Orthodontic palatal disjunctor device with bone anchorage

Abstract

The present invention pertains to the field of oral and maxillofacial surgery and relates, more specifically, to an orthodontic device for use in surgical palatal disjunctions, with skeletal fastening by means of titanium screws specifically for osteosynthesis. The palatal disjunctor device comprises a disjunction apparatus formed by left and right parts connected by guide screws and a threaded screw, wherein the left and right parts are joined to a support rail that connects to the lateral bars, the rails having folds at the ends, and the bars being formed by a central portion joined to at least one hexagonal link, which is connected to a semicircular link, wherein there is a fold for cutting between the joined parts, and the central portion has at least three holes, with each link having one hole.

Description

[0001] ORTHODONTIC DEVICE PALATINE DISJUNCTOR WITH BONE ANCHORAGE

[0002] Technological sector of the invention

[0003]

[0001] The present invention belongs to the field of oral and maxillofacial surgery, and refers, more specifically, to an orthodontic device for use in surgical palatal disjunctions, with skeletal fixation using titanium screws specific for osteosynthesis.

[0004] State of the Art

[0005]

[0002] Each individual's muscular, occlusal, and dental balance depends on the harmonious relationship between the maxilla and mandible. An inadequate transverse maxillomandibular relationship is relatively common and has several clinical implications. The degree of correction required, the type of alteration (skeletal or dentoalveolar), and the patient's age must be carefully considered when planning each treatment.

[0006]

[0003] Transverse maxillary deficiency constitutes an occlusal discrepancy in the transverse plane, which can be diagnosed in isolation or as part of a complex craniofacial or dentofacial deformity. Its prevalence is 8% to 23% in deciduous and mixed dentitions, and less than 10% in adult orthodontic patients.

[0004] The Rapid Palatal Expansion (RPE) technique has been applied for over a century, and its results have been considered beneficial, including with extensive, credible scientific documentation. However, the patient's age is considered a significant factor, as the structures present greater resistance to expansion over time, leading to undesirable effects such as alveolar bone dehiscence, tipping of the dental crown towards the buccal position, root resorption, reduced buccal bone thickness, marginal bone loss, and often rotation of the mandible in the inferior and posterior vertical direction.

[0007]

[0005] To overcome the problem of increased resistance to expansion caused by ossification of the structures, surgically assisted rapid palatal expansion (SARPE) was proposed by Brown in 1938. This surgery consists of a partial maxillary osteotomy at LeFort I level, under induction of general anesthesia. This surgical technique is generally performed early in the patient's treatment, after orthodontic compensation of the arches. However, it should be noted that SARPE has been described with some limitations, namely the high financial cost and the complexity of the treatment itself, which causes most patients to refuse this surgical procedure.

[0008]

[0006] More recently, miniscrew-assisted rapid palatal expansion (MARPE®) was developed as an alternative for patients with transverse maxillary deficiency. This technique consists of the application of a rigid device connected to four screws inserted in the midsagittal or parasagittal region, with bicortical bone anchorage. These microscrews are believed to transmit force more effectively, directly to the basal bone, maximize the skeletal effect, and allow the device to be anchored to a more robust bone structure, enhance primary bone stability, and maintain separation of the hemimaxillae during the bone consolidation period.Another recent model is the Rotterdam palatal distractor - KLS Martyn®, which has a diamond-shaped screw with two attachments on its sides and on opposite sides of the diamond. The attachments have “sharps” for fixation in the palatine mucosa. This fixation is provided by pressure through the activation of the breaker screw. This pressure is often insufficient to guarantee the stability of the device's fixation, a difficulty that is exacerbated in patients undergoing surgical maxillary disjunction after surgical “release” of the maxillary and palatine sutures, due to maxillary instability.

[0009]

[0007] Some models are also disclosed in patent documents, as demonstrated in US20160270883, US20030050641 , KR20230032529, KR20060086753, US20090130620, WO2018139690, which are devices that have the same purpose: bone distraction. However, the differences lie in the anchorage or support points, modeling or adaptation, extent of distraction in dimension (millimeters), dissipation of forces and comfort. Something that will be noticeable is that the device disclosed in the patent has four configurations and adapts to atresic or very small jaws, in addition to allowing cutting and adaptation of its extension and having more structural resistance than a mesh (as presented in KR20160133921 ​​).

