Tensile strength of orthodontic brackets bonded directly to fluorotic and nonfluorotic teeth: an in vitro comparative study

Bonding to Fluorosed Teeth: A Review of the Literature

Excessive fluoride availability during tooth formation can cause structural alterations in enamel and dentin. These alterations may negatively impact the adhesion of various dental materials to teeth with dental fluorosis. The aim of this review of literature is to identify updates in bonding to fluorosed teeth and summarize relevant recommendations. Findings from the available literature suggest that bonding procedures may be carried out reliably on most fluorosed teeth with consideration to the severity of fluorosis and the employment of additional bond-enhancing measures for the severely involved teeth.

Effect of Adhesion Boosters on the Shear Bond Strength of New Brackets Bonded to a Debonded Tooth Surface - An In vitro Study

Context:

Effect of adhesion boosters on shear bond strength of orthodontic brackets.

Aim:

The aim is to evaluate the shear bond strength and adhesive remnant index (ARI) score of new brackets bonded to a debonded tooth surface with and without the use of adhesion boosters.

Settings and Designs:

In vitro comparative study.

Materials and Methods:

Adhesion boosters: Enhance LC (Reliance, Itasca III) All Bond 2 (Bisco, Schaumsburg) and the Composite adhesives Transbond XT (3M UNITEK) Enlight (ORMCO) were used in this study. One hundred and eight extracted maxillary first premolar teeth were bonded with light cure composite to etched tooth surface. The brackets were then debonded with debonding pliers after 1 week and it was polished with low speed tungston carbide bur and rubber cup. The teeth were divided into six groups and they were etched, washed, and dried again. New brackets were rebonded to the tooth surface using composites with or without adhesion boosters. Then, the shear bond strength value was calculated for each bracket with a universal testing machine. ARI scores were also evaluated.

Statistical Analysis Used:

One-way ANOVA and least significant difference post hoc test was used for the association between variables. Probability value (P < 0.05) was considered statistically significant.

Results:

The results showed a statistically significant difference between the groups with a P < 0.001. There was no significant difference in ARI scores between the groups (P = 0.15).

Conclusions:

Both the adhesion boosters significantly improved the shear bond strength of orthodontic brackets. There was no statistically significant difference in the ARI scores.

Influence of the mode of application of universal adhesive systems on adhesive properties to fluorotic enamel

The objective of this study is to compare the resin-enamel bond strength (mμSBS), in-situ degree of conversion (DC), and the enamel-etching pattern (SEM/EDX) of universal adhesive systems when applied to sound and fluorotic enamel. Ninety-eight human molars were sectioned into 4 parts and divided into 24 groups according to 1) enamel surface (sound or fluorotic enamel), 2) adhesive system (Clearfil Universal Bond [CUB], Futurabond U [FBU], iBond Universal [IBU], and Scotchbond Universal [SBU]), and 3) application mode (etch-and-rinse [ER], active self-etch [Active-SE], and passive self-etch [Passive-SE]). Specimens were stored at 37 °C, for 24 hours and tested at 1.0 mm/min (μSBS). Enamel-resin interfaces were evaluated for in-situ DC. The enamel-etching pattern was evaluated under a SEM/EDX. Data from mμSBS and in-situ DC was analyzed using a three-way ANOVA and Tukey's test at 5 % level of significance. For all adhesives, the ER resulted in a statistically significant higher mean mμSBS than the passive-SE in both substrates (p < 0.001). For all adhesives, active-SE resulted in mean mμSBS (p > 0.31) and in-situ DC (p > 0.45) that were statistically similar to those obtained with the ERs in both substrates. A statistically significant, higher mean mμSBS and in-situ DC were obtained in sound enamel (p < 0.001) than in fluorotic enamel. In general, SBU showed higher mean values for mμSBS and in-situ DC compared to those of CUB and IBU (p < 0.001). ER and active-SE showed the deepest enamel-etching pattern in both substrates. A higher amount of fluor was observed in fluorotic enamel. The active application of universal adhesives in the SE-mode may be a viable alternative to increase the adhesive properties in sound and fluorotic enamel.

