Mechanical and numerical investigations of biodegradable magnesium alloy screws for fracture treatment.

Small fracture treatment includes the use of so-called "Herbert screws". In the past years, novel resorbable materials were introduced as an alternative to the classical titanium implants. The purpose of this study was to evaluate the influence of ongoing resorption/corrosion processes on the mechanical stability screws made from the magnesium alloy MgYREZr®. Our samples consisted of two partly resorbed screws, explanted due to medical reasons after 6 and 12 weeks, respectively, and five unused reference screws. We performed three-point bending tests to determine the stability of all screws. Additionally, with FE-models of the screws based on µCT-scans, we investigated whether any differences in the bending behavior of the screws can be attributed to the reduction of the material volume due to resorption alone. Both partly resorbed screws failed at a lower force than the reference screws (178.6 ± 5.5 N for the reference screws, 72.5 N and 74.5 N for the screw explanted after 6 and 12 weeks, respectively). FE simulations performed with the three different geometries and original material parameters (Young's modulus Enew  = 45 GPa, yield limit σnew  = 235 MPa) showed that the early fracture could not be attributed to the changed geometry alone. Material parameters for the partly resorbed screws were determined by fitting the numerical to the experimental force-displacement curves (E6week  = 15 GPa, σ6week  = 135 MPa and E12week  = 8 GPa, σ12week  = 135 MPa, respectively). Our results showed that both geometry of the screws and different material properties contribute to the overall stability. Understanding and controlling these two factors throughout the resorption process could enhance treatment options.

Variation of the modulus of elasticity of aligner foil sheet materials due to thermoforming.

OBJECTIVE: Investigate and compare the mechanical properties of different aligner materials before and after deep drawing and determine differences in the mechanical properties after thermoforming. MATERIALS AND METHODS: Four aligner film sheets from three manufacturers (Duran Plus® [Scheu Dental, Iserlohn, Germany]; Zendura® [ClearCorrect, Bay Materials LLC, Fremont, CA, USA]; Essix ACE® and Essix® PLUS™ [Dentsply Sirona Deutschland, Bensheim, Germany]) were tested in 3­point bending with support distances of 8, 16, and 24 mm. Dimension of the specimens was 10â€¯× 50 mm2. Two groups each were tested: (1) 10 specimens were investigated in the as-received state (before thermoforming), (2) 10 specimens were deep drawn on a master plate with cuboids of the dimension 10â€¯× 10â€¯× 50 mm3. Then, specimens were cut out of the upper side and lateral walls and were measured in 3­point bending. Forces and reduction in thickness were measured and corrected theoretical forces of drawn sheets after thickness reduction as well as Young's modulus were calculated. RESULTS: At a support distance of 8 mm and a displacement of 0.25 mm Essix® PLUS™, having the highest thickness in untreated state, showed highest forces of 28.2 N, followed by Duran Plus® (27.3 N), Essix ACE® (21.0 N) and Zendura® (19.7 N). Similar results were registered for the other distances (16, 24 mm). Thermoforming drastically reduced thickness and forces in the bending tests. Forces decreased to around 10% or less for specimens cut from the lateral walls. Young's modulus decreased significantly for deep drawn foil sheets, especially for Essix® PLUS™. CONCLUSIONS: Three-point bending is an appropriate method to compare different foil sheet materials. Young's modulus is significantly affected by thermoforming.

Numerical and biomechanical analysis of orthodontic treatment of recovered periodontally compromised patients.

OBJECTIVE: Generate a finite element (FE) model to simulate space closure and retraction mechanics for anterior maxillary teeth in periodontally compromised dentition, and compare the biomechanical effect of initial force systems with varying magnitude. MATERIALS AND METHODS: The geometry of an idealized finite element model (FEM) of a maxilla was adapted such that the teeth showed reduced periodontal support together with extruded and flared incisors. In a first step, leveling and alignment of the front teeth were simulated. In a second step, force systems for orthodontic space closure of residual spaces on both sides distal to the lateral incisors were simulated. A combined intrusion and retraction cantilever was modeled, to simulate en masse retraction mechanics with segmented arches and elastic chains. A commercial FE system was used for all model generations and simulations. RESULTS: Results of the simulations indicated that a force of 1.0 N is too high for space closure of flared front teeth in periodontally damaged dentition, as extreme strains may occur. En masse retraction using cantilever mechanics with lower forces showed a uniform intrusion and retraction movement and thus proved to be a better option for treating patients with a periodontally compromised dentition. CONCLUSION: The outcome of this study indicates that increased periodontal stresses resulting from severe attachment loss should be seriously considered by careful planning of the orthodontic mechanics and reduction of the applied forces is suggested. The presented cantilever mechanics seems to be an appropriate means for en masse retraction of periodontally compromised extruded front teeth.

