International Journal of Otolaryngology and Head & Neck Surgery, 2013, 2, 186-191
http://dx.doi.org/10.4236/ijohns.2013.25039 Published Online September 2013 (http://www.scirp.org/journal/ijohns)
Low Cost Osseointegrated Implant System
for Developing Countries*
Kayla M. Foyt, Jason Roberts#
Division of Otolaryngology/Head and Neck Surgery, Albany Medical Center, Albany, NY, USA
Received May 29, 2013; revised June 22, 2013; accepted July 3, 2013
Copyright © 2013 Kayla M. Foyt, Jason Roberts. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Obje ctive: Osseointegrated hearing implants have been readily available and extensively used in developed countries
for over twenty years. Despite a great need for this technology, use of these implants in developing countries has been
limited due to the prohibitive cost of the surgical implant system as well as the implant devices themselves. To address
this problem we have developed a drill and implant system that mimics the currently available instrumentation using
materials that are readily available at a fraction of the cost. Study Design: Proof of Concept. Methods: The construc-
tion of the drill and implant system will be described. Testing of the system so that it adhered to Cochlear’s™ Bone
anchored hearing aid system specifications including the drill speed and torque settings were measured. Temperature
readings were also recorded during procedures performed on human cadaveric temporal bones. Results: The speed of
the drill with the guide drill and countersink drill bits ranged from 1400 revolutions per minute (rpm) to 2300 rpm’s.
The temperature change of the room temperature temporal bones varied from 0 degrees to +0.2 degrees Fahrenheit dur-
ing the drilling process with both drill bits. All five implants were stable in the cadaver bone after being checked for
initial stability. Conclusion: This low cost implant system may make the BAHA technology more easily available to
developing countries pending future studies with animal models.
Keywords: Quality of Life; Implants; Otology; BAHA; Hearing Loss
1. Introduction
The Bone Anchored Hearing Aid (BAHA) was first im-
planted in 1977 by Dr Anders Tjellström in Sweden. The
BAHA was further refined and implanted in 14 patients
by him in 1981 for the treatment of conductive hearing
loss in the setting of chronic otitis media [1]. Since then,
over 100,000 implant procedures have been performed
worldwide for a variety of hearing disorders. Unfortu-
nately, the vast majority of these implants have been per-
formed mostly in developed countries that can afford the
technology. The incidence of conductive hearing loss
that can be corrected with osseointegrated implants in the
developing world is not known. However, the number is
likely much higher than in the United States due to a lack
of technology or finances available for advanced otologic
surgeries for hearing restoration such as ossicular chain
reconstruction. The BAHA is a reliable method of audi-
tory rehabilitation and improves the quality of life for
patients with middle and external ear deformities [2-7].
Further modifications of this Cochlear™ osseointe-
grated hearing device continue to develop and Oticon™
corporation has developed a device on the same principle.
Current BAHA implantation can cost as much as $30,000
in western countries. The cost of the implant drill system
alone is $10,000 (BAHA order form, Cochlear™ Corpo-
ration). The current BAHA implant system that is avail-
able from Cochlear™ Corporation is a combination of a
precision single speed drill and a variable selective
torque wrench. The drill is set between two modes: drill
and torque wrench. The drill rotates at 2000 rpm to cre-
ate both the initial guide hole perpendicular to the bone
and the subsequent countersink hole at a depth of 3 to 4
mm. This will accommodate the titanium implant (abut-
ment) in the next step. The torque wrench mode utilized
to implant the titanium abutment can be set between 0
and 50 Ncm2 with typical settings of 40 Ncm2 for adult
implants and 30 Ncms for pediatric implantations. The
drill can be dismantled and autoclaved for sterility (Co-
chlear Baha3 Surgery Guide, Cochlear™ Baha®.) Criti-
cal variables in the procedure include not touching the
*All work was performed at Albany Medical College Anatomy Lab;
N
o financial support was necessary for this projec
t
.
#Corresponding author.
C
opyright © 2013 SciRes. IJOHNS

K. M. FOYT, J. ROBERTS 187
abutment threads, irrigation for avoidance of heat pro-
duction during the drilling process, and a torque setting
to ensure that the implant does not strip its thread in the
bone. This process is followed systematically to optimize
osseointegration.
The success of BAHA implants and their ability to pro-
vide optimal bone conducted hearing results from an
active bond between the titanium implant and the living
bone tissue—a process called osseointegration. In previ-
ous studies in oral and orthopedic surgery, the most im-
portant factor for osseointegration is the avoidance of
heat production by the drill bits in the surrounding bone.
