Scand. J. Dent. Res. 1975:83:288-292
'
'
:..
..
(Key words: chlorhexidine; dental caries; dental plaque; dentifrice; gingivitis)
Effect of 2-yedrs' use of chlorhexidine-containing dentifrices on plaque, gingivitis, and caries JAN R. JOHANSEN, PER GJERMO AND HARALD M. ERIKSEN Departments of Periodontics and Operative Dentistry, Dental Faculty, University of Oslo, Oslo, Norway ABSTRACT - Chlorhexidine digluconate in 0.1 % and 0.4 % concentrations was added to dentifrices to evaluate its effect on plaque formation, gingival conditions and caries in 73 dental students over a 2-year period. No differences were found in the PI I and the G I indices between the active and the placebo dentifrices, but a possible effect on caries was demonstrated. Discolorations of anterior teeth and fillings were the only side effects observed. (Received for publication 5 March, accepted 13 April 1975)
Dental plaque is generally recognized as the main cause of gingivitis and caries. Ghlorhexidine has been shown to prevent plaque formation in many experiments (for review see OCHSENBEIN 1974 and GJERMO 1974), and also to inhibit the development of gingivitis (LOE & SCHIOTT 1970a,b). Furthermore, rat caries may be controlled (REGOLATI, KONIG & MUHLEMANN 1969, KORNMAN, GLARK, K R E I T Z MAN & ALVAREZ 1973) and experimental caries in humans prevented by topical application of chlorhexidine (LOE, FEHR & SCHIOTT 1972). The aim of the present study was to evaluate the effect of different concentrations of chlorhexidine digluconate in dentifrices on plaque formation, gingival condition and caries over a 2-year period. In
addition, attention was directed towards possible clinical side effects.
Material and methods
Seventy-three freshmen dental students, aged 19-23 years, volunteered to participate in the study and were randomly distributed into five groups. Two dentifrices of different abrasiveness were made. To dentifrice No. 1, which contained a conventional abrasive, 1 % oi chlorhexidine digluconate was added to one fraction (L-10) and 0.4 % to another (L-04). Thus two active dentifrices and one placebo (L-placebo) were obtained. From dentifrice No. 2, which did not contain abrasives, only a 0.4 % chlorhexidinecontaining version (F—04) was prepared in addition to the control (F-placebo). Agents known to interfere with the antibacterial activity of chlorhexidine (sulfates, phosphates) were excluded from the dentifrices (GJERMO &
EFFECTS OF CHLORHEXIDINE DENTIFRICE 1971). Coded tubes were distributed to the students in all five groups. A double blind approach was followed. Toothbrushes and dentifrices were given to the participants upon request. The number of tubes and toothbrushes requested by each student was recorded as an indication of the cooperation and active participation of the subjects. No efforts were made to influence their brushing habits except that they were advised to employ approximately one toothbrush-length of dentifrice (1 g) at each brushing (twice a day). At the initial screening the Plaque Index (PI I) and the Gingival Index (G I) (LOE 1967) were recorded and the participants received a thorough prophylaxis before caries registration. Caries was recorded clinically on smooth surfaces (buccal and lingual) according to the following criteria: Score 0 was used when no carious lesions or decalcified areas of the surface could be detected. It was also used for hard and discolored areas of arrested caries. Score 1 — Demineralized areas with hard, unbroken enamel ("white spot lesions"). Score 2 — Soft enamel lesions. Score 3 - Caries penetrating into the dentin, cementum caries and secondary caries. Proximal caries was evaluated on radiographs obtained according to a standardized technique (EGGEN 1971); the following classification was made: Score 0 — No caries. Score 2 - Enamel shadow without dentin involvement. Score 3 — Dentin involvement or secondary caries. Occlusal caries and caries in buccal or lingual fissures were not considered. The scores were added, multiplied by 100 and divided by the number of surfaces examined for each person in order to obtain an individual index figure to use as a basis for calculating group means. In addition the mean number of new and developing (active) carious lesions (surfaces with increased scores) per person during the 2-year period was compared with the mean number of reversed or arrested lesions (surfaces with decreased scores) within each experimental group. The method error in scoring the caries attacks was assessed by statistically analyzing the difference between duplicate registrations and was found to be small (s = 0.03). Registration of PI I, G I and caries was ROLLA
289
repeated after 6, 12, 18 and 24 months. The scoring of plaque and gingivitis was performed by two trained and calibrated dental hygienists; one of the authors (H.M.E.) made the caries examinations. To ensure a double blind approach a thorough projjhylaxis was given before each caries examination. Thus erroneous estimation due to chlorhexidine-induced discoloration was avoided. Student's t-test was used to evaluate the significance of group differences. Discolorations of tooth surfaces were evaluated microphotometrically. Results and details from this part of the study have been reported elsewhere (ERIKSEN & GJERMO 1973). The students were encouraged to report any general or oral observations that might be related to the experiment. Twice during the study the participants answered questionnaires regarding infectious and other diseases experienced during the test period.
