Chapter 2 Features of the AQB implant system
AQB Implant Team of Development and Clinical Research
I. Stability and safety of the AQB implant in vivo
The biggest advantage of the AQB implant is its one-piece structure, and yet it has long-term stability inthe body. Results of clinical trials show its treatment success rate to be roughly 95%, and it is highly
reliable 1), 2). Properties that support its success in trials are the processing of the implant surface, andtechnical advances that represent application of the vast number of research results that have been
accumulated that concern interactions with bone, and interactions with the gingivae.
The two-piece type and T-type, both of which were placed on the market later, have also adopted theadvantages of the system, and supported the concept of the one-piece type. The research and analysis of
the products of other companies have also been taken into consideration in order to improve the stability
and safety. Its outstanding features are described in the following chapter.

II. The features of surface treatment of the AQB implant
A. Re-crystallized hydroxyapatite
The methods of dental implant coating has been researched and applied over the years. Apart fromhydroxyapatite, the raw materials used for coating include calcium phosphate ceramics and titanium.
The main objectives of coating techniques are to enable rapid adhesion to bone. The most common method
used is plasma spraying (Fig. 4-2-1). The plasma spray method uses a high-temperature plasma flame(around 10,000°C) where the powered material is introduced into the plasma jet, and is propelled onto theimplant (titanium) surface. The speed of emission is greater than the speed of sound, resulting in theformation of a film that is strongly adsorbed onto the substrate.
Previous hydroxyapatite-coated implants were sold straight after coating with the plasma spray method.
The decline in temperature, from the high temperatures used to melt calcium phosphate to room
temperature, readily resulted in the formation of by-products. A coating layer made this way has calciumoxide (CaO) or tetracalcium phosphate (TeCP) incorporated in addition to the main hydroxyapatite
ingredient, which mostly consists of amorphous hydroxyapatite. The outstanding biocompatibility ofhydroxyapatite is only applicable to the pure, crystalline form. The impure forms described previously,that include impurities and amorphous forms, dissolve rapidly in vivo, weakening the coating layer. This
technical dilemma had been the prime reason for the poor worldwide reputation of hydroxyapatite
coatings.
However, the outstanding biocompatibility of hydroxyapatite was obvious from the results of animal tests.
Therefore, the AQB implant team sought methods that would retain the crystal structure ofhydroxyapatite, and discovered re-crystallized hydroxyapatite. We became the first in the world to apply
this.

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Fig. 4-2-1
Plasma spray

What is re-crystallized hydroxyapatite?
Re-crystallized hydroxyapatite is formed by subjecting tri-calcium phosphate, a type of calcium
phosphate that is the same as hydroxyapatite, to hydration reaction. Depending on the crystal type,tri-calcium phosphate can be categorized into a β- andα-type, and theα-type has been known to reactwith water, forming hydroxyapatite. The AQB implant uses β -type tri-calcium phosphate as thepowdered raw material in the plasma spray. The tri-calcium phosphate introduced into the spray flame isapplied onto the substrate in a similar manner to the usual plasma spray coating, forming a film. Here, inthe high-temperature flame, a phase transition occur s from β-tri-calcium phosphate toβ-tri-calcium
phosphate. The coated layer on the substrate surface is therefore an “α-tri-calcium phosphate coating”.
Since the temperature of the flame does not change in changing the raw material to tri-calcium
phosphate, by-products are still deposited at the time of film formation (as with the hydroxyapatite
coating of the past). Even though the melting temperature of tri-calcium phosphate is higher than that ofhydroxyapatite and it is more difficult to form by-products, yet production of these cannot be avoided. In
the AQB implant, a specialized technique has been developed to convert the α-tri-calcium phosphatecoating into a hydroxyapatite coating, under specific conditions. During this process, the by-products aremelted and dispersed in the atmosphere, then the dispersed by-products recycled and become
incorporated as a part of the pure crystalline hydroxyapatite crystals (Fig. 4-2-2).
The re-crystallized hydroxyapatite coating consists of a crystal body with a purity of >95%, close to that ofa sintered compact, and therefore including only a minute amount of by-products (Fig. 4-2-3-a,b). The
surface coating is covered with exposed, highly pure hydroxyapatite microcrystals (Fig. 4-2-4 a,b). Theirhigh biocompatibility was proven in both cell culture experiments (Fig. 4-2-5, 4-2-6) and animal testing(Fig. 4-2-7). These results therefore suggest that this process has overcome the disappointments
encountered with previous hydroxyapatite-coated implants.
This re-crystallized hydroxyapatite coating enables the AQB implant to fuse with bone. A cylindricalimplant with a diameter of 4 mm, coated with re-crystallized hydroxyapatite, and a non-coated titanium
implant were inserted into the femur of a dog, and the reactions of the surrounding tissues and force
required to pull these out of the bone were compared (Fig. 4-2-8-a,b). The implant with the re-crystallizedhydroxyapatite coating showed active cell differentiation at implantation, and by three months, maturebone was found to surround the implant structure, which was not observed with the non-coated implant.

Fig. 4-2-2
Manufacturing process of recrystallized hydroxyapatite2

Hydroxyapatite (Ca10(PO4)6(OH)2) is a type of the calcium phosphate that is the main constituent of thebone and teeth, therefore has a high biocompatibility with the biological tissues, and has the ability tobond with the biological bone with given time. The coating technology in the past was still insufficient toallow even coating without the impurity contents therefore often preventing interaction to be formed
between the implant and the structures in the body. The development of AQB implant was conductedwith the aim to obtain sufficient stability deriving at the final implant that was coated with recrystallized
HA. This has been produced using tri-calcium phosphate (TCP, Ca3(PO4)2) that is relatively resistant tohigh temperatures and show osteoinduction, which was applied to the implant body with the plasma
spray method into a thin coating layer, which was subsequently converted into the recrystallized HA by atreatment to achieve high biocompatibility for gingival attachment (Japan patent no. 3198125).
a)b)
Hydroxyapatite
Tetracalcium phosphate
Calcium oxide
Hydroxyapatite

Hydroxyapatite
TitaniumFig. 4-2-3-a,ba) The X-ray diffraction data of
coating layer sprayed with
HAb) The X-ray diffraction data of
coating

layer

after

undergoing the process forrecrystallized HA

To derive at a highly crystalline HA, several factors need to be considered: the plasma frame, spraying
distance, spraying speed, and the size of the raw materials. The resulting HA layer, coated with the past
manufacturing methods using HA powder as the raw material, included impurities with high pH such as
Calcium tetraphoshate (TeCP) and calcium oxide (CaO) (Fig. 4-2-3-a). TeCP and CaO both are highly
soluble therefore are thought to be the reason for the vulnerability of the HA coating layer. In contrary,
the purity of the recrystallized HA layer can be observed to be high from the X-ray diffraction analysis.
a)b)Fig. 4-2-4a) The coating layer sprayed with hydroxyapatite.
3

The rapid cooling from the high temperatures of the plasma spray results in decomposed anddissolved coating on the substrate that appears as a vitrified state. Strong alkaline agents such as
CaO are yielded as the by-product, resulting in low crystalline, low purity product.
b) The coating layer of recrystallized hydroxyapatite
The surface is covered with needle-like hexagonal microcrystals of highly pure HA. The coating layerof 35 µm is difficult to peel off. The layer is made up of HA, without presence of any decomposition
product from the high temperatures, and is highly crystalline. In immersion experiments, no changes
in the pH of biological saline that was used as the solvent could be detected, and its solubility has
been shown to be low in both in vivo and in vitro.
Fig. 4-2-5
An image of human healthy osteoblasts planted on AQB implant, takenwith scanning electron microscope (SEM) – the typical circular shapein some of the cells can be seen, but much of the others show anelongated shape to stabilize and to adsorbed onto the surface in vivo
(after 2 hour incubation period).

Fig. 4-2-6
4Healthy human osteoblast planted on the re-crystallized hydroxyapatite (HA) coated surface andtitanium surface. Transmission electron microscope (TEM) was used to analyze the interface between thematerial surface and the cells.
An accelerated differentiation of osteoblasts was observed on the surface of re-crystallized HA coatingeven at 24 hours, whereas the 20 mm gap at the interface between the cells could still be visible withthose planted on the titanium. There were no changes to be seen even after one week. These images
indicated that the differentiation of osteoblasts have been promoted on the surface of rexrystallized HA.
(Taken from Abstracts for the seventh IAI Clinical Research Presentation)

Fig. 4-2-7 a, b
The re-crystallized HA coated titanium was inserted into an animal bone, and the progress wasmonitored with optical microscope. After a month, the coating layer had already become covered with
newly generated bone (a. newly generated bone is shown in blue), and, a strong interaction can be seen
after 2 years (b). The high biocompatibility of recrystallized HA is evident from this data.

Fig. 4-2-8-a
The relationship between the pull-out strength of the bone and the duration of the implantation of
re-crystallized HA coated material
5Fig. 4-2-8-b
The interface between the surfaces of re-crystallized HA coat and the bone, after 3 months (Toluidine blue
stain)The HA coated material required 4.1 MPa after a month, and 6.3 MPa after 6 months of implantation forthe bone to separate, thus suggesting rapid interaction to be formed with the bone. Meanwhile, thetitanium-only material was able to be pulled out with 0.4 MPa after a month. A gradual increase in thestrength required to pull out the titanium implant could be observed, but the maximum strength was 3.6
MPa even after 16 months, the equal amount of strength required after a month with the re-crystallized
HA coated material. This data suggested that the recrystallized HA coat to have the ability to rapidlyinteract with the bone, with a sealing property that prevents the microorganisms from entering the body.

B. Surface treatment of pure titanium to improve its biocompatibility
In contrast to the field of orthopedics, the dental implant can be said to be under severe conditions, as it issubjected to the risk of contracting infection from the time of insertion. Infection in implants, which isprevalent at the initial stages of implantation due to movement within the socket, can be decreased withthe two-piece type, as the fixture is completely enclosed within the gingiva. However, as the majority of
AQB implants are of the one-piece type, the post-surgical state involves penetration of the bone and thegingiva by the implant structure. The incidence of peri-implantitis with the AQB one-piece type wassurprisingly no greater than with other implant types, and was associated with a good prognosis. The
re-crystallized HA coating, with its rapid integration with the bone, decreased the incidence of bacterial
infection.
Another factor is the mirror polishing of the pure titanium surface. Usually, the titanium surface iscovered by an oxide layer that is roughly 4 nm thick. Even if the surface is treated with acid to remove
this layer, another oxidized layer re-forms instantaneously on the titanium surface on exposure to air.
This oxidizing property inhibits the leaking of toxic metal ions into the blood circulation in vivo,
indicating the safety of titanium in the body.
In the AQB implant, the thickness of this oxide layer is increased by immersing it in a solution containing
calcium and phosphate, for a long period of time. This treatment increases the thickness of the mirror
polished part of the layer to 8 nm (Fig. 4-2-9-a, b, c). This oxide layer is much thicker than that of the puretitanium, thus improving the safety in vivo; it also incorporates more phosphate and calcium from thesolution, thereby providing increased biocompatibility (Fig. 4-2-10 a,b, Table 4-2-10a,b). The cell
amplification assay with fibroblasts also showed significant affinity, in comparison with the usual
titanium material, therefore sufficient gingival closure can be expected (Table 4-2-1-a, b, c).

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Fig. 4-2-9a) Before treatment
The titanium surface is usually covered with a thinoxide layer (4 nm).
b) Treatment for increasing biocompatibility to improvegingival attachment
Immersion of AQB implant in a solution containing
calcium ions and phosphate ions. The oxidation processof the titanium surface is accelerated by this treatment
and with simultaneous incorporation of calcium andphosphate.
c) Post-treatment
The thickness of the oxide layer is increased from 4 to 8 nmwith the treatment. Calcium and phosphate ions become
more concentrated close to the surface of the oxide layer,
therefore increased biocompatibility with the gum.

Table 4-2-1-a
The contents of surface titanium oxide
with

the

treatmentforincreasing

biocompatibility to improve gingival
attachment

Surface layer of recrystallized
HA

Enlarged view of Ca and P
Surface layer ofRecrystallized HA

The concentration distribution of thetitanium surface after the treatment

Concentration ratio (at %)Concentration ratio (at %)Fig. 4-2-10-aforincreasing

biocompatibility

toimprove gingival attachment

0.2 λ 0.4 λ

0.6 λ

0.8 λ

1.0 λ

Effective escape depth ofphotoelectron
0.00 λ

0.2 λ

0.4 λ

0.6 λ

0.8 λ

1.0 λ

Effective escape depth of photoelectron

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Table 4-2-1-b
The change in the concentration ratio of OHand Ti4+ ions with the treatment for increasing
biocompatibility

toimprovegingival

attachment. The oxidation and dehydration is
occurring on the titanium oxide surface layer.

Fig. 4-2-10-b
The change in the concentration ratio of OHand Ti4+ ions in the titanium surface oxide
layer after undergoing the treatment forincreasing biocompatibility to improve gingival
attachment. More oxidation can be observed at
the surface.

[Analysis of the surface structure of AQB implant fixture using X-ray photoelectron spectroscopy (XPS)]
Experimental
Pure titanium plate (10×10×1 mm) was mirror polished, washed with acetone using ultrasound,
treatment for increasing biocompatibility to improve gingival attachment, cooled to room temperature,
washed with de-ionized water and sterilized in autoclave, before the analysis with XPS.
Results and observation
The ratio of oxygen on the surface was higher after undergoing the treatment for increasing
biocompatibility to improve gingival attachment than those without. After, this treatment, the Ca and P
were detected (Ca was present in abundance on the surface, whereas only a scarce amount of P was
detected) (Table 4-2-1-a, Fig. 4-2-10-a). The thickness of the layer increased from 4 nm to 8 nm (Table
4-2-1-b). The OH- group on the oxide layer decreased after the treatment, while Ti4+ showed an increase,suggesting progress of dehydration and oxidation (Table 4-2-1-b, Fig. 4-2-10-b)
8

a)

b)

Fig. 4-2-11-aa) The change in number of attached cells with timeb) The change in the ratio of attached cells (reference: 100 %)The fixture of AQB implant is first mirror polished, followed by the treatment for increasing
biocompatibility to improve gingival attachment. The sealing ability was compared between the cell
culture that had been treated with one that was only mirror polished without the subsequenthydrothermal treatment step.
Experimental method
The titanium plate (10 mm) was immersed in culture solution before culture cell (1×105) was spread
evenly on its surface, and left incubating for 2 hrs, 4hrs and 6hrs to be left adsorbed. After washing thecells, the number was calculated using neutral red uptake method. As the replacement of the gingival
fibroblast, human normal skin fibroblast (NB1-RGB cells, Riken Genebank) was used as the cultured cell.
Results and observation
The sowing of the cells were faster on the surface that had undergone secondary treatment (AQB),
compared to the non-treated, and amplification and its stability were observed (Fig. 4-2-11-a). Setting thecontrol (untreated) value to be 100 %, the fraction of the adsorbed cells were found to be higher withshorter time period of the culture, at 2 and 4 hours, the fractions were 10 times, and twice of the control,
respectively. After 6 hours, only marginal differences were observed (Fig. 4-2-11-b). These results
suggested that the surface material of the fixture had excellent initial adhesive abilities to fibroblasts.

III. Design features of the AQB implant
A. Spiral cylinder form (Fig. 4-2-12)
Dental implants are broadly classed into screw-type and cylinder-type implants, depending on the
structural form of the portion buried within the jaw bone. The screw-type is the main type adopted in the
non-coating implants, and is self-tapped to establish primary stability. The self-tapping method is where
the hole is drilled smaller than the diameter of the screw groove, and the implant is delved deeper into
the hole with the use of the screw ridges to stabilize the implant. The residual stress to which the bone is
9subjected is the main concern with this type. The cylinder type, on the other hand is a simple pillar shape,and is stabilized in the bone by forcibly pressing it in. HA-coated implants often are in this form. The holein which it is buried has the same diameter as the cylinder, therefore, the bone is subjected to less stress,
but because the fixing force is gained by the frictional resistance, the primary stability of this type is lessthan those with the self-tapping method.
The AQB implant is classed as cylinder type due to its shape. In the AQB implant, the ridge of the screw
is of a flat, threaded type with a trapezoidal screw, and the implant body is rotated to achieve settlement
at insertion. The insertion hole is initially drilled to have a diameter that is the same as the external
diameter of the trapezoidal screw, therefore, it has no tapping effect. In this case, initial fixation is only
due to friction resistance between the ridge of the trapezoidal screw and the non-screw part of the fixture.
The AQB implant limits the damage to bone to a minimum, and interacts with and fits into the bone byvirtue of its excellent ability to adhere to bone. The bone adhesion is largely due to the re-crystallized HA
coating. Because the insertion hole is set to be the same size as the screw ridge, a gap between the screw
groove and the ridge exists at the time of implantation. This gap is filled up with blood, fractured pieces ofbone, and cancellous bone that result from the rotating and inserting motions of the screw. These
inclusions are beneficial for bone formation, and with the aid of the bone-inducing properties of the
re-crystallized HA, neonatal bone is developed.

Fig. 4-2-12
The screw for the AQB implant has employed the trapezoid screw
with a flat screw thread

B. Applying the “SOL form” to the interdigitations of the two-piece type
Typical interdigitations used in two-piece types are either hexagonal or octagonal. Hexagonal (HEX) can
be fitted in six different ways, and is resistant to rotational stress. However, depending on the angle ofinsertion, lateral force acts at the corners, causing breakage. Other interdigitation types include tapered
structures. Tapered structures have no corners, and thus have a high stress-distributing ability. However,the difficulty lies in the fact that the direction of abutment placement has to be remembered, andresistance to rotational stress is lower than with the hexagonal structure.
A unique structure was developed for the AQB two-piece type implant in order to eliminate the properties
that made previous two-piece implants vulnerable. The corners of the hexagon were removed, and the twopieces were joined with the use of smooth curves to form a unique interdigitation, called the “SOL system”.
SOL stands for Smooth Octagonal Lock. By erasing the corners, the concentrated stress that was exerted
on the hexagonal structure was no longer present, thereby reducing the incidence of breakage. Eightdifferent angles of interdigitation are now present, and therefore slight adjustments to the angle ofattachment to the abutment are possible. Regarding rotational stress, sufficient resistance is present, andthere is thus improved stability in comparison to the tapered type.
10

The only problem that may be caused by this approach is that in a similar manner to the tapered type,the high degree of freedom present with the octagonal shape means that the direction of attachment tothe abutment can be lost in the oral cavity. In such case, it is recommended to construct an apparatus thatindicates the direction of the interdigitation.

Fig. 4-2-13
The original interdigitation, “SOL system” for AQB
two-piece type implant

C. The internal joint of the fixture and abutment (Fig. 4-Two-14)
The attachment of the fixture and abutment uses an internal joint, fixed with screws composed oftitanium alloy. The junction between the fixture and abutment are sculpted with an ultra-precision
cutting technique. Scanning electron microscopy (Fig. 4-2-15) has confirmed that the accuracy of the fit isgood.

IV. Mutual use of abutments
The abutment of the AQB two-piece type is constructed with a fitting that is universal for fixture of any
size. In many other implant systems, several abutments are available for each of the fixture sizes in theirlineup, as the abutment diameter is dictated by the size of the fixture. For example, 15° angled abutment
for a 4 mm diameter fixture, as well as 15° angled abutment for a 5 mm diameter fixture.
There are instances where at the time of choosing the abutment, the straight type was deemed
appropriete, however, the use of angled type was more fitting in the oral cavity or at the stage of modeling.
With this universal style of AQB abutment, it is possible to switch freely from the straight type to theother regardless of the diameter of the fixture. It is important to note, if the same abutment is attached toa fixture of a different diameter (4 mm or 5mm), the total length (of the fixture and abutment) can differ
by around 0.5 mm. The superstructure of the abutment gives 5° of taper to both the straight type and theangle type, and the shoulder provides a heavy chamfer. This form is also a recommended design in the
manufacture of full ceramic crowns using CAD/CAM. By integrating the latest CAD/CAM system, design
and manufacture that uses the least amount of material will be possible in the future.
The sizes, SS, S, M, L; or WS, WM and WL (in which the diameter interacting with the gingivae is wider)
are included in the product lineup. The distinction between these lies in the length of the gingival
interaction that is chosen, depending on the thickness of the gingivae. Otherwise, the design of theimplant types is all the same. The angled abutments accommodate two different types (15° and 25°),
which are used in regions such as the front teeth or in areas where the installation socket requires
parallel adjustment.

11

Fig. 4-2-14
Theconnection

betweenthe

fixtureandabutment has employed internal joint

Fig. 4-2-15
Electron micrograph of the AQB implant joint,
featuring the high precision in the fitting

V. Mutual use of tools
The tools used (Fig. 4-2-16) for one- and two-piece types, as well as the T-type, are designed so that they
can be used for all types. In particular, the drill for hole creation is the same for all three. This has beenpossible because the diameters of all the parts inserted into the gingiva are designed to be of the same
size. In other implant systems manufactured by other companies, even if the implants are from the sameorganization, use of different tools is often required for each implant type. The AQB system has
minimized the number of tools that are specific for each type, therefore, simplifying the surgical operation,
widening the options for each patient, and meeting their needs.
A color-coded system is used in the tool box for each of the different types.
Fig. 4-2-16
The surgical tools for the implantation are common for all
AQB implant types, one-piece, two-piece and T-type. This is
another advantage of this implant system.

VI. Characteristic diagram of the T-type implant
The T-type was developed to overcome the common problems that were encountered with the one-piece
type. The one-piece type is characterized by a straight fixture, which had resulted in the following issues:
its finished appearance and sinking into cortical bone. The superstructure could not be fitted that
resulted in a natural eruption from the tooth cervix. The application of a two-piece type would solve this,but in terms of the cost, time and effort required for surgery, there were cases where a one-piece type
would have been more suitable.
The development of the T-type was able to overcome these issues. The T-type is designed with a taper thatstarts from the end of the HA-coating and with a fixture diameter that is 0.4 mm wider than that of thescrew tip. By widening the fixture, it became possible to fit a superstructure with a more natural outlook
than was the case with the straight, one-piece type. Secondly, this widening of the fixture part helped to12prevent the implant from sinking further into the bone. The straight one-piece type carried the risk ofdelving further into the bone on accidental application of external pressure (such as pressure from strong
biting) at the initial stages of implantation. In particular, in situations where the implant body protrudes
into the maxillary sinus due to sinus-lift procedures, or encroaches on the mandibular canal, thesubsidence of the implant further into the bone could result in a serious complication. The widening of the
fixture of the T- type acted as an effective wedge in the cortical bone, preventing these problems.
The only precaution that has to be considered when handling the T-type is that accuracy is required whendrilling a hole for implantation. With the straight one-piece type, even if the coating is left uncovered, it
can still be buried deeper but with the T-type, it may be necessary to remove the implant for carefulsecondary drilling, to deepen the hole, since the taper will inhibit further insertion into the bone.
Fig. 4-2-17
The T-type is tapered from the terminal surface ofthe coating layer, and the diameter of the abutment
Tapered parts

is 0.4 mm more than that of the screw head.

Same diameter as
AQB 1 piece typeφ (a + approx. 0.4 mm)

References
1)

Takarada H, Kinebuchi T. Clinical evaluation of hydroxyapatite-coated titanium artificial tooth root.

The journal of the Stomatological Society, Japan. Separate volume. 1993; 60(4).
2)

Chiba H, Katsuyama N, Kobayashi R, Mishiro F, Uchida M, Kamezawa H, Otani K, Kiuchi T, Hara S,

Clinical evaluation of hydroxyapatite-coated 1-piece implants (AQB Implant®). Odontology. Reprint.
1994; 81(5).

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