although regeneration is the desired outcome of any therapy , it is the most difficult to achieve . in periodontics , regeneration is being achieved using various approaches like guided tissue regeneration ( gtr ) , local application of growth factors / cytokines and host modulating agents etc . if the epithelial cells are excluded from the wound long enough for other cell types with regenerative potential to become established , epithelial down growth is prevented and regeneration achieved . the principle of gtr can also be applied to endodontic defects e.g. , root end surgery . combined endodontic and periodontal lesions present a clinical dilemma to the clinician as the endodontic and periodontal tissues share an embryonic , biologic , and functional interrelationship . teeth with periapical radiolucencies have approximately 2 mm less radiographic attachment in comparison to teeth without periapical radiolucencies . there is an approximate three - fold amplification of the rate of marginal radiographic bone loss ( 0.19 mm / year vs 0.06 mm / year ) for teeth in periodontitis - prone patients with an endodontic infection compared to teeth without an infection . persisting endodontic infection may be regarded as a contributing risk factor for aggravating marginal attachment loss . thomas von arx et al . , in 2001 , proposed a classification of membrane application in endodontic surgery based on typical periradicular lesions . 
 class i a  bone defect confined to periapical region;class i b  periapical bone defect with erosion of lingual cortical plate;class ii a  periapical and concomitant marginal lesions without communication;class ii b  periapical and concomitant marginal lesions with communication;class iii a lateral juxtaradicular lesion ; andclass iii b  lateral juxtaradicular lesion with communication to marginal lesion . class i a  bone defect confined to periapical region ; class i b  periapical bone defect with erosion of lingual cortical plate ; class ii a  periapical and concomitant marginal lesions without communication ; class ii b  periapical and concomitant marginal lesions with communication ; class iii a  lateral juxtaradicular lesion ; and class iii b  lateral juxtaradicular lesion with communication to marginal lesion . class ii b lesions ( apicomarginal communication ) are the most difficult to treat and warrant the use of the gtr principle with the objective of facilitating tissue regeneration by creating an optimum environment ( stable and protected wound ) and excluding non - desired fast proliferating cells which interfere with desired tissue regeneration . a 40-year - old male patient reported to the department of periodontology , bharati vidyapeeth dental college and hospital , pune , with the chief compliant of pain and mobility in lower front teeth since 10 days [ figure 1 ] . his dental history included root canal treatment ( rct ) and porcelain - fused - to - metal ( pfm ) crowns in 31 , 32 , 41 , 42 five years ago . h / o - repeat rct ( one month ago ) , crown lengthening with electrocautery ( 20 days ago ) zirconia crowns ( 10 days ago ) . periodontal findings on examination were bleeding on probing , pockets in 31 , 41 ( 9 - 10 mm ) , 32 , 42 ( 6 - 7 mm ) , mobility - grade iii- 31 , grade ii 41 , 42 , 31 . pre - operative photograph radiographic findings : root canal treated 31 , 32 , 41 , and 42 [ figure 2 ] . pre - operative radiograph widening of periodontal ligament space seen in 32 and 42 regions extending up to apical 1/3 and periapical radiolucency seen [ figure 3 ] . apicoectomies done with 31 , 32 , and 42 regions the case was of communicating endodontic the defect dimensions were approximately 2 cm  1 cm in 31 , 32 , and 41 regions and 5 mm  5 mm in the 42 region . as the defect was of considerable dimensions and the lesion a class ii b with 31 and 41 regions and a class ii a with 32 and 42 regions , it was decided to carry out gtr using xenograft ( bio- oss ) and a resorbable membrane ( perioguide ) . the mobility of the teeth had subsided ( from grade iii to grade i with 31 ) . however , after four months , a small sinus tract was seen in the 42 region . but when the patient came back with the same complaint six months post surgery , a surgical re - entry was planned [ figures 7 and 8 ] . after reflecting the flap , a class ii a lesion was evident associated with 41 and 42 regions . the most striking finding at the surgical re - entry was the bone fill seen in between 31 and 41 regions , where a bony defect had existed extending apicocoronally with total loss of the buccal cortical plate slight recession is noticed with 32 and 42 regions after the second surgical intervention [ figure 10 ] . bone graft ( bio - oss ) placed in defect bioresorbable membrane ( perioguide ) placed six months post - operative radiograph showing bone fill between 31 and 41 regions surgical re - entry at six months - dense hard tissue evident between 31 and 41 and apical to 31 and 32 regions . bony defect ( class ii a ) apical to 41 and 42 regions gtr carried out in 41 and 42 regions healing four months after surgical re - entry class ii b lesions have been found to be the most challenging to treat . in a clinical trial involving periapical surgery , by hirsch et al . only 27.3% of teeth with total buccal bone loss showed healing , whereas the success rate of teeth with an intact buccal bone plate was 49.5% . skoglund and persson carried out a retrospective evaluation of teeth which showed complete loss of buccal plate during periapical surgery and reported that after three years only 37% were successful , whereas the success rate was 90% for teeth with intact marginal periodontium . however , in 1996 , douthitt , demonstrated 89% bone fill in class ii b lesions treated using the membane , whereas only 67% in control sites . the membrane sites revealed a significantly better connective tissue attachment ( 4.1 mm vs 1.8 mm ) . in our case , the placement of a barrier membrane supported by an underlying xenograft resulted in a considerable amount of dense and hard tissue both radiographically and upon re - entry . the achievement in combining endodontic and periodontal surgical procedures would be to salvage a tooth or teeth on a long term basis that had been defined as hopeless at the initiation of treatment , thus proving to be a new ray of hope !
the use of guided tissue regeneration ( gtr ) has become a standard of care in periodontology . 
 gtr using membrane barriers and/or bone grafting materials has also been used in periapical surgery . 
 however , the application of the gtr principle , particularly in communicating endodontic - periodontal lesions with loss of the buccal cortical plate , is a very challenging task , with very few reported human clinical studies . 
 an interdisciplinary approach , combining endodontic and periodontal ( surgical ) procedures can save a tooth in the long run that has been defined as hopeless at the preliminary stage of treatment .