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1.
Clin Oral Investig ; 2021 Jan 28.
Artículo en Inglés | MEDLINE | ID: mdl-33506428

RESUMEN

OBJECTIVES: The aim of this study was, firstly, to analyse the long-time fatigue behaviour of crowns constructed from a novel polyetherketoneketone (PEKK) polymer, using artificial prepared teeth. Secondly, to determine the effect of the material's stiffness that used as an artificial prepared tooth on the fatigue life of the PEKK crowns in comparison to human prepared teeth. METHODS: Veneered crowns with a PEKK framework were constructed on three different prepared teeth: artificial polymethyl methacrylate (PMMA) teeth, artificial CoCr teeth and extracted human teeth. As far as applicable, the loading protocol was based on EN ISO 14801:2007 for fatigue testing of dental implants. After initial static fracture tests on three specimens from each group, the remaining crowns were loaded with different force levels until fracture or until 2 × 106 loading cycles were reached. The number of loading cycles until failure was recorded. Wöhler curves were created to display the fatigue limits. RESULTS: Static fracture limits as well as fatigue limits differed for all three core materials. The static fracture tests resulted in fracture limits of 1200 (± 293) N for the PMMA group, 1330 (± 219) N for the CoCr group and 899 (± 96) N for the human tooth group. Fatigue limits of 770 N, 840 N and 720 N were determined for the PMMA group, CoCr group and human tooth group, respectively. CONCLUSIONS: The determined fatigue limit of above 720 N (depending on the core material) is sufficiently high and a good performance of this crown material is expected in the clinical loading life. The results showed that using artificial teeth instead of natural teeth for fatigue testing of crowns might result in an overestimation of the fatigue limits of the crown material. CLINICAL RELEVANCE: PEKK-made crowns offer a stable and priceworthy treatment for patients, in particular those that suffer from metal allergy.

2.
Dent Mater ; 37(2): 284-295, 2021 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-33358016

RESUMEN

OBJECTIVE: The aim of this interlaboratory round robin test was to prove the robustness of the DIN EN ISO 6872:2019 and to identify the influence of processing and testing variations. METHODS: Each of the 12 laboratories participated (A-L) received 60 (n = 720) assigned zirconia specimens. All participants seperated the specimens from the blanks, sintered them, polished half of all specimens and performed the biaxial flexural test (DIN EN ISO 6872:2019). The surface roughness was determined by using tactile measuring device. Fractographic examination was performed under scanning-electron-microscopy (SEM). Data was analysed using Kolmogorov-Smirnov-, Kruskal-Wallis-, Mann-Whitney-U-test and two-parametric Weibull statistic (p < 0.05). RESULTS: The results for both preparation methods (as-fired and polished) showed significant differences for some participants. The values for as-fired groups ranged between 513 (I) and 659 (E) MPa. H showed higher Weibull modulus than C, E and I. Within polished groups flexural strengths values from 465 (L) to 1212 (E) MPa were observed, with a tendency to clustered groups A, I, J, L (465-689 MPa) and remaining groups (877-1212 MPa). E presented the highest and H the lowest Weibull modulus. Within A and J, no impact of the preparation method on flexural strength values was observed. Within L, as-fired specimens showed higher flexural strength than polished ones. The flexural strength increase did only associate to a certain extent with measured surface roughness. Fractography showed defect populations depending on polishing techniques, associated to the strength level, especially for polished groups. Reduced strength is related to machining defects, regardless of the surface state. SIGNIFICANCE: DIN EN ISO 6872:2019 can be seen as guidance to biaxial flexural strength testing but additional effort is necessary to ensure interlaboratory comparability. Calibrated furnaces and reliable sintering conditions are mandatory requirements together with detailed specifications on finishing or polishing procedures. Biaxial flexural testing is really a matter of understanding specimen preparation, alignment and mechanical testing by itself. DIN EN ISO 6872:2019 should further recommend reporting of mean surface roughness along with any biaxial flexural strength data. Fractography is a mandatory tool in interpretation and understanding of strength data.

