In vitro evaluation of surface characteristics comparing WaterLase (Biolase®) with tungsten carbide burs for composite removal: a pilot study
Publicado en línea: 14 jul 2022
Páginas: 194 - 201
Recibido: 01 nov 2021
Aceptado: 01 may 2022
DOI: https://doi.org/10.2478/aoj-2022-0022
© 2022 Mohammed Alkandari et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
The iatrogenic damage caused by debonding fixed appliances at the end of orthodontic treatment is a concern and has been the subject of previous investigations. The loss of tooth surface exposes the enamel prisms to the oral environment, thereby increasing their susceptibility to demineralisation.1–3 The change in surface composition and texture can lead to altered optical properties and the accumulation of pigments leading to sub-optimal smile aesthetics.4
A number of different methods are available to debond appliances and many have been subject to previous research.5 The removal of attached brackets has been shown to leave varying amounts of residual composite on the enamel surface.6–8 A clinically successful technique requires complete composite removal to reduce plaque retention, decrease staining and restore the natural aesthetics of the tooth.
A number of techniques have been proposed to achieve optimal composite removal with minimal damage to the enamel.9–13 Suggested methods include the use of mechanical instruments, such as tungsten carbide and diamond burs compatible with slow or fast handpieces, pliers, scalers, stones, ultrasonic instruments and sandpaper discs. The preferred and the most widely used technique for composite removal is a tungsten carbide bur in a slow-speed handpiece.5,11,12 This technique is time consuming and can cause damage to the surface enamel.14 Studies have shown that using a tungsten carbide bur in a slow-speed handpiece can create visible surface roughness, measuring 10 to 20 μm and a loss of up to 100 μm of enamel. Furthermore, mechanical debridement using burs often remains ineffective due to the penetration of resin tags within the enamel structure.15,16 Hence, there is a need for better and safer techniques to remove adhesive remnants at the end of orthodontic treatment.17
The WaterLase (Biolase® Inc, Irvine, CA, USA) is part of the Erbium-family of lasers of which there are two types; Er:YAG operating at a frequency of 2,940 nm and Er:YSGG with a frequency of 2,790 nm. Lasers are considered to be well suited for this clinical application due to their mode of action. The steam generated by the emission of energy causes tissue ablation by the entrapment of the laser-head water in the interstitial resin structure, without effect on the dental tissues.18
Further advantages of the WaterLase (WL) over rotary handpieces and burs include pulpal safety and patient experience, due to lower heat production and the absence of vibration, respectively.19
The use of lasers in orthodontics has been well documented20 and numerous studies have analysed the use of lasers for debonding procedures.21,22 Research has favoured carbon dioxide lasers for debonding ceramic brackets as their wavelength is absorbed much more readily;23 however, the efficacy of Er:YAG lasers has also been reported24 with safety margins further increased by the simultaneous use of cooling systems.25 The use of Er:YAG lasers for metallic brackets was reported by Grzech–Leśniak et al. with the results indicating a minor increase in pulp temperature but with less risk of enamel damage in comparison to conventional debonding procedures.26 A qualitative study using Er:YAG lasers in comparison to tungsten carbide burs has also proved their clinical scope of use; however, the enamel ablation was much higher than with a conventional bur.27 A further benefit of lasers has been cost-effectiveness through the possibility of recycling stainless steel orthodontic brackets.28 To date, few studies are available that have specifically evaluated the enamel surface roughness following the use of Er:YSGG lasers. In addition, there are no previous reports describing the use and enamel effects of WaterLase Biolase®.
The present pilot study aimed to evaluate the enamel surface roughness and composite remnants following removal with WaterLase Biolase® and tungsten carbide burs in a slow-speed handpiece (Synea WK56LT, W&H Bürmoos, Austria). A secondary aim was to evaluate the level of composite residue on the tooth surface by comparing the atomic composition of the surfaces between the three groups (untreated, WL and TC).
Twenty-one previously extracted lower premolars with sound enamel were selected for the present study. Prior to commencement, the surface roughness of each tooth was evaluated using SEM imaging. The roots of the teeth were subsequently embedded in acrylic so that the crown was exposed 1 mm occlusal from the cement–enamel junction.
