Method and apparatus for printing orthodontic brackets using ultra fine 3D printing resolution and variable layer thickness

Abstract

The present invention relates to a method and system for fabricating customized orthodontic brackets using 3D printing technologies with ultra-fine resolution to produce the orthodontic bracket with multiple layer thicknesses, and each layer thickness ranges from 0.05 micrometers to 100 micrometers. The process involves accessing data related to a 3D CAD bracket structure model for the customized orthodontic bracket. The 3D printing technologies with adaptive slicing dynamically adjust layer thickness based on geometric complexity and surface roughness, ensuring the variable layer ranges from 0.05 micrometers to 100 micrometers. By applying variable layer thickness, the method optimizes surface roughness.

Description

METHOD AND APPARATUS FOR PRINTING ORTHODONTIC BRACKETS USING ULTRA FINE 3D PRINTING RESOLUTION AND VARIABLE LAYER THICKNESSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C §1 19(e) to U.S. Provisional Application, U.S.S.N. 63 / 637,345, filed April 22, 2024, which is incorporated herein by reference.BACKGROUND OF THE INVENTION1. Field of the invention

[0002] The exemplary embodiment(s) of the present invention relates to the field of medical instruments. More specifically, the exemplary embodiment(s) of the present invention relates to processing and fabricating orthodontic apparatus.2. Description of the related art

[0003] Orthodontic brackets and tubes (orthodontic brackets and tubes, either non-selfligating or self-ligating, either for labial or lingual bonding, are referred to as brackets hereafter), either non-customized or customized, are used generically herein to describe a device used in orthodontic treatment to correct the alignment of teeth. The slot of a noncustomized or customized bracket provides the function of reception of the archwire and transfers the gentle force from the archwire to the tooth. The pad of non-customized or customized brackets is bonded to the tooth surface.

[0004] For a non-self-ligating bracket, either non-customized or customized, includes the main features of a slot, tie wings, and pad. The tie wings are structures to attach elastic ligatures or metal ties to hold the archwire in the slot, which exerts gentle force to move teeth into their desired positions. The main difference between a non-self-ligating and self-ligatingbracket is that a self-ligating bracket has a built-in clip or sliding door that locks the archwire inside the slot.

[0005] Non-customized brackets are designed with a set of generic parameters a.k.a. in-out, angle of torque, angulation, rotational offset, slot depth, slot height, and slot length (the parameters are defined as in ISO 27020-2019 hereafter). They are designed to accommodate the generic anatomy and size of different tooth types, a.k.a. upper central incisor, upper lateral incisors, upper canine, upper premolars, upper molars, lower central incisors, lower lateral incisors, lower canine, lower premolars, and lower molars.

[0006] However, customized brackets are designed and manufactured by a veiy different process. It starts with the intraoral scanning of a patient's teeth. After the patient's teeth are scanned, the digital file of the scan is imported into a treatment planning software that segments the digital file of the scan into individual teeth that can be programmed to move from the initial position to the final position. At the final position, teeth are lined up according to clinical standards accepted by the doctor or dental professional. In the embodiment of the present invention, scanning dentition data may be performed using a scanner including, but not limited to a CT scanner, intra-oral scanner, a coordinate measuring machine, a laser scanner, or a structured light digitizer.

[0007] At this final position, the treatment planning software will automatically place a set of bracket templates on the teeth. The template for each type of tooth is different based on the generic size and anatomy of that type of tooth a.k.a. upper central incisor, upper lateral incisors, upper canine, upper premolars, and upper molars, lower central incisors, lower lateral incisors, lower canine, lower premolars, and lower molars. The treatment planning software will customize the parameters of the bracket a.k.a. in-out, angle of torque, angulation, rotational offset, slot depth, slot height, and slot length, based on the final position of the teeth and the placement of the brackets on the teeth constrained and conditioned by thechosen archwire shape by the doctor, which results in all the slots in brackets are lined up along the arch wire at the final position of teeth.

[0008] The other portion of the bracket template that is customized to the patient's teeth is the pad (or called base by ISO 27020-2019). As the tooth anatomy of a specific patient is used to shape the pad for each template, the pad will well fit the patient’s tooth where the template is placed. Then the digital model of customized brackets can be output into a format that is transferable and compatible to a 3D printer.

[0009] The surface roughness of the bracket, either non-customized or customized, is a parameter that is critical to strength, aesthetics, friction force, and comfort for the following reasons:• The rough surface of the bracket will be more prone to fracture due to stress concentration at the peaks and valleys of the surface caused by impact force and fatigue. This stress concentration can cause the propagation of microcracks in the material and lead to the fracture of the non-customized or customized bracket.• The rough surface of the bracket will make it easier to catch food and drink residues, which can discolor the bracket, form biofilm, and cause hygiene issues.• The rough surface of the bracket can increase the friction force between the slot and the archwire. The increased friction force is considered as the impedance of tooth movement along the arch wire during treatment.• The rough surface of the bracket might also be felt as irritation and rubbing discomfort by some patients.

[0010] Many three-dimensional (“3D”) printing technologies can be used to print noncustomized or customized brackets. Specialized printing materials can be used with variousprinting technologies to produce brackets designed to offer strength, ascetics, and biocompatibility for clinical use.

