[0001] This application claims the benefits of U.S. Provisional application 62/360,330 entitled "A Dental Implant System and Digital Method Thereof filed on July 9, 2016, the disclosure of which is incorporated herein by reference as if set forth in full.

FIELD OF THE INVENTION

[0002] The present invention generally relates to CAD/CAM methods of making dental crown using a digital margin ring. It finds particular application in conjunction with dental crowns, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other dental prostheses such as veneers and bridges.

BACKGROUND OF THE INVENTION

[0003] According to the American Association of Oral and Maxillofacial Surgeons, statistics show that 70% of adults aged 35 to 44 years in the U.S. have at least one missing tooth due to an accident, tooth decay, gum disease, or dental fracture. For a tooth that is damaged or lost, a dentist will design a crown to be secured on the remaining dentin or on an implant, and restore the function of that tooth. In designing a dental crown, it is critically important that the crown can accurately fit the oral environment, particularly, to fit the spatial configuration of the gum area around the tooth, for the purpose of an aesthetic appearance, as well as the hygiene in the interfacial region between the gum, the crown and the dentin or abutment/implant. This necessarily involves measurement or acquisition of three dimensional model of existing dental structures.

[0004] For example, a crown often extends below the gum line, and measurement of dental structures below the gum line needs to be carried out. However, a precise measurement below the gum line is difficult for the following reasons. First, the gum bleeds after prep. Second, the soft tissue pushes back and occupies the space between the gum and prepped tooth. Third, the abutment shoulder is lower than the gum level and is buried inside in the gum tissue.

[0005] Dental impressions are a traditional technique for providing a model of the mouth. Generally, a cast is produced from the impression and the cast then is used to produce the prosthesis. Such techniques suffer from inaccuracy due to multiple manual steps which can be technically demanding on the dentist as well as invasive and uncomfortable for the patient, especially if subgingival measurement is necessary. In attempt to acquire a clear impression, the dentist numbs the patient's jaw, and then use a thick cotton thread called retraction cord to push away the gum and to stop the gum bleeding. Usually, the dentist will soak the retraction cord in a hemostat liquid if the gum bleeds seriously. The procedure will take about 10 to 15 minutes to prepare the retraction cord and then pack it inside the gum. However, this time-consuming and labor-intensive procedure still can't always guarantee a clear impression, because the gum will push back and resume more or less to its original condition, after the retraction cord is removed.

[0006] For a traditional implant crown, the retraction cord cannot be packed between the gum and implant, because the operation would separate the gum and the implant, and destroy the connection between the periodontal tissue and implant, which may cause the bone recession later. If serious, the operation may lead to the failure of the implantation. As such, dentists generally use an open tray, a close tray, or an OS-Tray to transfer the soft tissue or hard tissue impression to the stone model.

[0007] However, the procedure is complicated and needs to use a lot of small accessories. For implant methods, dentists have to transfer the soft tissue impression by using the impression copings and implant analogs to the lab, and a lab technician will pick up the abutment for them and modify it in the lab, then send back for the patient to try. This procedure eliminates the doctor's role in making the implant crown directly by working in the patient's mouth; reduces the accuracy of the operation; increases the lab fee and accessory expenses,; burdens the patient with more office visits; and demands a lot more steps for the doctor to bring back the abutment to the right position.

[0008] More recently, digital scanning techniques have offered increased accuracy and detail of measurement. However, such techniques are only able to image, measure and model visible parts of the patient's mouth and generally do not provide imaging of subgingival areas. CT scanning can provide measurement of subgingival areas, however it does not provide soft tissue measurement.

[0009] The use of CAD/CAM in dentistry makes the traditional crown procedure much easier. An image sensor is used to take the image of the prepared tooth, and the crown will be made right away in the doctor's office. Alternatively, the image is sent to a lab, where the crown will be made and then sent back to the doctor's office. There is no impression step involved in such a procedure. The CAD/CAM can't be used to make a crown on implant, because (i) currently there is no direct abutment set up in the patient's mouth; (ii) the direct modification of an implant abutment is currently not available; and (iii) the part of the abutment which is covered by the gum cannot be detected by the CAM/CAD sensor. As such, dentists set up the impression copings on the implant, and take impression of the implant and surrounding soft tissue. Subsequently, the lab technician builds up the stone model, and uses this model to make the abutment and the crown.

