Conventional non-surgical periodontal treatment, that is, root debridement using manual and ultrasonic means at baseline and surgery using the same means after 6 months in case of persistent deep pockets (Group 1)/ Er:YAG laser used in a non-surgical approach at baseline and surgery using the same laser after 6 months in case of persistent deep pockets (Group 2)/ Surgery at baseline using manual and ultrasonic means (Group 3). All patients will undergo supragingival maintenance on a yearly basis.

Inclusion Criteria:

• at least 35 years of age
• at least 18 teeth present that can be retained by means of therapy among which 4 multirooted teeth or more(wisdom teeth excluded)
• presence of at least one deep pocket per quadrant (6 mm PPD or more) with radiographic evidence of bone loss (>= 30% of root length)

Exclusion Criteria:

• pregnancy
• removable prosthesis