WO2008152384A1 - Novel dental prosthesis and cariostatic method - Google Patents

Abstract

A dental prosthetic having a physiologically acceptable base material and a surface deposit of antibacterial agent. The prosthetic may be a cap or crown, or orthodontic bracket. The antibacterial agent may be bacteriostatic or bactericidal in effect. The invention provides a novel approach to the problem of tooth decay, utilising an accepted mechanical base prosthetic combined with a novel intervention in the tooth environment which is intended to inhibit and arrest decay.

Description

Novel Dental Prosthesis and Cariostatic Method

This invention relates to the field of dentistry and offers particular benefits in paediatric dentistry. In particular it provides a novel approach to the problem of tooth decay, utilising an accepted mechanical solution combined with a novel intervention in the tooth environment which is intended to inhibit and arrest decay.

Background of the invention

Figures 1 and 2 present some background information on tooth structure and growth. Fig. 1 is a diagram of a tooth 1 comprising the crown 3 which sits above the gum and the root 5 which sits below the gum. The crown comprises a biting surface 7 and a side surface 9 which descends towards the gum 19 at interface area 11. The crown' s outer surface is made from enamel 13 inside which there is dentine 15 and pulp 17. The root 5 extends into bone 23 and comprises cementum 21, a number of blood vessels 25 and a nerve 27. Points 7, 9 and 11 are possible points of attach for cariogentc bacteria Fig.2 shows the emergence of deciduous teeth. The eruption periods (months) and shedding periods (years) for the teeth are as follows.

Upper teeth The central incisors 29 erupt at between 8-12 months and shed at between 6-7 years. The lateral incisors 31 erupt at between 9-13 months and shed at between 7-8 years. The canine teeth 33 erupt at between 16-22 months and shed at between 10-12 years. The first molars 35 erupt at between 8-12 months and shed at between 9-11 years. The second molars 37 erupt at between 25-33 months and shed at between 10-12 years.

Lower Teeth The central incisors 47 erupt at between 6-10 months and shed at between 6-7 years. The lateral incisors 45 erupt at between 9-13 months and shed at between 7-8 years. The canine teeth 43 erupt at between 17-23 months and shed at between 9-12 years. The first molars 41 erupt at between 14-18 months and shed at between 9-11 years. The second molars 39 erupt at between 23-31 months and shed at between 10-12 years.

Caries is the most widely recognised problem leading to progressive loss of teeth. The condition is initiated by the presence in the oral cavity of certain strains of bacteria, such as Streptococcus mutans, and Lactobacilli, which metabolise carbohydrates in the host's diet to release acids which in turn attack the teeth causing decay. Lactic acid for example is known to lead to demineralisation of the tooth, leaving a weak organic structure which readily cavitates and disintegrates. The bacteria only have access to the exposed surfaces of the tooth so that decay occurs first above the gum line at specific points, generally at contact points between adjacent teeth, but through cavity formation, decay can rapidly progress inwards down to the root. The decay can become aggravated if gingival recession is present as a complication. The currently favoured techniques considered by studies in cariology dictate a combination of removal of decayed material from the tooth by drilling and/or scraping, application of a restorative material (filling), and encouraging the patient to adopt a more rigorous oral hygiene regime. The treatment may involve a variety of reconstructive techniques involving fillings for cavities, resins to seal fissures, crowns or caps for more severe loss of tooth structure, and partial or total prosthetics in the last instance.

Typical filling materials comprise resins, porcelain, dental amalgam or gold. A crown may also be made from gold, gold alloy, palladium, nickel alloy, or chromium alloy, or porcelain, or porcelain fused to a metal (PFM) , usually an alloy of gold or another precious (noble) metal. A modern PFM may comprise a fluorapatite-leucite glass-ceramic material fused to an alloy core. In some severe cases, where pulpal necrosis has occurred, it is necessary to carry out root canal therapy before the restorative work can begin.