[0010] Both existing physical impression methods and digital impression methods of measurement of subgingival areas usually include the step of physically separating the gingiva from the circumference of the tooth (or teeth) to be measured when the measurements are taken. As described above, this separation usually causes bleeding which needs to be stemmed or prevented before measurements can be made. The process of separation sometimes causes trauma to the gingiva, which can lead to inflammation and permanent damage to the gingiva.

[001 1 ] Therefore, the dilemma is either to use damaging, painful, technically challenging methods to expose subgingival tooth areas (e.g., cord packing) for measurement, or to forgo subgingival measurements resulting in either ill-fitting prosthesis with unpl easing aesthetics where the border between the prosthesis and tooth structure is visible above the gum line.

[0012] Advantageously, the present invention overcomes the dilemma by providing a dental prosthesis comprising a standardized subgingival portion and a process of fabricating the same. The present invention exhibits numerous technical merits such as a clearer impression; simplified operation such as elimination the step of packing a retraction cord; less injury such as gum bleeding and avoidance of the bone recession; improved control over the fabrication of a crown; cost-effectiveness in terms of doctor chair time and lab cost; less usage of accessories; and fewer patient visits, among others. For example, one or more of these merits will be particularly exhibited when the present invention is combined with the modifiable abutment as disclosed in the co-pending patent application with Ser. No. 12/255,471 filed by the same applicant. The combination will enable a dentist to directly modify the abutment in a patient's mouth, and use the present invention with a CAD/CAM system.

SUMMARY OF THE INVENTION

[0013] One aspect of the present invention provides a first method of making a dental crown comprising:

(1) outside a patient's mouth, providing a physical margin ring combined with a physical dental abutment, wherein the physical abutment has a physical shoulder with a supporting surface, a physical neck that is above the supporting surface, and a physical head that is above the physical neck, wherein the physical margin ring sits snugly on the shoulder's supporting surface and around the physical neck like a collar,

(2) providing a digital margin ring, which is an exact 3D digital model of the physical margin ring in software,

(3) providing a three-part 3D digital model of three physical components in software including the physical margin ring, the physical neck and the physical shoulder, and excluding the physical head, wherein the three components in the three-part 3D digital model are configured as in step (1),

(4) inside the patient's mouth, securing the physical dental abutment combined with the physical margin ring from step (1) to an implant in the patient's mouth,

(5) scanning the physical head and a top portion of the physical margin ring in the patient's mouth with an oral scanner to generate a first 3D intraoral digital model that includes a scanned 3D digital model of the physical head and the top portion of the physical margin ring,

(6) combining the first 3D intraoral digital model with the three-part 3D digital model from step (3), to generate a second 3D intraoral digital model, in which the 3D digital models of the shoulder, the ring, the neck and the head are spatially aligned to each other as their physical counterparts are in step (1),

(7) removing the digital margin ring from the second 3D intraoral digital model to generate a third 3D intraoral digital model, wherein the third 3D intraoral digital model becomes a complete and accurate 3D digital model of the physical shoulder, the physical neck and the physical head combined,

(8) generating a crown 3D digital model using CAD/CAM based on the third 3D intraoral digital model,

(9) fabricating a physical crown from the crown 3D digital model using CAD/CAM, and

(10) securing the physical crown onto the physical abutment inside the patient's mouth.

[0014] Combining the physical margin ring with the physical dental abutment as describe in the first method may alternatively be carried out at step (4) rather than step (1). Therefore, another aspect of the invention provides a second method of making a dental crown comprising:

(i) outside a patient's mouth, providing a physical margin ring, and a separate physical dental abutment, wherein the physical abutment has a physical shoulder with a supporting surface, a physical neck that is above the supporting surface, and a physical head that is above the physical neck; wherein the physical margin ring can be combined with the physical dental abutment, and, when they are combined, the physical margin ring sits snugly on the shoulder's supporting surface and around the physical neck like a collar,

(11) providing a digital margin ring, which is an exact 3D digital model of the physical margin ring in software,

(iii) providing a three-part 3D digital model of three physical components in software including the physical margin ring, the physical neck and the physical shoulder, and excluding the physical head, wherein the three components in the three-part 3D digital model are combined and configured as described in step (i),

(iv) inside the patient's mouth, securing the physical dental abutment to an implant in the patient's mouth, and then combining the physical margin ring to the physical dental abutment in a manner as described in from step (i),

