The effect of static bone strain on implant stability and bone remodeling
Anders Halldin
a,b,
⁎
, Ryo Jimbo
a,d
, Carina B. Johansson
c
, Ann Wennerberg
a,d
, Magnus Jacobsson
a,b
,
Tomas Albrektsson
e,f
, Stig Hansson
b
a
Department of Prosthodontics, Faculty of Odontology, Malmö University, Malmö, Sweden
b
Astra Tech AB, Mölndal, Sweden
c
Dental Materials, Department of Prosthodontics, Institute of Odontology, The Sahlgrenska Academy, University of Gothenburg, Sweden
d
Department of Biomaterials/Handicap Research, Gothenburg University, Gothenburg, Sweden
e
Department of Biomaterials, Gothenburg University, Sweden
f
Department of Dental Materials Sciences & Technology, Malmö University, Sweden
abstractarticle info
Article history:
Received 21 April 2011
Revised 15 June 2011
Accepted 4 July 2011
Available online 14 July 2011
Edited by: David Burr
Keywords:
Static bone strain
Removal torque
In vivo experiment
Biomechanical FE simulation
Bone remodeling
Bone remodeling is a process involving both dynamic and static bone strain. Although there exist numerous
studies on the effect of dynamic strain on implant stability and bone remodeling, the effect of static strain has yet
to be clarified. Hence, for this purpose, the effect of static bone strain on implant stability and bone remodeling
was investigated in rabbits. Based on Finite Element (FE) simulation two different test implants, with a
diametrical increase of 0.15 mm (group A) and 0.05 mm (group B) creating static strains in the bone of 0.045 and
0.015 respectively, were inserted in the femur (group A) and the proximal tibia metaphysis (groups A and B
respectively) of 14 rabbits to observe the biological response. Both groups were compared to control implants,
withno diametrical increase (group C), which were placed in the opposite leg. At the time of surgery, the insertion
torque (ITQ) was measured to represent the initial stability. The rabbits were euthanized after 24 days and the
removal torque (RTQ) was measured to analyze the effect on implant stability and bone remodeling. The mean
ITQ value was significantly higher for both groups A and B compared to group C regardless of the bone type. The
RTQ value was significantly higher in tibia for groups A and B compared to group C while group A placed in femur
presented no significant difference compared to group C. The results suggest that increased static strain in the
bone not only creates higher implant stability at the time of insertion, but also generates increased implant
stability throughout the observation period.
© 2011 Elsevier Inc. All rights reserved.
Introduction
Bone is a unique material in its ability to adapt its mass and structure
in response to the loads to which it is exposed [1,2]. The loads induce
strains in the bone, and the modeling and remodeling stimulus has been
found to be dependent on strain magnitude, strain frequency [3],and
strain rate [4]. The bone mass can either be maintained by a relatively
small number of loading cycles with high strains, for example 4 loading
cycles per day with a strain of 2000 microstrain [5], or by a great number
of loading cycles with low strains, for example 10,000 loading cycles per
day with a strain of 400 microstrain [6]. It has also been found that the
osteogenic effect of strains increases with increasing strain rate [4].
The insertion of an implant with a certain torque means that static
strains will be induced in the surrounding bone. The magnitude of these
static strains depends on the bone anatomy, the bone quality, the
osteotomy preparation, the implant design, and on the implant surface
topography. While it is well known that dynamic strains are the driving
force behind bone modeling and remodeling [7,8], our knowledge about
the effect of static strains is limited. In a study performed on rats,
dynamic loads applied 18 s per day gave rise to new bone formation
while static loads of the same magnitude and duration did not modulate
bone modeling and remodeling [9]. In a study using dogs, osseointe-
grated implants with a static lateral load, superimposed on functional
dynamic loads, resulted in a densification of the bone adjacent to the
implant and in an increase in bone-to-implant contact [10].
Directly after implant installation, the implant stability depends
solely on mechanical interlock for stabilization. According to Szmukler-
Moncler et al. [11] micro-motions should be less than 50–150 μmin
ordertoavoidfibrous tissue encapsulation and implant instability. In the
classic implant installation protocol, dental implants were loaded after
3 months in the mandible and after 6 months in the maxilla [12].Ithas
later been suggested that early and even immediate loading of dental
implants can be practiced with predictable results, if the implants
exhibit a certain minimal primary stability [13].
Clinically, the stability of an implant is often evaluated by
measurement of the insertion torque [14]. The minimum insertion
Bone 49 (2011) 783–789
Abbreviations: RTQ, Removal torque; ITQ, Insertion torque; ROI, Region of interest.
⁎ Corresponding author at: Department of Prosthodontics, Faculty of Odontology,
Malmö University, Malmö, Sweden. Fax: +46 40 6658503.
E-mail address: anders.halldin@mah.se (A. Halldin).
8756-3282/$ – see front matter © 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.bone.2011.07.003
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