Glass material, living tissue replacement, and orthodontic part

Dentistry – Orthodontics – Bracket

Patent

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Details

433173, 501100, A61C 300, A61C 800

Patent

active

057951519

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to living tissue replacements made of semi-transparent or opaque glass and applicable as artificial dental crowns, artificial dental roots, artificial bones, bone screws, and artificial tracheas, orthodontic parts made of glass, and glass materials from which these parts are formed.


BACKGROUND ART

Alumina ceramics and various metal materials are used to form living tissue replacements such as artificial dental crowns, artificial dental roots, artificial bones, artificial junctions and bone fillers. However, metal materials suffer from a problem that metal ions are dissolved out. When metal materials are used as artificial dental crowns, their aesthetic appearance is poor. On the other hand, alumina ceramics are free from the concern about hazard to human bodies, but difficult to work into complex shapes. A great attention is paid to crystallized glass as dental repairs because of good biological affinity and high mechanical strength, and various proposals have been made therefor. In most of crystallized glass materials proposed as dental material, crystals of mica systems or calcium phosphate systems including apatite are precipitated. Therefore, alkali metal elements or phosphorus is an essential component and they are contained in relatively large amounts. However, alkali metal elements deteriorate the water resistance of glass while phosphorus-containing crystals and glass of calcium phosphate systems including apatite deteriorate acid resistance. Although crystallization improves chemical durability, a vitreous phase coexists with a crystalline phase in the case of crystallized glass, especially dental crown repairs where aesthetic appearance is keenly desired. It is thus understood that the relatively high content of alkali metal elements and phosphorus potentially involves a crucial problem to glass for use in the oral cavity which presents a rigorous environment to glass.
Glass materials which do not contain alkali metal elements and phosphorus as essential elements are described, for example, in Japanese Patent Publication (JP-B) No. 36107/1992 and "Fine Ceramics," Vol. 3, pp. 79-87, 1982.
JP-B 36107/1992 discloses crystallized glass for use as artificial bones and dental materials. This crystallized glass has a non-calcium phosphate system composition free of P.sub.2 O.sub.5. More particularly, it is "a P.sub.2 O.sub.5 -free crystallized glass having a composition wherein at least 90% consists of, in % by weight, structure having numerous fine wollastonite (CaO.SiO.sub.2) grains and diopside (CaO.MgO.2SiO.sub.2) grains dispersed in glass."
The crystallized glass disclosed in "Fine Ceramics," Vol. 3 has a composition comprising, in % by weight,
The crystallized glass described in JP-B 36107/1992 is prepared by molding glass powder, followed by firing and crystallization treatment. With the process of molding and firing glass powder, it is difficult to prepare dental crowns and other parts of complex shape. Since the molding step uses an isostatic press and the firing step uses a high temperature of 1,050.degree. C. as described in the publication, this process is quite difficult to practice in the dental office. The process takes a long time to completion since the firing step uses a slow heating rate of 30.degree. to 60.degree. C./hour and a slow cooling rate of 30.degree. to 120.degree. C./hour. Dimensional precision is low since firing entails a large shrinkage factor. Firing of powder after molding fails to provide sufficient strength. Preparation of glass powder requires cumbersome operation and considerable costs because molten glass must be converted into ribbon shape as by passing through water-cooled rollers. With this procedure, many voids are left after firing. Since biotic replacements vary in dimensions depending on a particular individual or application, it is important that doctors, dentists, and dental technicians can purchase the material at low cost and work it in a safe and simple manner using the existing machine. Conventional furnaces

REFERENCES:
patent: 5145365 (1992-09-01), Farzin-Nia et al.
patent: 5231062 (1993-07-01), Mathers et al.
patent: 5261814 (1993-11-01), Farzin-Nia et al.

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