[0011] The 3D printing technologies comprise but are not limited to laser sintering, stereolithography, digital light processing, two-photon polymerization, sub-pixel microscanning, electrochemical deposition, or ink jetting. Common materials used for 3D printing of orthodontic brackets are polymer materials, composite materials, metals, and ceramic materials. For example, polymer brackets can be printed by stereolithography (SLA) or digital light processing (DLP) using liquid polymer resins. Alternatively, composite materials are processed using fused deposition molding (FDM) or SLA technology to produce brackets. Metal brackets can be fabricated using techniques such as selective laser melting (SLM) or electron beam melting (EBM). These techniques melt metal powders layer by layer by means of a precise laser or electron beam to produce a highly reinforced bracket. Subpixel microscanning and ink jetting technologies can print brackets using polymer resins or ceramic slurries.

[0012] In the 3D printing process, the part is printed in layers along a build direction. The layer thickness and XY plane resolution have an important influence on the surface roughness of the printed part. When a surface with the normal not perpendicular to the build direction is printed by thick layers (Fig. 6A, the printed surface will be rougher than when it is printed by thin layers (Fig. 6B). In general, when a thick layer is used for 3D printing, the part is printed in a shorter time but greater surface roughness than when a thin layer is used. For example, although the DLP technology can be used for producing orthodontic brackets with speed, the XY plane resolution and the layer thickness can result in large surface roughness. While two-photon polymerization, sub-pixel microscanning, or ink jetting technologies can achieve XY plan resolution and layer thickness to a much finer degree, the printing process takes a much longer time. Therefore, a need arises for more efficient and accurate methods formanufacturing non-customized or customized brackets with balanced layer thickness and printing time to control the surface roughness.SUMMARY

[0013] In one aspect, the embodiments of the present invention disclose a process of providing an orthodontic device via an adaptive slicing method and 3D printing to dynamically adjust variable layers. For example, the process comprises accessing data related to a 3D bracket structure model for the orthodontic bracket. After applying adaptive slicing methods, the thickness of each layer of the orthodontic bracket can be dynamically varied based on surface roughness requirements. The process is capable of utilizing adaptive slicing techniques to produce optimal and multiple layer thicknesses, and each layer thickness ranges from 0.05 micrometers to 100 micrometers. Preferably, at least one of the multiple layer thicknesses from 0.05 micrometers to 5 micrometers is used to 3D print the orthodontic device. Specifically, the adaptive slicing method is an analytic slicing method to calculate the layer thickness sequentially from the first layer to the last layer based on the surface roughness requirements. More preferably, each layer thickness is an integral multiple of the minimal allowable layer thickness.

[0014] In one preferable embodiments of the present invention, the step of the adaptive slicing method comprises an analytic slicing to calculate the layer thickness based on surface roughness requirement, wherein the analytic slicing method comprises the following steps: (a) slicing a 3D model using the minimum allowable layer thickness to obtain a high- resolution initial slicing profile; (b) calculating a cusp length (r>) for each layer based on the geometric features at the intersection where the slicing plane meets the model; (c) calculating a maximum allowable cusp length (rmaxi) for each layer to serve as an acceptance criterion based on an applicable predetermined surface roughness (Ra) requirement; (d) comparing thecalculated cusp length (r,) of the layer against the corresponding maximum allowable cusp length rma.x i, and performing the following: if the calculated cusp length n is greater than or equal to the corresponding maximum allowable cusp length rmaxi, retaining the original layer thickness (hi); if the calculated cusp length n is less than or equal to rmaxi, merging the original layer with the preceding layer (ri-i)to form a combined layer with a combined layer thickness (hcombined) and recalculating the maximum allowable cusp length rmax i based on the combined layer thickness (hcombined); wherein if the recalculated merged cusp length is greater than the recalculated maximum allowable cusp length rraaxi, then retaining the current / original individual layer; otherwise, merging the two layers into a single layer; and, (e) iteratively performing steps (b) through (d) layer by laye until every layer satisfies the applicable predetermined surface roughness (Ra) requirement and generating a final adaptive slicing profile with multiple layer thicknesses.

[0015] Specifically, the maximum allowable cusp length rmaxi of the layer is calculated based on the following equation:wherein rmaxi is the maximum allowable cusp length of the layer, hi is the layer thickness, Rais the applicable predetermined surface roughness.

[0016] In another aspect, the embodiments of the present invention disclose an orthodontic bracket fabricated by the above process and comprising a customized or noncustomized pad designed to bond to a tooth, wherein the multiple layer thickness is adjusted dynamically within ranges from 0.05 micrometers to 100 micrometers. Preferably, at least one of the multiple layer thicknesses ranges from 0.05 micrometers to 5 micrometers.

[0017] In other aspects, the embodiments of the present invention disclose a computer network for fabricating orthodontic devices, the network comprising: a 3D printing systemcapable of printing orthodontic brackets with multiple layer thicknesses by applying an adaptive slicing method, wherein each layer thickness ranges from 0.05 micrometers to 100 micrometers.

