# Long-Term Stability of Er:YAG Laser Non-Surgical Periodontial Treatment
## 2 Materials and Methods  
The study is approved by the Ethics Committee of the Medical University of Plovdiv with protocol No. 3/05.07.2012.  
The study includes 30 patients with generalised moderate chronic periodontitis (which corresponds to Stage II and partially Stage III periodontitis according to the last classification) who visited the Department of Periodontology and Oral Mucosal Diseases of Medical University--Plovdiv, Bulgaria, in the period July 2012-February 2014 [18; 19]. Inclusion criteria are at least 2 teeth per quadrant with a probing depth between 3.6 mm and 6.4 mm (measured with periodontal probe); loss of clinical attachment up to 4 mm; bleeding on probing; no periodontal treatment in the last 12 months; no antibiotic intake in the last 6 months; and no systemic diseases or systemic intake of drugs that could affect the course of the disease or pregnancy. Included in the study are 451 teeth (1099 periodontal pockets). Patients are examined using Florida probe (Florida Probe Corporation, Gainesville, FL, USA) and probing pocket depth (PPD, as distance between the gingival margin and the depth of the pocket), gingival recession (GR, as distance between the cemento-enamel junction and gingival margin), clinical attachment level (CAL, as distance between cemento-enamel junction and depth of the pocket), bleeding on probing (BOP in %) and full mouth plaque score (FMPS in %) are included in the periodontal chart. After removing the supragingival calculus with the ultrasonic device Piezoon Master 400 (EMS Electro Medical Systems SA, Nyon, Switzerland) and supragingival tip--A, patients are treated subgingivally on the principle of split mouth design where 217 teeth (527 periodontal pockets) are allocated in the control manual instrumentation group (control group) and 234 teeth (572 periodontal pockets) in the test Er:YAG laser instrumentation group (laser group). Supra- and subgingival instrumentation was performed within 24 h on the principle of full mouth disinfection [20]. In the control group--C, subgingival scaling and root planing is performed with hand instruments--Gracey-curettes (Hu-Friedy Co., Chicago, IL, USA)--until clean and smooth root surfaces are achieved. In the test group--laser group, subgingival instrumentation is performed with an Er:YAG laser (Lite Touch, Light Instruments Ltd., Yokneam, Israel) with chisel type \(\times\) 17 mm/hard tissue mode/contact mode/energy 100 mJ/pulse frequency 15 Hz/water cooling level 6; and pocket debridement--with tip with diameter \(\times\) length--0.6 \(\times\) 17 mm/soft tissue mode/non-contact/energy 50 mJ/pulse frequency 30 Hz/water cooling level 6. Follow-up examination to register PPD, GR, CAL, BOP and FMPS is performed at 1, 3, 6 and 12 months after treatment.  
The statistical analysis is performed with SPSS for Windows, version 17 (SPSS Inc., Chicago, IL, USA). Data are presented as mean \(\pm\) 5x (SD). Independent samples \(t\) tests are used for comparison of the clinical variables (PPD, GR, CAL). Chi-square test is used for analysis bleeding on probing and plaque presence. Differences are considered statistically significant when the \(p\) value is <0.05.  
The null hypothesis is that the Er:YAG laser does not have better effectiveness in nonsurgical periodontal therapy neither immediately after treatment nor in long-term observations in comparison to the conventional treatment.