Validity and clinical significance of biomechanical testing of implant/bone interface

Validity and clinical significanceof biomechanical testingof implant/bone interface

Carlos AparicioNiklaus P. LangBo Rangert

Authors’ affiliations:Carlos Aparicio, Private Practice, Clinica Aparicio,Barcelona, Spain and Department of Biomaterials,Institute for Clinical Sciences, SahlgrenskaAcademy, Gothenburg University, Gothenburg,SwedenNiklaus P. Lang, School of Dental Medicine,University of Berne, Berne, GermanyBo Rangert, Nobel Biocare, Gothenburg, Swedenand Department of Biomedical Engineering,Rensselaer Politecnic Institute, Troy, New York,USA

Correspondence to:Carlos AparicioClinica AparicioGeneral Mitre 72–74 Bajos08017 BarcelonaSpainTel.: þ34 93 209 432Fax: þ34 93 202 2298e-mail: [email protected]

Key words: biomechanics, clinical assessment, diagnosis, finite elemente analysis, implant

stability, periotest, resonance frequency analysis

Abstract

Purpose: The aim of this paper was to review the clinical literature on the Resonance

frequency analysis (RFA) and Periotest techniques in order to assess the validity and

prognostic value of each technique to detect implants at risk for failure.

Material and methods: A search was made using the PubMed database to find clinical

studies using the RFA and/or Periotest techniques.

Results: A limited number of clinical reports were found. No randomized-controlled clinical

trials or prospective cohort studies could be found for validity testing of the techniques.

Consequently, only a narrative review was prepared to cover general aspects of the techniques,

factors influencing measurements and the clinical relevance of the techniques.

Conclusions: Factors such as bone density, upper or lower jaw, abutment length and

supracrestal implant length seem to influence both RFA and Periotest measurements. Data

suggest that high RFA and low Periotest values indicate successfully integrated implants and

that low/decreasing RFA and high/increasing Periotest values may be signs of ongoing

disintegration and/or marginal bone loss. However, single readings using any of the techniques

are of limited clinical value. The prognostic value of the RFA and Periotest techniques in

predicting loss of implant stability has yet to be established in prospective clinical studies.

The development of a firm implant/bone

interface is believed to be a major prerequi-

site for the short- and long-term clinical

functioning of an implant. Different im-

plant geometries and surfaces as various

host site conditions may influence the

interface development and its characteris-

tics. Therefore, it is of interest to develop

and evaluate assessment methods for dif-

ferent biomechanical properties of the

bone/implant interface, both for experi-

mental applications as well as clinical

practice and for prognostic evaluation.

This paper concentrated on documented

non-destructive intraoral testing methods,

such as resonance frequency analysis

(RFA), the Periotests

technique and inser-

tion torque measurements. RFA and

Periotests

have been suggested to assess

implant stability, while insertion torque

measurements only assess conditions at

the time of implant installation. As aspects

of implant installation, such as obtaining

primary stability and various bone tissue

characteristics are discussed by Molly

(2006), the validity of insertion torque

measurements both in terms of diagnostic

value for determining primary implant sta-

bility and prognostic outcome following

implant installation will be discussed in

that paper as well (Molly 2006).

Today, RFA is extensively used in clin-

ical research to monitor implant stability.

Mostly due to its higher reproducibility andr 2006 The Authors

Journal compilation r Blackwell Munksgaard 2006

To cite this article:Aparicio C, Lang N P, Rangert B. Validity and clinicalsignificance of biomechanical testing of implant/boneinterface.Clin. Oral Imp. Res., 17 (Suppl. 2), 2006; 2–7

2

reproducibility, RFA has replaced to a cer-

tain extent the Periotests

technique, which

has been developed for a similar purpose

(Lachmann et al. 2006a, 2006b).

