METHOD OF DENTAL TISSUE INJECTION

USING AN ARRAY OF MICRO-NEEDLES

BACKGROUND OF THE INVENTION 1. The Field of the Invention The present invention relates to methods for injecting a local anesthetic into the body of a patient for local infiltration, particularly for injecting a local anesthetic into dental tissues, such as the gums and/or tough, dense ligamentary tissue surrounding a tooth or teeth prior to work by a dental practitioner (e.g., extraction of a tooth, cleaning of a root canal, or other oral procedure). 2. The Related Technology

Operative dentistry often requires local anesthesia prior to performing the procedure. More than half of the teeth in the oral cavity can be effectively anesthetized locally by infiltrating an anesthetic composition near the location of the tooth root apexes. Because of the pain associated with such procedures, it is desirable to first administer a topical anesthetic (e.g., benzocaine) adjacent the tooth followed by injection of a local anesthetic (e.g., lidocaine) using a needle. In recent years, it has been found that the smaller the diameter and sharper the diameter of the needle, the less painful is the resulting injection. Because of this, very small needles are sometimes used when administering a local anesthetic adjacent the base of a tooth prior to such work. Unfortunately, because of the very tough and dense nature of the ligamentary tissue into which the needle is pressed, small diameter needles will often bend when attempting to push the needle into the tissue. In addition, as small as these needles are, they are nevertheless still large enough to induce pain because of the rich supply of very sensitive nerves within the oral cavity. Although it might be thought that the use of even smaller needles might further reduce pain, the use of such needles is not practical because of their greater tendency to bend upon attempting to push them through tough, dense tissue.

In addition, it can be very difficult to maintain the needle at a constant depth while attempting to inject the local anesthetic, as very high fluid pressures must be applied manually by the practitioner in order to effectively inject the anesthetic into the dense, tough ligamentary tissue. For example, fluid pressures of hundreds of

pounds per square inch ("psi") may be required during injection, which can make it very difficult to hold the needle steady and avoid pushing the needle further into the tissue, risking contact or penetration into the periosteum or bone covering adjacent the tooth root, which is very sensitive. Additionally, existing lever-type injection syringes can be clumsy to align, and can easily cause rocking motions when delivering the anesthetic. Finally, they are relatively costly, particularly to clinicians practicing in third-world countries.

In addition, current methods of injecting local anesthetic adjacent a tooth are rather complicated and conventional nerve blocks are rather complicated, requiring a significant amount of education and practice to perform them correctly and effectively. Some practitioners, particularly in third world countries, simply do not learn the techniques, but rather will perform a root canal, extraction, or other operative dental work without any anesthesia, which is extremely painful from the perspective of the patient.

Therefore, what is needed is a method of injection that would minimize pain during penetration into the tissue at the base of the tooth, but which would also minimize any tendency of the needle to bend or buckle during insertion as a result of the dense and tough nature of the ligamentary tissue, or to drift or contact the bone tissue adjacent the tooth root. It would be a further advantage if such a method were greatly simplified as compared to traditional techniques so that practitioners could more easily utilize such a technique.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to methods for injecting a local anesthetic into the dental tissue, such as the gums and especially tough ligamentary tissue surrounding a tooth. According to one embodiment, the method involves puncturing a patient's gingival tissue adjacent a selected tooth with a plurality (e.g., an array) of micro-needles so that the micro-needles penetrate into ligamentary tissue adjacent the tooth. The number of micro needles can range from 2-100, 4-20 or 5-10. A local anesthetic (e.g., lidocaine) is then injected through the micro-needles so as to deliver the local anesthetic in a diffuse manner to tissue surrounding a single tooth or multiple teeth.

