from osseoperception to implant-mediated sensory-motor

Review Article

From osseoperception to implant-mediated sensory-motor

interactions and related clinical implications*

R. JACOBS & D. VAN STEENBERGHE1 Laboratory of Oral Physiology, Department of Periodontology, Faculty of

Medicine, Catholic University of Leuven, Leuven, Belgium

SUMMARY Osseointegration of implants in the jaw

bone has been studied thoroughly, dealing with

various aspects such as bone apposition, bone qual-

ity, microbiology, biomechanics, aesthetics, etc. A

key issue that has received much less attention is

the physiologic integration of the implant(s) and the

associated prosthesis in the body. The latter aspect is

however very important to obtain new insights in

oral functioning with implant-supported pros-

theses. Amputated patients rehabilitated with a

lower limb prosthesis anchored to the bone by

means of an osseointegrated implant, have reported

that they could recognize the type of soil they were

walking on. Clinical observations on patients with

oral implants, have confirmed a special sensory

perception skill. The underlying mechanism of this

so-called osseoperception phenomenon remains a

matter of debate, because extraction of teeth

involves elimination of the extremely sensitive

periodontal ligaments while functional reinnerva-

tion around implants is still uncertain. Histological,

neurophysiological and psychophysical evidence of

osseoperception have been collected, making the

assumption more likely that a proper peripheral

feedback pathway can be restored when using

osseointegrated implants. This implant-mediated

sensory-motor control may have important clinical

implications, because a more natural functioning

with implant-supported prostheses can be attemp-

ted. It may open doors for global integration in the

human body.

KEYWORDS: osseoperception, dental implant, jaw,

trigeminal nerve, tactile function, physiology

Accepted for publication 1 January 2006

Introduction

Sensory feedback plays an essential role in fine tuning

of limb motor control. Thus, it is clear that amputation

of a limb will not only involve destruction of an

important part of the peripheral feedback pathways, but

also hamper fine motor control. Conventional socket

prostheses do not carry enough sensory information to

restore the necessary natural feedback pathways for

motor function (1). Comparable observations can be

made after extraction of teeth. The periodontal liga-

ment harbours a very rich innervation, carrying refined

mechanoreceptive properties by an intimate contact

between collagen fibres and Ruffini-like endings (2).

The role of periodontal neural feedback is well-known

(3, 4). After extraction of teeth however, this feedback

pathway may be damaged as periodontal ligament

receptors are eliminated. Thus, the impact of tooth

extraction on the sensory feedback pathway seems

considerable (36). Dentures can be compared with

socket prostheses and are not able to fully compensate

for normal tooth loading and force transfer. The

peripheral feedback mechanisms are more limited as

the mucosal mechanoreceptor function is less efficient

than the periodontal ligament function. Consequently,

oral function remains impaired (4).

*Based on the Journal of Oral Rehabilitation Summer School 2005 in

Bavagna, Italy. Kindly sponsored by Blackwell Munksgaard and Nobel

Biocare.1Holder of the P-I Branemark Chair in Osseointegration

2006 The Authors. Journal compilation 2006 Blackwell Publishing Ltd doi: 10.1111/j.1365-2842.2006.01621.x

Journal of Oral Rehabilitation 2006 33; 282292

It has been assumed that by anchoring prosthetic

limbs directly to the bone via osseointegrated implants,

partial sensory substitution can be realized (1, 5, 6). If

the feedback pathway can be restored, such concept of

bone-anchored limb prostheses would signify an

important step towards global integration of a pros-

thesis in the body. Amputated as well as edentulous

patients, rehabilitated with a bone-anchored prosthesis,

report a specific feeling around endosseous implants.

Psychophysical threshold determination studies con-

firmed that patients may perceive mechanical stimuli

exerted on osseointegrated implants in the bone

(1, 5, 6). This phenomenon has raised questions. Would

this special feeling result from a changed impact force

through the rigid implantbone interface, in contrast to

the cushioning effect of the skin or mucosa under the

socket prosthesis? Or would intra-osseous or periosteal

neural endings be involved?