[0018] By the comparison between the cusp length (n) and the maximum allowable cusp length (rmax;), the present invention can achieve the effect of dynamical ly adjusting the layer thickness of a specific portion, and enable specific or certain portions of the customized or non-customized bracket to achieve the required surface roughness (Ra). That is to say, the present invention has an advantage in providing variable layer thickness according to the geometry of the bracket by an automatic algorithm. In addition, the resolution of the XY plane must be matched to the layer thickness in order to achieve the required overall surface roughness of the orthodontic bracket.

[0019] Additional features and benefits of the exemplary embodiment(s) of the present invention will become apparent from the detailed description, figures, and claims set forth below.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The exemplary embodiment(s) of the present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only.

[0021] FIG. 1 is a diagram illustrating a sectioning plane on the bracket parallel to the build direction and perpendicular to the layer.

[0022] FIG. 2 is a diagram illustrating an evaluation profile of a portion of the bracket surface.

[0023] FIG. 3 is a schematic diagram illustrating the calculation of the reference line;

[0024] FIG. 4 is a schematic diagram illustrating the calculation of the surface roughness.

[0025] FIG. 5 is a flowchart illustrating the adaptive slicing method using the analytic method.

[0026] FIGs. 6A and 6B are diagrams illustrating a layer thickness showing a factor of surface roughness in 3D printing in accordance with one embodiment of the present invention. FIG.6 A shows the thick layer has a coarse surface, and FIG. 6B shows the thin layers have smooth surfaces.

[0027] FIG. 7A is a side view illustrating that is perpendicular to the slot comprising of 3 planar surfaces, two sides intersecting the base at 90 degrees.

[0028] FIG. 7B is a side view illustrating an evaluation profile of a generic bracket where the build direction is not perpendicular to the slot surface normal.

[0029] FIG. 7C is a diagram illustrating the relationship between the slicing plane and the slot surfaces as a section view from FIG. 7B.

[0030] FIGs. 7D and 7E are block diagrams illustrating a fixed layer thickness that doesn’t result in the same surface roughness throughout the part in accordance with one embodiment of the present invention. FIG. 7D shows the thick layers applied to the slope surface, and FIG. 7E shows the thin layers are applied to the slope surface;

[0031] FIG. 8A is a diagram illustrating that the generic bracket is oriented to align the slot to the build direction.

[0032] FIG. 8B is a diagram illustrating the profile from the sectioning plane, showing that the bracket is orientated to align the slot to the build direction.

[0033] FIG. 9 is a graph illustrating the modeled surface roughness Ra(0) as a function of build angle 9 in additive manufacturing.

[0034] FIG. 10 is a diagram illustrating a computer network capable of providing a format transformation in accordance with one embodiment of the present invention.

[0035] FIG. 11 is a block diagram illustrating a digital processing system capable of operating format transformation and computations in accordance with one embodiment of the present invention.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] Embodiments of the present invention are described herein in the context of a method and / or apparatus for processing and fabricating orthodontic devices.

[0037] The purpose of the following detailed description is to provide an understanding of one or more embodiments of the present invention. Those of ordinary skills in the art will realize that the following detailed description is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure and / or description.

[0038] In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be understood that in the development of any such actual implementation, numerous implementation-specific decisions may be made in order to achieve the developer’s specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be understood that such a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking of engineering for those of ordinary skills in the art having the benefit of embodiment(s) of this disclosure.

[0039] Various embodiments of the present invention illustrated in the drawings may not be drawn to scale. Rather, the dimensions of the various features may be expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all the components of a given apparatus (e.g., device) or method. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.

[0040] The term "system" or “device” is used generically herein to describe any number of components, elements, sub-systems, devices, packet switch elements, packet switches, access switches, routers, networks, computer and / or communication devices or mechanisms, or combinations of components thereof. The term "computer" includes a processor, memory, and buses capable of executing instruction wherein the computer refers to one or a cluster of computers, personal computers, workstations, mainframes, or combinations of computers thereof.

[0041] Different printing technology has different principles of operation. But commonly, parts are printed layer by layer along the build direction. The layer boundary, often referred to as build lines, will remain in the part after post-processing. Analytically, the effect of layer thickness on surface roughness is related to the surface normal of the model with respect to the build direction. Unless the surface normal of the model is perpendicular to the build direction, the thinner the layer, the smoother the printed surface. If the surface normal is perpendicular to the build direction, the layer thickness has no effect on the roughness of the printed surface. This will be explained in detail when one embodiment of the adaptive slicing is developed as follows.

[0042] One embodiment of the presently disclosed invention is methods and apparatus relating to three-dimensional (“3D”) printing technologies which can be used to print orthodontic brackets, either non-customized or customized, with controlled surface roughness.

[0043] In the present invention, adaptive slicing and its algorithm are used to adjust layer thickness dynamically to meet the required surface roughness for the intended design of the bracket. Specifically, adaptive slicing is a method used in 3D printing to optimize the slicing process to meet one or more requirements by vaiying the layer thickness. Instead of using a fixed layer height, adaptive slicing adjusts the thickness of individual layers based on geometric complexity, surface roughness, and other considerations.

