Impact of different pretreatments and attachment materials on shear bond strength between monolithic zirconia restorations and metal brackets

Can a Self-etching Primer be Effective in Bonding Aligner Attachments to Different Types of Ceramics?

Objective

This in vitro study aimed to evaluate the effectiveness of pretreatment with a self-etching primer for bonding aligner attachments to lithium disilicate (LD) and monolithic zirconia (MZ) ceramics.

Methods

Forty ceramics, including LD (n=20) and MZ (n=20), were divided into four study groups according to the surface pretreatments: LD specimens pretreated with universal primer (Monobond Plus, MP) after hydrofluoric acid etching (Group 1); MZ ceramics pretreated with MP after sandblasting (Group 2); LD ceramics pretreated with self-etching ceramic primer (Monobond etch & prime, MEP) (Group 3); and MZ ceramics pretreated with MEP after sandblasting (Group 4). The aligner composite (GC Aligner Connect) and universal adhesive (GPremio Bond) were used to prepare the resin attachments. The bond strength was evaluated by micro-shear bond strength (SBS) testing (0.1 mm/min) after thermocycling, and the remnant adhesive was scored according to the resin attachment remnant index (RARI). The SBS data were analyzed using ANOVA and Tukey tests, and the RARI scores were analyzed using the chi-square test.

Results

Group 1 had the lowest SBS, and group 2 had the highest SBS. There were significant differences between the groups in terms of bond strength (p<0.05). The RARI scores showed no significant differences, regardless of the pretreatment and ceramic type.

Conclusion

The use of a self-etching primer increased the bond strength of resin attachments on LD ceramics. For zirconia ceramics, both ceramic primers are recommended for aligner attachment bonding.

Impact of polishing system on surface roughness of different ceramic surfaces after various pretreatments and bracket debonding

OBJECTIVE

Evaluating various polishing methods after bracket debonding and excessive attachment material removal for different ceramics and pretreatments.

MATERIAL AND METHODS

Zirconia (ZrO2), leucite (LEU) and lithium disilicate (LiSi) specimens were pretreated with a) silica coated alumina particles (CoJet); LEU and LiSi additionally with b) hydrofluoric acid (HF), c) Monobond Etch&Prime (MEP), d) silicium carbide grinder (SiC) before bracket bonding, shearing off, ARI evaluation, excessive attachment material removal and polishing with i) Sof-Lex Discs (Soflex), ii) polishing paste (Paste), iii) polishing set (Set). Before/after polishing surface roughness (Ra) was measured with a profilometer. Martens hardness parameter were also assessed.

RESULTS

Irrespective of pretreatment Ra of LEU increased the most, followed by LiSi and ZrO2 (p < 0.001, SiC: p = 0.012), in accordance with the measured Martens hardness parameter. CoJet/SiC caused greater roughness as HF/MEP (p < 0.001). The ZrO2 surface was rougher after polishing with Paste/Set (p < 0.001; p = 0.047). Ra improved in the LEU/CoJet, LEU/SiC and LiSi/SiC groups with Soflex/Set (p < 0.001), in the LiSi/CoJet and LEU/HF groups by Soflex (p = 0.003, p < 0.001) and worsened by Paste (p = 0.017, p < 0.001). Polishing of HF or MEP pretreated LiSi with Set increased Ra (p = 0.001, p < 0.001), so did Paste in the LEU/MEP group (p < 0.001).

CONCLUSIONS

Paste couldn't improve the surfaces. Soflex was the only method decreasing Ra on rough surfaces and not causing roughness worsening. Polishing of LEU/LiSi after MEP, LEU after HF pretreatment doesn´t seem to have any benefit.

CLINICAL RELEVANCE

To avoid long-term damage to ceramic restorations, special attention should be paid to the polishing method after orthodontic treatment.

Shear Bond Strength between Orthodontic Brackets and Monolithic 4Y-TZP: An In Vitro Study

The aim of this study was to evaluate the effect of different surface treatments on the shear bond strength (SBS) between metal orthodontic brackets and monolithic zirconia surfaces bonded with resin composite. Fifty monolithic zirconia (4Y-TZP) disks were sintered and glazed. Specimens were divided into five groups (n = 10) for different surface treatments: control, nano second fiber laser, sandblasting, grinding and tribochemical coating (CoJet Sand 30-μm). Metal orthodontic brackets were bonded to monolithic zirconia surface by two-component orthodontic adhesive. After 500 cycles of thermocycling, shear bond strength values were measured by a universal testing machine at a cross head speed of 0.5 mm/min. The data was recorded as MPa and statistically analyzed with One-way ANOVA, Levene's LSD tests with Bonferroni corrections. The significance level was α = 0.05. The surface topography of one specimen of each group was evaluated by scanning electron microscopy (SEM). Statistically significant difference was observed among study groups (p = 0.018). The lowest shear bond strength was observed in the control group (3.92 ± 1.9). Tribochemical coating showed the highest bond strength (7.44 ± 2.9), which was statistically different from the control and nano second laser (4.3 ± 1.4) groups but not statistically different from grinding (6.15 ± 3.1) or sandblasting (6.47 ± 3.3). SEM images showed comprehensive results of each surface treatment on monolithic zirconia. All failure modes were recorded as adhesive between the composite resin and monolithic zirconia. Based on the findings of this study, it can be concluded that grinding, sandblasting and tribochemical coating techniques showed clinically acceptable bond strength within the range of 6-8 MPa. These surface treatments can be considered suitable for achieving a durable bond between metal orthodontic brackets and monolithic 4Y-TZP ceramic surfaces.

Impact of different pretreatments and attachment materials on shear bond strength of indirectly bonded brackets using CAD/CAM transfer trays to monolithic zirconia

OBJECTIVE

Investigating the impact of different pretreatment methods, attachment materials and aging regimens on shear bond strength (SBS) between zirconia and indirectly bonded brackets using CAD/CAM transfer trays.

METHODS

Zirconia substrates were conditioned with silica coated alumina (CoJet) and a) Clearfil Ceramic Primer Plus (CF), b) RelyX Ceramic Primer (RXP), c) Futurabond U (FU). Brackets were virtually placed, transfer tray designed (OnyxCeph) and 3D-printed for indirect bonding with a) Transbond LV (TBL), b) Nexus NX3 (NX3), c) Maximum Cure (MC). SBS testing was performed with a universal testing machine after 24 h, 500 thermal cycles, 90 d. Directly bonded brackets to human enamel using Transbond XT Adhesive served as control. The adhesive remnant index (ARI) was evaluated. Data was analyzed with Shapiro-Wilk, Kruskal-Wallis and Dunn's post-hoc test with Bonferroni correction, Chi² test (p < 0.05), and the Weibull modulus was calculated.

RESULTS

SBS ranged from 0.1 to 15.5 MPa and were influenced mostly by the attachment material. NX3 generally showed the highest values (9.5-15.8 MPa). Initially RXP/TBL and FU/TBL presented the lowest values (4.3/4.8 MPa). Aging regimens reduced SBS of MC irrespective of pretreatment, after 90 d values ranged from 0.1 to 0.9 MPa. ARI 1 was predominant in all MC groups and FU/NX3, 2 and 3 in the other groups. Weibull moduli ranged between 0.15 (MC/RXP/500 TC) and 6.24 (NX3/RXP/500 TC).

SIGNIFICANCE

MC seems not to be suitable for indirect bonding using CAD/CAM transfer trays to zirconia. NX3 showed similar SBS values compared to the control, TBL lower.

Comparative Evaluation of Two Bracket Systems' Bond Strength: Conventional and Self-Ligating

Adhesion remains a key element in dentistry, whether approached in prosthetics, odontology, or orthodontics. It is a continuously researched aspect, as improved materials and adhesive methods keep emerging in the market. No orthodontic treatment can be effective without the proper adhesion strength of the bonded elements on the teeth. The objective of this research, in the broad context of self-ligating versus conventional brackets, was to compare active and passive self-ligating systems with a conventional one by conducting an in vitro study on human-extracted premolars. Shear bond strength tests were executed by means of an advanced materials-testing machine that generated maximum load and tensile strength values. The data obtained underwent statistical analysis with a statistical threshold of p < 0.05. The results regarding the statistical significance were acquired when comparing the passive self-ligating system with the active self-ligating and conventional systems (load-at-maximum-load mean 204.9, SD 91.09, and p < 0.05). In this study, the passive self-ligating bracket system appears to present increased shear bond strength.