[0010]

[0008] Since there is no consensus in the scientific and patent literature regarding the number (two or four) and position of screws (mesial or lateral), as well as the recommended daily expansion, the implementation of a device that evaluates these variables is considered urgent. Screws are susceptible to failure. If fewer screws are used, for example, at the four vertices of a square, the failure of one can result in instability of the entire assembly. After all, force will be applied to the device in a vector, generating instability of the device, leading to failure in the applied vector or collapse upon activation. Some expansion protocols are described in the literature, but there is a well-established margin of success for the technique.Furthermore, the installation of screws must take into account the roots of the teeth, which have multiple positions that vary from patient to patient, so multiple possible positions as proposed would be an advantage.

[0011] Novelties and objectives of the invention

[0012]

[0009] In this context, the present invention reveals a new model of palatal expander for the treatment of facial deformities, for example, in children with special needs, and the aim to minimize the challenges inherent in treating such patients. Clearly, it is not for exclusive use in children, but it has advantages due to the possibility of adaptation with asymmetric reduction of the support points (cutting of the plates). This is due to the better anatomical adaptation to the palate, which in special children has a low tolerance threshold, being an advantage for the success of the treatment.

[0013]

[0010] With anatomical conformation juxtaposed to the palatal mucosa, the device is more comfortable, hygienic, and offers functional freedom for the patient when compared to other existing devices. These characteristics include a short distance from the palatal mucosa, thus preserving the phonetic space, a low profile making it more comfortable in relation to the patient's tongue, a hollow design facilitating hygiene, and stability guaranteed by its fixation with titanium miniscrews (skeletal anchorage).

[0011] The main objectives, then, would be to present a more anatomical and comfortable device for the patient, thus reducing impaction / accumulation of food in the region. In addition, it offers a customized solution for each patient within a standard device.Another objective of the invention is to present a device that can be used in the treatment of craniofacial development deformities, such as transverse maxillary atresia, maxillary hypoplasia, among others.

[0014]

[0012] Furthermore, another objective is to offer different positions for fixation to the bone due to its plates that allow for asymmetric adaptation. The palatal distractor has four configurations: medial and lateral positioning, two and four screws, with and without osteotomy. It also has a design that allows for the asymmetric removal of some "links" for better adaptation and performance of the device.

[0015] Description of the attached drawings

[0016]

[0017] In order for the present invention to be fully understood and put into practice by any technician in this technological sector, it will be described in a clear, concise and sufficient manner, based on the attached drawings, which illustrate and support it, listed below:

[0017] Figure 1 represents the perspective view of the palatal disjunctor device;

[0018] Figure 2 represents the perspective view of the device, highlighting the right and left devices and the circuit breaker screws;

[0019] Figure 3 represents the side view of the anchor bar;

[0020] Figure 4 represents Table 1 with the distractor configurations to be simulated;

[0021] Figure 5 represents Table 2 with the configuration and 3D SolidWorks® of the analyzed distractor configurations;

[0022] Figure 6 represents Table 3 with the comparison of standard conditions and analysis conditions;

[0023] Figure 7 represents the adequacy of the skull geometry; Figure 8 represents the skull geometries with and without osteotomy;

[0024] Figure 9 represents the stiffness test methodology (McElhaney et al., 1973);

[0025] Figure 10 represents the mechanical properties of the materials under study;

[0026] Figure 11 represents the adopted materials and characterization (mesh) of finite elements;

[0027] Figure 12 represents the conditions for fixing the geometry of the skull, where A and B refer to the condylar fossa, and C and the occlusion;

[0028] Figure 13 represents Table 3 with the translation and rotation restrictions for the skull geometry;

[0029] Figure 14 represents the displacements applied in the compressive tests, via FEA;

[0030] Figure 15 represents the stiffness curves for the compressive tests;

[0031] Figure 16 represents the geometries and adjustments made to the distractors;

