periodontal diseases ( pds ) constitute a series of infections caused by the 
 microorganisms that colonize sites at or below the gingival margin . these infections 
 commonly lead to periodontal inflammation and often result in the destruction of the 
 supportive periodontal tissues . the organisms that cause these diseases reside in 
 unique structures termed biofilms that offer partial protection to the colonizing 
 organisms from the defense mechanisms of the host , as well as from the 
 antimicrobials used for treatment . the 
 primary goal of conventional periodontal therapy is the alteration of subgingival 
 biofilms present on periodontally diseased sites that could be associated with the 
 progressive destruction of the supportive periodontal tissues . it is well documented that mechanical therapy combined with 
 oral hygiene instruction is effective in achieving this goal . comparisons between 
 manual and power - driven approaches to plaque and calculus removal and their effects 
 on clinical outcomes show that both are equally effective . over the last 3 decades , locally delivered , anti - infective pharmacological agents 
 have been employed in attempts to treat local bacterial infections associated with 
 gingivitis and periodontitis . techniques of the local anti - infective therapy with 
 pharmacological agents have varied widely , both in the methods of drug delivery and 
 in the pharmacological agents employed . drug delivery methods initially included 
 oral rinses , then irrigation devices , followed by subgingival irrigation using 
 syringes or powered irrigation devices . more recently , drug delivery has involved 
 the incorporation of anti - infective drugs in sustained - release vehicles enabling 
 subgingival administration of the drug . these sustained - release vehicles overcome 
 many of the problems inherent in other drug delivery methods , such as rinsing or 
 irrigation . these systems exhibit 
 shortcomings including inadequate or unpredictable penetration of the periodontal 
 pocket by the drug , rapid clearance of the drug from the pocket resulting in 
 inadequate time of the exposure of subgingival bacteria to the drug and poor patient 
 compliance . local anti - infective therapy has also employed an eclectic variety 
 of pharmacological agents from topical antiseptics to broad - spectrum antimicrobials . chlorhexidine , tetracycline , minocycline , metronidazole , doxycycline , as well as 
 other antimicrobials and antiseptics have been used in several forms . two systematic 
 reviews with the meta - analysis of data   from studies evaluating the 
 effect of locally delivered antimicrobials as an adjunctive therapy to scaling and 
 root planing ( srp ) revealed evidence of improved clinical outcomes in terms of the 
 greater pd reduction and/or clinical attachment gain compared to srp alone . this was 
 particularly true with the use of tetracyclines , although the clinical significance 
 remains questionable . the aim of the present study was to compare the clinical and microbiological effects 
 of scaling and root planing with hand instruments to a non - surgical treatment with 
 the use of an ultrasonic device combined with the application of locally delivered 
 doxycycline . the subjects for the present cohort study were recruited from the postgraduate clinic 
 of the department of preventive dentistry , periodontology and implant biology , 
 school of dentistry , aristotle university of thessaloniki , greece between september 
 2004 and march 2005 . the ethical committee of the school of dentistry of aristotle 
 university of thessaloniki , greece approved the study protocol and all participating 
 patients signed an informed consent at the beginning of the study . the patients ( n = 20 ) comprising the control group were the same as in our previous 
 study . another twenty adult patients 
 with generalised advanced chronic periodontitis   were recruited for the study following a screening examination of 28 
 patients by one examiner ( i.v . ) , which included full mouth probing and radiographic 
 examination , in order to comprise the control group . the inclusion and exclusion 
 criteria were as follows : ( i ) subjects must be adults between 18 and 70 years of age . ( ii ) subjects must have at least 4 sites with initial probing pocket depth ( ppd ) 
  5 mm in at least 2 quadrants , demonstrating bleeding on probing . ( iii ) subjects must not have received any periodontal treatment during the previous 6 
 months . clinical examinations were performed at the screening examination , 3 and 6 months 
 after treatment and involved assessment of ppd , clinical attachment level ( cal ) , 
 gingival bleeding index ( gbi )   and plaque 
 index . the measurements of ppd and cal 
 were performed at six sites per tooth with a manual periodontal probe ( hu - friedy 
 pcp - unc 15 , hu - friedy , chicago , il , usa ) to the nearest millimetre . prior to the 
 study , the intra - examiner variability test was carried out to assess the accuracy of 
 examiner 's measurements . in order to assure the reproducibility of 
 measurements , all recordings regarding ppd and cal were repeated after a period of 
 30 minutes . in the event of a difference of > 2 mm between the two measurements , the mean of pair of the 
 two closer measurements was evaluated for further analysis . the patients fulfilling the necessary prerequisites were assigned into 2 groups of 20 
 patients each : control group ( scaling and root planing with hand instruments - srp ) 
 and experimental group ( ultrasonic debridement + doxycycline - ud + doxy ) . at all 
 time points , the outcomes of research were assessed blind and the examiner ( i.v . ) , k.p . ) who were 
 also unaware of the treatment that the patient had received ( coded samples ) . experimental design and treatment procedures at the screening examination , a full mouth measurements of clinical parameters were 
 recorded and intraoral radiographs were taken . after a period of 1 week ( baseline 
 examination ) , subgingival plaque samples were taken from 6 preselected sites from 
 each patient . the sites were selected according to their initial probing depth and 
 were divided in 3 categories : ( i ) 2 sites with ppd  4 mm ( shallow pockets ) , 
 ( ii ) 2 sites with ppd > 4 to  6 mm ( moderate pockets ) and ( iii ) 2 sites 
 with ppd > 6 mm ( deep pockets ) . no furcation , endo - periodontic defects or third 
 molars were included in the study material . microbiological sampling at the same 
 sites , as at the baseline examination , and a full mouth clinical recordings were 
 repeated at 3 and 6 months after the baseline . at the same session , supragingival scaling was performed with hand instruments and 
 ultrasonics , and oral hygiene instructions ( ohi ) were given by the examiner . the ohi 
 included twice - daily tooth brushing , using the modified bass technique , and 
 once - daily inter - dental cleaning with inter - dental brushes . at the next appointment , 
 two weeks after the baseline examination , the allocated intervention was 
 initiated . hand instrumentation of the whole 
 dentition was performed at weekly intervals in three to four sessions by using 
 gracey curettes under the local anaesthesia ( sg 3/4 , 11/12 , 13/14 and after five 
 curettes sas 3/4 , 11/12 , 13/14 , hu - friedy pcp - unc 15 , hu - friedy , chicago , il , 
 usa ) . patients of the experimental group received debridement of whole dentition in 3 - 4 
 sessions , under the local anaesthesia , at weekly intervals , utilizing a 
 piezoelectric ultrasonic device ( ems piezon , ems , nyon , switzerland ) with a and p 
 instruments ( swiss instrumentspm , ems , nyon , switzerland ) under water irrigation . the 
 teeth were treated until a smooth , appropriately debrided surface was achieved . in 
 the four deeper , preselected pockets 8.8% doxycycline gel ( atridoxtm , atrix 
 laboratories , inc . , collins , co , usa ) was applied at the completion of therapy 
 and after the first re - examination at 3 months . in both groups the endpoint of the smoothness was judged by the supervisor ( i.v . ) , 
 who decided upon the completion of root instrumentation by using a periodontal probe 
 ( hu - friedy pcp 11 , hu - friedy , chicago , il , usa ) and an explorer ( hu - friedy 
 wilkins - tufts 17/23 , hu - friedy , chicago , il , usa ) . collins , co , usa ) is a 
 subgingival controlled - release product composed of a two syringe mixing system . syringe a contains 450 mg of the atrigel delivery system , which is a bioabsorbable , 
