Effects of customized resin base on bonding strength of spherical self-ligating brackets

PURPOSE

Fabricating resin bases has become an easy and economical method to achieve the customization of brackets. This study aimed to assess the effect of the resin base on bonding strength of spherical self-ligating brackets.

METHODS

A defined amount of adhesive was bonded to the bracket base and constituted the new resin base. The thickness of the adhesive was measured and controlled at 0.5, 1.0, 1.5 and 2.0 mm, and a group without a resin base was used as a control. Sixty extracted human premolars were randomly divided into five groups. The brackets in each group were bonded to the specimen, and debonding tests were conducted. The shear bond strength (SBS) was calculated according to the measured debonding force in relation to the base area. The adhesive remnant index (ARI) score and the residual location of the fractured resin base were recorded. Enamel damage was also analyzed by scanning electron microscopy. After assessing for data normality and homogeneity, statistical comparisons between the groups and correlations among parameters were determined. P < 0.05 was regarded as significant.

RESULTS

The correlation analysis revealed an inverse correlation between the resin base thickness and the SBS (Coeff = -0.719, P < 0.01). The highest SBS was 9.33 MPa, in the control group, which was significantly greater than the lowest SBS (6.03 MPa), in the 2.0-mm group (P < 0.05). Multiple comparisons analysis revealed no differences in SBS between the 1.0-, 1.5- and 2.0-mm groups. Nonparametric analysis found that only the ARI score in the 0.5-mm group (2.92) was significantly different (P < 0.05) from that in the control group (1.25). As the thickness of the resin base increased, the fractured resin base tended to remain at the bracket base, and the risk of enamel damage decreased.

CONCLUSIONS

As the thickness of the resin base increased, the bonding strength of the spherical bracket decreased. However, the required clinical bonding strength was still satisfied when the thickness was less than 2.0 mm. The existence of a resin base could protect the enamel surface from damage caused by debonding. The customization of spherical brackets by tailoring a resin base can be applied in clinical practice because of the clinically acceptable bonding strength.

Effect of sandblasting on the shear bond strength of recycled metal brackets: A systematic review and meta-analysis of in-vitro studies

INTRODUCTION AND OBJECTIVE

Sandblasting is an efficient and economic method of rebonding brackets. Literature is divided regarding the Shear Bond Strength (SBS) associated with sandblasted brackets. Hence this systematic review was conducted to obtain conclusive evidence on the same. The aim was to compare the SBS between sandblasted brackets bonded to extracted human teeth and new brackets bonded on extracted teeth that have not been previously bonded.

MATERIALS AND METHODS

The following databases were searched up to April 30, 2021: PubMed via Medline, Web of Science, LILACS, Cochrane, EMBASE and Scopus. Articles comparing SBS of a new bracket with that of a rebonded bracket following sandblasting were included. Two reviewers independently selected the studies, extracted the data and assessed the risk of bias which was based on a modification of the Risk Of Bias In Nonrandomized Studies of Interventions Tool (ROBINS-I). SBS data generated from the systematic review was summarized and a meta-analysis using random effects inverse-generic model was done.

RESULTS

Sixteen studies generated 521 samples for the new bracket group and 391 samples for the sandblasted group. These sixteen studies showed a low risk of bias. Meta analysis reported the mean difference between the SBS of new and sandblasted brackets to be 0.85. (95 CI of -0.24 to 1.94). This difference can be clinically disregarded. The high degree of heterogeneity indicated by an I² of 87% led to a subgroup analysis.

CONCLUSIONS

With the studies showing a high quality of evidence, it can be concluded that sandblasting is an efficient means of recycling debonded brackets without affecting SBS. The inherent deficiencies of in vitro bond strength studies should be borne in mind when making this conclusion. The study protocol was registered on the International Prospective Register of Systematic Reviews (Reg no: CRD42020193616).

Analysing the potential of hydrophilic adhesive systems to optimise orthodontic bracket rebonding

Introduction

Bond failure during fixed orthodontic treatment is a frequently occurring problem. As bracket rebonding is associated with reduced shear bond strength, the aim of the present investigation is to analyse the effect of different innovative rebonding systems to identify optimised rebonding protocols for orthodontic patient care.

Methods

Metallic brackets were bonded to the frontal enamel surfaces of 240 bovine lower incisors embedded in resin bases. Teeth were randomly divided into two major experimental groups: in group 1 a hydrophilic primer (Assure™ PLUS) was compared to commonly used orthodontic adhesives (Transbond XT™, BrackFix®, Grengloo™) and a zero control. In group 2 different rebonding systems were analysed using a hydrophilic primer (Assure™ PLUS), a methyl methacrylate-consisting primer (Plastic Conditioner) and a conventional adhesive (Transbond XT™). All teeth were tested for shear bond strength according to the DIN-13990 standard, the Adhesive Remnant Index and enamel fracture rate.

Results

The hydrophilic primer enhanced shear bond strength at first bonding (Assure™ PLUS 20.29 ± 4.95 MPa vs. Transbond XT™ 18.45 ± 2.57 MPa; BrackFix® 17 ± 5.2 MPa; Grengloo™ 19.08 ± 3.19 MPa; Meron 8.7 ± 3.9 MPa) and second bonding (Assure™ PLUS 16.76 ± 3.71 MPa vs. Transbond XT™ 13.06 ± 3.19 MPa). Using Plastic Conditioner did not seem to improve shear bond strength at rebonding (13.57 ± 2.94). When enamel etching was left out, required shear bond strength could not be achieved (Plastic Conditioner + Assure™ PLUS 8.12 ± 3.34 MPa; Plastic Conditioner: 3.7 ± 1.95 MPa). Hydrophilic priming systems showed decreased ARI-scores (second bonding: 2.63) and increased enamel fracture rates (first bonding: 55%; second bonding 21,05%).

Conclusions

Based on the present study we found that rebonding strength could be compensated by the use of hydrophilic priming systems. The additional use of a methyl methacrylate-consisting primer does not seem to enhance shear bond strength. No etching approaches resulted in non-sufficient bond strength.

Effect of multiple debonding sequences on shear bond strength of new stainless steel brackets

Objectives:

This in-vitro study aimed at evaluating the effect of three debonding sequences on the shear bond strength (SBS) of new stainless steel (SS) brackets.

Materials and Methods:

Stainless steel twin brackets (0.022-inch, American Orthodontics, Sheboygan, WI, USA) were bonded with light cure adhesive (Transbond XT, 3M Unitek, St. Paul, MN, USA) to 80 newly extracted human premolars after acid etching with 37% phosphoric acid (30 s). Brackets were debonded with a universal testing machine, and new brackets were bonded to teeth using the same adhesive and same manner. This process was repeated twice, and brackets were debonded within 24 h after bonding. The longitudinal changes of average SBS were assessed with the repeated measures ANOVA. Post-hoc tests using the Bonferroni correction were also used to compare the average SBS at three debonding sequences.

Result:

The mean SBS decreased significantly after each debonding sequence (P < 0.01). The corresponding mean values (standard deviation, 95% CI) after the first, second, and third debonding sequences were 22.88 MPa (4.08, 21.97-22.79), 19.36 MPa (4.54, 18.62-20.64), and 16.67 MPa (4.27, 15.72-17.62), respectively. There was no significant difference among the adhesive remnant index (ARI) scores of three debonding sequences (χ²= 5.067, df = 6, P = 0.53).

Conclusion:

Average SBS after three debonding sequences was significantly decreased, but was above the recommended 5.9-7.8 MPa. In-vivo studies are required to validate the finding of this study.

[Enamel cracks: influence of orthodontic process]

The presence of enamel cracks is not only due to the removal process. It is all the stages before that we need to consider. 1. The presence of risks factors before the treatment (cracks, trauma...) have to be explained to the patient and recorded. 2. The choice of bracket placement: the buccal side is responsible for less cracks than the lingual one. 3. Ceramic brackets need higher debonding forces than metal ones; metal reinforced orthodontic ceramic brackets could be an interesting approach. 4. CVIMR could be better than classic bonds. 5. In case of multiple rebondings, it is better not to etch enamel again but only to level the resin left on tooth surface. 6. Alternatives to removing brackets by pliers are studied, especially for the removal of ceramic brackets to thwart the high debonding force problem : heat, laser...