A PLURALITY OF DIFFERENT MATERIALS

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention generally relates to the field of liglit curing devices incorporating light sources and, more particularly, to the field of heat sinks configured for dissipating heat generated by the light sources of the light curing devices. 2. The Relevant Technology In the field of dentistry, dental cavities are often filled and/or sealed with photosensitive compounds that are cured when they are exposed to radiant energy, such as visible or ultraviolet light. These compounds, commonly referred to as light- curable compounds, are placed within dental cavity preparations or onto dental surfaces where they are subsequently irradiated by a light-curing dental device. Many light-curing devices are configured with a fiber optic wand for directing light from a light source into a patient's mouth. The light source may comprise, for example, a lamp, a halogen bulb or a light-emitting diode (LED). One end of the fiber optic wand is placed close to the light source so that the light emitted from the light source will be directed into the fiber optic wand. One problem with fiber optic wands is that they are generally unable to capture all of the light that is generated by the light source, particularly light emitted by LEDs, which may be emitted at angles of up to about 120°. Another problem is that fiber optic wands, being essentially solid glass, are relatively heavy and bulky.

One method for overcoming the limitations of fiber optic wands and for generally improving the lightness and efficiency of the light-curing devices is to place the light scmrce(s) of the light-curing device at the end of the light-curing device that is placed next to the composition being cured. Although this addressed problems associated with fiber optic wands, the proximity of the light source (s) to the patient's mouth creates its own problems. For example, heat generated by the light source(s) at the tip of the light-curing device can cause patient discomfort when the tip of the light-curing device happens to come in contact or immediate proximity to the

sensitive mouth tissues of the patient. Accordingly, it is desirable to minimize the heat at the tip of the light-curing device.

One method for minimizing the heat at the tip of the light-curing device is to mount the light source(s) on a heat sink that can. conduct heat away from the tip of the light-curing device. The ability of a heat sink to absorb and dissipate heat is generally controlled by the material properties and geometries of the heat sink. The arrangement and geometries of the mounting surfaces of the heat sink are also important factors to consider when determining how efficiently the heat sink will be able to absorb and dissipate heat.

Typically, heat sinks are formed of a homogenous material, for example a metal or metal alloy. The material properties that most affect the ability of a given material to act as an effective heat sink are thermal conductivity and specific heat of the material. Heat sink materials may be selected so as to have a high thermal conductivity or a high specific heat. When selecting a material for its high thermal conductivity, the material's specific heat may be lower than desired. Also, when selecting a material for its high specific heat, the material's thermal conductivity may be lower than desired.

It would be an improvement in the art to provide a heat sink formed of a plurality of layers or regions of different materials so as to increase the ability to absorb and dissipate heat. BRIEF SUMMARY OF THE PREFFERED EMBODIMENTS

The present invention is directed to a dental curing light having a heat sink specifically configured for effectively dissipating and absorbing heat generated by one or more light sources {e.g., LEDs) away from the tip of the dental curing light.

According to one embodiment, the dental curing light comprises an elongate hollow wand housing having a proximal first end, a distal second end, a light source disposed at the distal second end of the wand housing, and a heat sink disposed at least partially within the wand housing. The heat sink is in contact with the light source, and comprises a plurality of layers or regions comprising different materials. A first layer or region comprises a first heat sink material, while a second layer or region comprises a second heat sink material different from the first material. The thermal conductivity of the first heat sink material is greater than that of the second

heat sink material, and the specific heat of the second heat sink material is greater than the specific heat of the first material.

Thermal conductivity generally quantifies the ability of a given material to conduct and dissipate heat to the surrounding environment. Specific heat generally quantifies the ability of a given material to absorb heat. According to one embodiment, the first material {i.e., having a higher thermal conductivity) may comprise at least one of copper, aluminum, brass, steel, silver, another metal, a metal oxide ceramic, diamond, graphite, carbon fiber, or even a polymer based epoxy, silicone, or any other material having a higher thermal conductivity than the selected second material. According to one embodiment, the second material {i.e., having a higher specific heat) may comprise at least one of water, copper (so long as copper is not also used as the first material), nickel, beryllium, or any other material having a higher specific heat than the selected first material. A-Ccording to some embodiments, the second layer or region may comprise a solid, a liquid, or a gas core within the heat sink. It may comprise a solid or liquid material that undergoes a phase change above room temperature {e.g., up to 135°C) in order to absorb additional heat without causing a proportionate increase in temperature {e.g. , waxes, water, salt, fatty acids and esters, polyols, other hydrocarbons, iodine, and gallium).

Because specific heat is measured on a per uαnit mass basis, and because the volume of the heat sink may be relatively small, it may be advantageous in some embodiments for the second material to also have a relatively high density. The product of the selected material's density and specific heat quantifies the amount of heat that the second layer or region can absorb. According to one such embodiment, the product of the density of the second material and i"ts second specific heat is greater than the product of the density of the first material and its specific heat.

Each layer or region within the inventive heat sink is optimized for a particular purpose. The first layer or region acts to draw and conduct heat away from the one or more light sources. The second layer or region acts as a "sink" which absorbs heat already conducted away from the light source. The first layer or region may also act to dissipate heat into the air, away from the one or more light sources. The overall effect is a heat sink which effectively draws heat away from the one or more light

sources, provides for its absorption, and allows cooler operation of the light source(s) (e.g., LEDs) and the dental curing light.

According to one embodiment, at least a portion of the heat sink may be separated from the wand housing by an air gap. The air gap provides insulation, resulting in less heat diffusing out of the housing wand of the dental curing light in the region around the tip of the curing light, resulting in a cooler tip and greater comfort for the patient.

These and other advantages and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in "which:

Figure 1 is a bottom perspective view of a dental curing light according to the invention; Figure 2 is an top perspective view of the curing light of Figure 1;

Figure 3 is an exploded view of the dental curing light of Figures 1 and 2; Figure 4 is a cross sectional view of the dental curing light of Figure 1 and 2 taken along cutting line 4-4;

Figure 5 A is a cross sectional view of an alternative heat sink suitable for use with a dental curing light; and

Figure 5B is a cross sectional view of another alternative heat sink suitable for use with a dental curing light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Definitions and Introduction

A detailed description of the curing light of the invention will now be provided with specific reference to figures illustrating preferred embodiments of the invention. It will be appreciated that like structures will be provided with like reference designations.

The term "specific heat" is a parameter characterizing the quantity of heat required to produce a unit temperature rise per unit mass of material. The units of measure for specific heat are J/kg-K.

The term "thermal conductivity" is a parameter characterizing the ability of a material to conduct heat. The units of measure for thermal conductivity are J/sec-m- K.

The term "light source" includes any ligrxt source known in the art suitable for use with dental curing lights, examples of which, include incandescent lamps, halogen bulbs, light-emitting diodes (LEDs), and LED arrays. The term "LED light source" includes the electrical components of the LED as well as the integral lens or micro lens of the typical LED structure.

In general, the dental curing light comprises an elongate hollow wand housing having a proximal first end, a distal second end, at least one light source disposed at the distal second end of the wand housing, and a heat sink in contact with the light source and disposed within the wand housing.

The heat sink comprises a plurality of layers or regions comprising different materials. According to one embodiment, a fΪTSt layer or region comprises a first material having a first thermal conductivity and a first specific heat, while a second layer or region comprises a second material having a second thermal conductivity and a second specific heat. The thermal conductivity of the first material is greater than the thermal conductivity of the second material, while the specific heat of the second material is greater than that of the first material.

II. Exemplary Dental Curing Light Reference is first made to Figure 1 , whicli is a bottom perspective view of one embodiment of a dental curing light 100. As shown, the dental curing light 100

includes an elongate housing 102 that extends between a proximal first end 104 and a distal second end 106. Although the housing 102 is shown to be sleek and slender, it will be appreciated that the housing 102 of the dental curing light 100 may comprise any desired shape and size.

A light source 120 disposed at the distal end 106 of the dental curing light 100 is configured to emit light suitable for curing light-curable compounds, such as, for example, during dental restoration procedures. The light source 120, as shown, includes two LEDs. Although only two LEDs are shown, it will be appreciated that the light source 120 may also include more or less than two LEDs or other light sources. The light source 120 may also include an LED array, a plurality of LED arrays, and any combination of LEDs and LED arrays. The curing light 100 may also include a lens 140 sized and configured so as to cover the light source 120 at the distal end 106 of the body 102 and to focus light emitted by the light source 120.

According to one embodiment of the invention, the light source 120 and the distal end 106 of the elongate housing 102 are sized and configured so as to be easily inserted into the mouth of a patient, thereby enabling light generated by the light source 120 to be directly emitted into the patient's mouth without first passing through an elongated light guide (e.g., a fiber optic wand), as required by many conventional light curing devices.

According to one embodiment, the light source 120 is powered by a remote electrical power supply (not shown), which may include, but is not limited to, the power outlet of a wall receptacle, a battery, a generator, a transformer or any other source capable of supplying power to the dental curing light. A power cord 122 connected at the proximal end 104 of the dental curing light 100 operably connects the remote power supply with the dental curing light 100. According to one alternative embodiment (not shown), the proximal end 104 of the dental curing light is not connected to a power cord 122, but rather the dental curing light 100 is equipped with an integral battery pack that is capable of powering the dental curing light 100 and energizing the light source. The battery pack is advantageously rechargeable (e.g., by direct electrical contact or by induction). Figure 2 is a top perspective view of the dental curing light 100 shown in

Figure 1 and further illustrates controls that are disposed on the elongate housing 102

of the dental curing light 100. According to this embodiment, the controls are configured to enable a dental practitioner to control the activation of the light source 120.

According to this embodiment, the controls preferably include three different buttons 130, 132, 134. The first button 130, when depressed, selectively activates and deactivates the light source 120. In one embodiment, first button 130, when depressed, may activate the light source for a predetermined duration of time, such as, for example, 15 seconds, thereby enabling the dental practitioner to use the dental curing light 100 without having to continuously depress button 130 during use. The second and third buttons 132, 134 can be designed to increase or decrease the predetermined duration of time light is emitted by a desired increment of time, such as, for example, by 5 second increments. Alternatively, second and third buttons 132, 134 can be designed to selectively increase or decrease the intensity of light that is emitted. The buttons could alternatively be designed to switch between ramped, pulsed or continuous light output. Various embodiments of dental curing lights with ramped and pulsed output are disclosed in U.S. Patent Application Serial No. 10/916,283, filed August 11, 2004, and titled CURING LIGHT WITH RAMPED OR PULSED LEDS. The curing light 100 may, of course, include any desired number and functionality of buttons or controls.

The controls are advantageously ergonomically mounted on the elongate housing 102 of the dental curing light 100 for ease of use. In particular, the controls are advantageously disposed on the body 102 in a manner which enables them to be manipulated by the thumb or finger of the dental practitioner. It will be appreciated, however, that the dental curing light 100 of the invention is not limited to any particular configuration or type of controls. Rather, the dental curing lights of the invention may be configured with any type of controls that are attached to the body of the dental curing light or that are remotely located away from the curing light, as desired.

Referring to Figure 3, the dental curing light 100 also includes electronic circuitry 160 for controlling the operation of the curing light through buttons 130, 132, and 134 (or alternative controls) as illustrated and described in conjunction with Figure 2. Power may be provided to the electronic circuitry 160 through an electrical

connection (not shown) to power cord 122. Additional wiring (not shown) to provide power and control between the electronic circuitry 160 and the LEDs 120 may also be included, as desired.

Figures 3 and 4 illustrate an exploded view and a cross sectional view, respectively, of the dental curing light 100. As can be seen in Figure 3, the elongate housing 102 is hollow so as to allow room for the internal components of the dental curing light 100. The light source (e.g., LEDs) 120 may be mounted to heat sink 150. In any case, the heat sink 150 is configured so as to be adjacent to the light source 120 so as to draw away excess heat produced by the light source 120.

The heat sink 150 is formed of a plurality of layers or regions. Figure 4 illustrates one embodiment of a heat sink 150 having two layers or regions. First layer or region 152 is formed of a first material having a first thermal conductivity and a first specific heat. Second layer or region 154 is formed of a second material

^■ having a second thermal conductivity and a second specific heat. The thermal conductivity of the first material is greater than the thermal conductivity of the second material, while the specific heat of the second material is greater than the specific heat of the first material. In the illustrated embodimexit, layer or region 154 also comprises a core within heat sink 150. Such a core may comprise a solid, a liquid, or a gas. In this way, the portion of the first region 152 adjacent to the light source 120 helps draw heat away from the light source 120 and conduct or "deposit" it to the second region 154, and the portion of the first region separated from the light source by the second region 154 helps draw and dissipate heat away from the second region 154.

According to one embodiment, first layer or region 152 may comprise at least one of copper, aluminum, brass, steel, silver, another metal, a metal oxide ceramic, diamond, graphite, carbon fiber, silicon carbide, or even a polymer based epoxy or silicone. The thermal conductivity of the material within the first region is preferably at least about 120 J/sec-m-k, more preferably at least about 240 J/sec-m-k, and most preferably at least about 350 J/sec-m-k.

According to one embodiment, second layer or region 154 may comprise at least one of water, copper, nickel, beryllium, aluminum, magnesium, silicon, or any other material having a specific heat greater than the specific heat of the selected first material. The second layer or region may comprise a solid, liquid or gas core

encapsulated within the first layer or region. It may comprise a solid or liquid material that undergoes a phase change in order to absorb additional heat without causing a proportionate increase in temperature. In other words, heat is absorbed when the substance undergoes a phase change (e.g., solid to liquid, solid to gas, or liquid to gas) without a concomitant rise in temperature. In the context of a dental curing light, the phase change would advantageously occur between room temperature and about 135°C. Examples of materials that undergo a phase change include, but are not limited to, waxes (e.g., paraffin), water, Glauber's salt (sodium sulfate decahydrate), calcium chloride liexahydrate, linear crystalline alkyl hydrocarbonds, fatty acids, fatty esters, polyethylene glycols, long alkyl side chain polymers, pentaerythritol, pentaglycerine, neopentyl glycol, low melting metals and alloys, quaternary ammonium clathrates and semi-clathrates, salt hydrides, iodine, and gallium.

The specific heat of the material withim the second region is preferably at least about 380 J/Kg-k, more preferably at least about 900 J/Kg-k, and most preferably at least about 1800 J/Kg-k. The product of the specific heat and density of the material (i.e., "heat density") in the second region is preferably at least about 3 J/cm ³ -k, more preferably at least about 3.3 J/cm ³ -k, and most preferably at least about 3.5 J/cm ³ -k.

Because specific heat is measured orx a per unit mass basis, and because the volume of the heat sink may be relatively small and fixed, it may be advantageous in some embodiments for the second material t» also have a relatively high density. The product of the selected material's density and specific heat quantifies the amount of heat that the second layer or region can absorb. According to one such embodiment, the product of the density of the second material and the second specific heat is greater than the product of the density of the first material and the first specific heat. Table I below provides the densities, specific heats, thermal conductivities, and the heat densities (i.e., the products of density and specific heat) for some exemplary materials.

Table I — Properties of Various IVIaterials

Varies based on structure Varies based on method of manufacture Varies based on temperature and pressure varies based on structure

The inclusion of a plurality of layers or regions, with each layer or region selected so as to have desired properties with respect to thermal conductivity and specific heat allows the heat sink to more effectively dra_w away, dissipate, and absorb excess heat. First layer or region 152 acts to quickly and effectively draw excess heat away from LED light source 120. Second layer or region 154 acts to efficiently absorb and maintain the excess heat away from the LEE>. In addition, because second layer or region 154 comprises a core, the first layer o»τ region 152 may also act to further dissipate excess heat into the air so as to furtlxer cool the LED light source 120.

Figure 5A illustrates an alternative embodiment of a heat sink 250 that includes a first layer or region 252 and a second layer or region 254. According to one such embodiment, first layer or region 252 is formed of a first material (e.g., copper or aluminum) having a first thermal conductivity greater than the thermal conductivity of the second material of second layer or region 254, while second layer

or region 254 is formed of a second material having a second specific heat greater than the specific heat of the first material.

Figure 5B illustrates another alternative embodiment of a heat sink 350 that includes a first layer or region 352 formed of a first rαaterial (e.g., diamond, graphite, or carbon fiber) having a first thermal conductivity artd a first specific heat, a second layer or region 353 formed of a second material (e.g., copper) having a second thermal conductivity and a second specific heat, and a third layer or region comprising a core 354 formed of a third material (e.g., water) having a third thermal conductivity and a third specific heat.

According to one such embodiment, the thermal conductivity of the first material is greater than the thermal conductivity of tlαe second material, the thermal conductivity of the second material is greater than the thermal conductivity of the third material, and the specific heat of the third material is greater than the specific heat of the first material.

The first layer or region 352 is located adjacent to the light source 320, and may be relatively thin. The first layer or region 352 comprising a first material may have a thermal conductivity that is very high. For example, the thermal conductivity of the first material may be greater than the thermal conductivity of both the second and third materials. Such an embodiment may draw hieat away from light source 320 very quickly. Second layer or region 353 is formed of a second material having a thermal conductivity higher than the thermal conductivity of the third material, which effectively draws heat away from first layer or region 352. The core 354 is formed of a third material having a specific heat higher mart the specific heat of the first material. As such, core 354 is able to absorb heat that has been drawn away from light source 320 by first and second layers or regions 552 and 353, respectively. The relative thickness of each layer or region can be selected as desired. For example, according to one embodiment, the third layer or region comprising a third material having a relatively high specific heat (as compared to the other layers or regions) may comprise a relatively thick core, while the first and second layers or regions comprising materials with relatively high thermal conductivities (as compared to the other layers or regions) may be relatively thin.

According to one embodiment, the heat sink may have a diameter of about

3/8". By way of example, according to one embodiment such as that illustrated in Figure 5B, first layer 352 may be formed of diamond and have a thickness of about .1 inch or less, core 354 may occupy about half o>f the volume of heat sink 350, with second layer or region 353 occupying the remaining volume. As illustrated in the cross sectional view of Figure 4, there may be an insulating layer 170 between the heat sink 1 50 and the elongate housing 102. According to one embodiment, the insulating layer 170 may be an air gap, although it could alternatively be filled with any known heat-insulating material (e.g., insulating ceramics or polymers). Providing an insulating layer 170 surrounding the heat sink 150 reduces the amount of heat that would otherwise be dissipated out of the distal end of the curing light 100. Reducing dissipation of heat at the distal end 106 of the curing light 100, which is nearest the patient's teeth, mouth, and other sensitive tissue, may result in a more comfortable operation.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. What is claimed is: