A n in vivo study on the merits of two glass ionomers for the cementation of orthodontic bands F. Rezk-Lega,* B. Ogaard,* and J. Arends** Oslo, Norway and Groningen. The Netherlands The purpose of this study was to investigate the cariostatic effect of two glass ionomer cements on in vivo demineralization of partly uncovered enamel beneath orthodontic bands. A 4-week clinical trial was conducted on a group of five patients with nine pairs of premolars to be extracted for orthodontic purposes. Specially designed orthodontic bands were cemented with either Ketac-Cem (K-C) or Aqua-Cem (AoC). A local cariogenic milieu was created between the buccal surface of the premolars and the inner surface of the bands to secure plaque accumulation. The mineral content of the teeth was quantified by microradiography. The data were compared with data from a previous study of patients in the same age group with bands that had been cemented with a non-F cement. After comparison with the non-F group, the lesion depth (Id) was reduced by 63% for K-C and by 55% for A-C. This reduction was statistically significant at the 2.5% level (t test). The total mineral loss in teeth cemented with glass ionomer cements (&Z) was reduced, in comparison with the loss in teeth cemented with non-F cement, by 49% with K-C and by 27% with A-C. The differences were statistically significant only for the K-C group (t test, p < 0.025). There were no significant differences between the two glass ionomer cements with respect to either lesion depth or total mineral loss values (paired t test; p > 0.05). This investigation shows that fluoride released from glass ionomer cements contributes substantially to demineralization "reduction." However, these cements do not provide complete caries protection in sites where access is difficult. (AM J ORTHOD DENTOFAC ORTHOP 1991 ;99:162-7.)

G l a s s ionomer cements are being used more frequently as bonding agents in orthodontics. Interest in these cements has increased, in part, because of the increased prevalence of enamel decalcification beneath orthodontic bands. ~4 Plaque accumulation around and beneath ill-fitting bands can lead to visible white-spot lesions on the adjacent enamel. The whiteness of these lesions is caused by the loss of mineral substance in the surface or subsurface of the enamel. In the initial stage, such lesions are designated as surface-softened lesions, but later they develop into subsurface lesions? A well-established, major beneficial effect of fluoride is the inhibition of enamel demineralization. Fluoride is also generally acknowledged to increase the initial rate of remineralization; yet total in vivo repair has not been achieved. 69 Kvam et al. t° showed less enamel demineralization under orthodontic bands fastened with a glass ionomer cement than on bands fastened with conventional phosphate cement. The failure rate for bands cemented with glass ionomers is also *Department of Orthodontics, Dental Faculty. Uni'~ersityof Oslo. Norway. **Laboratory for Materia Technica, Dental School, University of Groningen. The Netherlands. 8/i/21368

162

significantly lower than the rate recorded for bands cemented with a polycarboxylate cement. '~ Glass ionomers may therefore be recommended for fixed retainers that are to remain in place for an extended period of t i m e - - f o r example, in cases where appliances are under particular mechanical strain; where abnormal crown shapes complicate band adaptation, ~° or anywhere that plaque and retentive spaces under brackets or bands may lead to undesirable white-spot lesions. ~"~-" The purpose of the present study was to investigate, in vivo, the inhibitory effect of fluoride released from two glass ionomer cements on early carious lesions, iatrogenically provoked underneath orthodontic bands. ~3.~4 MATERIALS AND METHODS Clinical trial

A group of five patients with nine pairs of premolars to be removed for orthodontic purposes agreed to participate in this investigation. The patients' ages ranged from I I to 13 years. Only teeth without caries, demineralization, or restorations were used. The selected premolars were cleaned with a nonfluoride pumice to remove plaque and pellicle, after which they were dried, and a buccal cariogenie milieu was created with

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Merits of glass ionomers for the cenzentation of bands

f

163

;

Cemented

'U.

B~

CemonteO

Fig. 1. Schematic presentation of the banding system.

specially designed bands. Two metal posts (0.8 mm thick) were welded to the inner surface of the bands to secure a space between the buccal surface of the tooth and the band. t3'~ These posts were shorter than the band's height to ensure that fluoride released from the glass ionomer would reach the buccal enamel surface. The distance between the posts was less than 6 mm, since the influence of fluoride released from glass ionomer cements is found in a zone of resistance to demineralization which is at least 3 mm around the glass ionomer restoration z6 (Fig. 1). Each pair was then cemented sequentially on the right and the left sides with Ketac-Cem (ESPE), or Aqua-Cem (De Trey). In K-C the polymer is a polycarbonic acid, whereas in A-C it is incorporated into the powder, which is mixed with water. A group of five patients in the same age group, with bands cemented with a non-fluoride cement (Ceramco, Johnson & Johnson), served as the control group. ~The experimental procedures, along with the microradiography technique used for the control group, were similar to the ones used for the exPerimental group. All the patients were given motivational instruction in a standard program of oral hygiene and supplied with a nonfluoride toothpaste. No further prophylaxis was given until the end of the investigation. The experimental teeth were removed after 4 weeks and stored at 100% relative humidity and 4 ° C until analysis.

Microradiography The mineral content of the samples was determined by microradiography and quantified by a microdensitometric method recently described in detail by Gelhard and Arends. ~ From each tooth several sections were cut longitudinally with saw blades as nearly perpendicular to the anatomic outer surface as possible. From each tooth at least two sections were made approximately 3 mm apart (Fig. 2). Each parallel sec-

Fig. 2. Schematic representation of the banding (horizontal dashed lines on the tooth) and the thin sections used for microradiography. On the right side of the figure, two sections with the enamel defects (dashed lines) are shown.

vol% mineral

t Vs

0

sound

---d 0

Id

Fig. 3. Schematic presentation of the microradiographic parameters AZ, the mineral loss in voi% x p.m (hatched area), and Id, the lesion depth in p.m. tion of approximately 200 ~tm thickness was cut and ground to approximately 100 ixm, and the sample's thickness was estimated with an accuracy of 1 i.tm (Sony digital gauging probe). For contact microradiography, the distance between the exit of a copper x-ray tube (Philips PW-1730; 20 kV and 15 mA) and the specimen was 29 cm. The sample, along with an aluminum step-wedge, was exposed to the x-rays for 20 seconds. To quantify the mineral content, the following microdensitometric method was used: Microdensitographic tracings were mad~ with a Leitz Ortholux II microscope-photometer (MPV compact), equipped with a Wallis-Unit 2 Pm photomultiplier. The densitographs were recorded on a Kipp BD 8 recorder at 2050 mV; the recorder speed was 100 and 200 nm/min. The slit dimensions were 6 × 73 la.m.s

164

Am. J. Orthod. Dentofac. Orthop. February 1991

Rezk-Lega, (~gaard, and Arends

KETAC-CEMENT / AQUA-CEMENT LESION D E P T H S

i i

~,

1o9

1 2 0 -,

100 -I

i

8 0 -~

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:

" 39.8

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.....

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- 2 o , o ........ 2~i

A-C ~:;~--'l e s i o n d e p t h .

4 WEEKS

Fig. 4. The lesion depth and the standard deviation in both glass ionomers and in the non-fluoride group.

To obtain the volume percentage of mineral, the formula of Angmar et al. 17 was used. Computation of this formula was done by means of a computer system type PDP I 1/05 (Digital Equipment International, Galway, Ireland) connected to a Complot DP-10 plotter (Houston Instrument). From each section four regularly spaced densitometric tracings (approximately 300 Ixm apart) were made in the demineralized area. The two important parameters of interest from microradiography are depth of the lesion, in microns (rtm), and mineral loss in the lesion (Fig. 3). Lesion depth (ld) is the distance between the outer enamel surface and a point where the mineral content is 5% lower than in sound enamel. Mineral loss (AZ) is expressed as the percentage of mineral by volume times micromillimeters (vol% × i.tm). The percentage of reduction in lesion depth and mineral loss for the glass ionomer group in comparison with the non-fluoride group was calculated according to the following formulas: Lesion Depth Mineral Loss ld nonF - ldc~ A Z non~ - Zc~ x 100% x 100% ld non~ A Z non~

The two glass ionomers were compared by means of the paired t test at the 5% level. When the two glass ionomers were compared with the control group, the data were analyzed according to Student's t test. The level of significance was set at 2.5% (instead of 5%) to adjust for multiple comparisons. RESULTS

Visual examination of the enamel surface showed no white spots on the teeth of both groups of patients treated with glass ionomers. This visual method is acceptable for scoring early demineralization of the tooth surface. ,o The microradiographic data in Figs. 4 and 5 show that the mineral loss was limited to the enamel surface, and no subsurface lesions were found. This finding confirms previous studies that showed that initial lesions are "surface softened. ''~ When these results were compared with those from the non-F cement, premolars that had been cemented with K-C had 63% less lesion development (ld) and those cemented with A-C had 55% less lesion development. These results were statistically significant at

Volume 99 Number 2

Merits of glass ionomers for cementation of bands

165

KETAC-CEMENT / AQUA-CEMENT MINERAL LOSS vol% x lure 1525

1107 1600 -

786

1400 1 2 0 0 -: 1000 -

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4 WEEKS Fig. 5. The mineral loss and the standard deviation in both glass ionomers and in the non-fluoride group.

the 2.5% level (t test). The total mineral loss (AZ), was reduced by 49% for K-C and 27% for A-C. The differences were statistically significant only for the K-C group (t test; p < 0.025). There were no significant differences between the two glass ionomer cements with regard to the lesion depths or the total mineral loss (paired t test; p > 0.05). DISCUSSION

The presence of white-spot lesions (early carious lesions) under orthodontic bands represents a serious problem of clinical importance even many years after treatment has been completed. 4 Recent studies have shown that glass ionomers may inhibit lesion development as a result of the cementing of orthodontic bands. 1° This outcome is generally attributed to the fluoride that is released from the cement. ,6 To isolate specifically the effect of fluoride released from glass ionomers, experiments were made on an in vivo caries model with orthodontic bands (Fig. 1). By creating a space between the band and the enamel surface, we could study the effect of fluoride release from the glass ionomer that had been used for cementing bands.

®

total coverage

©

total coverage after acid attack

®

partial coverage

®

partial coverage after acid attack

Fig. 6. Schematic presentation of the effect of fluoride adsorption onto the enamel crystalites. A, Total coverage. C, Total coverage after acid attack. B, Partial coverage. D, Partial coverage after acid attack. (Modified from Arends and Christoffersen?g).

Am. J. Orthod. Dentofac. Orthop. February 1991

166 Rezk-Lega, Ogaard, and Arends

CALCIUM-BRIDGE HYDROGENE LIAISONS & OTHER VAN DER WAAL'S FORCES SUBSTITUTION OF PHOSPHATE

GLASS IONOMER CEMENT

ENAMEL

Fig. 7. Schematic presentationof the chemical bonding mechanism of glass ionomer cements to the enamel. (Courtesy of Prof. H. Nordbo, Dental Faculty, University of Oslo, Norway.)

The group for which the glass ionomer cements had been used was compared with a matching age group in which the bands had been cemented with a non-F cement. Clinically, no white spots were seen on the buccal experimental surface in the groups with the glass ionomer cemented b a n d s - - i n contrast with the group for which non-fluoride cement had been used, in which white spots were clearly observable. The microradiographic data (Figs. 4 and 5) showed a significant reduction in lesion development in the group whose bands had been cemented with fluoridereleasing glass ionomer cement, compared with the group whose bands had been cemented with a non-F cement. This finding supports an earlier study done by Valk and Davidson in 1987) 8 The mechanism for the lesion inhibition o f fluoride released from the glass ionomer is not clearly established in all details. A possible explanation is that fluoride adsorbs onto the enamel and stabilizes the crystals. t9 Since no complete fluoride protection on lesion development and beneath orthodontic bands was obtained, we assume that fluoride released from the cement did not cover the enamel crystallites completely (Fig. 6). 19 Another possible reason is that the magnitude o f the cariogenic challenge behind the band was so intense that the plaque fluid was undersaturated with respect to both hydroxyapatite and fluorapatite. Below pH 4.5, fluoride will have a limited effect, since the liquid phase will be undersaturated with fluorapatite. 2° Caries inhibition obtained with a glass ionomer cement (Chem-bond, De Trey) in the study by K v a m et a l ) ° may therefore be partly attributable to a protection by this cement.

It is known that glass ionomers are bound to enamel through calcium bridges, hydrogen bonds, o r other Van der Waal forces; however, the most important bonding mechanism is a "phosphate substitution" ( F i g . 7 ) Y In this way, glass ionomer cements provide a stronger bond strength and are not as easily leached out as conventional cements. In conclusion, the present study showed that fluoride released from glass ionomer cements had carlostatic properties. However, orthodontic bands should be checked regularly, since fluoride released from the cement may inhibit lesion development incompletely under loose bands o r in areas where the cement is missing.

REFERENCES

1. Ogaard B, ROllaG, Arends J. Orthodonticappliances and enamel demineralization. Part 1. Lesion development. AM J ORTHOD DEN'TOFACORTHOP1988;94:68-73. 2. Norris S, McInnes-Ledoux P, SchwaningerB, Weinberg R. Retention of orthodontic bands with new fluoride-releasing cements. AMJ OR'rHOD1986;89:206-10. 3. Gorelick L, Geiger AM, Gwinnett AJ. Incidence of white spot formation after bonding and banding. AMJ ORTHODDENTOFAC ORTHOP 1982;81:323-31. 4. Ogaard B. Prevalence of white spot lesions in 19-year-olds: a study on untreated and orthodontically treated persons 5 years after treatment. AM J OR'I'HODDENTOFACORTHOP 1989;96: 423-7. 5. Arends J, Christoffersen J. The nature of early caries lesions in enamel. J DENYRES 1986;65:2-11. 6. Cate JM ten, Arends J. Remineralization of artificial enamel lesions. Caries Res 1977;11:277-86. 7. Cate JM ten, Arends J. Remineralization of artificial enamel lesions in vitro. IV. Influence of fluoride and diphosphonates on short- and long-term remineralization. Caries Res 1981;15: 60-9. 8. Bodde HE. The influence of fluoride applications on enamel

Volume 99 Number 2

9. 10.

1I. 12. 13. 14.

15.

16.

Merits of glass ionomers for cementation of bands

remineralization [Thesis]. Groningen, The Netherlands: University of Groningen, 1982. Jeansonne BG, Feagin IF. Fluoride action on acid resistance of unaltered human surface enamel. J Oral Pathol 1979;8:207-12. Kvam E, Broch J, Nissen-Meyer IH. Comparison between a zinc phosphate cement and a glass ionomer cement for cementation of orthodontic bands. Eur J Orthod 1983;5:307-13. Mizrahi E. Glass ionomer cements in orthodontics--an update. AM J OR'I'tIODDENTOFACOR'rHOP 1988;93:505-7. Zaehrisson BU. Fluoride application procedures in orthodontic practice: current concepts. Angle Orthod 1975;45:72-81. Hals E, Simonsen TL. Histopathology of experimental in vivo caries around silver amalgam fillings. Caries Res 1972;6:16-33. Ogaard B, Rolla G, Helgeland K. Alkali soluble and alkali insoluble fluoride retention in demineralized enamel in vivo. Scand J Dent Res 1983a;91:200-4. Gelhard TBFM, Arends J. Microradiography of in vivo remineralized lesions in human enamel. II. J Biol Buccale 1984;12:59-65. Wilson AD, Me Lean JW. Glass-ionomer cement. Chicago: Quintessence, 1988:126.

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17. Angmar V, Carlstrcm D, Glas JE. Studies on the ultra structure of dental enamel. J Ultrastr Res 1963;8:12-23. 18. Valk JWP, Davidson CL. The relevance of controlled fluoride release with bonded orthodontic appliances. J Dent 1987;I5:25760. 19. Arends J, Christoffersen J. Nature and role of loosely bound fluoride in dental caries. J Dent Res 1990;69:601-5. 20. Ogaard B. Effects of fluoride on caries development and progression in vivo. J Dent Res 1990;69:813-9. 21. Wilson AD, Me Lean JW. Glass-ionomer cement. Chicago: Quintessence, 1988:86.

Reprint requests to: Dr. BjOin Ogaard University of Oslo Dental Faculty Department of Orthodontics P.O. Box 1109, Blindem 0317 Oslo 3 Norway

AAO MEETING CALENDAR

1991--Seattle, Wash., May 11 to 15, Seattle Convention Center 1992--St. Louis, Mo., May 10 to 13, St. Louis Convention Center 1993--Toronto, Canada, May 16 to 19, Metropolitan Toronto Convention Center 1994--Orlando, Fla., May 1 to 4, Orange County Convention and Civic Center 1995--San Francisco, Calif., May 7 to 10, Moscone Convention Center 1996--Denver, Colo., May 12-15, Colorado Convention Center