(v) scanning the physical head and a top portion of the physical margin ring in the patient's mouth with an oral scanner to generate a first 3D intraoral digital model that includes a scanned 3D digital model of the physical head and the top portion of the physical margin ring,

(vi) combining the first 3D intraoral digital model with the three-part 3D digital model from step (iii), to generate a second 3D intraoral digital model, in which the 3D digital models of the shoulder, the ring, the neck and the head are spatially aligned to each other as their physical counterparts are in step (i),

(vii) removing the digital margin ring from the second 3D intraoral digital model to generate a third 3D intraoral digital model, wherein the third 3D intraoral digital model becomes a complete and accurate 3D digital model of the physical shoulder, the physical neck and the physical head combined,

(viii) generating a crown 3D digital model using CAD/CAM based on the third 3D intraoral digital model,

(ix) fabricating a physical crown from the crown 3D digital model using CAD/CAM, and

(x) securing the physical crown onto the physical abutment inside the patient's mouth.

[0015] Since there is only a minor difference between the first method and the second method, the following detailed description will refer mainly to the first method. The second method can be described, mutatis mutandis, in light of the first method.

[0016] The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0017] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. All the figures are schematic and generally only show parts which are necessary in order to elucidate the invention. For simplicity and clarity of illustration, elements shown in the figures and discussed below have not necessarily been drawn to scale. Well-known stmctures and devices are shown in simplified form in order to avoid unnecessarily obscuring the present invention. Other parts may be omitted or merely suggested.

[0018] Figure 1 A illustrates a physical margin ring in accordance with an exemplary embodiment of the present invention.

[0019] Figure IB illustrates a digital margin ring, which is an exact 3D digital model of the physical margin ring of Figure I A, in accordance with an exemplary embodiment of the present invention.

[0020] Figure 2 A schematically demonstrates a physical dental abutment in accordance with an exemplary embodiment of the present invention.

[0021] Figure 2B illustrates the meaning of "A conforms to B", "A immediately contacts B" and "A mates B".

[0022] Figure 3A shows that the physical margin ring in Figure 1A can have a mating relationship with the physical dental abutment in Figure 2A in accordance with an exemplary embodiment of the present invention.

[0023] Figure 3B schematically demonstrates a three-part 3D digital model saved in software in accordance with an exemplary embodiment of the present invention.

[0024] Figure 4 is a cross sectional view that schematically demonstrates the spatial relationship between a margin ring, a dental abutment, soft tissue and jaw bone in accordance with an exemplary embodiment of the present invention.

[0025] Figure 5 schematically demonstrates a step of intraoral scanning of the physical head and a top portion of the physical margin ring in accordance with an exemplary embodiment of the present invention.

[0026] Figure 6 schematically demonstrates a first 3D intraoral digital model in accordance with an exemplary embodiment of the present invention.

[0027] Figure 7 schematically demonstrates the combining the first 3D intraoral digital model with the three-part 3D digital model in accordance with an exemplary embodiment of the present invention.

[0028] Figure 8 schematically demonstrates a step of removing or subtracting the digital margin ring from a second 3D intraoral digital model in accordance with an exemplary embodiment of the present invention.

[0029] Figure 9 schematically demonstrates a step of generating a crown 3D digital model in accordance with an exemplary embodiment of the present invention.

[0030] Figure 10 schematically demonstrates a step of fabricating a physical crown from a digital crown using CAD/CAM technology in accordance with an exemplary embodiment of the present invention.

[0031] Figure 11 schematically demonstrates a step of securing a physical crown onto a physical abutment inside a patient's mouth in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It is apparent, however, to one skilled in the art that the present invention may be practiced without these specific details or with an equivalent arrangement.

[0033] In mathematics, a surface is a geometrical shape that resembles to a deformed plane. For example, a surface may be the boundary of a solid object in ordinary three-dimensional Euclidean space. Therefore, when surface (either physical or virtual) is mentioned in the present invention, unless otherwise specified, it is always related to a solid object (either physical or virtual) having at least that surface.

[0034] In the present invention, the exact 3D digital model (or digital counterpart) of a physical object X is simply called digital X. "Digital X" may be, for example, in STL ( STereoLithography ) file format. STL format is native to the stereolithography CAD software created by 3D Systems. STL is also known as "Standard Triangle Language" and "Standard Tessellation Language". The file format is widely used for rapid prototyping, 3D printing and computer-aided manufacturing (CAM). STL files describe only the surface geometry of a three-dimensional object without any representation of color, texture or other common CAD model attributes.

