Dental equipment

Abstract: A dental post 5 has a lower portion 4 that is fitted within a pre-prepared dental root canal 2, 3 and an upper portion 6 to which a dental crown 8 can be fitted. The root canal is provided with a plurality of projections 26 that extend downwardly and inwardly and the post, which is preferably tapered, and the lower portion of the post has a plurality of notches 16 that are preferably independent grooves that face upwardly. The post can then be secured substantially without screwing, by means of cement in the annulus 7 between the post and the canal. Preferably the lower portion of the post is tapered and has grooves or other notches that open upwardly and outwardly and the upper portion has grooves that open downwardly. The pitch of the grooves 16 in the lower portion is generally not more than 0.5mm. The invention also includes a dental reamer that can be used to form a profiled cavity in a tooth and that has an elongated cutting head (30, 31, 32) having a plurality of cutting elements (34) that can be used for cutting into the wall of the canal to define the projections 26.

Description: This invention relates to improved dental equipment used in particular for securing, by way of a dental post, a dental crown above a root canal in order to provide a secure bond and thereby provide a cosmetically desirable permanent dental crown. More specifically the invention relates to improved dental reamers. A dental post has an upper portion to which a dental crown can be secured and a lower portion that can be secured within a dental root canal and that extends downwardly from the upper portion. In this specification I am using the words "upper" and "upwardly" to indicate the direction towards the crown and the words "downward" and "downwardly" to indicate the direction into the root canal. The root canal is drilled out to a depth and diameter sufficient to receive the chosen length of the lower portion of the post, the post is fitted within the drilled cavity and is bonded in position by a cement that fills the annulus between the surface of the lower portion and the inner surface of the cavity. The crown is then secured on to the upper portion. The post must be bonded into the root canal sufficiently strongly and to a sufficient depth to prevent it becoming loosened, for instance due to the very powerful leverage forces that may be applied on to the post by normal biting on to the crown. In order to promote firm bonding of the post within the cavity, it is known to provide the lower portion of the post with a roughened, sand-blasted, surface. The resultant notches or recesses formed by the sand blasting are very small and will open outwardly in a direction substantially perpendicular to the axis of the post. Also a particular form of post (sold under the trade name Parapost) has a series of parallel grooves each of which extend substantially around the lower portion. The separation of each of these grooves is normally at least 1mm. In order that the angles defined by the side walls of each groove are such as to promote bonding, an inevitable consequence of having this spacing of at least 1mm is that each groove has a significant depth, relative to the diameter of the post. Other posts having a few widely spaced grooves are shown in EP 260446. In GB 2117641 a dental post assembly includes a coarsely screw threaded post which is inserted by rotating so that the spiral bites into the walls of the root canal. This places stress on the root of the tooth and imposes the risk of fracturing the remaining dental root. Other screw fitting systems are shown in GB 2117641 and U.S. Reissue 31948. A dental reamer for forming a profiled cavity in a tooth as defined in the first part of Claim 1 is generally known. Such a reamer typically comprises an elongated body, means for mounting the body for drilling rotation, and a cutting head mounted on the elongated body distant from the mounting means for rotation with the body. A disadvantage with this type of reamer is that a single cutting head is used to form each portion of the profile in turn, and this is inconvenient in practice. According to the present invention, the cutting head of a reamer of the type described above is elongated and has a plurality of cutting elements spaced along its length and these are shaped to profile into a wall of the cavity to define a plurality of inwardly and downwardly projecting ridges that each extend around part or all of the cavity and that are arranged substantially parallel to one another. The number and spacing of cutting elements will be chosen according to the desired spacing of the ridges in the cavity wall. The novel reamer is specifically designed for the formation of parallel ridges. The cutting head of the reamer may extend along the entire length of the elongated body, but generally it is mounted only at one end. The head can be cylindrical, but is preferably tapered. The cutting elements are usually outwardly extending teeth. The cutting head of the reamer may be designed such that it can be used for simultaneously drilling the cavity and forming the ridges or it can be such that the cavity is drilled to substantially the desired size by a conventional drill and the novel reamer is then used solely for removing sufficient of the tooth to define the ridges. The dimensions of the reamer will be sufficiently small that it can be used for forming a cavity in a tooth and will be selected according to the size of the cavity that is to be formed in the tooth. Usually it is of a size suitable for profiling a root canal. It can be made of materials that are conventional for dental reamers. The novel reamer is usually tapered along part or all of its length, especially when it is to be used for forming a tapered cavity for use with a tapered post. The angle of the taper can be for instance about 3 to 15°, often about 3 to 10°, and an angle of about 5° is often suitable for drilling a canal cavity. The novel reamer can form projections in the wall of the root canal that are discrete projections but preferably each is a ridge that extends around part or all of the canal wall, each ridge being defined by a lower ridge face and an upper ridge face wherein the lower ridge face is inclined at a greater angle to the axis of the canal, and is shorter than, the upper ridge face, the ridges being substantially parallel to one another. The ridges or other projections in the canal wall can be formed to have very small dimensions, both as regards pitch and, optionally, depth, for instance below 0.3mm. Typically however the ridges or other projections can have a pitch of from 0.2 to 3mm, often 0.2 to 1mm. The novel reamer of the invention may be used to prepare a dental root canal cavity to receive any suitable dental post. Preferably, however, the dental post is of a type described in divisional application EP-A-93202238.7. In this case, a method of securing a dental crown, that should be cosmetically desirable, above a pre-prepared dental root canal comprises securing the lower portion of the dental post inside the dental root canal, which has a plurality of projections that extend downwardly and inwardly that have been preformed in its walls by use of the novel reamer, such that the lower portion is positioned within the canal and defines an annulus between the post and the wall of the pre-prepared root canal, the annulus is filled with a curable cement and the cement is cured to secure the lower portion in the canal. As a result of the projections in the surface of the dental root canal, the cement between the post and the canal wall is trapped between notches in the post that open outwardly (and preferably upwardly) and projections in the wall of the canal that extend inwardly and downwardly. The securement of the post in the cavity therefore depends to a large extent on the shear strength of the cement rather than on the adhesive strength of the cement to the post and, especially, to the canal wall. This can result in the post being held in the canal much more securely. It also permits a much wider choice of cements since adhesion is not solely dependent on its adhesiveness to the surface of the canal cavity. A wide variety of dental cements can be used. According to a further aspect of the invention, a kit comprises at least one reamer as described above and at least one dental post having an upper portion to which a dental crown may be secured, a lower portion that can be secured within a dental root canal and that extends downwardly from the upper portion, and a plurality of notches in substantially the entire length of the lower portion. Preferably the dental post is of a type described in divisional application EP-A-93202238.7. The invention is now described with reference to the accompanying drawings in which: Figure 1 is an enlarged diagrammatic cross-section showing a dental post and a profiled canal cavity; Figure 2 is a longitudinal cross-section of a dental reamer suitable for forming the profile shown in Figure 1; Figure 3 is an enlarged cross-section on the line VII-VII in Figure 2. The profiling shown in Figure 1 can conveniently be achieved by use of a profiling tool or reamer that can have a conventional elongated body and mounting for fixing to a drill but which is provided with a novel type of cutting head, as shown at 30 in Figure 2. The cutting head is shown as having a substantially cylindrical portion 31 and a tapered portion 32 leading to a tapered end 35. In some instances the entire head can be tapered whilst in other instances the entire head can be cylindrical. The head is provided with a plurality of spaced apart cutting elements that comprise teeth 33 at the leading edge (during rotation) of ridges 34 that extend around part of the radius of the cutting head. The profiling of the ridges 34, and thus of the teeth 33, will be chosen so as to match the desired profile between the projections 26 in the tooth. The spacing between adjacent ridges will be the spacing that is required between adjacent projections 26, typically around 0.5 to 1.5mm. Normally there will be at least 3 and often 5 to 20 spaced apart cutting teeth along the length of the cutting head. The construction of the teeth 33 and the remainder of the cutting head can be such that it is conveniently used for the initial drilling of the root canal or can be such that the canal is drilled approximately to the desired size using a conventional drill and can then be profiled by the use of the described cutting head. The diameter of the cutting head is normally substantially less than the diameter that is desired in the cavity, in which event the cutting head has to be moved around the walls of the cavity while rotating, and for instance may be rotated eccentrically within the cavity. This can be achieved by manual movement of the axis of the cutting head along a circular path but a more convenient way of achieving this is to rely on the tip 35 of the cutting head being shaped as an eccentric point, as shown in Figures 2 and 3. The axis 36 of the cutting head is shown in dashed line. The effect of the eccentric point on reaching the bottom of a pre-drilled cavity, is to cause the axis of the cutting head to follow a circular path as the cutting head rotates and this forces cutting edges against the cavity wall so as to create the desired undercuts, for instance as shown in Figure 1.

Claims: A dental reamer for forming a profiled cavity in a tooth and comprising an elongated body, means for mounting the body for drilling rotation, and a cutting head mounted on the elongated body distant from the mounting means for rotation with the body, characterised in that the cutting head (30) is elongated and has a plurality of cutting elements (33) spaced along its length and the elements (33) are shaped to profile into the wall of the cavity a plurality of inwardly and downwardly projecting ridges (26) that each extend around part or all of the cavity (2) and that are arranged substantially parallel to one another. A reamer according to claim 1 in which the elongated cutting part is tapered at an angle of at least 3°. A reamer according to claim 1 or claim 2 in which the pitch of the cutting elements is 0.2 to 3mm and there are 5 to 20 cutting elements spaced along the head. A kit comprising at least one reamer according to any of claims 1 to 3 and at least one dental post having an upper portion to which a dental crown may be secured, a lower portion that can be secured within a dental root canal and that extends downwardly from the upper portion, and a plurality of notches in substantially the entire length of the lower portion.

Inventors: FILHOL STUART JULIAN, FILHOL, STUART JULIAN
Applicants: FILHOL STUART J, FILHOL, STUART JULIAN
Application year: 1989
Main classification: A61C13
IPC codes: A61C13