According to one embodiment, each micro-needle may advantageously be relatively short in length (e.g., less than about 10 mm, preferably less than about 3 mm, more preferably less than about 2 mm). Such a short length limits the depth of penetration of the micro-needles into the tissue. Because each micro-needle can be relatively short, and the maximum outside diameter of each micro-needle can be very small (e.g., between about 30 to 60 gauge, preferably between about 34 to 45 gauge), pain and discomfort to the patient is minimized during injection of the local anesthetic. Moreover, the success rate of providing anesthesia is greatly increased as the local anesthetic can be easily injected in a diffuse manner without special training.

The relatively short length of the micro-needles is also advantageous as it prevents individual micro-needles from bending or buckling tends to result when using significantly longer micro-needles, particularly those with very small diameters. Such an advantage is particularly pronounced when employing embodiments of micro-needles in which the micro-needle length is no more than about 3 mm, more preferably no more than about 2 mm. The use of a plurality of micro-needles provides for more diffuse injection over a wider area as compared to injection using a single needle. For example, when using a single needle, it may be necessary to perform multiple injections in a general area to be anesthetized. In contrast, a local anesthetic can be injected in one step using a plurality of spaced-apart (e.g., an array) of micro-needles that work together to provide local anesthesia over a relatively wide area. Also, the local anesthetic can be delivered at higher rates as compared to the use of a single small needle, as the use of multiple micro-needles can deliver the drug in parallel at multiple points underneath the tissue surface, thereby significantly increasing the rate of delivery.

According to one embodiment, the needles are provided on an injection tip of a syringe. The injection tip can be removably attached to the syringe, or it may be integrally formed as part of the syringe. Preferred injection tips preferably include a sufficient number of spaced-apart micro-needles (e.g., within an array) so as to provide a desired delivery rate and delivery density over the desired area.

Advantageously, the micro-needles may be formed of a ceramic material (e.g., an organically modified ceramic). Such materials provide the micro-needles with rigidity and strength, even under very small dimensional constraints (e.g., short length

and/or small diameter). Such rigidity and strength is particularly important when the micro-needles are pushed into the dense and tough ligamentary tissue surrounding a tooth to be anesthetized. For these reason, ceramic materials for the micro-needles are preferred, although micro-needles formed from other rigid materials, such as hardened stainless steel, are within the scope of the invention.

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 reference 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 IA is a perspective view of a syringe coupleable injection tip including a plurality of micro-needles for use in injecting a local anesthetic into ligamentary tissue;

Figure IB is a close up cross-sectional view of the distal portion of the injection tip of Figure IA;

Figure 2A is a perspective view of an exemplary individual micro-needle that may be included in micro-needle injection tips employed in methods of the present invention;

Figure 2B is a cross-sectional view of the exemplary micro-needle of Figure 2A;

Figure 2C is a perspective view of an alternative exemplary individual micro- needle that may be included in micro-needle injection tips employed in methods of the present invention;

Figure 2D is a cross-sectional view of the exemplary micro-needle of Figure 2C.

Figure 2E is a perspective view of another alternative exemplary individual micro-needle that may be included in micro-needle injection tips employed in methods of the present invention;

Figure 2F is a cross-sectional view of the exemplary micro-needle of Figure

2E;

Figure 3A illustrates a perspective view of the injection tip of Figure IA including a plurality of micro-needles positioned so as to inject a local anesthetic into the dense, tough ligamentary tissue adjacent a tooth to be anesthetized; and Figure 3B illustrates a partial cross-sectional view of Figure 3 A, showing penetration of the individual micro-needles of the injection tip through the gingival tissue and into the ligamentary tissue.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

The present invention is directed to methods for injecting a local anesthetic into soft dental tissue, such as the gums and/or ligamentary tissue surrounding a tooth.

According to one embodiment, the method involves puncturing a patient's gingival tissue adjacent a selected tooth with an injection tip that includes a plurality (e.g., an array) of micro-needles so that the micro-needles penetrate into ligamentary tissue adjacent the tooth. A local anesthetic is then injected through the micro-needles so as to deliver the local anesthetic into the ligamentary tissue surrounding the tooth.

