|Year : 2014 | Volume
| Issue : 1 | Page : 14-19
The effect of cavity preparation with erbium-doped: Yttrium-aluminum-garnet laser on marginal integrity of resin composite restoration-scanning electron microscope study
Shamshe-Alam Idrisi, Sucheta Sathe, Vivek Hegde
Department of Conservative Dentistry and Endodontics, Rangoonwala Dental College and Research Centre, Pune, Maharashtra, India
|Date of Web Publication||9-Jun-2014|
Department of Conservative Dentistry and Endodontics, Rangoonwala Dental College and Research Centre, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
Aim: To evaluate the effect of cavity preparation with erbium-doped:yttrium-aluminum-garnet (Er:YAG) laser on marginal integrity on resin composite restoration. Materials and Methods: A total of 40 human extracted teeth were divided into four groups, and class-V cavity of approximately 1.5 mm depth and 2 mm width were prepared on the buccal surface of each tooth. A total of 10 samples were kept as control group where cavities were prepared with carbide bur. Rest of 30 samples were divided into three groups with 10 samples each and cavity was prepared with Er:YAG laser keeping pulse energy constant at 200 mJ and pulse duration constant at super short pulse and frequencies used for three groups were 10, 15, and 20 Hz, respectively. For control group, restorations were done using etching and bonding method, and for the three laser groups, bonding agent was applied directly and composite resin was placed. After restoration, enamel cracks and gap formations at the cavosurface margins were evaluated using scanning electron microscope (SEM) on the surface and crosscut surface of the restoration. Results: Using SEM on the surface and crosscut surface of the restoration the preparation by Er:YAG laser at frequency 10 Hz showed better marginal integrity of resin composite restoration. Conclusion: Laser group showed better cavity preparation than that with rotary carbide bur.
Keywords: Cavity preparation, enamel cracks and gap formations, Er:YAG laser, marginal integrity
|How to cite this article:|
Idrisi SA, Sathe S, Hegde V. The effect of cavity preparation with erbium-doped: Yttrium-aluminum-garnet laser on marginal integrity of resin composite restoration-scanning electron microscope study. J Dent Lasers 2014;8:14-9
|How to cite this URL:|
Idrisi SA, Sathe S, Hegde V. The effect of cavity preparation with erbium-doped: Yttrium-aluminum-garnet laser on marginal integrity of resin composite restoration-scanning electron microscope study. J Dent Lasers [serial online] 2014 [cited 2023 Feb 8];8:14-9. Available from: http://www.jdentlasers.org/text.asp?2014/8/1/14/134113
| Introduction|| |
Recently, the attention to the adhesive systems has been addressing the easy application and is reduce time required for the procedure; however, contradictory outcomes have been presented in the literature on studies on the effectiveness of marginal sealing provided by multistep adhesive systems, based on the concepts of total etching and humid adhesion compared to self-etching adhesive systems.
Besides the search for adhesive materials that may allow perfect marginal sealing, dentistry has been investigating alternative equipments to the conventional rotary instruments that may not only cut the tooth structure but also allow more conservative preparations with more comfort to the patients during the procedure. These new alternatives include equipments of laser irradiation, more specifically erbium-doped: yttrium-aluminum-garnet (Er:YAG) laser.
Since the Er:YAG laser with a wavelength of 2.94 μm, was introduced in dentistry, , a lot of basic and clinical studies on Er:YAG laser have been published. The Er:YAG laser is absorbed by water and hydroxyapatite, which partially accounts for its efficiency in cutting enamel and dentin.  The Er:YAG laser could remove caries in tooth structures together with sound enamel and dentin with minimal thermal effects in the adjacent hard and soft tissues.  The Er:YAG laser appears to be one of the best suited laser types for cavity preparation. 
Generally, the cavity preparation using Er:YAG laser takes more time, compared to rotary cutting instruments. , However, that preparation method advantages include low noise and vibration, eliminating, in most cases, the need for local anesthesia.  Clinical studies suggested that the application of the Er:YAG laser system was a more comfortable alternative or adjunctive method than conventional mechanical cavity preparation. 
In 1997, the Food and Drug Administration of United States cleared for marketing the first Er:YAG laser for hard tissue application.  Clinically, Er:YAG laser was suitable for the caries removal and the cavity preparation based on the minimal intervention dentistry  and adhesive restorative dentistry. The Er:YAG laser system is promising as a new technical modality for caries treatment. 