3.
Materials (Basel) ; 13(23)2020 Nov 25.
Artículo en Inglés | MEDLINE | ID: mdl-33255839

RESUMEN

Various medicinal plant parts and extracts have been proven to be sources of biologically active compounds, many of which have been incorporated in the production of new pharmaceutical compounds. Thus, the aim of this study was to increase the antimicrobial properties of a glass ionomer cement (GIC) through its modification with a mixture of plant extracts, which were evaluated along with a 0.5% chlorohexidine-modified GIC (CHX-GIC) with regard to the water sorption, solubility, and flexural strength. Methods:Salvadora persica, Olea europaea, and Ficus carcia leaves were prepared for extraction with ethyll alcohol using a Soxhlet extractor for 12 h. The plant extract mixture (PE) was added in three different concentrations to the water used for preparation of a conventional freeze-dried GIC (groups 1:1, 2:1, and 1:2). Specimens were then mixed according to the manufacturer's instructions and tested against the unmodified GIC (control) and a GIC modified with 0.5% chlorhexidine. Water sorption and solubility were evaluated after 7 days of immersion in distilled water. Flexural strength was evaluated in a three-point bending test after 24 h using a universal material testing machine at a crosshead speed of 1 mm/min. One-way analysis of variance (ANOVA) was used for comparison between the groups. Tukey's post hoc test was used for pairwise comparison when the ANOVA test was significant. Results: There were no statistically significant differences between the control (M = 20.5%), CHX-GIC (M = 19.6%), 1:1 (M = 20.0%), 1:2 (M = 19.5%), and 2:1 (19.7%) groups with regard to the percentage of water sorption, while for water solubility the 2:1 (M = -0.39%) plant-modified group was significantly different from all of the other groups. Flexural strength test results showed that the 2:1 group (M = 26.1 MPa) recorded significantly higher mean values compared to all other tested groups. Conclusion and clinical relevance: The plant extracts did not negatively affect the water sorption and solubility of the GIC, while the flexural strength was improved by the addition of the plant extract at higher concentrations.

4.
J Orofac Orthop ; 2020 Dec 02.
Artículo en Inglés | MEDLINE | ID: mdl-33263771

RESUMEN

OBJECTIVE: The goal was to measure and compare the amount of force loss during tooth movement guided by archwires, including a newly introduced low-friction titanium molybdenum alloy (TMA), conventional TMA, and stainless steel archwires. METHODS: The force loss was measured using a specialized biomechanical set-up, the orthodontic measurement and simulation system (OMSS). A total of 30 specimen were used (10 low-friction TMA (TMA-Low), 10 conventional TMA (TMA-C), and 10 stainless steel (SS) archwires, each having a dimension of 0.016â€¯× 0.022 inches). The conventional and low friction TMA archwires served as test groups, while the SS archwires served as the control group. RESULTS: The mean values of force loss between the three types of wires (TMA­C, TMA-Low, and SS) were significantly different (p < 0.0001). The highest mean force loss during sliding movement was found in the conventional TMA group (72.1%), followed by low friction TMA (48.8%) and stainless steel wires (33.7%) in a descending order. CONCLUSION: The friction property of the low friction TMA archwire was superior to the conventional TMA archwire but was still inferior to the stainless steel archwire.

5.
Artículo en Inglés | MEDLINE | ID: mdl-33136452

RESUMEN

The paper is concerned with simulation of the periodontal ligament response to force in the initial phase of orthodontic tooth movement. This is based on two previous investigations, a in vitro experiment with specimens of porcine mandibular premolars and a in vivo experiment on human upper first incisors. For the curve fit of the in vitro experiment a model function, assuming viscoelasticity, was introduced. The viscoelastic model function was augmented by a ramp rise time term, to account for observed dependence of the response on actuator velocity, and a previous load history term, to account for the effect of the previous tests on the current test. The correlation coefficient of a curve fit for all tests grouped together was R 2 = 0.98 . Next, a curve fit of the in vivo experiment was done. Good correlation was found for a simplified model function, without viscoelastic term ( R 2 = 0.96 ). For both tests, in vitro and in vivo, the ramp rise time term improved correlation. A finite element model of the specimen of the in vitro experiment was created. For the PDL a hyperelastic constitutive model for compressible material was used and model parameters were identified. The present work indicates that the macroscopic response of the periodontal ligament to an external load can be simulated with a poro-visco-hyperelastic model. The simulation showed that poroelastic behaviour will gradually cease when viscoelastic relaxation progresses. This followed also from dimensionless analysis. As a consequence, for slow loading, or if initial response to fast loading is not of interest, a visco-hyperelastic model may suffice. To identify parameters of the finite element model several optimisation problems were solved. A model function, which can be regarded as a reduced order model, allowed a full factorial experiment (analysis) at low cost, to identify initial parameters. The thus found parameters were further refined with an optimum interpolation meta-model. That is, for limited number of parameter combinations the response was simulated with the finite element model and a refined parameter study was conducted by means of optimal interpolation. The thus found optimal parameters were verified by simulation with the finite element model. Optimal interpolation is computationally cheap, which allowed full factorial experiments at low cost.

6.
J Mater Sci Mater Med ; 31(12): 116, 2020 Nov 28.
Artículo en Inglés | MEDLINE | ID: mdl-33247427

RESUMEN

Literature lacks sufficient data regarding addition of natural antibacterial agents to glass ionomer cement (GICs). Hence, the aim of the study was to increase the antimicrobial properties of GICs through its modification with mixture of plant extracts to be evaluated along with an 0.5% chlorohexidine-modified GIC (CHX-GIC) with regard to biological and compressive strength properties. Conventional GIC (freeze-dried version) and CHX were used. Alcoholic extract of Salvadora persica, Olea europaea, and Ficus carcia leaves were prepared using a Soxhlet extractor for 12 h. The plant extract mixture (PE) was added in three different proportions to the water used for preparation of the dental cement (Group 1:1 PE, 2:1 PE, and 1:2 PE). Specimens were then prepared and tested against the unmodified GIC (control) and the 0.5% CHX-GIC. Chemical analysis of the extract mixture was performed using Gas chromatography-mass spectrometry. Antimicrobial activity was evaluated using agar diffusion assay against Micrococcus luteus and Streptoccocus mutans. Compressive strength was evaluated according to ISO 9917-1:2007 using a Zwick testing machine at a crosshead speed of 0.5 mm/min. Antimicrobial activity against Streptoccocus mutans was significantly increased for all the extract-modified materials compared to the unmodified cement, and the highest concentration was comparable to the CHX-GIC mixture. The activity against Micrococcus luteus was also significantly increased, but only for the material with the highest extract concentration, and here the CHX-GIC group showed statistically the highest antimicrobial activity. Compressive strength results revealed that there was no statistically significant difference between the different mixtures and the control except for the highest tested concentration that showed the highest mean values. The plant extracts (PEs) enhanced the antimicrobial activity against S. mutans and also against M. luteus in the higher concentration while compressive strength was improved by addition of the PE at higher concentrations.

7.
J Mech Behav Biomed Mater ; 111: 103985, 2020 11.
Artículo en Inglés | MEDLINE | ID: mdl-32861207

RESUMEN

Bilateral sagittal split osteotomy is one of the most frequently performed operations in orthognathic surgery. The health of the temporomandibular joint (TMJ) is an important prerequisite for its functionality. The aim of this finite element study was to assess the developed stresses during mouth opening after bilateral sagittal split osteotomy. Different osteotomy gap widths and disc positions were evaluated. Computed tomography and magnetic resonance data of a dentulous cadaver head were used in order to create two finite element models simulating split distances of 5 and 10 mm, respectively. The fixation of the distal and proximal segments was made by a four- or a six-hole titanium mini plate and four monocortical screws respectively. For both models, three different situations of the articular disc were created: a physiological disc position, anterior disc displacement and posterior disc displacement. The mandible was vertically displaced in the midline in order to simulate a mouth opening of 20 mm. The simulation showed high stresses in the area of the titanium plates (up to 850 MPa), implying an increased risk of material failure. High stresses were found within the discs in the models with normal disc position and anterior disc displacement as well (up to 8 MPa), indicating a higher risk of developing craniomandibular disorders. Regarding the stresses within the fixation screws, the highest values were recorded in the area of the upper thread. The degree of mandibular advancement after a bilateral sagittal split osteotomy affects the stress balance in the mandible and the articular discs during mouth opening.