[0032] Figure 17 represents the mechanical properties of ASTM F136 Titanium Alloy;

[0033] Figure 18 represents the characterization of the distractor geometry;

[0034] Figure 19 represents the fixing conditions and application of forces / load of the device;

[0035] Figure 20 represents the distribution of von Mises stresses from analysis A6;

[0036] Figure 21 represents the distribution of von Mises stresses from analysis A5;

[0037] Figure 22 represents the distribution of the maximum principal stresses of analysis A5;

[0038] Figure 23 represents the distribution of von Mises equivalent stresses in the distractor configurations;

[0039] Figure 24 represents the distribution of von Mises equivalent stresses in the bolts;

[0040] Figure 25 represents the distribution of the main maximum stresses in the palate;

[0041] Figure 26 represents the results of the voltages developed according to the configuration.

[0042] Detailed Description of the Invention

[0043]

[0013] The palatal disjunctor device comprises a disjunctor apparatus formed by a left (AE) and right (AD) part joined by guide screws (P1) and a threaded screw (P2), in which the left (AE) and right (AD) parts are integrated into the support rail (T) that joins the side bars (B), with the rails (T) having folds at the ends and the bars (B) being formed by a central portion (B1) integrated into at least one hexagonal link (B2) that is joined to a semicircular link (B3), in which between the integrated parts there is a fold for cutting (B4) and in the central portion there are at least three holes (B5) and in each link (B2)(B3) one hole (B5).

[0044] Structural analysis by Finite Element Method (FEM)

[0045]

[0014] It should be noted that through Finite Element Analysis, the biomechanical effects of various treatment modalities have been analyzed and the deformation and stress distribution in bones exposed to the forces of the maxillary disjunction apparatus have been calculated.

[0046]

[0015] Given the advances in clinical procedures that the device disclosed herein can bring, the structural analysis of the biomechanical behavior of the system is essential to evaluate the improvements proposed by the device, enabling its implementation. Therefore, the development of a computational model that aims to simulate the biomechanical behavior of the patient's palatal distractor prototype is proposed, using the Finite Element Method (FEM).

[0047]

[0016] This analysis considers a computational model with small deformations, along with limited bone tissue damage. The objective is to simulate situations of incremental (daily) expansion of 0.5 mm (8 activations back to the central position of the device), and not the intended total expansion (obtained at the end of the treatment). The model will not predict the damage and biological recovery, since the greater the deformation, the further the model would deviate from reality. Finally, the biomechanical simulation will predict, for the conditions of a skull with and without osteotomy (which in no way alters the construction of the device, but only its application, according to need and bone maturation), and the use of 2 and 4 screws for fixation of the device to the palate, in the mesial and lateral configurations, the following output variables: • Evaluation of the influence of surgical approaches on the skull;

[0048] • Assessment of the influence of surgical approaches on the distractor;

[0049] • Assessment of the influence of the number of screws in the skull;

[0050] • Influence of the position of the screws in the skull;

[0051] • Safety considerations regarding the daily expansion recommendation;

[0052] • Determination of the critical configuration for the distractor.

[0053]

[0017] The analysis was divided into 3 stages:

[0054] 1) Alignment between the responsible surgical clinics Faccial and MSC MED regarding the study requirements;

[0055] 2) Adequacy and functional evaluation of the biomechanical behavior of the skull geometry;

[0056] 3) Adaptation of the device geometries and execution of simulations with the configurations described in Table 1 of Figure 4.

[0057]

[0018] The mechanical properties of the materials used in the analyses followed standardized values ​​and were based on validated scientific literature. The material used for the distractor and screws was titanium alloy Ti-6 AI-4 V ASTM F136. For bone tissue, a constitutive model of linear isotropy was used, with a modulus of elasticity that was different for the bones of the skull and maxilla (PETERSON et al., 2003; PETERSON et al., 2006).