The latter observations brings along the discussions of

which receptor groups are responsible for this so-called

osseoperception phenomenon. New insights and more

objective non-invasive approaches may help clarifying

this question. First, Somatosensory Evoked Potentials

(SEPs), which are routinely used to screen for neuro-

logical disorders, could assist localizing the origin of

sensory phenomena observed upon implant stimula-

tion. For trigeminal SEPs, thorough signal analyses are

needed rather than visual inspection, to obtain reliable

data on the SEP signals and enable further interpret-

ation on the receptors activated upon implant stimula-

tion (7, 8). A most promising approach is the use of

functional Magnetic Resonance Imaging (fMRI), which

has the advantage of being a static and/or dynamic

imaging technique, without the drawback of exposure

to ionizing radiation (9). This fMRI might help visual-

izing activity centres on the pathway from the stimu-

lation site to the cortex. Both non-invasive approaches

offer new perspectives for osseoperception research and

may try linking the anatomical and histological back-

ground to the clinical observations. If such link is

present, osseoperception might help in physiologic and

functional integration of implants in the body.

The present review attempts to provide arguments

and scientific evidence to support this hypothesis.

Neurovascularization of the jaw bones

The jaws are richly supplied by neurovascular struc-

tures. This needs to be carefully considered when

performing surgical procedures in the jaw, such as

inserting implants. Pre-surgical localization of neuro-

vascular structures is essential to guarantee an

uneventful outcome (10). On the other hand, the rich

jaw bone innervation may help to sense mechanical

deformation during loading of oral implant and thus

contribute to restore peripheral feedback after tooth

extraction and implant placement. Even in the anterior

jaw bone, where the presence and functional signifi-

cance of neurovascularization was somewhat neglected

in the past, recent studies on a variety of human

cadaver material have confirmed a rich innervation

with clear sensory nerve characteristics (1012)

(Fig. 1). The neurovascular content of a well-defined

mandibular incisive and lingual canal and a maxillary

nasopalatine canal structure may explain a number of

altered sensations after anterior implant placement

(Fig. 2).

Histological background

Tooth extraction results in damage of a large number of

sensory nerve fibres and corresponds to an amputation,

where the target organ and peripheral nervous struc-

tures have been destroyed (13). After extraction of

teeth, the myelinated fibre content of the inferior

alveolar nerve is reduced by 20% (14). This finding

indicates that fibres originally innervating the tooth and

periodontal ligament are still present in the inferior

alveolar nerve. Linden and Scott (15) succeeded to

stimulate nerves of periodontal origin in healed extrac-

tions sockets, which implies that some nerve endings

remain functional. Nevertheless, most of the surviving

mechanoreceptive neurons represented in the mesen-

cephalic nucleus may lose some functionality (15).

These experiments have been the basis for a further and

long-lasting debate on the presence and potential

function of sensory nerves fibres in the bone and

peri-implant environment. Histological evidence indi-

cates that there may be some reinnervation around

osseointegrated implants (16, 17). Indeed, it has been

shown that endosseous implants may lead to degener-

ation of environing neural fibres by surgical trauma.

Soon however, sprouting of new fibres is observed and

the number of free nerve endings close to the bone-to-

implant interface gradually increases during the first

weeks of healing (18). Amore recent study in the dog has

succeeded to partially regenerate the periodontal liga-

ment on an implant surface (19). Whether such regen-

O S S EO P E R C E P T I O N AND S E N SOR Y -MO TOR I N T E RA C T I O N S 283

2006 The Authors. Journal compilation 2006 Blackwell Publishing Ltd

eration might also induce restoration of the peripheral

feedback pathway has however not been studied.

On the other hand, existing mechanoreceptors in the

periosteum may also play a role in tactile function upon

implant stimulation. It is evident that oral implants

offer another type of loading and force transfer than

teeth, considering an intimate bone-to-implant contact

with elastic bone properties instead of the characteristic

viscoelasticity of the periodontal ligament. Thus, forces

applied to osseointegrated implants are directly trans-

ferred to the bone and bone deformation may lead to

receptor activation in the peri-implant bone and the

neighbouring periosteum (20).

Cortical plasticity after tooth extraction

The cortex of the brain reveals a somatotopically ordered

representational map for movements that resembles a

distorted cartoon of the body (21). After limb amputa-

tion, the regions of the cortex deprived of a target acquire

new targets. Remodelling takes place at a cortical or

subcortical level (22). The potential cortical adaptation

and/or plasticity that might occur after tooth extraction

and implant placement has not yet been fully explored.