Impact of the endocannabinoid system on murine cranial and alveolar bone phenotype.

PURPOSE: The endocannabionoid signaling system has been demonstrated to be present in the skeleton, with involvement in the regulation of skeletal homeostasis. However, investigations substantiating these findings in cranial and alveolar bones are missing to date. The aim of our study was to investigate a potential impact of the endocannabinoid system on cranial and alveolar bone structures and phenotypes. BASIC PROCEDURES: CB1-/-, CB2-/- and WT mice (n = 5) were scanned via µCT. Reconstructed datasets were processed for analyses. Cranial cephalometric measurements were performed with OnyxCeph3TMsoftware. Alveolar bone densities were determined via mean grey value measurements with Mimics research 18.0. Alveolar bone heights around teeth in upper and lower jaws were morphometrically analyzed. Alveolar osteoclasts were quantified via TRAP staining of paraffin-embedded histologies. Bone-marrow derived macrophages isolated from murine hind legs were analyzed for CD40 and MMR expression via flow cytometry. MAIN FINDINGS: CB2-/- mice exhibited significantly higher bone densities with mean grey values of 138.3 ± 22.6 compared to 121.9 ± 9.3 for WT for upper jaws, and 134.6 ± 22.9 compared to 116.1 ± 12.9 for WT 134.6 ± 22.9. Concurrently, CB2 receptor knockout entailed reduced alveolar bone heights of about 50% compared to WT mice. Antigen-presenting cell marker expression of MMR was significantly diminished in bone-marrow derived macrophages of CB2-/- mice. Cranium dimensions as much as alveolar osteoclasts were unaffected by receptor knockouts.CB1 receptor knockout did not involve statistically significant alterations in the parameters investigated compared to WT mice. PRINCIPAL CONCLUSIONS: The endoncannabinoid system, and particularly CB2 receptor strongly affects murine alveolar bone phenotypes. These observations suggest CB2 as promising target in the modulation of oral bone phenotypes, probably by impact on bone dynamics via osteal immune cells.

Biomechanical analysis of initial incisor crowding alignment in the periodontally reduced mandible using the finite element method.

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.

Numerical investigations of bone remodelling around the mouse mandibular molar primordia.

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.

Comparative study on serum-induced arthritis in the temporomandibular and limb joint of mice.

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.

Effectiveness of photopolymerization in composite resins using a novel 445-nm diode laser in comparison to LED and halogen bulb technology.

Challenges especially in the minimal invasive restorative treatment of teeth require further developments of composite polymerization techniques. These include, among others, the securing of a complete polymerization with moderate thermal stress for the pulp. The aim of this study is to compare current light curing sources with a blue diode laser regarding curing depth and heat generation during the polymerization process. A diode laser (445 nm), a LED, and a halogen lamp were used for polymerizing composite resins. The curing depth was determined according to the norm ISO 4049. Laser output powers of 0.1, 0.5, 1, and 2 W were chosen. The laser beam diameter was adapted to the glass rod of the LED and the halogen lamp (8 mm). The irradiation time was fixed at 40 s. To ascertain ΔT values, the surface and ground area temperatures of the cavities were simultaneously determined during the curing via a thermography camera and a thermocouple. The curing depths for the LED (3.3 mm), halogen lamp (3.1 mm) and laser(0.5/1 W) (3/3.3 mm) showed no significant differences (p < 0.05). The values of ΔTsurface as well as ΔTground also showed no significant differences among LED, halogen lamp, and laser(1 W). The ΔTsurface values were 4.1LED, 4.3halogen lamp, and 4.5 °C for the laser while the ΔTground values were 2.7LED, 2.6halogen lamp, and 2.9 °C for the laser. The results indicate that the blue diode laser (445 nm) is a feasible alternative for photopolymerization of complex composite resin restorations in dentistry by the use of selected laser parameters.

The influence of enamel sandblasting on the shear bond strength and fractography of the bracket-adhesive-enamel complex tested in vitro by the DIN 13990:2017-04 standard.

OBJECTIVES: This study was conducted in order to investigate whether enamel sandblasting as an adjunct or substitute to the acid-etch technique has an effect on the shear bond strength (SBS) and fractography of the bracket-adhesive-enamel complex using the DIN 13990:2017-04 standard. MATERIALS AND METHODS: Upper central incisor brackets (discovery®, Dentaurum, Germany) were bonded using Transbond XT™ (3M Unitek, Germany) on bovine incisors prepared by four different methods (15 samples each): sandblasting with 27 µm Al2O3 at 1.2 bar (s), acid etching with 37.4% phosphoric acid (a), sandblasting with 27 µm Al2O3 at 1.2 bar followed by acid etching (s1a), and sandblasting with 50 µm Al2O3 at 5.7 bar followed by acid etching (s2a). The SBS and adhesive remnant index (ARI) were measured, followed by one-way analysis of variance and Fisher's exact tests at 5%. RESULTS: The SBS in groups s (5.6 ± 2.2 MPa), a (17.1 ± 4.3 MPa), s1a (18.3 ± 4.3 MPa), and s2a (18.5 ± 4.6 MPa) indicated that the s group was significantly inferior to all the other groups (p < 0.001). Likewise, the ARI analysis indicated a different performance of the s group (mostly ARI of 0) compared to the other groups (p < 0.001) and a tendency for different ARI between the a and s1a/s2a groups. CONCLUSIONS: In vitro enamel sandblasting could not substitute acid etching and did not offer improved SBS when used before acid etching, regardless of air pressure and powder granulation. Sandblasting without acid etching produced less residual resin on the tooth after debonding. CLINICAL RELEVANCE: The clinical use of adjunct enamel sandblasting prior to etching to enhance SBS has to be questioned.

Comparison of the efficacy of tooth alignment among lingual and labial brackets: an in vitro study.

Background/objective: The aim of this study was to evaluate the efficacy of tooth alignment with conventional and self-ligating labial and lingual orthodontic bracket systems. Materials/methods: We tested labial brackets (0.022″ slot size) and lingual brackets (0.018″ slot size). The labial brackets were: (i) regular twin brackets (GAC-Twin [Dentsply]), (ii) passive self-ligating brackets including (Damon-Q® [ORMCO]; Ortho classic H4™ [Orthoclassic]; FLI®SL [RMO]), and (iii) active self-ligating brackets (GAC In-Ovation®C [DENTSPLY] and SPEED™[Strite]). The lingual brackets included (i) twin bracket systems (Incognito [3M] and Joy™ [Adenta]), (ii) passive self-ligating bracket system (GAC In-Ovation®LM™ [Dentsply]), and (iii) active self-ligating bracket system (Evolution SLT [Adenta]). The tested wires were Thermalloy-NiTi 0.013″ and 0.014″ (RMO). The archwires were tied to the regular twin brackets with stainless steel ligatures 0.010″ (RMO). The malocclusion simulated a displaced maxillary central incisor in the x-axis (2 mm gingivally) and in the z-axis (2 mm labially). Results: The results showed that lingual brackets are less efficient in aligning teeth when compared with labial brackets in general. The vertical correction achieved by labial bracket systems ranged from 72 to 95 per cent with 13″ Thermalloy wires and from 70 to 87 per cent with 14″ Thermalloy wires. In contrast, the achieved corrections by lingual brackets with 13″ Thermalloy wires ranged between 25-44 per cent and 29-52 per cent for the 14" Thermalloy wires. The anteroposterior correction achieved by labial brackets ranged between 83 and 138 per cent for the 13″ Thermalloy and between 82 and 129 per cent for the 14″ Thermalloy wires. On the other hand, lingual brackets corrections ranged between 12 and 40 per cent for the 13″ Thermalloy wires and between 30 and 45 per cent for the 14″ Thermalloy wires. Limitation: This is a lab-based study with different labial and lingual bracket slot sizes (however they are the commonly used ones in clinical orthodontics) and study did not consider saliva, periodontal ligament, mastication and other oral functions. Conclusions: The effectiveness of lingual brackets in correcting vertical and anteroposterior displacement achieved during the initial alignment phase of orthodontic treatment is lower than that of the effectiveness of labial brackets.

Time-dependent behavior of porcine periodontal ligament: A combined experimental, numeric in-vitro study.

INTRODUCTION: The aim of this study was to analyze the time-dependent in-vitro behavior of the periodontal ligament (PDL) by determining the material parameters using specimens of porcine jawbone. Time-dependent material parameters to be determined were expected to complement the results from earlier biomechanical studies. METHODS: Five mandibular deciduous porcine premolars were analyzed in a combined experimental-numeric study. After selecting suitable specimens (excluding root resorption) and preparing the measurement system, the specimens were deflected by a distance of 0.2 mm at loading times of 0.2, 0.5, 1, 2, 5, 10, and 60 seconds. The deflection of the teeth was determined via a laser optical system, and the resulting forces and torques were measured. To create the finite element models, a microcomputed tomography scanner was used to create 3-dimensional x-ray images of the samples. The individual structures (tooth, PDL, bone) of the jaw segments were reconstructed using a self-developed reconstruction program. A comparison between experiment and simulation was conducted using the results from finite element simulations. Via iterative parameter adjustments, the material parameters (Young's modulus and Poisson's ratio) of the PDL were assessed at different loading velocities. RESULTS: The clinically observed effect of a distinct increase in force during very short periods of loading was confirmed. Thus, a force of 2.6 N (±1.5 N) was measured at the shortest stress duration of 0.2 seconds, and a force of 1.0 N (±0.5 N) was measured at the longest stress duration of 60 seconds. The numeric determination of the material parameters showed bilinear behavior with a median value of the first Young's modulus between 0.06 MPa (2 seconds) and 0.04 MPa (60 seconds), and the second Young's modulus between 0.30 MPa (10 seconds) and 0.20 MPa (60 seconds). The ultimate strain marking the transition from the first to the second Young's modulus remained almost unchanged with a median value of 6.0% for all loading times. CONCLUSION: A combined experimental-numeric analysis is suitable for determining the material properties of the PDL. Microcomputed tomography allows high-precision recordings with only minimum effort. This study confirms the assumption of time dependency and nonlinearity of previous studies.

Influence of tooth dimension on the initial mobility based on plaster casts and X-ray images : A numerical study.

AIMS: The goal was to determine the influence of different geometric parameters of the tooth on the initial tooth mobility and the position of the center of resistance employing numerical models based on scaled X-ray images and plaster casts. METHODS: The dimensions of tooth 21 were measured in 21 patients, using radiographs and dental casts. Length and mesiodistal width of the tooth were obtained from the X-ray image and the orovestibular diameter from the plaster cast. Finite element models were generated. Cortical and cancellous bone and the periodontal ligament were simulated to create realistic models. Root length (11-17 mm), mesiodistal width (6-10 mm) and orovestibular thickness (7-9 mm) were varied in 1-mm steps to generate 105 models. In the simulation, each model was loaded with a force of 10 N in vestibulopalatinal direction and with a torque of 10 Nmm to determine tooth displacements and center of resistance. RESULTS: Initial tooth displacement and thus mobility increased with decreasing total root surface. The shortest, slimmest and thinnest tooth showed a total deflection of 0.14 mm at the incisal edge, while the longest, widest and thickest tooth showed a total deflection of 0.10 mm. Changes in mesiodistal width had the greatest influence on initial tooth mobility and changes in orovestibular thickness the least. The teeth's center of resistance was positioned between 37 and 43% of the root length measured from the cervical margin of the alveolar bone. The center of resistance of the longest dental root investigated was located around 6% more cervically compared to the one of the shortest dental root. The influence of root width and thickness on the position of the center of resistance was significantly lower than root length. CONCLUSION: Geometric parameters significantly impact initial tooth mobility and position of the center of resistance. Thus, tooth dimensions should be considered in orthodontic treatment planning. Dental radiographs represent a sufficient validation tool to estimate the quality of a pure dental tipping during orthodontic treatment, as the orovestibular thickness has little influence. However, for three-dimensional tooth displacements all geometric parameters should be determined accurately using plaster casts or DVT.