For failures occurring within 3 months of insertion, these
studies found that bone overheating during the surgery
lead to failure of osseointegration. Bone necrosis was
found to occur when the bone was heated to a tempera-
ture of 47 degrees celcius (116.6 degrees F) for one min-
ute [8]. In order to decrease heat production in the bone,
in addition to irrigation, most studies have employed us-
ing a minimal load and low speed. However, one study
demonstrated that through increasing the load of the drill
while increasing the drill speed, they found this created
more efficient cutting and less frictional heat [8,9]. Tell-
strom adhered to these biological principles of osseoin-
tegration for the successful development of the bone an-
chored hearing aid system [1]. Our drill system was de-
veloped with these same principles in mind.
As the indications for these implants continue to broa-
den and develop in both adults and children, several gen-
erations of the BAHA sound system processor have been
developed by Cochlear™ to provide sufficient amplifica-
tion in different hearing situations [10-12]. We propose a
drill and torque wrench system that can be easily con-
structed from off-the-shelf components at a fraction of
the cost of the currently available drill system. Through
using explanted Cochlear™ BAHAs, performance meas-
urements were obtained including: drill speed; tempera-
ture variations in surrounding bone; ease of use of the
instruments; and implant stability. The drill bits could be
autoclaved for sterility and a sterile shield for the drill
and torque wrench was devised.
2. Materials and Methods
Determination was made through the Office of Research
Affairs at Albany Medical Center that this project does
not involve human subject research and so does not re-
quire approval by the IRB.
Various drill systems that would be appropriate for
this application were investigated. We investigated sev-
eral combined drill and torque wrench systems that could
mimic the performance of the standard osseointegrated
drill system. No drill and torque wrench system was
available off the shelf that was low cost, lightweight, and
precise enough for the BAHA procedure to be described.
The equipment was therefore purchased as two separate
components: a drill and a manual variable torque wrench.
We used previously used (one time) sterilized Coch-
lear™ drill bits as well as explanted Cochlear™ BAHA
abutments.
The experimental procedure was performed on human
cadaveric temporal bones. Drilling was performed with
aggressive saline irrigation similar to the recognized rou-
tine surgical procedure. The temporal bones were at
room temperature prior to doing any of the drilling for
the speed and heat measurements. Drills were compared
and evaluated for precision, compact design, drill speed,
and compatibility with the existing Cochlear™ BAHA
drill bits. We selected a lithium battery powered Dre-
mel™ drill with variable speed control (Dremel Stylus™,
Dremel, USA). This tool has worldwide distribution and
availability (www.dremel.com) In addition, it is an inex-
pensive (~$75.00 USD), lightweight and precise drill that
can be easily wrapped in a sterile cover. It has a low
torque motor that spins at 5000 rpm at its lowest setting.
While the drill rotates a higher speed than the Cochlear™
BAHA drill, we felt that the low torque property of the
drill in bone would slow the drill bit to acceptable levels.
The drill fits the Cochlear™ BAHA drill bits without
modification. Rotation speed during bone drilling with
the guide drill and countersink was measured by a strobe
(Cen-Tech Digital Photo Tachometer DT-838). The heat
production in the surrounding bone during bone drilling
was measured by a precision surface temperature probe
(Extech Dual input Digital Thermometer Model 421502).
The implant procedure was otherwise not modified from
the traditional surgery as described previously by Co-
chlear™.
Several electric torque wrenches were investigated for
this study. No electric tool that satisfied the requirements
of low cost, precision, desired torque range, and portabil-
ity could be found. Therefore, a hand driven precision
adjustable torque wrench was chosen (Screwdriver 61
NSM, CDI Torque Products) that was ideal for the sur-
gical procedure.
3. Results
Measurements were performed on human cadaveric tem-
poral bones at room temperature utilizing the drill system
as described in the materials and methods section (Fig-
ure 1). The Dremel drill was on a setting of #1 through-
out the testing. The guide drill revolutions per minute
(rpm) were measured initially with and without contact
on the temporal bone (Figure 2). The rpm’s ranged be-
tween 4800 to 5200 without contact and 2000 rpm with
initial skull contact. Five tests with skull contact were
performed with rpms ranging from 1400 to 2000 rpms
with no test measuring over 2000 rpms at a setting of 1
on the drill (Table 1). To assure we consistently meas-

K. M. FOYT, J. ROBERTS
188
Table 1. Measurement of revolutions per minute (rpm) with
the guide drill bit on temporal bone.
Test Rotations per minute
1 1400
2 1800
3 2000
4 1800
5 1800
Drill speed without temporal bone contact: 5200 rpm; Drill speed with
initial temporal bone contact: 2000 rpm.
Figure 1. Drill and torque wrench system with associated
drill bits, torque bit, and abutments in a temporal bone.
