Comparison of Shear Bond Strength of MIM Technology Brackets with Conventional and Rail-Shaped Mesh Bases: An In Vitro Study

The Effect of Bonding Surface Design on Shear Bond Strength of 3D-Printed Orthodontic Attachments

Introduction

This study compared the shear bond strength (SBS) of four innovative designs of the bonding surface of 3D-printed orthodontic attachments with conventional mesh design.

Methods

In this in vitro study, the bonding surface design in different groups was as follows: Group 1, flat surface without any feature as a negative control; Group 2, concentric circles with no cuts; Group 3, concentric circles with 16 radial cuts; Group 4, concentric circles with 32 radial cuts; Group 5, small cones with a flat end and rounded edges; Group 6, mesh-based commercially available metal brackets of the maxillary central incisor (standard edgewise, Dentaurum®) as a positive control (n = 20). In Groups 1-5, attachments were designed with SolidWorks® Software and printed with a 2K DLP-LCD printer with hard tough resin (eSun®). All the samples were bonded to the restorative composite resin (Solafil®) surfaces with orthodontic composite resin (CuRAY-ECLIPSE®). The samples were examined for SBS with a universal testing machine after thermocycling (1,000 cycles of 5‒55°C). Data were analyzed with Shapiro-Wilk, one-way ANOVA, and Bonferroni tests. The statistical significance level was set at 0.05.

Results

The mean SBS was significantly different between all the groups (P < 0.001) except for Groups 2 and 5 (P = 1.00) and Groups 2 and 6 (P = 1.00). Group 4 had the highest mean of SBS.

Conclusion

The bonding surface design significantly influenced the SBS of orthodontic attachments. The concentric circles with 32 cuts had higher bond strength than other designs and can be suggested as a new bonding surface design for orthodontic attachments.

Bonding Surface Designs in Fixed Orthodontic Attachments

Fixed orthodontic attachments/appliances work as a medium to transfer the force applied to the teeth. In bonded types, several factors affect the attachment bond strength and their clinical success. The primary approach for increasing the bond strength focused on altering the time and concentration of acid etching; however, the results showed that these changes might increase susceptibility to enamel decalcification. The bonding mechanism of orthodontic attachments may be chemical, mechanical, or a combination of both. Most attachment bonding surfaces (ABSs) have no chemical bond to resin composites. Hence, mechanical retention plays a major role. Developing more bonding surfaces by increasing the macroscopic size of the attachments has esthetic and hygienic limitations, so the ABS design plays a more important role in maintaining and improving the bond strength. In this research, different ABS designs are reviewed and categorized according to manufacturing methods and their features.

Is An Orthodontic Hydrophilic Composite Resistant to Contamination and pH Cycling? In vitro Results

Objective:

To evaluate the adhesive strength of a hydrophilic composite submitted to contamination and pH cycling, compared to a conventional composite.

Materials and Methods:

Seventy-two bovine incisors were prepared and randomly divided into 6 groups (n=12), bonded with Hydrophilic Composite (HC)(Transbond Plus Color Change) or with Conventional Composite (CC)(Transbond XT; control), with or without contamination and pH cycling as follows: G1-HC, with contamination, with pH cycling; G2-HC, with contamination, without pH cycling; G3-HC, without contamination, with pH cycling; G4-HC, without contamination, without pH cycling; G5-CC, without contamination, with pH cycling; G6-CC, without contamination, without pH cycling. Contamination in G1 and G2 consisted of fresh saliva applied after the self-etching primer for 5min before bonding with HC. After bonding, G1, G3, and G5 were submitted to pH cycling, immersed in the demineralizing solution for 22h and for 2h in remineralizing artificial saliva, repeated for 15 days. G2, G4, and G6 were kept in deionized water. The shear bond strength was tested using a load cell of 100N and the Adhesive Remnant Index (ARI) was assessed. Intergroup comparison was performed with one-way ANOVA, Tukey, and chi-square tests.

Results:

There was a statistically significant difference in G1, G2, and G3 in relation to G6. The highest rate of adhesive failure between the resin/bracket interface occurred with the HC, while CC failed more at the resin/tooth interface.

Conclusion:

Contamination and pH cycling did not decrease the shear bond strength of brackets bonded with the hydrophilic composite. However, the adhesive strength of the conventional composite was higher.

Sanches FS, Molina F, Henriques RP, Cruz EF, S. Freitas KM. Comparative Study of Adhesion of Brackets with Metal Injection Molding (MIM) Technology and Welded bases: In vitro Study

Introduction:

Brackets bonded to enamel surface depend on the adhesion material and the quality of the bracket base.

Objective:

The aim of this study was to compare the shear bond strength of metallic brackets with Metal Injection Molding (MIM) technology base or welded base.

Materials and Methods:

Forty mandibular extracted premolars mounted in acrylic resin blocks were divided randomly into two groups, both bonded with Transbond XT. In Group 1, brackets with MIM technology bases (Masel) were used, and in group 2, brackets with a welded base (Morelli) were used. After 24 hours, all brackets were tested for shear bond strength in a universal testing machine. Intergroup comparison was performed with an independent t test.

Results:

MIM base brackets showed a mean maximum load registered of 107.55 N, a mean shear bond strength of 9.58 MPa with a standard deviation of 5.80 MPa and the welded base brackets showed a mean maximum load of 167.37 N, a mean shear bond strength of 13.28 MPa with a standard deviation of 2.58 MPa. The difference between the two groups was statistically significant, indicating a higher shear bond strength of the welded base brackets.

Conclusion:

It was concluded that the brackets with welded bases presented a significantly higher shear bond strength than the brackets with MIM bases.