There were many in vitro researches about bonding of the adhesive materials to Er:YAG laser irradiated enamel and dentin, including micromorphological studies on their interface. However, there were few reports about marginal microleakage of the restoration of the cavity prepared by Er:YAG laser. The purpose of this in vitro study was to evaluate the effect of cavity preparation with Er:YAG laser on marginal integrity of resin composite restorations.
| Aims and Objectives|| |
- To evaluate the effect of cavity preparation with Er:YAG laser on marginal integrity on resin composite restoration
- To compare the effect of Er:YAG laser used at different frequencies on marginal integrity with scanning electron microscope (SEM) on surface and cross-surface of the restoration.
| Materials and Methods|| |
A total of 40 human extracted premolars were selected and randomly divided into four groups:
- Group-1(Er:YAG):200 mJ × 10 Hz
- Group-2(Er:YAG):200 mJ × 15 Hz
- Group-3(Er:YAG):200 mJ × 20 Hz
- Group-4(carbide bur): Control.
Each specimen was subjected to class-5 cavity preparation of 1.5 mm deep and 2 mm wide approximately. Preparation as follows: Cross-sectioning of the samples in buccolingual direction was done vertically. Etching was done for 15 s with 37% phosphoric acid. Rinsing the cavity with water for 5 s. Bonding agent was applied and curing was done for 20 s. Nanohybrid composite material was packed in the cavity and the increment was cured for 40 s. Margins were then exposed at the cavosurface for all the samples. Polishing was done on the cross-surface and surface for all the samples.
The samples were then subjected to SEM analysis to view the margins of the restorations.
| Results|| |
Group-1 (Er:YAG-200 mJ × 10 Hz) specimen showed better marginal integrity with enamel; that is, with the cavosurface margins [Figure 1] and as well as with the dentin on cross-surface [Figure 2] of the sample.
Group-2 (Er:YAG-200 mJ × 15 Hz) specimen showed better marginal integrity on the enamel surface [Figure 3], while the cross-surface showed slight amount of gap [Figure 4] between the restoration and the dentin approximately ranges between 3 and 4 microns.
Group-3 (Er:YAG-200 mJ × 20 Hz) specimen showed better marginal integrity on the enamel surface [Figure 5], while the cross-surface showed slight amount of gap [Figure 6] between the restoration and the dentin approximately ranges between 0 and 2 microns.
Group-4 (carbide bur:control) specimen showed better marginal integrity on the enamel surface with considerable amount of cracks [Figure 7] seen on the enamel margins, while the cross-surface showed slight amount of gap [Figure 8] between the restoration and the dentin approximately ranges between 1 and 1.5 microns.
| Discussion|| |
The use of the Er:YAG laser to treat dental hard tissue is both safe and effective for caries removal, cavity preparation, and enamel etching. By the investigation of the patients' response to Er:YAG laser preparation of teeth, the application of the Er:YAG laser is a more comfortable alternative or adjunctive method than conventional mechanical cavity preparation. , The Er:YAG laser is promising as a new technical modality for caries treatment and appears to be one of the best suited laser types for cavity preparation.
In the last 6 years, two wavelengths have been developed for use clinically on hard tissues. These include the Er:YAG (2.94 μm) and the erbium, chromium: yttrium-scandium-gallium garnet (Er, Cr:YSGG) at 2.78 μm, which by many scientific accounts have very similar properties. These two wavelengths make up the erbium family of lasers.
The mechanism of dental hard tissues removal by a laser is called "thermomechanical process," "photothermal fragmentation" or "ablation." The energy delivered by Er:YAG laser has one of the highest absorption in water and has a high affinity for hydroxyapatite. During irradiation, the water heats and evaporates, resulting in a high pressure of steam that causes a microexplosion of tooth tissue below its melting point.  Vaporization of the water within the mineral substrate causes the surrounding material to literally explode away. This mechanism characterizes the morphological aspects of the irradiated enamel and dentin surfaces.
At high energies and low pulse durations,  the speed of ablation is faster than the rate of diffusion of heat into the tissue, so that all of the laser energy is used up in cold ablation. , With decreasing energies and/or longer pulse durations, the layer of tissue, that has been thermally-influenced by the time the pulse ends, becomes thicker. Thermal effects become more pronounced and, with these, ablation efficiency is considerably reduced (warm ablation and, at even lower energies, hot ablation). At energies below the ablation threshold, there is no ablation and all the energy is released in the form of heat, independent of the laser pulse duration. The super short pulse (SSP) durations are extremely short (approximately >80 s) which is below the >100 s tissue relaxation time for enamel. The SSP pulses, are therefore, best suited for precise and fine ablation at low laser energies.
