Patent Application
20230338114
The present disclosure relates generally to dental applications, and more particularly to preparation guides used to facilitate dental restorations.
Millions of dental restorations are placed in patients every day. These dental restorations may take the form of direct restorations, commonly referred to as fillings, which involve preparing the tooth by removing the carious or damaged tooth tissues and forming a restoration in the prepared tooth intra-orally. Alternatively, dental restorations may be indirect, which requires fabricating part of the restoration outside of the mouth, such as is often the case with veneers, crowns, inlays, caps, or bridges. In both cases, the tooth or teeth that support the restoration will need to be prepared. The supporting portion of the tooth or teeth (e.g., after the tooth is drilled or cut to remove the damaged or decayed portion) is referred to as a preparation.
Historically, dentists have relied on their own judgement when preparing the tooth for dental restoration. This requires the dentist to examine the tooth and visually determine what sections of the tooth to remove before restoring. It is difficult for dentists to visually analyze the tooth and prepare it by hand in a way that will minimize stress on the restoration, supporting tooth or teeth, and their interfaces from chewing. Because this practice relies on the individual dentist, it takes time for preparation and there is room for error. Prolonged preparation can incur trauma to the pulp tissues of the tooth. Indirect restorations are also designed and fabricated days or even weeks after the preparation is made. Many dental restorations later fail through fracture, debonding, interfacial leakage, or recurrent caries from excessive masticatory stresses.
In order to develop a more precise practice, some dentists have used a preparation guide to prepare the tooth for indirect restoration. These guides include a block that rests around the tooth and provides the dentist with a channel that guides cutting. Dental preparation guides are roadmaps that direct dentists in preparing the tooth for restoration. However, conventional preparations are box-shaped and are not shape-optimized. Because of this, box-shaped preparations often lead to excessive stress on the restoration, supporting teeth, and their interfaces, which results in failure of the restoration.
Shape-optimized preparation has a more organic geometry which minimizes interfacial and bulk stresses. This in turn reduces the likelihood of restoration failure. Because of its organic geometry, however, shape-optimized preparations are difficult, if not impossible, to prepare by hand accurately. Additionally, preparations for direct restorations are still made by hand without a guide. Thus, there is a need for a dental restoration preparation guide for shape-optimized preparations for both direct and indirect restorations.
Moreover, having a preparation guide is very pertinent in the current COVID-19 pandemic environment. Reopening elective dental procedures bears the risk of exposing dental professionals and patients to SARS-COV-2. In order to ensure no or little nosocomial transmission of SARS-COV-2 (and other aerosol- or air-borne viruses) in the dental operatory setting, there is a demand for procedures that generate less aerosol and require fewer clinic visits.
Therefore, there is a need for a dental preparation and restoration system that provides shape-optimization for both preparation and restoration, to reduce failure of dental restorations by minimizing interfacial and bulk stresses. There also is a need for a dental restoration preparation and restoration system that reduces visits and minimizes the generation of aerosol to protect all individuals involved in the dental restoration.
In one embodiment, a dental preparation block guide comprises a chamber that is customized to receive at least one tooth of a patient for a shape-optimized restoration of the at least one tooth; and a channel formed in a surface of the block guide at a location selected relative to the shape-optimized restoration to be performed, the channel comprising an aperture extending through the surface to the chamber such that a dental handpiece can be inserted into and guided within the channel while a tool of the dental handpiece can interact with the at least one tooth in the chamber through the aperture to form a shape-optimized preparation in the at least one tooth to receive the shape-optimized restoration.
In another embodiment, a method of providing a dental restoration in at least one tooth of a patient comprises applying a finite element analysis operating on a computer system to a model of the at least one tooth of the patient to design a shape-optimized preparation in the at least one tooth of the patient; and applying the finite element analysis operating on the computer system to the shape-optimized preparation in the at least one tooth of the patient to create a shape-optimized restoration to be applied to the shape-optimized preparation in the at least one tooth of the patient.
Embodiments of the disclosure provide dentists and other practitioners with the ability to conduct a shape optimized direct or indirect restoration. For example, one embodiment may be used in the preparation of cavity restorations, although this and other embodiments could also be employed during other direct or indirect dental restoration procedures.