Effects of adhesion promoter on orthodontic bonding in fluorosed teeth: A scanning electron microscopy study

Introduction:

The objectives of the present study were to elucidate the effects of fluorosis in orthodontic bonding and to evaluate the efficiency of an adhesion promoter (Assure Universal Bonding Resin) in bonding to fluorosed teeth.

Materials and Methods:

Extracted premolars were divided into two groups on the basis of Thylstrup and Fejerskov Index. Ten samples from each group were etched and evaluated for etching patterns using scanning electron microscope (SEM). The remaining samples were subdivided into four groups of 20 each on the basis of adhesives used: IA, IIA - Transbond XT and IB, IIB - Transbond XT plus Assure Universal Bonding Resin. Shear bond strength (SBS) was measured after 24 h using the universal testing machine. Adhesive remnant index (ARI) scores were recorded using SEM. Statistical analysis was conducted using a two-way analysis of variance, and Tukey's post hoc test was performed on SBS and ARI scores.

Results:

Similar etching patterns were observed in both fluorosed and nonfluorosed teeth. No significant differences were found in the SBS values observed in both groups (8.66 ± 3.19 vs. 8.53 ± 3.44, P = 1.000). Increase in SBS was observed when Assure Universal Bonding Resin was used. Higher ARI scores were observed when adhesion promoter was used for bonding.

Conclusions:

Mild-moderately fluorosed teeth etch in a manner similar to the nonfluorosed teeth. Similar bond strengths were achieved in fluorosed and nonfluorosed teeth when conventional composite was used. Use of adhesion promoter increases the bond strengths in both groups of teeth.

Factors Affecting the Shear Bond Strength of Orthodontic Brackets - a Review of In Vitro Studies

The adhesive material used to bond orthodontic brackets to teeth should neither fail during the treatment period, resulting in treatment delays, untoward expenses or patient inconvenience nor should it damage the enamel on debonding at the end of the treatment. Although the effectiveness of a bonding system and any unfavorable effects on the enamel may be studied by conducting in-vivo studies, it is nearly impossible to independently analyze different variables that influence a specific bonding system in the oral environment. In-vitro studies, on the other hand, may utilize more standardized protocols for testing different bonding systems and materials available. Thus, the present review focused attention on in-vitro studies and made an attempt to discuss material-related, teeth-related (fluorotic vs non-fluorotic teeth) and other miscellaneous factors that influences the shear bond strength of orthodontic brackets. Within the limitations of this review, using conventional acid-etch technique, ceramic brackets and bonding to non-fluorotic teeth was reported to have a positive influence on the shear bond strength of orthodontic brackets, but higher shear bond strength found on using ceramic brackets can be dangerous for the enamel.

Efficacy of New Adhesion Promoters on Compromised Hypocalcified Enamel

INTRODUCTION

The amount of technological progress occurred in the last few years has brought an add up to the benefits of bonding in Orthodontics. Research-based findings have constantly led to the development of new materials that are aimed to simplify the clinical procedures like bonding of brackets to compromised enamel surfaces. Hence, the present study is aimed to assess the bond strength of orthodontic brackets on fluorosed enamel using adhesion promoters.

AIM

To evaluate the shear bond strength (SBS) of orthodontic brackets bonded on fluorosed enamel using conventional Transbond XT and new adhesion promoters such as Enhance LC and All Bond 3.

MATERIALS AND METHODS

The study involved 90 non carious, extracted teeth with mild to moderate fluorosis randomly divided into 3 Groups. In Group - I (control group) the teeth were bonded with conventional Transbond XT and cured with LED light. In Group - II Enhance LC was applied to fluorosed enamel before bonding and in Group - III All Bond 3 was used. Shear bond strength was tested by using Universal testing Instron machine. ANOVA and Post-Hoc Tukey's tests were used to compare shear bond strength. Adhesive remnant on the tooth was assessed and scored using adhesive remnant index (ARI).