Mechanical properties of different esthetic and conventional orthodontic wires in bending tests : An in vitro study.

AIMS: The goal of this study was to determine the mechanical properties of different esthetic and conventional orthodontic wires in three-point and four-point bending tests, and in a biomechanical test employing three bracket systems. METHODS: The behavior of round wires with a diameter of 0.46 mm (0.018″) were investigated: uncoated nickel titanium (NiTi) wires, surface modified NiTi wires; FLI® Orthonol Wire® and glass fiber reinforced plastic wires. The biomechanical bending test was performed using the following bracket types: metal brackets (Discovery®, Dentaurum), ceramic brackets (Fascination®, Dentaurum), and plastic brackets (Elegance®, Dentaurum). All bending tests were performed in the orthodontic measurement and simulation system (OMSS) at a temperature of 37 °C. The classical three-point bending test was performed according to an ISO standard (DIN EN ISO 15841:2007) using the appropriate thrust die and supports with a predefined span of 10 mm. In the other tests the supports or interbracket distances were chosen such that the free wire length was also 10 mm (5 mm between adjacent brackets). All wires were loaded centrally to a maximum of 3.1 and 3.3 mm in the biomechanical test, respectively. The force was measured upon unloading with a loading velocity of 1 mm/min. Each specimen was loaded twice and a total of 10 specimens tested for each product. Weighted means and the error of the weighted mean were calculated for each product. RESULTS: Fiber reinforced wires displayed lowest forces in three-point bending with values of 0.4 N at a displacement of 1 mm and 0.7 N at a 2 mm displacement. In four-point bending the forces were 0.9 N and 1.4 N, respectively, at the same displacements. Almost all of the translucent wires showed fracture upon bending at displacements greater than 3 mm, independent of the bending test and bracket type. The different investigated NiTi wires, surface modified or conventional, only showed minor variation, e.g., 2.2 N for rematitan® Lite White and 2.0 N for rematitan®, 2.1 N for FLI® Coated Orthonol® and 1.7 N for Orthonol® in four-point bending. The rhodinized wire generated forces between these values (2.1 N). CONCLUSION: The translucent wires had the lowest forces in all three bending tests; however, displacements above 3 mm resulted in increased risk of fracture. Forces of investigated NiTi wires were very high and in part above clinically recommended values.

Imaging of Dental Hard Tissue Surfaces Prepared by an Ultrashort Pulsed Laser System (USPL).

The aim of this study was to compare surface structures of laser-irradiated dental hard tissues using confocal (CFM), atomic force (AFM), and scanning electron microscopy (SEM). The general potential of the AFM in analyzing laser-irradiated surfaces was determined in this context. Specimens of human enamel and dentin were irradiated using an 8.6 W Nd:YVO4 laser with a pulse duration of 8 ps, λ Center=1,064 nm, and a pulse repetition rate of 500 kHz. Surface topology of irradiated areas (1 mm2) was investigated using AFM, CFM, and SEM. Surface roughness R z was measured only with the AFM and the CFM. For non-irradiated enamel and dentin surfaces, roughnesses for CFM and AFM are in the nanometer range. However, major differences in roughness were determined for laser-prepared surfaces. For enamel, R z (CFM)=2.33 µm is much higher compared with R z (AFM)=0.09 µm; in the case of dentin, R z (CFM)=5.35 µm is also much higher compared with R z (AFM)=0.093 µm. Information regarding structural properties of surfaces needs real dimensions, particularly for use in dentistry. In this respect, AFM technology provides no additional results that lead to a significant improvement.

