O Artigo Sobre Tracionamento Ortodontico

Shear bond strength of different attachment devices for traction of impacted teeth

ABSTRACT

In this study, the shear bond strength was verified in two dispositives used for dental traction: a button accessory with a handmade chain and a drop form accessory with a handmade chain. Twenty bovine teeth were utilized and divided into two groups.  Group I: a button accessory with a straight base form (American Orthdontics, Sheboygan, USA) and Group II: a drop form acessory (Aciflex 0 braided – Ethicon, San Angelo, USA). The dispositives were fixed with Transbond XT resin (3M Unitek, Monrovia, Calif, USA). The shear strength was evaluated with a universal assay machine (EMIC DL2000) at a speed of 0.5mm/min. The rupture force was recorded in MPa. Statistical analysis was performed using the Mann-Whitney test. The results demonstrated that the drop form accessory (33.98MPa) presented more shear strength resistance when compared with the button accessory (25.57MPa), however, the difference was not statistically significant p=0.315. Both dispositives showed adequate values of shear bond strenght for clinical application.  The use of the drop form acessory may be an alternative in cases of dental traction, as it demonstrates adequate shear bond strenght, allows complete polymerization of the adhesive material, provides a smoother external surface and is easy and inexpensive to fabricate.  However, more studies are necessary to verify the properties of this material.

Keywords: orthodontic, dental traction, impacted teeth.

                         

INTRODUCTION

Traction of impacted teeth is a conservative procedure that provides satisfactory reestablishment of function, aesthetics and patient self-esteem.1  However, this surgical-orthodontic approach is challenging due to the risk of contamination of the surgical field and to the great variability of materials available.2-5

Over the years, there has been an evolution in the techniques used for this procedure, and a number of factors has been altered, from the use of the drop form handmade acessory and crown perfuration to bonding the orthodontic acessories with chemically polymerization and light polymerization resins. 3,5-7 Direct fixation of acessories has become the preferred choice as it easier to perform and preserves dental and surrounding tissues. 7,8

There is a wide variety of adhesive materials and orthodontic dispositives, including brackets, buttons and accessories.9 Magnetic brackets 10 and hooks for traction 4 are two different alternatives for traction.

Each dispositive has positive aspects and specific limitations, and there is not a consensus among authors as to which orthodontic accessory is the most advantageous.9 Mesh bases have a smaller volume8 and width11, which provides dental traction with less trauma to the tissues.  However, when compared to buttons and brackets, they showed less resistance to traction.9  Buttons and brackets, on the contrary, have a greater volume, which may irritate tissues11, but show improved mechanical properties of retention.9

All dispositives require association with another material (handmade wire chains or elastic chains) to enable dental traction. Therefore, during the application of traction force there is a risk of rupture between the materials.  The use of a single material, e.g. a drop form acessory (Aciflex 0 braided – Ethicon, San Angelo, USA), is one interesting alternative, which is easy and inexpensive to use.    

Thus, the aim of this study was to compare the shear bond strenght of two dispositives: a button with straight base (American Orthdontics®, Sheboygan, USA) and a drop form acessory (Aciflex 0 braided – Ethicon, San Angelo, USA) in an in vitro experiment.

METHODS

The present study was approved by the Scientific and Ethics Committee of the Pontifícia Universidade Católica do Rio Grande do Sul.  Twenty bovine healthy teeth were chosen, the surrounding soft tissues were removed, and the teeth were cut at the cervical level.  Dental crowns with the vestibular face exposed were placed in acrylic tubes (20 mm diameter and 3 cm height) filled with self-cured acrylic resin (Acrylic chemically cured JET - Artigos Odontológicos Clássico, SP, Brasil).

The teeth were randomly divided into two groups with ten specimens each group (Figure 1, 2a and 2b):  

• Group I: button accessory with straight base (American Orthodontics, Sheboygan, USA);
• Group II: a handmade drop form accessory (Aciflex 0 braided – Ethicon, San Angelo, USA).

In both groups, the vestibular surface of the teeth was prepared as follows: prophylaxy at low rotation with a rubber cup and pumice, washing and drying. Then, the dispositives were fixed with Transbond TM XT Light Cure Adhesive resin (3M Unitek, Montrovia, Calif., USA) in the following steps: conditioning with 37% phosphoric acid for 15 seconds, washing and drying; application of the adhesive with a disposable brush; placement of resin on the dispositive and photopolymerization for 20 seconds, with a light cured Optilight Plus (GNATUS dental and medical equipaments Ltda, SP, Brazil).

After fixation, the samples were stored for 24 hours in distilled water at 37oC, after which they were submitted to the test of shear bond strenght in the universal assay machine (EMIC DL 2000) at 0.5 mm/min. Rupture force was expressed as Megapascals (MPa).

        The distribution of data for each group was obtained using the Kolmogorov-Smirnov test. Based on the distribution obtained, the non-parametric Mann-Whitney test was used for comparison between the groups.

RESULTS

In the comparison between groups I and II, greater values of shear bond strenght (MPa) were obtained for Group II. However, this difference was not statistically significant p=0.315 (Table 1).

DISCUSSION

        Among the wide variety of adhesive materials available for the treatment of dental traction, light cured adhesive Transbond TM XT - 3M Unitek was chosen in this experiment (Monrovia, Calif., USA) as it presents satisfactory mechanical properties for fixation of orthodontic accessories11-13 , and is often used as a control in experiments.14-16 Orthodontic buttons for bonding with straight base was chosen as it presents greater shear bond strength than other accessories such as brackets and mesh bases.9 It has a smaller external area than the orthodontic bracket, since it has been observed that the greater the area and salience of the dispositive, the greater the chance of traumatism to surrounding tissues during dental traction.3