[0044] Different methods of adaptive slicing aim to balance surface quality, printing speed, and material usage. In general, they can be broadly categorized into analytic methods and experimental methods based on their approach to determining optimal layer thickness.

[0045] As for the analytical methods, the analytic methods rely on mathematical models, geometric analysis, and predefined parameters to determine layer thickness. These methods are grounded in deterministic calculations based on the geometry of the 3D model and other input factors. They use equations, such as those based on cusp height, angle thresholds, area variations, or error tolerances, focus on optimizing slicing through exact computations, and do not require physical experiments or empirical data. For example, geometric feature-based methods dynamically adjust layer thickness based on geometric features such as sharp edges, curves, and flat surfaces. They analyze surface cusp heights, normals, angles, and other geometric parameters to ensure high resolution in critical regions while optimizing speed in less complex areas. Other error-based methods minimize the geometric error between the original CAD model and the printed object by adjusting layer thickness. They analyze metrics like volumetric deviation, area variation, or profile error to optimize layers where details are most needed. Medial axis-based methods calculate themedial axis (central skeleton) of slice contours to dynamically adjust layer thickness. The method ensures that contour fidelity is maintained while optimizing the layer thickness for regions requiring detailed structures. Area ratio-based methods adjust layer thickness based on the change in cross-sectional area between consecutive layers. A larger change in area triggers finer slicing to preserve detail, while smaller changes allow for thicker layers. It is to say, analytic methods are highly precise in determining layer thickness.

[0046] On the other hand, the experimental methods rely on empirical data, heuristics, or machine learning to determine optimal layer thickness. These methods adapt to real- world conditions by learning from physical tests or historical print data. They use observed performance data, material characteristics, or experimental feedback, may involve iterative optimization or data-driven predictions, and can employ machine learning or Al to predict slicing parameters. For example, machine learning methods leverage machine learning models to predict optimal layer thickness based on geometric complexity, print quality requirements, and prior training data. The algorithm continuously improves through iterative feedback. Hybrid methods may incorporate experimental heuristics into analytic frameworks for dynamic adaptability. That is to say, the experimental methods are adaptable to real- world conditions and variations in printing, and can optimize slicing for specific printers, materials, or environments, but require large amounts of experimental data.

[0047] To explain how adaptive slicing can be implemented for a customized or noncustomized bracket, the present invention provides an analytic method-based proposed without limiting the possibility of other methods of adaptive slicing being implemented to achieve the same or greater benefits. That is to say, if surface roughness is chosen as the metric, a relationship between surface roughness and layer thickness needs to be defined. Based on that relationship, the algorithm to determine the proper layer thickness for theevaluation surface of the bracket can be developed such that the surface roughness requirement for that portion of the bracket can be achieved.

[0048] In the embodiment of using the analytic method, the development of the relationship between surface roughness and layer thickness starts from the definition of surface roughness. Surface roughness as defined in ISO 21920-2 is a metric as it can be measured across the stairsteps on any profile perpendicular to the layers or parallel to the build direction of the 3D printed part, as shown in Equation 1.Equation 1

[0049] Where Ra, surface roughness, is the arithmetic mean of the absolute heights of the scale-limited surface from the reference line within an evaluation length; leis the evaluation length in the direction of the reference line; z(x) is the signed normal distance at position x from the reference line to the assessed roughness profile, which is obtained by removing the waviness and form by profile filters.

[0050] For 3D printing, an STL (Stereolithography) model is a tessellated model of the original CAD model commonly used for slicing. It represents 3D geometry using a mesh of interconnected triangles. Each triangle is defined by three vertices and a normal vector that specifies its orientation. This tessellation simplifies the representation of complex 3D surfaces by approximating them with a network of flat triangular facets, hi a sliced 3D model, each slicing plane, perpendicular to the build direction, intersects the triangles at a certain coordinate along the build direction of the tessellated model. Surface roughness can be evaluated on a planar or curved surface of the tessellated model. When the evaluation surface is curved, surface filters can be used to remove waviness and form according to standards. Therefore, in the following development of the analytic method, a planar portion of the bracket surface is selected for development. The algorithm to compute the triangular facetsintersected by the slicing plane and their characteristics, such as surface angle, normal, cusp height, cusp length, etc., are well known.

[0051] To express Equation 1 in terms of Raand layer parameters, a profile that is generated by sectioning the sliced tessellated model using a plane perpendicular to the layers is analyzed as shown in Fig. 1. An evaluation profile 10 of a portion of a sliced tessellated model 20 is shown in Fig. 2. If the evaluation profile 10 is zoomed in as shown in Fig. 3, a schematic diagram is generated to compute the reference line. A cusp is a point in the profile where two surfaces, lines, or curves meet, which can be the intersection of the slicing plane and the tessellated model, or the intersection point of two layers as shown in Fig. 3. The reference line is computed as follows in Equation 2, wherein S is the area on the profile that represents the surface deviation from the tessellated model; leis the evaluation length in the direction of the reference line; h is the layer thickness; r is the cusp length of the layer based on the distance between Cusp 3, where the slicing plane intersects the tessellated model, and Cusp 2, where the slicing plane intersects the next layer, as shown in Fig. 3; z is a z coordinate of the reference line, as shown in Fig. 3. From Equation 2, the reference line bisects the layer thickness h and cusp length r, which are the two legs of the right triangle depicted by area S.