Friction behavior of self-ligating and conventional brackets with different ligature systems.

OBJECTIVES: Self-ligating brackets are widely believed to offer better clinical efficiency and, in particular, less friction. Thus, the goal of this in vitro investigation was to assess the friction behavior of different bracket/archwire/ligature combinations during simulated canine retraction. An important aspect of this work was to determine whether conventional bracket systems behave differently in passive or active self-ligating brackets used with a Slide™ ligature, an elastic ligature, or a steel ligature. METHODS: Three conventional (Contour, Class One; Discovery(®), Dentaurum; Mystique MB, GAC) and six self-ligating (Carriere SL, Class One; Clarity™ SL, 3M Unitek; Damon3, Ormco; In-Ovation(®) C, GAC; Speed Appliance, Speed System™; QuicKlear(®), Forestadent(®)) bracket systems were analyzed. All brackets featured a 0.022″ slot (0.56 mm). Each conventional system was tested with a steel ligature (0.25 mm; Remanium(®), Dentaurum), an elastic ligature (1.3 mm in diameter; Dentalastics, Dentaurum), and a modified elastic ligature (Slide™; Leone(®)). Each combination was used with four archwires, including rectangular stainless steel (0.46 × 0.64 mm, 0.018 × 0.025″, Dentaurum), rectangular nickel-titanium with Teflon coating (0.46 × 0.64 mm, 0.018 × 0.025″, Forestadent(®)), round coaxial nickel-titanium (0.46 mm, 0.018″, Speed), and half-round/half-square (D-profile) stainless steel (0.46 mm, 0.018″, Speed). In the orthodontic measurement and simulation system (OMSS), retraction of a canine was simulated on a Frasaco model replicated in resin. Based on the force systems, the respective friction values were determined. For each combination of materials, five brackets of the same type were tested and five single measurements performed. RESULTS: Friction values were found to vary distinctly with the different combinations, modifiers being the ligature systems and the archwire types. Any significant friction differences between the steel-ligated, Slide™-ligated, and self-ligated brackets were sporadic. All three systems were associated with average friction values of 40 %. Active self-ligating brackets and elastic-ligated conventional brackets, by contrast, generally differed significantly from the three above-mentioned bracket systems and showed distinctly higher friction values averaging 59 and 67 %, respectively. CONCLUSIONS: While passive self-ligating bracket systems have frequently been touted as advantageous in the literature, they should not be regarded as the only favorable system. Steel-ligated and Slide™-ligated conventional bracket systems are capable of offering similar friction performance.

Friction behavior of ceramic injection-molded (CIM) brackets.

OBJECTIVES: Bracket material, bracket design, archwire material, and ligature type are critical modifiers of friction behavior during archwire-guided movement of teeth. We designed this in vitro study to compare the friction losses of ceramic injection-molded (CIM) versus pressed-ceramic (PC) and metal injection-molded (MIM) brackets-used with different ligatures and archwires-during archwire-guided retraction of a canine. METHODS: Nine bracket systems were compared, including five CIM (Clarity™ and Clarity™ ADVANCED, both by 3M Unitek; discovery(®) pearl by Dentaurum; Glam by Forestadent; InVu by TP Orthodontics), two PC (Inspire Ice by Ormco; Mystique by DENTSPLY GAC), and two MIM (discovery(®) and discovery(®) smart, both by Dentaurum) systems. All of these were combined with archwires made of either stainless steel or fiberglass-reinforced resin (remanium(®) ideal arch or Translucent pearl ideal arch, both by Dentaurum) and with elastic ligatures or uncoated or coated stainless steel (all by Dentaurum). Archwire-guided retraction of a canine was simulated with a force of 0.5 N in the orthodontic measurement and simulation system (OMSS). Friction loss was determined by subtracting the effective orthodontic forces from the applied forces. Based on five repeated measurements performed on five brackets each, weighted means were calculated and evaluated by analysis of variance and a Bonferroni post hoc test with a significance level of 0.05. RESULTS: Friction losses were significantly (p < 0.05) higher (58-79 versus 20-30 %) for the combinations involving the steel versus the resin archwire in conjunction with the elastic ligature. The uncoated steel ligatures were associated with the lowest friction losses with Clarity™ (13 %) and discovery(®) pearl (16 %) on the resin archwire and the highest friction losses with Clarity™ ADVANCED (53 %) and Mystique (63 %) on the steel archwire. The coated steel ligatures were associated with friction losses similar to the uncoated steel ligatures on the steel archwire. Regardless of ligature types, mild signs of abrasion were noted on the resin archwire. CONCLUSIONS: The lowest friction losses were measured with rounded ceramic brackets used with a stainless-steel ligature and the resin archwire. No critical difference to friction behavior was apparent between the various manufacturing technologies behind the bracket systems.

Experimental investigation of the fracture torque of orthodontic anchorage screws.

OBJECTIVES: In contrast to dental implants that remain in the bone, orthodontic anchorage screws serve as temporary anchorage for orthodontic tooth movement and are removed after completion of treatment. The aim of the present study was to evaluate the stability of various commercially available orthodontic anchorage screws against torsion. MATERIALS AND METHODS: The torsional deflection of ten different orthodontic anchorage screws from different manufacturers [Ortho Easy Pin (Forestadent), Benefit, quattro (both PSM Medical Solutions), Vector TAS (Ormco), AbsoAnchor(®) (DENTOS Inc.), OrthoLox, Dual-Top JA (both Promedia Medizintechnik), TAD (3M Unitek), INFINITAS (ODS) and tomas(®) (Dentaurum)] was tested in vitro in relation to the rotation angle using a self-developed set-up. The screws were positioned in a resin model with bone-like material properties. Shear tests were performed using the manufacturers' own screwdrivers. Ten screws each were turned manually until a sudden drop in the measured torque occurred. At this point, the screw head was twisted off. Fracture torque and the torque at which the screws deformed plastically were evaluated. Mean values and standard deviations were calculated. RESULTS: According to the German industrial standard, the torque of orthodontic anchorage screws should reach at least 20 Ncm. The majority of the screws reached this nominal torque; however, a few screws fractured before reaching this value. Five screw types displayed plastic deformation below the threshold, at approximately 16 Ncm. CONCLUSIONS: The results suggest that orthodontic anchorage screws generally meet the requirements of the standard and ensure safe clinical use. However, according to the present data, it may be assumed that a portion of the screws will be plastically deformed upon removal.

Nickel ion concentrations in the saliva of patients treated with self-ligating fixed appliances: a prospective cohort study.

OBJECTIVE: Orthodontic appliances are considered to be highly biocompatible although adverse effects attributed to the release of nickel ions (Ni(2+)) have been documented. Self-ligating brackets have grown in popularity for economic reasons and supposed friction reduction. The aim of the present prospective cohort study was therefore to determine salivary Ni(2+) concentrations in patients undergoing orthodontic treatment with self-ligating fixed appliances. MATERIALS AND METHODS: A group of 30 patients between 10 and 13 years of age were treated with self-ligating brackets (SmartClip™), molar bands, and nickel-titanium (NiTi) archwires. Unstimulated saliva samples were collected after different time points (before treatment, after self-ligating bracket and band placement, before archwire insertion, after archwire insertion, and finally 4 and 8 weeks afterwards) and analyzed with an ICP mass spectrometer followed by generalized estimating equation modelling with α = 5 %. RESULTS: The baseline median salivary Ni(2+) concentration was 21.85 µg/l, while the Ni(2+) concentrations at the following visits ranged between 13.73 and 85.34 µg/l. Significant increases in Ni(2+) levels compared to the baseline levels were detected after band/bracket placement [+59.76 µg/l; 95 % confidence interval (CI) 44.88-74.64 µg/l; P < 0.001] and after archwire insertion (+53.55 µg/l; 95 % CI 25.57-81.52 µg/l; P < 0.001). After 4 weeks, Ni(2+) concentrations returned to initial control levels or were lower. CONCLUSION: Self-ligating orthodontic appliances may affect salivary Ni(2+) concentrations in vivo over the short term. However, levels resembled those documented in conjunction with conventional bracket use and remained below the daily dietary Ni intake.