[0035] A reference number referring to a specific physical component will have a suffix "P", for example "physical component 1234P", while its digital counterpart will have a suffix "D", for example "digital component 1234D". 3D imaging, 3D modeling and CAD/CAM techniques are known to a skilled person in the field, and will not be repeated here for conciseness of the present invention.

[0036] With reference to Figure 1A, physical margin ring IP has a lower section HOP and an upper section 120P. The lower section HOP consists of a bottom surface H IP, an internal surface 112P, an external surface 1 13 P, and a top surface H4P The upper section 120P consists of pillars 12 IP that extend perpendicular from the top surface 1 14P of the lower section N OP. Pillars 121P each has a top surface 122P, and an internal surface Γ23Ρ with a first protrusion 124P pointing inward that generates pressure when the pillar 12 I P is pushed outward. Optionally, pillars 1 2 1 P each has an external surface 125P with a second protrusion 127P pointing outward that has an embedment capability in a curable material . Pillars 121P are separated by voids 126P to enhance the pressure generation and the optional embedment capability of each pillar.

[0037] Figure IB illustrates a digital margin ring ID, which is an exact 3D digital model of the physical margin ring of Figure 1A. Margin ring ID may be saved in software, for example, in STL (STereoLithography) file format. With reference to Figure IB, digital margin ring ID has a lower section HOD and an upper section 120D. The lower section HOD consists of a bottom surface H ID, an internal surface 1 1 2D, an external surface 113D, and a top surface 11.4D. The upper section 120D consists of pillars 12 I D that extend perpendicular from the top surface 114D of the lower section HOD. Pillars 121D each has a top surface 122D, and an internal surface 123D with a first protrusion 124D pointing inward. Optionally, pillars 12 I D each has an external surface 125D with a second protrusion 127D pointing outward. Pillars 12 ID are separated by voids 126D.

[0038] With reference to Figure 2 A, a physical dental abutment 2P includes a body 21 OP and a shoulder 220P. Shoulder 220P has a supporting surface 22 1 P for a future dental crown 88P (see Figures 10 and 11). The body 2 10P is connectable to, and support, the dental crown 88 P. Body 21 OP may be an integrated and continuous object, but for convenience, it may be conceptually viewed as consisting of two parts: a physical neck 2 I IP that is immediately above the supporting surface 221P, and a physical head 212P that is immediately above the physical neck 21 IP.

[0039] Dental abutment shoulder 220P's supporting surface 221P is designed to conform to the bottom surface 11 IP of the margin ring IP. The physical neck 2 1 1 P is designed to conform to the internal surface 112P of the margin ring IP Neck 21 IP also conforms to the protrusion 124P on the pillar 121 P of the margin ring IP such that a pressure is placed by the margin ring pillar protrusion 124P on neck 21 IP of the abutment 2P.

[0040] The phrases "A conforms to B", "A immediately contacts B" and "A mates B" are interchangeable, the meaning of which is illustrated in Figure 2B. The lower panel of Figure 2B can also be described as "A sits snugly on B".

[0041] Figure 3 A shows that the physical margin ring IP in Figure 1 A can have a mating relationship with the physical dental abutment 2P in Figure 2A. When margin ring IP is installed on abutment 2P, or when margin ring IP surrounds neck 21 IP, an assembly 1P2P is obtained.

[0042] Assembly I P2P can likewise have a digital counterpart assembly 1D2D (not shown), including 21 ID, 220D, 212D, and ID etc. However, according to the present invention, only a part of digital assembly 1D2D is saved in software, named as "three-part 3D digital model". As shown in Figure 3B, three-part 3D digital model 300D includes three components: digital neck 21 ID, digital shoulder 22.0D, and digital margin ring ID. Digital head 212D is not included in three-part 3D digital model 300D.

[0043] Margin ring IP is an example of the so-called "shape determiner" in co-pending U.S. application Ser. No. 13/138,726. Margin ring IP may be a regular or irregular ring directly surrounding or circling the apical (bottom) part (e.g. neck 21 I P) of dental abutment 2 P. It may also be a regular or irregular C-shaped structure incompletely surrounding dental abutment 2 P.