 low viscosity polymeric formulation composed of 36.7% poly(dl - lactide ) ( pla ) 
 dissolved in a biocompatible carrier of 63.3% n - methyl-2-pyrrolidone ( nmp ) . the 
 product , when mixed , is a pale yellow , viscous liquid with a concentration of 8.8% 
 doxycycline hyclate . the two syringes are coupled together mixing the two components 
 for 100 cycles . by the use of 23-gauge cannula attached to the delivery system the 
 test product was slowly introduced into the periodontal pocket , starting from the 
 base of pocket , until it reached the gingival margin . following withdrawal of the 
 cannula tip , a curette was used to pack any overflow of the drug down into the 
 pocket . no periodontal dressing or adhesive was used . upon contact with the 
 crevicular fluid , the liquid product solidifies and the patients were instructed not to perform 
 oral hygiene measures at the treated areas for 1 week . microbiological evaluation after the isolation with cotton rolls , drying and removal of supragingival plaque , 
 the subgingival samples were taken with a sterile gracey curette ( hu - friedy , 
 chicago , il , usa ) , were subsequently placed individually in 200 l of te buffer 
 ( tris hcl 10 mm , edta 1 mm , ph = 7.5 ) and stored after the treatment with an alkali 
 solution ( 0.5 m naoh ) at - 4 oc . the microbiological samples were evaluated separately for 3 bacterial species using 
 the " checkerboard " dna - dna hybridisation technique as described by 
 socransky et al . . the subgingival 
 species used for development of digoxigenin - labelled whole genomic probes were 
 porphyromonas gingivalis ( fdc 381 ) , tannerella forsythia ( fdc 338 ) and treponema 
 denticola ( td1 ) . the primary analysis was " per protocol "   and included all patients who attended the final 
 examination . data were entered into an excel sheet database ( ms office excel 2000 ; 
 microsoft corporation , redmond , wa , usa ) . mean and standard error of the mean ( sem ) 
 were calculated for every parameter . levene 's test for the quality of error 
 variance was applied in order to check the homogeneity of clinical parameters at the 
 baseline . the analysis was made for plaque index , gbi , ppd and cal based on full 
 mouth measurements ( the third molars were not included ) . a further analysis was 
 performed for ppd and cal for the three different categories , according to the 
 initial pocket depth . the first category comprised pockets with initial pocket depth 
 lesser or equal to 4 mm , the second pockets with initial pocket depth > 4 to 
  6 mm and the third pockets with pocket depth greater than 6 mm . bacterial species were quantified following the formation of reference curve , which 
 allowed the conversion of chemiluscent signals to total bacterial counts ( total lab 
 v2005 , nonlinear dynamics ltd , newcastle upon tyne , uk ) . the homogeneity of two 
 groups at the baseline for microbiological parameters was checked using the 
 mann - whitney test . averaged bacterial scores from each subject were averaged for 
 each group and compared at all time - points . a further comparison at the three 
 examinations was made for the sites with initial ppd > 4 mm ( moderate and deep 
 pockets ) , which were those that received the drug in the control group . the differences over time within groups for both clinical and microbiological results 
 were analysed with the non - parametric test wilcoxon signed ranks . the comparison 
 between control and control group was performed using the mann - whitney test . all statistical analysis was carried 
 out with the aid of statistical software ( spss version 12.0 , spss inc . , at the baseline examination 40 patients entered the study ( 20 in the srp group , 20 in 
 the ud + doxy group ) , from which 33 subjects completed the 6 month protocol ( 16 in 
 the srp group , 17 in the ud + doxy group , mean age 50.46 , range 37 - 69 years ) . four 
 patients did not return for any re - examination , while another three did not attend 
 the final examination . one patient moved , three patients started work , preventing 
 visits to the clinic and the other three were unwilling to finish the study for 
 personal reasons . the flowchart of the patients is illustrated in figure 1 and the characteristics of the patient 
 sample that completed the study are summarised in table 1 . the initial statistical analysis revealed no statistical 
 differences between the two groups at the baseline examination . the intra - examiner 
 variability test demonstrated that the reproducibility of the measurements of ppd 
 and cal within  1 mm was 90% . epidemiological characteristics of the patient sample ( mean  sem , per 
 protocol analysis ) ppd = probing pocket depth ; cal = clinical attachment level . an average of 69.1% of all pockets in the srp group and 71.5% in the ud + doxy group 
 had initially ppd  4 mm . at the 6 
 month examination in the srp group the shallow pockets represented 84.9% , the 
 moderate pockets 11.3% and the deep pockets only 3.8% of all pockets . in the ud + 
 doxy group the oral hygiene status , as assessed by the plaque index , during the course of study 
 is shown in table 2 . at the baseline the mean 
 full - mouth plaque scores were 88% in the srp group and 81% in the ud + doxy group . a 
 statistically significant decrease to 26% in the control group and to 37% in the 
 control group was recorded at the 6 month examination ( wilcoxon signed ranks test , p 
 < 0.05 ) . no statistically significant differences were observed between the two 
 groups at any interval ( mann - whitney test , p > 0.05 ) . mean plaque index and gingival bleeding index scores ( mean  sem [ mm ] ) at 
 different examination intervals for control and experimental group 
 patients statistically significant difference from baseline ( wilcoxon 
 signed ranks test , p < 0.05 ) . gingival bleeding index ( gbi ) a statistically significant reduction in gbi scores was observed in both treatment 
 groups following treatment . gbi indices also the improved following a similar 
 pattern in both groups ; at the 6 month re - examination the gbi was reduced from 59% 
 to 33% in the srp group and from 61% to 32% in the ud + doxy group ( wilcoxon signed 
 ranks test , p < 0.05 , table 2 ) . no 
 statistically significant difference in gbi between the two groups was observed at 
 any examination interval ( mann - whitney test , p > 0.05 ) . probing pocket depth ( ppd ) changes in the ppd are presented in table 3 . a marked mean ppd reduction was observed 
 for both treatment modalities at the 3 month re - examination ( 0.88 mm for the srp and 
 0.94 mm for the ud + doxy group , wilcoxon signed ranks test , p < 0.05 ) . during 
 the following observation period ( 3 to 6 month examination ) no statistically significant differences were observed between the two groups 
 at any interval ( mann - whitney test , p > 0.05 ) . the ppd measurements were further analysed for the three different categories of 
 initial pocket depth . for the shallow ( ppd  4 mm ) , the moderate ( > 4 to 
  6 mm ) and the deep pockets ( ppd > 6 mm ) the results are presented in 
 table 3 . in the deep pockets an 
 additional , statistically significant reduction was observed in ppd between 3 and 6 
 months in the experimental group ( wilcoxon signed ranks test , p < 0.05 , table 3 ) . probing pocket depth ( ppd ) scores for the various ppd categories at 
 different examination intervals for control and experimental group 
 patients statistically significant difference from baseline ( wilcoxon 
 signed ranks test , p < 0.05 ) . statistically significant difference from 3 months ( wilcoxon 
 signed ranks test , p < 0.05 ) . no statistically significant differences were observed 
 between groups ( mann - whitney test , p > 0.05 ) . clinical attachment level ( cal ) a statistically significant improvement of cal was revealed for both groups at the 3 
 month examination ( 0.50 mm for the srp group and 0.46 mm for the ud + doxy group 
 respectively , wilcoxon signed ranks test , p < 0.05 , table 4 ) . statistically significant differences between the two groups 
 were not recorded at any interval ( mann - whitney test , p > 0.05 ) . in the srp group the 6 month result remained significantly better compared to the baseline score 
 ( wilcoxon signed ranks test , p < 0.05 ) , whereas in the ud + doxy group the mean 
 cal score did not demonstrate a significant difference in comparison with the 
 baseline value ( wilcoxon signed ranks test , p > 0.05 ) . clinical attachment level scores for the various probing pocket depth 