The destructive methodologies, such as

removal torque assessment, pullout and

pushout techniques are generally used

only in pre-clinical applications. While

these methods may be of value as research

techniques, they are of limited value in

clinical use owing to ethical concerns asso-

ciated with the invasive nature of such

methodology. Hence, these techniques are

discussed elsewhere (Brunski 2006).

The scope of this report is to define and

characterize the techniques of RFA and

Periotests

as methods for testing the im-

plant/bone interface and to analyze their

validity, clinical significance and prognos-

tic value for assessing implant stability.

Search strategy

An initial search using the PubMed database

on the website of http//www. ncbi. nlm.nih.

gov./entrez/query.fcgi revealed that high-level

evidence publications, such as randomized-

controlled clinical trials (RCTs), and also pros-

pective cohort studies for validity testing of

the biomechanical implant/bone interface

testing methodology were virtually absent.

Although numerous studies on implant

therapy in various indications (n¼ 222 as

of February 2006) reported data from bio-

mechanical interface testing in their doc-

umentation of study outcomes, only a

limited body of literature is available to

validate such methodology (n¼23). As

controlled prospective studies are required

to determine the prognostic (positive pre-

dictive) value of diagnostic tests, such test

characteristics cannot really be determined

on the basis of the current literature.

Hence, the evidence level of case–control

studies or even case series had to be used to

identify the factors affecting methodology

and to discuss the clinical significance of

biomechanical interface testing.

Consequently, a narrative review was

prepared to cover the aspects of methodol-

ogy, the factors affecting it and its clinical

relevance.

RFA

RFA was first proposed by Meredith et al.

(1996). The technique originally used an

L-shaped transducer that was screwed to an

implant or its abutment. The transducer

beam was then excited over a range of

frequencies, typically from 5 to 15 kHz. A

frequency response analyzer subsequently

analyzed the response of the beam. At the

first flexural resonance of the beam, there

was a marked change in amplitude and in

phase of the received signal. The resonance

frequency can thus be identified in a plot of

the frequency (Hz) against the amplitude (V).

Initially, prototype instruments were

used in a number of studies indicating the

results in Hz. One disadvantage of the

technique is the fact that each transducer

has its own genuine RF and that the RF of

the same implant varies between transdu-

cers. A linear relation was found between

abutment length and RF, and measure-

ments with different transducers and im-

plants with different abutment lengths

have to be calibrated before submitting

the data to statistical analysis.

The first commercial version of the RFA

technique (Osstellt, Integration Diagnos-

tic AB, Goteborg, Sweden) used transdu-

cers that were calibrated by the manu-

facturer. Before performing RFA, a registra-

tion of the implant length was needed. RF

measurements were now expressed as the

implant stability quotient (ISQ) with va-

lues from 1 to 100. These are based on the

underlying and calibrated RF of the trans-

ducer used.

More recently, the commercial instru-

ment was modified; it is now wireless and

makes use of an aluminum peg attached to

an implant or abutment (Mentort, Integra-

tion Diagnostic). The peg is excited and

the RF is expressed electromagnetically as

ISQ units.

Factors influencing RFA

RF was determined by the stiffness of the

bone–implant complex as demonstrated

by performing repeated measurements

of implants placed in self-curing resin

(Meredith et al. 1996). A linear relationship

was found between exposed implant

heights in an aluminum block, which in-

dicated that vertical implant placement,

marginal bone height/ loss and abutment

height influenced RF.

Measurements of 56 implants in the max-

illa of nine patients demonstrated an increase

of RFA values from placement to abutment

connection for all but two implants that

were judged as having failed (Meredith

et al. 1996). Moreover, measurements

of 52 implants in nine patients after at least

5 years in function in the maxilla revealed a

significant relation between effective im-

plant length (abutment lengthþ and bone

loss) and RF, indicating an increase in stiff-

ness of the bone–implant complex with

time, except for the implants that failed.