Spacing and positioning of the micro-needles provides a desired diffuse distribution of the local anesthetic.

II. Exemplary Intraligamentarv Micro-Needle Array Injection Devices

Figures 1A-1B illustrate an exemplary syringe coupleable injection tip 100 including a micro-needle array 106 that may be employed with the present inventive methods. Injection tip 100 includes a hub 102 configured for coupling to a syringe or other fluid delivery device, a cannula 104, and an array 106 of micro-needles 108 at a distal end of device 100. Alternatively, injection tip 100 can be modified so as to be integrally joined to a syringe (not shown).

Each of micro-needles 108 is attached to a mounting pad 1 10 having an internal chamber 1 11 (Figure IB) so that fluid is able to flow through an internal chamber (now shown) in hub 102, through cannula 104, and into chamber 111 of mounting pad 110 for distribution to individual micro-needles 108. Chamber 111 is

in fluid communication with each micro-needle 108 so that fluid may be delivered in parallel through all micro-needles 108 and into the tissue simultaneously.

Hub 102 has two primary components, including body 112 and neck 114. Neck 114 is illustrated as being tapered, although it could alternatively be of constant outside diameter. Neck 114 is preferably narrower than body 112, as depicted. A tapered shoulder 116 may be included to provide a gradual rather than an abrupt, transition from body 112 to neck 114.

A nib 117 disposed at the distal end of neck 114 around a proximal end of cannula 104 assists in retaining cannula 104 within hub 102 and in providing a seal around cannula 104. Nib 117 may comprise an adhesive plug that has been cured after cannula 104 has been positioned within neck 114. Any suitable adhesive may be employed, such as commercially available epoxies intended for gluing stainless steel to plastics such as polypropylene. Alternatively, nib 117 may simply comprise a distal end of neck 114 (e.g., neck 114 may be molded around a proximal portion of cannula 104) and be formed of the same material as the remainder of neck 114. Hub 102 is preferably designed to be coupled to a syringe or other fluid delivery device for dispensing fluid through the plurality of micro-needles 108. Hub 102 further includes a male or female thread or groove coupling member 118 (e.g., a luer lock structure), which mates with another thread and groove structure to engage the syringe or similar device. Hub 102 preferably has a feature that provides a gripping surface to aid in coupling injection tip 100 on a syringe. The illustrated example includes wings 120 extending longitudinally from body 112, although ridges or another gripping structure may alternatively be used. In a further alternative, the hub may be an integral extension of a device such as a syringe, such that neither coupling structure 118 nor gripping structures need to be provided. Micro-needles 108 may be formed of any suitable rigid material, although ceramic (e.g., an organically modified ceramic) is preferred because of its high strength and rigidity, particularly when the micro-needles are formed so as to have very small dimensional characteristics. Exemplary organically modified ceramic materials are available from Fraunhofer-Gescllschaft, in Munich Germany. Details regarding such materials and methods of forming micro-needles therefrom are described in TWO PHOTON POLYMERIZATION OF POLYMER-CERAMIC

HYBRID MATERIALS FOR TRANSDERMAL DRUG DELIVERY, Int. J. Appl. Ceram. Technol., 4 [1] 22-29 (2007), which is incorporated herein by specific reference.

As disclosed in the foregoing article, ceramic micro-needles formed from organically modified ceramic materials were formed using a two photon polymerization (2PP) process involving both temporal and spatial overlap of photons to induce chemical reactions leading to photopolymerization and material hardening within well-defined highly localized volumes. The desired three-dimensional needle structures produced by polymerizing the material along a laser trace, which is moved in three dimensions using a galvano-scanner and a micropositioning system. The material outside the desired region does not participate in the reaction and can be washed away with an appropriate alcohol solution, e.g., to form a hole in the needle.