RESULTS

Results showed a reduced SBS values (9.43MPa ±3.03) with conventional Transbond XT on fluorosed enamel. Among the adhesion boosters used Enhance LC illustrated lesser SBS values (12.03 MPa ± 4.42) compared with All Bond 3 (14.38MPa ±4.92). ARI showed bond failure at bracket resin interface in group I & group II and at enamel resin interface in group III although statistically insignificant.

CONCLUSION

It was concluded that using adhesion boosters on fluorosed enamel showed higher bond strength compared to the control group. Among the two adhesion promoters used All Bond 3 expressed highest bond strength compared to Enhance LC although statistically insignificant.

Effects of long-term repeated topical fluoride applications and adhesion promoter on shear bond strengths of orthodontic brackets

Objective:

The purpose of this study was to assess the effects of long-term repeated topical application of fluoride before bonding and an adhesion promoter on the bond strength of orthodontic brackets.

Materials and Methods:

A total of 76 bovine incisors were collected and divided equally into four groups. In group 1, the brackets were bonded without topical fluoride application or adhesion promoter. In group 2, before bonding, the adhesion promoter was applied to nonfluoridated enamel. In group 3, the brackets were bonded without the application of the adhesion promoter to enamel, which had undergone long-term repeated topical fluoride treatments. Teeth in group 4 received the long-term repeated topical applications of fluoride, and the brackets were bonded using the adhesion promoter. All the brackets were bonded using BeautyOrtho Bond self-etching adhesive. The shear bond strength was measured and the bond failure modes were evaluated with the use of the adhesive remnant index (ARI) after debonding.

Results:

The mean shear bond strength was significantly lower in group 3 than in groups 1, 2, and 4, and there were no significant differences between the groups except for group 3. There were significant differences in the distribution of ARI scores between groups 2 and 3, and between groups 3 and 4.

Conclusions:

The adhesion promoter can recover the bond strength reduced by the long-term repeated topical applications of fluoride to the prefluoridation level and had a significantly great amount of adhesives left on either fluoridated or nonfluoridated enamel.

Shear bond strength evaluation of bonded molar tubes on fluorotic molars

OBJECTIVE

To study the shear bond strength (SBS), sites of failure, and micromorphology of bonded molar tubes used on teeth affected by dental fluorosis.

MATERIALS AND METHODS

This in vitro study included 140 first molars classified according to Dean's index for dental fluorosis. Samples were divided into seven groups: (1) healthy teeth etched for 15 seconds, (2) teeth with moderate fluorosis (MOF) etched for 15 seconds, (3) teeth with MOF etched for 150 seconds, (4) teeth with MOF microabrasion etched for 15 seconds, (5) teeth with severe fluorosis (SEF) etched for 15 seconds, (6) teeth with SEF etched for 150 seconds, and (7) teeth with SEF microabrasion etched for 15 seconds. All samples were incubated and were then submitted to the SBS test and evaluated with the modified adhesive remnant index (ARI) and analyzed by using a scanning electronic microscope.

RESULTS

The SBS mean value for healthy enamel was 20 ± 10.2 MPa. For the group with MOF, the etched 150-second mean value was the highest (19 ± 7.6 MPa); for the group with SEF treated with microabrasion and etched for 15 seconds, the mean value was (13 ± 4.1 MPa). Significant differences (P ≤ .05) were found in the ARI between healthy and fluorosed groups.

CONCLUSIONS

Fluorotic enamel affects the adhesion of bonded molar tubes. The use of overetching in cases of MOF and the combination of microabrasion and etching in SEF provides a suitable adhesion for fixed appliance therapy.

Effects of fluorosis on the shear bond strength of orthodontic brackets bonded with a self-etching primer

