Biomechanics and strain mapping in bone as related to immediately-loaded dental implants

Abstract

The effects of alveolar bone socket geometry and bone-implant contact on implant biomechanics, and resulting strain distributions in bone were investigated. Following extraction of lateral incisors on a cadaver mandible, implants were placed immediately and bone-implant contact area, stability implant biomechanics and bone strain were measured. In situ biomechanical testing coupled with micro X-ray microscopy (µ-XRM) illustrated less stiff bone-implant complexes (701-822 N/mm) compared with bone-periodontal ligament (PDL)-tooth complexes (791-913 N/mm). X-ray tomograms illustrated that the cause of reduced stiffness was due to limited bone-implant contact. Heterogeneous elemental composition of bone was identified by using energy dispersive X-ray spectroscopy (EDS). The novel aspect of this study was the application of a new experimental mechanics method, that is, digital volume correlation, which allowed mapping of strains in volumes of alveolar bone in contact with a loaded implant. The identified surface and subsurface strain concentrations were a manifestation of load transferred to bone through bone-implant contact based on bone-implant geometry, quality of bone, implant placement, and implant design. 3D strain mapping indicated that strain concentrations are not exclusive to the bone-implant contact regions, but also extend into bone not directly in contact with the implant. The implications of the observed strain concentrations are discussed in the context of mechanobiology. Although a plausible explanation of surgical complications for immediate implant treatment is provided, extrapolation of results is only warranted by future systematic studies on more cadaver specimens and/or in vivo models.

Keywords: Alveolar bone; Bone–implant contact; Digital volume correlation; Implant; Strain.

Fig. 1

(a) Photograph of an implant-bone complex specimen prepared for biomechanical testing and (b) schematics of the in situ biomechanical testing system coupled with μ-XRM.

Fig. 2

Figures (a) and (b) are radiographs of alveolar socket 23 after tooth extraction. The differences of the lamina dura (a) before and (b) after decortication are highlighted with arrows. Figure (d) and (e) are 3D rendered μ-XRM images of osteotomy for implant 26 when the implant was digitally removed. The outlines of two holes are highlighted with dashed lines. The inadvertently placed smaller drill hole is not clear in (c) the radiograph of implant 26.

Fig. 3

Virtual sections of μ-XRM tomograms for (a) implant 23 and (b) implant 26 placed in the osteotomies show that the implants and alveolar bone were only making contact at limited locations at the mesial and distal sides of the alveolar socket. Slice at ~4 mm below crestal bone level.

Fig. 4

The bone-implant contact area on the (a) distal and (d) mesial sides of alveolar socket 23 and (e) mesial and (h) distal sides of alveolar socket 26. As well as the contact area on (b) distal and (c) mesial sides of implant 23 and (f) mesial and (g) distal sides of implant 26. Videos are attached in supplementary data.

Fig. 5

(a)(f) Topography of the alveolar bone obtained using SEM; (b)(c)(d)(g)(h)(i) Elementary mapping of the alveolar bone; (e)(j) EDS spectra of highlighted spots and areas in the alveolar bone.

Fig. 6

(a) Repetitive compression tests (five times) resulted in similar force-displacement curves. Reactionary force-displacement curves obtained from the biomechanical testing for (b) bone-PDL-tooth complexes and (c) bone-implant complexes. (d) Stiffness analysis for the bone-PDL-tooth complexes and bone-implant complexes.

Fig. 7

Maximum principal strain distribution on the buccal and lingual outer surfaces of the alveolar bone and inside the alveolar sockets. 3D strains in the form of videos are attached as supplementary data.