A very interesting study was recently carried out on

mole-rats (23). Henry et al. (23) extracted the lower right

incisor in mole-rats. Five to 8 months afterwards, the

oro-facial representation in S1 was considerably reor-

ganized. Neurons in the cortical lower tooth representa-

tion were responsive to tactile inputs from surrounding

oro-facial structures. This studymay indicate that cortical

representation of teeth may significantly restructure

after tooth loss. These data parallel findings after deaf-

ferentation in the somatosensory hand area of primates

where tactile inputs from the chin and upper arm may

activate the hand cortical area.

Unfortunately, until now, similar evidence in

humans has not yet been produced. Future research

should therefore try to visualize cortical plasticity after

Fig. 2. Placement of implants in the anterior mandible may

present some risk for neurovascular damage. In the present cross-

sectional image of a cone beam CT of the anterior mandible, the

intimate contact between a canine osseointegrated implant and

the incisive nerve becomes obvious.

(a)

(b)

Fig. 1. Histological section (a) and high resolution MRI image (b)

show one bony canal branching into two canals. Figure (a)

visualizes two branches (arrow) of the canal on a histological

section. Figure (b) is an horizontal MRI section showing one bony

canal (grey arrow) branching into two canals (black arrows).

[Reprinted from Dentomaxillofacial Radiology, vol.34, Liang X,

Jacobs R, Lambrichts I, Vandewalle G, van Oostveldt D, Schepers

E, Adriaensens P, Gelan J. Microanatomical and histological

assessment of the content of superior genial spinal foramen and its

bony canal, pp 362368, Copyright 2005, with permission from

the British Institute of Radiology].

R . J A COB S & D . V AN S T E E N B E RGH E284


tooth extraction and further functional rehabilitation

with implants. It should be considered that an imme-

diate extraction and implant rehabilitation protocol

might induce a different cortical remodelling than a

traditional two-stage implant rehabilitation protocol.

An interesting phenomenon with respect to sensory-

motor integration of osseointegrated implants, may be

the so-called phantom tooth (after extraction) or

phantom limb (after amputation), allowing perception

of lost body parts (24). In fact, it could be assumed that

such a phantom feeling of the lost limb may overlap

with or enforce the feeling of a bone-anchored pros-

thetic limb (1, 5). In this way, phantom sensations

might contribute to physiological integration of a bone-

anchored prosthesis in the human body (5).

Neurophysiological versus psychophysicaldata

Information on oral tactile function can be examined by

neurophysiological as well as psychophysical methods.

Neurophysiological investigations on the sensory func-

tion of the trigeminal system in man are scarce.

Afferent nerve recordings of the human trigeminal

nerve require skilful performance and only few studies

have been reported so far (2527). [see also review by

Trulsson (28)].

Evidence can also be found by non-invasive approa-

ches for evaluation of oral tactile function. The first

approach is the recording of the so-called trigeminal

somatosensory evoked potentials (TSEP) after stimula-

tion of receptors in the oral cavity (7, 8). This set-up has

the advantage of obtaining information on the cortical

response of the trigeminal afferent system upon non-

invasive stimulation of oral receptors. Another non-

invasive method to assess sensory function is the

visualization of brain activities by fMRI (9). It is a very

promising technique, which has so far received hardly

any attention in relation to tactile function of teeth and

implants.

Conversely, psychophysical studies on the oral sen-

sory function are numerous (4). A major advantage of

this type of studies is that these are simple non-invasive

techniques that may be performed in a clinical

environment. Psychophysics includes a series of well-

defined methodologies to help determining the thresh-

old level of sensory receptors in man. Psychophysical

methods allow connecting the psychological response

of the patient to the physiological functions of the

receptors involved. When performed meticulously and

under standardized conditions, these studies may reveal

nearly as precise information as neurophysiological set-

ups (3, 4, 29).

Regardless of the tests used, one must keep in mind

that many variables contribute to the subjective nature

of psychophysical sensory testing. Some variables are

manageable, others are more difficult to deal with. The

influencing factors are found in the different compo-

nents of the experimental set-up (environmental influ-

ence, psychophysical approach, patient-related factors,

etc.) (3, 4, 29).

Environmental factors should be well-controlled as

background noise is distracting to patient and examiner.

Tominimize the effect of noise, testing should be done in

a quiet room with stable background illumination (29).

Different psychophysical procedures have been des-

cribed in order to reliably assess tactile function (30).

