Study of various adhesive systems’ bond strength for bracket placement

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Introduction

In 1955, Dr. Michael Buonocore introduced the enamel acid etching technique as a preliminary preparation of bonding surfaces to achieve better adhesion [1, 2]. It was first discovered that the application of phosphoric acid to the enamel surface significantly improves the strong bond due to the formation of microporosity.

This technique has become widespread not only in orthodontic practice, but also in various areas of clinical dentistry.

However, treating the enamel surface with phosphoric acid causes the decomposition of the crystalline layer, respectively, destroying the enamel, as well as increasing the surface porosity caused by etching and the retention of resinous protrusions inside the enamel, leads to discoloration and pigmentation. Enamel damage is facilitated by the process of removing braces and removing residual adhesive from the tooth enamel after the end of orthodontic treatment. Since the main task of an orthodontist is to maintain the integrity of tooth enamel after braces are removed, except for its deformation [3–5] some undesirable aspects of this technique have caused great concern among researchers and practitioners. Thus, various adhesive systems have been developed.

The first and most common development is resin [6, 7]. However, the main drawback of this system is the limited working time [8–11], due to which the abutments are not able to comfortably handle the resin and, accordingly, incorrect placement of the brackets on the tooth surface [12–16]. The desire to form a strong bond by reducing enamel damage and minimizing orthodontic manipulation led to the development of the image-­processed adhesive system.

In 1979, photocuring adhesives were first used in the laboratory as an orthodontic adhesive, and the research was completed five years later. Thus, the curing of the adhesive under the abutment base occurs upon direct exposure to light from different directions with an ultraviolet lamp [17] and the penetration of visible light into the dental tissues [18, 19].

Tavas and Watles showed that transmission of visible light through enamel allows the photostable resin to cure under a metal arch base. One of the most important features of this system is to allow the orthodontist to place the braces in the correct place on the tooth surface [20–23]. This reduces the need to adjust the tooth axis at the end of treatment.

The main problem with dental binders is their ability to bond effectively to substrates of various characteristics. The enamel requires acid etching, usually from 30 % to 40 % phosphoric acid, before applying a liquid adhesive resin. Typical processes include etching with acid, application of a liquid adhesive resin, micromechanical and crosslinking for durability. These multistage binders have been on the market since the early 1990s and today can still be considered “gold standard” adhesives [24].

In response to market demand for simplified bonding procedures, self-etching adhesive has been significantly developed in line with broader simplification trends. Innovations in the form of starter materials and self-etching adhesives are aimed at mitigating the negative effects of excessive etching, excessive or insufficient conditioning. An advantage of using self-etching adhesives is that there is no need to remove the smear layer and smear plugs beforehand, as these systems can adapt the tooth surface to the adhesive [25].

Manufacturers are constantly introducing new adhesive systems for ease of use, improved texture, and ability to bond to tooth structure. As a result, researchers feel compelled to carefully examine and confirm these claims. Previous studies have shown that the bonding effectiveness of some materials is very low, while the bonds of other materials are more stable [26, 27].

A new class of bonding system was introduced, as the manufacturer claims that it can be used in systems with full etching, self-etching, and selective etching (Tetric N Bond Universal Vivapen,).

Recently, a new type of single-­stage bonding system has been introduced for patient care, classified as “universal” or “multi-mode”, usable with or without acid pre-treatment. To overcome the low enamel bond strength reported for self-etching bonding systems, universal bonding systems can be used using either etching-with-rinse or self-etching methods [28].

According to Reynolds and his colleagues, the minimum adhesive limit capable of withstanding chewing force is (from 5,9 to 7,8) and the stronger bond (40–50) MPa increases the risk of damage to the enamel during disengagement.

The aim of this study is to compare the shear bonding strength of different generations of adhesive systems for metal brackets placement.