[0052] To compute the Ra, set the x-axis to coincide with the reference line and the z- axis perpendicular to the reference line as shown in Fig. 4. Therefore, the Racan be computed based on one layer by averaging the heights of the cusps from the reference line according to Equation 1 as follows. The schematic of this computation is shown in Fig. 4.1Ra - ~T ' (Si + S2+ S3)

[0053] Where Rais the surface roughness; leis the evaluation length in the direction of the reference line; h is the layer thickness; rmax is the cusp length of the layer when the surface roughness equals Ra.

[0054] From Equation 3, rmaxi, the maximum cusp length for a layer i, that meets the required surface roughness Raat the given layer thickness hi can be calculated. It can be used as the acceptance criteria to verify if the current layer thickness hi is small enough to meet the acceptance criteria for the surface roughness.

[0055] Although Equation 3 is based on one layer, if each layer across the evaluation length is assessed for surface roughness and meets the acceptance criteria, it is concluded that the surface roughness along the evaluation length meets the acceptance criteria too.

[0056] In practice, a 3D printer has the maximum and minimum allowable thicknesses due to the limitations of the 3D printer. No matter how complex the model is, the minimum allowable thickness is the highest resolution along the build direction achievable by the 3D printer. The actual layer thickness is an integral multiple of the minimal layer thickness.

[0057] An embodiment of an algorithm using this analytic method can be developed to slice the model using the minimum allowable thickness and run the algorithm of adaptive slicing on the sliced model to merge layers, which results in variable layer thickness in the range of minimum and maximum thicknesses, as shown in Fig. 5. The algorithm first slices the tessellated model with the minimum layer thickness, a.k.a. the highest resolution on thebuild direction. It calculates and stores the cusp length n at layer i with the minimum layer thickness and computes the maximum cusp length rmaxi at the layer thickness hi and requiredRa. If the n is greater than or equal to the rmaxi, the layer i (the original layer) is retained. If the n is less than rmaxi, layer i and layer i-1 are temporarily combined in terms of cusp length n and layer thickness hi. Then the combined layer thickness (hcombined) is used to compute rmaxi. If the combined n is greater than the rmaxi, then the original layer i is retained. If the combined n is less than the rmaxi, then the layer i and layer i-1 are merged into layer i. The adaptive slicing is output when all the layers generated at the minimum layer thickness are processed.

[0058] When non-customized or customized brackets are designed for 3D printing, the adaptive slicing algorithm can have additional functions to ensure the structure integrity and the strength will be retained in the 3D printed bracket, for which the algorithm will optimize parameters like wall thickness, fillet radius, and minimal feature size using but not limited to FEA (finite element analysis).

[0059] The adaptive slicing algorithm can be used to improve the overall surface roughness of the bracket and the printing efficiency. Through this adaptive slicing method, the system automatically calculates and distributes the appropriate layer thickness based on the build direction and bracket surface curvature, so that the balance of surface roughness and printing speed is achieved. To achieve a similar surface roughness to conventional orthodontic brackets, adaptive layer thickness and XY plane resolution of between 5 micrometers (pm) and 20 micrometers are desirable in 3D printing of non-customized or customized orthodontic brackets. To achieve a surface roughness superior to conventional orthodontic brackets, adaptive layer thickness and XY plane resolution of between 0.05 micrometers and 5 micrometers are preferable in 3D printing of non-customized or customized orthodontic brackets, referring to the publication on surface roughness of orthodontic brackets. It can also be applied only to some features / portions of the bracket such as the slot and the pad to meet ahigher surface roughness requirement from an analytic perspective. For instance, the layer thickness and XY plane resolution between 0.05 micrometers and 5 micrometers (less than 5 micrometers) can be used for the slot and pad of the customized bracket to achieve high precision and low surface roughness.

[0060] Post-processing has to be considered an adjustment that can modify the surface roughness of the printed part, in both increasing and decreasing the final surface roughness. Preferably, the post-processing techniques include but are not limited to precision polishing, chemical post-processing, or thermal processing.

[0061] One of the most popular conventional bracket prescriptions is MBT (a bracket prescription system developed by three orthodontists: McLaughlin, Bennett, and Trevisi). The MBT prescription has the following tip and torque as in Table 1. The sign can be ignored for this analysis because they indicate the clinical direction of the angle.Table 1

[0062] For example, a generic bracket for maxillary lateral incisor with a torque of10 degrees and tip of 8 degrees is taken as an example. As shown in Fig. 7A, the sectioning plane is perpendicular to the slot. The evaluation profile of the bracket in the section plane is as shown in Fig. 7B, wherein the torque angle is between the line bisecting the slot and the normal of the tooth surface, approximated by build direction, a.k.a. the normal of the build platform in this case. If the slot is zoomed in with the two slicing planes as shown in Fig. 7C, based on trigonometry, the slicing plane 1 intersects the two sides of the slot at 80 degrees, i.e. 90-10 degrees, and the slicing plane 2 intersects the base of the slot at 10 degrees. It can be derived from this example that the slot sides and the slot base will have different surface roughness resulting from the different angles between the corresponding surface normal 111, 112, and 113 and the build direction.

[0063] An adaptive slicing method can calculate the variable lay thickness by a given build direction and surface geometry of the bracket to meet a surface roughness specification. If there is a required surface roughness specified for the bracket slot, based on the analysis shown in Fig. 7A to Fig. 7C, it can be derived that the layer thickness w’ill be adaptive to thebracket for different teeth. It is the interest of this invention to provide a reference surface roughness for the sliced bracket using the analytical model and algorithm presented herein. One way to derive this reference surface roughness is to provide the upper limit of the surface roughness under certain conditions.

[0064] According to the development of Equation 3, the surface roughness can be calculated by Equation 4.

[0065] Referring to Fig. 3, the cusp length can be expressed in layer thickness h and the angle between the surface and the slicing plane 9, which equals the angle between the build direction and the normal of the surface sliced.

[0066] Therefore, Equation 4 can be expressed in layer thickness h and the angle between the build direction and the normal of the surface sliced as in Equation 5, wherein the range of the 9 is between 0 and 90 degrees.

[0067] Therefore, the surface roughness Rais a function of 0 at a given layer thickness h. When h = 1, the Rais plotted as the following Fig. 9. Therefore, for a given layer thickness h, the maximum surface roughness Raequals to 0.25*h when the 9 approaches zero. The minimum surface roughness equals to 9 when the 9 is 99 degrees, in which case the normal of the sliced surface is perpendicular to the build direction.

[0068] As stated before, the preferred adaptive slicing layer thickness range is from 0.05 micrometers to 100 micrometers. That is to say, when the layer thickness is 100 micrometers, the maximum surface roughness is 25 micrometers from an analyticalperspective; when the layer thickness is 5 micrometers, the maximum surface roughness is1.25 micrometers from an analytical perspective.

[0069] Figs. 7D and 7E illustrate how layer thickness affects surface roughness depending on the orientation of the surface normal relative to the build direction. In Fig. 7D, when a surface with a normal not perpendicular to the build direction is sliced with thick layers, the resulting surface is rougher than its counterpart sliced with thin layers, as seen in Fig. 7E. Conversely when a surface with a normal perpendicular to the build direction is sliced with thick layers (Fig. 7D), it exhibits the same surface smoothness as the one sliced with thin layers (Fig. 7E). This is because, analytically, the cusp height between adjacent layers is zero, leading to the surface roughness (Ra) of zero, as derived in Equation 5. Therefore, aligning the build direction perpendicular to a surface normal can theoretically yield zero surface roughness.

[0070] To improve the surface quality of a bracket slot — which consists of three planar surfaces intersecting at right angles (Fig. 7C) — a generic bracket model can be oriented such that the plane bisecting the slot is perpendicular to the build platform. This orientation aligns the normal of the three planar slot surfaces perpendicular to the build direction and minimizes cusp formation, resulting in zero surface roughness along the sliced planar surfaces of the slot as shown in Fig. 8A and Fig. 8B. However, the selection of build direction is affected by many factors. In the example shown in Figs. 8A and 8B, it will need to add support structures to the oriented bracket model. The addition of support structures will increase the material cost and printing time, which is not preferable in production. In fact, build direction often cannot be perpendicular to the surfaces normal in interest due to such factors as material cost, printing time, and the arrangement of the parts on the build platform. Another factor that can affect the surface roughness is the lower and upper limits of the layer thickness of the printing equipment. As can be seen from the flow chart in Fig. 5, if the r, isgreater rmaxi at the thinnest layer the equipment can print, the surface roughness will not meet the requirement at the corresponding layers. On the other hand, if the q is still less than rmax i at the upper limit of the layer thickness, the surface roughness will meet the requirements at the corresponding layers, though the printing time could be shorter given a greater upper limit of the layer thickness.

[0071] Fig. 10 is a diagram illustrating a computer network capable of facilitating a 3D printing process in accordance with one embodiment of the present invention. In this network environment, a system 600 is coupled to a wide-area network 1002, LAN 1006, format conversion network 1001, and a server 1004. Wide-area network 1002 includes the Internet, or other proprietary networks, including America On-Line ™, SBC™, Microsoft Network™, and Prodigy™. Wide-area network 1002 may further include network backbones, long-haul telephone lines, Internet service providers, various levels of network routers, and other means for routing data between computers.

[0072] Server 1004 is coupled to wide-area network 1002 and is, in one aspect, used to route data to clients 1010-1012 through a local-area network (“LAN”) 1006. Server 1004 is coupled to SSD 100 wherein the storage controller is able to decommission or logically remove defective pagc(s) from a block to enhance overall memory efficiency.

[0073] The LAN connection allows client systems 1010-1012 to communicate with each other through LAN 1006. Using conventional network protocols, USB portable system 1030 may communicate through wide-area network 1002 to client computer systems 1010- 1012, supplier system 1020, and storage device 1022. For example, client system 1010 is connected directly to wide-area network 1002 through direct or dial-up telephone or other network transmission lines. Alternatively, clients 1010-1012 may be connected through wide- area network 1002 using a modem pool.

[0074] Having briefly described one embodiment of the computer network in which the embodiment(s) of the present invention operates, Fig, 1 1 illustrates an example of a computer system, which can be a 3D printer, a host, a server, a router, a switch, a node, a hub, a wireless device, or a computer system,

[0075] Fig. 11 is a block diagram 700 illustrating a digital processing system capable of facilitating 3D printing operations in accordance with one embodiment of the present invention. A computer system or a signal separation system 800 can include a processing unit 1 101 , an interface bus 1 1 12, and an input / output (“10”) unit 1 120. Processing unit 1 101 includes a processor 1102, a main memory 1104, a system bus 1111 , a static memory device 1106, a bus control unit 1105, an I / O element 1130, and a 3D printing controller 1185. It should be noted that the underlying concept of the exemplary embodiment(s) of the present invention would not change if one or more blocks (circuit or elements) were added to or removed from Fig. 11.

[0076] Bus 1111 is used to transmit information between various components and processor 1102 for data processing. Processor 1102 may be any of a wide variety of general- purpose processors, embedded processors, or microprocessors such as ARM®' embedded processors, Intel® Core™ Duo, Core™ Quad, Xcon®, Pentium™ microprocessor, Motorola™ 68040, AMD® family processors, or Power PC™ microprocessor.

[0077] Main memory 1104, which may include multiple levels of cache memories, stores frequently used data and instructions. Main memory 1104 may be RAM (random access memory), MRAM (magnetic RAM), or flash memory. Static memory 1 106 may be a ROM (read-only memory), which is coupled to bus 1111, for storing static information and / or instructions. Bus control unit 1 105 is coupled to buses 1111-1112 and controls which component, such as main memory 1104 or processor 1102, can use the bus. Bus control unit 1105 manages the communications between bus 1 111 and bus 1112. Mass storage memory orSSD, which may be a magnetic disk, an optical disk, hard disk drive, floppy disk, CD-ROM, and / or flash memories are used for storing large amounts of data.

[0078] I / O unit 1120, in one embodiment, includes a display 1 121, keyboard 1122, cursor control device 1 123, and communication device 1 125. Display device 1 121 may be a liquid crystal device, cathode ray tube (“CRT”), touch-screen display, or other suitable display device. Display 1121 projects or display images of a graphical planning board.Keyboard 1122 may be a conventional alphanumeric input device for communicating information between computer system 1 100 and computer operator(s). Another type of user input device is cursor control device 1123, such as a conventional mouse, touch mouse, trackball, or other type of cursor for communicating information between system 1 100 and user(s).

[0079] Communication device 1125 is coupled to bus 1111 for accessing information from remote computers or servers, such as servers or other computers, through the wide-area network. Communication device 1125 may include a modem a network interface device, or other similar devices that facilitate communication between computer 1100 and the network. Computer system 700 may be coupled to a number of servers 1004 via a network infrastructure such as the infrastructure illustrated in Fig. 10. Preferably, the computer network further comprises a post-processing system connected to the network to refine the surface quality of the orthodontic brackets.

[0080] While particular embodiments of the present invention have been shown and described, it will be obvious to those of ordinary skill in the art that, based upon the teachings herein, changes and modifications may be made without departing from this exemplary embodiment(s) of the present invention and its broader aspects. Therefore, the appended claims are intended to encompass within their scope all such changes and modifications as are within the true spirit and scope of this exemplary embodiment(s) of the present invention.

Claims

CLAIMSWhat is claimed is:

1. A method of manufacturing an orthodontic bracket by 3D printing technologies, comprising: accessing data related to a 3D bracket structure model for the orthodontic bracket; applying an adaptive slicing method to determine each layer thickness of the orthodontic bracket based on surface roughness requirements; producing the orthodontic bracket with multiple layer thicknesses; and, wherein each layer thickness ranges from 0.05 micrometers to 100 micrometers.

2. The method of claim 1, wherein at least one of the multiple layer thicknesses ranges from 0.05 micrometers to 5 micrometers.

3. The method of claim 1, wherein at least one of the multiple layers has a surface roughness less than or equal to 25 micrometers.

4. The method of claim 3, wherein at least one of the multiple layers has a surface roughness less than or equal to 1.25 micrometers.

5. The method of claim 1, wherein the adaptive slicing method is an analytic slicing method to calculate the layer thickness sequentially from a first layer to a last layer based on the surface roughness requirements.

6. The method of claim 5, wherein each layer thickness is an integral multiple of a minimum allowable layer thickness.

7. The method of claim 6, wherein the analytic slicing method comprises:(a) slicing a 3D model using the minimum allowable layer thickness to obtain a high- resolution initial slicing profile;(b) calculating a cusp length (n) for a layer based on geometric features at the intersection where the slicing plane meets the model;(c) calculating a maximum allowable cusp length (rmax0 for the layer to serve as an acceptance criterion based on an applicable predetermined surface roughness (Ra) ;(d) comparing the calculated cusp length (r0 of the layer against the corresponding maximum allowable cusp length (rmax0 and performing the following: if the calculated cusp length (n) is greater than or equal to the corresponding maximum allowable cusp length (rmaxi), retaining the original layer thickness (hi); if the calculated cusp length (n) is less than the maximum allowable cusp length (rmaxi), merging the original layer with the preceding layer (ii-i) to form a combined layer with a combined layer thickness (hCOmbmed) and recalculating the maximum allowable cusp length (rmax i) based on the combined layer thickness (hcombined); wherein if the recalculated merged cusp length is greater than the recalculated maximum allowable cusp length (rmiix 0, then retaining the original individual layer; otherwise, merging the two layers into a single layer; and,(e) iteratively performing steps (b) through (d) layer by layer until every layer satisfies the applicable predetermined surface roughness (Ra) and generating a final adaptive slicing profile with multiple layer thicknesses.

8. The method of claim 7, wherein the maximum allowable cusp length (rmax0 of the layer is calculated based on the following equation:wherein rmaxi is the maximum allowable cusp length of the layer, hi is the layer thickness, Rais the applicable predetermined surface roughness.

9. The method of claim 8, wherein the minimum allowable layer thickness is derived from the highest resolution of a 3D printing apparatus used to produce the orthodontic bracket in the build direction.

10. The method of claim 7, wherein merging the two layers into a single layer at step (d) further comprises using the combined layer thickness as the layer thickness of the single layer and using the recalculated merged cusp length as the calculated cusp length of the single layer.11 . The method of claim 1, further comprising performing finite element analysis (FEA) to optimize structural integrity, including wall thickness, fillet radii, and minimum feature size of the brackets.

12. The method of claim 1, further comprising applying post-processing techniques to modify the surface roughness.

13. The method of claim 12, wherein the post-processing techniques comprise precision polishing, chemical post-processing, and thermal processing.

14. The method of claim 1, wherein the 3D printing technologies comprise laser sintering, stereolithography, digital light processing, two-photon polymerization, electrochemical deposition, sub-pixel microscanning, and ink jetting.

15. An orthodontic bracket fabricated by a 3D printing process, comprising: multiple layers whose shape are consistent with a 3D CAD bracket structure model of the orthodontic bracket; wherein the multiple layers are fabricated with multiple layer thicknesses by an adaptive slicing method, and each layer thickness ranges from 0.05 micrometers to 100 micrometers.

16. The orthodontic bracket of claim 15, wherein at least one of the multiple layer thickness ranges from 0.05 micrometers to 5 micrometers.

17. The orthodontic bracket of claim 15, wherein at least one of the multiple layers has a surface roughness less than or equal to 25 micrometers.

18. The method of claim 17, wherein at least one of the multiple layers has a surface roughness less than or equal to 1.25 micrometers.

19. A computer network for fabricating orthodontic devices, the network comprising: a 3D printing system configured to print orthodontic brackets with multiple layer thicknesses by applying an adaptive slicing method, wherein each layer thickness ranges from 0.05 micrometers to 100 micrometers.

20. The computer network of claim 19, further comprising: a treatment planning computing system configured to receive and process intraoral images of a patient’s dentition to a digital model, segment the digital model into individual teeth, and generate a treatment plan for repositioning the teeth from an initial position to a final position; a digital processing unit configured to perform format transformation and execute computations for fabricating orthodontic brackets; and a server communicatively coupled to the 3D printing system and the treatment planning computing system, the server being configured to enable remote access and facilitate data exchange across the network.21 . The computer network of claim 19, wherein the 3D printing system further comprises an adaptive slicing method for dynamically adjusting layer thickness based on geometric complexity and surface roughness requirements.

22. The computer network of claim 20, wherein the digital processing unit is further configured to execute format transformation to ensure that the digital model is compatible with 3D printing parameters.

23. The computer network of claim 20, wherein the server is further configured to interface with a wide-area network and a mass storage system.

24. The computer network of claim 23, wherein the mass storage memory comprises a magnetic disk, an optical disk, a hard disk drive, a floppy disk, a CD-ROM, a solid-state drive(SSD), and flash memories.

25. The computer network of claim 19, wherein the 3D printing system is configured to fabricate orthodontic brackets comprising polymers, composites, metals, and ceramics.

26. The computer network of claim 20, wherein the treatment planning computing system is configured to automatically calculate the orthodontic brackets along a predefined archwire shape based on the final position.

27. The computer network of claim 20, wherein the digital processing unit includes a finite element analysis (FEA) module configured to evaluate a structural integrity of the orthodontic bracket, including wall thickness, fillet radii, and minimum feature size.

28. The computer network of claim 19, wherein the 3D printing system is equipped with variable resolution control, which allows XY plane resolution adjustments based on build direction and layer thickness.

29. The computer network of claim 20, further comprising a scanning system configured to generate a high-resolution digital model of the patient’s teeth to customize the pad / base geometry of the orthodontic bracket to improve adhesion and customized fit.

30. The computer network of claim 20, further comprising a post-processing system connected to the network and configured to enhance the surface quality of the orthodontic brackets.

Images