[0044] Dental abutment 2P is an example of the so-called "crown base" in co-pending U.S. application Ser. No. 13/138,726. Dental abutment 2P may be a single piece with homogenous texture made of any suitable material such as metal, alloy, polymer, and composite material. Dental abutment 2P may be, for example, the dentin of a tooth under restoration, a ground down tooth, or an abutment with or without the portion of an implant that is on or above the surface of the jawbone where the implant sits. A common abutment is substantially cylindrical that is typically screwed into the endosseous implant, on top of which the crown can be affixed. In preferred embodiments, dental abutment 2P may be the modifiable abutment as described in the co-pending patent application with Ser. No. 12/255,471 filed by the same applicant, which is incorporated herein in its entirety.

[0045] Shoulder 220P as shown in Figure 2 A. is an example of the so-called "determiner stopper" in co-pending U.S. application Ser. No. 13/138,726, and it protects the nearby epithelial attachment against the pressure from margin ring IP Any form of shoulder 220P may be used, for example, one or more protrusions, or a regular or irregular circular shoulder.

[0046] Margin ring IP and dental abutment 2P may or may not be paired products and can be pre-determined regarding their shape, size and dimension etc. They can be pre-manufactured by mass production, and are commercially available from Zuga Medical Inc., 24400 Chagrin Blvd. Suite 250, Beachwood, OH 44122 (hereinafter "Zuga").

[0047] Briefly speaking, the method of the present invention relies on a standard physical ring IP, a standard digital ring ID, a standard three-part 3D digital model 300D, and a scanned but customized digital head 212D, to design and manufacture a desired dental crown 88P using CAD/CAM technology, as will be explained in the following. [0048] As generally known to a dentist, after certain time allowed for osteointegration of an implant, a healing cap is then removed from the implant. The nearby soft tissue should have grown around the healing cap but not over it so that it is easy to remove. Bone level implants are preferred when there is limited vertical space from the implant to the occlusal surface. Bone level implants have also shown less marginal bone loss when compared to tissue level implants after one year, allowing for better cosmetic result. The implant can have thread design for high stability, and higher amount of surface area, allowing dentists to establish better torque. The surface of the implant may be sand blasted, as sand blasting the implant will roughen its surface for maximized osteointegration. The implant may have a cylinder taper shape that is equipped with anti-rotation grooves, allowing for better torque and a higher chance of implant success.

[0049] Titanium implants available from Zuga have three diameters (3.5mm, 4.3mm and 5.0mm) and four lengths (8mm, IQmm, 13mm, and 15mm) to cover all placement needs. A sealing cap is used with the implant and has three diameters adapted to implant sizes (3.5mm, 4.3mm and 5.0mm).

[0050] Step (1 ): outside a patient's mouth, providing an assembly 1P2P as shown in Figure 3 A, that is, a physical margin ring IP combined with a physical dental abutment 2 P. The physical abutment 2P has a physical shoulder 22ΌΡ with a supporting surface 221P, a physical neck 21 IP that is above the supporting surface 22 IP (or above shoulder 220P), and a physical head 212P that is above the physical neck 21 IP As described above, the physical margin ring IP sits snugly on the shoulder's supporting surface 22 IP and around the physical neck 21 IP like a collar.

[0051] Step (2) is providing a digital margin ring ID as shown in Figure IB, which is an exact 3D digital model of the physical margin ring IP, saved in e.g. STL file.

[0052] Step (3) is providing a three-part 3D digital model 300D saved in software (STL file) of three physical components including the physical margin ring IP, the physical neck 21 IP and the physical shoulder 220P, but excluding the physical head 2Γ2Ρ. The three digital counterparts in the three-part 3D digital model 300D are configured, and conformed to each other as in step (1), or as shown in assembly 1P2P in Figure 3 A. [0053] Step (4) is carried out inside the patient's mouth. The dentist secures assembly 1P2P from step (1), i .e. the physical dental abutment 2P combined with the physical margin ring IP, to an implant (not shown) in the patient's mouth. For example, abutment 2P may be placed on top of the implant, and a fixation screw (not shown) is placed inside the abutment 2 P. The abutment 2P is then secured to the implant with a screw adaptor. Abutment 2P may be a standard titanium abutment designed with a morse taper which helps prevent crestal bone loss. Zuga abutments may also have three diameters (corresponding to implant 3.5mm, 4.3mm and 5.0mm) and two lengths (5.5mm and 7.0mm).

