Dental Materials Journal 5 (2): 217-224, 1986 217

Dental Materials Journal 5 (2): 217-224, 1986 217

Studies on Adhesion to Tooth Substrate

II. Synthesis and Adhesiveness of Monomers that have Amide Groups

Tohru HAYAKAWA*, Hiroshi ENDO*, Masahiro NAGASHIMA*, Masashi YUDA** and

Kozo HORIE** Department of Dental Materials , Nihon University School of Dentistry at Matsudo, 870-1 Sakaecho, Nishi-2 Matsudo, Chiba 271.

** Dental Technician Training School, Nihon University School of Dentistry, 1-8-13 Kanda surugadai, Chiyoda-ku, Tokyo 101, Japan

Received on September 26, 1986Accepted on November 5, 1986

The synthesis and adhesiveness of monomers that have amide groups as hydrophilic groups, i.e.

4-methacryloxybenzamide (MBA) and 4-methacyloylphenylpropionamide (MPPA) are reported.

MBA was prepared from the reaction of p-hydroxybenzamide with methacryloyl chloride in an alkaline

solution. MPPA was prepared from the reaction of p-hydroxyphenylpropionamide with methacryloyl

chloride in trifluoroacetic acid.

The bovine enamel and dentin were etched by a 10% citric acid -3% FeCl3 (10-3) solution. The

monomers were dissolved in MMA, and the adhesiveness of MMA and O-methacryloyl tyrosine amide

(MTYA) were also tested. The tensile bond strengths (MPa) after 1 day at 37•Ž water were measured. They

were MMA: 11.1•}5.3 (enamel), 5.7•}2.8 (dentin); MBA/MMA: 12.1•}6.0 (enamel), 12.3•}4.0 (dentin);

MPPA/MMA: 11.8•}2.5 (enamel), 12.1•}3.5 (dentin); and MTYA/MMA: 11.8•}3.5 (enamel), 14.1•}6.1

(dentin).

Key words: Adhesion, MTYA, Amide.

INTRODUCTION

Adhesion of dental materials to the tooth substrate plays a significant role in dental

clinics for recent years and has been widely studied by many investigators.

Bowen developed N-phenylglycine glycidyl methacrylate (NPG-GMA) and reported a

good adhesiveness of NPG-GMA to the tooth1). NPG-GMA has been considered to form

chelate compounds with calcium atoms of tooth. Moreover Bowen reported that the adhesion

to dentin could be improved by using ferric oxalate, NPG-GMA, and PMDM (adduct of

pyromellitic dianhydride and 2-hydroxyethylmethacrylate)2). He insisted that the good

adhesiveness was due to the formation of chelate complexes between monomers and ferric

irons on the solid surfaces.

Many investigators tried to get good adhesiveness by the chemical bond between

monomers and tooth. However, Nakabayashi et al speculated that there were few pos-

sibilities that such chemical reactions could take place on the tooth surface within 10 minutes

in 37•Ž water. They reported that the monomers containing both hydrophobic and hydro-

philic groups could penetrate and adsorb into or onto tooth substrates and promote the

adhesion to the tooth3,4). They prepared 2-hydroxy-3-ƒÀ-naphtoxypropyl methacrylate

(HNPM)5), 2-methacryloxyethyl phenyl phosphoric acid (phenyl-p)6), and 4-methacryloxyethyl

trimellitate anhydride (4-META)7), which are well known as good adhesive monomers.

218 T. HAYAKAWA, H. ENDO, M. NAGASHIMA, M. YUDA and K. HORIE

Suzuki and Munechika et al examined the adhesiveness of the adducts of ƒ¿-amino acid

and methacryloyl chloride to human teeth8-10). The adducts were used with HEMA as

UV-light cured bonding agents. N, O-Dimethacryloyl tyrosine (DMTY), which was the

adduct of tyrosine with methacryloyl chloride, showed a good adhesiveness to human dentin.

Previously we reported the synthesis of O-methacryloyl tyrosine amide (MTYA) and its

adhesiveness to fresh bovine dentin11). MTYA was dissolved in MMA and TBB-O was used

as a polymerization initiator. MTYA showed good adhesiveness to the bovine dentin etched

with 10% citric acid-3% FeC13 (10-3) solution. The adhesiveness of MTYA was also equal

to that of 4-META.

Here we report the synthesis of adhesive monomers which have amide groups as

hydrophilic groups, i.e. 4-methacryloxybenzamide (MBA) and 4-methacryloxyphenyl-

propionamide (MPPA), and their adhesiveness to bovine enamel and dentin to investigate

the relationship between the structures of monomers and their adhesiveness.

