Biomaterials 20 (1999) 183 — 190

In vitro corrosion resistance of titanium made using different

fabrication methods

夹

Zhuo Cai

*, Hiroshi Nakajima , Margaret Woldu , Anders Berglund,

Maud Bergman

, Toru Okabe

Department of Biomaterials Science, Baylor College of Dentistry, Texas A & M University System, 3302 Gaston Avenue, Dallas, TX 75246, USA

Umeas University, Faculty of Dentistry, Umeas, Sweden

Received 4 May 1998; accepted 6 July 1998

Abstract

The corrosion of cast or milled ASTM Grade II CP titanium with different surface conditions was studied by potentiodynamic

anodic polarization and immersion testing. Specimens were fabricated using three dental titanium casting systems and from machined
titanium. Three surface conditions were tested: (1) sandblasted with surface reaction layers remaining; (2) polished surface without
surface reaction layers; and (3) sandblasted surface without surface reaction layers. An acidic saline solution (0.1

M

lactic acid/0.1

M

NaCl [pH"2]) and an artificial saliva were used as the corrosion media. Anodic polarization was performed starting at 50 mV below
the rest potential and terminating at#2250 mV vs Ag/AgCl. Two surface conditions (sandblasted with the surface reaction layers and
polished without such layers) were examined in the immersion test. Specimens were immersed in the corrosion media at 37°C for six
months. The recovered solution was analyzed by an atomic absorption spectrophotometer for titanium dissolution. A distinctive
passive region on the polarization diagram, ranging from &0 to &#1300 mV, was observed for all specimens in both media. Great
similarity was observed for all the sandblasted specimens which had larger primary passive current densities and passive regions
compared to the polished ones. A current density peak at &#1600 mV seen for all the specimens with sandblasted surfaces was less
well defined for the polished specimens. Immersion testing in the acidic saline solution revealed no significant differences among the
polished specimens. A significant increase (P(0.05) in titanium dissolution was found for the sandblasted specimens with surface
reaction layers remaining on the surfaces made with phosphate-bonded SiO/AlO investment compared to the polished ones.

Significant differences were also found between sandblasted specimens with the surface reaction layers resulting from different
investment materials and different casting methods. Measurable amounts of titanium were not found for all specimens in the artificial
saliva after six months. It is evident that the corrosion behavior of cast CP titanium is similar to that of machined titanium. The
surface roughness appears to be a more prominent factor than do the surface reaction layers on the polarization behavior of the CP
titanium under the present experimental conditions. Surface roughness and the presence of the surface reaction layers both affect the
dissolution of titanium.

1998 Elsevier Science Ltd. All rights reserved

Keywords: Corrosion; Titanium; Casting; Surface

1. Introduction

Because of its excellent corrosion resistance and bio-

compatibility, and high strength-to-weight ratio, com-
mercially pure (CP) titanium has been adopted by the

夹

This study was presented at the Third International Congress on

Dental Materials, Honolulu, Hawaii, November 1997.

* Corresponding author. Tel.: [phone]; fax: [phone]-

8458; e-mail: [e-mail]

Present address: Meikai University School of Dentistry, Sakado,

Saitama, Japan.

dental profession as a metal for crown and bridge [1],
and metal-ceramic restorations [2, 3] for more than
a decade [4—7]. Many studies have been published on
the corrosion behavior of pure titanium. Due to its excel-
lent corrosion resistance, CP titanium is often included
as a benchmark in the corrosion studies of biomedical
alloys.

Hoar and Mears [8] investigated the corrosion resis-

tance of several implant alloys using in vitro and animal
experiments. Open-circuit potential and anodic polariza-
tion experiments were performed for pure titanium in
Hank’s solution, 0.17

M

NaCl solutions and human

0142-9612/98/$—See front matter

1998 Elsevier Science Ltd. All rights reserved.

PII: S 0 1 4 2 - 9 6 1 2 ( 9 8 ) 0 0 1 6 0 - 4

blood. Pure titanium showed a high breakdown poten-
tial of 6000 mV (Ag/AgCl) even in 8.0

M

chloride solu-

tion. Mueller and Greener [9] studied the corrosion
behavior of pure titanium and Ti—6Al—4V using poten-
tiostatic anodic polarization in an agitated Ringer’s solu-
tion. Titanium exhibited passive behavior at potentials
up to #1200 mV (SCE) with primary passive current
density at approximately 1

lA cm\. In a study by Solar

et al. [10], open-circuit potential measurement and anod-
ic polarization were used to characterize passive films
formed on titanium surfaces in Ringer’s solution at vari-
ous P-

and pH, with and without amino acid additions

in a closed experimental cell with controlled environ-
mental factors. Passivity was observed over the entire
experimental potential range (!400—#1400 mV vs.
SCE)

without

breakdown.