The micro-needles can alternatively be formed from other rigid materials, such are hardened metals or even extremely rigid plastics (e.g., when the micro needles are very short, such as having a length less than about 2 mm). According to one embodiment, the micro needles are formed in an additive way, such as by using a metal plating process.

High strength and rigidity are particularly advantageous when piercing through tough, dense ligamentary tissue. The required strength and rigidity can be provided by micro-needles formed from ceramic, even with very small outer diameters and very short lengths. Preferably, the micro-needles 108 each have a length between about 0.1 mm and about 10 mm, more preferably between about 0.2 mm and about 3 mm, and most preferably between about 0.5 mm and about 2 mm.

In addition, the outside diameter of each micro-needle is advantageously small so as to minimize pain upon penetration through sensitive oral tissue. For example, the outside diameter of each micro-needle is preferably between about 30 to 60 gauge, more preferably between about 34 to 45 gauge. Such small dimensions (i.e., both very short length and small maximum outside diameter) minimize pain to the patient during injection.

The number and arrangement of micro-needles can be selected so as to provide a desired injection area and pattern. According to one embodiment, the micro-needles are provided as a two-dimensional array. Alternatively, the micro-

needles can be provided in a staggered or even random configuration so as to provide a desired injection area and pattern. The number of micro-needles is preferably in a range of 2 to about 100 micro-needles, more preferably in a range of about 4 to about 20 micro-needles, and most preferably in a range of about 5 to about 10 microneedles. As illustrated, mounting pad 110 and micro-needles 108 can be mounted at an angle with respect to longitudinal axis A of hub 102 and cannula 104. Preferably, the angle α is in the range of about 15° to about 90°, more preferably, about 20° to about 70°, and most preferably, about 30° to about 60°. In the embodiment shown in Figure IB, the angle α is about 35°. An angle of about 45° may be optimal in some cases. An angle within the foregoing ranges, particularly the most preferred range, advantageously enables a practitioner to maneuver the tip without interference from adjacent structures near the injection area (e.g., the particular tooth to be anesthetized and/or adjacent teeth). For example, as shown in Figures 3A-3B, injection tip 100 can be moved comfortably and easily into position adjacent tooth 90 without any contact with tooth 90, the teeth of the opposite jaw by the practitioner's hand, an attached syringe, or coupled injection tip 100.

Although the angle is illustrated as being imparted by the mounting configuration between cannula 104 and mounting pad 110, other configurations are possible for imparting the desired angle. For example, neck 1 14 and/or cannula 104 may be angled (i.e., one or both may include a bend) rather than straight so as to impart the desired angle in addition to or in lieu of any angle provided at the mounting point between cannula 104 and pad 110.

Although illustrated with a particular mounting pad configuration (e.g., rectangular), other configurations may be possible. For example, mounting pad and the arrangement of individual micro-needles 108 thereon may be round, square, oval, or any other desired shape. The exact number of micro-needles within the injection tip may depend on the density with which they are mounted in a given mounting pad area, and micro-needle lumen diameter (e.g., the use of needles with smaller diameters generally requires more micro-needles to achieve the same overall drug delivery rates).

Figures 2A-2F illustrate various exemplary configurations of micro-needles that may be included within an injection tip (e.g., array 106). The injection tip may include micro-needles of identical design, or alternatively, differing designs may be included within a single injection tip. Figures 2A and 2B illustrate a perspective view and cross-sectional view, respectively, of an exemplary micro-needle 108. Micro- needle 108 may advantageously be formed of ceramic, and includes a body 122 which is continuously and smoothly tapered from a location near base 124 to tip 126. Micro-needle 108 includes a centrally disposed lumen 128 (Figure 2B) that terminates at tip 126 as opening 130 (Figure 2A), as well as a chamber 130 interior to base 124 in fluid communication with lumen 128. The dimensional characteristics of micro- needle 108 can be very small. For example, its length may be about 0.8 mm and the maximum outside diameter at base 124 may be about 0.25 mm.