8.
Restor Dent Endod ; 45(3): e32, 2020 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-32839713

RESUMEN

Objectives: To evaluate the polymerization efficiency of a matrix-modified bulk-fill composite, and compare it to a conventional composite which has a similar filler system. The degree of conversion (DC%) and monomer elution were measured over different storage periods. Additionally, fillers' content was examined. Materials and Methods: Cylindrical specimens were prepared, in bulk and incrementally, from Filtek Bulk Fill (B) and Filtek Supreme XTE (S) composites using a Teflon mold, for each test (n = 6). Using attenuated total reflection method of Fourier transformation infrared spectroscopy, DC% was measured after 24 hours, 7 days, and 30 days. Using high-performance liquid chromatography, elution of hydroxyethyl methacrylate, triethylene glycol dimethacrylate, urethane dimethacrylate, and bisphenol-A glycidyl dimethacrylate was measured after 24 hours, 7 days and 30 days. Filler content was examined by scanning electron microscopy (SEM). Data were analyzed using 2-way mixed-model analysis of variance (α = 0.05). Results: There was no significant difference in DC% over different storage periods between B-bulk and S-incremental. Higher monomer elution was detected significantly from S than B. The elution quantity and rate varied significantly over storage periods and between different monomers. SEM images showed differences in fillers' sizes and agglomeration between both materials. Conclusions: Matrix-modified bulk-fill composites could be packed and cured in bulk with polymerization efficiency similar to conventional composites.

9.
Int J Comput Dent ; 23(3): 211-218, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32789308

RESUMEN

AIM: To assess the accuracy of DigiBrain4, Inc (DB4) Dental Classifier and DB4 Smart Search Engine* in recognizing, categorizing, and classifying dental visual assets as compared with Google Search Engine, one of the largest publicly available search engines and the largest data repository. MATERIALS AND METHODS: Dental visual assets were collected and labeled according to type, category, class, and modifiers. These dental visual assets contained radiographs and clinical images of patients' teeth and occlusion from different angles of view. A modified SqueezeNet architecture was implemented using the TensorFlow r1.10 framework. The model was trained using two NVIDIA Volta graphics processing units (GPUs). A program was built to search Google Images, using Chrome driver (Google web driver) and submit the returned images to the DB4 Dental Classifier and DB4 Smart Search Engine. The categorical accuracy of the DB4 Dental Classifier and DB4 Smart Search Engine in recognizing, categorizing, and classifying dental visual assets was then compared with that of Google Search Engine. RESULTS: The categorical accuracy achieved using the DB4 Smart Search Engine for searching dental visual assets was 0.93, whereas that achieved using Google Search Engine was 0.32. CONCLUSION: The current DB4 Dental Classifier and DB4 Smart Search Engine application and add-on have proved to be accurate in recognizing, categorizing, and classifying dental visual assets. The search engine was able to label images and reject non-relevant results.


Asunto(s)
Redes Neurales de la Computación , Motor de Búsqueda , Humanos
10.
Int J Comput Dent ; 23(3): 245-255, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32789312

RESUMEN

AIM: The aim of the present study was to evaluate the number, strength, and position of occlusal contacts shown using an intraoral scanner (IOS) and a digital occlusal analysis system (T-Scan) compared with the current gold standard using occlusal foil (OF). MATERIALS AND METHODS: Occlusal contacts were analyzed for 70 volunteers using OF in maximum intercuspation (MI). The contact points obtained using the IOS were evaluated using a screenshot from Zirkonzahn.Modellier CAD software. Finally, the volunteers were asked to bite on the sensor sheet of the T-Scan system. For the evaluation of these data, the contact points of the OF and the IOS were graded as light, medium, and strong. Furthermore, the positions of the contact points were analyzed for the anterior region (premolars and molars). Parametric statistical tests were applied to analyze the differences among the three methods. RESULTS: The mean number of all contact points was similar: 29 ± 8 with the OF, 30 ± 12 with the IOS, and 24 ± 10 with the T-Scan. However, results were different in terms of the grading of the strength of contact points: mean number of light contacts: 8 ± 4 OF vs 17 ± 8 IOS and 17 ± 6 T-Scan; medium contacts: 12 ± 5 OF vs 8 ± 4 IOS and 5 ± 4 T-Scan; and strong contacts: 9 ± 5 OF vs 6 ± 6 IOS and 4 ± 2 T-Scan. The positions of the occlusal contact points were also different. CONCLUSION: The data sets showed that there were differences in the distribution of occlusal contact points evaluated using the OF, the IOS, and the T-Scan system. Although the number of detected occlusal contacts was similar, different occlusal contact protocols were determined by the three different methods.


