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Physicochemical properties of commercially available mouthrinses
J. Dent. 1990; 18: 147-l 50
147
Physicochemical properties of commercially available mouthrinses J. F. Perdok, H. C. van der Mei and H. J. Busscher Laboratory
for Materia
Technica, University
of Groningen,
Groningen,
The Netherlands
ABSTRACT This study evaluated physicochemical properties of eight commercially available mouthrinses, namely surface tension, in vivo enamel contact angle, viscosity, penetration coefficient, acidity and buffer capacity. The penetration coefficient. determined by the surface tension, contact angle and viscosity, is a measure of the ability of a liquid to penetrate into a capillary space, such as interproximal regions, gingival pockets and pores. The acidity is often determined by a compromise of the requirements for taste, enamel remineralization and stability of the solution. Among the eight mouthrinses evaluated, the physicochemical properties differed greatly, in particular, the penetration coefficient which varied by a factor of 1.8 over the products tested. Surprisingly several of the products tested were found to be extremely acidic. KEY WORDS: J. Dent, 1990; 1990)
Mouthwashes,
18: 147-l
Properties
50 (Received 6 November 1989; reviewed 19 December 1989; accepted 25 January
Correspondence should be addressed too: Mr H. J. Busscher, Laboratory for Materia Technica, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
INTRODUCTION are frequently used in dentistry to improve dental health. They can be useful in preventing plaque accumulation by addition of antibacterial compounds such as chlorhexidine (Lde and Rindom &hi&t, 1970; Segreto et al., 1986) or aminefluorides (Swing and Crawford, 1971; Perdok et al., 1988a). or alternatively in stimulating enamel remineralization by the addition of fluorides (Tinanoff ef al.. 1980; Katz, 1982). Current research on and evaluation of mouthrinses has focused on the overall effectiveness of the products, for example, their effects on plaque and enamel remineralization. In order to be effective on smooth surfaces, a mouthrinse should spread completely over the tooth surface to enlarge its contact area and to form a zero contact angle. A mouthrinse should be able to penetrate well in order to be effective in interproximal areas and gingival pockets. The capacity of a liquid to penetrate in pores and capillaries is determined by its viscosity, surface tension and contact angle on the capillary surface and is expressed by the penetration coefficient. A liquid with a low viscosity, a high surface tension and a low contact angle can penetrate rapidly into a capillary space (O’Brien and Ryge, 1978).
Mouthrinses
0 1990 Buttenvorth-Heinemann 0300-5712/90/030147-04
Ltd.
Considering the periodontal pocket as a capillary, the penetration coefficient becomes an important factor to enhance the effect of a rinse. A balance of requirements often govern product formulation, these include: antibacterial, remineralization and antidemineralization, stability (Pader, 1985) and, last but not least, taste requirements. Sometimes these requirements are conflicting, resulting in undesirably acidic products. It is the aim of this study to evaluate physicochemical properties of eight commercially available mouthrinses, namely: their surface tension, in vivo enamel contact angle, viscosity, penetration coefficient, acidity and buffer capacity.
MATERIALS AND METHODS Mouthrinses mouthrinses used in this study were purchased commercially and used ‘as received’ within 3 months of purchasing. The following products were evaluated: Hibident (containing 0.2 per cent chlorhexidine. as
All
J. Dent.
148
1990;
18: No. 3
provided by ICI, Belgium), Prodent (containing 0.5 per cent NaF; Intradal, Amersfoort, The Netherlands), Merocet (containing 1 : 2000 cetylpyridinium chloride; Mere11 Pharmaceuticals Ltd. UK), Meridol (containing 125 p.p.m. AmF and 125 p.p.m. SnF,; GABA, Basel, Switzerland), Listerine (containing various phenolic compounds; Lambert Chemical Co., Eastleigh, UK), Veadent (containing 0.05 per cent sanguinarine; Vipont Lab. Inc. Ft., Collins, USA), Act (containing 0.5 per cent NaF; Johnson & Johnson, Benelux, Amersfoort/Brussel) and Oraldene (containing 0.1 per cent hexetidine; Warner Lambert Health Care, Eastleigh, UK). Surface tension The surface tension (~1, mJ.m-2) was determined with a Lauda Autotensiomat equipped with a thermostat (Lauda, Kiinigshafen, FRG), The temperature was kept constant at 25 “C. The surface tension was measured with a Du Nouy ring (circumference 0.06 m), which travelled with a velocity of 1.4 X 10m4m-s-l, pulling a thin liquid film out of the bulk fluid. The force needed to disrupt the film is measured and computed by the Autotensiomat into the surface tension. Corrections were made for the weight of the film based on the Harkins Jordan factor (Adamson, 1976). The accuracy of the apparatus is 0.1 mJ.m-2. Contact
Viscosity The viscosity (q , kgm-l-s-l) of the products was measured with an Ubbelohde viscosimeter. The calibration was checked regularly by measuring the viscosity of water. This instrument is based on the principle of laminated flow through a cylindrical capillary under the influence of gravity. The flow time of a fixed volume of mouthrinses through the capillary is measured, yielding the viscosity according to: q = c-t
(1)
Where: c = calibration constant by the manufacturer t = flow time (seconds) The flow time was recorded four times per tilling, and two fillings were made for each mouthrinse, in order to create an accuracy of 0.0001 kgm-l as-l. Penetration
coefficient
The penetration coefficient (PC, m+-l) was calculated from the surface tension of the rinse, the contact angle of the rinse on the in vivo tooth surface and the viscosity, according to (O’Brien and Ryge, 1978): PC = r1
angles in viva
In order to determine the wetting properties of the rinses, the contact angle (0”) between the tooth surface and a liquid droplet of the rinse was measured in viva. Eight human subjects participated in this study. They were placed in a dental chair in such a way that the buccal surface of the central incisors was positioned horizontally. The subjects were requested not to drink tea or coffee 2 h prior to the measurements. After drying the surface with a vacuum suction tip for 60 s (Perdok et al., 1988b), a 1 ~1 droplet of the rinse was placed on the tooth surface avoiding those areas with visible plaque, and a colourslide was taken. The contact angle was subsequently calculated from the base width and height of the droplet (de Jonget al., 1981) measured on enlarged slides yielding an accuracy of lo per reading.
Acidity
- cos 0 2q
(2)
and buffer capacity
The pH of the rinses was measured with an A161 pH meter (Ankersmit, Brussels, Belgium) with an accuracy of 0.1 pH. A combined glass electrode was used to determine the pH of 15 ml of the rinse at room temperature. The electrode was stabilized in a pH of 7.00 and pH of 4.01 buffer solution. The pH was registered when the display was stable for 5 s. The buffer capacity (p, mol+-l) is defined as the number of moles of strong base or acid required to cause a one unit increase or decrease in the pH of 1 litre liquid, and was measured by adding small amounts (0.1 ml) of either a 0.05 M KOH solution or a 0.05 M HCl solution to 15 ml of a mouthrinse under constant stirring at 250 r.p.m., until the pH had changed one unit.
Table 1. Surface tension (r,), viscosity (q), in vivo contact angle (e), pH and buffer capacity (&OH, p~,-i) of the mouthrinses evaluated in this study VI (mJ.m-*) Hibident Prodent Merocet Meridol Listerine Ueadent Act Oraldene
39.5 35.0 30.6 32.7 33.7 32.1 37.0 30.9
(kg.m2-:.s-l)
0.1069 0.1052 0.1471 0.1065 0.1738 0.1402 0.1524 0.1158
et (degrees) 53 47 1: 49 54 42 37
*SD amounts 5 per cent over four fillings of the viscosimeter. tSD over eight test persons amounts 20 per cent on an average.
PK~H
PH 6.2 ::: :.: 4:2
(mmol+‘) 2.4 6.1 6.3 3.1 6.0 2.9 1.6 3.2
x x x x x x x x
1O-4 1O-3 1Ck3 1 O-3 1O-3 1 O-3 lo-* 1 O-3
PHCI
(mmoW1) 5.7 2.4 1.6 6.9 6.2 7.2 3.3 8.1
x x x x x x x x
1O-4 lo-* lO-* 10-j 1O-3 1 O-3 IO-2 1O-3
Physicochemical
Perdok et al.
Prodent I
7
.--
7 I
.-
a
.*.-- .w-
J
I
*.-- _x--
I
I
I
0 KOH
I 5 x 10-2 added
L
a
I
I
I
I
149
----C____e ----f-_
6
I
of mouthrinses
L----+__*____~
I
___A----
*.-- _+_--*-
6
*.--
,,”
properties
--‘Ic.--__+__ --*--__*
5
10 x10 -2
(mmol)
HCI added
(mmol)
6 Hibident ..* ,p--.7
I
*.--
P
.’
