Dentin structure in the area of the wedge-shaped defect after treatment with Er,Cr:YSGG laser in comparison with the traditional preparation method

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Authors

  • N.I. Kriheli 1, PhD in Medical Sciences, full professor of the Clinical dentistry Department
  • M.N. Bychkova 1, PhD in Medical Sciences, associate professor of the Clinical dentistry Department
  • S.V. Bolashova 1, postgraduate at the Clinical dentistry Department
    ORCID: 0000-0001-8714-1014
  • 1 Moscow State University of Medicine and Dentistry, 127473, Moscow, Russia

Abstract

During the study, the effect of Er,Cr:YSGG laser at various powers on the dentin structure in the area of the wedge-shaped defect was studied and a comparative assessment was made with the effect of traditional preparation.
Materials and methods.
In the study 20 removed teeth with wedge-shaped defects were used. Laser installation Waterlase IPlus (Biolase Tech, USA) at various parameters (2.75 W, 10 Hz, air 40%, water 10%; 4 W, 15 Hz, air 60%, water 30%; 5.25 W, 20 Hz, air 80%, water 50%) and a turbine tip with a water-cooled diamond bur, wedge-shaped defects were prepared, after which thin sections were made, subjected to carbon sputtering on an SPI Module Carbon Coater and examined on a Tescan Mira LMU scanning electron microscope.
Results.
When comparing the effect of chromium-erbium laser and traditional preparation on the structure of the cervical dentin, it was revealed that the 4 W laser creates the roughest surface with the largest number of wide-open dentinal tubules and almost completely removed the lubricated layer.
Conclusion.
Treatment of wedge-shaped defects using a 4 W Er,Cr:YSGG laser is optimal, since it improves the micromorphology of non-carious sclerotic dentin of the wedge-shaped defect, and therefore is more effective than the traditional method.

Key words:

erbium laser, wedge-shaped defect, electron microscopy, dentinal tubules

For Citation

[1]
Kriheli N.I., Bychkova M.N., Bolashova S.V. Dentin structure in the area of the wedge-shaped defect after treatment with Er,Cr:YSGG laser in comparison with the traditional preparation method. Clinical Dentistry (Russia).  2021; 24 (2): 10—14

Introduction

The adhesion of dental materials to dentin has always attracted increased attention of scientists in dentistry. All studies evaluate the adhesion of composite materials to healthy tooth tissues — enamel and dentin. It was shown that the structure of hard tissues in wedge-shaped defects has a number of special characteristics: dentin fractures, micro-scratches going to the other [1] and microcracks [2—5]. In this case, adhesion to sclerotic dentin is 25—40% less than to healthy one [6, 7].

A decrease in the level of adhesion in wedge-shaped defects is associated with partial or complete obliteration of dentinal tubules and the presence of an acid-resistant hypermineralized layer, in the area of which the width of the hybrid layer is much less than in the area of intact dentin, which prevents the penetration of the components of the adhesive system [8]. In addition, due to the deposition of mineral crystals in non-carious sclerotic dentin, collagen fibers of dentin encounter mineralized degeneration, which leads to the replacement of collagen-rich intertubular dentin with highly mineralized peritubular dentin [9—11].

Several studies have shown that roughing dentin with an Er,Cr:YSGG laser can improve the adhesion between dentin and composite material, which in turn will increase the bond strength [12, 13]. Based on this, to increase the efficiency of treatment of wedge-shaped defects, a method should be proposed that will allow partial or complete removal of mineral crystals from the dentin structure, as well as increase the surface roughness and the number of opened dentinal tubules.

In recent years, technological developments have led to the wider use of lasers in dentistry [14—18]. Nd:YAG, Er:YAG and Er,Cr:YSGG lasers can be used to prepare dental hard tissues. Er,Cr:YSGG laser as a new hydrokinetic biological laser system effectively removes hard tooth tissues without the formation of a smear layer and without thermal damage to the tooth surface or pulp [19—21]. The special advantages of the Er,Cr:YSGG laser, due to its unique wavelength of 2780 nm, allow it to be used in the treatment of both carious and non-carious lesions of dental hard tissues. During the studies carried out, it was proved that the treatment of dentin with an Er,Cr:YSGG laser increases the adhesion to the composite material in comparison with that achieved after the traditional processing with a high-speed handpiece with a diamond bur [22—24].

The impact of Er,Cr:YSGG laser on hard tooth tissues depends on several its technical characteristics, such as water/air ratio, repetition rate, pulse duration and output power. However, there are no data in the available literature on the effect of an Er,Cr:YSGG laser at various power parameters on the dentin structure in wedge-shaped defects.