A correlation between cutting resistance

at implant placement and primary RF va-

lues was reported for maxillary implants

(Friberg et al. 1999b). Repeated measure-

ments indicated that all implants reached

similar RF values at abutment connection

and after 1 year of loading irrespective of

initial stability at the time of installation.

In a study on one-stage implants in dense

mandibular bone, RFA showed small

changes over a 15-week period of time. A

small and significant decrease in RFA va-

lues was observed. However, this could be

explained by marginal bone loss and an

increase in effective implant length (Friberg

et al. 1999a).

More recently, studies using the Osstellt

technique have demonstrated higher stabi-

lity in maxillary than in mandibular bone

(Balleri et al. 2002; Barewal et al. 2003;

Bischof et al. 2004; Balshi et al. 2005;

Becker et al. 2005; Ostman et al. 2006).

A correlation was observed between bone

quality (Lekholm & Zarb index 1985) and

ISQ values in some studies (Bischof et al.

2004; Balshi et al. 2005; Ostman et al.

2006), while other studies failed to demon-

strate such a correlation (Zix et al. 2005).

Furthermore, the influence of gender, im-

plant diameter and implant location on RFA

values was documented as well (Ostman

et al. 2006). In that study, however, decreas-

ing ISQ values were recorded with increasing

implant lengths, which may be explained by

the fact that long implants may have a

reduced diameter in the coronal direction.

In a study with 106 ITI implants placed

in mandibular and maxillary bone, implant

position, length, diameter and vertical po-

sition (sink depth) did not affect the ISQ

values (Bischof et al. 2004).

It has been postulated that implants with

low ISQ values yielded more marked in-

creases in ISQ values with time than im-

plants with high ISQ values (Friberg et al.

1999a, 1999b; Barewal et al. 2003; Olsson

et al. 2003; Nedir et al. 2004; Becker et al.

2005; Sjostrom et al. 2005), indicating that

Aparicio et al . Biomechanical testing of implant/bone interface

3 | Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 2–7

differences in RFA values between im-

plants may diminish with time. It may be

speculated that similar bone densities will

result with time as a consequence of remo-

delling and adaptation to function.

Studies on one stage and immediately

loaded implants have demonstrated an

initial decrease of ISQ values that appeared

to increase within the subsequent 2–3

months (Barewal et al. 2003; Glauser

et al. 2004, 2005; Balshi et al. 2005),

reflecting changes in the bone/implant

interface during the process of osseointe-

gration (Huwiler et al. 2007).

A relation between marginal bone loss

and RFA was observed for mandibular im-

plants, and changes in ISQ values were

reported between implant installation and

a 6-month follow-up, but not between the

6- and the 12-month follow-up (Turkyil-

maz et al. 2006).

Prognostic value of RFA in predicting lossof implant stability

To monitor the outcome of implant instal-

lation and determine the prognostic value

of RFA in predicting loss of implant stabi-

lity, 75 one-stage implants in the edentu-

lous mandible were evaluated over time

(Friberg et al. 1999a). One implant showed

decreasing ISQ values from 2 to 15 weeks,

the observation time at which clinical

mobility was evident. Another patient

within the same study yielded three of

five implants that showed a dramatic de-

cline in ISQ values from 2 to 6 weeks

postoperatively, when the implants were

loaded with a relined denture. Unloading of

these implants subsequently resulted in

recovery of two and maintained stability

of one implant. Hence, the results seemed

to indicate that RFA might, indeed, iden-

tify the loss of implant stability.

A more recent study (Huwiler et al.

2007) assessed ISQ values at the time of

implant installation of ITI implants (Strau-

mann, Basel, Switzerland) and at 1, 2, 3, 4,

5, 6, 8 and 12 weeks thereafter. One im-

plant lost clinical stability after 3 weeks.