___c--
.-.
*.--
.-
&‘--
c-- +r
.’
.’ I n
.’ 5
.-- *‘.’
*.-6
J 0
I
I
1
I 1.5 x10
KOH
added
-2
I
I
I
I 3.5 x 1o-5
3 x 1o-2
HCI added(mmol)
(mmol)
Fig. 7. Changes in pH of Prodent and Hibident upon addition of small amounts of KOH or HCI to 15 ml of the mouthrinse.
RESULTS The results of the various measurements are compiled in Table I. The surface tensions of the rinses were all found to be in the range between 30 mJ.m-2 and 40 mJ*m-2. Listerine demonstrated the highest viscosity, and Prodent the lowest. In viva contact angles lay between 37’ and 54”. Oraldene and Meridol were the most acidic products (pH 3.6 and 3.7 respectively). The buffer capacities were relatively high for Act, Prodent and Merocet, whereas the buffer capacity of Hibident was low. Fig. 1 illustrates the effects of adding KOH or HCl on the pH of Prodent (high buffer capacity) and Hibident (low buffer capacity). Surface tensions, viscosities and contact angles (Table I) were used to calculate the penetration coefficients of the products summarized in Fig. 2. Analysis of the error propagation of surface tension, viscosity and contact angle revealed that on an average there was a variability of 20 per cent in the penetration coefficient calculated. Within this experimental variability, Hibident, Prodent, Meridol and Oraldene demonstrate the highest penetration coefficients, with the penetration coefficients of Listerine and Veadent being the lowest.
DISCUSSION In this study some physicochemical properties of commercially available mouthrinses have been evaluated.
10 '; E N I ” 2
9 8 7 6
EIHibident
?? Prodent
&! Merocet
?? Meridol
?? Listerine
[gveadent
?? Act
0 Oraldene
Fig. 2. Penetration coefficients (PC, m-s-‘) of the mouthrinses evaluated in this study, as calculated from the measured surface tension, in viva contact angle and viscosity of the products (see Equation (2)).
In the literature little attention is given to these properties, despite their importance to the penetration of the products in interproximal spaces and pores. The surface tension of the mouthrinses are all considerably smaller than that of pure water (72.2 mJ.m-2; Weast, 1979) and saliva (53.0-63.0 ml-m-$ Glantz, 1969). Furthermore it can be noted that the surface tension of Meridol, the product based on aminefluoridelstannous fluoride, is in the same range as that observed for pure aminefluoride solutions (Busscher et al., 1987). All
150
J. Dent. 1990;
18: No. 3
products are more viscous than water (0.1002, kgm-G--l; Weast, 1979). The in tivo contact angles of the mouthrinses on tooth surfaces are all between 37.0” and 54.0”, which is comparable to clinically registered contact angles of water on in tivo tooth surfaces (Perdok et al., 1989). Based on this in viva water contact angle (48’ + 4”) and assuming that the wettability of tooth surfaces is similar to that of pocket surfaces, it can be calculated that the penetration coefficient of water in gingival sulci is extremely high and equal to 0.241 ms-l (compare also Fig. 2), and that water will therefore penetrate a gingival sulcus more effectively than any of the mouthrinses evaluated in this study. Irrigation techniques are used increasingly in dental practice to enhance gingival health. Newman et al. (1989) observed that irrigation with water alone significantly reduced the gingival index (30 per cent), gingival bleeding (44.9 per cent) and bleeding upon probing (24.6 per cent), but it did not affect the amount of plaque. Lander et al. (1986) found similar results. Obviously water does not possess the antimicrobial properties required to reduce the oral microflora and to reduce the amount of plaque, but due to its extremely high penetration coefficient it does have a beneficial effect on the gingival health. This shows that it would be worthwhile to modify mouthrinse formulations in order to increase their penetration, although the capacity of a product to penetrate is only one of the many properties determining its ultimate efficacy. It is difficult to identify the reason why some manufacturers tend to produce relatively acidic mouthrinse formulations. A possible reason could be that taste requirements are met more easily by a more acidic product, or that acidic products are more stable (Pader, 1985). A combination of SnF, and AmF in Meridol, for example, is more stable at a low pH (Mtihlemann, 1983), and a low pH might stimulate the formation of CaF,, which is thought to form a protective layer on enamel from which F- ions are slowly released (Arends et al., 1984). Yet the combination of a low pH and a high buffer capacity seems undesirable and is likely to enhance enamel demineralization. In summary, it can be stated that large differences exist between surface tension, in tivo contact angle, viscosity, penetration coefficient, acidity and the buffer capacity of commercially available mouthrinses. On the basis of this study, and available literature, it is concluded that the subgingival action of mouthrinses can be stimulated by increasing penetration.
