Primary stability a predictable parameter

84 © 2016 Journal of the International Clinical Dental Research Organization | Published by Wolters Kluwer - Medknow
INTRODUCTION
The use of dental implants has become widespread and a
predictable treatment modality for the restoration of missing
teeth. It has become a part and parcel of routine therapy;
considering this, success of implant dentistry depends on the
stability of the implant, whether biological or mechanical.
Initial stability at placement (primary stability) and the
development of osseointegration in the following healing
process (secondary stability) are two important factors for
implant success [Figure 1].
It is important to verify the status of implant-bone interface
to decide the loading time of the implant. Generally, clinicians
evaluate primary stability using the percussion test or using
their own perception during the implant placement process.
In particular, peak insertion torque (IT) and resonance
frequency analysis (RFA) are the most used globally.[1]
Peak IT
is measured while the implant is inserted. The IT corresponds
to a combination of the cutting friction of the tip of the
implant in the bone, and the friction between the implant
surface and the preparation in the bone. If the osteotome is
narrow or the bone quality is high, the torque will be higher.
The torque will also depend on how sharp the cutting tip
Short Communication
Address for correspondence:
Dr. Dimple Bhardwaj, 13 Geetanjali, 234 SV Road, Bandra (West),
Mumbai - 400 050, Maharashtra, India.
E-mail: dimple_bh@yahoo.com
of the implant is, the surface properties of the implant, the
lubrication of the preparation (blood), and also the design of
Access this article online
Website: www.jicdro.org
DOI: 10.4103/2231-0754.176264
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Is primary stability a predictable parameter for
loading implant?
Ratnadeep Patil1,2
, Dimple Bharadwaj1
1
Department of Clinical Dentistry, Smile Care, Mumbai, Maharashtra, India, 2
Department of Prosthodontics and Biomaterial, Adjunct Professor, Centre for Dentistry
and Oral Hygiene Section, Oral Function, Prosthodontics and Biomaterial, University Medical Centre, The University of Groningen, Groningen, The Netherlands
ABSTRACT
Implant stability is important for osseointregration; without it, long-term success cannot be achieved.
Continuous monitoring in a quantitative and objective manner is important to determine the status of implant
stability. Measurement of implant stability is a valuable tool for making decisions pertaining to treatment
protocol and it also improves dentist-patient communication. Owing to the invasive nature of histological
analysis, various others methods have been proposed such as radiographs, cutting torque resistance,
reverse torque, and resonance frequency analysis (RFA). This review focuses on the objectives and various
methods to evaluate implant stability.
Key words: Insertion torque (IT), primary stability, secondary stability
Cite this article as: Patil R, Bharadwaj D. Is primary stability a predictable
parameter for loading implant?. J Int Clin Dent Res Organ 2016;8:84-8.
This is an open access article distributed under the terms of the
Creative Commons Attribution-NonCommercial-ShareAlike 3.0
License, which allows others to remix, tweak, and build upon the
work non-commercially, as long as the author is credited and the
new creations are licensed under the identical terms.
For reprints contact: reprints@medknow.com
Figure 1: primary stability comes with old bone. secondary stability comes with
new bone
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Patil and Bharadwaj: Primary stability predictable parameter for loading implants?
85Journal of the International Clinical Dental Research Organization | January-June 2016 | Vol 8 | Issue 1
the implant itself. The formula of higher IT torque translating
into higher primary stability may not always be true because
the quantity and quality of bone varies significantly among
patients.[1]
The torque values that we get during the placement of
the implant is the first contact of the implant surface with
the bone; these values will not be the same all along the
osteotome and so we require a smart physiodispenser, which
will give us a graphical representation of torque value of
each implant thread, which gets embedded inside the bone.
The current trends and the changes required to measure
the biological and mechanical stability will be explored in
this article.
Primary stability
Primary stability is defined as the absence of mobility in the
bone bed after the implant has been placed.[2]
It depends on
the mechanical engagement of an implant within the fresh
bone socket. During the early stages of healing, mechanical
stability decreases and biological stability increases. In
an osseointegrated implant, the stability depends on the
biological component.[3]
Primary stability is important for
good secondary stability as it prevents the formation of
connective tissue layer between implant and bone, ensuring
bone healing.