Pulse

potentiostatic

capacitance technique and Auger electron spectroscopy
analysis of the specimens after the corrosion experiments
indicated that the electrochemical reaction occurring on
the surface was the growth of a passive film.

In a study by Speck and Fraker [11] on the corrosion

behavior of Ni—Ti, Ti—6Al—4V and pure titanium in
Hank’s solution at various pH values, potentiostatic
anodic polarization was performed from 0 mV (SCE)
until the breakdown potential of the metals was reached.
Pure titanium showed a greater passive region and con-
siderably higher breakdown potentials at &#2200 mV
(SCE) with primary passive current density at about
0.1

lA cm\. In a study on the corrosion of several pure

metallic elements [12], pure titanium powder made by
spraying from the melt was placed for 16 h in buffered
saline with and without the protein serum albumin and
fibrinogen. The titanium concentration in the solution
determined by atomic absorption spectrophotometry
was at 0.2 ppm and was unaffected by the presence of
proteins. In a study on the corrosion of binary titanium
alloy systems [13] in modified Fusayama artificial saliva
using potentiodynamic anodic polarization, pure titan-
ium showed a breakdown potential at &#2300 mV
(SCE)

and

primary

passive

current

density

at

&

1

lA cm\. In an electrochemical study on Ti—6Al—

7Nb orthopedic alloy [14], the corrosion behavior of
pure titanium was also examined in a deaerated Ringer’s
solution by anodic polarization from 0 mV up to

#

2200 mV (SCE). Passive behavior was observed for

pure titanium with the primary passive current density at
about 10

lA cm\. Khan et al. [15] studied the corrosion

of several titanium alloys and pure titanium by cyclic
anodic polarization between 0 and 5000 mV (SCE) in
a phosphate-buffered saline (PBS). CP titanium showed
a breakdown potential at approximately 4000 mV (SCE)
and was considered to have the best corrosion resistance.
In a recent study by Okazaki et al. [16] on the corrosion
resistance of implant alloys in several types of media,
including 1% lactic acid, 5% HCl, calf serum, PBS and
Eagle’s MEM, pure titanium grade 2 showed good cor-

rosion resistance with breakdown potentials between
1000 and 2600 mV (SCE).

All the corrosion studies on pure titanium mentioned

above employed wrought pure titanium with various
surface preparations as the test specimens. Due to a high
melting temperature (1670°C) and active chemical behav-
ior at high temperatures, however, the titanium casting
surface is susceptible to oxygen contamination at the
surface and interaction with the investment materials
[17]. These drawbacks result in the formation of
a hardened surface reaction layer called ‘

a-case.’ A multi-

layer surface reaction layer &200

lm thick has been

observed on pure titanium surfaces [18] cast into a phos-
phate-bonded AlO/SiO investment. It is thought that

this structure forms through the decomposition of the
investment and diffusion of the resulting elements into
the casting. Similar structures of different thicknesses
were observed by Takahashi et al. [19] among castings
made with several phosphate-bonded SiO-type invest-

ment materials. Hashimoto et al. [20] used different pure
oxides to line the surfaces of patterns. They found that
the depth of penetration for the major elements of oxides
decreased in the order of quartz'alumina'magnesia
and zirconia. The depth of penetration (100—150

lm) was

also found to be dependent on the investment temper-
ature. In a study by Brauner [21] on CP titanium casting,
ZrO-based, zirconate- and titanate-containing invest-

ments yielded much thinner surface reaction layers than
did AlO/SiO-based ones. In addition, the thickness of

the surface reaction layers on CP titanium was found to
be related to the different types of casting methods
[22], although no explanations were provided. At 300°C
mold temperature, centrifugal casting yielded thinner
surface reaction layers than did gas pressure casting
for phosphate-bonded SiO investments, an MgO-based

MgO/AlO investment, and a phosphate-bonded

SiO )ZrSiO investment.