The buccal aspects of the premolars were cleaned, washed and air-dried. The surfaces were etched with 37% orthophosphoric acid gel for thirty seconds. Primer was applied (3M Unitek, Monrovia, CA, USA) and Transbond XP™ (3M Unitek, Monrovia, CA, USA) was used to bond a premolar bracket (Victory Series, 3M Unitek, Monrovia, CA, USA) to each premolar. A blue light (Ortholux™ Luminous Curing Light, 3M Unitek, Monrovia, CA, USA) emitting an intensity of 600W/cm2 was applied for thirty seconds to cure the composite in a process which was followed for the entire sample. The premolars were debonded using debonding pliers in a twisting motion by applying light pressure directed at the mesial and distal wings. This process was conducted by the same operator (M.A.) throughout the study.
Following the removal of the brackets, the teeth were randomly allocated into two groups. Containing five teeth, group 1 served as a control group in which residual composite was removed using a tungstencarbide bur (Alston, England) mounted in a slowspeed handpiece. In group 2 containing 15 teeth, residual composite was removed using the Waterlase Biolase® (Biolase Inc, Irvine, California, USA) based on ES:YSGG laser. The laser and repetition rate were set at 2.5 W and 20 Hz, respectively, and the water and air flow were set at 11% and 20% of the maximum levels. Composite removal was performed by the same operator using clinical judgement to assess complete resin removal. A JCM-6000 desktop scanning electron microscope (JEOL Ltd, Tokyo, Japan) was used to analyse the enamel surfaces coupled with Energy Dispersive X-ray Spectroscopy (EDS) to determine the composition of the enamel surface following Waterlase Biolase® (Biolase Inc, Irvine, CA, USA) composite removal from all teeth.
The
Six of the 15 samples in the WL composite removal group were randomly selected alongside one control sample of composite-only and the control tooth with untreated enamel. The teeth were sectioned to leave only the crown, coated with a 4.5 nm layer of carbon in the EM ACE600 High Vacuum Coater (Leica Microsystems (UK) Ltd), and fixed on stubs with double-sided conductive carbon tape. EDS measurements were taken of the six WL samples, the sound enamel control sample and the composite-only sample.
Subsequently, 10 further samples were selected; 5 TC-bur control and 5 WL composite removal samples. The samples were placed in acrylic, sectioned vertically in half with an Isomet 1000 precision saw and plated with gold-palladium alloy. The samples were analysed by SEM to assess the depth of pitting caused by the WL and TC bur. Ten measurements, which were repeated twice, were taken from the samples.
The 21 sound premolars were divided into three groups:
To determine the atomic percentage concentration, six of the samples from the WL group were randomly selected and analysed by EDS in a desktop SEM Neoscope™. Spectra were taken of two control samples as a comparison; one of composite-only and of one tooth with sound enamel. The concentration of each atomic element was recorded to produce the primary variables.
The statistical analysis was completed by general description for continuous variables; mean, standard deviation, range and median, differentiated by group. Due to the sample size, the normality of percentage atomic concentrations was not tested. For each element, 95% confidence intervals for medians were determined in the experimental group. Reference values for the composite and for the sound enamel were compared to these intervals.
For multivariable analysis (all atomic elements assessed at once), the Chi-squared Euclidean distance was computed to quantify the amount of similarity between patterns of the WL and control samples. A hierarchical cluster analysis was performed to explore levels of homogeneity. A linkage between the group method was used to aggregate samples into clusters. Non-standardised and standardised concentration variables were used to assess the effect of extreme differences in the presence of atomic elements.
Ten samples were selected, 5 from the WL group and 5 from the TC group. Each sample was imaged using SEM. The images were analysed twice by image processing software (ImageJ, National Institute of Health, University of Wisconsin, USA) for standardisation of surface roughness measurements. The mean of the two values was obtained and considered as the primary outcome. Confidence intervals at 95% were obtained and Mann–Whitney tests were carried out to assess the homogeneity of the distribution between the experimental and the control group. The level of significance was set at 5% (α = 0.05).
Using a Mann–Whitney test and considering an effective size to detect a 0.8 μm (large) difference, the statistical power reached was 0.38 for a confidence level of 95% for detecting differences in surface roughness (
The mean percentage distributions for sound enamel, WL and composite only samples are shown in Figure 1. The WL samples contained the following concentrations: oxygen (O) (62.7%), carbon (C) (17.3%), calcium (Ca) (11.4%) and phosphorus (P) (7.9%), making up 99.27% of the samples.
Figure 1.
Mean percentage concentrations by group.
The percentage atomic concentrations for the sound enamel sample had a greater concentration of C (28.5%) and lower levels of O (57%), Ca (7.8%) and P (5.8%).
