool for crown debonding.
Adv Clin Exp Med. 2021;30(1):7–15 13
Heat generated by an Er,Cr:YSGG laser has more time pulse of the mid-infrared wavelength, and continuous, un-
to spread deeper into the tissue, resulting in a thicker interrupted irradiation.35 The working parameters for both
indirectly-heated zone exerting greater thermal effects lasers used in this study were low and safe, yet provided
on the tooth. This undesirable heating of the surrounding efficient and reproducible debonding of the restorations.
tissue is also the reason energy is lost, resulting in less effi- Laser-assisted ceramic crown removal encompasses
cient ablation.24 To prevent thermal injury of the pulpal tis- several factors that may affect its efficiency: the chemical
sues, heat generation and accumulation should be minimal. composition and type of ceramic material, the thickness
An increase in pulpal temperature of 5.5°C can cause ir- of the restoration, the type, shade and thickness of the resin
reversible damage to the pulp tissue32; a rise in temperature cement, the shade and opacity of the ceramic material, and
of 10°C for 60 s on the root surfaces can cause irreversible the parameters of the laser (power, pulse duration, frequency,
damage to the periodontal ligament and bone that can lead and irradiation time).15,36–39 The advantage of retrieving
to bone resorption and tooth ankylosis.33,34 In this study, a crown with an erbium laser is to preserve the crown for
temperature changes measured in the pulpal chamber re-cementation. In this study, all the crowns were re-ce-
throughout the irradiation were minimal and did not ex- mented after the 1st debonding and tested again. The re-
ceed critical temperature changes. No significant tempera- sults of this study indirectly showed a predictable bond
ture increase was observed, even when the slightly higher strength after re-cementation of the crowns as the debond-
settings for Er,Cr:YSGG were used in the 2nd experiment. ing time did not decrease during the 2nd irradiation; it even
Both lasers provide continuous water cooling that was increased for the 2nd Er,Cr:YSGG laser group. The slightly
in this study effective in regulating temperature during higher power (0.5 W) used for the 2nd debonding (G2-BL2)
irradiation. Only temperature changes during laser irradia- should theoretically result in a shorter irradiation time
tion in relation to the baseline temperature were reported. but resulted in significantly increased debonding time.
The initial temperatures were not standardized for all ex- One possible explanation could be the use of a 50% water
periments and differed slightly due to variations in room spray, causing higher absorption of the laser on the wet
temperature on different days. surface of the crown, therefore lowering the energy effi-
The key factors of successful debonding include tech- ciency in the cement layer. Another possible explanation
nique, the duration of laser irradiation, fluency, an adequate could be a lighter tapping force employed by a different
Fig. 5. Following erbium laser irradiation, debonding of the crown resulted in either retention of the cement attached to the intaglio surface of the crown
(A–C) or the surface of the tooth (D–F)
14 J. Golob Deeb et al. Zirconia crown debonding using erbium lasers
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