Biomedical Engineering Reference
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were 22.36°±18.59° and 1.29°±2.67° in the heavy force (3 N) group and light force (0.5 N) group,
respectively. Moreover, in a study by Iwasaki et al. (2000), after applying a continuous retraction
force averaging 0.18 N, the maxillary canines underwent approximately 0.6° of rotation, and
another force averaging 0.6 N produced approximately 5.9° rotation. Overall, the distal crown tip
averaged 3.2° over the 84 days (12 weeks). In addition, under an average 8 N•mm torque, Qian
et al. (2008) calculated a tipping degree of 4.59° over four weeks. However, in our buccal tipping
simulation (case (a)), the rotational change in a tooth loaded by a 10 N•mm torque was only 5.5°
during a 16-week period. On the other hand, as far as tooth displacement is concerned, Pilon et al.
reported that after 16 weeks the displacement of three experimental sides in different dogs with
the same force of 1 N were 0.5, 4.7, and 7.2 mm, respectively, which implies that the rate of tooth
movement averaged 0.26 mm/week (Pilon, Kuijpers-Jagtman, and Maltha 1996). Furthermore,
experimental values reported by Ren et al. (2004) indicated that the mean maximum velocity of
human canine retraction was 0.29 mm/week when the force magnitude was 2.72 N. In our simula-
tion for bodily tooth movement (cases (c) and (d)), the averaged velocity of tooth movement was
0.15 mm/week under a force of 1 N, which is consistent with the abovementioned experimental
results.
20.4.2 t
raBecular
S
tructure
around
d
ental
i
mplant
A systematic review of the literature was undertaken to relate the numerical predictions to existing
in vivo data. In a study by Kingsmill and Boyde (1998), the real trabecular distribution in a photo-
graph of 2.0-mm thick bone sections from the mental foramen region of an edentulous mandible of
a human cadaver was investigated. They reported that the trabeculae had a strong horizontal compo-
nent and in some cases possessed a very ladder-like arrangement. Interestingly, a paper by Watzak
et al. (2005) presented an undecalcified thin ground section of the upper jaw at the molar region
(20 μm) of a baboon with different implant shapes after 18 months of occlusal loading, in which
cancellous bone trabeculae tended to be oriented in an apico-coronal direction from the host bone
to the peri-implant bone. The loaded dental implants in their experiments included a commercially
available pure titanium screw, grit-blasted and acid-etched screws, and a titanium plasma-sprayed
cylinder. Watzak et al. also suggested that these trabeculae were well oriented around screw-shaped
implants, whereas they were unoriented around cylindrical implants. Moreover, Gross et al. (1990)
reported on animal experiments in which they studied the effect of implant-to-bone bonding on bone
structure near the implant. When an implant was placed in living bone tissue, the tissue remodeled
itself to accommodate the implant and yielded the spoke trabecular architecture around it (Geramy
2000). In addition, a canine mandible was used in experimental studies of dental implant incorpora-
tion by Schenk and Buser et al. (1998). After a healing period of 3-5 months, bony anchors formed
in the cancellous part of the implant site and the threads were connected to pre-existing trabeculae
by newly formed bone bridges. Generally speaking, these experimental and clinical observations
can be mirrored by our numerical outcomes.
20.4.3 a
lVeolar
B
one
r
emodelinG
i
nduced
By
i
mplant
-S
upported
r
eStorationS
This numerical simulation can be validated in order to prove the reliability of the calculations. It
should be noted that supportive observations from in vivo or clinical studies are scarce, especially
regarding data from patients with bruxism or malocclusion. In this study, the radiographs were pro-
vided by a dentist to qualitatively compare the resemblance between the computational remodeling
results and the clinical data (Wang et al. 2013). For the cantilever prosthesis, it can be seen that at
18 months after the placement an increase in bone density was observed adjacent to the implant.
By comparison, for the non-cantilever prosthesis, the radiographic view at 18 months post-surgery
demonstrated that marginal bone density around the neck of the implants was lower than that asso-
ciated with the cantilevered FPD. This confirms the previously described regions of simulated bone
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