Dentistry – Prosthodontics – Holding or positioning denture in mouth
Reexamination Certificate
1999-11-23
2001-05-08
Lewis, Ralph A. (Department: 3732)
Dentistry
Prosthodontics
Holding or positioning denture in mouth
Reexamination Certificate
active
06227860
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dental implant for preparing tooth prosthesis. More specifically, this invention relates to a dental implant having the function for immediate loading after implant placement.
2. Description of the Prior Art
Modern dental implants are designed based upon the biological fact that a titanium-alloy implant and a bone integrate with each other very strongly, bearing a tensile strength more than 100 kg. This fact was found by Branemark of Sweden in 1969, and is called Osseointegration. Typical such osseointegrated implants comprise a tubular body portion called a fixture which is emblaced within a bore drilled in the bone.
As shown in
FIG. 9
, the dental implant
110
developed by Branemark is composed of a fixture
111
, an abutment
112
, a gold cylinder
113
, an abutment screw
114
, and a gold screw
115
(totally five pieces). The fixture
111
has a tublar body and is threaded externally, and when implanted in bone it is perfectly osseointegrated with alveolar bone after three to six months. The abutment
112
connects the fixture
111
to the gold cylinder
113
through soft tissue. The gold cylinder
113
connects the abutment
112
to a prosthesis (called an upper structure). The abutment screw
114
fixes the abutment
112
to the fixture
111
, and the gold screw
115
fixes the upper structure to the abutment
112
through the gold cylinder
113
.
In the method developed by Branemark for using the dental implant
110
, it has been ruled out to load by connecting the prosthesis to the implant until three to six months after placing an implant in the alveolar bone under mucous membrane, in order to keep the implant at rest. This is called delayed loading protocol. It was reported that micromotion of the implant was produced by omitting the delayed loading period and when the amount of micromotion exceeded 100 &mgr;m, some disorder was caused on the surface between the implant and the bone. On the other hand, in Branemark's method, even solid denture is contraindicated during the delayed loading period of three to six months after implant placement, as its protocol attaches importance for keeping the implant at rest during the period. Since this means to lengthen the necessary period for operation and to bring upon patient's pain, it has been regarded as a problem to be solved.
In order to overcome the drawbacks, it is indispensable to load immediately after implant placement without rest period. Hence, an effective countermeasure to prevent micromobility of the implant becomes necessary. Several types of implants using the mechanical locking means for securing the implant in place within the bore in the jawbone have been suggested. These types of implants have an expansion screw in the internal channel of the fixture, the lower half of the fixture being cut in to the end and divided into several legs, and when the expansion screw is rotated the legs are expanded radially and outwardly, causing the anchoring effect of the fixture in bone. The method to load immediately after implant placement is called immediate loading, and the design to secure the anchoring effect in bone by expanding the legs of the implant in immediate loading is called apical expansion design.
Referring to
FIG. 10
, the first dental implant
120
of apical expansion design issued in U.S. Pat. No. 2,721,387 to Ashuckian (1955) has spindle-like form imitating the socket of the extracted tooth. In the internal channel of the fixture
121
of the dental implant
120
, an expansion screw
122
is inserted. By rotating the expansion screw
122
, an expansion nut
123
is drawn upwards, thereby spreading apart two legs which are formed by dividing the lower half of the fixture
121
. Thus, the fixture
121
is anchored in bone so as to prevent micromotion of the implant.
As shown in
FIG. 11
, the dental implant
130
of apical expansion design issued in U.S. Pat. No. 3,708,883 to Flander (1973) has the structure that the lower half of a cylindrical fixture
131
is divided into two legs and a frustoconical head
132
is attached on one end of an expansion screw
133
which is inserted into the internal channel of the fixture
131
. By rotating a square nut
134
threaded into the other end of the expansion screw
133
, the expansion screw
133
is drawn upwards together with the head
132
and the legs of the fixture
131
are expanded.
As shown in
FIG. 12
, the dental implant
140
of apical expansion design issued in U.S. Pat. No. 5,087,199 to Lazarof (1992) has the structure that the lower half of a cylindrical fixture
141
is divided into plural legs and an expansion screw
142
having a conical head
143
is inserted into the internal channel of the fixture
141
. By rotating the expansion screw
142
, the point of the conical head
143
goes down into the hollow
144
at the internal center of the lower portion of the fixture
141
, and the legs of the fixture
141
are expanded.
Further, as shown in
FIG. 13
, the dental implant
150
of apical expansion design issued in U.S. Pat. No. 5,489,210 to Hanosh (1996) has the structure resembling closely to the dental implant
140
in that the lower half of a cylindrical fixture
151
is divided into plural legs and an expansion screw
152
having a conical head
153
is inserted into the internal channel of the fixture
151
. By rotating the expansion screw
152
, the point of the conical head
153
goes down into the hollow
154
at the internal center of the lower portion of the fixture
151
, and the legs of the fixture
151
are expanded.
These types of implants of apical expansion design, as described above, have codimon mechanism that they have an expansion screw in the internal channel from the head to the lower end of the cylindrical fixture, the lower half of the fixture being cut in to the end and divided into plural legs, and when th e expansion screw is rotated are expanded radially and outwardly, causing anchoring effect in bone preventing micromotion of the implant.
However, these designs have the risk of micro-leakage of bacteria called microorganisms from the head of the implant exposed in patient's intraoral cavity to the bottom of the implant placed in bone, passing through the micro-gap between the male threads of the expansion screw and the female threads of the internal channel of the fixture. Therefore, the dental implants of these types of apical expansion design may fail unless precautions attention is paid to potential contamination in the apical region, which could cause serious damage to periimplant bone crucial to achieve osseointegration, so that they do not have any practical value.
An improved dental implant
160
of apical expansion design is described in U.S. Pat. No. 5,681,187 issued to Lazarof (1997). The dental implant
160
, as shown in FIG.
14
(A), has a cylindrical fixture
161
, the lower half of which is divided into plural (four) blade-like legs. The fixture
161
has a circular ring-shaped internal shoulder
162
at the upper middle in the internal channel of the fixture
161
. A screw head
163
, the outer diameter of which is larger than the inner diameter of the internal shoulder
162
, and a male screw portion
164
which is inserted through the internal shoulder
162
constitute an expansion screw
165
.
When the expansion screw
165
is rotated, a frustoconically-shaped expansion nut
166
is drawn toward the middle of the implant with the result that, as shown in
FIG. 14
(B), the legs
167
of the fixture
161
located within the socket of the extracted tooth are spread apart, thereby anchoring the dental implant
160
in bone so as to prevent micromotion.
By means of the structure of the dental implant
160
of apical expansion design described above, when the expansion screw
165
is rotated and the frustoconically-shaped expansion nut is drawn upwards, then the legs
167
of the fixture
161
are expanded and reactive forces to return the legs
167
to their original form work against active f
Lewis Ralph A.
Ostrolenk Faber Gerb & Soffen
Twenty One Inc.
LandOfFree
Dental implant does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dental implant, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dental implant will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2508277