[0054] Alternatively, steps (1) and (4) can be carried out as steps (i) and (iv) in the second method, i.e. securing physical dental abutment 2P alone to the implant, and then combining margin ring IP to the abutment 2P, to obtain assembly 1P2P.

[0055] Platform switch is made possible with Zuga products. Zuga implants have a standardized platform which allows any implant to be cross matched with any abutment. This allows the proper abutment to fit on the proper implant regardless of situation. Using a smaller abutment on a bigger implant encourages better bone attachment and prevents initial peri-implant bone loss. Moreover, taper, anti-rotation hex and fixation screw can maximize the implant-abutment stability. The fixation screw connects the implant and abutment together for a tight, secure fit. Forces are directed from the crown to the implant which reduces stress on the crestal bone. The taper cone creates a consistently smaller abutment implant contact.

[0056] Figure 4 illustrate that the margin ring IP of matching width is placed snugly around neck 211P of the abutment 2P. Sometimes, the margin ring IP's external surface 113P is surrounded by soft tissue 33P . Abutment 2P is adjacent to bone 44.

[0057] The margin ring IP helps to fit every crown to any abutment. The ring (through its surface 11 IP) exactly conforms to ("mates") and exactly represents the design and dimensions of any stops, such as abutment shoulder 220P (through its surface 22 IP), a crown base shoulders, or the crestal jaw or other stop that prevents the margin ring from being seated any lower than optimal over the area of the implant and related structures. The ring IP/ID carries some future information for the internal and external design of the crown, and it transports the margin information needed to make the perfect crown. The ring 1P/D carries the shape information of the future interface between the crown and the gingiva. It also carries the information below the gingiva level, and the negative shape of the area between implant and abutment and crown base and the gingiva.

[0058] Sometimes, but not always, margin ring IP's external surface 113P is surrounded, covered, or blocked, by soft tissue 33 P. In preferred embodiments, margin ring IP may comprise a therapeutic and/or preventive medical agent such as a releasable hemostat agent for stopping the bleeding, for example, thrombin protein, kinases, chemicals, and vitamins. The surface of margin ring IP may be loaded with the medical agent by way of for example, roughened surface or absorption with gauze, sponge, pledget, collagen, and poly-fibers. One of such margin ring may be commonly named as, for example, a hemostat margin ring, which combines the function of hemostat cap and retraction cord.

[0059] Zuga margin rings have three diameters (corresponding to implant 3.5mm, 4.3mm and 5.0mm) and two heights (3mm and 5mm). The healing caps have three diameters (corresponding to implant 3.5mm, 4,3mm and 5.0mm) and one height (5mm). Zuga ring can be manufactured from plastic, titanium, silicone rubber, ceramic or other materials that ensures that the information for the future internal and external apical design of the crown is not lost in the restoration and crown manufacturing process.

[0060] In a preferred embodiment, the ring IP/ID may have a sinusoidal interface, when used in conjunction with an abutment 2P/2D with a sinusoidal wave shaped shoulder 220P/D. The sinusoidal features on the ring and shoulder exactly mate each other, like A and B in Figure 2B. The ring carries the information for the future internal and external apical design of the crown. The trough of the sinusoidal wave on the ring generally orients distal ly so that the information carried for the future internal and external apical design of the crown can create an improved and more aesthetically pleasing interface between the crown and the gingiva. A sine wave or sinusoid is a mathematical curve that describes a smooth repetitive oscillation. In an embodiment, there are a front trough and a rear trough, a left crest and a right crest on the ring and on the shoulder, when they are placed in a patient's mouth. In another embodiment, there are a front crest and a rear crest, a left trough, and a right trough on the ring and on the shoulder, when they are placed in a patient's mouth.

[0061] Sometimes, but not always, after step (4) and before step (5), the physical head 212P may be modified or reshaped to fit better into the intraoral environment, or to better support the future crown. Such an abutment with a modifiable head is an example of modifiable abutment as disclosed in the co-pending patent application with Ser. No. 12/255,471 filed by the same applicant, the content of which is incorporated herein in its entirety.

[0062] As shown in Figure 5, step (5) is scanning the physical head 212P (when it's shape finalized) and a top portion of the physical margin ring IP in the patient's mouth with an oral scanner 55 to generate a first 3D intraoral digital model 601D in the file format of e.g. STL.