The surface of enamel and dentin after irradiation of Er:YAG laser are specific characteristics which are different from the surface prepared by rotary cutting instruments. The enamel irradiated by the Er:YAG laser shows a characteristic chalky surface. Micromorphology of the Er:YAG laser-treated enamel depicted a retentive pattern similar to acid-etched enamel and the anatomical features of enamel rods were preserved.
The dentin surfaces irradiated by Er:YAG laser were irregular, scaly, or flaky and dentinal tubules were opened without smear layer. Vaporization of intertubular dentin is greater than that of peritubular dentin, showing a protrusion of the dentinal tubules with a cuff-like appearance. Although the dentin surface irradiated by Er:YAG laser seems to increase restorative material retention, this surface and subsurface contained acid-resistant layer and decalcified layer. However, the cavity preparation techniques did not alter the composition and microhardness of dentin tissue. These surface characteristics could affect the bonding to restorative materials.
Bond strengths to Er:YAG-lased tooth substrate reported in the literature are often confusing and contradictory.  Some studies reported the higher bond strengths to laser-conditioned dentin than to acid-etched dentin. , Laser irradiated samples improved bond strengths compared with acid-etched and handpiece controls. Er:YAG laser preparation of dentin leaves a suitable surface for strong bonding of an applied composite material. Er:YAG laser might eliminate the need for acid-etching dentin as a pretreatment for composite bonding  or was likely to slightly improve the resistance of resin-dentin interface to acid-base challenge.  However, others reported significantly lower bond strengths. ,,,, The total etch adhesive bonded significantly less effectively to lased than to bur-cut enamel and dentin, and laser conditioning was clearly less effective than acid etching. Cavities prepared by laser appear less receptive to adhesive procedures than conventional bur-cut cavities.  Er:YAG laser ablation to dentin adversely affected the microtensile bond strength and the sealing ability of Clearfil SE Bond bonded to dentin.  On the contrary, bond strength values obtained in bur-prepared samples were similar to Er:YAG laser values in terms of initial periods of evaluation.  Because of different experimental conditions, various results might be available.
There are many factors affecting bond of resin to tooth substrates. The conditions of laser irradiation were very effective, such as wavelength, pulse duration, irradiation time, power density, amount of water and air stream, distance between tooth and tip, free-hand versus uniform irradiation.  Other conditions can be also listed as follows, that is, methods of bond tests (shear bond test ,, vs. tensile bond test , vs. microtensile bond test), ,,, enamel versus dentin, sound dentin versus caries affected dentin, adhesive materials, with and without pulpal pressure,  superficial dentin versus deep dentin,  with/without thermal stress and long-term storage.  Bond strength is strongly related with the occurrence of marginal microleakage and adaptation of cavity wall and restored material. The adhesive resin used in present study is considered to be one of the best materials.
Marginal microleakage of the restoration induces recurrent caries. Improved marginal integrity and adaptation of the resin-cavity interface are essential for the prevention of recurrent caries.  In this study, small enamel cracks were detected around interface between enamel and composite resin. The cavosurface margins were located in the enamel, which is brittle. If the bonding is strong enough, the shrinkage stress may lead to crack initiation and propagation within the bonded substrate. Tooth fracture is still a frequently occurring problem caused by induced contraction stresses when the polymerization shrinkage takes place under constrained conditions with the composite bonded between cavity walls. ,,
Adaptation at the resin-cavity interface has often been investigated for in vitro evaluation of the restorative materials and techniques as well as bond strength. Although microleakage evaluation is one of the most common methods for assessing the sealing efficiency of restorative materials, a gold standard has not been established for this method yet.  In this study, surface and crosscut surface of the restoration were observed by a digital microscope. ,
In this study, irradiation with Er:YAG laser caused less enamel cracks and gap formation than rotary cutting instrumentation. Statistical differences were not found between the irradiation with the lower output energy and the higher one for enamel cracks and gap formation. It was concluded that the preparation by Er:YAG laser at suitable frequency with energy when kept constant showed the better marginal integrity of resin composite restorations than that by a rotary cutting instrument.
| Conclusion|| |
- Within the limitations of study
- The preparation by Er:YAG laser at frequency 10 Hz showed better marginal integrity of resin composite restoration
- Laser group showed better cavity preparation than that with rotary carbide bur
- In the laser group at frequency 10 Hz showed better marginal integrity than the group used at frequency 15 and 20 Hz.
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