Results
During the 2 years 13 participants withdrew from the experiment. Their distribution is shown in Table 1. The reasons for withdrawal were: leaving the faculty or not passing exams, discolorations of teeth (one in the L-10 and one in the L-placebo group), discontent with the consistency of the toothpaste (F-04), and unspecified reasons. PLAQUE
The initial mean PI I values varied from Table 1 Distribution of students leaving the stU'dy before its completion
F F L L L
placebo 0.4 placebo 0.4 10
Start
End
15 15 14 19 10
13 9 12 17 9
73
60
Withdrawals 2 6
2 -
2
1 13
JOHANSEN, GJERMO AND ERIKSEN
290
C l -loo F-plBcebo F-04 L-placebo — —
PLACEBO 0 4 2 CH.
L-10
v\ . . . . . - ' " • - . ^
.
—
,
0.6—
Fig. 3. Mean caries index (C I) on smooth surfaces. MONTHS
Fig. 1. Mean plaque index.
tistically significant differences between the groups were observed (Fig. 2 ) .
0.91-0.98. During the study the mean values dropped to about one-third in both active and inactive groups (Fig. 1). No statistically significant differences between the groups were detected at any scoring. However, the lowest scores were obsei^ved in the groups using abrasive dentifrices containing 0.4 % (L-04) and 1 % ( L 10) chlorhexidine.
CARIES
The group employing the dentifrice containing 1 % chlorhexidine (L-10) exhibited lower index values than did all other groups at all registrations (Fig. 3), but the differences were small. No differences could be detected between
GINGIVITIS
The mean G I values remained relatively constant throughout the 2 years. No sta- 9-
ACTIVE ATTACKS
I I
REVERSED AND ARRESTED ATTACKS
^
87654
\
3 2
•" '
F-04 L-plBCpho I.-04 L-10
j11 I/. C.H.
MONTHS
Fig. 2. Mean gingival index.
I
I 0.47.CH
I
PLACEBO
Fig. 4. Mean number of active reversed and arrested caries lesions per person. Smooth and proximal surfaces.
EFFECTS OF CHLORHEXIDINE DENTIFRICE the placebo groups (L-placebo and F placebo) and the groups using 0.4 % chlorhexidine-containing dentifrices (L04 and F-04). The L-10 group showed a decreasing number of active attacks and an increasing number of reversed and arrested lesions (Fig. 4).
SIDE EFFECTS
No clinically detectable untoward side effects were observed during the 2-year use of chlorhexidine-containing toothpastes except for the brownish discolorations of teeth and front fillings as reported previously (ERIKSEN & GJERMO 1973). The frequency and degree of staining could be correlated to the content of chlorhexidine in the dentifrices and to the presence of abrasives. The two questionnaires disclosed no differences in frequency of virus infections, digestion irregularities or other indications of general side effects between the various groups. A control study immediately after the cessation of the present experiment indicated that 2 years' exposure to chlorhexidine had not provoked the development of chlorhexidine resistant plaque-forming bacteria (GJERMO & ERIKSEN 1974). Discussion
In spite of the long duration only 13 subjects withdrew from the experiment and only one person in the 1 % chlorhexidine group (L-10). Thus it seemed as if the bitter taste of chlorhexidine was only a minor if any objection to its use for a prolonged period. This conclusion may be of interest in introducing chlorhexidine-containing dentifrices to the public. In considering the results of the present study, it should be borne in mind that the experimental subjects were highly selected.
