Biomedical Engineering Reference
In-Depth Information
Fig. 11. Different types of mini-implants.(A) Dual-top mini-implant ®(Jeil, Korea). (B) Link
orthodontic implant ®(MIS, Israel)
evaluating absence of micromovements, immediate loading is performed with magnitudes
ranging from 50 to 200 gr. Melsen & Costa (2002). These loads can be directly or indirectly
applied using rubber bands or closed-helical springs after a responsible healing time of two
weeks (Antoszewska et al., 2009; Zhao et al., 2009).
Once treatment has started, failure of the mini-implant may occur among other reasons
because of low bone density and improper cortical bone thickness at the insertion site
Motoyoshi, Inaba, Ono, Ueno & Shimizu (2009b). Experimental tests of these failure factors
suggest that minimal cortical bone thickness should be 1 mm (Motoyoshi, Inaba, Ono, Ueno
& Shimizu, 2009a). In addition, numerical analyses performed on mini-implant treatments
have evaluated these same failure factors. Results from these analyses resume the mechanical
conditions required for the use of mini-implants based on a predictive scheme supported on
experimental evidence Motoyoshi, Okazaki & Shimizu (2009); Sung et al. (2010).
3.1 Experimental assays
In recent years, there has been an increased concern for better understanding the behavior
of mini-implants as anchorage devices in the jaw bone. However, the suitable material,
surface treatment, screw design, self-perforating screwing capability, ideal timing for loading
and magnitude of loads are still not well defined Chaddad et al. (2008); Seong-Hun et al.
(2008). Although the mini-implant stability should be preserved during the entire orthodontic
treatment, this is something that not always can be assured since treatment times may vary
and in some cases are longer than a year Antoszewska et al. (2009); Costa et al. (1998); Deguchi
et al. (2006).
Immediate loading is one of the distinctive characteristics of mini-implants. Since bone
healing at the interface is a dynamic process and external mechanical loading induces
bone adaptation Klein-Nulend et al. (2005), keeping an unchanging long lasting interface
after loading seems somehow unfeasible. Furthermore, it is not clear if the mini-implant
may induce higher osseointegration ratios supporting immediate loading or if loads and
micromovements induce fibrillar tissue formation at the bone-implant interface that hinder
osseintegration Zhang et al. (2010). Recommended mini-implants are made of titanium due to