The composite sample showed an increased presence of C (38.2%), decreased O (44.1%) and an absence of both P and Ca. The spectra showed a large amount of silicone (Si) (11.5%) and some traces of other elements such as barium (Ba) and bromine (Br).
Calculated medians, shown in Table I, are very similar to the means shown in Figure 1. Except for Ca and P which were not present in the composite-only sample, there were no samples with outlying atomic values. Table I tabulates and compares the 95% confidence intervals of concentrations within the experimental group and of the control samples. The confidence intervals for medians coincide with the range and the sample size of The resultant interval differences for P K (7.22– 8.74) and Ca K (9.70–13.14) between the WL samples and the sound enamel sample were statistically significant. This is indicative of different atomic concentrations for these two elements between the two samples, with K representing the inner shell of electrons surrounding the nucleus of the respective elements captured in the spectra. Compared to control composite spectra, significant differences were observed and eight elements were present in significantly higher proportions than the control sample. These elements included; C K, O K, P K, Ca K, F K, Si K, Ba K and Br K.
Comparison of atomic concentrations: medians and 95% confidence intervals in six WaterLase Biolase® samples and individual values for control samples.
| WaterLase group | Sound enamel | Only composite | ||
|---|---|---|---|---|
| Median | 95% CI | Value | Value | |
| C K | 14.84 | (11.48–31.51) | 28.46 | 38.17* |
| O K | 64.64 | (47.04–68.25) | 57.08 | 44.13* |
| Na K | 0.20 | (0.00–0.58) | 0.38 | 0.00 |
| P K | 7.76 | (7.22–8.74) | 5.75* | 0.00* |
| Cl K | 0.00 | (0.00–0.18) | 0.13 | 0.00 |
| Ca K | 11.38 | (9.70–13.14) | 7.76* | 0.00* |
| F K | 0.00 | (0.00–0.00) | 0.00 | 2.01* |
| Si K | 0.00 | (0.00–0.00) | 0.00 | 11.47* |
| Br L | 0.00 | (0.00–0.00) | 0.00 | 1.64* |
| Ba L | 0.00 | (0.00–0.00) | 0.00 | 2.58* |
| Zr L | 0.48 | (0.00–0.69) | 0.44 | 0.00 |
*
There was greater similarly, of atomic concentrations between WL and sound enamel than WL and the composite samples.
Similarity, whole patterns could be achieved by means of Chi-squared Euclidean distance. This is a measurement of spectra similarity between two different samples. A cluster analysis joins the two samples of the highest similarity followed by the second highest similarity until all the spectra have been analysed. The key of this algorithm is to check, at what stage or level of similarity, the combination of the 8 different spectra, 6 WL and 2 controls, occurs.
The atomic composition of the samples n1 to n8 are shown in Figure 2 with sample n.3 sharing similar atomic concentrations with the ‘sound enamel’ sample.
Figure 2.
The atomic composition of the samples n1 to n8, with sample n.3 sharing similar atomic concentrations with the ‘sound enamel’ sample.
The analysis performed if the weight or importance is assigned to all elements independent of their abundance is called analysis for ‘standardised variables’. This indicates: Samples Samples There was no Zr L in sample n1, and it was therefore slightly different from The spectra of n8 (composite only) was absolutely heterogeneous when compared to the other samples.
Table II provides a statistical overview of the variable ‘depth of removal’ in both groups, whilst figure 3 shows the distribution of depth values for the WL and the TC groups measurements (Figure 3).
Statistical description of removal depth.
| GROUP | ||||
|---|---|---|---|---|
| Total | Waterlase (WL) | Tungsten carbide (TC) | ||
| Depth in Micrometers | N | 20 | 10 | 10 |
| Mean | 96.83 | 173.12 | 20.54 | |
| Standard Deviation | 94.90 | 77.40 | 9.40 | |
| Minimum | 9.62 | 76.37 | 9.62 | |
| Maximum | 285.23 | 285.23 | 37.69 | |
| Median | 57.03 | 166.31 | 17.62 |
Figure 3.
Distribution of depth values.
Descriptive differences for the experimental sample was more varied. For the WL sample, the range was wider as 25% showed a depth lower than 103.7 μm, 50% lower than the median value of 166.3 μm whilst 25% had a higher value than 250.4 μm. For the untreated group, the range of values was 11.5 μm and 28.7 μm with a median of 17.6 μm (Table III).