MATERIALS AND METHODS

1) Preparation of monomers

Figure 1 shows the synthetic route of MBA, and Fig. 2 that of MPPA.

i) Preparation of MBA

In a 200ml three-necked flask, 5.0g of p-hydroxyphenylbenzoate and 0.1g of sodium

methylate were dissolved in 100ml of methanol. Ammonium gas was introduced into the

solution for 2 hours. The solution was kept at room temperature overnight. Then the solvent

was evaporated under reduced pressure. The residue was the mixture of phenol and

p-hydroxybenzamide. Phenol was removed by dissolving with chloroform and 2.5g of

p-hydroxybenzamide was isolated. Recrystallization was carried out from water.

In a 100ml three-necked flask with a thermometer and a dropping funnel , 1.5g of

p-hydroxybenzamide was dissolved in a 50ml of 4N-NaOH aqueous solution. Into the

dropping funnel 1.5g of methacryloyl chloride was poured, and was added dropwise at a

temperature below 15•Ž for 30 minutes with stirring. The reaction products came to

precipitate during the reaction. After stirring for 30 minutes at room temperature, the

precipitates were filtered and collected. Thus 0.55g of MBA was obtained. The yield from

p-hydroxybenzamide was 18.0%. Recrystallization was carried out from water-methanol

mixture.

ii) Preparation of MPPA

In a 500ml Erlenmeyer flask fitted with a reflux condenser, 10.0g of p-hydroxy-

phenylpropionic acid, 3ml of sulfuric acid, and 300ml of methanol were placed and the

solution was heated under reflux for 8h. The methanol solution was diluted with water and

neutralized by sodium carbonate. The mixture was transferred to a separatory funnel, and

extracted by chloroform. The extracts were dried overnight over anhydrous sodium sulfate .

After removal of the drying agent by filtration, the chloroform was removed and 6 .5g of

methyl p-hydroxyphenylpropionate was obtained.

The amidation reaction was carried out as described above . In 200ml of methanol

saturated with NH3, 5.0g of methyl p-hydroxyphenylpropionate was allowed to stand for 1

ADHSION OF AMIDE MONOMERS 219

week at room temperature. After the evaporation of the solution, 4.6g of p-hydroxy-

phenylpropionamide was obtained.

The reaction with methacryloyl chloride was carried out by the method of Previero et

al.12) with a slight modification. In a 50ml round-bottomed flask, 0.3g of p-hydroxy-

phenylpropionamide and 16ml of trifluoroacetic acid were placed, and 0.25g of methacryloyl

chloride was added to the solution at room temperature with stirring. After 2h, solvent was

evaporated under reduced pressure and 0.29g of MPPA was obtained. The yield from

p-hydroxyphenylpropionamide was 72.0%. Recrystallization was carried out from water-

methanol mixture.

2) Adhesion test

The bovine tooth was stored at -70•Ž after extracted. The process of making the test

samples are same as previously reported11). The tooth were ground with emery papers #600

and #1000. The enamel and dentin surface were etched with 10-3 solution for 30 seconds, and

washed with water. After drying the surface, the silicone ring was fixed on the etched surface

with sticky wax. The diameter of the ring was 3.2mm and the depth was 2.0mm. MBA,

MPPA, and MTYA were dissolved in MMA at the concentration shown in Table 1. Partially

oxidized TBB (TBB-O) was well stirred with the MMA solution. And the solution was mixed

with PMMA powder to make the adhesive resin. The resin was filled into the cavity of the

silicone ring. After curing of the resin, the silicone ring was removed and the samples were

stored in 37•Ž water for 1 day. The samples were positioned in a tensile testing machine, and

the tensile strengths were measured at a crosshead speed of 2.0mm/min. The adhesiveness

of MMA alone was also tested similary.

Fig. 1 Synthesis of MBA.

Fig. 2 Synthesis of MPPA.


RESULTS

1) Prepatration of monomers

Table 2 shows the yields and analytical data of monomers.

MBA was prepared from the reaction of p-hydroxybenzamide with methacryloyl chlo-

ride in NaOH solution. MPPA was prepared from the reaction of p-hydroxy-

phenylpropionamide with methacryloyl chloride in trifluoroacetic acid. The yield of MBA from p-hydroxybenzamide was low, but that of MPPA from p-hydroxyphenyl-

propionamide was sufficient.The structure of monomers was confirmed by elementary analyses, IR spectra, and 1H

NMR spectra. Figures 3 and 4 show the IR and 1H NMR spectrum of MBA. 1H NMR

spectra were measured in DMSO-d6. The characteristic peaks are assigned as shown in the

spectrum.Analytical data and spectral data support the structure of monomers.

2) Adhesion tests to bovine tooth.

Table 3 shows the tensile bond strengths to bovine enamel and dentin.

In the previous study, 1.0 wt% MTYA in MMA was used11), but further study revealed

that 0.8 wt% MTYA in MMA showed the highest bond strength. In this study 0.8 wt% MTYA

was used as shown in Table 1.