The aim of this study was to compare the shear bond strength (SBS) of brackets bonded to fluorosed and non-fluorosed teeth with self-etching primer (SEP) and phosphoric acid (PA). The study involved 40 mildly fluorosed [Thylstrup-Fejerskov (TFT) Index = 1-3] and 40 non-fluorosed human premolar teeth. The fluorosed and non-fluorosed teeth were randomly divided into two subgroups. In the first subgroup, 37 per cent PA was applied for 30 seconds and in the second, a SEP (Transbond Plus) was used. The brackets were bonded with light-cure adhesive paste (Transbond XT) and cured for 20 seconds. The SBSs were measured after 1000 thermocyclies. Two-way analysis of variance, Tukey's multiple comparison test, and Weibull analysis were used for the evaluation of SBS values. Bond failure locations were determined with the adhesive remnant index (ARI) and were compared with the Kruskal-Wallis and Mann-Whitney U-tests. The mean SBS was 9.01 MPa for the fluorosed teeth bonded with SEP. This value was significantly different from those of fluorosed teeth etched with PA (15.22 MPa) and non-fluorosed teeth conditioned with SEP (12.95 MPa) and PA (15.37 MPa). The ARI scores of the fluorosed teeth conditioned with SEP were significantly lower than those of non-fluorosed teeth conditioned with SEP or PA. The results of this in vitro study suggest that there are no differences in the SBS of orthodontic brackets between mildly fluorosed and non-fluorosed enamel etched with 37 per cent PA for 30 seconds. The SEP showed lower SBS values for orthodontic brackets bonded to mildly fluorosed enamel. The findings provide some evidence that routine clinical use of a SEP to bond brackets to mildly fluorosed teeth cannot be supported.

Effects of adhesion promoters on the shear bond strengths of orthodontic brackets to fluorosed enamel

The aims of this in vitro study were to evaluate the effect of enamel fluorosis on the shear bond strength (SBS) of orthodontic brackets and to determine whether adhesion promoter, Enhance LC, increases the bond strength of brackets to fluorosed enamel. Forty-five (30 fluorosed and 15 non-fluorosed) non-carious fresh human premolar teeth, extracted for orthodontic reasons and without any caries or visible defects, were used in this study. The fluorosed teeth were selected according to the modified Thylstrup and Fejerskov index, which is based on the clinical changes in fluorosed teeth. In groups 1 (fluorosed teeth) and 3 (control), the brackets were bonded with Light Bond composite resin and cured with a halogen light. In group 2, Enhance LC was applied to fluorosed enamel before bonding. After bonding, the SBS of the brackets was tested with a universal testing machine. One-way analysis of variance and Tukey multiple comparison tests were used to compare the SBS of the groups. Any adhesive remaining after debonding was assessed and scored according to the modified adhesive remnant index. The results showed that while fluorosis significantly reduced the bond strengths of the orthodontic brackets (mean 13.94 +/- 3.24 MPa; P < 0.01), Enhance LC significantly increased bond strength on fluorosed enamel (mean 18.22 +/- 5.97 Mpa; P < 0.05). Groups 1 and 3 had greater bond failures at the composite-bracket interface, whereas group 2 showed bond failure primarily at the enamel-composite interface.

In Vivo Bonding of Orthodontic Brackets to Fluorosed Enamel using an Adhesion Promotor

Objectives: To determine the success of bracket retention using an adhesion promoter with and without the additional microabrasion of enamel.

Materials and Methods: Fifty-two teeth with severe dental fluorosis were bonded in vivo using a split-mouth design where the enamel surfaces of 26 teeth were microabraded with 50 μm of aluminum silicate for 5 seconds under rubber dam and high volume suction. Thirty-seven percent phosphoric acid was then applied to the enamel, washed and dried, and followed by placement of Scotchbond Multipurpose Plus Bonding Adhesive. Finally, precoated 3M Unitek Victory brackets were placed and light cured. The remaining teeth were bonded using the same protocol but without microabrasion.

Results: After 9 months of intraoral service, only one bond failure occurred in the control group where microabrasion was used. Chi-square analysis revealed P = .31, indicating no statistical significance between the two groups.

Conclusions: Bonding orthodontic attachments to fluorosed enamel using an adhesion promoter is a viable clinical procedure that does not require the additional micro-mechanical abrasion step.

Aesthetic management of severely fluorosed incisors in an adolescent female

BACKGROUND

Dental fluorosis is a condition of enamel hypomineralization due to the effects of excessive fluoride on ameloblasts during enamel formation. Delayed degradation of enamel matrix proteins or inhibited protein removal results in impaired and incomplete crystal growth, producing hypomineralized and porous enamel. Severely fluorosed teeth may undergo post-eruptive surface breakdown and post-eruptive dark brown to black staining.

