Controlling dentine penetration in computer microleakage tracer mapping

Objectives: Microleakage tracer penetration tests in dentine with simple sectioning are often confounded by dentine tubule penetration into the interface, leaching of water soluble tracers on wet sectioning, lack of standardized cavity dimensions affecting stresses, inadequate sectioning missing important tracer regions and airlocks obstructing tracer entry. The present aim was to create high resolution maps of stained interfaces without these confounding factors. Methods: Ten intact extracted permanent upper central incisors were horizontally sectioned through the upper root, one third of the root length from the mid-buccal enamel limit. A dentine-bonded resin composite (Scotchbond MP, Z100, 3M) restoration was placed in a cylindrical cavity milled centrally in the root face of the coronal portion of five teeth. Tubules were angled at a mean of 12.5 ± 4.8 ° to the root face, and travelled approximately radially from the interface, such that tubule penetration was directed sufficiently radially outward to be distinguished from vertical interface penetration. Waterfast silver nitrate staining was applied with initial vacuum at 30 mmHg. A precision grinding machine serially removed approximately 100 μm increments of the tooth until no tracer remained, and computer image analysis data for the 18 revealed surfaces were used to construct detailed interface tracer maps. Results: Control specimen tubule penetration was directed sufficiently radially outward to permit tubule penetration to be isolated from vertical interface penetration in test specimens, and ignored. Interface penetration ranged from approximately 0.3 to 1.6 mm in depth, and 0.90 to 5.09 mm2 in area. Conclusions: This method provided quantitative standardized high resolution mapping of interface tracer penetration, unconfounded by dentine penetration. None of the interfaces was fully sealed.