Impact of Fluorosis on the Tensile Bond Strength of Metal Brackets and the Prevalence of Enamel Microcracks

Effects of the conventional, soft start, and pulse delay modes produced by light-emitting diode device on metal brackets bond strength and enamel damage: An in vitro comparative study

OBJECTIVES

This study aimed to compare the bond strength and enamel damage following debonding of metal brackets cured by different light-curing modes: conventional, soft start, and pulse delay modes.

MATERIAL AND METHODS

Sixty extracted upper premolars were randomly divided into three groups according to the used light-curing mode. Metal brackets were bonded with a light-emitting diode device employing different modes. Group 1: conventional mode (10s mesial+10 s distal); group 2: soft start mode (15s mesial+15s distal); group 3: pulse delay mode (3s mesial+3s distal, followed by 3min of no photoactivation, then 9s mesial+9s distal). Radiant exposure was the same in all study groups. Shear bond strengths of the brackets were tested with a universal testing machine. A stereomicroscope was used to determine the number and length of enamel microcracks. One-Way ANOVA and Kruskal-Wallis tests were used to detect significant differences in shear bond strength and microcracks number and length among groups.

RESULTS

The soft start and pulse delay modes produced significantly greater shear bond strength than the conventional mode (19.46±4.90MPa; 20.47±4.97MPa; 12.14±3.79MPa, respectively, P<0.001). However, there was no significant difference between the soft start and pulse delay groups (P=0.768). The number and length of microcracks increased significantly after debonding in all study groups. The change in microcracks length was not different among study groups.

CONCLUSION

The soft start and pulse delay modes produced greater bond strength than the conventional mode without predisposing enamel to higher risk of damage. Conservative methods for debonding are still required.

Effects of fluorosed enamel on orthodontic bracket bonding : An in vitro study

OBJECTIVE

To investigate the effect of enamel deproteinization and air abrasion on shear bond strength (SBS), adhesive remnant index (ARI) scores, and surface topography when bonding orthodontic brackets to fluorosed enamel.

MATERIALS AND METHODS

The sample included 90 fluorosed and 30 normal premolars divided into four groups: group I (fluorosed premolars subjected to air abrasion before acid etching), group II (fluorosed premolars subjected to deproteinization before acid etching), group III (fluorosed premolars; control for groups I and II), and group IV (normal premolars; control for group III). Bonding procedures included etching with 37% phosphoric acid, priming with TransbondTM XT primer (3M Unitek, Monrovia, CA, USA), and application of TransbondTM XT adhesive paste (composite; 3M Unitek, Monrovia, CA, USA). Air abrasion was done using 50 µm aluminum oxide particles under 0.28 MPa pressure for 5 s with the micro-etcher held at a distance of 10 mm. Deproteinization was done for 60 s with 5% sodium hypochlorite (NaOCl).

RESULTS

Fluorosed premolars subjected to deproteinization showed the lowest (median = 6.57 MPa) SBS among the four groups, followed by 8.14, 8.90, 8.14 MPa for groups I, III, and IV respectively. ARI scores were significantly different between the four groups (p = 0.006). Fluorosed enamel etched after air abrasion or deproteinization with NaOCl showed a predominance of type 4 etching pattern with some areas appearing unetched.

CONCLUSIONS

Shear bond strength of all groups was within the 6-8 MPa acceptable range for orthodontic purposes. Fluorosed premolars subjected to deproteinization showed the lowest values. Further studies are recommended to scrutinize the deproteinization technique.

Saliva microbiome alterations in dental fluorosis population

Background

We aimed to explore saliva microbiome alterations in dental fluorosis population.

Methods

The prevalence of dental fluorosis was examined in 957 college students. Dean's fluorosis index was used to evaluate the dental fluorosis status. Changes in the composition of the salivary microbiome were assessed in a subset of these patients (100 healthy controls, 100 dental fluorosis patients).

Results

Dental fluorosis affected 47% of the student sample, and incidence was unrelated to gender. Compared with healthy controls, the microbiota of patients with dental fluorosis exhibited increased diversity, with increased abundance of Treponema lecithinolyticum, Vibrio metschnikovii, Cupriavidus pauculus, Pseudomonas, Pseudomonadaceae, Pseudomonadales, and decreased abundance of Streptococcus mutans, Streptococcus sanguinis, Gemella, and Staphylococcales. Function analyses showed increases in arginine biosynthesis in patients affected by dental fluorosis, together with reductions in amino sugar and nucleotide sugar metabolism, fructose and mannose metabolism, and starch and sucrose metabolism.

Conclusions

These results suggest that there are striking differences in salivary microbiome between healthy controls and dental fluorosis patients. Dental fluorosis may contribute to periodontitis and systemic lung diseases. There is a need for cohort studies to determine whether altering the salivary microbiota in dental fluorosis patients can alter the development of oral or systemic diseases.