 categories at different examination intervals for control and experimental 
 group patients statistically significant difference from baseline ( wilcoxon 
 signed ranks test , p < 0.05 ) . no statistically significant differences were observed 
 between groups ( mann - whitney test , p > 0.05 ) . a similar analysis as for the ppd measurements was made for the cal measurements as 
 well . the results for the shallow , moderate and deep pockets are shown in table 4 . the differences between 3 and 6 month 
 re - examinations and the baseline examination were statistically significant for the 
 two groups ( wilcoxon signed ranks test , p < 0.05 ) , whereas no statistically 
 significant , inter - group differences were observed ( mann - whitney test , p > 
 0.05 ) . the results for all the 
 investigated species and for all of the six sites per patient are summarised in 
 table 5 . at the 3 month of examination , this decrease was statistically 
 significant only for porphyromonas gingivalis ( wilcoxon signed ranks test , p < 
 0.05 ) . at the 6 month re - examination , a statistically significant difference with 
 baseline was observed in the experimental group for the treponema denticola 
 ( wilcoxon signed ranks test , p < 0.05 ) , attributable to a further reduction in 
 numbers of this species between the re - examinations . no statistically significant 
 differences were found between the two groups at any time interval ( mann - whitney 
 test , p > 0.05 ) . mean numbers ( x105 , mean  sem ) of the 3 microorganisms ' species 
 tested in various initial probing pocket depths at different examination 
 intervals statistically significant difference from baseline ( wilcoxon 
 signed ranks test , p < 0.05 ) . pg = porphyromonas gingivalis ; tf = tannerella forsythia ; td = 
 treponema denticola . the frequency distribution revealed an increase in the percentage of sites with less 
 or equal to 105 microorganisms for porphyromonas gingivalis , tannerella forsythia 
 and treponema denticola and a subsequent decrease in the percentage of sites with 
 more than 105 microorganisms ( table 6 ) . frequency distribution ( % ) of sites depending on various microorganisms 
 species concentration tested at different examination intervals pg = porphyromonas gingivalis ; tf = tannerella forsythia ; td = 
 treponema denticola . the results of further analysis that was performed for the sites that had initial ppd 
 > 4 mm , are presented in table 5 . a 
 statistically significant decrease was found for porphyromonas gingivalis in both 
 groups at the 3 month examination ( wilcoxon signed ranks test , p < 0.05 ) . no 
 statistically significant differences were found between the two groups at any time 
 interval ( mann - whitney test , p > 0.05 ) . the findings of the present study indicate that the adjunctive use of doxycycline 
 failed to significantly improve the therapeutic outcome of mechanical treatment . in 
 a previous study , the hand instruments 
 were compared to the ultrasonics in the treatment of chronic periodontitis , but no 
 difference was found between the two treatment modalities . the addition of locally 
 delivered doxycycline in the treatment protocol of present study did not seem to 
 offer any beneficial effect to the patients treated with ultrasonic debridement in 
 comparison to the conventional hand instrumentation alone . a marked reduction in every clinical parameter was observed for both treatment 
 modalities in this study . overall a statistically significant mean reduction in ppd 
 of 0.88 mm and a mean cal gain of 0.59 mm was recorded for the srp group . the 
 corresponding values for the ud + doxy group were 0.92 mm and 0.31 mm . cal scores at 
 the 6 month re - examination did not show a statistically significant difference 
 compared to baseline scores in the experimental group . in the deep pockets an 
 additional , statistically significant , reduction was observed in ppd between 3 and 6 
 months . this could be explained by the fact that the test drug was applied to 
 only 4 pre - selected pockets and therefore it would be very difficult to provide a 
 true clinical benefit as the measurements were performed for the whole 