A key factor for the implant primary stability is the
bone-to-implant contact (BIC)[4]
and thus, factors such as
implant shape, length, and diameter that cause an increase
in the contact area between the implant and bone may
increase the implant primary stability. Furthermore, the
quality of bone bed plays an important role in shaping
the BIC area.[5]
Factors influencing primary stability:[6]
Implant geometry.
Bone density and quality.
Surgical protocol (osteotomy preparation) including the skill
of the surgeon.
Implant geometry
Mechanical stability occurs where friction occurs between
the implant and the surrounding bone, giving rise to
resistant torque at time of insertion. This resisting torque
is proportional to the effort required to seat the implant; it
depends largely on the characteristics of the implant, the
density of the bone, and size of the osteotomy, as it pertains
to the diameter of the implant. The implants with treated
surfaces show greater roughness, a higher friction coefficient,
and demand a larger IT than machined implants.[7]
The results
of the surface roughness and friction coefficients are in
accordance with the results of the IT. The difference, across
the IT values, between conical and cylindrical implants can
be explained by the different contact surface areas among
the thread geometry of these implants.[5]
It is clear that higher ITs fulfill the desire to achieve a high
degree of mechanical stability as interpreted through manual
perception. It is typical for manufacturers to provide some
guidance on optimal IT, with some implant designs being
specifically tailored to deliver higher ITs. This yields a sense
of comfort for the clinician that the implant is initially
“stable.”[8]
However, such a high torque has not been shown
to be propitious to the surrounding bone. Numerous studies
have been published, which clearly demonstrate that the
critical pressure at this high torques leads to microfracture
of the bone, with a net resorption in the cortical zone and
an unfavorable, indeed delayed healing process with reduced
BIC. Such a response might well shift the onset for secondary
stability and thereby delay or extend the period of potential
vulnerability. This is clearly counter to the goal we are trying
to achieve with immediate or even early loading protocols
where we want to transfer from simple mechanical fixation
to full osseointegration in the shortest possible time.[8]
Bone density and quality
Bone quality is often referred to as the amount (and their
topographic relationship) of cortical and cancellous bone
in which the recipient site is drilled. A poor bone quantity
and quality have been indicated as the main risk factors for
implant failure as it may be associated with excessive bone
resorption and impairment in the healing process, compared
with higher density bone.[2]
Clinical studies have reported
dental implants in the mandible to have higher survival rates
compared to those in the maxilla, especially for the posterior
maxilla. It has been shown that achieving optimum primary
stability in soft bones is difficult and is also related to a higher
implant failure rate for the implants placed in such bones.
Thus, the density of the surrounding bone seems to play an
essential role in high occlusal forces and therefore, the high
BIC percentages of a thin, “carpet”-like bone in contact with
the implant surface seems to be not clinically significant
compared to the lower rate of BIC in a thick bone.
Surgical protocol
Theclinicalperceptionofprimaryimplantstabilityisfrequently
based on the cutting resistance of the implant during its
insertion. Different surgeons have different preparation
protocols, depending on the patient bone densities. Among
the surgical factors that influence osseointegration, implant
bed preparation is of critical importance. Drilling the implant
bed not only causes mechanical damage to the bone but also
increases the temperature of the bone directly, adjacent to
the implant surface.[7]
Mechanical and thermal damage to

86 Journal of the International Clinical Dental Research Organization | January-June 2016 | Vol 8 | Issue 1
the tissue surrounding the implant during drilling can have
a destructive effect on the initial state of the cavity housing
the implant.[6]
A correlation between cutting resistance at
implant placement and primary resonance frequency (RF)
values was reported for maxillary implants.[9]
Subjective evaluation
In clinical work, primary stability can be evaluated by
percussion test, Periotest, RFA and placement torque.
Percussion test
The percussion test may involve the tapping of a mirror
handle against the implant carrier and is designed to elicit
a ringing sound from the implant as an indication of good
stability or osseointregration.[10]
However, this method
may be subjective according to the examiner and may give
inaccurate measurements for implants because of the high
rigidity of implants and the lack of periodontal ligaments.[3]
The result is displayed digitally and audibly as Periotest values
(PTVs) on a scale of –8 (low mobility) to 50 (high mobility).