Acknowledgement The authors would like to thank Mrs M. SchakenraadDolfing for preparing the manuscript.
References Adamson A. W. (1976) Physical Chemistry of Surfaces, 3rd edn. New York, John Wiley, pp. 21-23. Arends J., Nelson D. G. A., Dijkman A G. et al. (1984) Effect of various fluorides on enamel structure and chemistry. In: B. Guggenheim (ed.), Cariology Today. Basel, Karger, pp. 245-258. Busscher H. J., Uyen H. M., Kip G. A. M. et al. (1987) Adsorption of aminefluorides onto glass and the determination of surface free energy, zeta potential and adsorbed layer thickness. CoJJoids Surfaces 22, 161-169. de Jong H. P., van Pelt A. W. J. and Arends J. (1981) Contact angle measurements on human enamel-an in vitro study of the influence of pellicle and storage period. J. Dent. Res. 62, 11-13. Glantz P. 0. (1969) On wettability and adhesiveness. Odontol. Rev. 20, (Suppl. 17), S-124. Katz S. (1982) The use of fluoride and chlorhexidine for the prevention of radiation caries. J. Am. Dent. Assoc. 104, 164-170. Lander P. E., Newcomb G. M., Seymour G. J. et al. (1986) The antimicrobial and clinical effects of subgingival irrigation of chlorhexidine in advanced periodontal lesions. J. CJin. Periodontal. 13, 74-80. Llie H. and Rindom Schicatt C. (1970) The effect of mouthrinses and topical application of chlorhexidine and the development of dental plaque and gingivitis in man. J. Periodont. Res. 5, 79-83. Miihlemann H. R. (1983) En&vi&lung der Aminfluoride und ihre Anwendung in der Kariesprophylaxe. Dtsch. Zahnarztl. Z. (Special Issue) S3-S5. Newman M. G., Flemmig T., Doherty F. et al. (1989) Enhancement of gingival health by oral irrigation with chlorhexidine. .I Dent Res. 68, 611. O’Brien W. J. and Ryge G. (1978) An Outline of Dental Materials and their Selection. Philadelphia, Saunders, pp. 49-51, 388-394. Pader M. (1985) Surfactants in oral hygiene products. In: Rieger M. M. (ed.), Surfactants in Cosmetics. New York, Marcel Dekker, pp. 293-348. Perdok J. F., Busscher H. J., Weerkamp A. H. et al. (1988a) The effect of an aminefluoride-stannous fluoride containing mouthrinse and enamel surface free energy and the development of plaque and gingivitis. CJin. Prev. Dent 10, 3-9. Perdok J. F., Weerkamp A. H., van Dijk L. J. et al. (1988b) Clinical determination of contact angles on tooth surfaces in vivo. .I. Dent. Res. 67, 701. Perdok J. F., van der Mei H. C., Genet M. J. et al. (1989) Elemental surface concentration ratios and surface free energies of human enamel after application of chlorhexidine and adsorption of salivary constituents. Caries Res. 23, 297-302. Segreto V. A.. Collins E. M. and Beiswanger B. B. (1986) A comparison of mouthrinses containing two concentrations of chlorhexidine. J. Periodont. Res. 21, (Suppl.), 23-32. Swing K. K. and Crawford J. J. (1971) Inhibition of plaqueforming streptococci and diphtheroids by organic compounds. .I Dent. Res. 50, (Suppl.), 104. Tinanoff N., Hock J., Camosci D. et al. (1980) Effect of stannous fluoride mouthrinse on dental plaque formation. J. CJin. Periodontal. 7, 223-241. Weast R. C. (1979) Handbook of Chemistry and Physics. 5th edn. West Palm Beach, USA, CRG Press.
