Dental Tribune United Kingdom Edition

‘Nowadays the laser devices available for clinical use are capable for effective and controlled ablation of hard dental tissues’ February 14-20, 201126 United Kingdom EditionClinical a dessicator. Dried specimens are fixed on metal stand and covered with gold layer (200- 250nm) by cathode atomisa- tion under vacuum. Scanning microscopy is performed with the electron microscope of Philips (Holland) 515 model SEM with accelerating voltage of 25kV in secondary emission mode. On each specimen were made re- spectively five pictures with the same magnification (x2000) of randomly chosen areas and dif- ferent numbers of photos with other magnification. On SEM photos are rated, described and compared mor- phological findings and differ- ences in enamel and dentin tissues after treating with alter- native methods for caries remov- al and cavity preparation. Results Cavity forms prepared with Er:YAG laser (Group 1) are characterised by a lack of defi- nite and precise geometric con- figuration and outlined cav- ity elements. There is rough and irregular surface with- out presence of smear layer (Fig 2 a). Dentinal tubules orific- es are clearly exposed. Intertubul dentin is ablated more than peritubular dentin and that made dentinal tubules appear- ance more prominent (Fig 3 b). Laser ablation changes enamel and the surfaces appeared strong retentive (Fig 2 c). In Group 2 (preparation with diamond burs, air turbine and water cooling) a thin, smooth and in some places missing smear layer was observed (Fig 3 a). In the area of water turbu- lence marked dentinal tubules orifices can be seen, but without having a clear outline of both tubules lumens and peri-and in- tertubular dentin (Fig 3 b). The boundary between enamel and dentin is unclear and the cavity forms heve smooth contours. When analysing the SEM photomicrographies of the specimens examined, it is found that the conventional meth- od of cavity preparation with steel burs and micromotor at low speed without water cool- ing (Group 3) leaves contami- nated surface covered with smear layer of dentin debris without visible dentinal tubules orifices. (Fig 4 a, b). Thick smear layer covers all treated surfaces. The walls of the cavities are smooth and rounded and the border between enamel and den- tin is not perceptible. Discussion The philosophy of minimally invasive cavity preparation ap- proach is based on several main principles – to remove only irre- versibly damaged dental tissues and to avoid macroretention preparation in healthy tissues.1 Additionally these techniques should protect the underlying pulp and to leave the treated surface suitable for adhesive bonding.1 Antibacterial effects of the alternative preparation techniques must not be lower than those of standard necroto- my with rotary instruments and even to excel them.1 Nowadays the laser devices available for clinical use are ca- pable for effective and controlled ablation of hard dental tissues;2 however, not all researchers agree with these conclusions. Therefore, such studies should be periodically updated due to constant introduction of new technologies. The experimental results of the presented study revealed significant differences in the surface morphology of the studied samples, which would affect the ability to perform ef- fective adhesive bonding. These morphological differences are highly dependent on the mecha- nism of action of the used prepa- ration systems. Laser devices use a vari- ety of physical media as sources for generating different wave- length that is absorbed and in- teract with specific molecules in human tissues. The explana- tion for the hard tissue ablation is the water content that evapo- rates when exposed on laser radiation creating high internal pressure and subsequent mi- croexplosions. In this interac- tion of laser radiation with tis- sue if inadequate water cooling occurred, that will lead to un- desirable thermal effects.3 De- pending on parameters such as pulse energy and frequency CO2 lasers, Nd: YAG and Er: YAG lasers cause changes in enamel and dentin as roughing, cra- ters, cracking, slicing, carboni- fication, melting and recrys- tallisation described in many previous studies.4, 5, 6 These changes depend on the laser type, mode of operation, system for water cooling and proper operation.3 Additionally, the opportunities to ablate cari- ous dentin and enamel strong- ly vary according to different experimental studies. 4, 5, 6 For argon-fluoride laser (ARF) and the excimer laser there are data on their ability to remove dental caries, which is not of suf- ficient efficiency.5 Krypton fluo- ride excimer laser emitting in ul- traviolet range has been shown to remove dentin, but enamel resists the attempt for ablation.5 Used in this experimental study, LiteTouch Er:YAG laser incorporates special software, which allows for the broadest range of energy and frequency settings. The unique LiteTouch optical system incorporated in the ergonomic hand piece pre- vents loss of energy and along with the precision control over pulse duration, pulse energy and repetition rate optimise, al- lows for a wide range of hard tissues procedures. Another characteristic of this laser is the wavelength (2940nm) which is absorbed mostly by the water and also sapphire tips, show- ing stability in providing fo- cused energy of laser radiation.8 The mechanism of LiteTouch action is based on interaction be- tween laser radiation and hard tissues incorporated water that results in microexplosions. It is believed that this process is the mechanism of ablating particles from dental tissues without over- heating, and without smear layer formation.7 This combination al- lows precise microinvasive cav- ity preparation with minimal heating and optimal rate of radi- ation absorption by the hydroxy- lapatite incorporated water.7 The program “hard tissue mode” removes enamel, dentin and dental caries effectively and without visible carbonisation or disturbance of the dental micro- structure. Evaluated under SEM the dental tissues treated with Er: YAG laser showed rough and irregular surface without pres- ence of smear layer, open denti- nal tubules orifeces were found as well. Intertubular dentin is ablated more than peritubular giving a characteristic appear- ance of the dentinal surface with mild prominent dentinal tubules. Enamel shows preserved pris- matic structure, but also strong retentions due to microexplo- sions on its surface. Overall the cavity form is irregular, devoid of strict geometry and dotted with microretentions, but with- out presence of contaminants or smear layer. The observed changes correspond to changes in hard dental tissues reported by other authors in previous studies page 25DTß Figs 1 a, b: Laser preparation with Er: YAG laser LiteTouch (Syneron, Israel) “Hard tissue mode” (400mJ/20Hz; 8.00W) 1a 1b