Active/passive dental posts

Abstract: A dental post for securely retaining a dental restoration in a prepared tooth stub. The dental post (26) is formed of an elongated cylindrical rod having an active threaded portion (38) and a passive portion (42). The dental post is threadedly engaged with a sleeve (62) secured in the tooth stub, which sleeve has at least an active threaded portion.

Description: BACKGROUND OF THE INVENTION This invention relates to dental posts, and more particularly to a dental post with an active occlusal portion and a passive apical portion, which improves its retention within a prepared tooth stub on which a dental restoration will be erected. In addition, this invention relates to the use of a sleeve with an active portion positioned in a tooth stub. The active portion of the dental post is engaged with the active portion of the sleeve to improve its retention within the prepared tooth stub. Furthermore, this invention contemplates forming the sleeve by positioning a mandrel with an active portion in an adhesive prepared bore in a tooth stub and curing the adhesive to form the sleeve. In one embodiment the adhesive is cured by transmitting light through the mandrel to cure the adhesive. In restoring dentition, one procedure is to build up a dental prosthetic structure on a tooth stub. The tooth stub is initially prepared by cutting it down to provide a suitable support on which the prosthetic structure will be built. A bore is formed into the tooth stub in which a dental post is inserted. In one type of dental post, referred to as an active post, there are threads provided on the post and the post is threaded into the bore in the tooth stub. Other posts are referred to as passive posts and they are secured in the bore by means of cement. The passive posts typically include a contoured surface for improving its retention in the bore formed in the tooth stub. Suitable dental cement is used for retaining the dental post in the bore. A portion of the dental post extends occlusally of the surface of the tooth stub so that as the dental prosthetic structure is formed or built up onto the tooth stub, it is retained in place on the tooth stub by means of the extending portion of the dental post. By way of example, an early type of active post has been suggested in U.S. Patent No. 702,111 describing a post with screw threads which are screwed into the root cavity of a tooth. Threaded engagement of an active post into the dentin of a tooth has been found to cause stress in the tooth thereby contributing to its possible fracture. On the other hand, using passive posts produce less stress in the tooth. However, the retention of passive posts are not as great as the active post. To improve the retention, various types of contoured surfaces have been suggested. By way of example, U.S. Patent No. 4,479,783, issued October 30, 1984 for "Helically Fluted Dental Post", assigned to the assignee of the present invention, suggests contouring the surface of a passive dental post with helical flutes in a sequence with designated flutes being deeper than alternating shallow flutes to improve retention of the dental post. Improvements in the capabilities of dental posts are also described in U.S. Patent No. 4,729,736, issued March 8, 1988 for "Contoured Dental Posts", assigned to the assignee of the present invention, which includes helical grooves and annular retaining ledges axially spaced along the post to both improve retention of the post and increase the strength of the post to reduce the possibility of post shear. The use of sleeves in a prepared bore of a tooth stub has been suggested in the prior art related to retention of a dental post within a bore in a tooth stub. By way of example, there has been suggested in U.S. Patent No. 965,246 the use of a sleeve in a cavity in a tooth stub into which a pin attached to a crown is inserted and held either by friction or cement. In addition, U.S. Patent No. 4,622,012 suggests the use of a sleeve positioned in a bore of a tooth through which an adhesive is introduced into the bore. A dental post is then introduced into the sleeve to force the adhesive through holes in the sleeve to distribute the adhesive in the bore. Upon hardening of the adhesive, the post is retained in the sleeve. U.S. patent 4,400,160 discloses an endodontic assembly for retaining a dental restoration on a prepared tooth stub, which includes a sleeve insertable into the tooth stub and securable to a surface of the tooth stub and an elongated rod insertable into the sleeve. While the aforementioned dental posts and sleeves have provided improvements with respect to the retention of a post in a bore, still further improvements in such retention would be beneficial. These improvements would be particularly beneficial if they can be achieved without increasing the risk of breaking the dental post or adding stress to the tooth. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved dental post. A further object of the present invention is to provide a dental post having improved retention capabilities when secured in a prepared bore in a tooth stub. Still a further object of the present invention is to provide a dental post with a threaded active portion and either a smooth or contoured passive portion for securing the post to the tooth. Another object of the present invention is to provide a dental post which is secured to a tooth by engaging a sleeve positioned in a prepared bore in the tooth stub. Still another objective of the present invention is to secure a dental post having an active portion and a passive portion by providing a sleeve in a prepared tooth cavity, which sleeve engages the active portion of the post. Yet a further object of the present invention is to provide a sleeve in a prepared bore in a tooth, which sleeve is complementary to a dental post having an active portion and a passive portion. Still another object of the present invention is to provide a dental post with an active portion and a passive portion within a cement prepared sleeve which in turn is formed in a prepared bore of a tooth stub, thereby improving the retention of the post in the tooth stub. Briefly, in accordance with the present invention there is provided a dental post assembly for securely retaining a dental restoration on a prepared tooth stub. The dental post includes an elongated cylindrical rod having an elongated longitudinal axis. The rod has a threaded active portion with threads formed in the periphery of the rod and a non-threaded passive portion which may be contoured. The assembly further includes a sleeve having a closed apical wall and being insertable in a bore of a tooth stub and having on an inner surface thereof a threaded active portion with threads complementary to the threads in the active portion of the rod and a non-threaded passive portion. The threaded engagement of the active portions of the rod and sleeve improve the retention of the rod in the tooth stub without causing stress on the tooth. The sleeve is made of a curable hardened adhesive to be secured to the surface of the tooth stub. The sleeve may be made by positioning a mandrel having a threaded occlusal portion of the same size and shape as the active occlusal portion of the rod of the dental post, in a prepared bore of a tooth stub and introducing an adhesive into the bore which when it hardens, forms the sleeve. The mandrel is withdrawn from the sleeve leaving a threaded occlusal portion for the threaded portion of the rod to engage. According to the invention, the mandrel is made of a light transmitting material and the adhesive which forms the sleeve is made from a light curable material. Light is transmitted by the mandrel to the light curable material which hardens and adheres to the bore in the tooth stub to form the lining. The aforementioned objects, features and advantages of the invention, will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention taken, in part, with the drawings which form an integral part thereof. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Fig. 1 is a cross sectional view taken through a tooth stub showing the normal preparation of an endodontically treated tooth stub ready for utilization of the dental post of the present invention; Fig. 2 is another view of the tooth stub shown in Fig. 1, being sized to prepare the canal in the tooth stub for the post; Fig. 3 is a cross sectional view of a drilled tooth stub with a prepared canal, showing a light transmitting mandrel positioned in the canal and surrounded by an adhesive; Fig. 4 is another cross sectional view of the tooth stub shown in Fig. 3 with the mandrel removed leaving a preformed sleeve in the bore of the tooth stub; Fig. 5 is a perspective view of a dental post having an active occlusal portion and a passive apical portion in accordance with the present invention; Fig. 6 is a perspective view of another embodiment of a dental post having an occlusal active portion and a passive apical portion in accordance with the present invention; Fig. 7 is a perspective view of another embodiment of a dental post having an occlusal active portion and a passive apical portion in accordance with the present invention; Fig. 8 is a cross sectional view of a tooth stub, showing a dental post in accordance with the present invention retained within the stub; Fig. 9 is a cross sectional view of a tooth stub and dental restoration, showing the use of the present invention for securing the dental restoration on the tooth stub; and Fig. 10 is a cross sectional view of a tooth stub, showing a sleeve having a threaded active portion in the occlusal part of the stub. In the various figures of the drawings like reference characters designate like parts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, in Fig. 1 there is shown a tooth stub 10 in cross section within a gum area 12, where the occlusal end of the tooth has been impaired. The tooth has been initially cut down, typically to provide a suitable occlusal surface 14 to support a dental restoration. In order to build up a dental restoration or other super structure onto the tooth stub 10, there is required a retaining member, such as the dental post of the present invention. Initially, conventional root canal work is carried out by cleaning out the canal 15 of the tooth along the canal section 16 of a tooth stub. The canal is sealed with a suitable sealant 18 such as gutta percha. As shown in Fig. 2 a twist drill 20 is used to remove gutta percha and to size the canal to the desired bore 22 in the canal section 16 of the tooth stub. Referring to Fig. 5, the dental post of the present invention is shown generally at 24 and comprises an elongated cylindrical rod 26 having an enlarged longitudinal axis and a substantially flat apical end 28 and a head 30 at its occlusal end. The head 30 includes a pair of spheres 32, 34 with elongated indentations 36 triangularly positioned about the spheres. The occlusal portion 38 of the shaft 26 has threads 40 formed in the periphery of the rod. Since, as will be described later, the threaded occlusal portion positively engages threads in a sleeve, the threaded portion is also referred to as an active portion. The apical portion 42 of rod 26 has a smooth outer surface 44 and an elongated vertical channel 46 which serves as a vent during insertion of the post 24 into a tooth stub. Since the apical portion 42 is not threaded, it serves as a passive portion. Fig. 6 depicts another post 24 of the present invention wherein the apical passive portion 42 of the rod 26 is provided with multiple helical grooves 48 which wind about the periphery of the pin. These grooves are typically flutes of the type described in the aforementioned U.S. Pat. No. 4,479,783. As therein described, certain of the flutes are deeper flutes 50 and are interspersed with shallower flutes 51. As a result of the multiple flute lines which terminate at the apical end 28, the flute lines serve as a vent during insertion of the post 24 into a tooth stub. Fig. 7 depicts another post 24 of the present invention wherein the apical passive portion 42 of the rod 26 is provided with multiple helical grooves 52 and 53 which wind about the periphery of the pin. Grooves 52 and grooves 53 wind in opposite directions about the pin and intersect to form a diamond-shaped pattern. As a result of the multiple grooves which terminate at the apical end 28, the grooves serve as a vent during insertion of the post 24 into a tooth stub. Numerous other configurations of the passive portion 42 of the present invention are within the contemplation of the present invention. For example, the configuration described in aforementioned U.S. Pat. No. 4,729,736 which includes helical grooves and annular retaining ledges could be used. Referring next to Fig. 3, there is shown a mandrel 54 having an occlusal portion 56 and an apical portion 58. The mandrel 54 is cylindrical with an elongated longitudinal axis and has threads 60 formed in the periphery of the occlusal portion 56. The threads 60 have substantially the same pitch and diameter as threads 40 formed in the occlusal portion 38 of cylindrical rod 26. The occlusal threaded portion of the mandrel 56 is also referred to as the active portion of the mandrel. The apical portion 58 of the mandrel is smooth and is also referred to as the passive portion of the mandrel. In accordance with the present invention, mandrel 54 is placed with its passive portion 58 inserted in enlarged bore 22 of the tooth stub 10. A sleeve or liner 62 is cast by filling the space between the mandrel 54 and the inner surface 64 of the tooth with an adhesive which will cure and harden in the manner of forming a cast. The adhesive may be any one of the many dental adhesives used to attach a dental post to a tooth stub, e.g., a self curing adhesive. In the preferred embodiment of the invention, the mandrel 54 is made of a light transmitting medium and acts as a light pipe. The adhesive is a light-curable composite which will begin to cure when light is transmitted to its surface. Light from a light source 66 is shined on mandrel 54 which transmits the light to the composite to cause curing. The mandrel 54 is also made of a material which will not form a strong bond with the composite. Alternatively, mandrel 54 can be coated with a compound which will prevent it from forming a strong bond with the composite. Alternately, the adhesive can be a self-curing composite and it will set by itself in adequate time. After the composite has hardened, mandrel 54 is unscrewed from the cured composite leaving cast sleeve 62 (Fig. 4) bonded to the inner surface 64 of tooth stub 10. Although not necessary to the success of the present invention, mandrel 54 is preferably placed coaxially in bore 22 to form a sleeve 62 of fairly uniform dimensions. As shown in Fig. 4, sleeve 62 with mandrel 54 removed has an occlusal portion 68 with threads 70 formed by the threads 60 of the mandrel. Sleeve 62 has an apical portion 72 with a smooth inner surface 74. The threaded occlusal portion of the sleeve is also referred to as the active portion of the sleeve. The smooth apical portion of the sleeve is also referred to as the passive portion of the sleeve. Dental post 24 having either a smooth or a contoured apical portion 42 will threadedly engage sleeve 62 since the pitch and diameter of the threads 40 of the post 24 are the same as those of the threads 60 used to form threads 70 in the sleeve. Consequently, dental post 24 is secured to tooth 10 by inserting rod 26 into sleeve 62 and threading the active portion 38 of the rod into the active portion 56 of the sleeve. In one embodiment of the invention shown in Figs. 8 and 9, dental post 24 is threadedly engaged with sleeve 62. In addition, the sleeve 62 has been prepared with a dental cement 67 which will bond both the active and passive portions of the post to the active and passive portions of the sleeve. The use of the cement gives even further improved retention of the post in the tooth stub. Head 30 of post 24 extends upwardly above the upper surface 14 of tooth stub 10. A superstructure 68 can then be suitably formed onto the tooth stub in accordance with standard well known techniques in the dental line. The superstructure 68 is retained onto the mating spheres 32, 34 and is held securely in place. An alternate embodiment is shown in Fig. 10 in which a sleeve 69 has only an active portion 70 with threads 71. One way of forming sleeve 69 is to use a mandrel (not shown) with a passive portion having an outer diameter equal to the inner diameter of a prepared bore 72 in a tooth stub 73. When the mandrel is positioned in bore 72 of tooth stub 73, a curable adhesive is introduced around the active portion of the mandrel. The adhesive will not enter the bore 72 since the tight fit of the passive portion of the mandrel in the bore prevents the adhesive from flowing into the bore. When the adhesive has cured, the mandrel is removed leaving a sleeve 69 with only an active portion 70. Dental post 24 is positioned in tooth stub 73 with the passive portion 42 in bore 72 and active portion 38 threadedly engaged with threads 71 of sleeve 69. A dental cement is used between dental post 24 and sleeve 69. Cement is introduced into bore 72 to increase retention of post 24 by bonding the passive portion 42 of post 24 within the tooth stub. It should be noted that the use of cement to increase the retention of the post 24 in a tooth stub, requires that the dimensions of the post and the sleeve be selected so that the cement will not interfere with placing the post in the tooth stub, i.e. there must be sufficient clearance between the post and the sleeve. There has been described a preferred and alternate embodiments of the invention. However, it should be understood that various changes and modifications may be made thereto without departing from the scope of the invention.

Claims: A dental post assembly for securely retaining a dental restoration on a prepared tooth stub comprising a sleeve (62,69) insertable into the tooth stub and securable to a surface of the tooth stub; and an elongated rod (26) insertable in said sleeve, characterized in that said sleeve has a wall having on an inner surface thereof an active threaded portion (68,70) and a non-threaded passive portion (72); said sleeve (62,69) is made of curable hardened adhesive to be secured in a canal section of the tooth stub and has a closed apical wall; said elongated rod (26) has an active threaded portion (38) and a non-threaded passive portion (42), said active portion (38) of said rod (26) having threads (40) of a pitch and diameter corresponding to a pitch and diameter of threads of said active threaded portion (68) of said sleeve (62, 69) to permit the rod (26) to be threadedly engaged with the sleeve (62,69). A dental post assembly as in claim 1, wherein said active portion (68,70) and passive portion (72) of said sleeve (62,69) are formed by hardening said curable adhesive in the canal section of the tooth stub. A dental post assembly as in claim 1, wherein said passive portion (42) of the rod (26) is contoured. A dental post assembly for securely retaining a dental restoration on a prepared tooth stub comprising a sleeve (62,69) insertable into the tooth stub and securable to a surface of the tooth stub, and an elongated cylindrical rod insertable in said sleeve, characterized in that said sleeve (62,69) includes on an inner surface thereof an active threaded portion (68,70) and a non-threaded passive portion (72) and has a closed apical wall; said sleeve (62,69) is formed of a non-metallic material securable to the surface of the tooth stub to be secured in a canal section of the tooth stub; said cylindrical rod (26) has an active threaded portion (38) and a passive portion (42), said active threaded portion (38) of said rod (26) being threadedly engaged within said active threaded portion (68,70) of the sleeve (62,64) to retain the rod in the tooth stub. A dental post assembly as in claim 4, wherein the passive portion (42) of the cylindrical rod (26) is positioned within the passive portion (72) of the sleeve (62,69). A system for forming a lining in the canal of a tooth stub comprising a reamer (20) for reaming the canal to a desired size and depth, characterized by a light curable composite (62) for filling the canal and a mandrel (54), having an active threaded portion and a non-threaded passive portion, insertable into the canal and made of a light transmitting material.

Inventors: WEIL EBERHARD, WEIL, EBERHARD
Applicants: COLTENE WHALEDENT INC, COLTENE/WHALEDENT, INC.
Application year: 1991
Main classification: A61C13
IPC codes: A61C19, A61C13