147
Physicochemical properties of commercially available mouthrinses J. F. Perdok, H. C. van der Mei and H. J. Busscher Laboratory
for Materia
Technica, University
of Groningen,
Groningen,
The Netherlands
ABSTRACT This study evaluated physicochemical properties of eight commercially available mouthrinses, namely surface tension, in vivo enamel contact angle, viscosity, penetration coefficient, acidity and buffer capacity. The penetration coefficient. determined by the surface tension, contact angle and viscosity, is a measure of the ability of a liquid to penetrate into a capillary space, such as interproximal regions, gingival pockets and pores. The acidity is often determined by a compromise of the requirements for taste, enamel remineralization and stability of the solution. Among the eight mouthrinses evaluated, the physicochemical properties differed greatly, in particular, the penetration coefficient which varied by a factor of 1.8 over the products tested. Surprisingly several of the products tested were found to be extremely acidic. KEY WORDS: J. Dent, 1990; 1990)
Mouthwashes,
18: 147-l
Properties
50 (Received 6 November 1989; reviewed 19 December 1989; accepted 25 January
Correspondence should be addressed too: Mr H. J. Busscher, Laboratory for Materia Technica, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
INTRODUCTION are frequently used in dentistry to improve dental health. They can be useful in preventing plaque accumulation by addition of antibacterial compounds such as chlorhexidine (Lde and Rindom &hi&t, 1970; Segreto et al., 1986) or aminefluorides (Swing and Crawford, 1971; Perdok et al., 1988a). or alternatively in stimulating enamel remineralization by the addition of fluorides (Tinanoff ef al.. 1980; Katz, 1982). Current research on and evaluation of mouthrinses has focused on the overall effectiveness of the products, for example, their effects on plaque and enamel remineralization. In order to be effective on smooth surfaces, a mouthrinse should spread completely over the tooth surface to enlarge its contact area and to form a zero contact angle. A mouthrinse should be able to penetrate well in order to be effective in interproximal areas and gingival pockets. The capacity of a liquid to penetrate in pores and capillaries is determined by its viscosity, surface tension and contact angle on the capillary surface and is expressed by the penetration coefficient. A liquid with a low viscosity, a high surface tension and a low contact angle can penetrate rapidly into a capillary space (O’Brien and Ryge, 1978).
Mouthrinses
0 1990 Buttenvorth-Heinemann 0300-5712/90/030147-04
Ltd.
Considering the periodontal pocket as a capillary, the penetration coefficient becomes an important factor to enhance the effect of a rinse. A balance of requirements often govern product formulation, these include: antibacterial, remineralization and antidemineralization, stability (Pader, 1985) and, last but not least, taste requirements. Sometimes these requirements are conflicting, resulting in undesirably acidic products. It is the aim of this study to evaluate physicochemical properties of eight commercially available mouthrinses, namely: their surface tension, in vivo enamel contact angle, viscosity, penetration coefficient, acidity and buffer capacity.
MATERIALS AND METHODS Mouthrinses mouthrinses used in this study were purchased commercially and used ‘as received’ within 3 months of purchasing. The following products were evaluated: Hibident (containing 0.2 per cent chlorhexidine. as
All
J. Dent.
148
1990;
18: No. 3
provided by ICI, Belgium), Prodent (containing 0.5 per cent NaF; Intradal, Amersfoort, The Netherlands), Merocet (containing 1 : 2000 cetylpyridinium chloride; Mere11 Pharmaceuticals Ltd. UK), Meridol (containing 125 p.p.m. AmF and 125 p.p.m. SnF,; GABA, Basel, Switzerland), Listerine (containing various phenolic compounds; Lambert Chemical Co., Eastleigh, UK), Veadent (containing 0.05 per cent sanguinarine; Vipont Lab. Inc. Ft., Collins, USA), Act (containing 0.5 per cent NaF; Johnson & Johnson, Benelux, Amersfoort/Brussel) and Oraldene (containing 0.1 per cent hexetidine; Warner Lambert Health Care, Eastleigh, UK). Surface tension The surface tension (~1, mJ.m-2) was determined with a Lauda Autotensiomat equipped with a thermostat (Lauda, Kiinigshafen, FRG), The temperature was kept constant at 25 “C. The surface tension was measured with a Du Nouy ring (circumference 0.06 m), which travelled with a velocity of 1.4 X 10m4m-s-l, pulling a thin liquid film out of the bulk fluid. The force needed to disrupt the film is measured and computed by the Autotensiomat into the surface tension. Corrections were made for the weight of the film based on the Harkins Jordan factor (Adamson, 1976). The accuracy of the apparatus is 0.1 mJ.m-2. Contact
Viscosity The viscosity (q , kgm-l-s-l) of the products was measured with an Ubbelohde viscosimeter. The calibration was checked regularly by measuring the viscosity of water. This instrument is based on the principle of laminated flow through a cylindrical capillary under the influence of gravity. The flow time of a fixed volume of mouthrinses through the capillary is measured, yielding the viscosity according to: q = c-t
(1)
Where: c = calibration constant by the manufacturer t = flow time (seconds) The flow time was recorded four times per tilling, and two fillings were made for each mouthrinse, in order to create an accuracy of 0.0001 kgm-l as-l. Penetration
coefficient
The penetration coefficient (PC, m+-l) was calculated from the surface tension of the rinse, the contact angle of the rinse on the in vivo tooth surface and the viscosity, according to (O’Brien and Ryge, 1978): PC = r1
angles in viva
In order to determine the wetting properties of the rinses, the contact angle (0”) between the tooth surface and a liquid droplet of the rinse was measured in viva. Eight human subjects participated in this study. They were placed in a dental chair in such a way that the buccal surface of the central incisors was positioned horizontally. The subjects were requested not to drink tea or coffee 2 h prior to the measurements. After drying the surface with a vacuum suction tip for 60 s (Perdok et al., 1988b), a 1 ~1 droplet of the rinse was placed on the tooth surface avoiding those areas with visible plaque, and a colourslide was taken. The contact angle was subsequently calculated from the base width and height of the droplet (de Jonget al., 1981) measured on enlarged slides yielding an accuracy of lo per reading.
Acidity
- cos 0 2q
(2)
and buffer capacity
The pH of the rinses was measured with an A161 pH meter (Ankersmit, Brussels, Belgium) with an accuracy of 0.1 pH. A combined glass electrode was used to determine the pH of 15 ml of the rinse at room temperature. The electrode was stabilized in a pH of 7.00 and pH of 4.01 buffer solution. The pH was registered when the display was stable for 5 s. The buffer capacity (p, mol+-l) is defined as the number of moles of strong base or acid required to cause a one unit increase or decrease in the pH of 1 litre liquid, and was measured by adding small amounts (0.1 ml) of either a 0.05 M KOH solution or a 0.05 M HCl solution to 15 ml of a mouthrinse under constant stirring at 250 r.p.m., until the pH had changed one unit.
Table 1. Surface tension (r,), viscosity (q), in vivo contact angle (e), pH and buffer capacity (&OH, p~,-i) of the mouthrinses evaluated in this study VI (mJ.m-*) Hibident Prodent Merocet Meridol Listerine Ueadent Act Oraldene
39.5 35.0 30.6 32.7 33.7 32.1 37.0 30.9
(kg.m2-:.s-l)
0.1069 0.1052 0.1471 0.1065 0.1738 0.1402 0.1524 0.1158
et (degrees) 53 47 1: 49 54 42 37
*SD amounts 5 per cent over four fillings of the viscosimeter. tSD over eight test persons amounts 20 per cent on an average.
PK~H
PH 6.2 ::: :.: 4:2
(mmol+‘) 2.4 6.1 6.3 3.1 6.0 2.9 1.6 3.2
x x x x x x x x
1O-4 1O-3 1Ck3 1 O-3 1O-3 1 O-3 lo-* 1 O-3
PHCI
(mmoW1) 5.7 2.4 1.6 6.9 6.2 7.2 3.3 8.1
x x x x x x x x
1O-4 lo-* lO-* 10-j 1O-3 1 O-3 IO-2 1O-3
Physicochemical
Perdok et al.
Prodent I
7
.--
7 I
.-
a
.*.-- .w-
J
I
*.-- _x--
I
I
I
0 KOH
I 5 x 10-2 added
L
a
I
I
I
I
149
----C____e ----f-_
6
I
of mouthrinses
L----+__*____~
I
___A----
*.-- _+_--*-
6
*.--
,,”
properties
--‘Ic.--__+__ --*--__*
5
10 x10 -2
(mmol)
HCI added
(mmol)
6 Hibident ..* ,p--.7
I
*.--
P
.’
___c--
.-.
*.--
.-
&‘--
c-- +r
.’
.’ I n
.’ 5
.-- *‘.’
*.-6
J 0
I
I
1
I 1.5 x10
KOH
added
-2
I
I
I
I 3.5 x 1o-5
3 x 1o-2
HCI added(mmol)
(mmol)
Fig. 7. Changes in pH of Prodent and Hibident upon addition of small amounts of KOH or HCI to 15 ml of the mouthrinse.
RESULTS The results of the various measurements are compiled in Table I. The surface tensions of the rinses were all found to be in the range between 30 mJ.m-2 and 40 mJ*m-2. Listerine demonstrated the highest viscosity, and Prodent the lowest. In viva contact angles lay between 37’ and 54”. Oraldene and Meridol were the most acidic products (pH 3.6 and 3.7 respectively). The buffer capacities were relatively high for Act, Prodent and Merocet, whereas the buffer capacity of Hibident was low. Fig. 1 illustrates the effects of adding KOH or HCl on the pH of Prodent (high buffer capacity) and Hibident (low buffer capacity). Surface tensions, viscosities and contact angles (Table I) were used to calculate the penetration coefficients of the products summarized in Fig. 2. Analysis of the error propagation of surface tension, viscosity and contact angle revealed that on an average there was a variability of 20 per cent in the penetration coefficient calculated. Within this experimental variability, Hibident, Prodent, Meridol and Oraldene demonstrate the highest penetration coefficients, with the penetration coefficients of Listerine and Veadent being the lowest.
DISCUSSION In this study some physicochemical properties of commercially available mouthrinses have been evaluated.
10 '; E N I ” 2
9 8 7 6
EIHibident
?? Prodent
&! Merocet
?? Meridol
?? Listerine
[gveadent
?? Act
0 Oraldene
Fig. 2. Penetration coefficients (PC, m-s-‘) of the mouthrinses evaluated in this study, as calculated from the measured surface tension, in viva contact angle and viscosity of the products (see Equation (2)).
In the literature little attention is given to these properties, despite their importance to the penetration of the products in interproximal spaces and pores. The surface tension of the mouthrinses are all considerably smaller than that of pure water (72.2 mJ.m-2; Weast, 1979) and saliva (53.0-63.0 ml-m-$ Glantz, 1969). Furthermore it can be noted that the surface tension of Meridol, the product based on aminefluoridelstannous fluoride, is in the same range as that observed for pure aminefluoride solutions (Busscher et al., 1987). All
150
J. Dent. 1990;
18: No. 3
products are more viscous than water (0.1002, kgm-G--l; Weast, 1979). The in tivo contact angles of the mouthrinses on tooth surfaces are all between 37.0” and 54.0”, which is comparable to clinically registered contact angles of water on in tivo tooth surfaces (Perdok et al., 1989). Based on this in viva water contact angle (48’ + 4”) and assuming that the wettability of tooth surfaces is similar to that of pocket surfaces, it can be calculated that the penetration coefficient of water in gingival sulci is extremely high and equal to 0.241 ms-l (compare also Fig. 2), and that water will therefore penetrate a gingival sulcus more effectively than any of the mouthrinses evaluated in this study. Irrigation techniques are used increasingly in dental practice to enhance gingival health. Newman et al. (1989) observed that irrigation with water alone significantly reduced the gingival index (30 per cent), gingival bleeding (44.9 per cent) and bleeding upon probing (24.6 per cent), but it did not affect the amount of plaque. Lander et al. (1986) found similar results. Obviously water does not possess the antimicrobial properties required to reduce the oral microflora and to reduce the amount of plaque, but due to its extremely high penetration coefficient it does have a beneficial effect on the gingival health. This shows that it would be worthwhile to modify mouthrinse formulations in order to increase their penetration, although the capacity of a product to penetrate is only one of the many properties determining its ultimate efficacy. It is difficult to identify the reason why some manufacturers tend to produce relatively acidic mouthrinse formulations. A possible reason could be that taste requirements are met more easily by a more acidic product, or that acidic products are more stable (Pader, 1985). A combination of SnF, and AmF in Meridol, for example, is more stable at a low pH (Mtihlemann, 1983), and a low pH might stimulate the formation of CaF,, which is thought to form a protective layer on enamel from which F- ions are slowly released (Arends et al., 1984). Yet the combination of a low pH and a high buffer capacity seems undesirable and is likely to enhance enamel demineralization. In summary, it can be stated that large differences exist between surface tension, in tivo contact angle, viscosity, penetration coefficient, acidity and the buffer capacity of commercially available mouthrinses. On the basis of this study, and available literature, it is concluded that the subgingival action of mouthrinses can be stimulated by increasing penetration.
Acknowledgement The authors would like to thank Mrs M. SchakenraadDolfing for preparing the manuscript.
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