[0058]

[0019] The biomechanical behavior study was performed through finite element analysis, using the commercial software ANSYS® Mechanical Pro (Brazil), whose numerical algorithms and mathematical models are validated and established. The equivalent von Mises stress distribution and maximum principal stresses were obtained, thus enabling the determination of the behavior of the device, screws, and skull, following the control conditions of the current clinical procedure. The different results can be compared with the different distractor configurations, number of screws, as well as the upper jaw osteotomy process. Table 2 of Figure 5 illustrates the different distractor configurations analyzed. Standard requirements

[0059]

[0020] To better represent the clinical application and obtain the complete stress result of the device and bone tissue, the conditions recommended in the technical standard ASTM F2996-13 Standard Practice for Finite Element Analysis (FEA) of Non-Modular Metallic Orthopaedic Hip Femoral Stems were adopted as good practice criteria for computational simulation, as described in Table 3 shown in Figure 6.

[0060] Adequacy and validation of skull geometry

[0061]

[0021] Using the MSC MED database, a 3D structural model of a standard human skull was obtained. However, for its application in clinical conditions involving the use of palatal distractors, this geometry required some modifications. This began with smoothing and joining the regions of the original model using organic (non-parametric) 3D modeling, in addition to applying symmetry throughout the 3D model, using the midsagittal plane as a reference.

[0062]

[0022] Previous analyses demonstrated high rigidity in the geometry of the skull, which needed to be corrected by removing the portion corresponding to the trabecular bone, thus forming a bicortical structure with an average thickness of 1.5 mm, aiming to represent a biomechanical behavior closer to that of human bone. Thus, the simulations disregarded the existence of trabecular tissue due to its negligible mechanical properties.

[0063]

[0023] The maxillary region was separated from the rest of the skull to allow the application of different biomechanical properties in the simulation environment. The adjustments in the skull geometry are illustrated in Figure 7. Subsequently, the osteotomy of the appropriate skull model was performed, based on the clinical application in the definitions with the principal investigator. Both osteotomy cuts (mesial and lateral) were made with 1.0 mm thickness, as can be seen in Figure 8.

[0064]

[0024] The validation of the mechanical behavior of the skull was based on the reproduction of the stiffness presented by the methodology of McElhaney et al. (1973), where they analyzed the response of 23 human cadaver heads (20 men, 3 women) subjected to a compressive load produced by two parallel steel plates (150.0 mm in diameter). A total of 12 tests were performed, loading the frontal and occipital bone (anteroposterior compression), and 12 tests were performed by applying forces to the right and left temporoparietal regions (mediolateral compression). As a conclusion of this analysis, McElhaney, Stalnaker & Roberts (1973) reported that the stiffness in the anteroposterior direction ranged from 1400 to 3500 N / mm, while the stiffness in the laterolateral direction ranged from 700 to 1750 N / mm. The reproduction of the tests presented is illustrated in Figure 9.

[0065] Material model for the skull

[0066]

[0025] A linear elastic material model was used to simulate the behavior of bone tissue, with different values ​​for the modulus of elasticity for the skull and maxilla region. The 150.0 mm diameter steel plates were considered as rigid, non-deformable bodies, considering the large difference between the stiffness of bone and steel. The mechanical properties of the skull (modulus of elasticity and Poisson's ratio) were obtained based on scientific literature (PETERSON; DECHOW, 2003; PETERSON; WANG; DECHOW, 2006), and are shown in Table 4 of Figure 10.

[0067] Characterization of the stiffness test

[0068]

[0026] The geometry of the skull was characterized using second-order tetrahedral element techniques (Software - SOLID187® - USA). For the skull bones, an element technique with a maximum edge size of 10.0 mm was initially used. For the upper jaw / maxilla, an element technique with a maximum size of 6.0 mm was used. Figure 11 demonstrates these details.

[0069] Boundary conditions and validation of skull stiffness

[0070]

[0027] Different restrictions for translation and rotation movements were applied in the condylar fossa and occlusal contact regions, preventing these restrictions from having an undesirable influence on the stiffness response, as described in Table 5 of Figure 13. In the numerical modeling, replicating the mesiolateral compression test, a prescribed displacement of 4.0 mm was applied (for each steel plate), totaling 8.0 mm of displacement. For the anteroposterior test, 2.7 mm of prescribed displacement was applied to each plate, totaling 5.4 mm, as illustrated in Figure 12.