[0063] This "digital impression" by 3D modeling is functionally similar to traditional impression. To obtain an intraoral 3D digital model, a dentist can use any known imaging systems, such as a digital scanning system. For example, a scanner 55 may be positioned proximate to dental abutment 2P, so that the distance between the scanner and dental abutment 2P is within the depth of focus of the optics of the scanner. A scanning system may capture a series of two-dimensional images containing surface information, and then generate an accurate three-dimensional computer model from the captured images. The surface configuration in three dimensions of space can be represented as a mathematical model, i.e., a virtual model, which can be displayed on any workstation or computer 66 using software tools. The mathematical model can be viewed in any orientation in space, permitting detailed analysis of the surface. The virtual model can be transported from one computer to another computer anywhere in the world essentially instantaneously over communications links such as the Internet. The model can be replicated in a computer and thus shared and used by multiple users simultaneously.

[0064] The scanning system further includes at least one memory and one data processing unit, e.g., the central processing unit of a computer or a digital signal processor, which processes the images. Multiple processing units can be used to reduce the amount of time it takes to process the two-dimensional images, calculate three-dimensional coordinates for points in each image, and register frames of three-dimensional coordinates relative to each other to generate a complete virtual model. The processing unit and the memory can be located at a separate location, or be constructed in a single unit. A suitable cable may be used to connect the scanner device to a workstation to thereby supply the processing unit with scan data, and to receive commands (ill umination commands, start/stop commands, etc, ) from the workstation.

[0065] As shown in Figure 6, digital model 601 D includes a scanned 3D digital model of the physical head 2 12D, the top portion of the physical margin ring 1 D, and other intraoral environmental 3D digital image such as gum tissue 3 D.

[0066] Sometimes, once the physical margin ring IP and the physical abutment 2P are placed inside the patient ^' s mouth at or before step (4), a portion of the physical margin ring 1 P that is immediately above the shoulder 220P may be covered by a gum tissue, or it may be buried between the neck 21 IP and gum tissue 33 P, and therefore becomes invisible to the oral scanner 55.

[0067] As shown in Figure 7, step (6) is combining the first 3D intraoral digital model 60 1 D with the three-part 3 D digital model 300D, to generate a second 3 D intraoral digital model 602 D or 1 D2D\ In doing so, digital shoulder 220 D, digital ring ID, digital neck 21 ID, and digital head 2 12D are spatially aligned to each other exactly as their physical counterparts in 1P2P of Figure 3 A, except that, in some embodiments, physical head 212P may have been modified or reshaped; as a result, digital head 212D from the oral scanning may not be exactly the same as the original head 212P (hence 212D', 2D' 1D2D' are used instead). The "combining ^" operation in step (6) should be understood as adding, matching, overwriting, overlapping, overlaying, joining or any combination thereof, as known in the technical field of 3 D modeling and CAD/CAM. Some existing structural features of the digital ring 1 D may be used as the "marks ^" for the purpose of matching digital ring 1 D with the scanned image of the upper portion of the physical ring 1 P, for example, pillars 12 1 D, top surface 114D, top surface 122D, protrusion 124D, protrusion 127D, and voids 126D. If necessary, new registration marks can be added to margin ring IP or ID.

[0068] As shown in Figure 8, step (7) is removing or subtracting the digital margin ring ID from the second 3D intraoral digital model 602 D or 1D2D' to generate a third 3D intraoral digital model 603 D or 2D'. Digital model 603 D or 2D ^" becomes a complete and accurate 3D digital model of the physical shoulder 220D, the physical neck 21 ID and the physical head 212D/212D' (either original or modified) combined, plus some optional intraoral images such as gum tissue 33D, and adjacent teeth (not shown) etc.

[0069] As shown in Figure 9, step (8) is generating a crown 3D digital model 88D using CAD/CAM based on the third 3D intraoral digital model 603D or 2D'.

[0070] As shown in Figure 10, step (9) is fabricating a physical crown 88P from the crown 3D digital model 88D using CAD/CAM technology.

[0071] As shown in Figure 11, step (10) is securing the physical crown 88P onto the physical abutment 2P inside the patient's mouth. In preferred embodiments, the physical crown 88P sits snugly onto the physical abutment 2P. A margin portion 818P of the physical crown 88P sits snugly on the physical shoulder 220 P and around the physical neck 21 IP as the physical margin ring 2P does (like a collar) to shoulder 220P and neck 21 IP as shown 1P2P in Figure 3 A. Portions of the crown 88P other than the margin portion 818P also sit snugly on/around the head 212P of the physical abutment 2 P.

