Objectives: Missing teeth in the anterior part of the jaws often lead to special prosthodontic problems. Osseointegrated implants in this area act as single root forms and the position of the head of the fixture can give rise to restoration heights of considerable variation. A study was carried out to investigate the effect of variations of restoration height on the integrity and strength of the implant-abutment connection.

Methods: Test assemblies were constructed by placing 3.3mm diameter Brånemark fixtures in aluminium alloy holders. Custom abutments at heights of 8, 13 and 18mm were secured to the fixtures by abutment screws tightened to the manufacturer's recommended torque level. The investigation analysed each abutment height by subjecting assemblies to compressive bending testing at a thirty-degree off-axis inclination. The force-displacement curves for the tests were analysed and a curve reading made drawing a line at a point corresponding to 0.2 mm displacement on the graph parallel to the initial straight section of the charting.

Results: In static conditions, the 18mm abutment height exhibited 50% of the strength of the 8mm abutment. The 13mm abutment height showed a corresponding strength value of 65% when compared to the 8mm abutment.

Conclusion: Increased restoration height creates a greater challenge on the clamping force of the joint and the preload within the abutment screw. Further investigations are necessary to evaluate the full effect of varying restoration height on the long-term success of single implant units placed in sites with compromised vertical bone height.

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