title: Effect of posterior crown margin placement on gingival health. Placement of the preparation line and periodontal health--a prospective 2-year clinical study.
abstract: STATEMENT OF PROBLEM The clinical impact of  posterior crown margin placement on gingival health has not been thoroughly quantified . PURPOSE This study evaluated the effect of posterior crown margin placement with multivariate analysis . MATERIAL AND METHODS Ten general dentists review ed 240 patients with 480 metal-ceramic crowns in a prospect i ve clinical trial . The alloy was r and omly selected from 2 high gold , 1 low gold , and 1 palladium alloy . Variables were the alloy used , oral hygiene index score before treatment , location of crown margins at baseline , and plaque index and sulcus bleeding index scores recorded for restored and control teeth after 1 year . The effect of crown margin placement on sulcular bleeding and plaque accumulation was analyzed with regression models ( P<.05 ) . RESULTS The probability of plaque at 1 year increased with increasing oral hygiene index score before treatment . The lingual surfaces demonstrated the highest probability of plaque . The risk of bleeding at intrasulcular posterior crown margins was approximately twice that at supragingival margins . Poor oral hygiene before treatment and plaque also were associated with sulcular bleeding . Facial sites exhibited a lower probability of sulcular bleeding than lingual surfaces . Type of alloy did not influence sulcular bleeding . CONCLUSION In this study , placement of crown margins was one of several parameters that affected gingival health The aim of this prospect i ve clinical 2-year study was to determine whether the placement of the proximal margins of crowns within the zone of the biologic width results in periodontal alterations . In 41 patients , 116 prepared teeth as well as 82 unrestored , healthy contralateral teeth were examined . The following indices were determined before as well as 3 , 6 , 12 , and 24 months after preparation :  hygiene index , papillary bleeding index ( PBI ) , and probing depth .  After preparation , the distance between the restoration margins and the alveolar crest was measured with a modified periodontal probe on both proximal aspects of each tooth . These values were classified into 3 groups : I = < or = 1 mm between crown margin and alveolar crest , II = 1 to 2 mm , and III = > 2 mm . In addition , radiographs were taken directly after cementation of each restoration and after 12 and 24 months . The hygiene index did not significantly vary during the investigation , but PBI increased in all groups . The highest PBI increase was found in group I ; in this group , the most significant increase was found between 3 and 6 months after preparation . The mean probing depth only increased in group I during the first 3 months after preparation on the mesial aspects . Only minor changes were found on the distal aspects of the teeth in group I and on all aspects in groups II and III . No alterations of the bone levels were diagnosed on the radiographs . These results indicate that the location of the restoration margins within the zone of the biologic width may impair the periodontal health of restored teeth
target: Due to the small number and the limitations of the included studies the results do not provide conclusive evidence as to the effect of prosthetic margin placement on the incidence of secondary caries
background: nan