At this time, the ISQ had declined signifi-

cantly from 70, 69 and 68 to 45. However,

the loss of clinical stability was coinciden-

tal to the low ISQ, but not to be predicted

by RFA. In the remaining 16 implants of

identical length, sink depth and diameter

in nine patients, the ISQ at the time of

installation did not correlate with a micro-

CTanalysis of the bone density or the bone

trabecular connectivity of the parent jaw-

bone. ISQ values decreased slightly after

2–4 weeks and increased thereafter to the

levels of the time at implant installation or

higher, reflecting the changes observed at

the bone/implant interface during the pro-

cess of osseointegration (Abrahamsson

et al. 2004). It has to be noted that in the

reported study (Huwiler et al. 2007), the

numerical value of the implant having lost

stability after 3 weeks (ISQ¼ 45) was only

marginally outside the range of the ISQ

values reported for all the other implants

at all observation periods.

In a longitudinal study on immediate

loading, RFA was performed on 72 stable

implants and compared with nine implants

that had lost stability during the course of 1

year (Glauser et al. 2004). Both groups of

implants showed a high degree of initial

stability documented by an ISQ¼ 70. The

implants losing stability showed a contin-

uous decrease in ISQ values until clinical

failure was evident. The mean ISQ value

was statistically lower for the group with

implants having lost stability (ISQ¼52)

than for the group with stable implants

(ISQ¼ 68). The lower the ISQ value was

after 1 month of immediate loading, the

higher was the risk for future loss of stabi-

lity. The risk for loss of stability was 18.2%,

if ISQ values were between 49 and 58.

In a study on implant stability in grafted

maxillae, only a tendency towards lower

initial ISQ values was found for 17 im-

plants that lost stability during the study

(ISQ¼ 54.6) compared with 195 implants

that remained stable (ISQ¼ 62) (Sjostrom

et al. 2005).

Comparing immediately loaded ITI im-

plants with implants loaded after 3 months

of healing, the RFA technique was judged

to be an unreliable methodology for the

identification of mobile ITI implants

(Nedir et al. 2004). However, implant sta-

bility was reliably determined for implants

with an ISQ447. The insensitivity of de-

tecting unstable implants was explained by

the nature of the RFA technique, which

appears to determine stability as a function

of stiffness. Mobile implants display extre-

mely low stiffness and hence, the first

resonance frequency may not be identifi-

able, resulting in false increased ISQ values

that may correspond to the second reso-

nance frequency (Meredith 1998a, 1998b).

Conclusions for RFA

Although extensively used in clinical re-

search 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 yield-

ing high 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 ques-

tioned.

Further research is needed to establish

threshold ranges for implant stability and

for implants at risk for losing stability for

different implant systems.

Periotests

(braking point)

Periotests

(Gulden-Medizintechnik, Ben-

sheim an der Bergstra�e, Germany) is an

electronic instrument originally designed to

perform quantitative measurements of the

damping characteristics of the periodontal

ligament surrounding a tooth, thereby estab-

lishing a value for its mobility (Schulte et al.

1983; Schulte & Lukas 1993). The Periot-

ests

instrument comprises a hand piece

containing a metal slug that is accelerated

towards a tooth by an electro-magnet. The

contact duration of the slug on the tooth is

measured by an accelerometer. The soft-

ware in the instrument is designed to relate

contact time as a function of tooth mobility.

The result is displayed digitally and audibly

as Periotests

values (PTVs) on a scale of �8

(low mobility) to 50 (high mobility). The

technique has also been used to determine

implant mobility, and typical values ob-

tained were defined as ranging from �5 to

þ 5, thus representing a narrower range over

the scale of the instrument than for tooth

mobility measurements. A stable implant

will exhibit different stiffness characteristics

compared with those of teeth that are

connected by a periodontal ligament.



Factors influencing PTVs

Inter-operator and inter-instrument varia-

bility has been studied extensively (Teer-

linck et al. 1991; Manz et al. 1992a,

1992b; Chai et al. 1993; Derhami et al.

1995). A linear relationship between con-

tact time and PTVs resulted for implants

assessed in vitro and in vivo, indicating the

robustness of the instrument (Meredith

et al. 1996; Meredith 1998a, 1998b).

Both in vitro and in vivo studies indi-

cated a linear relationship between the

vertical distances from the striking point

to the first bone contact on the PTVs (Chai

et al. 1993; Meredith et al. 1996; Haas

et al. 1999). It was, therefore, concluded

that single Periotests

measurements do not

allow any prognosis for the stability of an

implant, but that an individual implant

may and should be measured repeatedly

during follow-up.

A mathematical model illustrating the

effect of various geometric and clinical para-

meters on the PTV was developed (Faulkner

et al. 2001). In addition, the model was

validated in an in vitro experiment. The

results showed that PTVs were sensitive to

the position on which the Periotests

im-

pacted on the abutment and hence, de-

pended on the angulations of the hand

piece. A change in position of 1 mm in

striking height may produce a difference in

PTVs between 1 and 2 (Olive & Aparicio

1990; Teerlinck et al. 1991; Tricio et al.

1995a, 1995b). As the outcome of Periot-

ests

measurements is influenced by the

distance from the striking point to the first

bone contact, it is evident that the place-

ment of the implant in vertical dimension,

abutment height, the level of marginal bone

loss and the striking position on the abut-

ment/implant are critical factors for accu-

racy and/or reproducibility. Clinical studies

using various implant systems have demon-

strated significantly lower PTVs in mandib-

ular than in maxillary bone, indicating

higher stability in the former than in the

latter location (Buser et al. 1990; Olive &

Aparicio 1990; van Steenberghe et al. 1995;

Salonen et al. 1997).

Based on measurements of 2212 im-

plants of various designs, the lowest PTVs

were characteristic for very dense bone

(Class 1: Lekholm & Zarb 1985). How-

ever, no linear correlation between the

degree of bone density and PTVs was es-

tablished (Truhlar et al. 1997, 2000). An

inverse correlation between insertion tor-

que values and PTVs as well as between

bone density around implants in fresh bo-

vine ribs and PTVs was demonstrated in an

in vitro study (Tricio et al. 1995b). Also, a

relationship between number of engaged

cortical layers (no cortical bone, mono-

and bicortical anchorage) and PTVs was

established (van Steenberghe et al. 1995).

For TPS bicortical screws, lower PTVs

were observed than for ITI implants (Salo-

nen et al. 1997), while, in another study

and evaluating very similar ITI implants,

no correlation could be detected between

PTVs and bone density determined histo-

logically in bone core biopsies from im-

plant sites in the mandible (Mericske-Stern

et al. 1995).

Regarding the effect of implant length on

PTVs, contradictory results have been re-

ported. While a correlation was postulated

by some authors (van Steenberghe et al.

1995), others only described this for the

maxilla (Olive & Aparicio 1990; Teerlinck

et al. 1991; Tricio et al. 1995a; Salonen et al.

1997) and another group of authors did not

find any correlations (Haas et al. 1995; Mer-

icske-Stern et al. 1995; Tricio et al. 1995b).

Evaluating four different implant sur-

faces in an animal model, neither a correla-

tion between PTVs and marginal bone

height nor between PTVs and bone con-

tacts as determined histologically was

found (Caulier et al. 1997).

Subjecting screw-shaped implants to exces-

sive occlusal load and comparing these with

implants subjected to plaque accumulation in

primates, some, but not all excessively loaded

implants showed signs of clinical mobility

while all implants with plaque accumulation

were stable after 18 months (Isidor 1998).

The PTVs correlated with the marginal bone

loss and degree of bone–implant contact.

However, for the clinically stable implants,

thus excluding the unstable ones, no correla-

tion could be demonstrated. In a primate

model (Carr et al. 1995), the relation be-

tween PTVs and removal torque to induce

loss of stability for three types of implant

surfaces was judged to be too weak for the

Periotests

to predict torque to failure and

vice versa. The Periotests

instrument was

also evaluated to measure implant mobility

in a controlled in vitro model (Chavez et al.