Figure 2. Utilizing the Cen-Tech digital photo tachometer
DT-838 to measure the revolutions per minute during drill-
ing of the temporal bone utilizing the guide drill bit and
countersink drill bit.
ured the rpms, we utilized the weight of the drill with
minimal pressure because we noted that enough pressure
could be applied to stop the drill completely. We allowed
the drill speed and drill bit to perform the work in order
to drill the guide hole precisely. The lowest rpm was
noted initially on test 1 when too much pressure was ap-
plied with the guide drill.
After the guide drill hole was performed, the second
step of the BAHA drill system involved the countersink
portion of the procedure. Five tests were performed with
the countersink and the rpm’s were measured. We found
the rpms in each of the five tests to range from 1600 to
2300 while drilling in the cadaveric temporal bones (Ta-
ble 2).
The third portion of the test involved temperature
measurements of the temporal bone utilizing the digital
thermometer. Prior to applying the temperature probe to
the temporal bone (Figure 3), variations in the digital
thermometer were measured with irrigation. Temperature
measurements varied from no change to −0.2 degrees
with irrigation to +4 degrees without irrigation (Table 3).
When the temperature probe was applied to the bone, the
bone temperature measured 71.5 deg F which was con-
sistent with the room temperature of the testing center.
As stated previously, the drill was set at #1 setting and 5
measurements were run with the guide drill and counter-
sink drill to evaluate temperature changes. With contin-
uous irrigation with sterile water, the increase in tem-
perature ranged from 0 degrees to 0.2 degrees (Table 4).
The final portion of the experiment involved using the
Table 2. Measurement of revolutions per minute with coun-
tersink drill bit on temporal bone.
Test Rotations per minute
1 1800
2 2000
3 1900
4 1600
5 2300
Table 3. Temperature probe measurements sensitivity un-
der irrigation (not attached to temporal bone).
Test Initial temperature (72.3˚F)
1 No change
2 −0.2 degrees
3 No change
4 −0.1 degrees
5 +4 degrees ( no irrigation)
Table 4. Temperature probe measurements with probe at-
tached to temporal bone.
Test Guide Drill
Initial Temperature (65.5˚F)
Countersink Drill
Initial Temperature (71.5˚F)
1 +0.1 degrees +0.2 degrees
2 No change +0.1 degrees
3 +0.1 degrees +0.1 degrees
4 +0.2 degrees No change
5 No change No change

K. M. FOYT, J. ROBERTS 189
Figure 3. Utilizing the Extech dual input digital thermome-
ter model 421502 to measure the temperature of the tem-
poral bone adjacent to the drill hole while drilling with the
guide drill and countersink drill.
torque wrench to determine what setting to determine if
the implant could successfully be drilled and was grossly
stable. The abutment could be easily adapted to this
torque wrench for placement. The setting of the torque
wrench was approximately 25 Ncm which is the setting
recommended by the Cochlear Surgery Guide (Coch-
lear™ Baha®) for compromised or soft bone. In all 5
temporal bones, the torque wrench was able to drill the
Cochlear™ BAHA abutments. The implanted abutments
were grossly stable with manual manipulation (Figure
4).
4. Discussion
The World Health Organization reports that over 275
million people worldwide suffer from some degree of
hearing loss with a majority of those people (80%) in low
to middle income nations (WHO fact sheet). Hearing loss
can have an enormous impact on the quality of life as
well as impact on the productivity of an individual. De-
veloped countries are able to improve hearing through
the various technologies available ranging from cochlear
and brainstem implants to ossicular chain reconstructions.
Bone anchored hearing aids have also been available in
these developed countries for over 20 years as a reliable
method of auditory rehabilitation that improves the qual-
ity of life for patients with conductive, sensorineural or
mixed hearing loss due to many causes [2-7]. Since its
creation, several generations of the BAHA sound system
processors have been developed by Cochlear to provide
sufficient amplification in different hearing situations
[10-12]. This technology, which relies on the unique
concept of osseointegration, requires expensive and stan-
dardized equipment for its use and therefore, developing
countries are unable to utilize this technology where it
would provide significant benefit. This technology could
be more beneficial in those developing countries as it
Figure 4. Utilizing the manual torque wrench to the implant
the BAHA abutments.
would bypass the middle ear in patients’ with a wide
array of pathologies. Unfortunately, the cost of the tech-
nology to implant these BAHAs is prohibitive. Our goal
was to develop a system that could be utilized in a sterile
manner in these developing countries so that this valu-
able hearing technology could be expanded.
Through our temporal bone studies with our off-the-
shelf surgical instruments, we have shown that this is a
possibility. With temporal bone contact, the speed of the
Dremel drill proved to be comparable to the standard
Cochlear™ BAHA instrumentation through the utiliza-
tion of sterilized previously used Cochlear™ sharp drill
bits. At a setting of #1 on the the drill, the highest speed
recorded was 5200 rpms without bone contact, yet with
initial skull contact the drill speed dropped to 2000 rpms.