The above summary is not intended to describe each illustrated embodiment or every implementation of the subject matter hereof. The figures and the detailed description that follow more particularly exemplify various embodiments.
Subject matter hereof may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying figures, in which:
Embodiments are directed to shape-optimized dental restoration preparation guides. A purpose of shape-optimized dental preparation guides is to allow dentists to easily create specific restorations that are less likely to fail than conventional restorations created without shape-optimized dental preparation guides. By using shape-optimization technology to develop the preparation guide, the dental restoration can limit interfacial and bulk stresses. If not addressed, these stresses may lead to shortened restoration life or complete failure. By providing a preparation guide for shape-optimized preparations and restorations, the restorations can be more efficient, precise, and durable.
The use of shape-optimized dental preparation guides according to the disclosure also can have the benefit of reducing the number of patient visits necessary to complete a dental restoration, while also reducing damage to the prepared tooth and practitioner exposure to aerosol generation via shorter patient visits. In embodiments, the shape-optimization is algorithmically created specific to the patient and the restoration type.
Referring to
Adaptor 108 is designed to interact with block guide 104 such that dental handpiece 102 can be manipulated by a dentist or other practitioner to bring tool 110 in proximity to the patient's tooth or teeth requiring preparation(s) and/or restoration(s), guided by block guide 104. In some embodiments, adaptor 108 has a standardized shape and configuration, while in other embodiments adaptor 108 itself is also adapted or formed to interact with block guide 104. For example, adaptor 108 can be a custom component created for a particular patient and restoration and configured to fit onto dental handpiece 110. Adaptor 108 additionally can be customized to fit a particular dental handpiece 102. In some embodiments, other components of preparation guide system 100, or devices that interact with preparation guide system 100, also can be custom components configured to fit onto or otherwise interact with one or more dental handpieces.
Referring also to
In particular, block guide 104 comprises patient-customized chamber 118 for the tooth or teeth of a patient. Thus, chamber 118 is formed for a particular patient's tooth or teeth (such as from a dental impression) and can be customized for the particular restoration to be performed on the patient's tooth or teeth.
Block guide 104 also comprises a customized channel 120 that is configured to guide dental handpiece 102 (via adaptor 108) into and within block guide 104 such that tool 110 can be brought proximate the tooth or teeth via tool aperture 122 formed within channel 120. The complementary forms of adaptor 108 and channel 120 enable a dentist or other practitioners to manipulate dental handpiece 102 as adaptor 108 is guided within channel 120, thereby manipulating tool 110 (such as a rotary cutting instrument) proximate the tooth or teeth in chamber 118 to make the shape-optimized cavity preparation in the tooth or teeth, or to perform one or more other tasks, such as imaging, profiling, or polishing, related to preparation of a dental restoration.
Though depicted as extending longitudinally on a top surface of block guide 104 in
The designs of chamber 118 and channel 120 also can include its depth, length, width, and other characteristics of their configurations. For example, in
Tool aperture 122 formed within channel 120 also can be customized in conjunction with channel 120 and adaptor 108. While channel 120 is formed to accommodate adaptor 108, tool aperture 122 is formed to accommodate tool 110 such that tool 110 can be brought into proximity with the tooth or teeth of the patient in chamber 118 when dental handpiece 102 is manipulated to insert adaptor 108 into channel 120 of block guide 104, thereby inserting tool into tool aperture 122.
The data necessary to create block guide 104 (and adaptor 108, and/or other components in some embodiments) can be obtained from a dental impression, a digital scan, or some other form or image of the relevant tooth or teeth, or data related to the tooth or teeth. In embodiments, block guide 104 can be derived from an optimized design of the preparation/restoration. For example, channel 120 can be reverse engineered by digitally placing tool 110 with adaptor 108 on the preparation surface and tracing the paths and surface covered by adaptor 108 while tool 110 scans the preparation surface. The design and shape optimization of the preparation, restoration, and block guide 104 are conducted using CAD/CAM and finite element analysis (FEA) software in conjunction with an internal or external shape optimization routine to minimize interfacial and bulk stresses.
FEA can be a cost-effective way to analyze the overall stress distributions in different dental structures and to predict their potential failures. Different designs and structures can be modeled, evaluated, and compared before fabrication and testing using FEA, but conventional approaches that do not also incorporate shape-optimization can result in repeated design modifications and numerical analyses through a trial-and-error process, which is time-consuming and inefficient. Thus, embodiments disclosed herein that additionally incorporate internal or external shape optimization routines can predict and thereby minimize interfacial and bulk stresses, addressing the aforementioned inefficiencies and provide an improved clinical result. In various embodiments, predicted stress distributions can be used as feedback to iteratively but automatically modify restoration designs.
After the designs of the preparation and restoration are shape optimized, such as by using FEA software, preparation guide system 100 can be designed using CAD/CAM software. Block guide 104 (and adaptor 108, and/or other components in some embodiments) can be physically formed via three-dimensional (3D) printing, molding, or some other suitable process. Suitable materials for block guide 104 comprise polymers, ceramics, composites, metals, combinations of these materials, or other suitable materials, including materials that are biocompatible. In some embodiments, multiple preparation guides can be used in sequence to make preparations that are more complicated (e.g., with multiple curvatures at different locations).
In use, and referring to
The number of impressions taken during the process will depend on the type of restoration to be made. For a direct restoration (e.g., filling a cavity), one impression typically will be made. For an indirect restoration (e.g., veneers, crowns, inlays, caps, or bridges), two impressions typically will be made. The first impression is of the unprepared tooth and the adjacent teeth so that block guide 104 can be made and the FEA can be performed. The second impression is of the cavity, taken after the cutting is completed, and is used to fabricate the indirect restoration itself. Although the cavity and the indirect restoration typically will be designed at the same time using FEA, it can be helpful to check the cut cavity (with a second impression) against what has been designed for the restoration.
The restoration itself can be prepared, such as by using industry-standard FEA or other algorithms and programs to customize and optimize the restoration for the patient, and the dentist or other practitioner can apply the restoration to the patient. In some embodiments, particularly direct restoration, block guide 104 and one or more dental handpieces 102 can be used to apply the restoration. In one particular example, a new block guide 104 can be created to assist in applying the restoration.
The inventors conducted a study aimed to optimize the design of a posterior 2-unit cantilevered bridge which is attached to the abutment tooth via an inlay. The study considered both the abutment cavity design for the inlay as well as the fiber layout in the cantilever pontic.
Materials and Methods
Structural optimization of a 3-unit inlay-retained fiber-reinforced (FRC) fixed partial denture (FPD) was performed using a stress-induced material transformation (SMT) technique. Similar methods were used to optimize the 2-unit cantilevered FRC bridge in this study. Since the cantilevered design only has a single retainer, lowering the interfacial stresses at the abutment-retainer connection was first considered, prior to optimizing the FRC substructure in the prosthesis, to reduce the risk of debonding. Hence, a two-step approach was adopted for the structural optimization of the 2-unit inlay-retained cantilevered bridge.
Finite Element Model Construction
A human mandibular first molar and second premolar were embedded in orthodontic resin to form a physical model as shown in
The whole assembly then was scanned by using a micro-CT scanner (e.g., with a XT H 255 by Nikon Metrology) with a tube voltage of 100 kV and a tube current of 170 μA. A total of 720 projections and four frames per projection were taken. The acquired images were reconstructed into a three-dimensional (3D) volume (e.g., using CT Pro 3D by Nikon Metrology). Subsequently, segmentation of the 3D volume was performed (e.g., using Avizo 6.0 by Visualization Sciences Group) to divide it into its constituent materials, i.e. enamel, dentin, bone, and resin composite. The 3D surfaces for each component were created and then exported as a stereolithography (STL) file for finite-element model construction (e.g., using Hypermesh 10.0 by HyperWorks-Altair Engineering).