Comparison of depth of removal between groups: medians and 95% confidence intervals in ten WaterLase Biolase® and ten tungsten carbide samples.
| WaterLase group | Tungsten carbide | |||
|---|---|---|---|---|
| Median | 95% CI | Median | 95% CI | |
| Depth | 166.3 | (86.6–263.1) | 17.6*** | (10.5–28.9) |
*
**
***
The difference of depth between both groups was statistically significant (
Fixed appliances may be bonded to teeth using a variety of adhesives of which the most common is composite resin. Unlike dental restorations, orthodontic composite requires removal following the completion of treatment. The risk of permanent damage to the enamel surface while removing resin is ever present.
The resin infiltration resulting from enamel etching can penetrate up to 50 μm,29 and so the complete removal of resin using rotary instruments will inevitably cause removal of the surface enamel layer. The present study has shown that WaterLase Biolase® (Biolase, Inc, Irvine, California, USA) is effective at completely removing the composite resin within the enamel tubules following bracket removal; however, it results in higher surface roughness compared with the use of a tungsten carbide bur.
Several methods may be used to measure the depth of enamel depletion following composite removal. The stylus used in contact profilometry may not always reach the deepest area of the examined sample; however, the defect sizes detected surpassed this depth-measurement deficiency.
To assess the composite remnants remaining on the teeth, energy dispersive x-ray spectroscopy (EDS) was employed, which allows a standardless semi-quantitative analysis of samples. The data collected was compared to values from standard factory settings stored within the EDS system software (JEOL Proprietary Software, Tokyo, Japan). The limitation of quantitative analysis using EDS is that lighter elements such as hydrogen, helium and lithium are unable to be analysed. However, these elements are not expected to be in the composite samples examined in the current investigation. The carbon coating of the samples allowed for non-conducting materials to be analysed, resulting in the high carbon readings. The key advantage of semi-quantitative analysis is that it eliminates the subjective observation involved in qualitative analysis. The semi-quantitative method uses an index or reference data for comparison; in this case, data collected from the standard factory settings stored in the software of the EDS system.
The results of the present study showed significant differences in the experimental element composition, compared to the composite sample. The composition had a higher level of similarity against the sound enamel sample, whereas the composite sample showed no calcium nor phosphate but relatively high concentrations of silicon, barium and bromine. In contrast, the WaterLase Biolase® and sound enamel samples were composed of the same elements with moderate concentration differences of calcium and phosphate. The closest atomic structure was shown by experimental sample
The concentration of silicon was relatively high in the composite sample and almost zero in the sound enamel sample. This indicates that the silicon concentration in treated samples may provide, in future studies, a reliable measure to determine the level of residual composite. The tungsten carbide sample was not evaluated with EDS because previous investigations have shown that the depth of resin tags can be up to 50 μm,29 and enamel removal ranges from 2 μm to 28 μm.2 This compares well with the current investigation in which the respective data were 9 μm to 37 μm. Resin removal using a tungsten carbide bur is also known to leave residual composite on the enamel surface.
Significant differences were found between the enamel removal depth in the WaterLase Biolase® and tungsten carbide treated samples, the former removing significantly more enamel. An advantage of using the WaterLase Biolase® appears to be the complete removal of composite from the enamel as opposed to the tungsten carbide bur which only removes the composite from the surface, leaving the resin tags intact. The residual resin tags can lead to changes in the colour and optical properties of the enamel.
Throughout the experiment only one set of parameters from the WaterLase Biolase® instrument was applied. The laser power and repetition rate were set at 2.5 W and 20 Hz, respectively, and the water and air flow were set at 11% and 20% of the maximum levels. According to current knowledge, there are no previous independently reviewed results outlining the use of this type of laser for debonding in orthodontics and no reference settings were provided by the manufacturer. Therefore, further studies need to be undertaken to determine the appropriate settings resulting in better surface characteristics, when using the WaterLase Biolase® for debonding orthodontic appliances.
The atomic concentrations of samples debonded by the WaterLase Biolase® were similar to sound enamel, suggesting that the composite remnants were removed.
The WaterLase Biolase® (Biolase, Inc, Irvine, CA, USA) was efficient at removing composite remnants from within the enamel tubules.
The differences in the median range of surface roughness between the WaterLase Biolase® sample and the TC sample was statistically significant.
The clinical translation of the use of WaterLase Biolase® for debonding procedures from the setting tested in the present study, could result in increased enamel surface roughness in comparison to the conventional use of TG burs.