A few studies have been published on the corrosion

behavior of cast pure titanium covered by a surface
reaction layer. One such study was performed by Doi
et al. [23]. In their study, CP titanium was cast into
a phosphate-bonded SiO investment using a gas pres-

sure casting machine. The thickness of the surface reac-
tion layers was less than 100

lm. Cyclic polarization was

performed in deaerated 0.9% NaCl solution on three
surface conditions: ultrasonically cleaned, sandblasted,
and polished with the reaction layers removed. The ultra-
sonically cleaned surface, which kept the surface reaction
layers intact, showed the lowest corrosion resistance
among the three conditions. The other two conditions
showed a similar behavior, although the current density
for sandblasted surfaces was almost ten times larger. In
a study by Geis-Gerstorfer [24], cast CP titanium with
the surface reaction layers resulting from reaction with
MgO showed inferior corrosion resistance compared to
cast titanium without such layers. Recently, Mimura and

184

Z. Cai et al. / Biomaterials 20 (1999) 183—190

Table 1
Fabrication methods used to prepare CP titanium specimens

Fabrication

Titanium casting

Casting

Investment

Specimen

methods

equipment

method

material

code

Cast

Castmatic

Gas pressure

Rematitan plus

C

Cast

Cyclarc

Gas pressure

Titavest C & B

M

Cast

Titaniumer

Centrifugal

Rematitan plus

T

Machined

—

—

—

P

Iwatani Co. Ltd., Osaka, Japan.

Dentaurum, Ispringen, Germany.

J. Morita Co., Tokyo, Japan.

Ohara Co. Ltd., Osaka, Japan.

Permascand AB, Ljungaverk, Sweden.

Miyagawa [25] studied the effects of various surface
conditions on the corrosion resistance of CP titanium
cast into a phosphate-bonded SiO investment in a pres-

sure difference casting machine. Potentiodynamic anodic
polarization was performed on the cast CP titanium
sandblasted surface with the surface reaction layers re-
maining, on the acid-treated Si-rich layer, the ground
acid-treated surface, and on the ground bulk surface. All
surface conditions except the sandblasted condition
showed similar corrosion resistance in 1% NaCl solu-
tion, while the sandblasted surface showed a reduced
passive region and a considerable increase in the primary
passive current density. The corrosion resistance of bulk
cast CP titanium was equal to or higher than that of
wrought pure titanium.

The objectives of this study were to characterize the

corrosion resistance of CP titanium cast with different
casting systems and having various surface conditions;
and to compare the corrosion behavior of cast and
wrought titanium through potentiodynamic anodic po-
larization and immersion testing.

2. Materials and methods

2.1. Potentiodynamic anodic polarization

ASTM Grade II CP titanium (Permascand AB, Ljun-

gaverk, Sweden) was used in this study. Specimens
(10 mm

;10 mm;2 mm) were fabricated using three

dental titanium casting systems and were also cut from
a machined titanium sheet. Eighteen specimens were
prepared for each of the three different casting systems,
and 12 specimens were made from the machined tita-
nium. The methods used to fabricate the corrosion speci-
mens are listed in Table 1.

Potentiodynamic anodic polarization was performed

on the following three surface conditions for specimens
fabricated by each of the three casting methods. (1) Sand-
blasted with surface reaction layers remaining. Six speci-
mens made with each casting method were used. Each

specimen was connected to a thin copper wire and em-
bedded in an epoxy resin block (Epoxide, Buehler, Lake
Bluff, IL) with one of its 10 mm

;10 mm surfaces ex-

posed at one end of the block. The surface of the speci-
men was sandblasted with AlO particles (50 lm) for

15 s. The distance between the specimen surface and the
abrasive nozzle was kept at about 1.0 cm, and the air
pressure used was approximately 0.59 MPa (85 psi). The
specimens were immersed into the electrolyte within
5 min after the sandblasting. (2) Polished surface without
the surface reaction layers. Six specimens made with each
casting method and six machined specimens were used.
In order to completely eliminate the surface reaction
layer from each cast specimen, the surfaces were ground
using a dental handpiece and SiC bur until 300

lm metal

was removed from the surfaces. All the specimens were
then embedded following the method described above
and dry polished through a series of SiC abrasive papers
to 800 grit. Again, the specimens were immersed into the
electrolyte within 5 min after the final polishing. (3) In
order to study the effect of the surface reaction layers on
the corrosion behavior of titanium under similar surface
roughness conditions, sandblasted surfaces without the
reaction structures were also tested. Another six speci-
mens made from each casting method and machined
specimens were used. Specimens were prepared as de-
scribed above, except that the surfaces were dry polished
through 600 grit SiC abrasive paper and sandblasted
with AlO particles (50 lm) as described before. Ex-

posed porosities in the mounting epoxy resin at the
metal—resin interface were sealed with melted dental
sticky wax.

