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ePaper created 2017-03-17, 12:41:55 | version 1.38.0
research | Fig. 2: Irradiation effect by absorp- tion of the Er:YAG laser energy in hydroxyapatite in dentine. After 10 s of irradiation with no water at 25 Hz, dentine will be carbonised even with an applied fluence of only 20 J/cm2. A tooth irradiated for 10 s with a fluence of ~ 60 J/cm2 becomes very hot, quite warm at ~ 40 J/cm2 and still warm at ~ 20 J/cm2. In enamel there is less ablation but a strong heating. Fig. 3: A “hot spot” at the fibre end of the diode laser is black burned tissue. Energies emitted with such a fibre end would bring the contrary desired therapeutic effect. laser 1 2017 07 Fig. 2 Fig. 3 creates a strong subsurface pressure and leads to an explosive removal of the surrounding mineral.24,25 The removal of hard tissue is done by micro-explo- sions far below the melting point of these tissues. If water does not cover the irradiated surface of bone or teeth, e.g. when the dentist’s assistant sucks off the water spray during cavity preparation, the tissue water of the hard substances would be consumed by absorption very fast and the absorption takes place in the secondary absorber, the hydroxyapatite, which leads immediately to a strong overheating.26 The clinical effect is carbonisation of the irradiated tissue (Fig. 2). The chromophores that an Er:YAG or Er,Cr:YSGG laser in a periodontal pocket can identify are water or hydroxyapatite (Fig. 1). The laser user executing a closed curettage by such a laser has to avoid any absorption in hydroxyapatite. Therefore, the tissue water in the pocket must be sufficient to provide an absorption of the energy solely in water. Calculus removal in a closed subgingival situation working with an Er:YAG laser must obey the same bio- physical background. The water content of calculus27 is similar to fresh dentin. Therefore the ablation threshold for both materials must be close together. If big masses of subgingival calculus should be re- moved only by an Er:YAG or Er,Cr:YSGG laser, working efficiently demands high energy densities. The risk to remove healthy subgingival dentin by a wrong angu- lation of the laser tip towards dentin or a too high en- ergy (180 mJ) then is very high.28 In safety guidelines for laser removal of dental calculus29 the Japanese society for laser dentistry recommends that the laser tip should be parallel30,31 to the root surface and the applied laser energy be about 40 mJ. Er:YAG and Er,Cr:YSGG lasers are suitable tools for working in the subgingival periodontal area because of its biophysical background. Ablation of soft and hard subgingival deposits without any pathological thermal side effects is possible, bactericidal ef- fects18–20 with energy densities far below 10 J/cm2 are given, bone healing is stimulated21, and no discomfort for the patients after treatment is to be expected. The most important thing for closed working in very deep pockets of 10 mm and more with these wavelengths is to avoid any absorption of the laser energy in hy- droxyapatite. There are many authors32–35 working in a closed subgingival setting with Er:YAG lasers and power settings of 160 mJ, 10 Hz and energy densities of 20 J/cm2 and more. But it is obvious that the higher the applied energies and the deeper the periodontal pockets are, the greater is the risk of causing damage in the hydroxyapatite-containing tissues like alveolar bone or root dentine because of absorption of the laser energy in the secondary absorber. To minimise this risk, we present seven cases working with the Er:YAG laser with energy densities close above the ab- lation threshold of bone and dentin.36 2. Material and Methods Seven clinical cases, four of women and three of men aged between 48 and 74 years are presented. Eight periodontal pockets larger than 9 mm were treated with pocket depths between 10 and 12 mm. The tooth mobility degree (TM) of six teeth was 4. Not only was the horizontal mobility measured, but also the vertical mobility. One tooth 33 in case 4 had been already fixed by a crown to the neighbouring tooth and tooth 16 in case 5 had enough stability despite the 11 mm deep pocket. All patients had to pass a strict therapy protocol including: – patient instruction for an adequate oral hygiene, – evaluation and elimination of the pockets’ cause, – splinting the teeth except TM < 3 – conventional pocket therapy with scaling and root planing (SRP) – laser irradiation Laser irradiation includes three wavelengths of = 670 nm, = 810 nm, and = 2,940 nm.