Patent Application
20190247151
This invention is generally related to a dental prosthetic system such as a dental implant system of the type having an implant body, an abutment and a dental prosthetic. More particularly, the invention relates to a dental prosthetic may be temporarily be placed upon a support surface such as an abutment or a prepared tooth in a removably secure manner in order to ascertain proper positioning of the dental prosthesis before permanent installation.
It is known in the dental restorative arts to use a dental prosthesis such as a crown, bridge, inlay, onlay or an implant. A tooth is often prepared by excavating diseased or damaged material, creating a prepared tooth surface. A crown or other dental prosthesis can then be fit to the prepared surface. In the case of a dental implant, the implant body is secured in a jaw bone, and an abutment having a prosthesis supporting surface is then affixed to the implant body. The prosthesis is then affixed to the abutment supporting surface.
Whether a crown, implant or other restorative system is used, the restoring prosthesis is often dry-fit by the dental practitioner. That is, the prepared restorative prosthesis is placed over the support surface to make certain of its fit and position in the oral cavity. Often and normally, the prosthesis is then cemented to the support surface. A cement gap or a space is intentionally created between the prosthesis and the support surface in order to provide room for the cement used in the affixing step.
By “dental prosthesis” or “dental prosthetic” and similar terms, it is intended herein to include any dental restorative that is dry-fit prior to permanent affixation. This includes without limitation, crowns, bridges, inlays and the like without limitation. The invention is often exemplified herein with reference to a crown, but such is not intended to limit the invention to only crowns.
It is important that the dry-fit and the final cementing or the prosthesis is accomplished with precision so that the permanent affixation of the prosthesis is in substantially the same position as the approved dry-fit position. Previously, the two parts (the support surface and the prosthesis) do not dry-fit together snugly, and may in fact fall apart if not physically held together during the procedure, prior to cementation. Also, the two parts can move relative to one another by an amount equal to the size of the cement gap. This effect happens translationally, but there is a similar effect rotationally. As a result, adjustments made to the crown during the dry-fit may be off by the amount of the cement gap after cementation. See
During prosthesis try-in in a doctor's office, and prior to cementation, the doctor needs to hold the crown in place or risk it falling off the abutment (or other support substructure), possibly falling down the patient's throat. In addition, the act of holding the part in place obstructs the doctor's view of the part and reduces their ability to evaluate the correct fit and esthetic quality. The features of the present invention hold the crown in place without the need for a doctor to hold it in place (typically with their finger).
This problem sometimes doesn't show itself with traditional dental manufacturing techniques. It turns out that those techniques often include precision errors that cause the parts not to properly fit by an amount that allows them to stay in place without being held by the doctor. With more precise manufacturing techniques, as in the present invention, these errors are not large enough to potentially keep the restoration in place.
According to the invention, these features not only provide a predictable dry-fit retention, they also allow for a more precise manufacturing technique to have this similar physical characteristic as less-precise parts often display.
During the same crown try-in procedure, the doctor will make adjustments to the crown/restoration to make it properly fit relative to neighboring teeth and other anatomy. This is done by making small modifications to the restoration until the doctor determines that it fits correctly.
After such modification, the doctor removes the now-adjusted crown adds a layer of cement and places the part back in the patient's mouth as part of the final cementation step. But, the final cemented position could be different from the position that the doctor made the final adjustments using. The difference could be up to the size of the cement gap, both translationally and rotationally. The ultimately results in a poor fit in the patient's mouth, causing the doctor to make an additional set of adjustments if possible.
An additional benefit of the present invention is that it reduces the size of these potential errors to the same amount as the machining error of the added features. That machining error is significantly smaller than the cement gap of the parts.
