- Review of Literature for Er,Cr:YSGG lasers in Endodontics
Total elimination of bacteriafrom infected root-canal systems remains the most important objective of endodontic therapy. However, in spite of a plethora of new products and techniques, achieving this objective continues to elude our profession. Historically, endodontic treatment focused on root canal disinfection with “entombment” of remainingbacteria within dentinal tubules and inaccessible areas of the root-canal system.
Although many factors have been implicated in the etiology of endodontic failures, it has become evident that these “entombed” bacteria play a pivotal role in the persistence of endodontic disease (Siqueira et al, 2008). With the introduction of Cone Beam CT, it has been reported that from 30% to 75% of radiographically successful endodontic-treated teeth show signs of Apical Periodontitis when viewed with CBCT (Wu et al, 2009; Estrela et al, 2008)In teeth where reduced size of the existing radiolucency was diagnosed by radiographs and considered to represent periapical healing, enlargement of the lesion was frequently confirmed with CBCT (Wu et al, 2009).
Although impressive results have been obtained in vitro, laser energy alone has not been able to achieve total bacterial kill in extracted teeth. From a clinical perspective, it is apparent that a combination of different treatment modalities will be required in order to eventually be able to sterilize root canal systems. In addition, many clinical obstacles exist that further complicate the clinician’s ability to achieve this goal. These include, but are not limited to: restricted endodontic access, complex root-canal anatomy, limitations of irrigation and instrumentation techniques, inability to entomb bacteria, and the inability to reach and eliminate bacteria deep within the tooth structure.
The erbium, chromium-doped yttrium, scandium, gallium and garnet (Er,Cr:YSGG) laser, operating at a wavelength of 2,780 nm, has been suggested as a valuable toolin endodontics. Since this wavelength is very similar to the absorption maximum of water in hydroxyapatite, photo-ablation occurs where water evaporates instantaneously, thereby ablating the surrounding tissue. Gordon et al (2007)postulated that it was possible to achieve expansion and collapse of intratubular water as deep as 1000μm or more into dentin. This micropulse-induced absorption was capable of producing acoustic waves sufficiently strong to remove smear layer, disrupt biofilm and kill intratubular bacteria. These findings are significant, as bacteria have been identified in dentin at depths of 1100μm, with E. faecalis at depths of 800μm (Kouchi et al, 1980; Haapasalo and Orstavik, 1987). Irrigants such as sodium hypochlorite have a limited effect on these bacteria with penetration depths of only 100μm into dentinal tubules (Berutti et al, 1997).
Smear Layer Removal: Smear layer (SL) removal is considered to be an important requisite of successful endodontic treatment. By increasing dentin permeability,SL removal enhances the penetration of intracanal medicaments and laser energy into dentin. In addition, SL removal facilitates penetration of sealers into the dentinal tubules. Yamada et al (1983) have extolled the virtue of smear layer removal and how it promotes a better apical seal due to sealer penetration into dentinal tubules.
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