Browsing by Subject "Printing, Three-Dimensional"

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    Comparison of guided endodontic access with and without pin fixation in 3D printed teeth with simulated pulp canal obliteration
    (2021-06) Long, Jacob Daniel; Spolnik, Kenneth; Ehrlich, Ygal; Dutra, Vinicius; Bringas, Josef; Warner, Ned
    Introduction: In order to successfully treat an infected root canal system (RCS), it is required to locate all root canals and have an access path to the apex of each canal. This can be challenging in teeth with pulp canal obliteration (PCO), often leading to increased chair time and increased risk of iatrogenic errors. Guided endodontic access (GEA) combines information from a cone-beam computed tomography (CBCT) scan with an intra-oral scan to create a stent. GEA stents with or without fixation pins have been shown to be successful in accurately negotiating a RCS with PCO. Objective: Compare the degree of deviation and difference in 3D offset at the base to apical tip of the drill from the designed access path when a GEA stent with and without pin fixation is used to access tooth #8 with PCO. Materials and Methods: A 3-D printed maxillary model of an anonymous patient had a GEA stent designed using coDiagnonstiX software. The stent extended from tooth #3 to tooth #14 with the guide sleeve over tooth #8. Tooth #8 with no calcification, calcification to the cervical third, and calcification to the middle third of the RCS were designed in the coDiagnostiX software. Tooth #8 will be accessed using a 1.3 mm drill that fits a 1.3 mm sleeve used for both access and pin fixation. 15 of the 30 GEA samples will utilized pin fixation, while the other 15 samples did not utilize pin fixation. Following GEA in all 30 samples a CBCT was taken of each sample. Each post-operative CBCT was aligned with the pre-operative CBCT in the coDiagnostiX software. The coDiagnostiX software was able to calculate the degree of deviation and difference in 3D offset between the base and apical tip of the drill during GEA. Paired t-tests were used to test each group for significant differences in 3D offset between base and tip. Two-way ANOVA was used to evaluate the effects of pin fixation and calcification on the degree of deviation and the deviation of 3D offset of the entry point and tip. Results: There was a significant interaction between use of pin fixation and calcification level on the degree of deviation of GEA. GEA with pin fixation had a significantly larger degree of deviation than GEA without pin fixation with calcification extending to the middle third of the RCS. GEA with and without pin fixation did not have a significant difference when calcification extended to the cervical third of the RCS or no calcification was present. There was a significant interaction between use of pin fixation and calcification level on 3D offset difference. GEA with pin fixation had a significantly larger 3D offset difference than GEA with no pin fixation for calcification in the middle third of the RCS. For GEA with and without pin fixation there was no significant difference when calcification extended to the cervical third of the RCS or no calcification was present. Conclusion: The use of pin fixation did not result in a decrease of degree of deviation or difference in 3D offset during GEA access. It can be concluded that the use of pin fixation is not necessary for GEA of teeth with PCO when a full dentition is present to provide stability and retention of the stent.
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    Effects of a checkpoint kinase inhibitor, AZD7762, on tumor suppression and bone remodeling
    (Spandidos Publications, 2018-09) Wang, Luqi; Wang, Yue; Chen, Andy; Jalali, Aydin; Liu, Shengzhi; Guo, Yunxia; Na, Sungsoo; Nakshatri, Harikrishna; Li, Bai-Yan; Yokota, Hiroki; Biomedical Engineering, School of Engineering and Technology
    Chemotherapy for suppressing tumor growth and metastasis tends to induce various effects on other organs. Using AZD7762, an inhibitor of checkpoint kinase (Chk) 1 and 2, the present study examined its effect on mammary tumor cells in addition to bone cells (osteoclasts, osteoblasts and osteocytes), using monolayer cell cultures and three-dimensional (3D) cell spheroids. The results revealed that AZD7762 blocked the proliferation of 4T1.2 mammary tumor cells and suppressed the development of RAW264.7 pre-osteoclast cells by downregulating nuclear factor of activated T cells cytoplasmic 1. AZD7762 also promoted the mineralization of MC3T3 osteoblast-like cells and 3D bio-printed bone constructs of MLO-A5 osteocyte spheroids. While a Chk1 inhibitor, PD407824, suppressed the proliferation of tumor cells and the differentiation of pre-osteoclasts, its effect on gene expression in osteoblasts was markedly different compared with AZD7762. Western blotting indicated that the stimulating effect of AZD7762 on osteoblast development was associated with the inhibition of Chk2 and the downregulation of cellular tumor antigen p53. The results of the present study indicated that in addition to acting as a tumor suppressor, AZD7762 may prevent bone loss by inhibiting osteoclastogenesis and stimulating osteoblast mineralization.
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    Step-Stress Fatigue, Fracture Toughness and Load to Failure of an Additively Manufactured Ceramic Filled Hybrid Crown Material
    (2024-05) Roberts, Evan; Chu, Tien-Min G.; Platt, Jeffrey; Morton, Dean
    Background: The prevailing trend in dental practice is toward fully digital workflows with additive and subtractive manufacturing. Computer Aided Design Computer Aided Manufacturing (CADCAM) and subtractive manufacturing have led to a proliferation of established restorative materials. In September 2021, the FDA approved Varseosmile Crown Plus, by Bego, for utilization as a permanent crown. This novel composite is the first additive manufactured material to receive approval as a ceramic hybrid for permanent single crowns, inlays, onlays and veneers.[1] The manufacturer categorizes Varseosmile Crown Plus as a ceramic filled hybrid composed of esterification products of 4.4'-isopropylidiphenol, ethoxylated and 2-methylprop-2enoic acid, silanized dental glass.[2] The total content of inorganic fillers (particle size 0.7 μm) is 30 – 50 % by mass.[2] Information published on the mechanical properties of Varseosmile Crown Plus is limited due to its novelty. Hypotheses: There will be no difference in step-stress fatigue on disc specimens, no difference in fracture toughness on bar shaped specimens and no difference in load to failure on tooth shaped specimens between Varseosmile Crown Plus and Vita Enamic. Methods: Two materials were assessed in three tests. Six bars of both materials were utilized to assess fracture toughness following the ISO6872:2015[3] standard. The fracture toughness was assessed utilizing the single edge v-notch beam (SEVNB) in a three-point bending test. Ten samples of each material were used to evaluate the fatigue resistance utilizing the stepwise stress method on disc samples according to ISO6872:2015[3] with a piston-on-three-ball configuration at room temperature under dry conditions. The final material property assessment was load-to-fracture in crown shaped samples adhesively bonded to dentin analogs. A mandibular right first molar (#30) was prepared on a typodont. The preparation was scanned and digitized to make twenty two dentin analogs (NEMA grade G10). A restoration was designed, and eleven crowns were printed or milled from each material. Restorations were bonded to the G10 analog with self-adhesive resin cement. Each crown was axially loaded utilizing a universal testing machine until failure. Results were recorded and compared between groups using two-sample t-tests and Weibull survival analysis. Results: Step-stress fatigue testing revealed Vita Enamic had an average maximum tensile stress of 143.3  12.7 MPa and Varseosmile Crown Plus demonstrated an average maximum tensile stress of 107.5  21.8 MPa. The differences in fatigue failure load (p<0.001), number of loading cycles survived (p<0.001), number of steps survived (p=0.006) and average maximum tensile stress (p<0.001) were all statistically significant between the two materials tested. The fracture toughness testing resulted in an average fracture toughness of 1.343 ± 0.067 MPam for Enamic and 0.878 ± 0.095 MPam for Varseosmile Crown Plus. The difference in fracture toughness between the tested materials was statistically significant (p<.001). The 95% confidence interval for the average KIC value was 1.2735 to 1.4132 MPam for the control and 0.7787 to 0.9771 MPam for the experimental material. The average flexural strength for Varseosmile Crown Plus was 73.619 ± 21.76 MPa. The load to failure testing on crown shaped specimens produced an average failure load of 2342.46 ± 225.46 for Varseosmile Crown Plus and 1871.09 ± 455.07 N for Vita Enamic. Conclusion: A clinical use of Varseosmile Crown Plus should expect a reduction in service life relative to an equivalent restoration of Vita Enamic based on the significantly reduced mechanical properties of fatigue strength and fracture toughness. The load to failure on a crown shaped specimen suggests high initial resistance to compressive force vectors. An established protocol for best practice methods of mixing the composite resin before printing needs to be identified. Once established, the mechanical properties should be re-evaluated, and clinical studies conducted to evaluate for real-world clinical outcomes.