Occlusal stress distribution in the human skull with permanent maxillary first molar extraction: A 3-dimensional finite element study.

INTRODUCTION: The objective of this research was to analyze the effect of orthodontic treatment with maxillary permanent first molar extraction on the occlusal stress distribution and displacement in the human skull. METHODS: A 3-dimensional finite element model was constructed on the basis of a computed tomography scan, and it was used as the pretreatment model. The software used for geometric modeling was Solid Works (Dassault Systèmes, Paris, France). For the extraction model, the maxillary permanent first molar was removed, followed by a repositioning of the anterior and posterior segments to create a space closure model. Stress distribution was evaluated under the simulation of 1000 N for occlusal forces and 400 N for masseter muscle force. RESULTS: The highest von Mises stress was observed at the zygomatic process of the temporal bone across all 3 models (25 MPa), whereas stress at the pterygomaxillary suture area was almost 50% less. However, the stress in the pterygomaxillary suture area was lowest in the extraction model (18%) and space closure (30%). Stress in the zygomatic process of the frontal bone and frontal process of the maxilla increased from pretreatment to extraction model followed by space closure model. CONCLUSIONS: The occlusal forces were transferred through maxillonasal, maxillozygomatic, and maxillopterygoid stress trajectories. The mesial displacement of the molars may weaken the role of maxillopterygoid stress trajectory while strengthening the role of maxillonasal stress trajectory.

Comparative assessment of surface irregularities of enamel after bonding with different techniques followed by three composite removal methods: An atomic force microscopic study.

Background: To compare and assess the enamel surface roughness by Atomic Force Microscopy between ceramic and metal brackets after adhesive removal with 3 different methods. Methods: 90 extracted premolars were collected and divided equally into 3 groups G, Y, and R. With group G bonded with metallic brackets (using primer and Transbond XT), group Y with ceramic brackets (primer and Transbond XT), and group R with ceramic brackets (silane and Transbond XT). Each group was subdivided into 3 sub-groups (10 premolars each) based on the resin removal method as A: 12- flute tungsten carbide (TC) bur (high speed), B: 12- flute TC bur (low speed), and C: 30 flute TC bur (low speed). Surface roughness values were calculated and compared before bonding and also after adhesive removal by atomic force microscope (AFM). Measured data were analyzed using paired student t-test, ANOVA, and Tukey's tests. Results: Among the groups, group G showed increased surface roughness after debonding compared to group Y and group R, with Rq value showing a statistically significant difference (P<0.047). Whereas, within the subgroups, subgroup A (12-flute TC, high speed) with Rq showed increased surface roughness which was found to be statistically significant (P<0.042). Conclusion: None of the adhesive removal methods was capable to restore the enamel to its earlier morphology; a statistically significant increase in surface roughness parameters was reported with a high-speed 12 flute TC bur for Rq and Rt.

Evaluation of Aloe vera as matrix metalloproteinase inhibitor in human dentin with and without dentin-bonding agent: An in vitro study.

Background: Proper hybrid layer formation lays the foundation of resin-dentin bonding. The resin infiltration in demineralized dentin collagen couples with the adhesive/resin composites in the mineralized dentin surface. However, the activation of enzymatic activity in the collagen matrix can degrade the hybrid layer. Over the time, it leads to reduced bond strength. Mainly, the enzymes involved are matrix metalloproteinases (MMPs) which are involved in degrading most of the extracellular matrix components. Aloe vera is an herb with an anti-inflammatory effect, but its role in human dentin as an enzyme inhibitor has not been verified yet. Aims: The purpose of the study was designed for evaluating the inhibitory action of Aloe vera on MMP in human dentin with and without dentin bonding agents. Materials and Methods: A total of 15 freshly extracted healthy human teeth were collected and stored at 4°C until use. The roots were separated. The enamel and remnant pulp tissue were removed, and collected teeth were pulverized with liquid nitrogen in the minimum volume of 50-mM phosphate buffer to obtain dentin powder extract. The dentin powder extract is the source of MMPs, and therefore, the extract was treated with A. vera solution and incubated to assess the enzyme inhibition by the plate assay method and zymographic analysis. Results: A. vera treated sample with and without dentin bonding agent showed inhibition of dentin MMP's activity by plate assay method and confirmed by zymogram analysis. Conclusions: A. vera has the potential for inhibiting the MMPs enzyme activity of human dentin collagen with and without dentin bonding agents.