Adaptive methods are generally recommended for

threshold level determination, as these seem very

effective and consistent. Such approaches are called

adaptive as the subsequent stimulus value depends on

the subjects response in the preceding trials. In the

staircase method, the stimulus value is changed by a

constant amount. When the answer shifts from one

answer to another, the stimulus direction is changed. The

threshold is then determined by averaging the peaks and

valleys throughout all runs. Some patients may imagine

a stimulus when there is none. Others admit feeling a

sensation only if they are absolutely positive that it was

felt. The inclusion of false alarms (implying that no

stimulus is presented in the specified time interval) may

exclude response bias and a guessing strategy of the

subject. A thorough and standardized instruction to all

subjects is important in this perspective.

Other patient-related factors that should be consid-

ered are of physical origin and include age, gender,

dental status, and dexterity. Age is an important

variable with respect to implant physiology, consider-

ing the fact that edentulous patients are usually found

amongst the elderly. In general, motor changes occur

with age leading to impairment of balance and

unsteadiness of motion. Besides, a deterioration of

most sensory modalities in the distal extremities occurs

(31). A decline in oral sensory function is also

established. After the age of 80, the ability to differ-

entiate tactile and vibratory stimuli on the lip decrea-

ses and two-point discrimination deteriorates on the

upper lip, on the cheeks and on the lower lip, but not



on the tongue and the palate (32). The stereognostic

ability also declines with age (33, 34). It is clear that

this age-effect should be considered in experimental

studies.

In contrast to age, the existence of some gender effect

remains a matter of debate. Taking into account the

important inter-individual variability, clear-cut gender

differences are not easily discerned with regard to oral

sensory function. There is no marked gender effect on

stereognostic ability or vibrotactile function (35, 36).

The tactile sensory systems of men and women seem to

operate similarly at both threshold and suprathreshold

levels of stimulation (37, 38). However, females seem to

have greater ability to discern subtle changes in lip,

cheek and chin position than males (38). Dexterity is

another patient-related variable. Although there is

some relation between masticatory performance and

dexterity (39), this is the case for neither tactile

function nor stereognosis (29, 40).

Tactile function of oral implants

Periodontal neural receptors play an essential role in

oral tactile function (3). Most receptors can be found in

the periodontal ligament, which is evidently lacking

around permucosal oral implants. In that case, remain-

ing receptors in gingiva, alveolar mucosa and periost-

eum may take over part of the normal exteroceptive

function.

It seems attractive to explain the observed tactile

sensitivity of endosseous implants, coined osseopercep-

tion, by the surrounding endosseous and periosteal

neural endings. To prove it, part of the evidence is

provided by a series of psychophysical and neurophys-

iological experiments in man (4, 5). Neurophysiological

evidence can be found in some experiments evoking

TSEPs upon implant stimulation. By triggering sweeps

in the electroencephalogram by means of an implant

stimulation device and by cumulating and advanced

analysis of the sweeps, one can finally note significant

waves. The experiments indicate that it is indeed

endosseous and/or periosteal receptors around the

implants, which convey the sensation (8, 41).

Psychophyscial testing has been performed by active

and passive (vibro)tactile detection and discrimination

tasks as well as by oral stereognosis (4, 29). During

active threshold determination, subjects are asked

detecting foils placed in between the teeth. During

passive threshold level assessment, the concentrated

patient is undergoing an external force applied to the

implant (Fig. 3). As soon as the subject detects the foil

or the force, he has to signal it (29). From several

studies, it has been established that the oral tactile

function is influenced by tooth position and dental

status (3, 4, 6, 29). The tactile function of teeth is

primarily determined by the presence of periodontal

ligament receptors. Vital or non-vital teeth show a

comparable tactile function (4) (Table 1). However,

when periodontal ligament receptors are reduced in

numbers or eliminated (e.g. periodontitis, chewing,

extraction, anaesthesia, etc.), tactile function is

impaired (4). This clinically implies that the patients

ability to detect occlusal inaccuracies is decreased in

these situations. Indeed, exteroceptors inform the

nervous system on the characteristics of the stimulus,

which then allows modulation of the motoneuron pool

to avoid overloading. Elimination of these exterocep-

tors by tooth extraction may reduce the tactile function

to an important extent (4, 6, 42, 43). Even after

rehabilitation with a prosthesis, the tactile function

remains impaired. The inappropriate exteroceptive

feedback may thus present a risk for overloading the

Fig. 3. Set-up of passive threshold determination of a maxillary

front tooth by applying axial pushing forces against the tooth.