The tensile bond strengths of MBA, MPPA, and MTYA to enamel were similar to those

of MMA, and there were no differences among the monomers.

On the other hand, the bond strengths to dentin differed with the kind of monomer. The

tensile bond strength of MMA alone was only about 6.0MPa. When the monomers were

added to MMA, the strengths were almost twice those of MMA alone. Especially MTYA

showed the highest bond strength.

Table 1 Concentration of monomer and number of samples

Table 2 Yields and analytical data of MBA and

MPPA


DISCUSSION

1) Preparation of monomers

MBA was prepared from p-hydroxybenzamide in NaOH solution. On the other hand , MPPA was prepared from p-hydroxyphenylpropionamide in trifluoroacetic acid . As previously reported11), MTYA could be prepared from the reaction of tyrosine amide with

Fig. 3 IR spectrum of MBA.

Fig. 4 1H NMR spectrum of MBA.


Table 3 Tensile bond strength to bovine enamel and dentin

after storage in 37•Ž water for 1 day (MPa)

(): standard deviation

methacryloyl chloride in trifluoroacetic acid. At first we tried to prepare the MBA in

trifluoroacetic acid, but the desired compound could not be obtained. This is thought to be

due to the difference of basicity of amide groups. The basicity of the amide group of

benzamide was weaker than that of p-hydroxyphenylpropionamide. Thus MPPA could be

prepared in trifluoroacetic acid, but MBA could not be prepared. The yield of MBA was very

low. This is because the amide group was hydrolyzed to carboxylic acid in alkaline solution.

The structure of the monomers was confirmed by elementary analyses, IR spectra,

and 1H NMR spectra. The elementary analyses data are consistent with the calculated

values as shown in Table 2.

In the NMR spectra, amide peak happened to appear at about 7.0•`7.5ppm, and the peak

was observed over the peaks of phenyl group.

Thus we could confirm the structure of the monomers.

2) Adhesiveness to bovine tooth.

At first we used 65% phosphoric acid as an enamel etching agent. Abe et al. reported

that the tensile bond strength of MMA/TBB-O resin to enamel etched with 65% phosphoric

acid was about 13MPa13). However we could not get such a high strength to enamel etched

with phosphoric acid. The bond strength of MMA to phosphoric acid etched enamel was

about 5MPa, and that to 10-3 etched enamel was about 11MPa. So we used the 10-3 solution

as a etching agent of enamel.

Phosphoric acid is widely used in clinics as an enamel etching agent. It was surprising

that phosphoric acid was less effective than the 10-3 solution. Abe et al. also reported that

10-3 etching gave a higher bond strengths than phosphoric acid etching in the adhesion to

enamel13). The effectiveness of 10-3 etching to dentin is widely known, but that to enamel is

not.

The bond strengths were almost the same despite the kind of monomers. They were

about 11•`12MPa. The interlocking mechanism and the mechanical property of resin were

considered to be significant in the adhesion to enamel. In our study the difference in the

monomer could not affect the adhesion to enamel, and this hypothesis was supported.

The effectiveness of monomers in the adhesion to dentin could be clearly observed.

MBA, MPPA showed about twice the strengths of MMA alone, and the tensile strengths of

both monomers were about 12MPa. MPPA has two methylene chains and is more hydro-

phobic than MBA, but such a difference did not affect the adhesiveness to dentin. MTYA

showed the highest bond strength, which was about 14MPa.

The collagen of the dentin was protein and constructed by amide bonds. The monomers

which have amide groups are thought to have a kind of interaction with collagen, and show


good adhesiveness to dentin.

It is generally thought that the bonding to dentin is more difficult than that to enamel.

In our study, the bond strengths to dentin were characteristically higher than those to enamel.

It is suggested that MBA, MPPA, and MTYA is more useful to dentin than to enamel.

CONCLUSION

We were able to prepare monomers that had amide groups, i.e. MBA and MPPA. The

adhesiveness of MBA, MPPA, and MTYA were measured.

1) MBA was prepared from the reaction of p-hydroxybenzamide with methacryloyl

chloride in NaOH solution. MPPA was prepared from the reaction of p-hydroxy-

phenylpropionamide with methacryloyl chloride in trifluoroacetic acid. The struc-

ture of monomers could be confirmed by elementary analyses, IR spectra, and 1H NMR

spectra.

2) The bond strengths to bovine enamel etched with 10-3 were MMA: 11.1•}5 .3; MBA/

MMA: 12.1•}6.0; MPPA/MMA: 11.8•}2.5; MTYA/MMA: 11.8•}3.5 (MPa).

3) The bond strengths to dentin etched with 10-3 were MMA: 5.7•}2.8; MBA/MMA:

12.3•}4.0; MPPA/MMA: 12.1•}3.5; MTYA/MMA: 14.4•}6.1 (MPa).