291
being young dental students with good oral hygiene, healthy gingiva and low caries activity. Influenced by the environment of a dental school, and possibly by the experiment itself, their oral hygiene improved during the first 6 months of the study, then stayed relatively constant for the next 12 months. When the students at this time started their clinical training, a further drop in the PI I values was observed in all groups (Fig. 1). Thus it seems conceivable that a plaque-inhibiting effect of chlorhexidine in the present investigation may have been masked by the excellent mechanical toothcleansing performed by the test subjects. Similar observations have been reported earlier (FLOTRA, GJERMO, ROLLA & WAERHAUG 1972, HANSEN, GJERMO & ERIKSEN 1975).
No effect on the gingival condition was observed in the present study by the method employed. This may be explained by the index system itself, since Score 1 indicates a very slight degree of inflammation which may even be caused by vigorous toothbrushing. In the entire material relatively few scores indicating clinical gingivitis were found. Even though one of the hygienists was responsible for the scoring of the G I and the other scored the PI I throughout the study, intraindividual variations cannot be outruled. Unfortunately, the indices used offer limited possibilities for checking the method error. Garies seemed to be influenced by the application of the dentifrice containing 1 % chlorhexidine (Figs. 3 & 4). However, the group employing this dentifrice (L-10) also exhibited the lowest index values initially. This may reflect a lower caries activity in the students comprising this group even before the experiment started. The observation of a .reduced number of active caries attacks and an increased number of reversed and arrested attacks in this particular group, as com-
292
JOHANSEN, GJERMO AND ERIKSEN
pared with the other groups (Fig. 4), gives support to the impression of a caries reducing effect. Similar observations have been made in a group of Danish students after they used chlorhexidine mouthrinses for 2 years (SCHIOTT, personal communication). This may have been caused by a change in the plaque pathogenicity rather than in plaque quantity, since Streptococcus mutans seemed to be almost eliminated during long-term use of chlorhexidine (SCHIOTT, BRINER & LOE 1975). The present study did not indicate any systematic side effects. Furthermore, the long-term use of chlorhexidine in the oral cavity did not seem to affect the oral mucosa. This is in agreement with histologic and chenaical findings (NuKi, BERGQUIST & ORGAN 1972, MACKENZIE, NUKI & BUT-
BAUGH 1973, MACKENZIE 1974). These important observations may justify the longterm use of the drug in plaque preventive programs for mentally and physically retarded population groups. In addition it seems ethically acceptable to perform extramural experiments in groups with high caries activity and poor gingival conditions. References
EGGEN, S.: Simplification and standardization of intraoral radiology. Quintessence Int. 1971: 1: No. 1: 93-96. ERIKSEN, H . M . & GJERMO, P.: Incidence of
stained tooth surfaces in students using chlorhexidine-containing dentifrices. Scand. J. Dent. Res. 1973: 81: 533-537. FLOTRA, L., GJERMO, P., ROLLA, G . & WAER-
HAUG, J.: A 4-month study on the effect of Address: Jan R. Johansen Department of Periodontics, Dental Faculty Geitmyrsveien 69 Oslo 4 Norway
chlorhexidine mouth washes on 50 soldiers. Scand. J. Dent. Res. 1972: 80: 10-17. GJERMO, P.: Chlorhexidine in dental practice. /. Clin. Periodontol. 1974: 1: 143-152. GJERMO, P. & ERIKSEN, H . M . : Unchanged
plaque-inhibiting effect of chlorhexidine after 2 years of continuous use. Arch. Oral Biol. 1974: 19: 317-319. GJERMO, P. & ROLLA, G.: The plaque-inhibiting effect of chlorhexidine-containing dentifrices. Scand. J. Dent. Res. 1971: 79: 126-132. HANSEN, F., GJERMO, P. & ERIKSEN, H . M . :
The effect of a chlorhexidine-containing gel on oral cleanliness and gingival health in young adults. / . Clin. Periodontol. 1975: 2: in press. KoRNMAN, K. S., CLARK, W . B., KREITZMAN, S.