Table 1. Factors influencing the tactile function of teeth (6, 28,

41, 42)

Dental status

Active detection

threshold (lm)Passive detection

threshold (g)

Vital tooth 20 2

Non-vital tooth 20 2

Removable prosthesis 150 150

Implant-supported

prosthesis

50 100



prosthesis (1, 5). In comparison with the tactile func-

tion of natural dentitions, the active threshold is seven

to eight times higher for dentures but only three to five

times higher for implants (42) (see Table 1). For the

passive detection of forces applied to upper teeth,

thresholds for dentures are 75 times increased and for

implants 50 times (43) (see Table 1). The large discrep-

ancies between active and passive thresholds can be

explained by the fact that several receptor groups may

respond to active testing, while the passive method

selectively activates periodontal ligament receptors. The

latter are eliminated after extraction, which may

explain the reduced tactile function in edentulous

patients. After rehabilitation with a bone-anchored

prosthesis however, edentulous patients seem to func-

tion quite well. These patients perceive mechanical

stimuli exerted on osseointegrated implants in the jaw

bone (43). If subjects are followed up after implant

placement, there is a noticeable improvement in tactile

function with oral implants following a 3-months

healing period (44). Some people rehabilitated with

osseointegrated implants even note a special sensory

awareness with the bone-anchored prosthesis, coined

osseoperception (1, 5). The existence of this phenom-

enon could imply that the feedback pathway to the

sensory cortex is partly restored with an hypothetical

representation of the prosthesis in the sensory cortex

allowing a more appropriate modulation of the moto-

neuron pool leading to a more natural functioning and

avoiding overload.

Oral mechanoreceptors activated duringoral tactile function

When performing psychophysical testing, various types

of oral mechanoreceptors may be activated. Mecha-

noreceptors in the oral region may be located in

the periodontal ligament, oral mucosa, gingiva, bone,

periosteum, and tongue. Mechanoreceptors in the

periodontal ligament contribute to the very high

sensitivity of teeth to mechanical stimuli (3, 4). The

periodontal ligament is richly supplied with mecha-

noreceptors, with the majority being identified histo-

logically as Ruffini-like endings (2). During passive

threshold determination, these receptors will be acti-

vated. The assessment of the active tactile threshold

level however is not solely based on activation of

periodontal mechanoreceptors. Temporomandibular

joint (TMJ) receptors are found to play only a minor

role but muscular receptors are important in the

discriminatory ability for mouth openings of 5 mm

and more (45). In the oral mucosa, different types of

mechanoreceptors can be identified including Meiss-

ners corpuscules, glomerular endings, Merkel cells,

Ruffini-like endings, and free nerve endings. The

number of nerve fibres per unit area is greater in

the anterior areas of the oral cavity, making this region

the most sensitive part of the oral mucosa (46).

The gingiva contains round and oval lamellar cor-

puscles (2). These receptors respond to mechanical

stimuli and are involved in the co-ordination of lip and

buccal muscles during mastication (25, 26). Cutaneous

mechanoreceptors in the facial skin are activated by

skin stretching or contraction of facial muscles and may

operate as proprioceptors involved in facial kinaesthesia

and motor control (47).

The periosteum contains free nerve endings, complex

unencapsulated and encapsulated endings. The free

nerve endings are activated by pressure or stretching of

the periosteum through the action of masticatory

muscles and the skin (20). When applying forces to

osseointegrated implants in the jaw bone, it might be

assumed that the pressure build-up in the bone is

sometimes large enough to allow deformation of the

bone and its surrounding periosteum (43). The involve-

ment of bone innervation in mechanoreception

remains however a matter of debate (48).

Oral stereognosis and osseointegration

Another functional test is the so-called stereognosis.

The stereognostic ability is defined as the ability to

recognize and discriminate different forms presented as

a stimulus (49). While touch may obtain information

on the mechanoreceptors activated by simple detection

or discrimination of mechanical stimuli, stereognosis is

a more complex process. It is a function of both

peripheral receptors (touch and kinaesthetic) and cen-

tral integrating processes (49). It may give an idea on

daily functioning and may be applied to measure

sensory impairment because of the presence of general

or local pathology (speech pathology, blindness, deaf-

ness, cleft lip and palate, temporary sensory ablations,

etc.).

