Composition for implantation into the human and animal body

Details Composition for implantation into the human and animal body Composition for implantation into the human and animal body

2001-04-13

2004-03-16

Page, Thurman K. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Implant or insert

C424S423000, C424S426000

Reexamination Certificate

active

06706273

ABSTRACT:

The invention relates to compositions for implantation into the human and animal body.
These implantable compositions serve in particular for the replacement or repair of bones or teeth as well as parts thereof. They are particularly preferably used in the field of dentistry, i.e. in teeth and the bones of the masticatory apparatus, and therefore as dental materials. The compositions consist in particular of powder mixtures and admixing liquids, which are mixed directly before use, i.e. implantation, to form curing pastes. An essential part of the powder mixture comprises a powder of differing composition containing calcium phosphate. The admixing liquid is e.g. demineralized water or an aqueous solution, with the addition of substances, inter alia for improving the biological degradability and/or the acceleration of the tissue integration. Antibiotics and/or disinfectants can also be added to the compositions, to avoid infections.
The aim of the present invention is to avoid disadvantages which are present in the implantation systems for bone replacement corresponding to the state of the art. These disadvantages are as follows:
The following is disadvantageous when using bone implants made from solid material:
A costly adaptation involving the implant or the bone tissue is necessary in order that the hole to be filled in the bone tissue is completely closed.
When using implants which can be admixed to produce pastes, the previously mentioned disadvantage does not occur, but there are a series of other disadvantages, as follows:
The curing times of the admixed pastes are sometimes very short, which is a major hindrance during complicated operations. There are also pastes with very long curing times, which is also undesired.
After they are introduced into the bone tissue and before curing, the pastes are in part not resistant to liquids such as e.g. blood, i.e. they absorb liquid and soften.
The strength values of the cured pastes are sometimes low. In particular, the initial strength is in many cases too low.
In the paste-based implant materials which have become known, the rate at which the tissue integration and resorption occurs is only low.
Such implants are either not at all, or only slightly, biodegradable.
Details on this point emerge from the state of the art as described below:
The mineral bone material occurring in human and animal bodies consists predominantly of a hydroxyl apatite-like structure, the essentially occurring elements being calcium and phosphorous. Other elements also occur, however, in the bone substance, such as sodium, calcium, magnesium and barium.
The replacement of lost bone tissue by natural bone still presents considerable problems even today. This applies in particular in maxillofacial surgery, in accident surgery as well as in orthopaedics. These problems result from the limited availability of autologous bone or the great cost of procuring it, or the insufficient quality when using allogenic bone, combined with the risk of the transfer of diseases.
However, the synthetic bone replacement materials such as Bio-Oss®, Synthacer® or the bioglasses, which are available at present as a solid substance also have considerable disadvantages. These are e.g. that due to their preformed, granular structure, they are not to be optimally implanted into the osseous defects. This applies in particular in dentistry because of the lack of space in the oral cavity, where preformed bone replacement is to be positioned only with great difficulty. A further disadvantage of these sometimes sintered materials is that although they are integrated as bone, they are not completely degraded and replaced by natural bone.
For some time, calcium phosphate-containing powders have also been used, which are present initially as a paste after being admixed with water or aqueous solutions and then cure after a certain time. After curing, these materials display a structural similarity to the mineral phase of natural bone in the x-ray diffractogram. There are thus no longer problems with the adaptation to bone defects of the patient, as the pastes exactly match the existing structures.
Disadvantages occur, with the paste-based implants which have become known according to the state of the art, in the curing times, resistance to liquids acting from the outside, strength after curing, tissue integration as well as biodegradability. These matters are discussed below, in the further description of the state of the art.
One of the first powder- or paste-based implants is the BoneSource® invented by Brown and Chow in 1965, in which the powder component consists of CaHPO
4
and tetracalcium phosphate. After admixing with water, a curing cement paste results, the cured end-product of which is a nano-crystalline hydroxyl apatite with a calcium/phosphorous ratio (Ca/P) of 1.67 (i.e. 1.67 calcium atoms per phosphorous atom). A disadvantage of such a calcium phosphate cement is its relatively long curing period and the disadvantageous property of decomposing in the early phase of setting when in direct contact with liquids. This applies in particular in the case of direct introduction into bleeding bone wounds.
In the publication by Driessens et al, Bioceramics Vol 9, 1996, pages 231-234, amorphous calcium phosphate cements are described, the calcium/phosphorous ratio of which (Ca/P) is<1. These cements consist of Ca(H
2
PO
4
)
2
.H
2
O=mono-calcium phosphate monohydrate (MCPM) and CaKPO
4
or mixtures of MCPM and Ca
2
NaK(PO
4
)
2
. As a result of their relatively high solubility in body fluids, they have lower compressive strengths than the previously described cements with a high Ca/P ratio. The reduced compressive strength is a disadvantage of these implant materials.
On the other hand, a degree, albeit small, of solubility of such materials in the body fluids is desired, as the materials can then be opened up more quickly by body cells, compared with cements which are insoluble in human or in animal body fluids and must essentially be described as osteotransductive.
The system comprising MCPM and CaKPO
4
, apart from the disadvantage of its low compressive strength after curing, also has the disadvantage that its working time is less than 3 minutes.
This working time is clearly to short for difficult implant operations. The MCPM and Ca
2
NaK(PO
4
)
2
system also mentioned has higher compressive strengths, but the curing period is clearly too long compared with the system comprising MCPM and CaKPO
4
.
Such cement systems and the products which result from them after curing, such as Ca(H
2
PO
4
)
2
.H
2
O (=MCPM), hydroxyl apatite Ca
10
(PO
4
)
8
(OH)
2
and others are known from patents U.S. Pat. Nos. 4,673,355, 5,053,212 or EP 0543765. The resorbability of these materials as well as the curing period are, as mentioned, still not satisfactory however.
For this reason, the object of the invention is to develop new implantable compositions with which curable, calcium phosphate-containing pastes can be admixed. Improved biological properties were important for the clinical success in patients, but also more favourable handling properties for the doctor providing treatment e.g. as regards the curing time. The composition according to the invention fulfils these conditions in an ideal manner.
It offers in particular the following advantages:
As it can be admixed to produce curing pastes, the result is an ideal adaptability to the existing bone structure in the patient.
Through variation of the composition, the curing time can be changed, which is extraordinarily advantageous during use.
During curing, the composition is resistant to liquids acting from outside, such as e.g. blood, which can occur with bleeding bone wounds.
After the implant paste has cured, a high initial strength of the implant very quickly results.
The tissue integration can be considerably accelerated by additives.
The special type of composition leads to a good biological degradability, the speed of which can be influenced by the added additives.
In the case of the implants corresponding to the state

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