Jan Lindhe. Clinical Periodontology

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OSSEOINTEGRATION: HISTORIC BACKGROUND AND CURRENT CONCEPTS •

817

Fig. 33-21.

In vitro

studies are scientifi

cally very controlled, but simultane-

ously of very low clinical relevance.

The clinical case report is of lower sci

entific but higher clinical relevance

than

in vitro

and

in vivo

studies. The

prospective, randomized, controlled

clinical study is at an intermediate

level of scientific but a high level of

clinical relevance.

33-19). A good example is overload. Overload is det-

rimental to osseointegration during the first few

months after implant insertion, because interfacial

movements will stimulate soft tissue formation in the

interface, but once osseointegrated, the interface is

capable of carrying occasional strong loads. Continu-

ous, dynamic overloading of osseointegrated im-

plants, however, will lead to micromovements and

subsequent bone resorption. If the conditions are not

altered in time (precise time/load relations are un-

known), continuing bone resorption will result in in-

creasing micromovements, eventually leading to im-

plant failure (Hoshaw et al. 1994, Isidor 1996, 1997).

This sequence of events is, in fact, typical for cylindri-

cal oral implants without any macroscopic retention

elements in the form of threads (Fig. 33-20) (Al-

brektsson 1993). Another documented secondary fail

ure load of oral implants is peri-implantitis, defined

a combination of inflammation and bone loss

(Lindhe

et al 1992, Berglundh 1993). It is not known

which of

these two secondary implant failure modes

clinically most common.

OSSEOINTEGRATION IN THE

CLINICAL REALITY

Although there are a great number of scientific inves-

tigations behind osseointegrated implants, a high pro

portion of the hardware and software preferences are

based on empirical data only. We have simply learnt

to follow a certain protocol that, if used in combination

with a well-investigated oral implant, will result in a

predictable outcome under defined conditions. It is

indeed reasonable to challenge the osseointegrated

protocol, provided this is done in a scientifically con-

trolled manner. Obviously, more basic science is

needed to learn more about optimal biomaterials, de-

signs and surfaces of oral implants. However, one

must interpret such data with some caution.

In vitro

findings may be of some scientific interest, but the

glass disk represents a highly artificial environment

devoid of blood flow, hormonal or loading influences.

It is not uncommon for

in vivo

studies to produce

results opposite to those of the test tube.

In vivo

studies

in animals over short and long follow-up times do

provide interesting data. Such studies should be man

datory before the clinical trial is initiated. Yet, even

those generally referred to as long-term animal stud-

ies span a follow-up time limited to about 1 year.

Therefore, when the animal studies have been com-

pleted, we are not even halfway to collecting data

necessary for widespread clinical introduction. There

is now the need for controlled, preferably prospective,

clinical studies that should be carried out under the

guidance of a university ethical committee, with every

patient consenting to treatment with a changed clini-

cal routine or an untested product, spanning a mini-

mum of 5 years. Only when the new clinical routine

or novel implant has passed all these hurdles would

widespread clinical usage seem reasonable (Fig.

33-

21). However, this is indeed a wish for the future,

since the oral implant community of today does not

seem to ask for anything but some animal pre-

studies.

Lamentably, the high standards of clinical reporting

set by Adell et al. (1981) were not followed in later

times. Instead, osseointegration was regarded as

equivalent to long-term implant success. New oral

implant systems appeared and were marketed based

only on sketchy short-term animal data with evidence

of direct bone to implant contact. Well-known exam-

ples of such untested products that achieved great

popularity despite lack of clinical documentation

were a threaded, hollow cylinder device and a solid

cylindrical implant with or without hydroxyapatite.

These different types of implants had two things in

common: they were supported by experimental evi-

dence of osseointegration but, unknown to the treat-

ing dentist, they were prone to lose their bone anchor

age with time due to progressive bone saucerization,

which often resulted in subsequent implant failure

(

Albrektsson 1993). Furthermore, many types of screw

design implants were introduced claiming that docu-

mentation was unnecessary since they allegedly re-

sembled the original, well-documented Swedish c.p.

titanium implant. This reasoning was based on the

opinion that oral implants represent generic products

–

a misconceived notion at this stage. The various

look-

alike implants differ from one another with re-

818 • CHAPTER 33

Fig. 33-22. Calcium incorporated, oxidized titanium im

plants are probably anchored to bone through ionic

bonding. These implants have a unique porous surface

and differ from non-oxidized c.p. titanium implants in

other aspects such as crystallinity and presence of inter

facial calcium ions.

spect to titanium composition, thread configuration

and surface topography (Wennerberg et al. 1993). In-

deed, the observed differences in surface topography

alone are such that they will clearly influence the

results in experimental studies (Wennerberg 1996). At

present, there is insufficient knowledge about what

governs the incorporation of an oral implant and we

lack a great deal of information about optimal compo

sition of the biomaterial, the design and the surface

finish of an implant. Therefore, every oral implant

must be supported by clinical documentation of the

specific product without reference to any other im-

plant of assumed similarity.

Unfortunately, the progress with respect to clinical

reporting has been quite slow. When papers claiming

high success rates of oral implants for 5 years are

scrutinized, all too often there are numerous short-

comings, making the true results difficult to interpret.

Common errors in most reports of the clinical outcome

of oral implants are a failure to account for patients

who dropped out, misinterpretation of survival and

success, forgetting to report on bone height levels and

claiming a 5-year outcome when implants have been

followed only for up to 5 years. When critically ana-

lyzed, by far the best documented oral implant is the

original Branemark screw (Albrektsson et al. 1986,

Albrektsson & Sennerby 1991, Lang & Karring 1994).

However, there is no long-term clinical documenta-

tion of the novel, oxidized TiUnite implant from the

same company. The turned version of the Astra Tech

implant has been documented with positive results

for 5 years (Arvidsson et al. 1998), whereas the newer

Tioblast design has been reported for long term only

in clinical materials, most limited in size (Palmer et al.

2000, Norton 2001). The original ITI solid screw im-

plant has been positively documented for survival for

more than 5 years, but the lack of reported bone height

data makes any evaluation of implant success uncer-

tain. Newer ITI designs, such as the Osseotite implant,

lack proper long-term documentation. The same is

true for the 31 implant. Another implant that has been

positively documented for a full 5 years, at least in the

mandible, is the Endopore (Deporter et al 1999).

FUTURE OF OSSEOINTEGRATED

ORAL IMPLANTS

New developments of oral implants have, generally,

been focused on changes in the hardware of the im-

plant, i.e. new materials, designs or surfaces have been

introduced with simultaneous claims of these being

superior to those used in the past. Albeit of some

relevance for biomaterials research, this approach has

not been without pitfalls. Hydroxyapatite-coated im-

plants have not been documented with good clinical

results for 5 years or more, despite these implants

being originally launched in the mid 1980s (Al-

brektsson 1998). The clinical results of intermediary

roughened implants have not been as positive as once

postulated, since the only three controlled clinical

studies as yet published have failed to find any clear

advantages of such implants in comparison to

smoother controls (Lindhe 1997, Karlsson et al. 1998,

Astrand et al. 1999). The only published, long-term

clinical study of oxidized implants (Graf et al. 2001) is

of a quality that does not seem to allow for any reliable

conclusions with respect to the outcome of the im-

plants. Naturally, this does not prevent oxidized im-

plants being of interest for the future, particularly

since there is some evidence (Sul 2002) of the establ-

ishment of a bioactive implant surface, at least with

certain types of anodized implants (Fig. 33-22).

However, if we base our look at the future on what

is known today, there are obvious ways to improve

clinical results. Although the main focus in the past

has been on the three hardware parameters, the pre-

sent authors foresee a substantial development in the

realization of the importance of software parameters

such as surgery and prosthodontics. Improvements of

the surgical technique seem to be a reliable way of

increasing oral implant success (Albrektsson 2002).

The future of osseointegrated implants will mean a

greater understanding of the important contributions

by the responsible surgeon and prosthodontist (Bry-

ant 2001).

OSSEOINTEGRATION: HISTORIC BACKGROUND AND CURRENT CONCEPTS • 819

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CHAPTER 34

Surface Topography of

Titanium Implants

ANN WENNERBERG, TOMAS ALBREKTSSON AND JAN LINDHE

Implant surface / osseointegration

Measurement of surface topography

Instruments

Procedure

Implant surface roughness

Experimental studies

Surface roughness of some commercially available

implants

IMPLANT SURFACE

OSSEOINTEGRATION

Dental implants supplied with a turned surface con-

figuration have been used for more than 30 years and

have been shown to have great long-term success

when used for the rehabilitation of the partially den-

tate and fully edentulous patient (Albrektsson & Sen-

nerby 1991, Eckert et al. 1997, Roos et al. 1997,

Arvidsson et al. 1998). Based mainly on results from

experimental studies, however, several manufactur-

ers of dental implants have gradually substituted the

"old-fashioned" turned implant with implants de-

signed with enlarged surfaces. It was suggested that

implants with such modified surfaces can be loaded

at an earlier time following installation than was gen-

erally recommended for implants with a turned sur-

face. Thus, arguments used in the promotion of sur-

face modified implants were that they (1) provided a

better mechanical stability between bone and implant

immediately following installation — established by a

greater contact area, (2) provided a surface configura-

tion that properly retained the blood clot, and (3)

stimulated the bone healing process. Indeed, findings

from experimental studies documented that a firmer

bone fixation (osseointegration) was established to

implants with a roughened surface than to implants

with a turned surface (Carlsson et al. 1988, Feighan et

al. 1995, Gotfredsen et al. 2000, Ivanoff et al. 2001).

Examples of methods that are used to alter the

surface topography of commercially available dental

implants include

grit blasting, titanium plasma spraying,

etching

and/or

coating. Such

surface conditioning

methods will result in

irregularities of height, wave-

length

and

spatial dimension.

It is currently not known

whether it is variation in height of the irregularities of

given surface or their wavelength or a combination

the two factors, that will promote the rate of incor-

poration of the implant in bone tissue.

It is reasonable to assume that new surface modifi-

cations of dental implants will be introduced and

claims will be made that this or that particular surface

will most ideally promote osseointegration. Thus, it

will become important for the student of dentistry to

understand how a surface is changed, how this sur-

face is characterized and how it may indeed enhance

bone healing and osseointegration.

The characterization of a surface requires not only

the use of an appropriate measuring device but also

knowledge regarding how the results of the measure-

ments should be interpreted.

MEASUREMENT OF SURFACE

TOPOGRAPHY

Instruments

The surface topography describes (1) the degree of

roughness

that the surface exhibits as well as (2) the

orientation

of the irregularities on the surface. Surface

roughness occurs in two principal planes: one perpen

dicular to the surface and one in the plane of the

surface (Thomas 1999). The orientation of the irregu-

larities may be either isotropic or anisotropic.

For a proper topographical characterization of a

surface, instruments and methods must be used that

822 • CHAPTER 34

Sample distance

Fig. 34-1. Too large a distance between the measuring

points will result in a loss of information and an artifi

cial increase of wavelength.

Fig. 34-2. A drawing that demonstrates the measuring

areas – top, flank and valley – of a threaded oral im-

plant.

provide both numerical and visual data. Currently

three groups of instruments are available that may

provide such information:

mechanical contact stylus instruments

optical instruments

scanning probe microscopes (SPM).

Each of the above instruments has its own area of

application. However, in studying the surface charac-

teristics of screw-type oral implants only optical in-

struments may provide proper information (Wenner-

berg & Albrektsson 2000). Among the optical instru-

ments that are available, confocal laser scanning pro-

filometers and interferometers are preferred. It must

be realized that the horizontal resolution in such an

optical instrument is dependent on the wavelength of

the light used and cannot be much better that 0.3 µm,

while the vertical resolution may approach values

close to 0.05 nm. The size of the area of the implant

surface to be analyzed is about 1 m

and the vertical

range for the optical instruments is about 100 µm. It is

also important to define a proper sampling distance,

i.e. the interval or distance between the points to be

measured along the profile of the surface. If this dis-

tance is too long, important surface features will be

lost and the surface (profile) may appear to be

smoother than is actually the case (Fig.34-1).

Measuring and evaluating procedure

The threaded portion of a screw-shaped implant has

three typical regions: the top, the flank and the valley

region (Fig.34-2). Of the three different sites, the top

region generally has the roughest surface (Wenner-

berg & Albrektsson 2000). If we assume that all parts

of an implant are equally important with respect to

osseointegration, a proper characterization of the im-

plant surface must include measurements made in all

three regions. The number of measurements required

for the characterization depends on the homogeneity

of the surface structure within the three regions (Ben

nett & Mattson 1989). Findings from an analysis of

dental implants reported by Wennerberg (1996) indi-

cated that for threaded implants nine measurements

are sufficient for a comprehensive surface charac-

terization — three from the top, three from the flank

and three from the valley regions. Further, three-di-

mensional (3D) measurements are more reliable than

two-dimensional (2D) determinations due to the in-

creased amount of data obtained in the 3D assessment.

The topography of a surface is defined in terms of

form, waviness

and

roughness

(Fig.34-3). Waviness and

roughness are often presented together under the term

texture

(Thomas 1999). Undercuts present in the sur-

face are not possible to measure (Fig.34-4).

In the analysis, data describing form and waviness

are first determined, after which the roughness is

assessed. As can be seen in Fig. 34-3, the roughness

describes the smallest irregularities in the surface,

while form relates to the largest structure (profile).

Surface roughness is further described in terms of

amplitude, spatial distribution

(spacing) and

hybrid

pa-

rameters. For the proper characterization of dental

implants at least one parameter from each of the three

groups — amplitude, spacing and hybrid — must be

included in the topographical evaluation of the top,

SURFACE TOPOGRAPHY OF TITANIUM IMPLANTS • 823

Fig. 34-3. A schematic drawing of

an implant, which demonstrates

the terms form, waviness and

roughness.

the flank and the valley regions (Wennerberg & Al-

brektsson 2000).

Amplitude parameters

describe the vertical height of the

irregularities and are determined in both 2D and 3D

measurements (for example correspond the 2D pa-

rameters Ra, Rq, Rz with the 3D Sa, Sq, Sz) (Fig.34-5).

Spacing parameters

describe the space between the ir-

regularities and are also determined in both 2D and

3D measurements. Sm (2D) and Scx (3D) report the

average length between profile peaks (Fig.34-6).

Hybrid parameters

(Sdq and Sdr) include information

regarding both amplitude and spacing.

These parameters describe whether the irregularities

have rounded or pointed curvatures (Fig.34-7).

IMPLANT

SURFACE ROUGHNESS

Surface structures without a dominating direction are

called

isotropic.

Techniques to produce such surfaces

include abrasive blasting, plasma spraying, etching

and oxidizing. Other processes such as turning or

milling result in a surface that has a distinct and

regular pattern. Such a surface structure is denoted

anisotropic.

Experimental studies investigating surface

roughness and osseointegration

Several studies including

in vivo

experiments have

reported that a better bone fixation (osseointegration)

will be achieved with implants with an enlarged, iso-

tropic surface as compared to implants with a turned,

anisotropic surface structure (e.g. Wennerberg 1996,

Ivanoff et al. 2001). In some studies, by for example

Hahn & Palich 1970, Roberson et al. 1976, Carlsson et

al. 1988, Gotfredsen et al. 2000, a positive correlation

was found between increasing surface roughness and

degree of implant incorporation (osseointegration),

while in other studies no such direct correlation was

observed (Vercaigne et al. 1998).

Wennerberg and co-workers (Wennerberg et al

1995a,b, 1996a,b,c, 1997) performed a series of inves

tigations in an attempt to identify the surface structure

of the "optimal" implant. Threaded (screw-type) im-

plants made of commercially pure titanium were

Fig. 34-4. Undercuts cannot be measured; a loss of spa

tial information will occur.

used. They all had a diameter of 3.75 mm and a

pitch-height of 0.6 mm. Implants with a turned surface

were used as negative controls. The surface structure

of the test implants was altered by exposing the im-

plants to different blasting materials and of different

particle size. The blasting materials used were either

TiO

or Al

and the particles used for blasting were

25 µm, 75 µm or 250 tm large. Following the surface

modification procedure, the implants were cleaned in

an ultrasonic bath and their surface topography char

acterized with the use of an optical confocal pro-

filometer.

The implants were subsequently implanted in the

tibia of rabbits and allowed to heal for 4, 12 or 52

weeks. The degree of bone fixation (osseointegration)

was determined by mechanical (torque removal force)

and histologic (amount of bone to implant contact)

means. The analysis of the findings from these

in vivo

experiments revealed that implants designed with a

surface characterized by the following exhibited the

most ideal degree of osseointegration:

•

Sa value (amplitude 3D) of 1.45 µm

•

Scx value (spacing 3D) of 11 tm

•

Sdr ratio (hybrid 3D) of 1.5

In a second study, the research protocol was slightly

amended in that each individual, screw-shaped im-

plant was prepared with two different surfaces with

different roughness. The implant was thus acting as

its own control. The same blasting technique, materi-

als and particle size were used to modify the surface

as in the previous study. The implants were inserted,

allowed to heal and were exposed to the same deter-

minations as in the experiments described above. The

mechanical and histologic measurements performed

revealed again that a surface with a S

value of 1.45

µm, a S,value of 11 µm and a S

value of 1.5 provided

824 • CHAPTER 34

Fig.

34-5. A

profile demonstrating

how 2D height amplitude descrip

tive parameters are calculated.

Fig.

34-6. A

profile demonstrating

how 2D spatial descriptive pa-

rameters are calculated.

Fig.

34-7. A

profile demonstrating

how 2D hybrid parameters are cal

culated.

the most ideal conditions for bone fixation and The implants were allowed to heal for 4 months (man-

osseointegration (Wennerberg et al. 1998).

dible) and 6 months (maxilla) and were subsequently

In a third study (Ivanoff et al. 2001) "micro-sized"

removed in a biopsy and prepared for a histological

screw type implants with either a turned or a TiO

examination. It was observed that significantly larger

blasted surface were installed in human volunteers.

amounts of bone-to-implant contact had been establ-

SURFACE TOPOGRAPHY OF TITANIUM IMPLANTS • 825

Fig. 34-8. A blasted surface,

Tioblast

, a flank area showing

an isotropic surface with fine ir-

regularities. Each section of the

red and white bars represents a

length of 10 µm.

Fig. 34-9. A blasted and etched sur

face, SLA

"', a flank area demon-

strating two dominating surface

features, pronounced pits (A) and

high frequency irregularities (B).

Each section of the red and white

bars represents a length of 10 µm.

ished to the implants that were prepared with a rough

surface than to the control device. The study further

documented that the S

value used to characterize a

surface may be of lesser importance than the S

value

and the S

ratio in discriminating between surfaces

that may promote osseointegration.

The findings from the studies by Wennerberg and

co-workers, discussed above, were confirmed in a

thesis by Hallgren Hostner (2001). In this series of

studies it was observed that implants with blasted

isotropic surfaces were superior to implants with an-

isotropic or chequered surface patterns in terms of

bone fixation and osseointegration.

Surface roughness of some commercially

available implants

All values presented below are from measurements

made with a confocal laser scanning profilometer

(TopScan 3D, Heidelberg, Germany). The diameter of

the helium-neon laser beam used in this instrument is

approximately 1 µm. All measurement areas had a size

of 250 x 250 µm. Nine measurements were taken from

each implant (three top regions, three valley regions

and three flank regions) and three implants from each

manufacturer were included in the assessments. A

Gaussian filter, sized 50 x 50 pm, was used to separate

roughness from errors of form and waviness.

Blasted surface

(Tioblast

"', AstraTech AB, Molndal, Sweden.) A sur-

face blasted with TiO

particles. The blasting proce-

dure resulted in an isotropic surface; no topographical

remnants from the underlying machining process

were

visible. The implants had an average height

deviation (S

) of 1.07 µm, an average wavelength (S

)

of 10.11 µm

and an increased surface area (

) of 29%

(Fig.34-8).

826 •

CHAPTER 34

Fig. 34-10. An etched surface,

Osseotite

, with a flank area with

fine irregularities and a pro-

nounced isotropy. A smoother sur-

face compared to the Tioblast sur-

face in Fig. 34-8. Each section of

the red and white bars represents

a length of 10 µm.

Fig. 34-11. An implant surface

coated with hydroxyapatite, Ste-

riOss

. This surface has a rather

increased average height devia-

tion and short average wave-

length resulting in an intermedi-

ately increased surface area. Each

section of the red and white bars

represents a length of 10 µm.

Blasted

etched surface

(SLA

, Institute Straumann AG, Waldenburg, Swit-

zerland.) The surface is blasted followed by acid etch-

ing. The measurements disclosed a surface that in-

cluded high frequency wavelength and medium fre-

quency wavelength. The implant surface had an aver-

age height deviation of 1.42 gm (S

), an average wave-

length of 16.60 gm (S

and an increased surface area

of 33% (S

) (Fig.34-9).

Etched surface

(Osseotite

, 3i, Implant innovations, Palm Beach,

Florida, US.) The surface is etched in a two-step pro-

cedure. The surface examination disclosed an iso-

tropic

surface with high frequency irregularities vis

ible (Fig.

34-10). The measured implants had an aver-

age height

deviation of 0.94 hm (S

), an average wave-

length of 11.

68 gm (S

) and an increased surface area

of 20%

(Sdr).

Hydroxyapatite coated surface

(SteriOss

, Replace system, Nobel Biocare, US.) With

the coating procedure used not only the surface chem-

istry but also the topography will be altered. In gen

eral

this procedure gives a rather rough and isotropic

surface. The surface of the SteriOss HA coated im

plants

were found to have an average height deviation of 1.68

gm (S

), an average wavelength of 13.74 am

)

and an

increased surface area of 55% (S

) (Fig.34-

11).

Oxidized surfaces

(TiUnite

, Nobel Biocare AB, Goteborg, Sweden.) The

surface is oxidized in a manner that progressively

increases the thickness of the oxidized layer in "api

cal"

direction. The process results in an isotropic surface

that is characterized by the presence of craterous

structures. The implant surface was found to have an

average height deviation of 1.08 gm (S

), an average

wavelength of 10.98 gm (S,

) and an increased surface

area of 37% (S

) (Fig.34-12).