Figures 2C-2D illustrate a micro-needle 108' having an alternative configuration. Micro-needle 108' includes a body 122', base 124', tip 126', lumen 128' and chamber 130'. The principal difference between micro-needle 108' and micro- needle 108 of Figures 2A-2B is the configuration of tip 126' and lumen 128'. Lumen 128' is slightly offset from a central longitudinal axis of body 122', resulting in a tip 126' having a hole 130' with a teardrop or somewhat beveled configuration where lumen 128' exits tip 126'.

Figures 2E-2F illustrate a micro-needle 108" having another alternative configuration. Micro-needle 108" includes a body 122", base 124", tip 126", lumen 128" and chamber 130". The principal difference between micro-needle 108" and micro-needle 108' of Figures 2A-2B is the larger degree of offset of lumen 128" relative to a central longitudinal axis of body 122", resulting in a tip 126" having a hold 130" the appearance of a teardrop, but opens through a side, rather than the end, of tip 126'. In addition, both tips 126' and 126" may exhibit increased sharpness relative to tip 126, because of the offset structural relationship of the exit holes 130' and 130" relative to tips 126' and 126", respectively. Such configurations may be preferred as they decrease the force required to pierce and penetrate the patient's gingival and ligamentary tissue during use. Figures 3 A and 3B illustrate an inventive method in which an injection tip 100 including an array 106 of micro-needles 108 (Figure 3B) is positioned adjacent the

base of tooth 90 for injecting a composition, such as a local anesthetic. Examples of useful local anesthetics that can be used in connection with the micro-needles according to the invention include, but are not limited to, lidocaine, tetracaine, benzocaine, chloroprocaine, cocaine, cyclomethycine, demethocaine, propoxycaine, procaine, proparacaine, articaine, bupivacaine, carticaine, cinchocaine, etidocaine, levobupivacaine, mepivacaine, and piperocaine.

By simply pressing the pad 110 against gingival tissue 150, micro-needles 108 penetrate through gingival tissue 150 and down into ligamentary tissue 152, which is dense and relatively tough. Use of such a plurality of micro-needles 108, particularly in which the micro-needles are relatively short and of small maximum diameter, minimizes pain experienced by the patient. The use of relatively short micro-needles (particularly within the more preferred length ranges) is advantageous as this helps the micro-needles to resist the tendency to bend, buckle, or break, particularly when they micro-needles are formed of a ceramic material. Mounting pad 110 further acts as a stop member so that the injection tip penetrates just through the gingival tissue 150 and into the ligamentary tissue 152 and not beyond. This further minimizes pain and provides a correct depth of needle penetration and injection of liquid (e.g., local anesthetic).

As shown, the very short micro-needles 108 and the presence of mounting pad 110 (which acts as a stop) aids a practitioner in easily injecting a local anesthetic into the ligamentary tissue 152 adjacent gum tissue 150. Such a technique can be easily learned and practiced while minimizing the risk of damage to adjacent tooth structures. The relative short length of micro-needles 108 prevents excessive penetration of the needles, so as to prevent entry into bone tissue 156, the ligamentary tissue nearest tooth 90, the cementum 154, or the root of tooth 90. Excessive penetration (e.g., into cementum 154 or root of tooth 90) of needles can result in unnecessary damage to the tooth and also severe pain to the patient.

In addition, use of a plurality (e.g., an array) of micro-needles provides for more diffuse injection over a much larger area than can be accomplished using a single needle. For example, when using a single needle, it may be necessary to perform multiple injections in a general area to be anesthetized. The use of a plurality of micro-needles in the inventive method requires only a single injection at a central

location to provide local anesthesia over a wide area. Also, local anesthetic can be delivered at higher rates as compared to methods employing a single small needle, as the injection tip includes multiple spaced-apart micro-needles that deliver the drug in parallel, significantly increasing the rate of delivery. This can further decrease pain and discomfort to the patient. 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: