Novel approach to assessing the primary stability of dental implants under functional cyclic loading in vitro: a biomechanical pilot study using synthetic bone

Abstract

Purpose: This pilot study was conducted to develop a novel test setup for the in vitro assessment of the primary stability of dental implants. This was achieved by characterising their long-term behaviour based on the continuous recording of micromotions resulting from dynamic and cyclic loading.

Methods: Twenty screw implants, each 11 mm in length and either 3.8 mm (for premolars) or 4.3 mm (for molars) in diameter, were inserted into the posterior region of 5 synthetic mandibular models. Physiological masticatory loads were simulated by superimposing cyclic buccal-lingual movement of the mandible with a vertically applied masticatory force. Using an optical 3-dimensional (3D) measuring system, the micromotions of the dental crowns relative to the alveolar bone resulting from alternating off-centre loads were concurrently determined over 10,000 test cycles.

Results: The buccal-lingual deflections of the dental crowns significantly increased from cycle 10 to cycle 10,000 (P<0.05). The deflections increased sharply during the first 500 cycles before approaching a plateau. Premolars exhibited greater maximum deflections than molars. The bone regions located mesially and distally adjacent to the loaded implants demonstrated deflections that occurred synchronously and in the same direction as the applied loads. The overall spatial movement of the implants over time followed an hourglass-shaped loosening pattern with a characteristic pivot point 5.5±1.1 mm from the apical end.

Conclusions: In synthetic mandibular models, the cyclic reciprocal loading of dental implants with an average masticatory force produces significant loosening. The evasive movements observed in the alveolar bone suggest that its anatomy and yielding could significantly influence the force distribution and, consequently, the mechanical behaviour of dental implants. The 3D visualisation of the overall implant movement under functional cyclic loading complements known methods and can contribute to the development of implant designs and surgical techniques by providing a more profound understanding of dynamic bone-implant interactions.

Keywords: Biomechanics; Dental implants; Immediate dental implant loading; In vitro test.

Figure 1. Experimental principle for the superimposition of lateral movements of the mandibular component with a vertically applied chewing force. (A) Test setup concept. (B) Detailed view of the alternating off-centre loading of the dental crown.

Figure 2. Experimental setup with optical 3-camera image correlation system.

Figure 3. Positions of the optical markers M1-M4 and MR, providing a representative example of absolute spatial motion and definition of the global coordinate system.

Figure 4. Geometric relationships necessary for extrapolating the 3-dimensional motion and shifting of the measurement points (P1 and P2), as well as the reference points on the coronal plane (Cor), cervical plane (Cer) and apical plane (Api) along the implant axis. The diagram compares the initial position (solid line) to a shifted position (dotted line).

Figure 5. Mean buccal-lingual deflections of the dental crowns of the experimental groups CamPM, CamM, ConePM and ConeM over the 10,000-cycle testing period.

Figure 6. Buccal-lingual deflections in the experimental groups at the beginning (cycle 10) and the conclusion (cycle 10,000) of testing.

^*P<0.05, ^**P<0.01.

Figure 7. Overall spatial movement of the implant axis, using a single test object (a molar) as an example. The movements at cycles 10, 100, 1000, and 10,000 are shown, with the trace curves of the reference points Cor, Cer, and Api marked in red.