[0072] The crown 88P may be cemented on top of the abutment 2P inside the mouth. Because the margin ring IP/ID has captured the crucial margin information for the dental lab to construct the crown, the crown 88P fits the patient perfectly and comfortably (i.e. "snugly ^" ). A dental crown may be selected from an implant crown, a regular crown, a bridge, and a Cerac Crown. The material used to make to the crown is preferably inert and non -toxic in an oral environment. The crown should have chemical durability in an oral environment, sufficient structural integrity to resist the forces of mastication, wear characteristics which are similar to natural human teeth, and have esthetic qualities, such as coloration similar to human teeth with a slightly translucent appearance. [0073] The crown 88P may comprise any material selected from porcelain, metal, metal alloy, ceramic material, glass-ceramic material, polymeric material, and any combination thereof. In a preferred embodiment of the present invention, the ceramic material is a translucent polycrystalline material, because the natural tooth enamel has a high translucency, whereas dentine has a lower translucency. A polycrystalline material has a multiplicity of randomly oriented crystals joined at grain boundaries. Preferably, the ceramic material is substantially nonporous to maintain a high degree of optical translucency. Translucency is the property of a specimen by which it transmits light diffusely without permitting a clear view of objects beyond the specimen and not in contact with it. A translucent material is an advantage because a crown, for example, formed from such a material effectively blends in with its surroundings and assumes the color of the underlying tooth and the teeth adjacent to it. This can provide improved aesthetics as compared to more opaque materials. In some embodiments, a dentist may need to color-match a crown with the color and shade of the dentition that surrounds the crown. In an embodiment, the ceramic material for the crown is an alpha aluminum oxide. Aluminum oxide is particularly desirable since its optical transmittance is substantially constant throughout the visible spectrum and it therefore does not change the color of light passing through.

[0074] In addition to the margin ring, the abutment, the implant, accessories and tools for this process are also available from Zuga to enable the implementation of the process as described above, including impression analog for all implants (3.5mm, 4.3mm and 5.0mm), universal scan body, universal fixation screw, bone graft material for placing the implant, a motor, a handpiece, a ratchet, 3 tap drills (3.5mm, 4.3mm and 5.0mm), 12 twist drills (D = 3.5mm, 4.3mm and 5.0mm times L = 8mm, 10mm, 13mm, and 15mm), 3 gum punches (3.5mm, 4.3mm and 5.0mm), one placement pin, one ratchet implant adaptor, one ratchet restoration adaptor, and one pilot drill. Regarding the motor, a controller can simplify the process of placing implants. Features of the controller include adjustable torque settings up to 50 ncm and programmable buttons to store common procedures. The handpiece may be a 20: 1 contra angle handpiece that has an integrated titanium design, a small head for easier access, and that is economically designed for practitioner's comfort.

[0075] A CAD/CAM system may be employed in the present invention to make the crown 88P. 3D modeling is the basis for CAD/CAM. In 3D computer graphics, 3D modeling is the process of developing a mathematical representation of any three-dimensional surface of an object via specialized software. 3D model can be displayed as a two-dimensional image through a process called 3D rendering. The model can also be physically created using 3D printing devices. Finally, CAM is used to fabricate a dental crown from the second 3D digital model of the crown. As a result, the margin ring's internal surface, bottom surface and external surface are transferred to the finished crown.

[0076] While digital data processing prior to the fabrication of crown can be accomplished using known Computer-Aided Design (CAD) techniques, the fabrication per se can be accomplished using known Computer- Aided Manufacturing (CAM) techniques. CAD/CAM dentistry uses subtractive processes (such as CNC milling and turning) and additive processes (such as 3D printing) to produce the crown from 3D models. Milling is the machining process of using rotary cutters to remove material from a workpiece. With computer numerical control (CNC), milling machines can be equipped with automatic tool changers, tool magazines or carousels, CNC control, coolant systems, and enclosures. Crown can be manufactured with multitasking machines (MTMs) using any combination of milling and turning operations.

[0077] In the foregoing specification, embodiments of the present invention have been described with reference to numerous specific details that may vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the invention, and what is intended by the applicant to be the scope of the invention, is the literal and equivalent scope of the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction.