This study evaluated the effect of high fluoride dentifrice on the bond strength of brackets after erosive challenge. Eighty-four enamel specimens were divided into seven groups
Many factors may influence the retention of brackets during orthodontic treatment with fixed appliances [
The dental enamel should be healthy to permit bonding of brackets; however, dental caries and erosion are common factors that cause loss of mineral components of teeth [
Diets rich in carbonated beverages, fruits, and other acids are being consumed more frequently, which consequently has been increasing the dental erosion [
One of the treatment options to avoid mineral loss is the use of substances with high fluoride concentration, including varnishes and dentifrices. High fluoride dentifrices (above 5000
However, other studies have demonstrated that the use of fluoridated solutions negatively interferes with the bond strength of orthodontic brackets [
This study evaluated the effects of regular and high fluoride dentifrices on the bond strength of brackets to enamel submitted to acid challenge. The null hypotheses tested were as follows: (i) the bond strength of brackets is not affected by acid challenge; (ii) the type of dentifrice does not influence the bond strength of orthodontic brackets.
Eighty-four permanent bovine incisors were collected and their crowns were separated from the roots, cleaned with periodontal curettes, and stored in distilled water for a maximum period of six months at a temperature of 5°C. The procedures were performed following the specific protocol TR 11405 established by the International Organization for Standardization (ISO) [
The buccal aspects of crowns were cleaned with fluoride-free prophylactic paste (Dentsply, Konstanz, Germany) for 10 seconds and rinsed with water for the same period.
The 84 specimens were randomly assigned to seven groups (
The groups were divided according to treatment and acid challenge.
Group | Treatment | Toothpaste | Acid challenge |
---|---|---|---|
WN | Distilled water | No | |
W3C | 3 cycles | ||
W6C | 6 cycles | ||
|
|||
RF3C | Regular fluoride toothpaste | Colgate Tripla Ação dentifrice, 450 |
3 cycles |
RF6C | 6 cycles | ||
|
|||
HF3C | High fluoride toothpaste | Duraphat dentifrice, 5000 |
3 cycles |
HF6C | 6 cycles |
The specimens were immersed in dentifrice (dilution: 3 g of dentifrice/10 mL of distilled water, adding up to 153 g of dentifrice/510 mL of distilled water) for 3 minutes at controlled temperature and pH under constant shaking, using a magnetic shaker (IKA Laboratory Equipment, Staufen im Breisgau, Germany). However, specimens of WN, W3C, and W6C groups were immersed in 600 mL of distilled water under the same conditions of dentifrice treatment.
The treatment cycles were conducted for 7 days, twice a day. After treatment, the specimens were carefully rinsed with distilled water.
Metallic brackets for maxillary central incisors (Morelli, Sorocaba, Brazil) with base area of 14 mm2 were placed on enamel surfaces of all specimens. The buccal aspect of crowns was conditioned with 35% phosphoric acid (Ultradent, South Jordan, USA) for 20 seconds, rinsed with water, and air-dried. The primer of Transbond XT (Unitek, Landsberg, Germany) was applied following the manufacturer’s instructions. Then, the Transbond XT adhesive (Unitek, Landsberg, Germany) was applied on the bracket base, the assembly was placed on the buccal aspect of the crown and a standardized force of 500 g was applied. The excess material was removed with a dental probe (Duflex, Juiz de Fora, Brazil).
A single operator performed all procedures. Each bracket was light cured at a distance of 1 mm from the bracket base to the light-curing tip for 40 seconds, being 10 seconds on each side of the bracket. The specimens were then stored in distilled water (37°C, 24 hours).
The specimens were suspended in 1 L beaker containing 600 mL of orange juice (Del Valle, Santa Bárbara D’Oeste, Brazil) (pH
The acid cycles were performed for 7 days. Twelve specimens in each group were exposed to 3 cycles per day and the other half of specimens were exposed to 6 cycles of acid challenge per day (15 minutes for each cycle). The specimens were stored in artificial saliva during rest. Among cycles, specimens were kept in artificial saliva for 2 hours.
The specimens were stored in artificial saliva at controlled temperature and pH. The artificial saliva was prepared as follows: 0.5 mmol/L Ca(NO3)2 4H2O; 0.9 mmol/L Na2HPO4 2H2O; 150 mmol/L KCl; 0.02 mol/L H2NC(CH2OH)3 (TRIS); 0.05
For the bond strength test, an occlusogingival force was applied by the mechanical testing machine on the upper surface of the bracket between the upper wings and the brackets base, at a speed of 0.5 mm/min [
After the shear bond strength, the specimens were photographed with a digital camera (Nikon, Tokyo, Japan) connected to a 100 mm lens (Nikon, Tokyo, Japan). A calibrated ruler was used in the photograph to be used as proportional scale. Thereafter, the area of adhesive bonded to the tooth was calculated on the software Adobe Photoshop CS5 (Adobe Systems Incorporated, San Francisco, USA) (Figure
Photograph for analysis of the total area of adhesive bonded to the tooth after debonding of the bracket. Note that a scale was used to serve as reference for the digital scale. Thereafter, the area was calculated on the software Adobe Photoshop CS5.
Schematic drawing of the methodology used in this study.
The Shapiro-Wilk normality test and Levene homogeneity test were applied for bond strength tests and area of adhesive remaining data. Bond strength data showed normal distribution and they were analyzed by one-way ANOVA and post-hoc Tukey tests (
The means and standard deviations are presented in Figure
Bond strength values of groups submitted to the shear bond strength test. Different letters indicate statistical difference (one-way ANOVA and post-hoc Tukey tests,
Values in mm2 of adhesive material bonded to the tooth after debonding of brackets. Different letters indicate statistical difference (Kruskal-Wallis and post-hoc Dunn’s tests,
This study investigated the effects of regular and high fluoride dentifrices on the bond strength of brackets after acid challenge. The results of this study rejected the null hypotheses as the bond strength of brackets is not affected by acid challenge and the type of dentifrice does not influence the bond strength of orthodontic brackets.
This type of dentifrices application and acid challenge has been effective in
The sustained force of 500 g was applied on the bracket to avoid interference in the outcome of bond strength. Studies [
The treatment was performed before bonding of brackets to evaluate if the dentifrices, especially with high fluoride concentration, interfere with the bond strength of brackets in patients presenting dental erosion. Additionally, this sequence of the methodology was made to simulate the regular use of these dentifrices. If the treatment was performed after bonding of brackets, this study did not confirm the second null hypothesis. Therefore, the present results revealed that the high fluoride dentifrice did not negatively interfere with the bonding of brackets, corroborating previous studies using substances with high fluoride concentrations before bonding of brackets [
Other earlier studies demonstrated that substances with high fluoride concentration might interfere negatively with bonding [
Previous studies have demonstrated the efficacy of high fluoride dentifrices to prevent tooth demineralization, acting by the deposition of components, especially fluoride particles, and remineralization of the affected substrate [
Dentifrices with 1450
Many studies employ the Adhesive Remnant Index to evaluate the type of failure occurring after the shear bond strength testing [
The acid challenge provides significantly lower bond strength values compared to control group (no acid challenge). The high fluoride dentifrice was able to prevent better the reduction in bond strength values of brackets than regular fluoride dentifrices after 6 cycles of acid challenge.
Professors Roger P. Ellwood and Ian Pretty work in Colgate Palmolive Dental Health Unit, Manchester, UK.
This research was supported by FAPEMA-Brazil (no. 01324/12).