N. & ALVAREZ, C : Caries control in the albino rat with chlorhexidine gluconate (Hibitane). Arch. Oral Biol. 1973: 18: 165170. LOE, H . : The gingival index, the plaque index and the retention index systems. /. Periodontol. 1967: 38: 610-616. LOE, H . , FEHR, F . R . V. D. & SCHIOTT, C . R . :
Inhibition of experimental caries by plaque prevention. The effect of chlorhexidine mouthrinses. Scand. J. Dent. Res. 1972: 80: 1-9. MACKENZIE, I., NUKI, K . , BUTTERBAUGH, J.:
Effects of oral administration of chlorhexidine on epithelial mitotic rate. Int. Assoc. Dent. Res. Meeting 1973. Abstract No. 141, p. 94. MACKENZIE, I.: A study of the stratum corneum of normal and chlorhexidine-exposed human oral mucosa. Int. Assoc. Dent. Res. Meeting 1974. Abstract No. 662, p. 220. NUKI, K . , BERGQUIST, J. J. & ORGAN, R . : Quantitative microchemistry of chlorhexidine treated attached gingiva. Int. Assoc. Dent. Res. Meeting 1972. Abstract No. 206, p. 99. SCHIOTT, C . R . , BRINER, W . W . & LOE, H . :
Two years use of chlorhexidine against human diseases. III. Changes in sensitivity to chlorhexidine of the salivary flora. / . Periodontal Res. 1975: 10: in press.
'
'
:..
..
(Key words: chlorhexidine; dental caries; dental plaque; dentifrice; gingivitis)
Effect of 2-yedrs' use of chlorhexidine-containing dentifrices on plaque, gingivitis, and caries JAN R. JOHANSEN, PER GJERMO AND HARALD M. ERIKSEN Departments of Periodontics and Operative Dentistry, Dental Faculty, University of Oslo, Oslo, Norway ABSTRACT - Chlorhexidine digluconate in 0.1 % and 0.4 % concentrations was added to dentifrices to evaluate its effect on plaque formation, gingival conditions and caries in 73 dental students over a 2-year period. No differences were found in the PI I and the G I indices between the active and the placebo dentifrices, but a possible effect on caries was demonstrated. Discolorations of anterior teeth and fillings were the only side effects observed. (Received for publication 5 March, accepted 13 April 1975)
Dental plaque is generally recognized as the main cause of gingivitis and caries. Ghlorhexidine has been shown to prevent plaque formation in many experiments (for review see OCHSENBEIN 1974 and GJERMO 1974), and also to inhibit the development of gingivitis (LOE & SCHIOTT 1970a,b). Furthermore, rat caries may be controlled (REGOLATI, KONIG & MUHLEMANN 1969, KORNMAN, GLARK, K R E I T Z MAN & ALVAREZ 1973) and experimental caries in humans prevented by topical application of chlorhexidine (LOE, FEHR & SCHIOTT 1972). The aim of the present study was to evaluate the effect of different concentrations of chlorhexidine digluconate in dentifrices on plaque formation, gingival condition and caries over a 2-year period. In
addition, attention was directed towards possible clinical side effects.