A dental implant system includes a dental implant body configured to be securable in a jaw bone; an abutment secured or securable to said implant body and having a first end affixable to said implant body, and a second end configured to receive a dental prosthetic; and, a dental prosthetic receivable on and cementable to said second end of said abutment, such that an outer surface of second end of said abutment is positioned opposite to an inner surface of said dental prosthetic when said dental prosthetic is received on said second end of said abutment. A cement gap is configured between said abutment and said dental prosthetic when said dental prosthetic is received on said abutment; and the outer surface of said abutment is provided with a plurality of regularly or irregularly spaced dry-fit features, such that when said dental prosthetic is received on said second end of said abutment, said dry-fit features create a removable friction fit between said outer surface of said second end of said abutment and said dental prosthetic.
There is also provided according to the present invention, a dental implant system including a dental implant body configured to be securable in a jaw bone; an abutment secured or securable to said implant body and having a first end affixable to said implant body, and a second end configured to receive a dental prosthetic; and, a dental prosthetic receivable on and cementable to said second end of said abutment, such that an outer surface of second end of said abutment is positioned opposite to an inner surface of said dental prosthetic when said dental prosthetic is received on said second end of said abutment. A cement gap is configured between said abutment and said dental prosthetic when said dental prosthetic is received on said abutment; and wherein said inner surface of said dental prosthetic is provided with a plurality of regularly or irregularly spaced dry-fit features, such that when said dental prosthetic is received on said second end of said abutment, said dry-fit features create a removable friction fit between said inner surface of said dental prosthetic and said second end of said dental abutment.
In another embodiment of the invention, a dental restoration includes a prepared tooth having a preparation surface; and a dental prosthetic having an inner surface receivable on said preparation surface. A cement gap is configured between said preparation surface and said dental prosthetic when said dental prosthetic is received on said preparation surface; and wherein said inner surface of said dental prosthetic is provided with a plurality of regularly or irregularly spaced dry-fit features, such that when said dental prosthetic is received on said preparation surface, said dry-fit features create a removable friction fit between said inner surface of said dental prosthetic and said preparation surface. The inner surface of a crown is designed to be slightly larger than the outer surface of the abutment it is intended to be cemented to. This is to provide room for the cement. This extra space is called a cement gap. See
According to the present invention, there is created an article of manufacture that adds dry-fit features such as spherical or other shapes of bumps or protrusions to the surface of the abutment, the interior of a prepared dental prosthesis or the like, to both locate the abutment, prepared tooth surface or other support structure, and the crown relative to one another. This provides sufficient frictional fit between the two parts such that the crown doesn't fall off the abutment during dry-fit.
The dry-fit features according to the invention may be placed on any opposing surface between the dental restorative prosthetic and the support surface upon which it is to be dry-fit prior to cementation. It will be understood that the dry-fit features are intended to be protrusions of any shape or size, whether regularly shaped or irregularly shaped, and all such features will be collectively referred to by the term dry-fit features, bumps or the like for simplicity of this disclosure.
A method for retaining crowns to abutment during dry-fitting includes calculating appropriate (not necessarily optimal) places to put the dry-fit features to achieve dry-fit retention; adding the dry-fit features to the abutment model (or crown model); and, manufacturing the two parts together with the added bumps.
Detailed Description of the Invention
According to the present invention, a dental restoration is achieved with the ability to secure a dental prosthesis such as a crown, in the oral cavity of the patient prior to cementation or other affixation of the prosthetic. During dry-fit, dry-fit features assure a snug or tight fit between the prosthesis and its support surface (such as a dental abutment or a prepared surface of a tooth) such that proper placement of the restorative is accomplished after the dry-fitting procedure.
A dental prosthesis system having such dry-fit retention features according to the invention is shown by way of example by the number 10 on the attached drawings. It will be appreciated that dry-fit features or bumps 11 may be positioned upon the interior of the dental prosthesis 12; an exterior support surface such as abutment 13 or prepared tooth surface 14; or, both simultaneously. For simplicity, the dry-fit features 11 will be exemplified herein and on the drawings as being positioned on one surface or the other, it being understood that such features can be positioned upon both opposing surfaces according to the invention.
As shown in
As shown in the prior art series of drawing
According to the present invention, dry-fit features or bumps 11 are provided upon a surface such as outer surface 13a or abutment 13 that extend into cement gap 22. Preferably, each bump 11 is similarly sized and are placed at various locations about surface 13a, such that crown 21 having an interior surface 21a is correctly positioned upon the support surface 13b or abutment 13 in a correctly aligned manner. Further still each bump 11 is preferably extends into cement gap 22 to a distance such that each physically touches or engages interior surface 21a of crown 21. The longest dimension of a given bump 11 may even be slightly greater than the cement cap 22 dimension when crown 21 is placed upon abutment 13 or other support. In this manner, it will be appreciated that before cementation or the filling of cement gap 22 with cement, crown 21 may be placed upon its intended support surface such as abutment 13 and will be temporarily retained in its correct alignment to be reviewed by the dental practitioner. If dimensioned properly, a friction fit between bumps 11 and the opposing surface such as interior surface 21a of crown 21 may be created by the physical engagement, thereby securely yet temporarily holding crown 21 to abutment 13 during the dry-fit procedure. Once the correct alignment has been confirmed and the crown removed, cement may be applied and the crown re-seated upon the abutment 13. Bumps 11 ensure correct replacement of crown 21 in the positioned confirmed during dry-fit, without compromising the integrity of the ensuing cement bond.
Although any number of dry-fit features or bumps 11 may be employed, it is preferred to use at least three. It will also be appreciated that bumps 11 may be placed regularly or irregularly spaced upon a support surface 13a at any location. As shown in
Dry-fit features of bumps 11 may also be placed upon the interior 21a of dental prosthesis or crown 21, as is shown in
According to another embodiment of the present invention, a dental prosthesis 21 having bumps 11 on its interior surface 21a as described above, may be supported upon the prepared surface 30 of a tooth 31. A cement gap 22 is provided as also above described. Bumps 11 serve to allow the dental practitioner to dry-fit crown 21 upon prepared surface 30 of tooth 31, and to facilitate proper alignment and securing during such dry-fit and during the subsequent cementation step. Other than being positioned upon a prepared surface 30 of a tooth 31, the invention is utilized in a manner as characterized hereinabove.
In still another embodiment of the present invention as shown in
Similarly, as shown in
In restorative dentistry, cement retained restorations are typically built using three components:
During the fitting procedure in doctor's office, the crown is placed on the abutment without cement to test its shape and give an opportunity for adjustments prior to final cementation. We call this “dry-fitting.”
The typical restorative procedure is shown in
The inner surface of the crown is designed to be slightly larger than the outer surface of the abutment it is intended to be cemented to. This is to provide room for the cement. This extra space is called a cement gap. See
There are a few problems that need to be overcome because of the need for this cement gap:
This invention helps address these problems by adding as set of small features between the crown and abutment. These small features (in one incarnation spherical bumps on the abutment wall) are slightly bigger than the cement gap. Yet, they take up very little of the surface area to be bonded by cement. As a result, the two parts are modified by a manufacturing process to have the following additional characteristics:
The method described here is to digitally apply small features on either surface in contact with the cement gap to meet the following conditions:
It is helpful to explain more about the need for a minimum of 3 features as noted in item 8 above. In mechanics, objects are described as having six degrees of freedom: translation in the x, y and z directions, and rotation about the x, y and z axes. Preventing an object from moving requires restricting its movement in these six degrees of freedom.
Note that some disciplines refer to twelve degrees of freedom. This is no different than the six mentioned in that each linear direction has both positive and negative motion, and each rotational direction has both clockwise and counterclockwise motions. In practice, is can be useful to think of restricting motion by restricting both directions of each degree for a total of twelve degrees of freedom to restrict. Some people clear up this apparent confusion by describing twelve degrees of “movement” in the six degrees of “freedom.”
You can restrict movement in a linear direction by putting an obstacle in the path of that movement. That obstacle can take the form of a rigid feature that resists motion. Sometimes this is accomplished by clamping, which uses friction as a block to movement. The exact needs to restrict all six degrees of freedom depend on the geometry of the object to be restricted. (For example, you can't restrict rotational motion of a sphere with point obstacles alone, but must also include some clamping force to resist the rotation.)
Manufacturing generally accepts that it takes six point locations plus one clamp to restrict motion of a generic object. It is easy to see that linear motion can be restricted in all three degrees of freedom by six points. A single clamp can add restrictions on all the rotational aspects.
Irregular shapes can be constrained without clamps, but clamps make the problem easier. Imagine the case of a cube. It can be constrained linearly by a single point obstacle on each surface. With perfect rigid objects, those six points will also prevent rotation. This would happen because as the cube rotates relative to the points, the distance between the two points on the surface of the cube would get bigger. In practice, the amount of flexibility in the cube material, and the point obstacles allow for a certain amount of linear and rotational play. Different counts of points, locations of the points and the addition of clamps can improve the amount of resistance the part has to movement.
In the case of a custom abutment and crown configuration, these items are typically irregular in shape, which makes fixing their relative locations easier to solve. To restrict most linear motion requires three points on the vertical walls of the interface and one point to restrict vertical motion along the axis of the abutment core. But, for a crown connection, there is another constraint that simplifies the problem. There is medical value to having the crown and the abutment have as close to no cement gap as possible along the margin edge where they meet. That is, we want the crown and abutment to touch along the marginal edge.
The reason for this is that research shows that cement can irritate soft tissue, so dental practitioners work to limit contact with cement against the tissue. We help my designing the crown and the abutment to mate as tightly as possible in this region, to the extent possible using machining techniques to provide this zero cement gap feature. It is well known in basic mechanics that such a connection will actually be in precise contact in at least 3 points, and we can count on this relationship to provide 3 of our needed contact points, while also maintaining the correct marginal fit.
The result though is that we can fully constrain the cap motion in 11 of the 12 degrees of freedom by taking advantage of the vertical restriction imposed by the margin contact, and adding at least 3 distributed contact points around the core of the abutment (or inner surface of the crown).
These four points will not restrict the crown from slipping off the abutment. For this we need a clamping force, which is achieved by making at least two of the points on vertical surface bigger than the cement gap, providing clamping friction induced by the force of overcoming the interference during insertion.
With an irregular cross section, the three points on the vertical section are sufficient to prevent axial rotation. But, to restrict rotation along the two other rotational directions requires the contacts created by the intimate contact with the margin. Together with the contacts along the abutment walls these provide at least three obstacles when the part is rotated about the axis created by any two other points.
In this way, a minimum of six points and one induced clamping force is sufficient to both locate and constrain the relative positions of a crown and abutment in a dry-fit situation.
(There is the possibility that the mating surface forms a perfect cylinder. In this case, a system can be designed that restricts rotation about the central axis of the cylinder using clamping. But there is no system that can deterministically locate such a cylinder, just prevent its rotation. Fortunately, in restorative dentistry, with patient specific crowns and abutments, it is extremely unlikely that a specific case would have such a perfectly cylindrical mating surface. A practitioner can correctly ignore this edge case. And, should it actually occur sufficiently often to warrant, a constraint can be added to the custom design process to prevent perfect cylindrical shapes.)
It is important to note that the proper location and constraint can be achieved by precise placement of three contact points. But, we can simplify the needed precision of placement by adding more points of constraint. So, while three points are the minimum, in practical application using more points simplifies the calculations needed and provides redundant support. But, adding more points need to be done with a mind to not overly reducing the area of cement application, and not excessively increasing the frictional forces applied between the two surfaces.
In practice, we can add as many contact points as we like so long as the total contact area is small enough to ensure sufficient remaining cement area on the part. We are currently practicing using 16 feature points distributed around the core of the abutment. This is partly to account for variability in the wall geometry of the abutment core. Abutments are affixed to the implant via a screw, and that screw is inserted via a screw access hole. The screw axis hole cuts through the abutment core surface someplace, and typically cuts away some of the abutment wall. Rather than calculate where the hole is and position a small number of contact points to avoid the hole, we add enough contact points such that there continue to be sufficient contact points no matter how many are cut away by the screw access hole.
There is no need for precision in the number of contact points in the abutment (or crown) wall. So long as there are at least three and you don't add so many that they don't leave sufficient room for cementation strength, you can pick any number that efficiently works for your placement calculation algorithm.
In addition, there is no need for precise placement of the contact points around the abutment core. So long as they are placed so that no radial span is large enough to allow translation of the part through the gap created, the radial distribution will be fine. In practice, this means that the parts should be distributed so that no radial span leaves a gap greater than or equal to 180 degrees.
Finally, there is no need for precise placement of the contact points vertically along the abutment core. The goal should be to distribute the points vertically, such that they take up greater than half of the total vertical span of the abutments. That is, the distance between the lowest point and the highest point should be greater than half of the abutment core. All the other points can be randomly distributed in the remaining vertical space. In practice, it makes sense to distribute them evenly in this space, but there is no mechanical need for this implementation.
Also, with truly rigid bodies, the two surfaces will naturally only come into contact with precisely six of the obstacle points. Adding more points would have no impact on theoretically perfect and rigid parts. That said, we do not have theoretical parts in the real world. Our parts yield when mated, and we take advantage of this feature of matter to induce friction. In this real-world view, many more than six points will interact contributing to the friction component. But, it is not necessary that more than six points engage, and in fact it is acceptable in practice of some of the extra points do not, in fact engage.
In other words, with more than three wall contact points, it is possible that (in fact likely) that some of the contact points will actually not be in contact with the opposite wall. In true force closure situations, this is undesirable, since force closure would want to precisely control which 3 points were in contact. In our invention, it is unimportant which three points are in contact, simply that there are 3 in contact. And the mechanics of the situation will also assure that at least three of the contact points will be naturally distributed so as to provide repeatable repositioning.
It is worth some notes on the size of the contact points. While we plan to practice a shape that is largely semi-spherical, there are only two factors that matter in this feature size and shape: the cross sectional area and the height of the feature from the surface it is placed on.
The cross sectional area needs to be large enough so that it has sufficient mechanical strength in the material it is manufactured out of to not break off in normal use. For our materials in their normal use, that means we need a cross sectional area on the order of 0.01 mm2. Again, there is no need for precision here. This can be as large as you like so long as the total remaining area for cementation continues to be sufficient. In practice, the features could be as large a 1.0 mm2, and still be small enough. This can be validated either experimentally or with a calculation based on remaining area and cementation needs.
The height of the features needs to be slightly larger than the cement gap. It cannot be smaller than the cement gap, or there will be no friction induced. But the exact extra height is difficult to describe precisely, and can be determined best by experimentation on specific material choices. The correct extra height depends on two factors. The first factor is the desired level of friction. The larger the interference, the greater the friction induced. This impacts both the finger force required to set the two parts together, and the amount of force needed to separate the two parts. This is incredibly difficult to calculate, and is best determined by experiment and user experience. The second factor is that the feature must be smaller than the elastic modulus of the two materials would cause either part to fracture. This can be determined using standard finite element analysis methodologies, or simple experimental techniques. But, it practice this is unnecessary, since the force required to fracture the material will (for most practical materials) be larger than could practically be applied by a finger pushing the two parts together.
In our implementation we use:
There is prior art that uses a precise number of features such that the crown is placed in a precise location with each placement. This approach on its face seems remarkably similar to this proposed invention, but differs in a number of key ways and because of those differences is an inferior approach to this invention:
At first glance it might seem difficult to distinguish between the force closure based prior art and our invention. In reality, there are a number of features that make distinguishing these two approaches easy:
It will be appreciated:
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US17/53390 | 9/26/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62400175 | Sep 2016 | US |