 dentition . the question of whether the adjunctive use of locally delivered antimicrobials to 
 mechanical treatment offers an improved clinical and microbiological outcome over 
 srp alone remains unanswered . a number of studies have reported only limited 
 improvement of cal and ppd recordings when comparing the combined treatment protocol 
 ( srp plus locally delivered antimicrobials ) to conventional mechanical treatment 
 alone [ 17 - 20 ] . generally a ppd reduction of 1 - 1.5 mm in moderate pockets ( 4 - 6 mm of initial ppd ) 
 and of 2 - 2.5 mm in deeper sites has to be expected after mechanical root 
 instrumentation [ 21 - 26 ] . this occurs concomitantly with a cal gain of approximately 
 0.5 mm and 1.5 mm in the moderate and the deep pockets respectively . any additional 
 pocket reduction or cal gain , following the administration of the drug , would 
 therefore represent a true clinical benefit and hence may reduce the need for 
 additional periodontal surgery . previously published studies referring on the utilization of locally delivered 
 doxycycline polymer focused on its effects when used as a monotherapy . comparable 
 efficacy of the 2 treatments in the terms of reduction in pocket depth and gain in 
 clinical attachment level was reported in two parallel multicenter studies comparing 
 the locally delivered doxycycline to the srp alone . in another multicenter study , heijl et al .   using a split mouth design , 
 observed changes in probing depth comparable to this study for each treatment . the 
 difference between the responses to scaling alone and scaling combined with 
 tetracycline fibers were small and not statistically significant . in a systematic 
 review , the reviewers generally found 
 modest differences for ppd favouring the combined treatment . these , even when 
 statistically significant , ranged from 0.1 mm to 0.5 mm , and were of little clinical 
 importance . effects for cal gains were smaller and statistical significance was less 
 common . in very accurately designed study two 
 different approaches were evaluated for the non - surgical treatment of moderate 
 periodontal pockets . traditional srp was compared to ultrasonic debridement followed 
 by 8.5% doxycycline hyclate administration in sites deeper than 5 mm . at the 3 month 
 examination better results regarding ppd and cal were observed in the ultrasonic 
 debridement group than in the srp group . a retreatment of non - responding sites ( ppd 
 > 5 mm ) consisting of ultrasonic debridement combined with doxycycline 
 application in the srp group at this time point lead to a similar clinical outcome 
 for both groups 6 months after baseline . taking into account the reduced time needed 
 for ultrasonic treatment the authors concluded that simplified , subgingival 
 debridement in conjuction with doxycycline application could be a justified approach 
 for deeper periodontal pockets . although , in the present study the time required for the instrumentation was not 
 specifically recorded , the therapists felt that ultrasonic debridement was less time 
 consuming than hand instrumentation . the patient - centered outcome variables , like 
 reduced treatment time , are considered of importance in the evaluation of treatment 
 outcome today . simplified , less time and effort demanding procedures like ultrasonic 
 debridement combined with locally delivered antimicrobials , i.e. doxycycline 
 hyclate , could represent a reliable alternative in treating moderate periodontal 
 pockets or can be an option for patients where a surgical intervention is not 
 indicated . in this respect the findings of the present study are in accordance with 
 those of the wennstrom et al . adjunct use of the locally delivered drugs seems to have a beneficial effect in 
 smokers and in retreatment of the patients with persisting periodontal pockets . the 
 adjunctive use of locally delivered doxycycline in smokers may offer some benefit 
 for the active and supportive periodontal treatment in both clinical 
 and microbiological findings . initial studies on maintenance patients 
 have shown that the local application of tetracyclines seems to offer improved 
 results [ 19 - 34 ] , although more recent data failed to support those findings . 
 in accordance with that , tomasi et al . 
