Shear bond strength of different adhesives tested in accordance with DIN 13990-1/-2 and using various methods of enamel conditioning

Finite Element Analysis of Fixed Orthodontic Retainers

The efficacy of retainers is a pivotal concern in orthodontic care. This study examined the biomechanical behaviour of retainers, particularly the influence of retainer stiffness and tooth resilience on force transmission and stress distribution. To do this, a finite element model was created of the lower jaw from the left to the right canine with a retainer attached on the oral side. Three levels of tooth resilience and variable retainer bending stiffness (influenced by retainer type, retainer diameter, and retainer material) were simulated. Applying axial or oblique (45° tilt) loads on a central incisor, the force transmission increased from 2% to 65% with increasing tooth resilience and retainer stiffness. Additionally, a smaller retainer diameter reduced the uniformity of the stress distribution in the bonding interfaces, causing concentrated stress peaks within a small field of the bonding area. An increase in retainer stiffness and in tooth resilience as well as a more oblique load direction all lead to higher overall stress in the adhesive bonding area associated with a higher risk of retainer bonding failure. Therefore, it might be recommended to avoid the use of retainers that are excessively stiff, especially in cases with high tooth resilience.

Influence of Individual Bracket Base Design on the Shear Bond Strength of In-Office 3D Printed Brackets-An In Vitro Study

(1) Background: Novel high-performance polymers for medical 3D printing enable in-office manufacturing of fully customized brackets. Previous studies have investigated clinically relevant parameters such as manufacturing precision, torque transmission, and fracture stability. The aim of this study is to evaluate different design options of the bracket base concerning the adhesive bond between the bracket and tooth, measured as the shear bond strength (SBS) and maximum force (F_max) according to DIN 13990. (2) Methods: Three different designs for printed bracket bases were compared with a conventional metal bracket (C). The following configurations were chosen for the base design: Matching of the base to the anatomy of the tooth surface, size of the cross-sectional area corresponding to the control group (C), and a micro- (A) and macro- (B) retentive design of the base surface. In addition, a group with a micro-retentive base (D) matched to the tooth surface and an increased size was studied. The groups were analyzed for SBS, F_max, and adhesive remnant index (ARI). The Kruskal-Wallis test with a post hoc test (Dunn-Bonferroni) and Mann-Whitney U test were used for statistical analysis (significance level: p < 0.05). (3) Results: The values for SBS and F_max were highest in C (SBS: 12.0 ± 3.8 MPa; F_max: 115.7 ± 36.6 N). For the printed brackets, there were significant differences between A and B (A: SBS 8.8 ± 2.3 MPa, F_max 84.7 ± 21.8 N; B: SBS 12.0 ± 2.1 MPa, F_max 106.5 ± 20.7 N). F_max was significantly different for A and D (D: F_max 118.5 ± 22.8 N). The ARI score was highest for A and lowest for C. (4) Conclusions: This study shows that conventional brackets form a more stable bond with the tooth than the 3D-printed brackets. However, for successful clinical use, the shear bond strength of the printed brackets can be increased with a macro-retentive design and/or enlargement of the base.

Orthodontic shear bond strength and ultimate load tests of CAD/CAM produced artificial teeth

OBJECTIVES

To investigate whether artificial CAD/CAM processed (computer-aided design/manufacturing) teeth could be a feasible option for the production of dental in vitro models for biomechanical testing.

MATERIAL AND METHODS

Disks (n = 10 per group) made from two different CAD/CAM-materials, one fiber-reinforced composite (FRC; Trinia, Bicon) and one polymethylmethacrylate-based resin (PMMA; Telio CAD, Ivoclar Vivadent), as well as bovine teeth (n = 10), were tested for their shear bond strength (SBS) and scored according to the adhesive remnant index (ARI). In addition, CAD/CAM-manufactured lower incisor teeth were tested for their ultimate load (F_u).

RESULTS

With regard to SBS, both PMMA (17.4 ± 2.2 MPa) and FRC (18.0 ± 2.4 MPa) disks showed no significant difference (p = 0.968) compared to bovine disks (18.0 ± 5.4 MPa). However, the samples differed with regard to their failure mode (PMMA: ARI 4, delamination failure; FRC: ARI 0 and bovine: ARI 1.6, both adhesive failure). With regard to F_u, FRC-based teeth could withstand significantly higher loads (708 ± 126 N) than PMMA-based teeth (345 ± 109 N) (p < 0.01).

