The effect of endodontic access cavity preparation and subsequent restorative procedures on incisor crown retention

Endodontic treatment often will require access through existing crowns. This study was undertaken to determine whether endodontic access cavity preparation affected the retention of crowns in anterior teeth and then to determine whether this retention can be regained by amalgam or post-retained amalgam restorations. Twenty extracted human incisors were mounted in acrylic blocks and prepared for crowns. Metal copings were fabricated and cemented with zinc phosphate cement and the forces required to displace the copings after various procedures were measured with a tensile testing machine. Retention values for all stages were compared with the initial retentive value for each coping without an access cavity which was set at 100 per cent. Group one specimens had the following means: copings with access cavity, 85.64 +/- 28.65 per cent of the initial values; amalgam flush with lingual dentine, 95.81 +/- 36.2 per cent; amalgam flush with coping, 114.89 +/- 34.5 per cent. Group two means were: copings with access cavity, 89.95 +/- 21.42 per cent; posts and amalgam, 177.37 +/- 77.5 per cent. Statistical analysis with the two sample t test showed that retention with post-retained amalgam restorations showed significantly higher values when compared with access cavities without restorations (p < 0.05). Retention values for post-retained restorations were significantly different from those just using amalgam. This study demonstrated that endodontic access cavities reduced the retention of the crowns, and subsequent restoration with amalgam or a post can regain the retention.(ABSTRACT TRUNCATED AT 250 WORDS)