Forty freshly extracted maxillary first premolars (they were extracted for therapeutic reasons), which were non carious without any cracks and were not fractured, were selected for this study. All the collected teeth were cleaned of blood and saliva and they were stored in a buffered saline solution at room temperature. They were divided into 2 groups of 20 teeth each. In Group A – Ceramic (Transcend series 6000, 3M Unitek) brackets were bonded and in Group B – Stainless steel (Mini Dynalock straight wire metal brackets, 3M Unitek) brackets were bonded [Table/Fig-1].

[Table/Fig-1]:

Brackets used in study. Group A: Transcend 6000 series ceramic bracket Group B: Mini Dynalock Straight wire metal brackets

The bonding procedure: All the extracted teeth were cleaned with a scaler and then with a fine pumice by using a rubber prophylaxis cup on a slow speed conventional hand piece (2000 – 5000 rpm). A 37% phosphoric acid solution was applied to each enamel surface with a disposable foam pellet, for 30 seconds. The teeth were than rinsed with a stream of water for 20 seconds and dried with oil free compressed air for 15 seconds.

A no-mix orthodontic adhesive system was used. The teeth were left at room temperature for 30 minutes to allow full polymerization of the adhesive (chemically activated resin) and they were then stored at room temperature in saline to prevent dehydration before they were tested. Each tooth was held in a mounting jig [Table/Fig-2]. An Instron universal machine was used to perform the debonding tests [Table/Fig-3]. The shear stress at the bond failure was recorded for each bracket and the bond strength was calculated. The statistical analysis of the findings was done and the standard deviation and mean were calculated. The Student’s ‘t’ test was used to compare the mean bond strengths of the two groups.

[Table/Fig-2]:

Mounting of specimen into jig

[Table/Fig-3]:

Instron universal machine to measure shear bond strength

The shear bond strengths of the two groups have been shown in [Table/Fig-4] and [Table/Fig-5]. The mean SBS was significantly higher for the ceramic group (20.68 ± 3.89 MPa) as compared to that of the metal bracket group (12.15 ± 1.32 MPa). Student’s ‘t’ test [Table/Fig-6] and [Table/Fig-7] showed a significant difference in the mean shear bond strengths between the two groups (p < 0.05).

[Table/Fig-7]:

Shear bond strength of ceramic and stainless steel bracke

Aesthetic considerations are of key importance for the patients who undergo orthodontic treatment. Aesthetic orthodontic brackets have been developed to meet this demand of the patients. However, at the same time, other material properties such as the bond strength, the structural integrity, the bonding mechanism etc., have to be considered, in order to meet the clinical requirements.

Metal brackets, though they are aesthetically inferior to ceramic brackets, can be deformed considerably without fracturing, even in the presence of impurities and at sharp intersections [12]. They do not fracture under stress and are available at relatively low costs as compared to the ceramic brackets. Metal brackets, because of their comparative low bond strength, cause minimal enamel damage during debonding [5].

Ceramic brackets bond to the tooth surface by forming both mechanical and chemical bonds. Silanisation of the bracket because of the silane coupling agent is responsible for the chemical bond and it improves the bond strength. Because of a significant increase in the bond strength, the stress of debonding can also be shifted from the bracket – adhesive interface to the adhesive-enamel interface, which is likely to damage the enamel surface during the debonding procedure [13].

In the present study, the shear bond strengths of the ceramic brackets (Transcend series 6000) and the metal brackets (Mini Dynalock brackets) were compared. A minimum of 10 specimens is recommended to perform the SBS testing [14]. However, a sample size which is greater than 10 per group is recommended for the bond strength testing of natural teeth, where variations in the tooth shape exist [15]. The maxillary premolar teeth are the teeth which are most frequently extracted as an integral part of the orthodontic therapy. Therefore, the premolar tooth form was selected to allow a clinical simulation and to compare the outcome of the present study with those of previously reported investigations [9,11].

The mean SBS of the ceramic bracket group was found to be superior as compared to that of the metal bracket group. This finding was in agreement to those of previous studies [6,16,17].

In this study, the Transcend 6000 series ceramic brackets were used. These are different from the original transcend brackets in a very important aspect i.e. these brackets lack the silane primer on the base and therefore, they rely totally on the micromechanical retention. When the Transcend 6000 brackets were debonded, a majority of the adhesive remained on the tooth surface, thus assuring the highest level of protection on the tooth surface.

The Transcend 6000 series brackets are aesthetically superior and they provide a greater bond strength as compared to the metallic brackets.