Symmetric and asymmetric expansion of molars using a Burstone-type transpalatal arch. Biomechanical and clinical analysis.

OBJECTIVES: A transpalatal arch (TPA) directly connecting the maxillary first molars can be used in passive (for stabilization) and active (for molar or segment movement) modes. Activation may be symmetric or asymmetric. This study was performed to analyze the effectiveness of TPAs for transverse expansion treatment by measuring both the force systems they deliver and the clinical tooth movements thus achieved. MATERIALS AND METHODS: Ten patients (six with symmetric and four with asymmetric transverse discrepancies) were treated using a TPA made of titanium-molybdenum alloy (TMA) and fitted with 0.032" × 0.032" Burstone lingual brackets. The force systems exerted by these TPAs and the resultant tooth movements were first simulated and measured inside the orthodontic measurement and simulation system (OMSS). All TPAs, whether used in the symmetric or asymmetric activation mode, were adjusted to an expansive force of 4 N. After a treatment of 12 weeks, their effectiveness was analyzed by comparing the clinical tooth movements to the movements simulated in the OMSS. RESULTS: Clinically, the symmetric treatments resulted in a mean correction of 4.5 ± 1.0 mm and a mean of buccal crown tipping of 10.1°, compared to 9.6° for the movements simulated in the OMSS. The four cases of unilateral crossbite were treated with an asymmetrically activated TPA (including a force on one side and a combination of force and negative torque on the other side). The intended unilateral expansion was achieved in all four cases. Vertical side effects were acceptably small in both the symmetric and the asymmetric treatment cases. The tooth movements could be implemented as planned in all 10 patients, whereby in 5 patients complete correction of the occlusal width discrepancy was achieved by the end of the 12-week treatment. CONCLUSION: Given this combination of good efficacy and minor side effects, the TMA/TPA appliance may be recommended as a suitable approach to correct transverse discrepancies. Recommendations expressed in previous studies for the use of Burstone-type TMA/TPA in these situations is confirmed by our study.

Effect of archwire cross-section changes on force levels during complex tooth alignment with conventional and self-ligating brackets.

INTRODUCTION: Our objective was to investigate the effect of archwire cross-section increases on the levels of force applied to teeth during complex malalignment correction with various archwire-bracket combinations using an experimental biomechanical setup. METHODS: The study comprised 3 types of orthodontic brackets: (1) conventional ligating brackets (Victory Series [3M Unitek, Monrovia, Calif] and Mini-Taurus [Rocky Mountain Orthodontics, Denver, Colo]), (2) self-ligating brackets (SmartClip, a passive self-ligating bracket [3M Unitek]; and Time3 [Rocky Mountain Orthodontics, Denver, Colo] and SPEED [Strite Industries, Cambridge, Ontario, Canada], both active self-ligating brackets), and (3) a conventional low-friction bracket (Synergy [Rocky Mountain Orthodontics]). All brackets had a nominal 0.022-in slot size. The brackets were combined with 0.014-in and 0.016-in titanium memory wires, Therma-Ti archwires (American Orthodontics, Sheboygan, Wis). The archwires were tied to the conventional brackets with both stainless steel ligatures of size 0.010-in and elastomeric rings. A malocclusion of the maxillary central incisor displaced 2 mm gingivally (x-axis) and 2 mm labially (z-axis) was simulated. RESULTS: The forces recorded when using the 0.014-in archwires ranged from 1.7 ± 0.1 to 5.0 ± 0.3 N in the x-axis direction, and from 1.2 ± 0.1 to 5.5 ± 0.3 N in the z-axis direction. When we used the 0.016-in archwires, the forces ranged from 2.6 ± 0.1 to 6.0 ± 0.3 N in the x-axis direction, and from 2.0 ± 0.2 to 6.0 ± 0.4 N in the z-axis direction. Overall, the increases ranged from 16.0% to 120.0% in the x-axis and from 10.4% to 130.0% in the z-axis directions. CONCLUSIONS: Increasing the cross section of the wire increased the force level invariably with all brackets. Wires of size 0.014 in produced relatively high force levels, and the force level increased with 0.016-in wires.