1993). The range of mobility as determined

by the Periotests

instrument in vivo was

�6 to þ 2. The authors concluded that

clinically stable implants were not comple-

tely immobile as revealed by PTVs, but

yielded a range of mobility.

Time elapsed since implant installation

appears to influence implant stability. This

is rationalized by the fact that lower PTVs

are usually encountered with increasing

time of follow-up (Teerlinck et al. 1991;

Mericske-Stern et al. 1995; Tricio et al.

1995a, 1995b; van Steenberghe et al. 1995;

Naert et al. 1997, 1998a, 1998b, 2004;

Aparicio et al. 2001; Tawse-Smith et al.

2001). Decreasing PTVs were observed up

to the fifth year of follow-up for 213

mandibular implants used for the retention

of overdentures (van Steenberghe et al.

1995). This was interpreted as ongoing

remodelling and stiffening of the interface

following implant installation.

Prognostic value of PTVs in predicting lossof implant stability

Evaluating PTVs of eight implants that lost

stability after prosthesis placement (Olive

& Aparicio 1990), six of eight implants

showed PTVs of þ 4 or higher as deter-

mined at the time of abutment connection.

All eight implants demonstrated PTVs

from þ13 to þ30 at the time of loss of

stability. Nine other implants with high

initial PTVs (þ3 to þ 8) were left un-

loaded for at least 4 months. This resulted

in a decrease of PTVs (final measurements

were from 0 to þ5). In addition, two cases

demonstrated high PTVs at the time of loss

of implant stability. Derived from single

case reports, the data suggest that high

PTVs at abutment connection may indicate

questionable osseointegration and may

suggest increased risk for loss of stability

if loaded. However, the level of evidence

remains anecdotal and precludes the prog-

nostic value of the Periotests

.

When evaluating PTVs of four different

implant systems after an average of 22.5

months after installation, 14 of 204 im-

plants lost stability with all those yielding

positive PTVs (Salonen et al. 1997). Also,

significantly higher PTVs were found than

for stable implants, except for the ITI im-

plants in the maxilla.

In a sequential study in 40 patients eval-

uating PTVs after implant abutment connec-

tion, prosthetic impression, placement of the

prosthesis and 6 and 12 months after occlu-

sal loading (Drago 2000), The Periotests

instrument was able to identify 64% of the



non-integrated implants at abutment con-

nection and 12 months after occlusal load-

ing. However, PTVs recorded at abutment

connection failed to predict loss of implant

stability at 12 months of functional loading.

In an attempt to validate PTVs and other

clinical and radiographic parameters for the

detection of alveolar bone loss around 32

cylindrical implants in 16 patients (Verhoe-

ven et al. 2000), it was demonstrated that

radiographs disclosed pathological loss of

alveolar bone at the bone–implant contact

area, while other parameters including

Periotests

assessments did not.

Conclusions for Periotests

Although the Periotests

instrument has

been extensively evaluated in experimental

and clinical research, prognostic value to

detect loss of implant stability cannot be

documented. A variety of factors, such as

the striking position (abutment length,

supracrestal implant length) and loca-

tion within the jaw (mandible/maxilla),

have been shown to influence the PTVs.

It is evident that negative PTVs indicate

stability of implants, while high and

positive PTVs may suggest loss of stabi-

lity. However, such increases in PTVs

are often realized after the fact indicating

a high specificity of the Periotests

, while

its sensitivity may be low. Owing to

a variety of factors, the reproducibility

of assessments is questionable. Single read-

ings of Periotests

determinations are

of limited clinical value and have not

been demonstrated to reflect the nature

of the bone/implant interface. By perform-

ing repeated measurements of the same

implant over time, implant stability may

be confirmed.

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