Unbreakable disposable photocuring guide

A disposable dental curing light guide which can be made of a low cost polymer. The light guide can be radioactively sterilized and packed in a sterilized dispensing envelope to maintain it in a sterilized and clean state. The light guide can provide satisfactory transmission of light between 400 nm and 500 nm for dental curing purposes.

BACKGROUND OF THE INVENTION 
This invention relates to a light curing device and in particular to a 
disposable light guide or probe suitable for dental curing purposes. 
In photocuring, particularly for dental photocuring purposes, commonly a 
stationary or Dartable light generating device is used. For convenience in 
manipulation, in the portable light generating device, light is provided 
by a hand-held gun unit which generates the light suitable for dental 
curing. The gun unit may be operated by alternating current power or by 
direct current power supplied by a rechargeable battery power. A 
relatively short light guide or probe is removably mounted at the front 
end of the un unit for transmitting the curing light from the gun unit to 
the location at which photocuring is required. For a system with a 
stationary light generating device, the light is transmitted from the 
light generator by an elongated flexible guide to the curing location. A 
short guide or probe again may be adapted at the free end of the elongated 
light guide for carrying out the light curing operation at a location 
remote from the stationary light generator. The short probe or guide is 
made of a plurality of optical fibres fused in a glass cladding which 
maintains the optical fibres in a compact composite bundle. The composite 
bundle is then covered in a protective sheathing material which also 
prevents the light travelling through the guide from leaking through its 
peripheral surface. Silicon or glass or metal is commonly used as the 
sheathing material for such guides. Such guide or probe construction is, 
for example, shown in U.S. Pat. No. 4,846,546 by Joseph Cuda. The main 
drawbacks of such common guide or probe are that they are expensive and 
difficult to fabricate; and furthermore, the sheathing and cladding 
deteriorate rapidly under repeated autoclaving sterilization operation 
particularly when the sterilization operation may not be properly carried 
out in a general dental office. The sterilization is essential to prevent 
the transmission of disease virus from a contaminated probe to a patient. 
Also, such glass cladded probe or guide, particularly after subjected to 
repeated autoclaving sterilization operations, is breakable, so that it 
presents a hazard to the patient during use as the breakage of the glass 
components can occur when the probe is located in the patient's mouth 
cavity. 
SUMMARY OF THE INVENTION 
The principal object of the present invention is to provide a light curing 
guide which is simple in construction and is easy to produce. 
Another object of the present invention is to provide a light curing guide 
which is inexpensive to produce such that it is disposable after use. 
Another object of the present invention is to provide a light curing guide 
which is presterilized and packed in a sterilized packaging such that it 
does not require sterilization before it can be used by the dentist. 
Yet another object of the present invention is to provide a light curing 
guide which can be produced easily with an injection moulding process. 
Still another object of the present invention is to provide a light curing 
guide which is unbreakable and is safe to use within a patient's mouth 
cavity without any potential health hazard to the patient. 
The disposable probe comprises a generally cylindrical rod made of a 
plastic material having a low light refraction characteristics. The rod 
has a light receiving end and a curing end. The light receiving end has 
larger diameter tapering gently to the curing end which has a smaller 
diameter, and an arcuate bend portion is formed in the curing end.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the drawings in which like reference numerals designate 
corresponding parts in the several views, the light curing guide of the 
present invention is a generally cylindrical rod 10 made of a clear 
plastic material having a low light refraction characteristics such that 
it can transmit light in the range of from 300 nanometers (nm) to 800 
nanometers (nm). Light in such range is commonly used in photocuring 
operations and in particular in the range of 400 nanometers (nm) and 500 
nanometers (nm) is used in dental curing operations. Inexpensive amorphous 
homopolymer such as polymethyl methacrylate and polycarbonate are suitable 
for such purposes. It has been found that light guides rely on total 
internal reflection to transmit light efficiently. Total internal 
reflection occurs if a light wave is incident upon a boundary going from a 
denser medium of refractive index to a rarer medium of refractive index 
above a certain angle of incidence. The relationship of the critical angle 
to the refractive index at a boundary is outlined in the following 
formula: 
EQU Sin (Theta)=n1/n2 
in which 
Theta is the critical angle. 
n1 is the refractive index of the first medium, 
for air n1 is equal to 1. 
n2 is the refractive index of the second medium. 