Recommended oral hygiene regimes and therapeutic interventions frequently involve use of chemicals which are intended to have an inhibitory or prophylactic effect. Thus fluoride therapy is widely practised in Western societies by inclusion of fluoride in toothpastes, oral hygiene rinses and dental preparations, and even by pre-treatment of the public drinking water supply. Fluoride has a valuable benefit for the infant whose teeth are in development due to promotion of the formation of fluoroapatite in the mineral structure of the teeth. The process of decay can begin as soon as a tooth emerges from the gum. This means that the infant can suffer decay if its diet is sufficiently rich in carbohydrates. Sweet sugary drinks often given to young children by ill- informed parents or carers, are widely recognised by practitioners as key promoters for paediatric dental disease.

It has been observed that the first permanent molar, which erupts behind the last baby molar is particularly vulnerable, being 10 times more likely to suffer decay than any other permanent tooth in children. When this tooth develops decay, it occurs either on the surface of the tooth (occlusal decay) or it is just below the contact point between that tooth and the baby tooth in front (proximal decay) . Around 50% of decay occurs below the contact point .

The fact that an infant's teeth are subject to decay, increases the likelihood that its emerging "adult" teeth will also begin to decay. Each decaying tooth facilitates proximal decay of its neighbour. Initially, the decay may be observed at the contact point between teeth, but it may also occur at the base of a damaged tooth e.g. at a fissure. Thus the primary deciduous teeth if subject to decay, will in turn initiate the process of decay in the emerging permanent teeth, and the teeth which are contiguous to a decaying tooth are vulnerable to attack. A continuing degenerative process begun in infancy can only be interrupted by improved oral hygiene and interventions to remove or stop decayed teeth. An object of the present invention is to provide a new approach to therapeutic and prophylactic interventions in dental care.

Summary of the Invention

According to the present invention there is provided a dental prosthetic comprising a physiologically acceptable base material and a surface deposit of an antibacterial agent.

The prosthetic may comprise a cap or crown, or orthodontic bracket. The base material is preferably of a pliable material to permit conformity when positioned upon a tooth. The antibacterial agent may be bacteriostatic or bactericidal in effect. The antibacterial agent may be a metallic deposit. The metallic deposit may be positioned at discrete locations e.g. just below the contact point or applied as a barrier layer in a target region intended specifically to address proximal decay. The metallic deposit may be applied as a dot at a selected position, for example at the contact point between neighbouring teeth, or in the proximal area to an emerging tooth.

The metallic deposit is conveniently applied by electro- deposition or electroplating but other methods such as chemical vapour deposition, or "dot-printing" or another spot contact deposition process may be used. Typically a suitable deposit zone will be of the order of 2mm by 2mm. Preferably, the metallic deposit is a physiologically tolerable transition metal such as copper or zinc, or an alloy containing at least 75% of such a metal.

Use of another metal having bactericidal properties, such as silver, is not excluded. However, noble metals even though they are well tolerated by the human body, have a cost disadvantage. Therefore, a preferred metallic deposit is copper metal, i.e. not a salt or alloy thereof, but that which would typically be available as "pure" copper on the market. Considering the current high demand for "pure" copper in the electronics industry, copper of up to 99.9999% purity is already available on the market, so that copper of satisfactory purity for the present purpose will be readily available too.

Whereas copper has been considered as a component of palladium alloys for dental reconstruction, there is a known problem with copper in that copper can cause porcelain of the PFM to discolour. Previously copper phosphate has been used in dental cements and a cariostatic effect has been observed on carious dentine in vivo, (Foley J, Blackwell A, Caries Research 2003; 37: 254-260) . That study reported that the use of the dental cement to isolate and seal the carious process together with the cariostatic properties of metal ions therein gave reductions in observed microorganisms. The importance of obtaining complete seals is emphasised to avoid caries activity continuing.

