Index
1 Introduction..................................................................................................................................... 2
2 What is dental glazing material?..................................................................................... 3
2.1 Monomer............................................................................................................................3
2.2 Photoinitiator and the absorption wavelength....................................................................3

3 Features of “Nu:le Coat”....................................................................................................... 6
3.1 Transparency......................................................................................................................6
3.2 Curing strain and crack suppression..................................................................................7
3.3 Pencil hardness...................................................................................................................9
3.4 Thickness of coated layer................................................................................................ 10
3.5 Applicable time............................................................................................................... 10
3.6 Curing property............................................................................................................... 11
3.7 Durability........................................................................................................................ 12
3.8 Adhesion to PEEK.......................................................................................................... 14
3.9 Adhesion to resin (various materials and adhesion mechanisms)................................... 15
3.10 Conditions of light irradiation (wavelength, LED, halogen)........................................ 17
3.11 Viscosity and thickness................................................................................................. 18

4 Usage of color types................................................................................................................20
5 Joint use with polycarbonate............................................................................................23
6 Biological safety assessment of “Nu:le Coat”.....................................................25
6.1 Acute systemic toxicity................................................................................................... 26
6.2 Genotoxicity.................................................................................................................... 26

7 Conclusion......................................................................................................................................29
Supervision
YAMAKIN Ph. D. Group
Dr. Teruo Anraku (Ph.D. in Engineering)
Dr. Hiroyuki Itoigawa (Ph.D. in Science)
Dr. Takahiro Kato (Ph.D. in Engineering)
Dr. Takeshi Sakamoto (Ph.D. in Pharmaceutical Science)
Dr. Yuji Sato (Ph.D. in Entrepreneurial Engineering)
Dr. Hidekazu Tanaka (Ph.D. in Engineering)
Dr. Miki Hayashi (Ph.D. in Medicine)Dr. Ritaro Matsuura (Ph.D. in Agriculture)
Dr. Yusuke Mizuda (Ph.D. in Engineering)
Dr. Masatoshi Yamazoe (Ph.D. in Dentistry)Dr. Hirohisa Yamamoto (Ph.D. in Entrepreneurial Engineering)
Advisor of YAMAKIN Ph.D. Group
Dr. Bunishiro Yamada (Ph.D. in Engineering)

What is the YAMAKIN Ph.D. Group?
This is a group of experts in various specialized fields who bring together their knowledge, experienceand technical expertise to act as a prime motivator in the continuous generation of innovation.

1. Introduction
In the finishing touch of dental restoration, it is required that the material surface is abundant in terms ofaesthetical purposes and the inhibition of plaque adhesion.
While traditional methods involving mirror finishing with grinding tools and abrading agents have been
indispensable to glaze the material surface, there is a growing trend toward the use of surface glazing
material which can easily glaze the surface in a short time.
Performance requirements for the dental glazing material are as follows: to be able to be applied thinly
and evenly on the material surface, to form a hard coating, and to be stable in the oral cavity. Technicalchallenges in designing a dental glazing material include cure shrinkage strain of resin, discoloration after
curing, and the restraint of a decrease in luster caused by abrasion.
“Nu:le Coat”, released by YAMAKIN in September 2021, is a dental glazing material that has a lower
strain hardening, less discoloration after curing, and better gloss retention. In this technical report, theconcept of “Nu:le Coat”, usage instructions and physical properties are introduced from a perspective
based on material science and engineering. We hope that this product will be of interest to you.
Leader, Organic Materials Development Section, Master Degree (Physical Science) Takafumi Nakano
Specially Appointed Chief Researcher Doctor (Engineering) Takahiro Kato
Chief Researcher, Laboratory of Bioscience and Safety Doctor (Medicine) Miki Hayashi

22. What is dental glazing material?
The application of dental glazing material can create a smooth surface. The surface should be smooth andscratch-resistant without any unpolymerization after curing and have less discoloration after curing. To
accomplish these functions, it is important to consider the selection of monomers or photoinitiators. The
optimal monomers and photoinitiators for dental glazing material are explained below.

2.1. Monomer
Dental glazing material requires monomers characterized by high reactivity and reduced susceptibility tooxygen, which can impede polymerization inhibition of the material surfaces. The unpolymerized layer
after curing will hinder the development of a gloss finish. It is often used Methacrylate Monomers such
as Urethane Dimethacrylate (UDMA) for light-cured indirect composite resin for the crown, however,it can reduce oxygen inhibition by using Acrylate Monomers that are more reactive or monomers
with polyfunctional groups in the monomer and higher cross-linked density, such as Dipentaerythritol
Hexaacrylate (DPHA), which has six functional groups, for glazing material (Figure 2-1). In addition,
DPHA alone is impractical for direct application due to its high viscosity, therefore, monomers withmonofunctional groups such as Methyl methacrylate (MMA) are often used together to adjust viscosity.
MMA is also used in autopolymerizing resin for denture bases but it has a volatile and specific odor, so
dental glazing material basically has an odor derived from MMA before curing.

O

O

O

O

O

O

O

O
O

O

O

O
O

O

O

Dipentaerythritol Hexaacrylate(DPHA)

Methyl methacrylate(MMA)

Figure 2-1 Structures of monomers

2.2. Photoinitiator and the absorption wavelength
As mentioned above, since it cannot prevent polymerization inhibition by oxygen completely even using
monomers with polyfunction groups, methods that reduce the relative impact of oxygen inhibition areused, including adding the amount of photoinitiator (hereinafter referred to as initiator) and increasing
the radical generation per unit time by combining a high-power light source. Dental glazing material uses
radical polymerization as same as light-cured indirect composite resin for the crown, but the initiator isdifferent. A light-cured indirect composite resin such as TWiNY (YAMAKIN CO., LTD.) mainly uses a
camphorquinone-based initiator (example; camphorquinone; CQ, Figure 2-2), and causes radical by blue3

light with a wavelength around 470 nm (Figure 2-3) 1, 2).
Therefore, commercial light irradiators for dental use basically have a light source emitting blue light.
Although CQ absorbs blue light efficiently, CQ itself has a strong yellow color. There is no problem using
CQ in light-cured indirect composite resin for the crown since it uses little initiator and the yellow color in
the dental crown does not stand out; however, for dental glazing material, the yellow color ruins the shadeof the applied surface. In addition, CQ does not react sufficiently to acrylic monomers used in dental
glazing material.
For this reason, generally, phosphine oxide-based initiators (e.g., 2, 4, 6-trimethylbenzoyl
diphenylphosphine oxide; TMDPO, Figure 2-2) are used in hardening and dental glazing material
applications. Since this initiator has an absorption wavelength of around 395 nm and reacts to violet light,
polymerization equipment for dental laboratories or dental polymerization light irradiators corresponding
to glazing material basically needs to have a light source emitting violet light (Figure 2-4).
One of the characteristics of TMDPO is that it does not affect the color of the monomer before curing
because it becomes colorless and transparent when dissolved in the monomer 1, 2). However, evenphosphine oxide-based initiators in large amounts will turn reddish brown after curing, so it is necessary
to adjust the amount and suppress the color change before and after curing as much as possible. Other
initiators used in dental glazing material are, for example, 1-Phenyl-1,2-propanedione (PPD) and Bis(2,4,6-trimethoxyphenyl) phenylphosphine oxide (BTMPO).

CH3
O
CH3

O

C

Camphorquinone (CQ)

2, 4, 6-Trimethylbenzoyl diphenylphosphine oxide(TMDPO)
CH3

O

C

C

CH3

H3C
CH3

1-Phenyl-1,2-propanedione
(PPD)

O

O

O

C

P

C

H3C
CH3
H3C

Bis (2,4,6-trimethoxyphenyl)
phenylphosphine oxide (BTMPO)

Figure 2-2 Chemical formulas of initiators

4

O

CH3

O

O

P

600

TMDPO (24)ε (L /m o l･c m )LED lamp
400

200

BTMPO (25)Tungsten lamp
CQ

PPD (20)
0
350

400

450

500

550

Wavelength (nm)Light output

Figure 2-3 Absorption wavelength of initiators 1, 2)

TMDPO
380

400

CQ
420

440

460

480

500

Wavelength (nm)Figure 2-4 Wavelength of dental polymerization light irradiator and absorption
wavelength of initiators

53. Features of “Nu:le Coat”
Also, as plus one application, it can be used for pre-treatment of PEEK before applying resin materials(Figure 3-1).
Plu 

 
 





  s One

  Figure 3-1 Features of Nu:le Coat
In order to confirm these concepts, the following tests were carried out using reference samples of “Nu:leCoat Liquid Clear” (hereinafter Liquid Clear) and “Nu:le Coat Gel” (hereinafter Gel), which consist of
approximately twice as much initiator loading as “Nu:le Coat”.

3.1. Transparency
Since Liquid Clear has high transparency after curing (Figure 3-2), it has an insignificant effect on theoriginal color tone of dental restorations even after layering, and is usable for whitening shades such as
A0-GR of “KZR-CAD HR Block 4 E-VA (YAMAKIN CO., LTD.)” (hereinafter referred to as E-VA)(Figure 3-3).
• Test condition(1) Pellet
We checked the appearance of a pellet which was made by pouring Liquid Clear into a jig with a diameterof 12 mm and a thickness of 1 mm, and light-cured for 60 seconds by “LED CURE Master (YAMAKIN
CO., LTD.),” a curing light for indirect composite resin. As a reference, we also created pellets formed
from the reference samples.
(2) Application on a whitening shade
We checked the appearance of samples, which were made by applying Liquid Clear and the reference
samples to “E-VA” (A0-GR), light cured for 5 seconds by “LED CURE Master,” afterward, applied eachsample once more, and light-cured for 60 seconds by “LED CURE Master”.

6• Test result
As shown in Figure 3-2, 3-3, discoloration was visually confirmed on reference samples with a large
amount of photoinitiators (Figure 3-2). Discoloration was also seen in the case when applied and cured
on “E-VA” (A0-GR) (Figure 3-3). Instead, Liquid Clear remains almost colorless and transparent with athickness of 1mm, and the appearance when applied on “E-VA” is almost unchanged as abrasive finishing.

Prototype

Clear

Pellet thickness (immediately after light curing): 1.0 mm

Figure 3-2 (left) Liquid Clear (right) reference sample(immediately after light-curing) thickness 1.0 mm

Figure 3-3 “E-VA” (A0-GR)(left) only polishing (middle) Liquid Clear two-layer coating(right) reference sample two-layer coating

3.2. Curing strain and crack suppression
The combination of flexible polyfunctional monomers and tough cross-linkable monomers reduced curing
strain. Therefore, cracks and/or floated surfaces are less likely to occur even if the applied layer becomes
thicker because of overglaze. As below, the existence of curing strain or cracks was examined in the casethat “Nu:le Coat” or the reference sample is applied on a pellet or the pit and fissure.
• Test condition(1) Evaluation of curing strain
Material is set in the model with a diameter of 12 mm and a thickness of 0.5 mm, inserted between
transparent PET films, and light-cured for 60 seconds.
By measuring the entire thickness of a light-cured pellet four times in increments of 45° by using a caliper“ABS digimatic caliper” (Mitsutoyo Corporation), the strain amount is defined as the amount calculated
by subtracting the thickness before light-curing (0.5 mm) from the thickness after curing (it becomes
thicker compared to before curing by the curl due to strain) (n=3). Three types of pellets were made from7

Liquid Clear, Gel and the reference sample.
(2) Evaluation of cracks
After light-curing Liquid Clear and a reference sample dripped directly into the pit and fissure of crowns,
the presence of cracks and the floated surface is assessed by a microscope.
• Test result(1) Result of curing strain evaluation
Compared to the thickness of a pellet before light-curing (0.5 mm), the curing strain of the relative sample
is approximately 0.7 mm, and the strain can also be visually observed. On the other hand, the curing strainof “Nu:le Coat” is under 0.1 mm, which marks a substantial reduction (Figure 3-4).



1.0




0.5

Evaluation of Curing Strain
0.0

Prototype

Clear

Figure 3-4 Evaluation of curing strain(2) Result of crack evaluation
When evaluated under the assumption that a lot of liquid has been applied onto the pit and fissure ofcrowns or the junction, the emergence of cracks is seen in the reference sample, whereas there is noappearance of cracks on Liquid Clear (Figure 3-5). These results indicate that “Nu:le Coat” is expected toinhibit cracking and floated surface.









Figure 3-5 Evaluation of crack on the pit and fissure of crowns
83.3. Pencil hardness
The hardness of surface coating material is evaluated by various tests, including the pencil hardness test,
the steel wool abrasion test, the cross-cut test, and other tests. Particularly, in recent years, the pencil
hardness test has been used as an index for familiar coating materials such as the screen protector ofsmartphone screens. The hardness of “Nu:le Coat” is evaluated by the pencil hardness test.
• Test condition
Resin pellets are prepared by filling E3 of “Luna-Wing” (YAMAKIN CO., LTD.), a composite resin forcrowns, into a mold with a diameter of 15 mm and a thickness of 1mm. The mold is then sandwiched
between two transparent PET films and light-cured for 90 seconds each from both faces. Both Liquid Clear
and Gel are applied on each resin pellet and light-cured for 60 seconds by “LED CURE Master”, a curing
light for indirect composite resin.
Afterward, the pencil hardness of the surface after light-cured is measured in accordance with JIS K 56005.4 (Scratch hardness (Pencil method)) (n=3).
• Test result
The test result shows that the 7H pencil for Gel and the 9H pencil for Liquid Clear did not leave the pencil
scratch (Figure 3-6).

Pencil Hardness (H)







Gel

Liquid Clear

Figure 3-6 Pencil Hardness
Additionally, Figure 3-7 illustrates the examples of the pencil hardness and Mohs hardness for materials
familiar to us. The pencil hardness of 9H that Liquid Clear results in is equivalent to nearly 5 of Mohs
hardness, which corresponds to the hardness between platinum and the blade of a knife.
Mohs hardness

1

2

3

4

5

6

7

8

9

10

Ceramics
Plaster

Nail

PlatinumThe blade of a
knife

Glass

Diamond

Automobile painting
Pencil hardness

H 2H
Nail

4H

9H
The limit of glass coating

Figure 3-7 Pencil hardness and Mohs hardness 3)
9

3.4 Thickness of coated layer
Dental glazing material needs to be applied thinly and evenly to give smoothness because problems suchas affecting the adaption of dental prosthesis can occur when the coated layer is thick. The thickness ofthe coated layer is evaluated for Liquid Clear and Gel.
• Test condition
Pellets with a thickness of 1 mm are made by using “Luna-Wing,” and after polishing the surface, Liquid
Clear or Gel is applied onto pellets and light cured. The thickness of the coating layer is measured bycomparing the thickness before and after application with a micrometer.
• Test result
The thickness of one coating layer, as shown in Figure 3-8, is about 5 µm for Liquid Clear and about 20µm for Gel (Figure 3-8). When using Gel, Liquid Clear needs to be used as the base layer. Hence, thethickness of the Gel is 25 µm. The contact zone between adjacent teeth of crown restorations should range
from 50 µm to 110 µm, and it is appropriate the condition where a contact gauge of 50 µm can be inserted
but that of 110 µm cannot be inserted. Also, it is said that the interdental space of 150 µm can cause
food impaction, food stuck between the gaps, with a high probability4). The Gel can be used to adjust theThickness of coating layer (µm)

contact in the case when the gap between adjacent teeth is large after setting in the oral cavity.

25
20
15
10
5
0

Gel

Liquid Clear

Figure 3-8 Thickness of coating layer

3.5. Applicable time
Since dental glazing material generally contains various components, they should be used as soon as
possible after collection. Similarly, “Nu:le Coat” contains volatile components, which will volatilize andlead to increased viscosity if they are left unattended. However, there may be cases in which some timeafter collection is required depending on work. In this study, we collected Liquid Clear on an ordinary
mixing pad or a dedicated plate attached to the product and confirmed whether or not it is possible toapply after a certain amount of time has elapsed.

10• Test condition
Liquid Clear is collected on an ordinary mixing pad or a dedicated plate, and evaluated to see if it could
actually be applied with a brush after 10 seconds, 30 seconds, 1 minute, 2 minutes, 4 minutes and 5
minutes.
• Test result
Table 3-1 Applicable time of Liquid Clear depending on collecting methods
Mixing pad

Dedicated plate

Usable up to 1 minute after collection

Usable up to 4 minutes after collection

The volatile components of Liquid Clear volatilized within one minute after being collected on a mixing
pad, the increased viscosity made it impossible to apply it evenly with a brush.
On the other hand, the dedicated plate allowed uniform application with a brush even after 4 minutes.
Therefore, we recommend the use of the dedicated plate when time is required after collection, such as
when applying to multiple teeth.
Another technique, which will be explained in a later chapter, is to collect the liquid color type on amixing pad and leave it for more than one minute to volatilize the MMA, thereby increasing the viscosityand making it easier to apply color to certain parts of the teeth.
If MMA is volatilized too much, however, it resembles the composition of Gel, and adhesion to thesurface of the material by itself is reduced. When using this technique, accordingly, it is necessary toapply one layer of Liquid Clear and light irradiation (10 seconds) before characterization.
Although there is no problem with the dedicated plate made of polypropylene, care should be taken whenusing a collection plate made of polystyrene because the MMA contained in “Nu:le Coat Liquid” maydissolve the components of the collection plate and affect the quality of the product.

3.6. Curing property
Indirect composite resin usually leaves an unpolymerized layer on the surface unless an air barriermaterial is used during polymerization. In ordinary circumstances, this unpolymerized layer is wiped off
with alcohol after polymerization, or removed during morphological modification or polishing by using
a diamond bar or the like. The use of dental glazing material with an unpolymerized layer remaining
is contraindicated because it may cause insufficient polymerization and performance degradation. The
surface smoothness and pencil hardness of Liquid Clear are measured when it’s applied to indirectcomposite resin with an unpolymerized layer.
• Test condition
A mold with a diameter of 15 mm and a thickness of 1 mm was filled with “Luna-Wing” and polymerized

11

with the surface exposed to air, and pellets with an unpolymerized resin layer remaining were prepared(unpolymerized side). Conversely, the pellets cured according to the standard method were used ascomparison samples (polymerized side). Liquid Clear was applied to each pellet, and the smoothness ofthe surface was checked after light cure. The test was conducted to evaluate the smoothness by visualinspection and pencil hardness (Figure 3-9).
• Test result

Pencil hardness






Insufficient curing
Not measurable


Polymerized surface
1 coatUnpolymerized surface Unpolymerized surface
1 coat2 coats

Figure 3-9 Pencil hardness when applied to polymerized/unpolymerized surfaces
When Liquid Clear was applied to an unpolymerized surface, the first coated mixed with theunpolymerized layer of composite resin and did not produce a smooth film due to the dental glazing
material, and pencil hardness could not be evaluated. When Liquid Clear was reapplied (two coats) to thesurface, the same smoothness and pencil hardness were confirmed as those of the film applied once to thepolymerized surface.

3.7. Durability
A toothbrush abrasion test was conducted under clinical conditions to measure changes in gloss andsurface roughness, by applying “Nu:le Coat” to the resin block for CAD/CAM “KZR-CAD HR Block 2
BG” (YAMAKIN CO., LTD.).
• Test condition
Test samples were rectangular pellets of 14.5 mm in length and width and 1mm in thickness made of“KZR-CAD HR Block 2 BG”, coated with Liquid Clear and photo-polymerized for 60 seconds (coatedwith “Nu:le Coat”). The samples polished to a mirror surface were used as comparison samples (polishedfinish). Toothbrush conditions were in accordance with ISO 14569-1, with a load of 2.0 N in a slurry totoothpaste: water =1:2 5). The back-and-forth toothbrush abrasion test was performed 50,000 times, andthe gloss and surface roughness were measured every 10,000 cycles. The number of 50,000 toothbrushabrasion tests is equivalent to about 7 years, assuming that the toothbrushing is done twice a day and each
tooth is brushed 10 times per toothbrushing.
12• Test result
In the evaluation of the toothbrush abrasion test (50,000 times), both the gloss and surface roughness of
the “Nu:le Coat” coating were equal to or more than those of the polished finish, confirming its excellent
abrasion resistance. It is reported that plaque adhesion increases rapidly when the surface roughness
exceeds 0.2 µm 6), but the surface roughness was less than 0.1 µm even after 50,000 toothbrush abrasion
tests (Figure 3-10).
In the gloss change by toothbrush abrasion test, the durability of “Nu:le Coat” was confirmed to be equal
to or more than that of polished surfaces (Figure 3-11).
Polished

Coated with “Nu:le Coat”

Surface roughness Ra (µm)

0.20

0.15

0.10

0.05

0.00

0

10,00020,00030,00040,00050,000Toothbrush movement (times)

Figure 3-10 Scratch resistance by toothbrush abrasion test

Polished

Coated with “Nu:le Coat”

Gloss rate 60°(%)

100

80

60

40

0

10,00020,00030,00040,00050,000Toothbrush movement (times)

Figure 3-11 Change in gloss by toothbrush abrasion test
In addition, the “Nu:le Coat” liquid color type (blue and orange) for characterization was applied and was
similarly subjected to the toothbrush abrasion test for 50,000 cycles. It was confirmed that it was fixed to
the resin block surface without peeling (Figure 3-12).

13
Brushing direction

 

Figure 3-12 Peel resistance by toothbrush abrasion test

3.8. Adhesion to PEEKPolyaryletherketone (PAEK)-based super engineering plastics (PEEK, PEKK, etc.) have been attracting
attention in recent years for their high shock absorption properties, which are expected to mitigate theimpact on bone. They have also been used as dental materials in recent years due to their lightness
and durability. “Nu:le Coat” can be used as a pretreatment material for PEEK, and light-cured indirectcomposite resin (such as “Luna-Wing”) and light and heat-cured indirect composite resin (such as“TWiNY”) can be built up on PEEK frames. The bond strength was measured when “Nu:le Coat” wasused as a pretreatment material for PEEK.
• Test condition
PEEK pellets of 14 mm in length and width and 2 mm in thickness made of PEEK material wereprepared. The bonding surface of the PEEK pellets was polished with P1000 abrasive paper, sandblasted
with 50 µm alumina particles for 6 seconds at a pressure of 0.2 MPa, and ultrasonically cleaned in an
alcohol solution. After that, a masking tape with a hole of 5 mm in diameter was applied to define theadhesive area. Three test samples were prepared: two layers of Liquid Clear were applied to the masking
area, a mixture of Liquid Clear and Gel at a volume ratio of 1:1 was applied, and sandblasting alone wasused as a comparison sample. For each test specimen, TWiNY’s Opaque OA3 was applied to fit the holes
in the masking tape, and after polymerization, TWiNY’s Dentin DA3 was used to build up a cylindricalshape with a diameter of 5 mm and a height of 2 mm. The test samples were then placed in distilled waterat 37°C for one day, and shear bond strength was evaluated by applying a load parallel to the bonding
surface to the cylindrical part using the EZ-Graph universal testing machine (SHIMADZU PRECISIONINSTRUMENTS, INC.)• Test result
As shown in Figure 3-13, it has been confirmed that the shear adhesion to the resin to be built up is
improved when two layers of Liquid Clear were applied as a pretreatment material for PEEK. In addition,
mixing Liquid Clear and Gel at a ratio of 1:1 in advance gives it the proper viscosity as a pretreatment
material and allows pretreatment with only one layer for the pretreatment material. The shear bondstrength was equivalent to that of two layers of Liquid Clear.

14

No treatment(Sandblast only)

Suitable viscosity for
pre-treatment can begained by mixing Clear
and Gel at 1:1 ratio.

2 layers of Clear andlight curing
1 layer of Clear + Gel(mixed 1:1 ratio) andlight curing
0

5

10

15

20

Shear Bond Strength (MPa)Figure 3-13 Shear bond strength of resin build-up on PEEK coated with “Nu:le Coat”

3.9. Adhesion to resin (various materials and adhesion mechanisms)
The durability of Nu:le Coat was evaluated using adhesion strength to various materials as an index.
• Test condition
The bonded surfaces of the various materials were polished with P1000 abrasive paper, sandblasted with
50 µm alumina particles at a pressure of 0.2 MPa for 6 seconds, and ultrasonically cleaned in alcohol.
Then, Liquid Clear was applied and light-cured for 30 seconds, the area other than the bonded area wascovered with masking tape with a 3 mm diameter hole to define the bonding area, indirect composite resin“Luna-Wing” was applied, and after light-curing, resin cement was bonded and fixed with a stainlesssteel rod. Figure 3-14 shows a schematic diagram of the tensile bond test. The samples were then placedin distilled water at 37°C for 1 day, and the tensile bond strength was evaluated by tensile bond test using“EZ-Graph,” the universal testing machine.

Light
irradiation①Sandblasting with 50 μm
alumina particle at 0.2 MPa for
6 seconds and cleaning② Applied Liquid Clear③ Photo-polymerization
10N

Light
irradiation⑤ Applied Indirectcomposite resin Opaque④ Masking with a seal with a
Φ3 mm hole

⑥ Photo-polymerizationLight
irradiation⑦ Stainless steel molding rod(Φ5 mm) fixed on the sample
again with resin cement.

Figure 3-14 Schematic diagram of tensile bond test
To investigate the effect of MMA on various materials, the surface roughness and surface condition of
the material surfaces were observed under a microscope (50x), after polishing with P1000 water-resistantabrasive paper and after immersion in MMA for 5 seconds and wiping off the MMA.

15

• Test result
As shown in Figure 3-15, Liquid Clear bonded to all the materials tested in this study and showed bondstrengths of 5 MPa or higher, with the exception of polypropylene (PP). This indicates that the adhesivestrength is durable enough.

Tensile bond strength (MPa)

25

20

a
a,b

15

a,b,c

10

a,b,c

a,b,c

a,b

a,b

a,b,c

b,c

b,c
c

5

0

Polyethylene terephthalate

Dental polycarbonate

Polycarbonate

Polypropylene

Polyamide

PEEK material

Acrylic resin

Composite resin

Light and heat-cured
indirect composite resin

Indirect composite resin

Resin blocks

Figure 3-15 Tensile bond strength to various materials(significant difference between different alphabets (p<0.05)
Figure 3-16 shows the surface roughness of various materials before and after immersion in MMA. The
surface roughness of polycarbonate, Acrylic resin, and Polyethylene terephthalate was increased byimmersion in MMA. All of these three materials exhibit high tensile bond strength in Figure 3-15, and it
is assumed that the roughening by MMA contained in Nu:le Coat is affected by this. Resin blocks, lightand heat-cured indirect composite resins, and composite resins also exhibited high tensile bond strengthsof 10 MPa or higher, but no change in surface roughness by MMA was observed. For these materials,
the flexural strength of the materials themselves was greater than 150 MPa, and the high strength of thematerials is thought to have influenced the high bond strength by making it difficult for the materials to
fracture at the bond interface. It is also suggested that the use of methacrylic acid monomers in theseresin-based materials may have slightly impregnated MMA, resulting in higher adhesive strength.

16

Resin blocks

Light-cured indirectcomposite resin

Light andheat-cured indirectcomposite resin

Composite resin

Acrylic resin

PEEK material

0.49

0.46

0.44

0.48

0.47

0.59

0.48

0.52

0.47

0.48

0.81

0.63

Polyamide

Polypropylene

Polycarbonate

Dentalpolycarbonate

Polyethylene
terephthalate

0.51

0.57

0.49

0.57

0.56

0.53

0.54

1.72

1.75

1.92

P1000
polishing

Ra (µm)MMA
immersion

Ra (µm)P1000
polishing

Ra (µm)MMA
immersion

Ra (µm)1 mm

Figure 3-16 Photographs of various material surfaces before and after MMA immersion andsurface roughness (Ra)3.10. Conditions of light irradiation (wavelength, LED, halogen)
As an initiator for dental glazing materials, TMDPO with an absorption peak around 400 nm wavelengthis used, as described in section 2-2. Since there are several light sources for light curing and lightirradiators used in dentistry, as described in Table 3-2, commercially available light irradiators: LED (with
400 nm peak (with purple LED) and without 400 nm peak (without purple LED)) and halogen lamp (widewavelength range) were evaluated for their adaptation to “Nu:le Coat”.
• Test condition
The 15 mm diameter, 1 mm thick molds were filled with “Luna-Wing” (E3) light-cured indirect composite
resin for crowns, sandwiched between transparent PET film on both sides and light-cured from both sides
for 90 seconds to prepare resin pellets. The resin pellets were then coated with a sample, and the pencil
hardness was evaluated after light irradiation using “LED CURE Master”, a curing light for indirectcomposite resin, “ a dental LED light curing equipment(effective wavelength: 400±20 nm and 460±20nm)”, and a dental halogen light curing unit.

17• Test result
Table 3-2 Pencil hardness of “Nu:le Coat” Liquid Clear under various light exposure conditions
Product namePlace of use

Polymerization
time

Pencil hardness

LED CURE Master

Dental laboratory

60 sec9H

Dental LED light curing equipment

Dental clinics

20 sec9H

LED(without 400 nm)

Dental LED light curing equipment

Dental clinics

60 secNo polymerization

Halogen lamp

Dental halogen light irradiator

Dental clinics

20 secNo polymerization

40 sec

9H

Type
LED
(with 400 nm)(effective wavelength: 400±20 nm and 460±20 nm)(effective wavelength: 460 nm)

As a result of the test, it was confirmed that the pencil hardness of “LED CURE Master” and “a dental
LED light curing equipment(effective wavelength: 400±20 nm and 460±20 nm)” became 9H by lightirradiation for the specified time (60 seconds and 20 seconds, respectively) as described in the electronic
attachment of “Nu:le Coat”. It was also confirmed that the halogen light irradiator did not polymerize
in 20 seconds, and that light irradiation for 40 seconds resulted in a pencil hardness of 9H. The possible
reason for this is that the light intensity of the halogen lamp was weaker than that of the LED lamp, andpolymerization took longer. Polymerization was not confirmed even after 60 seconds of light-curing
using the LED light-curing unit with an effective wavelength of 460 nm. Since “Nu:le Coat” cannot be
polymerized with a light illuminator without the wavelength (400 nm) of the purple LED, it is necessary
to confirm that the light illuminator has an effective wavelength and light intensity for polymerization inadvance.

3.11. Viscosity and thickness“Nu:le Coat” Liquid is pursued an optimal viscosity that is easy to apply.
Thanks to its low viscosity design, it is hard to remain traces of brushand easy to apply thinly and evenly. It can produce a thin hard coat layer

Thickness of 1 layer●Liquid : 5-15 μm●Gel : 20-50 μm

of approximately 5 µm per layer, allowing coating and characterization
without affecting the surface shape of dental restorations. Also, the gel type is suitable for thicker layers.
Dark brown HV (20~50 µm) is designed to be suitable for the application on the pit and fissure of crowns.
※Procedure for use at the laboratory and chairside (for use as dental glazing material)
The procedures for laboratory-side and chairside use as dental glazing material are as follows.

18

For Laboratory Use

After shape modification

Roughen the surface(Alumina Sandblast etc.)

Application of Nu:le Coat(characterizing and glazing)

Light Curing
Completion(60 sec. by LED CURE Master)

For Chairside Use

Filling composite

Point

After light irradiation, shape
Application of Nu:le Coat
modification and roughening (glazing)
the surface.

Gel is recommended to use for the parts where need thickness.

12
   

Light irradiation

Completion*Light irradiators should have an output
peak wavelength of 400±20 nm, and also
should contain the purple LED

For Color types, shake the bottle well before use as thecolouring material may settle.
Please avoid using this product for occlusal parts wherepressure is applied.

 

Figure 3-17 Procedure for laboratory use and chairside use

19

4. Usage of color types
There are White, Gray, Brown, Yellow, Orange, Blue, Red, Pink, Black, Gum, and Dark Brown HV in
Nu:le Coat Liquid color types that allow for free characterization. There are A plus, B plus, C plus, and Dplus lineups that allow fine adjustment of the shade. (Figure 4-1, lineup as of June 2023.)
Figure 4-2 shows an example of shade adjustment of CAD/CAM resin block “E-VA” for anterior teeth,and Figure 4-3 and Figure 4-4 show examples of characterization using color type. Dark Brown HV usedin Figure 4-4 is designed to have high viscosity and can be applied with a viscosity suitable to adjust theshade of the pit and fissure.

White

Gray

Brown

Yellow Orange

A plusBlue

B plusRed

C plus

Pink

Black

Gum Dark Brown
HV

D plus

A2 Crown

Applied 1 layer of A plus.

B2 Crown

Applied 1 layer of B plus.

C2 Crown

Applied 1 layer of C plus.

D2 Crown

Applied 1 layer of D plus.

Figure 4-1 The color line-up of Nu:le Coat and examples of shade plus use

20

Nu:le Coat Liquid

E-VA

Applied 1 layer

B2-GR

D2-GR

B

Apply 1 layer of B plus

C

Apply 1 layer of C plus

plus

C2-GR

plus

D

plus

Applied 2 layer(Equivalent to B3)(Equivalent to C3)

Apply 1 layer of
D plus(Equivalent to D3)

B

plus

D

plus

B

Apply 2 layer of B plus

C

Apply 1 layer of C plus

plus

plus

(Equivalent to B4)(Equivalent to C4)

Apply 1 layer of
B plus and D plus (1:1)(Equivalent to C4)

Figure 4-2 Shade adjustment of “E-VA” by shade plus

Yellow
Blue
Gray
White

Brown
OrangeFigure 4-3 Characterization by color type

Dark Brown HVFigure 4-4 Reproduction of pit and fissure of a molar by Dark Brown HV

21

Key points for use ①
It is possible to express a various color tone because each Liquid can bemixed. Also, by mixing Liquid Clear, you can dilute the color.

A plus+Liquid Clear

A plus

A plus+OrangeKey points for use ②
You can apply Liquid with suitable viscosity by leaving it on the mixing
pad for a certain period of time.
*If coloring components are separated, mix before use.
Also, it is necessary to apply and light cure (10 sec.) Liquid Clear on the material surface
in advance when using Liquid with high viscosity because the adhesion to material
surface is reduced. Regarding Dark Brown HV, it is designed to have high viscosity, andcan be applied with viscosity suitable to adjust the shade of the pit and fissure.

Expression of white band

Expression of cracks
and hairline

Shade adjustment of the pit
and fissure

22

Fine shade adjustment
around the incisal

Shade adjustment of thecusp apex and the margin5. Joint use with polycarbonate“KZR-CAD Provisional PC” (YAMAKIN CO., LTD., hereinafter referred to as Provisional PC) is amaterial for dental milling and machining made of polycarbonate to make a provisional restoration.
Provisional restoration materials made of polycarbonate are already used in many countries, and it isrecognized for their high usefulness. On the other hand, PMMA is the mainstream in Japan. Polycarbonate
exhibits the highest impact resistance of all plastics.
Polycarbonate has excellent characteristics listed below7).
1. Impact resistance: exhibits the highest impact resistance of all plastics.
2. Operate temperature range: exhibits stable characteristics in a wide temperature range (-100°C~130°C).
3. Electrical characteristics: there is no change in the wide operating temperature range, and exhibits
excellent characteristics as an insulation material.
4. Transparency and weatherability: it is the only one that has transparency among general-purpose
engineering plastics, and can be used outdoors for a long time.
5. Dimension stability: it has excellent creep properties, and has very little dimension change by moistureabsorption, temperature, and time.
6. Heat resistance: it has excellent heat resistance equivalent to UL Certification.
It is possible to improve the aesthetics by using “Nu:le Coat” and “Provisional PC” together. Figure 5-1
shows Provisional PC (anterior teeth) applied Liquid Clear, A plus, B plus, C plus, and D plus of shadeplus.
In the usual polished finish, the workpiece is roughly polished with a paper cone, sandblasted only at
the junction with the lathe, and polished with an abrasive and deerskin buff. By applying Liquid Clear,
it is possible to omit the polishing process. Especially in long bridge cases, as it takes time to polish,
it is expected to improve work efficiency by using Nu:le Coat. Also, it allows us to adjust the shade byusing color types together. A2 of Provisional PC is designed to have a shade close to A2 of zirconia disk
for cutting “KZR-CAD Zirconia” (YAMAKIN CO., LTD.). However, it is possible to shift shades orrecreate gradation by using shade plus. With A plus, A2 can be adjusted to A3, and with B plus, to B3.
For example, in cases of long-term wearing is required, the use of Nu:le Coat provides a more esthetics
provisional restoration by adjusting shades and adding esthetics.

23However, care should be taken when using Nu:le Coat on flexible materials such as Polycarbonate
because of the flexibility differences between the flexible area and Nu:le Coat layer by applying various
layers and making the surface thick may cause cracks and increase the risk of fracture of the material
itself.
As cited below, it is specified to apply less than 3 layers in cases of a single crown and less than 2 layers
in areas that are easily deformed in the Instruction for Use of Nu:le Coat.
(1) Note that when using this product on crowns and resin materials for dentures (PMMA, Polycarbonate,etc.) without fillers, applying thick layers may cause cracks (coating thickness less than 40 µm,
approximately up to 3 layers).
(2) Note that when using this product on bridges made of PMMA and Polycarbonate without fillers,
applying thick layers may cause cracks (coating thickness less than 30 µm, approximately up to 2
layers). Especially in areas where the product tends to accumulate.
Clear

KZR-CAD Provisional PC
Clear

A plus ×1

A plus

A plus ×2

A plus×2

B plusB plus×

C plusC plus

D plus

D plusFigure 5-1 Image of shade shift of Provisional PC (A2) by Nu:le Coat Liquid

Figure 5-2 Reproduction of Gum Shade of copied denture made from Provisional PC
by using Nu:le Coat Liquid Gum

24

6. Biological safety assessment of “Nu:le Coat”
Biological safety assessment evaluates the risk of adverse effects on human health. All medical device thatcomes into contact with the human body is proven to the risk is acceptable to be used in medical treatmentby the evaluation of biological safety.
As shown in Table 6-1, the biological safety evaluation items to be considered for medical devices
are established on the basis of the site of contact with the body (surface-contacting medical devices,
externally communicating medical devices, and implant medical devices) and the contact period (limited
exposure, prolonged exposure, long-term exposure).
In this chapter, test examples when the acute systemic toxicity and genotoxicity were evaluated using test
samples made of raw materials as same as “Nu:le Coat” is introduced.
Table 6-1 Endpoints to be addressed in a biological risk assessment
Endpoints of biological evaluation
Degradation

Reproductive/developmental toxicity

Carcinogenicity

Genotoxicity

Hemocompatibility

Implantation effects

Chronic toxicity

Subchronic toxicity

Subacute toxicity

Acute systemic toxicity

Non-contact
medical devices

Material mediated pyrogenicity

Irritation or intracutaneous reactivity

Sensitization

Cytotoxicity

Physical and/or chemical information

Contact duration(accumulation):A-limited(≦24h),
B-prolonged(>24h to 30 days),
C-Long term (>30
days)

None of the evaluations are required
×

E

E

E

B

×

E

E

E

C

×

E

E

E

Mucosalmembrane

A

×

E

E

E

B

×

E

E

E

E

E

C

×

E

E

E

E

E

×

E

E

E

E

E

B

×

E

E

E

E

E

E

C

×

E

E

E

E

E

E

A

×

E

E

E

E

E

A

B

×

E

E

E

E

E

E

C

×

E

E

E

E

E

E

×

E

E

E

E

E

E
E

E

E

E

E

E
E
E

E

E

E

E

E

B

×

E

E

E

E

E

E

C

×

E

E

E

E

E

E

A

×

E

E

E

E

E

A
B

×

E

E

E

E

E

E

C

×

E

E

E

E

E

E

Tissue/bone

A

×

E

E

E

E

E

Blood

Implant medical
deviceCirculating
blood

Externally communicating
medical device

Breached or Blood path, Tissue/bone/compromised
indirectdentinesurface

Intact skinSurface medical device

A

B

×

E

E

E

E

E

E

C

×

E

E

E

E

E

E

A

×

E

E

E

E

E

B

×

E

E

E

E

E

E

C

×

E

E

E

E

E

E

E
E

E

E

E

E

E

E

E

E

E

E

E

E

E
E

E

E

E

E

E

E

E

E

E

E

E

E

E

E

E
E

E

E

E

E

E

E

E

E

E

E

E means endpoints to be evaluated in the risk assessment (either through the use of existing data, additional endpoint-specific testing, or arationale for why assessment of the endpoint does not require an additional data set). If a medical device is manufactured from novel materials,
not previously used in medical device applications, and no toxicology data exists in the literature, additional endpoints beyond those marked“E” in this table should be considered. For particular medical devices, there is a possibility that it will be appropriate to include additional or fewer
endpoints than indicated.

25

6.1. Acute systemic toxicity
Systemic toxicity test evaluates the toxicities in the organs all over the body when exposed to medical
devices or raw materials. It is classified into 1) Acute systemic toxicity: adverse effects occurring at
any time within 72 hours after single, multiple or continuous exposures of a test sample for 24 hours,2) Subacute systemic toxicity: adverse effects occurring after or continuous exposure between 24 hours
and 28 days, 3) Subchronic systemic toxicity: adverse effects occurring after the repeated or continuous
administration of a test sample for a part of the lifespan, 4) Chronic systemic toxicity: adverse effects
occurring after the repeated or continuous administration of a test sample for a major of the lifespan.
In this section, acute toxicity test (intravenous/ intraperitoneal administration) in accordance with
ISO 10993-11:2017, Biological evaluation of medical devices --Part 11: Tests for systemic toxicity is
explained. Extracts of test samples were prepared by extracting at 121°C for an hour in physiologicalsaline or sesame oil. Empty extracts were prepared in the same method for each extraction solvent. After asingle dose of each extract was administered to mice, changes to general condition and body weight were
measured after 72 hours, and the results were determined according to Table 6-2.
Table 6-2 Evaluation table
Acute systemic toxicity

Through the period of observation, all animals in the extract-treatedgroup had strong biological reactions compared to the animals in theempty extract-treated group.

No acute systemic toxicity

More than 2 animals in extract treated animals die, more than 2 test
animals show significant toxic symptoms such as convulsion andweakness, or more than 3 animals lost more than 10% of body weight.

Reexamination

Any of the animals in the extract-treated group show a slight biologicalreaction compared to the animals in the empty extract-treated group,
or only one animal shows a strong biological response.

Based on the evaluation results, physiological saline or sesame oil extracts were determined as “no acutesystemic toxicity” because all animals in the extract-treated group did not show strong biological reactions
compared to the animals in the empty extract-treated group throughout the observation period.

6.2. Genotoxicity
Genotoxicity test determines the direct or indirect effects of medical devices or raw materials on the
structure or function of DNA, or general disorders caused as a result. Genetic disorder in DNA means
genetic mutation or chromosomal abnormalities or recombination, and cancer can be caused by it.
Therefore, the genotoxicity test is a screening test for carcinogenic. In principle, more than 2 types of tests
are required because one test cannot detect all mechanisms of genotoxicity.
In this section, it is explained reverse mutation test using bacteria and chromosome abnormality test using
mammalian cultured cells compliant with ISO 10993-3:2014, Biological evaluation of medical devices-Part 3: Tests for genotoxicity, carcinogenicity and reproductive toxicity.

261) Reverse mutation test using bacteria
Reverse mutation test analyses if there is a property of causing genetic mutation (mutagenicity) causedby medical devices or raw materials. It used Salmonella and Escherichia coli (amino acid auxotrophic
strains) with mutations in genes involved in amino acid metabolism in the test. Normally, these bacteria
cannot grow on a medium that has not added amino acid since it is impossible to synthesize the aminoacid necessary for growth in the bacteria. However, in cases of genetic mutation, it becomes possible tosynthesize amino acids, multiply, and form colonies. Using this principle, mutagenicity is assessed bycomparing the test sample with negative control (control sample without mutagenicity) colony formation.
Test samples were extracted with dimethyl sulfoxide at 37°C for 48 hours with shaking, and the resulting
extract was used as the test stock solution. Substances that exhibit genotoxicity when metabolized wereassessed by test conditions that do not involve the metabolic activation method that directly interacts
with the test sample and the genotoxicity of the sample that was evaluated under metabolic activation
conditions using a metabolic enzyme (S9mix) to detect substances that exhibit genotoxicity whenmetabolized.
The results showed that the extracts of the samples did not increase the number of reversion mutant
colonies compared to the negative control under any of the test conditions, and therefore, the genemutagenicity of the samples was concluded to be negative.
2) Chromosome abnormality test using mammalian cultured cells
The chromosome abnormality test evaluates mutations caused by medical devices or raw materials
at the chromosome level. Chromosomes are string-like structures that store multiple pieces ofgeneric information, and there are 46 in a normal human. Chromosome abnormalities can be divided
into structural abnormalities, in which the shape of the chromosomes is abnormal, and numericalabnormalities in which the number of chromosomes changes, and both can be evaluated by observation
using an optical microscope. In this test, the frequency of cells with chromosomal aberrations less than
5% was considered negative, between 5% and 10% was considered suspicious-positive, and 10% ormore was considered positive. For the test, the sample were extracted with shaking for 48 hours at 37°C
in the test medium, and the resulting extract was used as the test stock solution. The cells used were
Chinese hamster lung fibroblasts (CHL/IU). Tests were performed with three doses of the test stock
solution at 25, 50, and 100% by short-time and continuous treatment methods. The cells were cultured
for 3 days after seeding and then treated with and without the metabolic enzyme (S9mix). In the shortterm culture treatment method, each plate was cultured for 6 hours, then the medium in the plates was
replaced with a test medium, and cultured for another 18 hours. In the continuous treatment method, thecells were cultured for 24 hours. Chromosome samples were prepared after culturing. In addition, thecells in the plates were counted at the start and at the end of the culture, and the relative increase in cellcounts (RICC) was calculated.

27

RICC (%) = Increase in cell number at each test dose in test groups
treated with sample and positive control
Increase in cell number in test group treated with negative control

×100

Chromosomal abnormalities were recorded according to the classification in Table 6-3.
Table 6-3 Classification of chromosomal abnormalities

Chromosome structuralabnormalities

ctb: chromatid breakcte: chromatid exchange
csb: chromosome breakcse: chromosome exchange
Others (fragmentation, compound anomaly)

Chromosome numericalabnormalities (polyploidy)

Polyploidy*
Others (endoreduplication)

Remarks*Cells with 38 or more chromosomes were recorded as polyploidy.

As a result, the frequency of cells with chromosomal structural abnormalities and the frequency of cellswith chromosomal numerical abnormalities (ploidy) in the test samples were both less than 5%, and it
was concluded that the samples were negative for inducing chromosome abnormalities under the test
conditions.
The above is a part of the biological safety evaluation of the safety required by laws and systems(Pharmaceuticals and Medical Devices Act) using actual samples mixed with the ingredients contained in
the Liquid and Gel types of “Nu:le Coat”. In addition to the biological safety tests introduced here, “Nu:leCoat” has been evaluated for biological safety which is considered necessary in consideration of the usage
form of the material, and it has been confirmed that there are no problems in any of the evaluation items.

28

7. Conclusion“Nu:le Coat“ is a dental glazing material for finishing dental restorations with reduced curing strain,
improved transparency, durability, flexibility in color tone with color types, and ease of application withlow viscosity.
It can be also used as a pretreatment material for resin build-up on PEEK as an additional application. The
aesthetic element of CAD/CAM crown materials used for anterior teeth is defined as “a layered structureof multiple shades including enamel (incisal color), dentine (cervical color), and transitional colors(intermediate colors)” in Japan 8). However, the number of shades is limited even with a stacked structureof multiple shades that meets this definition, making it difficult to achieve optimal color expression foreach individual patient. The use of “Nu:le Coat” color type enables characterization that more closely
resembles natural teeth.
CAD/CAM crowns are expected to become increasingly popular in the future, and this product canstreamline the finishing process. Of course, this product can be used not only for CAD/CAM crowns but
also for indirect composite resin and intraoral composite resin treatment. We hope that this report willencourage the use of dental glazing material.

29References
1) Bunichiro Yamada: Basic Knowledge of Chemistry and Application of Dental Organic Materials (2016):
YAMAKIN CO., LTD.
2) Neumann MG, Miranda Jr WG, Schmitt CC, Rueggeberg FA, Correa IC: Molar extinction coefficientsand the photon absorption efficiency of dental photoinitiators and light curing units. J. Dent., 33: 525532, 2005.
3) About the hardness of glass coatings: Japan Coatings Association https://www.coating.or.jp/
coatingkijun (Confirmed 2022/1/27)
4) Haruka Kusakari: Study on Contract Points, Especially on the Degree of Interdental Separation:
Prosthetic Journal: 9(2) 161-182, 1965
5) ISO/TR 14569-1:2007 Dental materials —Guidance on testing of wear —Part 1: Wear by toothbrushing6) Bollen. M. et al.: Dental Mater, 13(4) 258-269, 1997.
7) Hirotsugu Kuroda, On Polycarbonate. Journal of the textile machinery of Japan, 44(5), 227-235, 1991.
8) Partial revision of the “Matters to be noted for implementation in accordance with the partial revisionof the calculation method of medical fees,” etc., August 31, 2020, Health Insurance Bureau Notification
No. 0831, No.1.

30

31

Nu:le Coat Product Report

The performance and key points for the use of “Nu:le Coat” inresponse to clinical practice

Published on Aug 29, 2024, the 1st Edition
Publisher: Shigenari Yamamoto
YAMAKIN CO., LTD.
Head Office: 1090-3 Kamibun, Kagami-cho, Konan-shi, Kochi, 781-5451, Japan
P: +81-88-888-0290
F: +81-88-888-0291
URL https://www.yamakin-global.com/

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