Material and methods
Seventy-three freshmen dental students, aged 19-23 years, volunteered to participate in the study and were randomly distributed into five groups. Two dentifrices of different abrasiveness were made. To dentifrice No. 1, which contained a conventional abrasive, 1 % oi chlorhexidine digluconate was added to one fraction (L-10) and 0.4 % to another (L-04). Thus two active dentifrices and one placebo (L-placebo) were obtained. From dentifrice No. 2, which did not contain abrasives, only a 0.4 % chlorhexidinecontaining version (F—04) was prepared in addition to the control (F-placebo). Agents known to interfere with the antibacterial activity of chlorhexidine (sulfates, phosphates) were excluded from the dentifrices (GJERMO &
EFFECTS OF CHLORHEXIDINE DENTIFRICE 1971). Coded tubes were distributed to the students in all five groups. A double blind approach was followed. Toothbrushes and dentifrices were given to the participants upon request. The number of tubes and toothbrushes requested by each student was recorded as an indication of the cooperation and active participation of the subjects. No efforts were made to influence their brushing habits except that they were advised to employ approximately one toothbrush-length of dentifrice (1 g) at each brushing (twice a day). At the initial screening the Plaque Index (PI I) and the Gingival Index (G I) (LOE 1967) were recorded and the participants received a thorough prophylaxis before caries registration. Caries was recorded clinically on smooth surfaces (buccal and lingual) according to the following criteria: Score 0 was used when no carious lesions or decalcified areas of the surface could be detected. It was also used for hard and discolored areas of arrested caries. Score 1 — Demineralized areas with hard, unbroken enamel ("white spot lesions"). Score 2 — Soft enamel lesions. Score 3 - Caries penetrating into the dentin, cementum caries and secondary caries. Proximal caries was evaluated on radiographs obtained according to a standardized technique (EGGEN 1971); the following classification was made: Score 0 — No caries. Score 2 - Enamel shadow without dentin involvement. Score 3 — Dentin involvement or secondary caries. Occlusal caries and caries in buccal or lingual fissures were not considered. The scores were added, multiplied by 100 and divided by the number of surfaces examined for each person in order to obtain an individual index figure to use as a basis for calculating group means. In addition the mean number of new and developing (active) carious lesions (surfaces with increased scores) per person during the 2-year period was compared with the mean number of reversed or arrested lesions (surfaces with decreased scores) within each experimental group. The method error in scoring the caries attacks was assessed by statistically analyzing the difference between duplicate registrations and was found to be small (s = 0.03). Registration of PI I, G I and caries was ROLLA
289
repeated after 6, 12, 18 and 24 months. The scoring of plaque and gingivitis was performed by two trained and calibrated dental hygienists; one of the authors (H.M.E.) made the caries examinations. To ensure a double blind approach a thorough projjhylaxis was given before each caries examination. Thus erroneous estimation due to chlorhexidine-induced discoloration was avoided. Student's t-test was used to evaluate the significance of group differences. Discolorations of tooth surfaces were evaluated microphotometrically. Results and details from this part of the study have been reported elsewhere (ERIKSEN & GJERMO 1973). The students were encouraged to report any general or oral observations that might be related to the experiment. Twice during the study the participants answered questionnaires regarding infectious and other diseases experienced during the test period.
Results
During the 2 years 13 participants withdrew from the experiment. Their distribution is shown in Table 1. The reasons for withdrawal were: leaving the faculty or not passing exams, discolorations of teeth (one in the L-10 and one in the L-placebo group), discontent with the consistency of the toothpaste (F-04), and unspecified reasons. PLAQUE
The initial mean PI I values varied from Table 1 Distribution of students leaving the stU'dy before its completion
F F L L L
placebo 0.4 placebo 0.4 10
Start
End
15 15 14 19 10
13 9 12 17 9
73
60
Withdrawals 2 6
2 -
2
1 13
JOHANSEN, GJERMO AND ERIKSEN
290
C l -loo F-plBcebo F-04 L-placebo — —
PLACEBO 0 4 2 CH.
L-10
v\ . . . . . - ' " • - . ^
.
—
,
0.6—
Fig. 3. Mean caries index (C I) on smooth surfaces. MONTHS
Fig. 1. Mean plaque index.
tistically significant differences between the groups were observed (Fig. 2 ) .
0.91-0.98. During the study the mean values dropped to about one-third in both active and inactive groups (Fig. 1). No statistically significant differences between the groups were detected at any scoring. However, the lowest scores were obsei^ved in the groups using abrasive dentifrices containing 0.4 % (L-04) and 1 % ( L 10) chlorhexidine.
CARIES
The group employing the dentifrice containing 1 % chlorhexidine (L-10) exhibited lower index values than did all other groups at all registrations (Fig. 3), but the differences were small. No differences could be detected between
GINGIVITIS
The mean G I values remained relatively constant throughout the 2 years. No sta- 9-
ACTIVE ATTACKS
I I
REVERSED AND ARRESTED ATTACKS
^
87654
\
3 2
•" '
F-04 L-plBCpho I.-04 L-10
j11 I/. C.H.
MONTHS
Fig. 2. Mean gingival index.
I
I 0.47.CH
I
PLACEBO
Fig. 4. Mean number of active reversed and arrested caries lesions per person. Smooth and proximal surfaces.
EFFECTS OF CHLORHEXIDINE DENTIFRICE the placebo groups (L-placebo and F placebo) and the groups using 0.4 % chlorhexidine-containing dentifrices (L04 and F-04). The L-10 group showed a decreasing number of active attacks and an increasing number of reversed and arrested lesions (Fig. 4).
SIDE EFFECTS
No clinically detectable untoward side effects were observed during the 2-year use of chlorhexidine-containing toothpastes except for the brownish discolorations of teeth and front fillings as reported previously (ERIKSEN & GJERMO 1973). The frequency and degree of staining could be correlated to the content of chlorhexidine in the dentifrices and to the presence of abrasives. The two questionnaires disclosed no differences in frequency of virus infections, digestion irregularities or other indications of general side effects between the various groups. A control study immediately after the cessation of the present experiment indicated that 2 years' exposure to chlorhexidine had not provoked the development of chlorhexidine resistant plaque-forming bacteria (GJERMO & ERIKSEN 1974). Discussion
In spite of the long duration only 13 subjects withdrew from the experiment and only one person in the 1 % chlorhexidine group (L-10). Thus it seemed as if the bitter taste of chlorhexidine was only a minor if any objection to its use for a prolonged period. This conclusion may be of interest in introducing chlorhexidine-containing dentifrices to the public. In considering the results of the present study, it should be borne in mind that the experimental subjects were highly selected.
291
being young dental students with good oral hygiene, healthy gingiva and low caries activity. Influenced by the environment of a dental school, and possibly by the experiment itself, their oral hygiene improved during the first 6 months of the study, then stayed relatively constant for the next 12 months. When the students at this time started their clinical training, a further drop in the PI I values was observed in all groups (Fig. 1). Thus it seems conceivable that a plaque-inhibiting effect of chlorhexidine in the present investigation may have been masked by the excellent mechanical toothcleansing performed by the test subjects. Similar observations have been reported earlier (FLOTRA, GJERMO, ROLLA & WAERHAUG 1972, HANSEN, GJERMO & ERIKSEN 1975).
No effect on the gingival condition was observed in the present study by the method employed. This may be explained by the index system itself, since Score 1 indicates a very slight degree of inflammation which may even be caused by vigorous toothbrushing. In the entire material relatively few scores indicating clinical gingivitis were found. Even though one of the hygienists was responsible for the scoring of the G I and the other scored the PI I throughout the study, intraindividual variations cannot be outruled. Unfortunately, the indices used offer limited possibilities for checking the method error. Garies seemed to be influenced by the application of the dentifrice containing 1 % chlorhexidine (Figs. 3 & 4). However, the group employing this dentifrice (L-10) also exhibited the lowest index values initially. This may reflect a lower caries activity in the students comprising this group even before the experiment started. The observation of a .reduced number of active caries attacks and an increased number of reversed and arrested attacks in this particular group, as com-
292
JOHANSEN, GJERMO AND ERIKSEN
pared with the other groups (Fig. 4), gives support to the impression of a caries reducing effect. Similar observations have been made in a group of Danish students after they used chlorhexidine mouthrinses for 2 years (SCHIOTT, personal communication). This may have been caused by a change in the plaque pathogenicity rather than in plaque quantity, since Streptococcus mutans seemed to be almost eliminated during long-term use of chlorhexidine (SCHIOTT, BRINER & LOE 1975). The present study did not indicate any systematic side effects. Furthermore, the long-term use of chlorhexidine in the oral cavity did not seem to affect the oral mucosa. This is in agreement with histologic and chenaical findings (NuKi, BERGQUIST & ORGAN 1972, MACKENZIE, NUKI & BUT-
BAUGH 1973, MACKENZIE 1974). These important observations may justify the longterm use of the drug in plaque preventive programs for mentally and physically retarded population groups. In addition it seems ethically acceptable to perform extramural experiments in groups with high caries activity and poor gingival conditions. References
EGGEN, S.: Simplification and standardization of intraoral radiology. Quintessence Int. 1971: 1: No. 1: 93-96. ERIKSEN, H . M . & GJERMO, P.: Incidence of
stained tooth surfaces in students using chlorhexidine-containing dentifrices. Scand. J. Dent. Res. 1973: 81: 533-537. FLOTRA, L., GJERMO, P., ROLLA, G . & WAER-
HAUG, J.: A 4-month study on the effect of Address: Jan R. Johansen Department of Periodontics, Dental Faculty Geitmyrsveien 69 Oslo 4 Norway
chlorhexidine mouth washes on 50 soldiers. Scand. J. Dent. Res. 1972: 80: 10-17. GJERMO, P.: Chlorhexidine in dental practice. /. Clin. Periodontol. 1974: 1: 143-152. GJERMO, P. & ERIKSEN, H . M . : Unchanged
plaque-inhibiting effect of chlorhexidine after 2 years of continuous use. Arch. Oral Biol. 1974: 19: 317-319. GJERMO, P. & ROLLA, G.: The plaque-inhibiting effect of chlorhexidine-containing dentifrices. Scand. J. Dent. Res. 1971: 79: 126-132. HANSEN, F., GJERMO, P. & ERIKSEN, H . M . :
The effect of a chlorhexidine-containing gel on oral cleanliness and gingival health in young adults. / . Clin. Periodontol. 1975: 2: in press. KoRNMAN, K. S., CLARK, W . B., KREITZMAN, S.
N. & ALVAREZ, C : Caries control in the albino rat with chlorhexidine gluconate (Hibitane). Arch. Oral Biol. 1973: 18: 165170. LOE, H . : The gingival index, the plaque index and the retention index systems. /. Periodontol. 1967: 38: 610-616. LOE, H . , FEHR, F . R . V. D. & SCHIOTT, C . R . :
Inhibition of experimental caries by plaque prevention. The effect of chlorhexidine mouthrinses. Scand. J. Dent. Res. 1972: 80: 1-9. MACKENZIE, I., NUKI, K . , BUTTERBAUGH, J.:
Effects of oral administration of chlorhexidine on epithelial mitotic rate. Int. Assoc. Dent. Res. Meeting 1973. Abstract No. 141, p. 94. MACKENZIE, I.: A study of the stratum corneum of normal and chlorhexidine-exposed human oral mucosa. Int. Assoc. Dent. Res. Meeting 1974. Abstract No. 662, p. 220. NUKI, K . , BERGQUIST, J. J. & ORGAN, R . : Quantitative microchemistry of chlorhexidine treated attached gingiva. Int. Assoc. Dent. Res. Meeting 1972. Abstract No. 206, p. 99. SCHIOTT, C . R . , BRINER, W . W . & LOE, H . :
Two years use of chlorhexidine against human diseases. III. Changes in sensitivity to chlorhexidine of the salivary flora. / . Periodontal Res. 1975: 10: in press.