Surprisingly, it has been found that rather than relying upon cements or other carriers to deliver metal ions to the carious teeth, positioning of metal at a selected site offers both prophylactic and cariostatic effects. This offers remarkable benefits in arresting progress of caries from primary teeth to emerging teeth and generally in prophylaxis with regard to caries.

Accordingly, the invention also offers the opportunity to provide preventative measures whereby an intervention in infancy with regard to primary teeth can preserve the growing child' s opportunity to retain a full set of adult teeth.

Therefore, according to another aspect of the invention, there is provided a method of inhibiting or arresting carious decay of teeth comprising the step of applying a surface deposit of an antibacterial agent to a selected position on a tooth. Preferably the antibacterial agent is a durable material having an effective period spanning at least several months.

The most convenient way of introducing the surface deposit of antibacterial agent is by way of a cap or crown, or orthodontic bracket formed from any suitable base material or typical dental reconstructive substrate, the said cap or crown or orthodontic bracket having the applied surface deposit at a selected point or region. Typically the deposit region will be of the order of 2mm by 2mm. The base material is preferably of a pliable material to allow for pressure e.g. by biting, to enhance conformity with the treated tooth.

The antibacterial agent may be bacteriostatic or bactericidal in effect. The antibacterial agent may be a metallic deposit. The metallic deposit may be positioned at discrete locations e.g. just below the contact point or applied as a barrier layer in a target region intended specifically to address decay. The metallic deposit may be applied as a dot at a selected position, for example at the contact point between neighbouring teeth, or in the proximal area to an emerging tooth, or around an orthodontic bracket.

The metallic deposit is conveniently applied by electro- deposition or electroplating but other methods such as chemical vapour deposition, or "dot-printing" or another spot contact deposition process may be used. Preferably, the metallic deposit is a physiologically tolerable transition metal such as copper or zinc, or an alloy containing at least 75% of such a metal. In the simplest and most patient-acceptable use of the novel crown provided in accordance with this invention, the crown is applied over a carious tooth with minimal surface preparation and caries removal and the patient is invited to bite down upon the crown to press it home to a tooth conforming position. This follows a procedure referred to in the literature as the "Hall Technique" after the Scottish practitioner (Dr Norma Hall) who pioneered the technique which is beneficial for children since it minimises potentially frightening work preparatory to reconstructive work. Whilst it is not suitable for all cases, it is quicker and less traumatic for the child patient.

In essence the technique provides a preformed metal crown (PMC) , which is positioned without anaesthetic and neither caries removal, nor tooth preparation. The PMC is prefilled with a suitable glass ionomer cement, seated upon the tooth, and pressed home by finger pressure or by the child patient's own occlusal force. The capped tooth isolates the carious decayed part from the oral environment from which the caries-causing bacteria derive nutrition, thereby arresting the decay process, and permitting the tooth to survive longer and in some cases regenerate to a condition that precedes the condition on the day of treatment. The Hall Technique has been reviewed by Innes N. P. T. et al in British Dental Journal 2006; Vol. 200, Issue No. 8, pp 455-459, 22 April 2006, "A novel technique using preformed metal crowns for managing carious primary molars in general practice — A retrospective analysis"; http: //www. nature.com/bdj/journal/v200/n8/index. html .

Description of the Drawings The invention will now be described by way of illustration by reference to the accompanying drawings in which:

Fig. 1 is a section through an adult molar tooth illustrating points of possible attack by cariogenic bacteria;

Fig. 2 is a schematic plan view representing the emergence of deciduous teeth

Fig. 3 is a side view of a deciduous tooth with an emerging adult tooth;

Fig. 4 is a side view of a deciduous tooth bearing a pliable crown of the invention with antibacterial deposit shown in a proximal location; Fig. 5 is a perspective view of a pliable crown of the invention with a metallic deposit positioned below the predicted contact point; and

Fig.6 is a perspective view of an orthodontic bracket attached to a tooth surface.

Description of Embodiments and Modes for Performance

A juvenile patient presenting with evidence of dental caries in early stages is assessed as suitable for receiving a dental reconstruction for a deciduous molar. A pliable crown is designed and adapted for arresting decay due to cariogenic bacteria by depositing an amount of copper metal upon a region of around 2mm by 2mm on a side surface of the crown predicted to coincide when fitted with the proximal surface of an emerging adult tooth.

Referring to Figs. 3 to 5, Fig.3 shows a deciduous tooth 49 beside an emerging adult tooth 51. Figs 4 and 5 show a dental prosthetic crown 53 which in this embodiment is formed from a nickel-chromium base material 54 and which is susceptible to deformation by occlusion when in situ, allowing the crown to conform to the tooth being capped. The crown 53 is sized to closely fit over the tooth. An antibacterial metallic deposit 55, in this case copper, is selectively electro-deposited upon the base material at a discrete zone intended to confront an emergent tooth in proximity to the deciduous molar being capped. In use of the crown 53 of this embodiment, a suitable dental cement, e.g. a glass-ionomer resin based cement, is carefully filled into the recess within the crown 53, taking care to avoid entrapping air bubbles. The tooth 49 may be dried, if possible, just before placing the crown upon the tooth. Care should be taken to correctly orient 53 the crown so that the antibacterial deposit is presented in the appropriate position. A slight finger pressure may be applied, and excess cement wiped off before the patient tastes it. The patient is then invited to bite down upon the crown. This step may cause further cement to exude, and so it may be necessary to remove further cement. The opportunity may be taken to make sure that the crown has not been displaced before encouraging the patient to continue to bite upon the crown for an acceptable period. Usually 2 to 3 minutes should be sufficient.

In alternative embodiments, the antibacterial deposit may be another metal such as zinc, and the base material may be dental stone or another conventional accepted restoration material, or orthodontic bracket, to which an antibacterial deposit may be affixed.

Dental braces (also known as orthodontic braces) are used in orthodontics to correct alignment of teeth and their position with regard to a person's bite. The brace typically comprises a number of orthodontic brackets which are typically glued onto the teeth of the patient, an arch wire which is attached to the brackets to realign the teeth and a band which can be placed upon the teeth to hold on part of the braces. There are many types of braces, the brackets for which can be made from materials such as stainless steel, other metals, metal alloys and ceramics.

One problem associated with the fixing of brackets and other materials such as bands onto a tooth is that bacteria can build up at or near the edge of the bracket over the weeks and months that the bracket is in place and can cause discolouration of the tooth. In addition, the discolouration is especially prominent because the area of the tooth that is underneath the bracket has not been subject to the bacteria and is significantly cleaner. In some cases, the bacteria can cause permanent discolouration of the tooth.

Fig. 6 shows a further embodiment of the present invention when applied to orthodontic brackets in which a bracket 61 is glued to the surface of a tooth 59. The surface of the bracket forms the base material which is coated with an antibacterial metallic deposit. In this example, the metallic deposit is silver because it is less subject to obvious discolouration and in many cases, is the same or similar in appearance to the other parts of the brace.

In this embodiment, the present invention is used to prevent blemishes from developing on the surface of teeth where contact is made between the bracket and the tooth enamel.

The metallic deposit is electro-deposited upon the base material at positions at or near those where bacterial build up is likely to occur. In this embodiment of the present invention, the metallic deposit forms a coating across the entire surface of the brace. In another embodiment of the present invention, the antibacterial agent is present on preselected areas of the bracket. The antibacterial agent can be added onto any part of the base material which allows it to function effectively as an antibacterial agent.

The antibacterial agent is conveniently applied by electro-deposition or electroplating but other methods such as chemical vapour deposition, or "dot-printing" or another spot contact deposition process may be used. Printing or otherwise fixing the metallic deposit to the bracket surface is particularly effective when the bracket is made from a ceramic material.

Industrial Applicability

The invention finds utility in the field of dental practice generally, but especially in paediatric dentistry for therapeutic and prophylactic purposes.

Improvements and modifications may be incorporated herein without deviating from the scope of the invention.

Claims

1. A dental prosthetic comprising a physiologically acceptable base material and a surface deposit of an antibacterial agent.

2. A dental prosthetic as claimed in claim 1 comprising a cap or crown, or orthodontic bracket.

3. A dental prosthetic as claimed in claim 1 or claim 2 wherein the base material is pliable to permit conformity when positioned upon a tooth.

4. A dental prosthetic as claimed in any preceding claim wherein the antibacterial agent is bacteriostatic in effect.

5. A dental prosthetic as claimed in any preceding claim wherein the antibacterial agent is bactericidal in effect.

6. A dental prosthetic as claimed in claim 5 wherein the antibacterial agent is a metallic deposit.

7. A dental prosthetic as claimed in claim 6 wherein the metallic deposit is positioned at one or more discrete location on the base material.

8. A dental prosthetic as claimed in claim 7 wherein the antibacterial agent is positioned at or near the contact point or applied as a barrier layer in a target region intended specifically to address proximal decay.

9. A dental prosthetic as claimed in claims 6 to 8 wherein the metallic deposit is applied as a dot at a selected position on the base material.

10. A dental prosthetic as claimed in claims 6 to 9 wherein the metallic deposit is applied by electro- deposition or electroplating.

11. A dental prosthetic as claimed in claims 6 to 9 wherein the metallic deposit is applied by chemical vapour deposition, or "dot-printing".

12. A dental prosthetic as claimed in claims 6 to 11 wherein the metallic deposit is a physiologically tolerable transition metal.

13. A dental prosthetic as claimed in claim 12 wherein the physiologically tolerable transition metal is copper or zinc or silver.

14. A dental prosthetic as claimed in claim 12 or claim 13 wherein the physiologically tolerable transition metal is an alloy containing at least 75% of such a metal.

15. A method of inhibiting or arresting carious decay of teeth comprising the step of applying a surface deposit of an antibacterial agent to a selected position on a tooth.

16. A method as claimed in claim 15 wherein the antibacterial agent is a durable material having an effective period spanning at least several months.

17. A method as claimed in claim 15 or claim 16 wherein the surface deposit of antibacterial agent is introduced by way of a cap or crown, or orthodontic bracket formed from a base material.

18. A method as claimed in claim 17 wherein, the surface deposit is applied at a selected point or region of said cap or crown or orthodontic bracket.

19. A method as claimed in claims 15 to 18 wherein, the antibacterial agent is bacteriostatic or bactericidal in effect.

20. A method as claimed in claims 15 to 19 wherein antibacterial agent is a metallic deposit.

21. A method as claimed in claim 20 wherein the metallic deposit is positioned at one or more discrete location on the base material.

22. A method as claimed in claims 15 to 21 wherein the antibacterial agent is positioned at or near the contact point or applied as a barrier layer in a target region intended specifically to address proximal decay.

23. A method as claimed in claims 20 or 21 wherein the metallic deposit is applied as a dot at a selected position on the base material.

24. A method as claimed in claims 20 to 23 wherein the metallic deposit is applied by electro-deposition or electroplating.

25. A method as claimed in claims 20 to 24 wherein the metallic deposit is applied by chemical vapour deposition, or "dot-printing".

26. A method as claimed in claims 20 to 25 wherein the metallic deposit is a physiologically tolerable transition metal.

27. A method as claimed in claim 26 wherein the physiologically tolerable transition metal is copper or zinc or silver.

28. A method as claimed in claim 26 or claim 27 wherein the physiologically tolerable transition metal is an alloy containing at least 75% of such a metal.

29. A method as claimed in claims 15 to 28 wherein the base material is of a pliable material to permit conformity when positioned upon a tooth.