Materials and methods

The study sample consisted of 40 recently removed human upper premolars. The teeth were of normal shape and size, the surface was free from defects and distortions such as dysplasia, there were no calcifications, caries, restorations and defects visible to the naked eye such as cracks and chips, and they were not subject to teeth whitening or fluoro diagnostics. The premolars were rinsed with running water, blood removed from them, the remnants of gum tissue and ligamentous fibers and left for storage for a week in packages containing 10 % formaldehyde solution to prevent bacterial accumulation on them. A root canal was used for mechanical fixation of teeth within acrylic resin cast in aluminum molds (cube-shaped, 10 cm long, 2 cm wide, 3 cm high) to the level of the enamel junction, bearing in mind that the longitudinal axis of the crown is perpendicular to the mold. Then expose the entire vestibular surface and return it to distilled water to ensure the hardening of the acrylic resin. The study used metal brackets for upper premolars (Gemini Bracket MBT, 3M Unitek, USA) with a micro-­patterned base, the area of which was defined as 10.61 mm2. After the teeth were removed from the distilled water, they were thoroughly dried with compressed air, then the vestibular surfaces of each premolar are brushed for 5–10 seconds with the brush to remove tartar and pumice powder, rinsed with a stream of water and compressed air for 5–10 seconds, then dried again with compressed air. This process was repeated on all teeth.

The first group used Transbond XT 3M Unitek.

Teeth were treated with 37 % phosphoric acid for 30 seconds, then rinsed thoroughly with a stream of water and dried with compressed air for 10 seconds until a uniform chalky spot appeared. Then a thin layer of base material Transbond XT 3M Unitek monovia, CA, USA. was applied to the etched area with a clean brush, a second layer of adhesive (Transbond XT 3M Unitek) was applied to the bracket base and glued to the marked area parallel to the longitudinal axis, removing excess glue from the edges of the base of the arch, taking care not to change the position of the arch. Then a light curing is performed for 30 seconds.

The second group used Beauty Ortho Bond (Japan).

It is a self-adhesive system that releases fluoride components, allowing brackets to be placed in one step, according to the company’s instructions, applying the solution to the surface with a clean brush for three seconds without pre-etching the enamel. Then the enamel is dried with light pressure and the brackets are glued with a special paste from the same manufacturer. Then a light curing is performed for 20 seconds.

The third group the brackets are bonded using Tetric N bond Universal (Vivapen).

Teeth were treated with 37 % phosphoric acid for 30 seconds, and then rinsed thoroughly with a stream of water and compressed air for 10 seconds until a uniform chalky appearance appeared. Then, a thin layer of Tetric N bond Universal was applied with a clean brush to the prepared area, and Tetric N bond Universal (Vivapen) adhesive putty was applied to the base of the bracket and glued to the marked area parallel to the length of the longitudinal axis, removing excess adhesive (Table 1). Along the edges of the base of the mount, bearing in mind that the position of the mount does not shift or reposition if necessary, and light cured within 30 seconds.

The fourth group is Tetric N bond Universal (Vivapen).

The same previous steps were performed in the third group, but without acid etching with phosphoric acid and only applying the basic bond while stirring for 5 seconds and then applying a light curing for 30 seconds.

All teeth were preserved after gluing in 4ml of distilled water in closed vessels for 24 hours.

Shear strength test method. Mechanical tests were performed on a standard test machine (Instron Universal Test). When the teeth were attached to the apparatus so that the base of the arch was parallel to the shear force, and with a sharp-end metal blade attached to the movable upper jaw of a mechanical test apparatus, an occlusal shear force was applied at a rate of 1 mm/min, and a shear force was applied, at which adhesion would not occur, and the occlusal force was applied. Recorded in kilograms, then converted to Newtons, then the shear-­resisting adhesion force was calculated according to the following equation: Adhesion shear-­resistance force (MPa = force (newtons)) ÷ arc base area (10.61) square millimeter.

Statistical analysis. Order to study the significant differences in the strength of adhesion and resistance to shear force between the study groups, one-way analysis of variance was used, and the TUKEY test, which is one of the methods of dimensional comparisons, provided that it is significant (F) in the table of analysis of variance and the most accurate to find out the reason for the significant differences If any, among the study groups. Before starting the analysis of variance, it is necessary to make sure of the conditions of the normal distribution of the dependent variable (on all study groups) and also check the homogeneity of the variance among them, where the Anderson-­Darling test and the Leven test were used for each of them, respectively.

Results and discussion

1. Results of the normal distribution test

The results showed that the condition of the normal distribution was fulfilled for all study groups, where the value of the A-D test was estimated, 0,185, 0,105, 0,141, 0,187 with significance (P Value) of about 0,927, 0,85, 0,957, 0,873, all of which are greater than the level of significance (5 %) for groups from the first to the fourth respectively (fig. 1–4).

Fig. 1. Results of the Anderson-Darling normal distribution test group of the Transbond

Fig. 2. Results of the Anderson-Darling normal distribution test group of the Beauty Ortho Bond

Fig. 3. Results of the Anderson-Darling normal distribution test group of the Tetric N bond Universal

Fig. 4. Results of the Anderson-Darling normal distribution test group of the Tetric N bond Universal

2. Results of the heterogeneity test

The results showed the condition of homogeneity of variance was fulfilled between the study groups, where the value of the Leven test was estimated at 0,149 (Fig. 5) (P_Value = 0.26 > 0.05) fig. (5).

Fig. 5. Levene’s test multiple comparison intervals of the deviation

Table 1. Statistical analysis

3. Results of the analysis of variance and Tukey test

The results of the analysis of variance showed that significant differences in the strength of adhesion resistance to shear force between study groups where the value of (F) was estimated at 7.4 and the value of significance was estimated at 0,001 > 0,05 (Table 2).

Table 2. Results of the analysis of variance

The results of the analysis of variance showed the results of the TUKEY test are significant, the difference between the average strength of adhesion resistance to shear strength of the group Ortho BeautyBond (Japan) and the average of the rest of the groups, and that decrease, for example, the difference was estimated at 6,938 between them and the group Transbond XT, with the significance of the differences at the level of significance was established (Table 3 and fig. 6, 7).

Table 3. Tukey tests results Grouping information Using the Tukey Method and 95 % confidence

Fig.6. Difference of means of Transbond, Beauty ortho, Tetric N bond, the fourth group

Fig. 7. 95 % CL for the mean

Conclusion

This study concluded, in the circumstances in which it was conducted, that there are no statistically significant differences when comparing the Universal system with or without etching with the Transbond system. As for the use of Beauty Ortho Bond, it achieved the lowest adhesion force with a statistically significant difference from the rest of the groups, and this could make its use weak in practice, as the acceptable average strength is from 5.9 to 7.8 MPa. The average adhesive force in this study was 5.3 MPa.

About the authors

Hayan Almokaddam

Email: Hayanalmokaddam5@gmail.com
ORCID iD: 0000-0002-5131-8401
Moscow, Russian Federation

Nikolay S. Tuturov

Email: Hayanalmokaddam5@gmail.com
ORCID iD: 0000-0001-8048-5703
SPIN-code: 4892-3880
Moscow, Russian Federation

Imad Katbeh

Author for correspondence.
Email: Hayanalmokaddam5@gmail.com
ORCID iD: 0000-0002-4591-7694
SPIN-code: 8267-2898
Moscow, Russian Federation

References

Supplementary files

Supplementary Files

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1. Fig. 1. Results of the Anderson-Darling normal distribution test group of the Transbond

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2. Fig. 2. Results of the Anderson-Darling normal distribution test group of the Beauty Ortho Bond

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3. Fig. 3. Results of the Anderson-Darling normal distribution test group of the Tetric N bond Universal

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4. Fig. 4. Results of the Anderson-Darling normal distribution test group of the Tetric N bond Universal

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5. Fig. 5. Levene’s test multiple comparison intervals of the deviation

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6. Fig.6. Difference of means of Transbond, Beauty ortho, Tetric N bond, the fourth group

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7. Fig. 7. 95 % CL for the mean

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