A change in the oral cavity by means of partial or

complete loss of the dentition certainly creates certain

changes to the oral sensory function. In dentate

subjects, the role of periodontal neural receptors



and of the tongue seems essential. After a bilateral

mandibular block, the stereognostic ability decreases

with about 20% (50). When comparing teeth with full

dentures, a far better stereognostic ability is noted for

natural teeth when freely manipulating the test pieces

(49, 50). When removing the denture(s) in complete

denture wearers, a considerable reduction in stereo-

gnostic ability is noted (50). An interesting observation

is that edentulous subjects showing a lot of problems

and a low satisfaction level after insertion of their new

denture demonstrate higher levels of oral stereognostic

ability than those subjects having few or no problems

(51), but this could not be confirmed by Muller et al.

(34).

Lundqvist (52) demonstrated an improvement of

the stereognostic ability after rehabilitation with oral

implants. Jacobs et al. (53) compared different pros-

thetic superstructures and noted no significantly

different stereognostic ability with implant-supported

fixed or removable prostheses, even when elimin-

ating the involvement of tongue- and lip receptors

(Fig. 4).

Oral mechanoreceptors activated duringoral stereognosis

To assess the stereognostic ability, test pieces are

inserted in the oral cavity and in most experimental

set-ups free manipulation of the test pieces is allowed.

The latter implies activation of a large number of

receptor groups (periodontal, mucosal, muscular, arti-

cular, etc.]. As the tip of the tongue is one of the most

densely innervated areas of the human body, it plays an

important role in stereognosis of objects inserted in the

mouth (49). Based on studies involving anaesthesia of

the tongue, the palate or the absence of teeth, it could

be stated that oral stereognostic ability is determined

mostly by receptors in the tongue mucosa, the palate

and to a lesser extent the periodontal ligament (49).

A major modification to the experimental set-up is the

insertion of a toothpick in each test piece to eliminate

the involvement of lip and tongue receptors, to allow

easy handling and standardized placement in between

two antagonistic teeth (53) (Fig. 5).

The role of the TMJ receptors is less clear. In fact, in

studies on tactile function, an interocclusal thickness of

5 mm and more seems able to activate receptors in the

TMJ and the jaw muscles (4, 45). In the stereognostic

ability tests, pieces are mostly manipulated inside the

mouth and seldom kept between two antagonistic

teeth, which excludes very often the need for a mouth

opening of 5 mm or even more.

Stereognostic ability testing is not designed to detect

specific receptor groups, it rather reflects an overall

sensory ability. A good result in a stereognosis test

should indicate that the subject receives full and

accurate information about what is going on in the

mouth. Even if manipulation is allowed to identify the

0

10

20

30

40

50

60

70

80

90

100%

Cor

rect

iden

tific

atio

ns

Fixed

prost

hesis

on im

plants

Over

dentu

re on

impla

nts

Full d

entur

e

Teeth

with p

erido

ntitis

Healt

hy tee

th

Fig. 4. Average of correct identifica-

tions out of 10 for all the groups in

the oral test. [Reprinted from Clinical

Oral lnvestigations, vol. 1, Stereo-

gnosis with teeth and implants: a

comparison between natural

dentition, implant-supported fixed

prostheses and overdentures on

implants, pp 8994, Copyright 1997:

with kind permission of Springer

Science and Business Media].



test piece, identification itself is a sensory rather than a

motor accomplishment (49). It is an indicator of

functional sensibility including synthesis of numerous

sensory inputs in higher brain centres (49).

From osseoperception to implant-mediated sensory motor interactions

During the last few decades, millions of patients have

already been rehabilitated by means of osseointegrated

implants. Although part of the peripheral feedback

mechanism is lost after tooth extraction, edentulous

patients seem to function quite well, especially when

rehabilitated with a prosthesis retained by or anchored

to osseointegrated implants (5). These findings corres-

pond well to the observation in amputees rehabilitated

with a bone-anchored prosthesis rather than a socket

prosthesis. During skeletal reconstruction, psychophys-

ical testing reveals an improved tactile and vibrotactile

capacity with an osseointegrated implant and the bone-

anchored prosthetic limb (Fig. 6). Furthermore, both

edentulous patients and amputees seem to report an

improved awareness and special feeling with the

implant-supported prosthesis, allowing a partial restor-

ation of the peripheral feedback pathway with a

hypothesized potential representation of the artificial

limb feeling in the sensory cortex. If that could be

confirmed, osseointegrated implants in the jaw or

other skeletal bones might contribute to an implant-

mediated sensory-motor control allowing physiological

Fig. 5. The stereognostic ability is defined as the ability to

recognize and discriminate different forms presented as a stimulus.

