Biomedical Engineering Reference
In-Depth Information
its biocompatibility and bioactivity Ellingsen et al. (2006); Ratner et al. (1996) but have smooth
polished surfaces that may explained reduced osseointegration rates Davies (2007). However,
a convenient osseointegration ratio may improve mini-implant stability during long lasting
orthodontic treatments. Although evidence shows that mini-implants do not osseointegrate,
there is no consensus on this matter and further experimental studies are needed to provide
more details about the interface behavior Serra et al. (2008).
We have therefore performed a self-conducted experimental assays to analyze samples of bone
surrounding mini-implants and evaluate the formation of the bone-implant interface. A total
of fifteen 3-months-old male Wistar Rats SPF mean weight 350 gr. were housed with a 12-hour
light/dark cycle and fed with a standard pellet diet and tap water at pleasure throughout
the experiments Casale & Rivera (2010); Casale & Saavedra (2010). Principles of laboratory
animal care and national laws were observed for the present study. Authorization for these
experiments was issued by the Ethics Committee of the Dentistry Faculty of the Universidad
Nacional de Colombia. Screw-shaped titanium (Ti
6
Al
4
Va) mini-implants of 10 mm length and
1.6 mm diameter (Link ®, MIS, Israel) were used in the assays. Sample screws were provided
by MIS Implants Ltd. Immediate loading of 150 gr. was applied to all the mini-implants. A
radiographic image of the insertion site is shown in Figure 12. Histological tissue behavior
was evaluated 0, 8, 15, 45 and 120 days after insertion. A control group without immediate
loading was also used.
Fig. 12. A) SPF Wistar rat femur radiograph after mini-implant insertion and immediate
loading using a nitinol spring (150gr). B) Digital radiograph after sacrifice.
Experimental data analyses (not shown) suggest that immediate loading does not affect
the wound healing pattern. Histological observation of loaded samples showed that
inflammation is activated between 0 and 15 days after insertion, bone activity under
mechanical tension is started after 15 days of insertion and mature bone formation is started
at day 45 after insertion. The histological activity in unloaded samples showed suitable bone
healing barely starting on day 45 after insertion. These results suggest that wound healing and
osseointegration at unloaded samples is similar to that exhibited on dental implants inserted
in the cortical region.
Comparative additional experiments for orthodontic immediate loading of 150 gr and 350 gr.
showed that higher loading is not feasible in mini-implants because mobility, displacement
and screw instability are increased. Conversely, the application of this higher loading on
mini-implants unloaded during the entire 45 days experimental time (late loading) showed
no mobility or screw displacement.
According to this, we provide histological evidence of