The aim is to study the effect of an erbium laser at different powers on the structure of cervical dentin in a wedge-shaped defect.

Material and methods

In study were used 20 teeth (incisors, canines, premolars), removed for orthodontic and periodontological indications in persons 18—35 years old, with wedge-shaped defects on the vestibular surface, without carious lesions and signs of destruction.

Dissection of hard dental tissues was carried out using a Waterlase IPlus laser device (BiolaseTech, USA) and the traditional method using a turbine handpiece with a diamond bur under water cooling.

The teeth were divided into 4 groups of 5 samples each. In group I, laser treatment was carried out in the mode 2.75 W, 10 Hz, air 40%, water 10%; in II —4 W, 15 Hz, air 60%, water 30%; in group III — 5.25 W, 20 Hz, air 80%, water 50%. In group IV (control) preparation was carried out by the traditional method using a water-cooled turbine handpiece with medium-grain diamond burs.

In groups I, II and III, acid etching of samples with 37% orthophosphoric acid was carried out for 5 seconds, and in group IV for 20 seconds. Then, the adhesive system Adper Single Bond 2 (3M, USA) was applied to all samples according to the manufacturer's instructions, but without polymerization. Then, to remove adhesive monomers, the samples were placed in acetone for 5 minutes followed by immersion in deionized water for 5 minutes, then in 96% ethanol for 5 minutes and again in deionized water for 5 minutes.

The processed samples were used to make thin sections, on which a thin layer of carbon was sprayed on the SPI Module CarbonCoater to increase the conductivity, required in the study by scanning electron microscopy.

The study of the samples was carried out on a scanning electron microscope Tescan Mira LMU in a high vacuum mode. Images were acquired using a BSE Backtrack Electron Detector, 3 images were taken for each sample at 5000x magnification. The total area of dentinal tubules in each image was recorded using the ImageProPlus 6.0 software. Then, in the same image, the open region of the tubule was delineated using software and summarized. The proportion of the area of open tubules of each sample was calculated as the ratio of the area of open tubules to the total area. For statistical analysis of the data, three measurements were averaged per sample. Comparison in the groups was carried out using the χ2 test.

Results and discussion

Fig. 1, 2, 3 and 4 shows SEM images of dentin wedge-shaped defects in all groups. In group I, the surface of non-carious sclerotic dentin was rougher than in other groups, and most of the dentinal tubules were partially open. In group II, the surface of the samples was also rough; in addition, the proportion of open dentinal tubules was greater than in group I. In group III, the dentin is also rough, the dentinal tubules are all partially open, but they appeared on the surface.

The diagram of the proportion of open dentinal tubules in the cervical region by groups is shown in Fig. 5. In samples in groups I — III, the proportion of the area of open dentinal tubules is greater than in group IV (13%). In group III, the largest proportion of open dentinal tubules was observed (28%), but it did not differ significantly from the indicator in group II (26%). In group IV, the proportion of open dentinal tubules is comparable to group I (13%), but significantly lower than in groups II and III (p<0.05).

This study showed that when processing wedge-shaped defects with an erbium-chromium laser, the main parameter affecting the structure of dentin at the cervical area is the output power. Radiation less power results in less changes on the dentin surface. The use of excessively high laser power leads to the appearance of cracks on the surface of the dentin, which reduces the strength of the tooth.

In the present study, using SEM, it was revealed that that a smeared layer does not form on the surface of sclerotic dentin in wedge-shaped defects treated with an erbium-chromium laser; the surface remains clean and rough.

The surface treatment of wedge-shaped defects with Er,Cr:YSGG laser effectively reduces the clogging of dentinal tubules with mineralized crystals in comparison with the traditional method of preparation of wedge-shaped defects.

Conclusions

Based on the study of the surface of the cervical dentin in wedge-shaped defects, treated using an Er,Cr:YSGG laser with a wavelength of 2780 nm, a power of 4 W is optimal, since it improves dentin micromorphology. Thus, the treatment of wedge-shaped defects using an erbium laser at a power of 4 W is more effective than the traditional preparation method.

Fig. 1. Group 1: SEM of dentine treated by laser at power 2.75 W (mag. 5000x)
Fig. 2. Group II: SEM of dentine treated by laser at power 4 W (mag. 5000x)
Fig. 3. Group III: SEM of dentine treated by laser at power 5.25 W (mag. 5000x)
Fig. 4. Group IV: SEM of dentine, treated with the traditional method (mag. 5000x)
Fig. 5. Average percentage of open dentinal tubules

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Received

April 8, 2021

Accepted

May 24, 2021

Published on

June 1, 2021