Asunto(s)
Oclusión Dental , Diente Molar , Diente Premolar , Humanos , Programas Informáticos
12.
Dent J (Basel) ; 8(3)2020 Jul 17.
Artículo en Inglés | MEDLINE | ID: mdl-32709056

RESUMEN

This study compared two resin composites with similar filler systems and different matrix compositions. The depth of cure (DoC), polymerization shrinkage, and marginal leakage were evaluated. A Filtek Bulk Fill resin composite (FB) and a Filtek Supreme resin composite (FS) were used. For the DoC and polymerization shrinkage, cylindrical specimens with different thicknesses were prepared. The DoC was attributed to the bottom/top ratios of Vickers microhardness numbers. For polymerization shrinkage, each specimen was firstly scanned using micro-computed tomography (µCT) then cured for 20 s, then for 10 s, and then for 10 s, and they were rescanned between each curing time. Data were processed using the Mimics software. For marginal leakage, standardized 5 mm cavities were prepared in 90 molars. After etching and bonding, materials were packed according to groups: FB-bulk, FB-incremental, and FS-incremental, which were cured for 20, 30, and 40 s, respectively. After thermo-cycling, teeth were stored in 1% methylene blue dye for 24 h and then sectioned and observed for dye penetration. The results showed insignificant differences in the shrinkage and leakage between the different packing techniques and curing times of both materials. In conclusion, the introduction of a novel matrix into resin composite composition enabled bulk-filling in one layer up to 5 mm deep while keeping a tolerable polymerization shrinkage.

13.
Z Orthop Unfall ; 2020 Jul 23.
Artículo en Inglés | MEDLINE | ID: mdl-32702758

RESUMEN

As the percentage of overweight individuals in the population rises, diseases associated with excess weight resulting from poor nutrition are becoming more and more widespread. So far, the influence of weight or nutrition on bone health has shown conflicting results. In the literature, the existing studies disagree about the effect of diet on bones. Therefore, this study investigated the impact of a long-term, high-fat, and high-cholesterol diet on the spine in a mouse model. Wild-type mice were randomly separated into two groups; one group received a high-fat and high-cholesterol diet, and a control group was fed with a regular diet since birth for a duration of 8 months. The first to fifth thoracic vertebrae were extracted and investigated using histology and micro-CT. Samples were analyzed regarding different parameters: percentage of bone structure compared to the whole vertebra and the amount and thickness of the trabeculae. Both methods of the analysis showed similar results. Diet did not have a significant impact on the bone density of the vertebrae. The micro-CT examination showed that the average bone percentage of the examined vertebra was 6% (p = 0.2330) higher in the control group compared to the diet group. The same tendency was demonstrated in histology even though with a smaller difference of only 5%. The results of both methods were comparable and showed trends for the influence of different diets but not significant impacts. In summary, this study showed that a high-fat and high-cholesterol diet has a slightly negative impact on bone density. In order to further analyze the effects of different diets on bone composition, structure, and density, additional long-term studies should be carried out, and more parameters such as movement and genetic factors should be analyzed. Furthermore, other parameters such as exercise and genetic factors that could have a secondary influence on obesity should be investigated.

14.
J Orofac Orthop ; 81(1): 30-40, 2020 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-31834419

RESUMEN

AIM: Precise bonding of attachments in aligner treatment is crucial to achieve the intended tooth movement. Thus, we evaluated five different bonding protocols for attachments used in aligner treatments with the goal of identifying the most precise protocol. METHODS: One ellipsoid and one rectangular attachment were exemplarily chosen and examined. All attachments were bonded using the same template aligner, which was produced by thermoforming. The bonding process was repeated 30 times with each protocol for statistical analysis. The protocols differed in the type of composite used (high viscous, low viscous), the additional application of a perforation in the attachment reservoir, and the use of a two-phase procedure with high viscous composite. All bonded attachments were laser scanned and compared to the attachments of a master model using a surface/surface matching algorithm to determine the precision, i.e., highest aberrations (maximum vertical distance) between the attachment of the master and results obtained from the various bonding protocols. Furthermore, the excessive amounts of composite bonded around the attachments were measured and compared. RESULTS: The two-phase procedure had a median aberration of 0.13 mm and a median amount of excessive composite of 7.40 mm2 (ellipsoid attachment). With the low viscous composite without a perforation in the template reservoir, similar results were achieved (median 0.13 mm) regarding the maximum vertical distance, but had an excess area of 33.50 mm2. CONCLUSION: In this in vitro study, the bonding protocol influenced the precision of bonded attachments. The bonding protocol with high viscous composite without a perforation in the attachment reservoir was the most inaccurate. The use of a low viscous composite or attachments made by a two-phase procedure with high viscous composite revealed more precise results.