METHODS

A 13 year old girl presented with severely discoloured maxillary central incisors. Initial aesthetic management of these teeth was conservative, including in-office tooth whitening, microabrasion and take-home whitening.

RESULTS

Dark brown to black staining of the teeth was reduced successfully without the need for gross mechanical preparation of the enamel. Further improvement of aesthetics was achieved with composite veneers.

CONCLUSIONS

Conservative treatment options such as tooth whitening and microabrasion can dramatically improve severely discoloured fluorosed teeth. This can provide a satisfactory interim outcome or minimize the removal of discoloured enamel and dentine prior to the provision of composite veneers. The use of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) may enhance remineralization and decrease postoperative sensitivity following tooth whitening and microabrasion procedures in hypomineralized teeth.

Caries susceptibility of human fluorosed enamel and dentine

OBJECTIVE

Objective of our laboratory study was to determine the impact of dental fluorosis severity on the formation of caries in the human enamel and dentine.

MATERIALS AND METHODS

Thirty-three human molars were grouped according to modified Thylstrup-Fejerskov index (TFI) into normal (N, TFI 0), mild fluorosis (ML, TFI 1-3) and moderate fluorosis (MD, TFI 4-6). Three mesio-distal sections were made in corono-apical axis of the tooth, giving enamel and dentine samples. They were embedded in an epoxy resin, and polished. Half of the polished surface was covered with an acid resistant varnish and immersed in standard acidified buffer solution (pH 4.5) for 48 h to create artificial caries lesions. They were treated with 5% NaOCl for 45 min and sectioned longitudinally along the center into two halves. Cut surfaces were polished and observed under a confocal laser scanning microscope for depth of demineralization. Morphology of the demineralized zones was observed under a field emission scanning electron microscope (FE-SEM). Data were analyzed using one-way ANOVA and Sheffe test (p=0.05).

RESULTS

Statistically significant difference in depth of demineralization was found between N and MD groups (p=0.046) in the enamel, and between N and ML (p=0.002), N and MD (p<0.001), ML and MD (p=0.029) in dentine. FE-SEM observation of the normal enamel showed direct dissolution with large fissures. Spongy appearance of intertubular dentine gradually disappeared from N to MD.

CONCLUSIONS

Moderately fluorosed enamel showed a significant caries resistance. In contrast, mild and moderately fluorosed dentine was significantly caries susceptible in vitro.

Micro-shear bond strength and morphological analysis of a self-etching primer adhesive system to fluorosed enamel

PURPOSE

The aim of this study was to evaluate micro-shear bond strength and morphological analysis of a self-etching primer adhesive system to fluorosed enamel.

MATERIALS AND METHODS

Extracted human molars were classified according to the severity of fluorosis using Thylstrup and Fejerskov index into four groups (TFI: 0, normal; 1-3, mild fluorosis; 3-6, moderate fluorosis; 6-7, severe fluorosis) and divided into following two sub-groups. For the first sub-group, a self-etching primer adhesive system was applied to the ground enamel surfaces and the other sub-group was conditioned with 37% phosphoric acid for 30s prior to application of the same adhesive system. Teeth were then restored with a resin composite, stored for 24h in water and micro-shear bond strengths were measured. After shear testing, the fracture modes were observed under a laser scanning microscope. Morphological study of etching patterns and adhesive interface was done under a scanning electron microscope (SEM). The data were analyzed using two-way ANOVA and Sheffe test (p=0.05).

RESULTS

No statistically significant difference was there between the different degrees of fluorosis in each sub-group. However, significant difference in the bond strengths between phosphoric acid etching and self-etching was found in moderate and severe groups. The SEM observations showed at the resin-enamel interface, thick resin tag like extensions penetrated around 3.5 microm into the enamel etched with phosphoric acid, while self-etching primer created, 1 microm lamina like penetration.

CONCLUSION

Severity of fluorosis affects the micro-shear bond strength of a self-etching bonding system to fluorosed enamel.