[0071] Results for validation of skull stiffness

[0072]

[0028] Following the methodology presented by McElhaney et al (1973) and using the average elastic moduli for the regions of interest from (PETERSON et al., 2003; PETERSON et al., 2006), a stiffness of 2326.8 N / mm was obtained for the mesiolateral compression test, and 1029.6 N / mm for the anteroposterior test. In other words, the skull configuration presented stiffness values ​​close to the average of the scientific literature used as a basis (see Figure 14). The stiffness curves, obtained via Finite Element Application (FEA), for both tests, are presented in Figure 15. A convergence analysis of the generated mesh was performed, using a variation of up to 5% of the maximum principal stress as the convergence criterion. This procedure compares the maximum values ​​of the variable of interest obtained in a model with an initial mesh, then a refinement of the mesh is carried out, significantly increasing the number of nodes and elements of the model.

[0073] Suitability, materials, characterization and boundary conditions of the distractor

[0074]

[0029] Three-dimensional models of the device, in both mesial and lateral configurations, were submitted by the principal investigator. However, the geometries needed to be modified for clinical application (attached to the palate). The modifications focused on the geometry of the "skis" and the cylindrical bars connecting them to the device body. The geometries received, as well as the adjustments made, are illustrated in Figure 16. For the mesial configuration, the screws adopted were 12.0 mm long (both passive). For the lateral configurations, the screws used were 6.0 mm long (non-passive), aiming to avoid overlap with the tooth root.

[0030] A linear elastic material model was used to simulate bone tissue behavior, varying the modulus of elasticity for the cranial and maxillary regions.To simulate the titanium alloy device and screws (ASTM F136), an elastoplastic model with linear properties was used. The mechanical properties of the materials were obtained using current standards and are reported in Table 6 of Figure 17.

[0075]

[0031] The distractor geometries were characterized using the second-order tetrahedral element technique (Software - SOLID187 - USA), with a maximum edge size of 0.3 mm, with a refinement of the mesh in the contact regions with the screws, and the cylindrical bars that connected the "skis" to the device body. The convergence analysis of the generated mesh was repeated at this location, using as a convergence criterion a variation of up to 5% of the von Mises equivalent stress. The final characterization of the distractors can be seen in Figure 18.

[0076]

[0032] The boundary conditions adopted consist of a cylinder support restriction on the internal face of the guide pin channel (these were not considered in the modeling), as well as the prescribed displacement applied to the internal face of the spindle channel (0.25 mm in each direction, in opposite directions) - see Figure 19. At the contact interface between the screws and the “skis”, as well as between the palate and the screws, a frictional contact was adopted, using a friction coefficient of 0.2.

[0077]

[0033] The eight configurations described in Table 1 were subjected to finite element analysis techniques to obtain the values ​​of equivalent von Mises stresses (device and screws) and maximum principal stresses (bone tissues). Among all the analyses, the configuration that presented the highest von Mises stress values, that is, the most critical configuration for the device, was A6, as seen in Figure 20, with values ​​of o = 879.36 MPa.

[0078]

[0034] It is possible to observe that the stress in the critical region was lower than the yield stress y = 973 MPa. This indicates that there are likely no regions of permanent deformation in the device. Since clinical application does not involve cyclic loads, the results showed that the device can be used with a daily application of 0.5 mm opening without failure due to ductile rupture or fatigue.

[0079]

[0035] However, when analyzing the stresses occurring in the bolts, it is possible to observe some regions of plasticization, that is, which will possibly present permanent deformations but without reaching rupture. Analysis A6 was the one that conditioned the highest von Mises stresses in the bolts. VO n = 1090.4 MPa. The most significant von Mises stress values ​​obtained for the configurations with only 2 bolts stand out, aggravating the tensile forces exerted axially on the bolts (see Figure 21).

[0080]

[0036] Finally, analyzing the resulting stresses in the palate, the highest maximum principal stress values ​​were found in analysis A5, o = 255.74 MPa. Additionally, it was found that the highest stress value was obtained in the analysis with the 2-screw configuration (A5), inferring a greater probability of localized bone microfractures, or even detachment of the screws and possible release of the palatal expansion device (see Figure 22).

[0081]

[0037] The results obtained through FEA, of the von Mises stresses for the device and screws, as well as the maximum principal stresses in the palate, are presented in Figure 23. In both simulations, a convergence analysis of the generated mesh was performed using as a convergence criterion a variation of up to 5% of the von Mises stress.

[0082]

[0038] The values ​​of the von Mises stresses for the device and screws, as well as the maximum principal stresses in the palate, are shown in Figure 25, showing their respective values ​​described in Table 7 of Figure 26.

[0083] Results

[0084] • The influence of the surgical approach on the palate is evidenced by the difference between the averages of the maximum main stresses in the screw holes, being o = 75.1 MPa for skulls with osteotomy and oimed = 190.3 MPa for skulls without osteotomy (Conditions A and B);

[0085] • The influence of the surgical approach on the distractor was negligible and is evidenced by the small difference between the average von Mises stresses, being OvMmed = 856.2 MPa for skulls with osteotomy and OvMmed = 858.1 MPa for skulls without osteotomy;

[0086] • The influence of the number of screws in the skull was slightly more significant, as evidenced by the small difference between the average maximum principal stresses in the bone tunnel, with oimed = 150.2 MPa in skulls with 2 screws and oimed = 15.1 MPa in skulls with 4 screws;

[0087] • The influence of the position of the screws in the skulls, that is, the mesial and lateral configuration of the distractor, was significant, as evidenced by the large difference between the average maximum principal stresses in the bone tunnel, with oi med = 189.6 MPa in the skulls with the medial distractor, and oimed = 75.8 MPa in the skulls with the lateral distractor;

[0088] • Regarding the safety of the 0.5 mm daily expansion, it was found that, for the 8 analyses, 7 presented von Mises stress values ​​below the yield point, both for the device and for the screws. For analysis A6, a small plasticization was observed in the screws, a behavior that did not imply failure due to ductile fracture or fatigue, since the device was not subjected to cyclic loads;

[0089] • For the maximum principal bone stresses (palate), 5 analyses (with the exception of A2, A4, and A8) presented values ​​above the bone tissue rupture stress (90 MPa). However, as can be seen in Figure 22 (the most critical case for the bone tunnel, analysis A5), the stresses are located at the apex of the screw tunnel, which presented higher values ​​due to the geometry with sharp edges and a high stress gradient. This result demonstrates that there are small regions subject to fracture; however, given the nature of the prescribed displacement request, there will be no crack propagation, as it will be contained by the adjacent regions of the bone tissue.

[0090] • The critical configuration in relation to the highest von Mises stresses in the distractor was obtained in analysis A6 (without osteotomy, with 2 screws and lateral position), presenting the value of OVM = 879.3 MPa.

[0091] • For the screws, the configuration with the highest von Mises stresses was A6, with OVM = 1090.4 MPa;

[0092] • For the bone tunnel, the configuration that resulted in the highest maximum principal stresses was A5 (without osteotomy, with 2 screws and medial configuration), with oi = 255.7 MPa;

[0093]

[0039] It is important to emphasize that the figures and descriptions provided do not have the power to limit the forms of execution of the inventive concept proposed herein, but rather to illustrate and make understandable the conceptual innovations revealed in this solution. Therefore, the descriptions and images must be interpreted in an illustrative and not limitative manner, and there may be other equivalent or analogous forms of implementation of the inventive concept disclosed herein that do not escape the spectrum of protection outlined in the proposed solution.

Claims

CLAIM 1- ORTHODONTIC DEVICE PALATINE DISJUNCTOR WITH BONE ANCHORAGE that has a disjunctive device formed by a left (AE) and right (AD) part joined by guide screws (P1) and a threaded screw (P2), characterized by the left (AE) and right (AD) parts being integrated into the support rail (T) that joins the side bars (B), with the rails (T) having folds at the ends and the bars (B) being formed by a central portion (B1) integrated into at least one hexagonal link (B2) that is joined to a semicircular link (B3), in which between the integrated parts there is a fold for cutting (B4) and in the central portion there are at least three holes (B5) and in each link (B2)(B3) one hole (B5).

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