This study focused on the stress distributions within the restoration and the coronal portion of the abutment tooth. Therefore, the morphology of the mandibular jaw bone, which was sufficiently distant from the region of interest, did not need to be modeled accurately. Simply, and as shown in
Two-Step Structural Optimization
The structural optimization of the 2-unit cantilevered bridge was carried out in two steps (e.g., using ABAQUS 6.10-EF1 by Dassault Systemes Simulia) in conjunction with a user-defined material (UMAT) subroutine that defined the constitutive model of a material which was stress-state dependent. The first step was to obtain the optimal shape for the cavity preparation/retainer on the abutment by applying the subroutine to the tooth tissue only. In the second step, with a shape-optimized retainer, the subroutine was applied to the restoration to seek an optimal fiber layout for the FRC substructure.
In the first step, the enamel and dentin of the abutment tooth were assigned with a stress-dependent user-defined material. Thus, at every step increment, the UMAT subroutine was called to update the material properties of the tooth tissues using the predicted stresses from the previous increment. Initially, the material properties of these tooth tissues were given their natural values. Subsequently, their elastic moduli were modified iteratively based on the predicted local stresses in order to reduce the stresses at the base of the cantilever. Specifically, all the elements within the tooth with stresses larger than the assumed failure stress were given the properties of the “softer” resin composite. All the other parameters, including the material properties for the remaining tooth tissues and bones, the applied load, and the boundary conditions, were kept the same during the whole analysis. In this way, a retainer with reducing cohesive and interfacial stresses gradually grew from the pontic into the abutment tooth.
In the second step, an inlay retainer and the matching cavity preparation were created within the abutment tooth using the design derived in the first step. The remaining enamel and dentin were assigned with their natural material properties, while the restoration began as a uniform structure of resin composite and gradually acquired the user-defined material properties which now assumed those of the anisotropic unidirectional fibers. To obtain a suitable fiber-reinforcing layout within the restoration, regions with local stresses higher than the assumed failure stress were gradually replaced with the “stronger” fiber material. More importantly, the UMAT subroutine was able to align the fibers with the direction of the maximum principal stress. In this way, fiber reinforcement could be achieved most effectively.
There is a wide range of values reported for both the bond strength between teeth and restorations and the fracture strength of resin composites. A parametric study was therefore performed to understand the influence of the assumed bond strength on the shape of the cavity preparation, and that of the assumed fracture strength of the resin composite on the fiber layout. For both steps of the structural optimization, the assumed failure stress ranged from 5 to 30 MPa, in steps of 5 MPa. The stress-induced material transformation process continued iteratively until the results converged, i.e. when the interfacial or cohesive stress dropped below the assumed failure stress.
Comparison Between the Conventional and Optimized Designs
The designs provided by the optimization exercise may sometimes contain features that cannot be realized easily in practice. Therefore, when finalizing the optimized design, practical issues, such as a cavity shape that can actually be made, need to be considered, and simplifications or smoothing of the edges may have to be made. The final design for the optimized FRC bridge is thus a simplified and smoothed out version of that suggested by the structural optimization. As a comparison, a stepped box-shaped cavity/retainer was used for the conventional 2-unit cantilevered FRC dental bridge. The width of the box started at 2.5 mm in the mesial fossa of the first premolar and increased to 3.5 mm on the marginal ridge. The occlusal inlay was 2-mm thick and the occlusal step was 4-mm high. This is depicted in
Stress analyses of the optimized and conventional designs were carried out to compare their mechanical performance numerically. To assess their resistance against retainer debonding and restoration fracture, the stresses at the tooth-restoration interface and those within the restoration were compared between the two designs.
Optimized Structure of the 2-Unit Cantilevered FRC Bridge
The results based on a failure stress of 25 MPa were used conservatively to construct the model for the second step of structural optimization. After smoothing the optimized retainer's contour (e.g., using Hypermesh 10.0 by HyperWorks-Altair Engineering), its size (26.1 mm3) was similar to that of the conventional box-shaped design (26.2 mm3). However, in terms of the area of bonding between the cavity and retainer, the optimized design is 17.5% smaller than the conventional one (31.3 mm2 versus 38.0 mm2).
According to the results from the second step of the SMT optimization, fibers should be placed at the top of the connector region where tensile stress is highest, as shown in
Comparison of Stresses Between Conventional and Optimized Designs
Finite element models without the fiber substructure were first used to evaluate the effect of the cavity shape on the stress distribution within the restored tooth. The optimized cavity of
Referring to
The present study showed that the optimized design of the two-unit cantilevered FRC bridge has better mechanical performance than the conventional design for equal amounts of reinforcing fibers. Specifically, even with a smaller bonding area, the optimized cavity has much lower interfacial stresses (70% reduction), thus significantly reducing the risk of debonding of the pontic. Comparison between the stress profiles of the two designs further confirms that the optimized fiber substructure is better aligned with the maximum principal stress. Thus, by default, the normal and shear stresses at the resin-fiber interfaces are minimized to lower the risk of delamination. The much reduced maximum principal stress within the veneering resin of the optimized design (by 45%) is also expected to decrease the occurrence of cracking within the restoration.
It has been reported that inlay-retained FRC bridges often failed at lower loads than those retained by more extensive coverage of the abutment. However, the latter designs do not follow the spirit of minimally invasive dentistry. The optimized cavity design proposed here can preserve more tooth tissues by improving the retention for inlay-retained cantilevered bridges. The much shorter retainer margin is also expected to reduce the risk of secondary caries.
In this study, a bond strength of 25 MPa between the tooth and the restoration was selected so that the optimized design and the conventional one had a similar cavity size. This allowed the two cavity designs to be compared fairly. The actual bond strength between the tooth and resin composite can be higher than 25 MPa. Consequently, the size of the cavity preparation can be even smaller and more tooth tissue can be preserved. Clinically, the currently recommended dimensions of the inlay cavity are at least 2 mm wide by 2 mm deep. The cavity size derived from the SMT optimization based on a 25-MPa failure stress (σRef) conforms to this clinical guideline. Despite the fact that the area of bonding is reduced by 17.5% due to the more rounded shovel shape, the lower interfacial stress of the optimized design is expected to improve the retention of the restoration.
As shown in
The SMT optimization suggested that the fibers be placed at the top of the connector. With this configuration, the high tensile stresses will be suitably borne by the fibers, thus reducing the maximum principal stress in the veneering composite by around 45%.
Clinically, the FRC cantilevered bridge restoration has been mainly used as an interim prosthesis, and most of the studies focused on its application in the anterior region. However, compared to 3-unit bridges, cantilevered bridges generally involve less tooth preparation and allow easier maintenance of oral hygiene. With these advantages and improved mechanical performance, the optimized FRC cantilevered bridge can be a viable long-term treatment option for both the anterior and posterior regions.
Thus, the present study by the inventors proposed a shovel-shaped retainer for the two-unit cantilevered FRC bridge where the reinforcing fibers are placed at the top of the connector area. With its lower interfacial and structural stresses, this optimized design is expected to outperform mechanically the conventional box-shaped design. This can potentially offer a more conservative treatment option for replacing the single missing tooth.
This study is an example, and the particular materials, tools, devices, and other factors mentioned therein are merely exemplary and not limiting with respect to the disclosure or claims. Those skilled in the art will recognize that suitable alternatives may be used, and that in some examples adjustments, adaptations, or substitutions may be needed in light of particular circumstances or factors.
Though embodiments discussed herein primarily related to dental restorations, other applications also are possible, such as dental procedures other than restorations, orthodontic procedures, other human medical treatments and therapies, veterinary procedures, and the like that involve the joining of different materials or components. Thus, even engineering application can be possible.
Embodiments disclosed herein can provide numerous advantages over conventional approaches to restorations and other dental and medical procedures. These include using shape optimization for both the preparation and restoration, as well as design and use of a block guide and adaptor, to provide restorations with more organic geometries that are subject to less interfacial and bulk stresses and therefore less likely to fail prematurely; and shortening visit length and the number of visits necessary to prepare and complete a restoration, to subject dentists, other practitioners, and patients to less generated aerosol, which is particular pertinent to the current COVID-19 pandemic but will also have applicability to reducing the transmission of other airborne illnesses.
Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the claimed inventions. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the claimed inventions.
Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted.
Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended.
Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein.
For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. § 112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.
The present application claims the benefit of U.S. Provisional Application No. 62/706,976 filed Sep. 22, 2020, which is hereby incorporated herein in its entirety by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/071554 | 9/22/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62706976 | Sep 2020 | US |