Both an acidic saline solution (0.1

M

lactic acid/0.1

M

NaCl adjusted at pH"2) [26] and a modified
Fusayama artificial saliva [27] were used as corrosion
media in this study. The chemical composition of the
artificial saliva is listed in Table 2. About 300 ml of
deaerated and agitated fresh solution maintained at 37°C
was used for each specimen. Deaeration of the media was
achieved by bubbling argon gas through the media at
least 60 min before and during the experiment. Three

Z. Cai et al. / Biomaterials 20 (1999) 183—190

185

Table 2
Composition of artificial saliva used in the present study

Component

Amount in 1000 ml H

2

O (g)

NaCl

0.4

KCl

0.4

CaCl )2HO

0.795

NaHPO ) 2HO

0.78

NaS ) 5HO

0.005

Urea

1.0

individual specimens for each surface condition were
tested in each medium. Potentiodynamic anodic polar-
ization was performed using a potentiostat (Potentio-
stat/Galvanostat Model 273, EG & G Applied Research,
Princeton, NJ) controlled by a personal computer with
dedicated software (M342C Softcorr, EG & G Applied
Research). An Ag/AgCl electrode (Model 90-01, Single
Junction Reference Electrode, Orion Research Inc., Bos-
ton, MA), connected to the electrochemical cell via a salt
bridge (agar with saturated KCl), was used as the refer-
ence electrode, and a graphite electrode was used as the
counter electrode.

Approximately 5 min after the immersion of the speci-

men into the medium, the polarization scan started at
50 mV below the rest potential and terminated at

#

2250 mV (Ag/AgCl) at a rate of 0.5 mV s

\. The polar-

ization curve was recorded for each specimen. The cor-
rosion behavior of CP titanium was characterized with
regard to the corrosion potential, the primary passive
current density, the range of passive region and break-
down potential.

2.2. Immersion test

Twelve plate-shaped specimens (20 mm

;20 mm;

2 mm) were fabricated using each of the three casting
methods, and six specimens were made from the machin-
ed titanium as described above. Two surface conditions,
sandblasted with surface reaction layers remaining and
polished without the surface reaction layers, were used
for the test. The details of the surface preparation are
provided above. The 0.1

M

lactic acid/0.1

M

NaCl

(pH"2) solution and modified Fusayama artificial sal-
iva were used as media for the immersion tests. No
attempt was made to deaerate the media during the
immersion test. Each specimen was immersed in 50 ml
solution at 37°C for six months. The immersion period
was selected based on our previous experience. The re-
covered solution was analyzed in an atomic absorption
spectrophotometer (Varian Spectr AA20, Mulgrave, Vic-
toria, Australia) with an acetylene—nitrous oxide flame
for titanium dissolution. The mass of titanium released
per unit area of the specimen was calculated for each

surface condition. The results were statistically analyzed
using one-way ANOVA and Scheffe´’s test (

a+0.05).

3. Results

3.1. Potentiodynamic anodic polarization

The surface preparation technique used in this study

yielded consistent results for most of the conditions.

3.1.1. In 0.1

M

lactic acid/0.1

M

NaCl (pH"2) solution

A corrosion potential of&!500 mV was shown for all

the sandblasted cast specimens with surface reaction
layers. All the specimens exhibited distinctive passive
regions on their polarization diagrams ranging from

&

!

100 mV (C specimens) or #100 mV (T & M speci-

mens) to#1300 mV (Fig. 1). The primary passive current
densities in the passive region were about 10

lA cm\.

A current density peak at &#1600 mV with a current
density between&40 (T specimens) and 200

lA cm\ (M

specimens) was observed. A smaller peak was also re-
vealed at about #1800 mV for all the specimens. A
considerably larger current density was observed for
M specimens at potentials above#1500 mV. Repassiva-
tion behavior was observed above &#2000 mV for all
the specimens.

For specimens with polished surfaces, great similarity

was found among all the specimens made with different
methods (Fig. 2). A distinctive passive region (&#200 to

&

#

1300 mV) was also revealed, but with a somewhat

reduced range compared to the last group. The primary
passive current densities (&5—10

lA cm\) were slightly

less than those seen in the sandblasted group with the
surface reaction layers. The current density peak at

&

#

1600 mV observed in the former group appeared to

be less well defined in this group, and the peak observed
at &#1800 mV in the sandblasted specimens dis-
appeared. Polarization diagrams for the sandblasted
specimens without the surface reaction layers (Fig. 3)
resembled the ones with such structures (Fig. 1), and
showed greater similarity among all the specimens.

3.1.2. In modified Fusayama artificial saliva

A trend similar to that observed in the 0.1

M

lactic

acid/0.1

M

NaCl solution was observed in the artificial

saliva (Figs. 4—6). As in the acidic saline solution, polar-
ization diagrams for the sandblasted specimens with sur-
face reaction layers (Fig. 4) resembled the sandblasted
ones without such layers (Fig. 6). The small current
density peak seen at &#1800 mV in the acidic saline
solution was not observed in the artificial saliva.

3.2. Immersion test

After six-month immersion in the acidic saline solu-

tion, no visible bacterial or fungal growth was observed.

186

Z. Cai et al. / Biomaterials 20 (1999) 183—190

Fig. 1. Potentiodynamic anodic polarization diagram for CP titanium
in 0.1

M

lactic acid/0.1

M

NaCl (pH"2) solution after sandblasting

with surface reaction layers remaining.

Fig. 2. Potentiodynamic anodic polarization diagram for CP titanium
in 0.1

M

lactic acid/0.1

M

NaCl (pH"2) solution with polished surface.

Fig. 3. Potentiodynamic anodic polarization diagram for CP titanium
in 0.1

M

lactic acid/0.1

M

NaCl (pH"2) solution with polished and

sandblasted surface.

Fig. 4. Potentiodynamic anodic polarization diagram for CP titanium
in artificial saliva after sandblasting with surface reaction layers re-
maining.

The results of the atomic absorption spectrophotometry
analyses are listed in Table 3. The detection limit for
titanium ions in the 0.1

M

lactic acid/0.1

M

NaCl solution

was 2 ppm in the present experiment. No significant
differences were found among all the polished specimens
(P"0.492). However, a significant increase in the
amount of titanium dissolution was found for cast speci-
mens C and T with sandblasted surfaces and surface
reaction layers remaining compared to the polished sur-
faces (P(0.05). Significant differences were also found

between sandblasted specimens in the following pairs:
M vs. C specimens (P"0.012) and M vs. T specimens
(P"0.006).

No measurable amount of titanium ions was obtained

for the immersion test in the modified Fusayama artifi-
cial saliva by atomic absorption spectrophotometry be-
cause the titanium ion concentration in the test solution
was found to be below the detection limit of 3 ppm in this
solution.

Z. Cai et al. / Biomaterials 20 (1999) 183—190

187

Fig. 5. Potentiodynamic anodic polarization diagram for CP titanium
in artificial saliva with polished surface.

Fig. 6. Potentiodynamic anodic polarization diagram for CP titanium
in artificial saliva with polished and sandblasted surface.

Table 3
Dissolution (

lg cm\) of CP titanium in 0.1

M

lactic acid/0.1

M

NaCl

(pH"2) solution at 37°C after six month immersion

Fabrication

Polished surface

Sandblasted surface with

methods

surface reaction layers

C

0.10$0.02

1.85$0.47

M

0.10$0.02

0.23$0.06

T

0.08$0.01

2.07$0.59

P

0.10$0.02

—

Entries are mean$standard deviation (N"3).

4. Discussion

The specimen surface preparation employed in this

study was based on our previous experience. This
method yielded very consistent results for CP titanium. It
is understood, however, that clinically there is a certain
period of time between the surface finishing and the
actual use of the titanium restoration. During this period,
the metal may contact different substances that modify
its surface. Because of the active chemical nature of
titanium, such a surface modification will often favorably
change its corrosion resistance.

Different scan rates ranging from 0.1 mV min

\ [11]

to 3.3 mV sec

\ [15] were used in published polarization

studies on CP titanium or titanium alloys. Since the
polarization process involves oxidation and reduction of
the metal surface in the test medium, changes in scan rate
may affect such surface reactions and alter the polariza-
tion behavior of the metal. However, the results from the
published studies suggest that scan rate variations have
only small effects on CP titanium.

In the present study, deaerated media were used for the

anodic polarization experiments. Although the human
oral cavity is an oxygenated environment, oxygen is
depleted in some situations, such as in gingival crevices
or under biofilms. The deaerated media used in the pres-
ent study can simulate such situations.

It was suggested that a more rigorous surface prepara-

tion on titanium surfaces may result in a surface oxide
film with lower integrity or thickness [28]. In the present
study, for the surfaces without the reaction layers, sand-
blasting may prepare CP titanium surfaces more rigor-
ously than dry polishing, and may consequently produce
surfaces with increased activity. The results, however,
showed no such pattern based on the corrosion poten-
tials measured.

The somewhat reduced primary passive current den-

sity on the polarization diagrams observed for the
polished vs. the sandblasted specimens is probably due to
the increased surface area created by sandblasting. If the
actual surface area on sandblasted specimens were in-
deed used in the plot of the polarization diagram, the
primary passive current density might be very close to
those of polished specimens. Pitting corrosion [29] re-
sulting from the rough surfaces created by sandblasting is
unlikely to contribute to such a behavior in the experi-
mental conditions used in this study. The great similarity
in the polarization diagrams between the sandblasted
surfaces with surface reaction layers and those without
such layers (Fig. 1 vs. Fig. 3; Fig. 4 vs. Fig. 6) suggests
that the surface reaction layer is a less influential factor
than surface finishing (polished or sandblasted) on
the corrosion behavior of the CP titanium in the cor-
rosion media used in this study. Concerning the electrical
potential range (!58—#212 mV vs. SCE) that could be

188

Z. Cai et al. / Biomaterials 20 (1999) 183—190

experienced in the normal human oral environment [30],
the electrochemical behavior for CP titanium was only
slightly affected by the different surface finishing tested in
this study.

The results from the present study are consistent with

those from previously published studies. In a study by
Doi et al. [23] using deaerated 0.9% NaCl solution, the
polarization behavior of sandblasted surfaces with sur-
face reaction layers remaining resembled that of polished
surfaces, except for the increased current density. The
large current density increase on the polarization curve
at about #1400 mV (SCE) corresponds to the break-
down potential of &#1600 mV (Ag/AgCl) observed in
this study. In a study by Mimura and Miyagawa [25]
using 1% NaCl solution without deaeration, sandblasted
surfaces with surface reaction layers remaining showed
reduced passive regions and increased primary current
density compared to the other three surfaces. The break-
down potential was observed at &#1100 mV (SCE),
which is lower than that observed by Doi et al. [23]. It
has been reported [15] that for CP titanium in a given
solution, the breakdown potential is usually lower in
deaerated conditions compared to non-deaerated ones.
The lower breakdown potential in Mimura and
Miyagawa’s study compared to the study by Doi et al. is
probably due to the differences in their test media.

Hashimoto et al. [20] showed that when used as a re-

fractory material for investment, quartz produces
a thicker reaction layer on a cast CP titanium surface
than the layers produced by MgO. In this study, speci-
mens M were cast into an investment using MgO/AlO

as the major refractory component, while specimens
C and T were cast into an investment using SiO/AlO

as the major refractory component [7]. The difference
between the structure and chemical nature of the reaction
layers may contribute to the differences in the amount of
titanium ions released during the immersion test. The
significant reduction in titanium ions released from
polished surfaces compared to sandblasted surfaces with
surface reaction layers for C and T specimens (Table 3)
may be attributed to the elimination of surface reaction
structures, reduced surface area and different surface
preparation. One study showed that different surface
treatments affect the dynamic dissolution of CP titanium
in saline solution [31].

5. Conclusion

The corrosion behavior of cast CP titanium appeared

to be similar to that of the machined specimens. The
surface roughness significantly affected the polarization
behavior of CP titanium. This appears to be a more
prominent factor than the presence of surface reaction
layers on the polarization behavior of the CP titanium
under the present experimental conditions. Both the sur-

face reaction layers and surface roughness may affect the
dissolution of titanium into the test media.

Acknowledgements

Support for this study was received from NIH/NIDR

Research Grant DE 11787. The authors would like to
thank Mrs Jeanne Santa Cruz for her assistance in the
preparation of the manuscript.

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