Acoustic emission monitoring of compression tests on titanium dental implants
Compression tests (1 mm/min.) were performed on five series of differently sized grade 4-titanium dental implants. Load was applied with 0° (correct position) and 25° inclination (incorrect application) through two AISI 316 cylinders with a central hole dimensioned on the implant, forming a 0° or a 25° angle with Y-axis.
Mechanical results: much greater dispersion of ultimate stress values on 0° specimens than on 25° specimens, presenting however much lower absolute values.
Compression curves (0°) with four different regions:
1. Elastic behaviour
2. First stiffness decrease and end of implant function due to the onsets of its inclination
3. Subsequent stiffness decreases: complete screw neck crack opening
4. Maximum stress reaching and large plant inclination with Y axis
During compression tests on 25° curved specimens, no stiffness reduction was apparent.
The maximum stress was attained some time before failure, because of loading angle variation.
Acoustic emission (AE) global approach:
* Mechanical behaviour (four regions) and elastic limit observed both on 0º and on 25º angle specimens
* Emphasis on mechanical values dispersion 0° specimens, while rather concentrated values for AE onset (300 N) in 25° specimens, but composed stress effect
Acoustic emission structural approach:
up to the first plastic deformation phenomena (about 50 seconds).
Onset plastic deformation ~ Acoustic activity initiation (5% of total AE cumulative counts).
Difficulties in AE failure localisation and in total released energy approach.
* 0° compression: neck failure between stump and threaded part.
* 25° compression, screw failure at junction between stump and threaded shank (lower ultimate stress).
· Conclusions: structural problems were observed in both cases at stresses much greater than those produced in chewing. Plastic deformation phenomena, shown by AE, may take place even at lower stresses than in vivo, where however the whole system is not rigid, like in these tests.