Asunto(s)
Recubrimiento Dental Adhesivo , Diente , Técnicas de Movimiento Dental
15.
Orthod Craniofac Res ; 22 Suppl 1: 62-68, 2019 May.
Artículo en Inglés | MEDLINE | ID: mdl-31074156

RESUMEN

OBJECTIVE: To assess validity and reliability of palatal superimposition of holograms of 3D digital dental models using a customized software, (Ortho Mechanics Sequential Analyzer OMSA), installed on Microsoft HoloLens device as compared to the OMSA application running on a regular computer screen. METHODS: The sample consisted of pre- and post-treatment digital maxillary dental models of 20 orthodontic cases (12.3 ± 1.9 years) treated by rapid maxillary expansion (two turns per day). For each case, the pre- and post-treatment digital models were superimposed using hand gestures for marking the dental models holograms in mixed reality using the Microsoft HoloLens. The same models were then superimposed using the conventional landmark-based method with OMSA software running on a regular computer screen. The same set of dental arch parameters was measured on the superimposed 3D data by the two software versions for comparison. Agreement in the superimposition outcomes among the two superimposition methods was assessed using Dahlberg error (DE), concordance correlation coefficients (CCCs) using two-way ANOVA mixed model for absolute agreement and Bland-Altman analysis. RESULTS: Repeatability was acceptable for all variables based on the high values of CCCs over 0.99 with a lower 95% confidence limit over 0.95 for any variable. The DE ranged from 0.14 mm to 0.36 mm. The absolute error did not exceed 0.5 mm for any variable. CONCLUSION: Using the depth vision capabilities of the Microsoft HoloLens, 3D digital dental models can be reliably superimposed allowing virtual assessment of orthodontic treatment outcomes.


Asunto(s)
Modelos Dentales , Imagenología Tridimensional , Arco Dental , Maxilar , Reproducibilidad de los Resultados
16.
J Orofac Orthop ; 80(4): 184-193, 2019 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-31139844

RESUMEN

AIMS: To reduce remaining plaque niches due to dental malocclusion after periodontal treatment and to avoid reinflammation of periodontitis, severe anterior crowding can be treated orthodontically. The treatment indication is motivated by aesthetic and functional needs. In this study the biomechanical behaviour of crowded lower front teeth in reduced periodontium is analysed. METHODS: Using the finite element (FE) method, a model of the mandible was constructed with an anterior crowding of 4 mm and a vertical bone loss of 4 mm in the front tooth area. A 0.3 mm (0.012″) round superelastic nickel titanium (NiTi) arch wire was fitted to an ideal positioned teeth set-up and was inserted into the brackets of teeth 34 to 44 in the crowded model. The premolars were used as the anchorage unit. Material parameters were adopted from previous investigations, including bone (homogenous, isotropic, E = 2 GPa), teeth (E = 20 GPa) and healthy periodontal ligament (PDL, bilinear elastic; E1 = 0.05 MPa; E2 = 0.2 MPa; ε12 = 7%). All simulations were compared to simulations with a physiological periodontal model to assess the effect of bone loss at teeth 42 to 32. Additionally, the influence of three arch wire materials (nonsuperelastic NiTi, superelastic NiTi and stainless steel) were analysed in a reduced model, including only brackets in position of the crowded front teeth, wire and ligatures. Wire force levels and stresses were determined to assess the influence of material variation. RESULTS: Initial tooth mobility is increased by a factor of 2.5 in case of a moderate periodontal defect. Front teeth with reduced attachment display increased strains in the periodontal ligament up to a factor of 2. Forces in the model with reduced periodontium were decreased by a factor of 2. Comparing different aligning arch wires, stainless steel appears to have the highest force and stress levels. Force levels of this alloy were 7.5 times higher than with the superelastic NiTi wire. Force levels of nonsuperelastic NiTi appeared to be 1.8 times higher than superelastic NiTi. Calculated stresses with stainless steel were 5 times higher than with the nonsuperelastic NiTi and 10 times higher than with superelastic NiTi. CONCLUSION: Periodontally reduced incisors 42 to 32 are associated with an increased load on periodontal tissue and increased level of tooth mobility during fixed orthodontic treatment. This has to be considered by reducing orthodontic force levels and by selecting mechanics that reduce the load to the tissue.