REFERENCES

1) Bowen, R.L.: Adhesive bonding of various materials to tooth tissues II. Bonding to dentin promoted

by a surface-active comonomer, J Dent Res 44 (5): 895-902, 1965.

2) Bowen, R.L. Cobb, E.N. and Rapson, J.E.: Adhesive bonding of various materials to hard tooth

tissues: Improvement in bond strength to dentin, J Dent Res 61 (9): 1070-1076, 1982.

3) Nakabayashi, N.: Adhesion promoting monomers to tooth substrates. Hybridization of tissue and

polymer, Yuki Gosei Kagaku Kyokaishi 42 (11): 1031-1040, 1984. (in Japanese)

4) Nakabayashi, N.: Bonding of restorative materials to dentin: the present status in Japan, Int Dent

J 35 (2): 145-154, 1985

5) Masuhara, E., Nakabayashi, N., Tarumi, N., Tanaka, S. and Tsuji, H.: Studies on dental self-curing

resins (14), Effect of 2-hydroxy-3-ƒÀ-naphthoxypropyl methacrylate on adhesive strength of tooth and

poly (methyl methacrylate), J Japan Soc Dent Appar Mat 16 (36): 185-188, 1975. (in Japanese)

6) Yamauchi, J., Nakabayashi, N. and Masuhara, E.: Adhesive agents for hard tissue containing phos-

phoric acid monomers, ACS polymer preprints 20: 594-595, 1979.

7) Takeyama, M., Kashibuchi, S., Nakabayashi, N. and Masuhara, E.: Studies on dental self-curing

resins (17), Adhesion of PMMA with bovine enamel or dental alloys, J Japan Soc Dent Appar Mat 19

(47): 179-185, 1978. (in Japanese)

8) Suzuki, K., Munechika, T., Nemoto, K. and Horie, K.: Studies on polymers having adhesiveness to

tooth substance (part 1), Synthesis, photopolymerization and adhesiveness of N, O-dimethacyloxy

tyrosine, J Japan Res Soc Dent Mat Appl 36 (3): 322-329, 1979. (in Japanese)

9) Suzuki, K., Munechika, T., Matsukawa, S. and Horie, K.: Studies on polymers having adhesiveness to

tooth substance (part 2), Synthesis and adhesiveness of methacrylate monomer with ƒ¿-amino acid used

as skelton, J Japan Res Soc Dent Mat Appl 37 (1): 114-119, 1980. (in Japanese)

10) Munechika, T.: Studies on the adhesion mechanism between the surface of tooth substance and

restorative materials, J J Dent Mat 2 (2): 197-231, 1983. (in Japanese)

11) Hayakawa, T., Endo, H., Horie, K., Hara, T. and Ishida, S.: Studies on adhesion to tooth substrate.

I. Synthesis of methacryloyl tyrosine derivatives and evaluation of their adhesiveness to tooth sub-

strate, J J Dent Mat 4 (6): 754-760, 1985. (in Japanese)

12) Previero, A., Barry, L.-G. and Coletti-previero, M.A.: Specific O-acylation of hydroxylamino acids in

presence of free amino groups, Biochim Biophis Acta 263: 7-13, 1972.


13) Abe, Y. and Nakabayashi, N.: Comparison of Bond strength to dentin and enamel with the adhesion

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296

歯質との接着に関する研究

その2 アミド基を有するモノマーの合成とその歯質接着性

早川徹＊,遠藤浩＊,長嶋正博＊,湯田雅士＊＊,堀江港三＊

＊日本大学松戸歯学部歯科理工学教室＊＊日本大学付属歯科技工士専門学校

アミド基を官能基として有するモノマー,4-メタク

リロキシベンズアミド(MBA),4-メタクリロキシ

フェニルプロピオンアミド(MPPA)を合成し,その接

着性を調べた。対照としてMMA, O-メタクリロイル

チロシンアミド(MTYA)を用いた。

被着体としては,新鮮牛エナメル質,および象牙質を

用いた。エナメル質,象牙質ともに,10%クエン酸-3%

FeCl3水溶液で30秒間処理した。各モノマーをMMA

に溶解し,TBB-Oを重合開始剤として用いた。その結

果,次のような接着強さ(MPa)が得られた。MMA:

11+5.3(エナメル質),5.7±2.8(象牙質);MBA/

MMA: 12.1±6.0(エナメル質),12.3±4.0(象牙質);

MPPA/MMA: 11.8±2.5(エナメル質),12.1±3.5(象

牙質);MTYA/MMA: 11.8±3.5(エナメル質),

14.1±6.1(象牙質)。

Dental Materials Journal 5 (2): 217-224, 1986 217

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