CONCLUSION

Unlike PMMA-based teeth, teeth made from FRC showed sufficiently high fracture resistance and comparable SBS. Thus, FRC teeth could be a promising alternative for the production of dental in vitro models for orthodontic testing.

CLINICAL RELEVANCE

CAD/CAM-processed teeth made from FRC enable the use of standardized geometry and constant material properties. Using FRC teeth in dental in vitro studies has therefore the potential to identify differences between various treatment options with rather small sample sizes, while remaining close to the clinical situation.

Effect of surface treatments and flash-free adhesive on the shear bond strength of ceramic orthodontic brackets to CAD/CAM provisional materials

OBJECTIVES

To evaluate the effect of surface treatments and flash-free adhesive on the shear bond strength of ceramic orthodontic brackets bonded to materials used for the fabrication of CAD/CAM provisional crowns.

MATERIALS AND METHODS

Specimens (n = 160) from each provisional material (CAD-Temp and C-Temp) were categorized into four groups according to the surface treatment methods: C (no surface treatment), HP (37% H₃PO₄), DB (mechanical roughening by diamond bur), and SB (mechanical roughening by blasting). Maxillary central incisor ceramic brackets (Clarity™ Advanced ceramic brackets, 3 M Unitek) were bonded to the conditioned provisional materials according to the used adhesive system (n = 20), APC PLUS or APC flash-free. All specimens were evaluated for shear bond strength testing (SBS) and the adhesive remnant index (ARI). Data were analyzed using Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

C-Temp significantly recorded higher SBS than CAD-Temp (24.0 and 16.0 MPa, respectively) (p < 0.001). DB and SB groups utilizing flash-free adhesive significantly recorded higher SBS (18.2 and 24.0 MPa, respectively) (P < 0.05) compared to other groups in the tested materials. Higher ARI scores were recorded in CAD-Temp and flash-free adhesive.

CONCLUSIONS

Mechanical surface treatments and flash-free adhesive would enhance SBS of ceramic orthodontic brackets to CAD/CAM provisional materials. The higher ARI scores reported with CAD-Temp and flash-free adhesive reduce chair time for excess removal.

CLINICAL RELEVANCE

Bonding of orthodontic brackets to provisional restorations is a challenge for orthodontists in adult comprehensive cases that could be improved by an appropriate provisional material, surface treatments, and adhesive system.

Effect of in vitro aging by water immersion and thermocycling on the mechanical properties of PETG aligner material

PURPOSE

The mechanical properties of orthodontic aligners made from thermoplastic polymers decrease over time in the intraoral milieu. However, there is a lack of information on this topic in the literature. Thus, the elastic properties of polyethylene terephthalate glycol (PETG) aligner films were investigated in vitro under extreme temperature changes simulated by thermocycling, environmental temperature and water absorption.

MATERIALS AND METHODS

A total of 60 specimens made from PETG aligner films (CA Clear Aligner, Scheu Dental, Iserlohn, Germany) were divided into three groups (immersed in distilled water, subjected to accelerated ageing by thermocycling, control). These groups were again divided and tensile testing was performed for all groups at 22 and at 37 °C. Young's modulus (E), 0.2% offset yield strength (R_p02) and ultimate tensile strength (UTS) were evaluated. Water absorption was determined using an analytical scale.

RESULTS

All treated specimens showed water absorption, whereby specimens that were thermocycled absorbed 48% more water than the immersed ones. Young's modulus and UTS were significantly lower for all three groups at 37 °C compared to the corresponding groups tested at 22 °C. Thermocycled and immersed groups showed a significantly lower Young's modulus compared to the control group tested at the same temperature. The mean R_p02 was statistically different when comparing the control group tested at 22 °C to the one tested at 37 °C.

CONCLUSIONS

The results of this study add to the understanding of the clinically well-known degradation of orthodontic aligners during wear time. Extreme alternating temperatures along with warming up to intraoral temperature and water absorption can reduce the material's Young's modulus and may therefore promote a decrease of resulting orthodontic forces.

Evaluation of the effect of different surface conditioning methods on shear bond strength of metal brackets bonded to aged composite restorations

INTRODUCTION

There are controversies regarding the most reliable conditioning method of the aged composite surface to ensure optimum bond strength. The purpose of this study was to evaluate the shear bond strength of metal brackets to microhybrid composite restorations after different surface preparation techniques.

MATERIALS AND METHODS

A total of sixty microhybrid composite samples were prepared using upper right central incisor celluloid crown as a mold. Samples were treated with 4 different surface conditioning methods: (1) etching, (2) sandblasting, (3) grinding, and (4) CO₂ laser irradiation. Samples were then bonded with metal brackets and underwent shear bond strength testing. A scanning electron microscope was carried out and the data was analysed by one-way ANOVA and post-hoc Tukey test. Bond failure was examined by stereomicroscope and scored based on adhesive remnant index (ARI). Kruskal-Wallis test was used to compare ARI values (α=0.05).

RESULTS

Shear bond strength values in the sandblasting group (17.18±1.53MPa) were significantly higher than the other groups. There was no significant difference between the grinding (12.87±3.38MPa) and laser (11.08±1.37MPa) groups (P=0.09). The lowest values were recorded in the etching group (6.78±1.69MPa). There was a significant difference in ARI scores among the four groups (P<0.001). ARI scores were mostly 2 and 3 in the sandblasting and grinding group, while in the etching and laser groups ARI was mostly 0 and 1.

CONCLUSIONS

Surface preparation by sandblasting and CO₂ laser provides clinically acceptable results with regards to bond strength and ARI score, however grinding and acid etching failed to produce the same results.

The influence of enamel sandblasting on the shear bond strength and fractography of the bracket-adhesive-enamel complex tested in vitro by the DIN 13990:2017-04 standard

OBJECTIVES

This study was conducted in order to investigate whether enamel sandblasting as an adjunct or substitute to the acid-etch technique has an effect on the shear bond strength (SBS) and fractography of the bracket-adhesive-enamel complex using the DIN 13990:2017-04 standard.

MATERIALS AND METHODS

Upper central incisor brackets (discovery®, Dentaurum, Germany) were bonded using Transbond XT™ (3M Unitek, Germany) on bovine incisors prepared by four different methods (15 samples each): sandblasting with 27 μm Al₂O₃ at 1.2 bar (s), acid etching with 37.4% phosphoric acid (a), sandblasting with 27 μm Al₂O₃ at 1.2 bar followed by acid etching (s1a), and sandblasting with 50 μm Al₂O₃ at 5.7 bar followed by acid etching (s2a). The SBS and adhesive remnant index (ARI) were measured, followed by one-way analysis of variance and Fisher's exact tests at 5%.

RESULTS

The SBS in groups s (5.6 ± 2.2 MPa), a (17.1 ± 4.3 MPa), s1a (18.3 ± 4.3 MPa), and s2a (18.5 ± 4.6 MPa) indicated that the s group was significantly inferior to all the other groups (p < 0.001). Likewise, the ARI analysis indicated a different performance of the s group (mostly ARI of 0) compared to the other groups (p < 0.001) and a tendency for different ARI between the a and s1a/s2a groups.

CONCLUSIONS

In vitro enamel sandblasting could not substitute acid etching and did not offer improved SBS when used before acid etching, regardless of air pressure and powder granulation. Sandblasting without acid etching produced less residual resin on the tooth after debonding.

CLINICAL RELEVANCE

The clinical use of adjunct enamel sandblasting prior to etching to enhance SBS has to be questioned.

Effects of reducing light-curing time of a high-power LED device on shear bond strength of brackets

PURPOSE

To assess the effects of reducing the curing time of a high-power light-emitting diode (LED) unit (Valo, Ultradent, South Jordan, UT, USA) on shear bond strength (SBS) of metal brackets and on the amount of adhesive remnant of two orthodontic composites.

METHODS

Eighty human premolars were divided into four groups (G1-4) according to curing time and composite: G1 (Transbond XT, 6 s), G2 (Opal Bond MV, 6 s), G3 (Transbond XT, 3 s), and G4 (Opal Bond MV, 3 s). Twenty-four hours after bonding, brackets were subject to a SBS test performed with a universal testing machine. Enamel surface was analyzed by SEM and the amount of adhesive remnant was assessed by the Image J software area calculation tool. Two-way analysis of variance was used for statistical analysis of SBS data, while Friedman and Mann-Whitney post hoc tests were used to analyze data on the amount of adhesive remnant.

RESULTS

Time and composite significantly affected SBS (p < 0.001). The 6 s curing showed a higher SBS value (21.56 MPa) in comparison to 3 s curing (15.79 MPa). Transbond XT composite showed a significantly higher SBS value (21.06 MPa) compared to Opal Bond MV (16.29 MPa). After the SBS test, Opal Bond MV showed a significantly greater amount of composite adhered to enamel (p < 0.001).

CONCLUSION

Reducing exposure time from 6 to 3 s significantly decreased mean values of SBS, even with the use of a high-power LED unit. Reduction in time did not affect the amount of adhesive remnant.

Effects of enamel sealing on shear bond strength and the adhesive remnant index : Study of three fluoride-releasing adhesives in combination with metal and ceramic brackets

OBJECTIVES

Selected combinations of materials were used to create tooth-adhesive-bracket complexes to evaluate shear bond strength (SBS) and the adhesive remnant index (ARI) with regard to enamel sealing.

METHODS

Four adhesive systems also appropriate for use as enamel sealants were combined with four bracket types, resulting in 16 adhesive-bracket combinations, each of which was tested on 15 permanent bovine incisors. Sealant-adhesives included two recently introduced fluoride-releasing systems (Riva bond LC^® and go!^®), one established primer (Opal^® Seal™), and one commonly used adhesive as control (Transbond™ XT). Brackets included two metal (discovery^® by Dentaurum and Sprint^®) and two ceramic (discovery^® pearl and GLAM^®) systems. After embedding the bovine teeth, bonding the brackets to their surface, and storing the resultant samples as per DIN 13990-2 with modifications, an SBS test was performed by applying the shear force directly at the bracket base in an incisocervical direction. Then the ARI scores were determined.

RESULTS

Discovery^® + Transbond™ XT yielded the highest (47.2 MPa) and GLAM^® + go!^® the lowest (17.0 MPa) mean SBS values. Significant differences (p < 0.0001) were found between metal and ceramic brackets of the same manufacturers (Dentaurum and Forestadent). Our ratings of the failure modes upon debonding predominantly yielded ARI 0 or 1. The high SBS values and low ARI scores observed with discovery^® + Transbond XT™ were reflected in a high rate of enamel fracture, which occurred on 11 of the 15 tooth specimens in this group.

CONCLUSIONS

All sealant-bracket combinations were found to yield levels of SBS adequate for clinical application. SBS values and ARI scores varied significantly depending on which sealant-brackets were used.

Shear bond strength and debonding characteristics of a new premixed self-etching with a reference total-etch adhesive

Background

To determine the shear bond strength and adhesive remnant index of a new premixed self-etching primer and adhesive (Tectosan, BonaDent, Germany) for orthodontic appliances in comparison to a reference total-etch system Transbond XT.

Methods

Bovine incisors were embedded in resin and randomly divided into two groups of 16 samples each. Brackets (Discovery, Dentaurum, Germany) were bonded in group 1 (total-etch-system, Transbond XT) and in group 2 (self-etch-system, Tectosan) with curing light for 40 s. Shear bonding strengths were measured after 24 h of storage in distilled water at 37 °C with a Zwicki 1120 testing machine (Zwick Roell, Germany). A force was applied on the bracket base at the wings in occluso-gingival direction. Then the adhesive remnant index (ARI) was determined.

Results

No statistical differences on SBS were found for both bonding agents (p = 0.63). ARI scores however differed statistically significantly (p = 0.035): in the total-etch group more adhesive remained on the teeth, whereas in the self-etch group more adhesive remained on the brackets. There were no visible enamel damages in both groups.

Conclusions

No differences in the shear bond strength were found between both bonding agents. In our study the self-etch-system shifted the adhesive remnant index from more adhesive on the teeth to more adhesive on the bracket - as other already published self-etch systems did - with the new benefit of not increased enamel damages. Tectosan might therefore be a promising alternative to adhesive systems.