Asunto(s)
Maloclusión , Soportes Ortodóncicos , Estética Dental , Análisis de Elementos Finitos , Humanos , Incisivo , Mandíbula , Alambres para Ortodoncia , Titanio , Técnicas de Movimiento Dental
17.
Biomed Tech (Berl) ; 64(5): 555-562, 2019 Sep 25.
Artículo en Inglés | MEDLINE | ID: mdl-30875315

RESUMEN

The aim of this study was to investigate the retention forces of secondary telescopic crowns made of polyetherketoneketone (PEKK) in combination with primary crowns made of four different dental alloys and to determine whether the retention forces change in the course of up to 5000 simulated wear cycles. A total of four groups of telescopic crowns were investigated: group 1: 10 primary crowns made of a gold alloy (NEOCAST®3), group 2: 10 primary crowns made of a non-precious metal alloy (Girobond NB), group 3: 10 primary crowns made of zirconium (Cercon®base) and group 4: 10 primary crowns made from PEKK (Pekkton®ivory). The corresponding secondary crowns were made from PEKK in all the four groups. Each pair was fixed axially in a wear simulator specifically designed for the study. Overall, 10,000 joining and separating cycles were performed for each group. To simulate intraoral conditions, a saliva substitute served as a lubricant. Force transducers were used to record the retention forces and after completing 10,000 cycles, the surface of each primary crown was examined using a scanning electron microscope (SEM). All groups showed an increase in the retention force for the first 2000 cycles which stayed constant for the remaining 8000 cycles. The Pekkton®ivory/Pekkton®ivory and NEOCAST®3/Pekkton®ivory combinations displayed mean retention force values of 16 N after a slight increase in the retention force. The Cercon®base/Pekkton®ivory and Girobond NB/Pekkton®ivory combinations displayed an initially high increase in the retention force and then showed a mean retention force of up to 29 N. All primary crowns displayed surface wear. Zirconium primary crowns showed the least wear compared to PEKK and the gold and non-precious metal alloys.


Asunto(s)
Análisis del Estrés Dental/instrumentación , Aleaciones de Oro/química , Coronas , Aleaciones Dentales , Humanos , Circonio
18.
J Orofac Orthop ; 80(2): 68-78, 2019 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-30758513

RESUMEN

AIMS: The aim of this study was to compare force loss due to friction (Fr) during simulated canine retraction using different archwire dimensions and materials between conventional and new self-ligating brackets. METHODS: The tested brackets were (1) conventional brackets (Victory series, GAC twin and FLI twin), (2) self-ligating brackets (Damon-Q, FLI-SL, new/improved FLI-SL (I FLI-SL), SPEED, GAC innovation (R) and Ortho Classic) and (3) a low-friction bracket (Synergy). All brackets had a 0.022″ slot size. The tested archwires were stainless steel (0.018″; 0.016″x0.022″; 0.017″x0.025″; 0.018″x0.025″ and 0.019″x0.025″); nickel titanium (NiTi; 0.016″x0.022″; 0.017″x0.025″; 0.018″x0.025″ and 0.019″x0.025″) and titanium molybdenum alloy (TMA; 0.016″x0.022″; 0.017″x0.025″; 0.018″x0.025″ and 0.019″x0.025″). Canine retraction was experimentally simulated in a biomechanical set-up using a NiTi coil spring that delivered a force of 1 N. The simulated retraction path was up to 4 mm. Force loss due to friction was compared between groups using the Welch t­test. RESULTS: Force loss due to friction increased with increasing archwire size. Also, TMA showed the highest and stainless steel the lowest force loss due to friction. FLI-SL brackets showed the lowest Fr (31%) and Ortho Classic showed the highest (67%). CONCLUSIONS: Increasing wire size generally showed increasing force loss due to friction. FLI-SL brackets showed the lowest, while Ortho Classic showed the highest friction.