Peak insertion torque
The IT used during placement of implants was measured
through a surgical handpiece; it can be used to predict implant
survival and to estimate healing time.[11]
However, this method
is nonsubjective, noninvasive, and extensively used in clinical
practice during implant placement to assess primary stability.
Peak IT gives us a static measurement, which is taken only
once while force that is required for each and every thread
of the implant to go through the bone will not be at the
same torque. Thus, it allows only a single measurement at
implant insertion and cannot be used for evaluating secondary
stability. IT only assesses condition at the time of implant
placement.[9]
Periotest
Periotest (Gulden-Medizintechnik, Bensheiman der
Bergstrae, Hesse, Germany) is an electronic instrument
originally designed to perform quantitative measurements
of the damping characteristics of the periodontal ligament
surrounding a tooth, thereby establishing a value for its
mobility.[9]
As the outcome of Periotest measurements
is influenced by the distance from the striking point to
the first bone contact, it is evident that placement of the
implant in the vertical dimension, abutment height, the
level of marginal bone loss, and the striking position on
the abutment/implant are critical factors for accuracy and/or
reproducibility.[9]
Single readings of Periotest determinations
are of limited clinical value and have not been demonstrated
to reflect on the nature of the bone/implant interface. By
performing repeated measurements of the same implant
over time, implant stability may be confirmed.[9]
Resonanace frequency analysis
RFA measures the stability by apply a bending load,
which mimics the clinical load and direction and provides
information about the stiffness of the implant-bone junction.
It evaluates the micromobility or displacement of the implant
in bone under a lateral load, applying microscopic lateral
forces to the implant with a vibrating transducer.[11,8]
The
first commercial version of the RFA technique (Osstellt,
Integration Diagnostic AB, Goteborg, Västergötland and
Bohuslän, Sweden).
The results are given as implant stability quotients (ISQs),[10]
which are affected by three main factors:
• The stiffness of the implant fixture
• The interface with surrounding tissue
• The design of the transducer and the total effective
implant length above bone level.
The stiffer the interface between the bone and implant, the
higher the frequency and higher the frequency, higher is the
ISQ level. The ISQ unit is based on the underlying RF and
ranges from 1 (lowest stability) to 100 (highest stability). We
already know from the literature that an implant can tolerate
a degree of micromotion, thought to be 100-150 μm, and
this is what ISQ measures.
The RFA values are still not definitive as no actual threshold
value has been established to differentiate a stable, integrated
implant from a failing/failed implant; however, it has been
suggested that an ISQ value above 57 at 1 year after loading
represents a successful implant outcome[7]
while a value
below 50 indicates a risk of implant failure.[12]
There is a lack of correlation between IT and the ISQ as
measured by RFA in an implant that is driven in at 30 ncm
and has the same ISQ as the one that required 100 ncm of
torque. Since ISQ is measuring axial stiffness, could it be that
axial stiffness is far more relevant than rotational friction in
ensuring implant integration?
It has been postulated that implants with low ISQ values yield
more marked increases in ISQ values with time than implants
with high ISQ values, indicating that differences in RFA values
between implants may diminish with time.
It may be speculated that similar bone densities will result
with time as a consequence of remodeling and adaptation
to function.
Although extensively used in clinical research as one
parameter to monitor implant stability, it has to be
realized that RFA is affected by factors such as bone tissue
characteristics and implant sink depth, diameter, and surface
characteristics. Research indicates that implants yielding high

87Journal of the International Clinical Dental Research Organization | January-June 2016 | Vol 8 | Issue 1
ISQ values during follow-up appear to maintain stability. Low
or decreasing ISQ values may be indicative of developing
instability. However, no established normative range of ISQ
values is available as yet.
Consequently, a single determination of the ISQ value
does not define bone/interface characteristics or provide a
quantitative evaluation of bone tissue integration. Similarly,
no prognostic value for developing implant instability can
be attributed to RFA. Hence, at the present time, the validity
and relevance of RFA for clinical use have to be questioned.[9]
The destructive methodologies, such as removal torque
assessment and pullout and pushout techniques are generally
used only in preclinical applications. While these methods
may be of value as research techniques, they are of limited
value in clinical use owing to ethical concerns associated
with the invasive nature of such methodology.
Biological stability
The gradual shift from primary stability to biological stability is
poised at around 3 weeks; this is seen as to be the least stable
time point where viscoelastic stress relaxation of the bone,
along with remodeling, results in the loss of primary stability.[13]
While secondary stability is the progressive increase in stability
related to biologic events at the bone-to-implant interface
such as new bone formation and remodeling,[14]
it is absent
at the time of implant placement and increases with time.[15]
Secondary stability is a biological phenomenon, the result
of the healing that takes place around the implant, i.e., the
osseointregration. This process is dependent on many factors,
e.g., the implant surface properties, loading conditions, and
the individual host response
Bone-to-implant contact
The concept of initially placing more bone within the
immediate vicinity of the implant surface has been termed
initial bone-to-implant contact (IBIC). Maximizing IBIC has
two major benefits:
1. The greater the IBIC, the greater the mechanical stability,
thus enhancing the implant’s ability to withstand
micromovement while secondary stability develops and
2. Reducing the osteogenic migration distance decreases
the time for osteoconduction to occur.
DISCUSSION
The seating torque is the final torque value that is achieved
when the implant is inserted. Depending on the implant
design and bone properties, the value can be higher or
lower. Torque measures the rotational friction between the
implant and the bone, together with the force required to
cut the bone. However, torque does not necessarily correlate
to implant stability. The value which we get during the
placement of the implant is the first contact of the implant
surface with the bone; this torque value will not be the
same all along the osteotome and thus, we require a smart
physiodispenser, which would record the torque value at
each thread level and a graph can be attained helping us to
decide whether we can load an implant immediately or if
we need to wait. Although we have fixed IT values, implant
with low IT will not be removed and it has to be left to be
healed. Due to biology of bone, dynamics process takes
place which will lead to ossteointegration and there will be
micromechanical fixation.
Osseo integration is the basis of a successful endosseous
implant. The process itself is quite complex and there are
many factors that influence the formation and maintenance
of bone at the implant surface.[7]
The stiffness of the implant
is a function of its geometry and material composition
(length, diameter, and overall shape). Second, the stiffness of
the implant tissue interface depends on the bond between
the surface of the implant and the surrounding bone. The
stiffness of the surrounding tissue is determined by the
ratio of cancellous to cortical bone and the density of the
bone with which an implant engages. Stiffness found at the
bone-to-implant interface changes over time; thus, primary
stability decreases with time and mechanical stability takes
over. During this period of transition between primary and
secondary stability, the implant faces the greatest risk of
micromotion and consequent failure. It is estimated that this
period in humans occurs roughly 2-3 weeks after implant
placement when osteoclastic activity decreases the initial
mechanical stability of the implant but not enough new
bone has been produced to provide an equivalent or greater
amount of compensatory biological stability.[8]
This is related
to the biologic reaction of the bone to surgical trauma
during the initial bone remodeling phase; bone and necrotic
materials resorbed by osteoclastic activity is reflected by
a reduction in implant stability quotient (ISQ) value. This
process is followed by new bone apposition initiated by
osteoblastic activity, therefore leading to adaptive bone
remodeling around the implant.[4]
Hypothetically, if the level of primary stability can be
increased and the rate of osseointegration at the same time
can be accelerated, the dip in total stability can be reduced
and the implant is made less susceptible to micromovement
and potential failure. Our goal must be the rapid onset
of secondary stability, with minimal critical pressure to
the poorly vascularized cortical bone so that unfavorable
resorptive responses and delayed healing are avoided. At
the same time, we need to employ an objective measure of
constraint that reliably ensures that the implant can tolerate

88 Journal of the International Clinical Dental Research Organization | January-June 2016 | Vol 8 | Issue 1
early or immediate loading; the accuracy of primary stability
prediction is not good enough to prevent mistakes when
using an immediate loading technique. Therefore, a more
systematic use of objective measurements is encouraged.[12]
A simple, predictable, noninvasive test to quantify implant
stability and osseointegration is highly desirable.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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Primary stability a predictable parameter

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