Effect of Different Types of Adhesive Agents on Orthodontic Bracket Shear Bond Strength: A Cyclic Loading Study

Bracket failure is one of the most important problems encountered during fixed orthodontic treatment. For this reason, different types of adhesive agents have been developed over the years. Consequently, the aim of this study was to evaluate the shear bond strength of brackets bonded to teeth etched with a conventional acid etching method in a laboratory environment by using different types of adhesive agents and comparing the number of shear strokes. Sixty human maxillary premolars were divided into three groups and Gemini stainless steel metal brackets (3M Unitek, Monrovia, CA, USA) were bonded to all teeth. In Group 1, Transbond™ XT Primer (3M Unitek, Monrovia, CA, USA) and Transbond™ XT Light Cure Adhesive Paste composite (3M Unitek, Monrovia, CA, USA) were used. In Group 2, BracePaste® MTP Primer (American Orthodontics, Sheboygan, CA, USA) and BracePaste® Adhesive composite (American Orthodontics, Sheboygan, WI, USA) were used. In Group 3, Ortho Solo™ Primer (Ormco, Orange, CA, USA) and Grengloo™ Adhesive composite (Ormco, Brea, CA, USA) were used. The samples were subjected to a shear test with a closed-loop controlled, low-cycle fatigue machine with a capacity of 10 N and a crosshead speed of 300 mm/min. The number of shear strokes of the brackets was recorded. According to the Kruskal−Wallis and Mann−Whitney U tests performed on the data obtained, statistically significant differences were found between the groups in terms of the numbers of shear strokes (p < 0.05). Significantly higher numbers of shear strokes and higher shear bond strengths were observed in Group 3 compared with Group 1 and Group 2 (p < 0.05). There was no statistically significant difference between the numbers of shear strokes for Group 1 and Group 2 samples (p > 0.05). To conclude the study, it was observed that the type of adhesive used had an effect on the bond strength of the bracket and that the Grengloo™ adhesive agent showed higher shear bond strength. It was observed that BracePaste® Adhesive and Transbond™ XT Light Cure Adhesive Paste adhesive agents had similar shear bond strengths.

Influence of the use of remineralizing agents on the tensile bond strength of orthodontic brackets

This study aimed to evaluate the influence of the use of remineralizing agents on the tensile bond strength. The study sample consisted of 80 recently extracted molars, which were randomly divided into four experimental groups (n = 20): groups FG1 and FG30, in which fluoride varnish was used, and groups RG1 and RG30, in which Recaldent tooth mousse was used. The mesiobuccal surfaces served as experimental, and distobuccal as control (n = 80). Brackets were bonded to both surfaces and were submitted to a tension test at different time intervals (T1 and T30). Tensile bond strength (TBS) and the amount of adhesive remnant (ARI) were assessed. A statistically significantly lower mean of TBS compared to the control group was found only in the FG1 group (p < 0.001), and no significant difference was found between the other groups. The FG1 group showed significantly higher ARI scores (p < 0.001) compared to the control group. No significant difference was found between the other groups. In conclusion, bonding brackets one day after applying fluoride varnish significantly reduced the TBS, but after 30 days it was set back to an optimal value. The use of Recaldent before orthodontic treatment had no adverse effect.

Comparative Evaluation of Two Antioxidants on Reversing the Immediate Bond Strength of Bleached Enamel: In Vitro Study

Background

Tooth bleaching causes a significant decrease in the bonding strength between the resin and human enamel. Nevertheless, the effects of different antioxidant types on the immediate bonding strength of resin and bleached enamel were significantly different. Therefore, the objective of this study was to compare the effects of 2 antioxidants for enhancing the bond strength of the resin to bleached enamel.

Material/Methods

There were 48 enamel blocks performed from 48 recently extracted maxillary central incisors. There were 8 groups: NC (negative control, no bleached specimens restored without antioxidants); NA (no antioxidant, bleached specimens bonded immediately without any antioxidants); SA30, SA60, and SA120 (bleached specimens accepted the management of 10% sodium ascorbate (SA) for 30 minutes, 60 minutes, and 120 minutes, respectively, before restored); PC30, PC60, and PC120 (bleached specimens received treatment of 5% proanthocyanidins (PC) for 30 minutes, 60 minutes, and 120 minutes, respectively, before restored). We measured the micro-tensile bond strength of specimens and used 2-way ANOVA to analyze the data.

Results

The mean±standard deviation bond strength measured were: NC, 29.99±4.00; NA, 14.90±1.97; SA30, 18.60±2.20; SA60, 22.57±2.71; SA120, 26.15±3.85; PC30, 16.78±2.29; PC60, 19.13±2.24, PC120, 23.90±2.01 MPa. In addition, the fracture types were mainly of an adhesive mode (88.75%), followed by mixed (7.5%), and cohesive (3.75%).

Conclusions

10% sodium ascorbate provided a comparatively more promising improvement for immediate bond strength than 5% proanthocyanidins when the same duration of antioxidant was applied.