Asunto(s)
Diente Canino , Soportes Ortodóncicos , Alambres para Ortodoncia , Técnicas de Movimiento Dental/instrumentación , Análisis del Estrés Dental , Fricción , Humanos , Estrés Mecánico
19.
Ann Anat ; 222: 146-152, 2019 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-30599239

RESUMEN

The formation of the alveolar bone, which houses the dental primordia, and later the roots of tooth, may serve as a model to approach general questions of alveolar bone formation. In this respect, this study aimed to investigate the potential interactions between the alveolar bone formation and tooth eruption by using finite element (FE) methods, and to figure out whether the expanding tooth systems induce shear stresses that lead to alveolar bone formation. 3D geometric surface models were generated from the 3D histological data of the heads of mice (C57 Bl/6J) ranging from stages embryonic (E) to postnatal (P) stages E15 to P20 using the reconstruction software 3-Matic. Bone, dentin, enamel and dental follicle around the primordia were generated and converted into 3D FE models. Models were imported into the FE software package MSC.Marc/Mentat. As material parameters of embryonic dentine, pulp, enamel, dental follicle, and bony structures basically are unknown, these were varied from 1% to 100% of the corresponding known material parameters for humans and a sensitivity analysis was performed. Surface loads were applied to the outside surface of dental follicle ranging from 0.1 to 5.0N/mm2. The validity of the model was analysed by comparing the activity pattern of the alveolar bone as determined in the histological study with the loading pattern from the numerical analysis. The results show that when varying the surface loads, the distribution of shear stresses remained same, and while varying the material properties of the hard tissues, the location of highest shear stresses remained stable. Comparison of the histologically determined growth regions with the distribution of shear stresses computed in the numerical model showed a very close agreement. The results provide a strong proof to support Blechschmidt's hypothesis that the bone in general is created under the influence of shear forces.


Asunto(s)
Desarrollo Óseo/fisiología , Mandíbula/crecimiento & desarrollo , Diente Molar/crecimiento & desarrollo , Adulto , Proceso Alveolar/crecimiento & desarrollo , Animales , Animales Recién Nacidos , Esmalte Dental/crecimiento & desarrollo , Pulpa Dental/crecimiento & desarrollo , Saco Dental/crecimiento & desarrollo , Dentina/crecimiento & desarrollo , Femenino , Análisis de Elementos Finitos , Humanos , Imagenología Tridimensional , Mandíbula/embriología , Ratones , Ratones Endogámicos C57BL , Diente Molar/embriología , Embarazo , Erupción Dental
20.
Int J Rheum Dis ; 22(4): 636-645, 2019 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-30666791

RESUMEN

INTRODUCTION: The subject of the present study was a systematic comparative analysis of the rheumatoid arthritis (RA)-induced pathomechanisms in the temporomandibular joint with those of the limb joints using the serum-induced arthritis K/BxN model. METHODS: In 18 BALB/c mice the induction of RA was performed according to the Kouskoff method. Another healthy cohort served as controls (n = 12). Joint swelling of the paws was measured using a micrometer. Functional data were obtained analyzing locomotion. Three-dimensional examination of the temporomandibular joint was performed with micro-computed tomography imaging, followed by histological evaluation of the extremity joints and the temporomandibular joint. Additionally, immunohistochemical investigations were carried out to evaluate inflammatory and immunological changes. RESULTS: Measurement of joint swelling showed a significant increase in the diameter of the paws, as well as a decrease in locomotor activity compared to control animals and the time before arthritis induction. Histological and immunohistochemical investigations showed clear signs of inflammation in the extremity joints. In contrast, no histological or immunohistochemical indications of an inflammatory process were detectable in the temporomandibular joint. In addition, the three-dimensional analysis by micro-computed tomography of the temporomandibular joints did not show any obvious morphological changes. CONCLUSION: For the first time, using the K/BxN model we could demonstrate that, due to its anatomical and mechanical conditions, the temporomandibular joint seems to be less susceptible to the initiation of RA compared to limb joints. Therefore, additional investigations are needed on other arthritis models as well, in order to further improve our understanding of the pathogenesis and defense mechanisms of the disease.


Asunto(s)
Artritis Experimental/fisiopatología , Articulaciones del Pie/fisiopatología , Locomoción , Articulación Temporomandibular/fisiopatología , Animales , Artritis Experimental/sangre , Artritis Experimental/diagnóstico por imagen , Artritis Experimental/inmunología , Autoanticuerpos/sangre , Autoanticuerpos/inmunología , Citocinas/sangre , Citocinas/inmunología , Articulaciones del Pie/diagnóstico por imagen , Articulaciones del Pie/inmunología , Glucosa-6-Fosfato Isomerasa/inmunología , Inmunohistoquímica , Ratones Endogámicos BALB C , Articulación Temporomandibular/diagnóstico por imagen , Articulación Temporomandibular/inmunología , Microtomografía por Rayos X
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