(a) To eliminate the involvement of lip and tongue receptors, as

well as to allow easy handling and standardized placement in

between two antagonistic teeth, a toothpick is inserted in each test

piece. (b) As soon as the subject has identified the form of the test

piece, he has to indicate it on a chart visualizing the various forms

presented in the mouth.

(a)

(b)

Fig. 6. Vibrotactile testing of a lower arm (a) and a lower leg (b)

prosthesis yields superior functioning with such bone-anchored

prosthetic limbs as compared with conventional socket prostheses.

[Reprinted from Prosthetics and Orthotics International, vol. 24,

JacobsR,BranemarkR,OlmarkerK,RydevikB, vanSteenbergheD,

Branemark P-I. Evaluation of the psycho-physical detection

threshold level for vibrotactile and pressure stimulation of prosthe-

tic limbs using bone anchorage or soft tissue support, pp 133142,

Copyright 2000, with permission from Taylor and Francis].

O S S E O P E R C E P T I O N AND S E N SOR Y -MO TOR I N T E RA C T I O N S 289


integration of the implant in the human body. The

phenomenon of the so-called osseoperception might

contribute to physiological integration and more nat-

ural functioning. Originally, osseoperception has been

defined as the conscious perception of external stimuli

transmitted via a bone-anchored prosthesis by activa-

tion of neural endings and/or receptors in the peri-

implant environment such as the bone and more likely

the periosteum (5). To put stress on the incorporation

of the tactile function in a series of sensory-motor

interactions, a recent consensus statement on osseo-

perception added the aforementioned sensory-motor

interactions to the definition, yielding: (i) the sensation

arising from mechanical stimulation of a bone-

anchored prosthesis, transduced by mechanoreceptors

that may include those located in muscle, joint,

mucosal and periosteal tissues; together with (ii) a

change in central neural processing in maintaining

sensorimotor function (54). The present review sug-

gests keeping the original definition of osseoperception,

but consider this phenomenon as part of an overall

sensory-motor integration of the endosseous implants

in the human body.

Clinical implications of implant-mediatedsensory-motor interaction

Psychophysical testing on various bone-anchored pros-

theses confirm an improved tactile function leading to a

better physiological integration of the limb. If percep-

tion upon implant stimulation is working well, periph-

eral feedback mechanism may be restored and help

tuning fine motor control. This implant-mediated

sensory-motor interaction may thus help to achieve a

more natural function with the bone-anchored pros-

thesis (1, 5). Osseointegrated thumb prostheses even

allow patients to perform the activities of daily life

without any problem (55).

Considering the increased tactile threshold level for

oral implant stimulation, one should however consider

a few clinical implications. During rehabilitation by

means of implant-supported prostheses, dentist should

not rely on the patients perception of occlusion. In this

respect, one should also be aware of gradually increas-

ing tactile function during the healing period after

implant placement. This may be of particular import-

ance when dealing with immediate loading protocols.

To avoid any overloading related to suboptimal feed-

back mechanisms, patients should be encouraged to

limit chewing forces by soft food intake during the

healing period. Furthermore, parafunctional habits

such as grinding or clenching, might have a negative

impact during the implant healing phase. Bruxism has

therefore been defined as a relative contra-indication

for immediate loading protocols (56). [see also Review

by Lobbezoo (57)].

Conclusions

Endosseous implants are routinely used to rehabilitate

amputations of limbs or teeth. In order to reach

satisfactory clinical function with such bone-anchored

prostheses, physiological as well as psychological integ-

ration of the implant(s) should take place. Clinical

observations on patients with oral implants indicate the

presence of sensory perception after some time. The

underlying mechanism of this so-called osseopercep-

tion phenomenon remains a matter of debate. In any

case, scientific evidence allows to state that implant-

mediated sensory-motor interactions may offer poten-

tials for physiological integration of the implant in the

human body. The latter might help restoring the

peripheral feedback pathways and attempt a more

natural functioning. It could even be assumed that

such physiological integration might lead to better

acceptance and improved psychological integration.

This is a step forward towards total implantbody

integration. However, further research is required to

make practical use of osseoperception in the design of

novel bone-anchored prosthetic appliances and bionic

limbs.

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Correspondence: Reinhilde Jacobs, Laboratory of Oral Physiology,

Department of Periodontology, Faculty of Medicine, Catholic Univer-

sity of Leuven, Kapucijnenvoer 7, 3000 Leuven, Belgium.

E-mail: [email protected]



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