Polymethyl methacrylate such as acrylic having a light refractive index of 
1.49 in air, the critical angle is 42 degrees, and polycarbonate having a 
light refractive index of about 1.586, the critical angle is 39 degrees. 
Thus, these material provide satisfactory light transmission for dental 
curing purposes. 
The rod 10 has a generally circular cross sectional shape and having a 
larger diameter at the light receiving end 11 tapering gently to a smaller 
diameter curing end 12. The tapering is, for example, about 2 degrees 
relative to a plane parallel to the longitudinal axis of the rod 10 as 
best shown in FIG. 1. The curing end portion 13 is bent at an obtuse 
arcuate angle from the longitudinal axis of the light receiving end 
portion 14. The bent portion may have a length, for example, governed by a 
60 degrees radian angle as shown FIG. 1. The rod 10, typically has a 
diameter of from 2 millimeters to 15 millimeters and about 76 mn to 127 mm 
long. The generally flat surfaces provided at the light receiving end 11 
and curing end 12 are smooth clear surfaces to facilitate maximum amount 
of light transmission. 
The tapering shape of the rod 10 enhances the concentration of light 
transmitted therethrough. Generally, when light is incident upon a 
boundary going from a denser medium of refractive index to a rarer medium 
of refractive index, the incident light must be within a critical angle to 
be reflected totally from the boundary. For acrylic material having a 
refractive index of 1.586, the critical angle is about 39 degrees. The 
relatively small tapering angle of the surface of the rod 10 ascertains 
that the critical angles for the guide will not be exceeded over the 
length of the guide, so as to limit the light losses through the boundary 
to a minimum. 
The obtuse arc in the curing end portion from the light receiving end 
portion also reduces the light losses through the peripheral surface. The 
equation that relates the minimum bend radius in a guide for not 
theoretical light losses through the surface with light beam passing 
therethrough is as follows: 
EQU R=D*(n1+n2)/2*(n1-n2) 
in which 
D=Diameter of the rod. 
n1=Refractive index of the rod material. 
n2=Refractive index of the cladding. 
R=Center radius of the bend. 
since no claddings is provided on the rod 10, the refractive index for n2 
is 1 for air, and a relatively large arc will considerably reduce the 
surface light losses. 
Following the formation of the rod 10 by injection moulding, it is then 
cleaned to ascertain a clean surface to reduce any light scattering 
effects from uneven surfaces and the adherence of dust particles thereon. 
It is then packaged in a sealed envelope and the entire package is 
subjected to proper and fully controlled sterilization by radiation or 
autoclaving. Since the guide is completely sterilized, it does not require 
further sterilization by the dentist before being used. Thus, a clean and 
properly sterilized guide is provided for ready use without presenting any 
health hazard to the patient. It does not depend upon the sterilization 
operation to be carried out by the dentist such as in the known 
photocuring guide. Such user sterilization operation often is 
unsatisfactorily and/or carelessly carried out so that it can present a 
serious health hazard to the patient. Furthermore, since the guide can be 
made inexpensively with the above process, it is not intended for re-use, 
therefore, a highly clean and disposable curing guide is provided. 
The guide may be coupled to a curing gun of a portable curing unit or the 
free end of the elongated flexible light guide of a stationary curing 
light unit through a mounting adaptor. A suitable filter may be provided 
in the adaptor for heat filtering or other desirable purposes. 
The bending in the guide enhances the location of its curing end onto the 
curing location within the patient's mouth cavity for on-the-spot dental 
curing. 
Whilst in the illustrated embodiment presently preferred features of the 
invention have been put forward herein, it is to be understood that the 
invention :is not limited to the precise forms illustrated herein as an 
example, and that chances may be made thereto without departing from the 
spirit and substance of the invention.