Moshabab A. Asiry

Effect of two-step and one-step surface conditioning of glass ceramic on adhesion strength of orthodontic bracket and effect of thermo-cycling on adhesion strength

PURPOSE The adhesion strength of orthodontic brackets bonded to dental glass ceramics was evaluated after ceramic surface was treated with two-step and one-step surface conditioning systems, and subjecting to thermo-cycling. MATERIALS AND METHOD A total of forty specimens were fabricated from silica based glass ceramic (lithium disilicate) by duplicating the buccal surface of maxillary first premolar. The specimens were randomly assigned to two experimental groups (n = 20), group one specimens were treated with two-step surface conditioning system (IPS ceramic etching gel™ and Monobond plus™) and group two specimens were treated with one-step surface conditioning system (Monobond etch and prime™). The surface roughness of the specimens after treatment with two-step and one-step surface conditioning system was measured using non-contact surface profilometer. Ten randomly selected specimens from each group were subjected to thermo-cycling and the remaining ten served as baseline. The shear bond strength of the specimens was measured using universal material testing machine. The adhesive remnant index score was calculated, and the results of surface roughness and bond strength were tabulated and subjected to analysis of variance and post hoc tukeys test at a significance level of p < 0.05. RESULTS The results of the study showed that the specimens treated with two-step conditioning system had higher surface roughness and bond strength than one-step conditioning system. The majority of the specimens treated with both two-step and one-step conditioned specimens showed adhesive failure after subjecting thermo-cycling. CONCLUSIONS Traditional two-step conditioning provides better bond strength. The clinical importance of the study is that, the silane promoted adhesion significantly reduces on exposure to thermo-cycling.

Efficacy of Yttrium (III) Fluoride Nanoparticles in Orthodontic Bonding

Our study evaluated the adhesion strength and antibacterial effect of a conventional orthodontic composite resin blended with yttrium fluoride (YF₃) nanoparticles. Yttrium fluoride nanoparticles (NP) were added to the conventional orthodontic composite resin (Transbond XT) at concentrations of 1%, 2%, and 3% (w/w), and the blended composite resins were labeled as NP1, NP2, and NP3, respectively. A total of 60 extracted human premolars was randomly allocated to four groups of 15 samples (n = 15). Orthodontic brackets were bonded using the conventional (control) and experimental composite resins (NP1, NP2, and NP3). The adhesion strengths of the composite resins were determined using a universal testing machine. The debonding sites were assessed and scored using the adhesive remnant index (ARI). The antibacterial effect of YF₃ nanoparticles against Streptococcus mutans was assessed by the viable cell counting method. For the same, 40 composite disc specimens were prepared using the control and experimental composite resins (n = 10). The data was analyzed by one-way ANOVA and Tukeys post hoc analysis. In all the tests, the significance level was determined to be 0.05. The highest adhesion strength values were found in the control group (11.61±0.23) and the lowest values were found in the NP3 group (10.49±0.17). A significant difference was observed between the control and experimental groups, NP2 and NP3 (P < 0.05). NP1 group showed insignificant (P = 0.388) adhesion strength values compared with the control group. There was no significant difference between the ARI scores of the conventional and experimental groups (P > 0.05). The highest colony forming units (CFU) were found in the control group (75.85±1.15) and the lowest CFU were found in the NP1 group (2.24±1.14). A significant difference between the mean CFU of the conventional and experimental composite groups was observed (P < 0.05). Despite higher antibacterial activity in the NP1 group compared with NP2 (P = 0.146) and NP3 (P = 0.117), the difference was not significant. Similarly, no significant difference was observed between NP2 and NP3 groups (P = 0.97). Our results suggested that yttrium fluoride nanoparticles, blended with a conventional resin at 1% concentration, demonstrated significant antibacterial effect and did not compromise adhesion strength.

Biological aspects of orthodontic tooth movement: A review of literature

This review of literature describes the cellular and molecular biology of orthodontic tooth movement, including various theories and effect of chemical mediators on tooth movement. The better understanding of the tooth movement mechanism will inspire the clinicians to design and implement effective appliances that will result in maximum benefits and minimum tissue damage to the patients. This paper also emphasizes the applied aspect of different medication and hormones, during orthodontic treatment, on the signaling molecules which produce bone remodeling.