 concluded that locally delivered doxycycline failed to improve the healing outcome 
 following the re - instrumentation with a piezo - ceramic ultrasonic device of 
 periodontal pockets with post - therapeutic depth greater or equal to 5 mm . at the 3 month re - examination both therapeutic approaches resulted in a statistically 
 significant reduction of the number of porphyromonas gingivalis only . a profound , yet not statistically significant , reduction was observed for tannerella forsythia 
 and treponema denticola as well , but in no case was eradication of the 
 periopathogenic species found . following the administration of drug , an adjunct 
 effect of doxycycline on the presence of treponema denticola no statistically significant differences were observed between 
 the two groups regarding the microbiological parameters . the findings are in 
 accordance with earlier studies comparing scaling and root planing alone with 
 scaling and root planing followed by the application of locally delivered drugs in 
 initial   and supportive periodontal treatment . in contrast , goodson et al .   in a large , multicenter trial showed a greater reduction in 
 the numbers and proportions of red complex bacteria following the adjunctive use of 
 minocycline microspheres . in order to be effective antimicrobials must reach their target site and be 
 maintained there in sufficient concentrations long enough for their antimicrobial 
 effect to occur . the concentration 
 required for efficacy is often estimated from the minimum inhibitory concentration 
 ( mic ) , although this has substantial shortcomings ; in particular , the fact that mic 
 is assessed in vitro whereas the drug is active in vivo in a constantly changing 
 host environment . other problems related to estimating effective drug concentrations 
 in vivo are the large number of periodontal subgingival organisms and the large 
 variation in the mics of isolates . 
 defining the minimally effective concentration is complex and most dosages are based 
 on in vitro experiments in which bacteria were grown under planktonic conditions . it 
 is known that bacteria are organized into biofilms when present in the periodontal 
 pocket . these biofilms will probably require a significantly higher concentration of 
 antimicrobial to kill those bacteria where cargill et al .   found that legionellae in biofilms were 135 times more 
 resistant to iodination when compared to microorganisms growing in non - organised or 
 planktonic fashion [ 42 - 44 ] . this is a strong indication that locally delivered 
 antimicrobials should be used adjunctively with mechanical instrumentation to 
 disrupt the biofilms . a concern in the use of antimicrobials in the treatment of chronic periodontitis is 
 the risk for the emergence of an antibiotic - resistant complex of species . this issue 
 in relation to the use of locally applied , sustained - release doxycycline was 
 evaluated in a recent study of walker et al . . it was concluded that doxycycline treatment did not result in a 
 change of actual number of resistant bacteria or in the acquisition of antibiotic 
 resistance . according to the findings of present study the adjunctive use of locally delivered 
 doxycycline did not seem to add any beneficial effect to the active treatment of 
 chronic periodontitis . only in deep pockets an additional improvement was observed 
 between 3 and 6 months in the experimental group , which however was not strong 
 enough to provide a statistically significant difference between the two groups . in 
 conclusion , it is suggested that more long - term studies focusing on the outcome of 
 the combined therapy during supportive periodontal treatment are needed , where more 
 favourable results could be expected , especially in the case of deep pockets .
abstractobjectivesto evaluate the efficacy of locally delivered doxycycline as an adjunct to 
 non - surgical treatment with the use of an ultrasonic device compared to 
 scaling and root planing using hand instruments , by means of clinical and 
 microbiological criteria.material and methodsthirty three patients with chronic periodontitis participated in this cohort 
 study and were divided into two groups . 
 patients in control group received 
 scaling and root planing using hand instruments , whereas patients in control 
 group received ultrasonic debridement and 8.8% doxycycline gel was applied 
 after initial therapy and at 3 months at preselected sites . 
 clinical 
 recordings concerning probing pocket depth , clinical attachment level , 
 plaque index and gingival bleeding index were performed at baseline , 3 and 6 
 months after baseline . 
 subgingival samples were analysed using the 
 " checkerboard " dna - dna hybridisation technique for porphyromonas 
 gingivalis , tannerella forsythia and treponema denticola.resultsboth treatments resulted in significant improvement in all clinical 
 recordings . 
 six months after the treatment a statistically significant 
 decrease was observed for porphyromonas gingivalis in both of groups and 
 treponema denticola in the control group ( p < 0.05 ) . 
 no inter - group 
 differences were observed ( p < 0.05).conclusionsboth treatment modalities provided comparable clinical and microbiological 
 results in the treatment of chronic periodontitis .