An optimized synthetic substrate for orthodontic bond strength testing

OBJECTIVE

The purpose of this study was to investigate the suitability of different synthetic calcium phosphate based substrates as a biomimetic enamel surface model for orthodontic bond strength testing.

METHODS

Carbonated apatite, amorphous calcium phosphate and commercial hydroxyapatite specimens were prepared as substrates for orthodontic bond strength testing. Carbonated apatite specimens were prepared by pressing, sintering and treatment with NaF. The shear bond strength was measured with a universal testing machine.

RESULTS

Hydroxyapatite, amorphous and cold pressed carbonated hydroxyapatite exhibited fractures within the substrate after debonding. Mean bond strength values for carbonated hydroxyapatite were 7.38 (1.75) MPa for specimens pressed at 300 degrees C and 9.55 (2.23) MPa for specimens pressed at 300 degrees C and then sintered at 600 degrees C. An additional NaF treatment after sintering resulted in lower bond strength measurements of on average 6.52 (1.03) MPa.

SIGNIFICANCE

Hot pressed and sintered carbonated hydroxyapatite showed acceptable shear bond strength values and may represent a suitable biomimetic model for orthodontic bond strength testing.

Effect of fluorosis on dentine shear bond strength of a self-etching bonding system

The purpose of this study was to investigate the effect of dental fluorosis on shear bond strength of a composite material to dentine. Forty human premolar teeth were classified according to the severity of fluorosis using the Thylstrup and Fejerskov index and were divided into four groups (TFI scores of 0, 3, 4 and 5) of 10 teeth. Non-fluorosed teeth (TFI score of 0) served as the control group. A self-etching light-cured bonding system, Clearfil SE Bond, and a micro-hybrid light-cured composite, Clearfil AP-X were selected for the study. Buccal surfaces of mounted teeth were ground flat to expose the dentine. Composite cylinders, 4 mm diameter and 4 mm length, were bonded to the treated dentine surfaces. Shear bond strength was measured with an universal testing machine at a cross-head speed of 0.5 mm min-1. After failure, the fracture surfaces were examined under a stereo microscope. The mean bond strength was 24.37 +/- 3.54 MPa for non-fluorosed teeth and varied between 22.72 +/- 3.52 and 27.02 +/- 5.91 MPa for fluorosed teeth. The difference between the mean values for bond strength was not statistically significant (P > 0.05). Adhesive mode of failure was most prevalent in non-fluorosed teeth. It can be concluded that fluorosis does not affect the shear bond strength of composite material to human dentine.

Occurrence and management of dental fluorosis

The prevalence of dental fluorosis is on the increase in different parts of the world, even in areas with fluoride-deficient public water supplies. This may be due to increased use of fluoride in preventive dentistry. In some countries, exposure to apparently low fluoride concentrations in drinking water has resulted in severe dental fluorosis in some children. This underscores the importance of taking into consideration all sources of fluoride intake in a community before prescribing fluoride supplements or recommending appropriate fluoride concentration for the public water supply. Preventive management of dental fluorosis includes de-fluoridation of drinking water in endemic areas, cautious use of fluoride supplements and supervision of the use of fluoride toothpaste by children aged below 5 years. Aesthetically objectionable discolouration of fluorosed teeth may be managed by bleaching, micro-abrasion, veneering or crowning. The choice between these treatments depends on the severity of the fluorosis and this may be satisfactorily determined by the Thylstrup and Fejerskov index.

A comparison of the stresses developed in tension, shear peel, and torsion strength testing of direct bonded orthodontic brackets

Strength testing of direct bonded orthodontic bracket systems is commonly performed with tension, shear peel, or torsion loads. In general, the results of these tests are reported as an average stress that is computed by dividing the experimentally measured force at failure by the area of the bracket base. The average value, obtained in this manner, implies an evenly distributed stress field. In this project, finite element model (FEM) calculations were used to determine the more realistic stress distributions generated within the cement. The results indicate that the three loading modes produce very different non-uniform stress field patterns. Furthermore, the calculated stress peaks and the stress component proportions depend on the loading method. It was therefore concluded that the manner of loading affects the strength measurements and that the average stress does not adequately characterize bond strength.