We attempted to utilize #2 setting on the drill but this
tended to strip the bone during drilling. Therefore, we
utilized a setting of #1 on the drill throughout the study
for our measurements. The lowest speed recorded was
found to be 1400 rpms which was due to applying too
much pressure. We believe that the #1 drill speed is ap-
propriate for the guide drill and countersink drill. Other
rotary drills systems could be tested for application of
this Cochlear technology. However, the Dremel drill con-
sistently provided us with an adequate rotation speed for
the guide drill and countersink drill. In addition, through
utilizing the standardized digitial photo tachometer, the
rpm’s of the drill did not vary considerably.
For the heat measurements, we utilized a standardized
digital temperature probe on the room temperature tem-
poral bones. Prior to attaching the probe to the temporal
bone, the variability of the thermometer was minimal
with constant irrigation. The thermometer was secured
adjacent to the hole that was being drilled in order to ac-
curately measure any change in the temperature of the
temporal bone. Although this would not record the tem-
perature of the bone in the drill hole, we can assume that
this bone temperature was very close to that of the adja-

K. M. FOYT, J. ROBERTS
190
cent drill hole. Five runs were performed for measuring
the speed and temperature during the guide and counter-
sink drilling. Due to minimal changes in the values dur-
ing these five runs, no further runs were deemed neces-
sary for this proof of concept design study. We did use
human temporal bones and proved that this concept is
applicable. The compromised and softer nature as well as
the lower temperature of the human cadaveric temporal
bones make it necessary to carry out these same studies
in animal models prior to performing this in humans.
The abutments were placed with a manual torque
wrench at the settings specified by Cochlear™. No heat
measurements were performed during this portion of the
procedure but the speed was minimal during this part of
the study and would not impede osseointegration. Al-
though osseointegration was not determined with this
drill system, the abutments were secure with manual ma-
nipulation. Adhering to the implant surgical guidelines
and minimizing heat production during the drilling proc-
ess, osseointegration should not be a problem utilizing
this drill system.
A factor that could impede osseointegration is previ-
ously utilized explants that had been sterilized. The Co-
chlear™ guidelines are to never touch the threaded por-
tion of the titanium abutment due to its titanium oxide
coat and the reported important factor this plays in os-
seointegration. Studies have shown that the oxidized
coating is an important factor to increase the surface area
which assists with osseointegration [13]. To the best of
our knowledge, no studies were found in the literature
which determine the extent of osseointegration after ster-
ilizing these explanted models. Our belief is that osseoin-
tegration will occur without the titanium oxide coating
on the implants.
We developed a simple method of sterilizing these
tools. The drill bits utilized with the guide Dremel drill
could be sterilized in the autoclave which is available in
most developing countries. The Dremel drill was small
and although this could not be placed in the autoclave,
different techniques to keep this drill sterile were at-
tempted. We attempted to use the plastic covering from
the intra-operative ultrasound and intraoperative lym-
phoscintigrophy scan used for parathyroid localization.
These sterile drapes are prohibitive however in that they
are specific to these instruments and not readily available
in developing countries. Therefore, we were able to use a
sterile glove which is more readily available. We found
that placing the Dremel into the sterile glove trough one
of the finger tips, size 7 or higher, and puncturing a small
hole in the tip with the drill allowed us to keep the drill
sterile. The glove could be changed for subsequent use of
the drill. The actual sterility and bacterial counts after
subsequent use of the drill is something that should be
measured prior to expanding this methodology to hu-
mans.
The cost of the drill was $75.00 and Dremel is an in-
ternational company with distribution centers worldwide.
This drill could easily be obtained for developing coun-
tries. The cost of the drill bits and abutments could be
prohibitive if they were to be purchased from Cochlear™.
Fortunately, these tools could be donated and sterilized
as they were done for this study. In terms of the abut-
ments, the previous patients’ abutments were removed
for various reasons and used in this study. Most compa-
nies and otologists have a handful of explanted abut-
ments or prior generations of abutments that could be
made available to developing countries. In addition, the
drill bits used in our study were only used once previ-
ously in the operating room setting. These bits are ex-
tremely sharp after only one use and could be sterilized
for use in future implants. In our study, we used the same
drill bit and countersink for 5 runs each and it did not
alter the temperature or rpms. These additional tools after
being sterilized could be donated or collected from pre-
vious surgeries to be taken or sent to developing coun-
tries. It is important to emphasize that sterility of previ-
ously utilized drill bits, and abutments including bacterial
counts should be the subject of future animal studies.
5. Conclusion
We developed this novel system using off-the-shelf pro-
ducts and measured different aspects of this system to
assure it complied with the specifications used by the
Cochlear™ BAHA. We also demonstrated this systems’
applicability and ease of use. However, prior to sharing
this BAHA technology with developing countries world-
wide, future animal studies are necessary for utilizing our
system.
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