# Compressive Strength Comparison of Different Orthodontic Metal Bracket Systems
## 4 Discussion
[24] bonded Mini Diamond bracket upper lateral brackets to extracted human third molars and measured an average shear bond strength of 20.39 MPa. In contrast, the average bond strength in the Mini Diamond group in our study was 11.73 MPa. These differing bond strength results may be due to [PERSON] et al. 's use of third molars with smaller lateral incisor brackets and shear force testing. Further research is needed to compare both shear and compression strengths of the Mini Diamond bracket. Furthermore, the shear bond strength (SBS) of five different metal brackets bonded to bovine incisor enamel surfaces was compared by [PERSON] et al. [25] using Transbond XT (3M Unitek, Monrovia, CA, USA). They reported an average SBS of 200.60 N, 33.00 MPa for Mini Sprint brackets (Forestat, Pforzheim, Germany). In our study, we used the modified version; Mini Sprint II bracket. Although different debonding methods were applied, and the next generation of the bracket was used, the average values for the Mini Sprint II group in our study were similar, at 318.72 N and 33.18 MPa for the samples that debonded. Additionally, in a study conducted by [PERSON] et al. [26], they found the shear bond strength for the Legend maxillary incisor bracket to be 16.9 MPa, with most samples having an ARI score of 2. In our study, we used the Experience model, a self-ligating metal bracket from the same manufacturer (GC Orthodontics), and found all ARI scores to be 3. The compressive bond strength in samples that resulted in debonding was found to be an average of 56.84 MPa. The differences in our study values appear to be due to the use of compressive force to debond the bracket, as opposed to shear force. Moreover, when we compare our results with the results of [PERSON] et al. [27], all brackets in our study exhibited higher debond/drop values, possibly due to differences in brackets, adhesive systems, and debonding pliers used. The average bond strength for compression debonding with Howpliers was recorded as 80.4 N in [PERSON] et al. [27]. In addition, the average shear bond strengths of BioQuick and Damon Q brackets were examined by [PERSON] et al. [28], with values determined as 16.80 MPa and 19.23 MPa, respectively. [PERSON] et al. [29] found an average tensile strength of 4.52 MPa for the Damon Q group. In our study, only one sample from each of the Damon Q and BioQuick groups resulted in debonding under compression forces. The remaining samples experienced drops due to plastic deformation, so that forceps unable to grip the brackets. The debonded samples exhibited values of 68.21 MPa for the Damon Q group and 20.01 MPa for the BioQuick group. The higher values obtained in our study compared to those of [PERSON] et al. and [PERSON] et al. can be attributed to the partial absorption of isolated compression forces by plastic deformation, resulting in less stress on the bracket-adhesive-enamel system. Despite the numerous studies on bonding strength available in the literature, there is a lack of data regarding the onset of plastic deformation and the yield point in brackets when subjected to the compressive forces encountered during debonding. However, there are multifactorial aspects in the conducted studies that could influence the experiments. Given the different variations in tooth type, bracket type, bracket geometry, test apparatus, cross head speed, type of plier used, and adhesive type in the tests conducted, directly comparing these tests may yield ambiguous results. To mitigate such situations, standardized experimental procedures have been recommended by [PERSON] et al. [30]. In our study, while the primary aim was to determine the yield strength, which marks the onset of plastic deformation of the selected bracket types in the experimental setup, the maximum strength and failure points were also calculated at the end of the experiment.