FR2848409A1 - Metal device or implant used in dento-facial orthopedics or stomatology is made from stainless steel with coating of black rhodium under precious metal layer - Google Patents

Abstract

Device or implant, e.g. a bracket, ring, tube or hook used e.g. to straighten a patient's teeth, is made from stainless steel coated with an intermediate layer of black rhodium (derived from rhodium containing a hydride and an oxide) and a covering layer of palladium, platinum or rhodium. The covering layer can be made, for example, from an alloy of precious metals of the platinum family, and a semi-precious metal such as nickel at a rate of below 5 per cent, or cobalt at under 10 per cent. In variants the basic metal can be of titanium and the black rhodium replaced by ruthenium.

Description

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  The present invention relates to metallic medical devices used in orthodontics and stomatology for straightening teeth. These devices consist of a base metal, an intermediate layer and an upper layer composed of metals increasing the performance of the medical device (biocompatibility, corrosion resistance, hardness, etc.). The intermediate layer consists black rhodium. The black rhodium acts as a wear indicator due to its color.

  State of the art The metallic devices used in dento-facial orthopedics are numerous and various: brackets, rings, arches, tubes, lingual buttons, restraints, quad helix, circuit breakers, springs, lip bumpers, hooks ...

  These devices can include one or more articulated or welded elements. The metals used are stainless steel or titanium. The solders and alloys are composed of precious or semi precious metals: gold, silver, 15 nickel, tin ...

  They are in direct contact with saliva except for the parts stuck to the teeth. According to Directive 93/42 / EEC which classifies medical devices, use is long term, implantation being more than a month. Some devices, such as brackets and rings can remain in the patient's mouth for more than two years.

  Studies carried out on brackets deposited at the end of treatment have shown that corrosion is very low on certain steels such as 316 L stainless steel but stronger on others. Likewise, if the gold solders resist very well, there are others more susceptible to corrosion.

  Corrosion of orthodontic devices has several harmful effects: -the release of non-toxic ions taking into account the concentration but allergens for certain patients. Allergic reactions are manifested by inflammation of the oral tissue or by distant reactions from other parts of the body. They generally require the cessation of treatment and therefore the impossibility of treating the patient. The increasing allergic risk is difficult to predict, which places the practitioner in a certain insecurity at the start of the treatment.

  -the modification of the dimensional tolerances, such as the widening of the groove of the brackets which receives the arch. A prolongation of the treatment or a relative ineffectiveness of the latter results.

  -the risk of breakage of the parts which can have consequences in the event of ingestion of a pointed element (hook, wire ...).

  To reduce the above risks, several solutions have been considered and implemented to date.

  -In 1995/1999, the brackets manufacturers coated the brackets for allergic patients with gold. Gold constitutes an excellent corrosion barrier but it has the defect of having a very low hardness (50 HV) or rapid wear of certain parts of the devices. By way of example, the total disappearance of the gold on the external face of the studs of the brackets at the end of treatment is noted. In 1999/2001, several coating processes were implemented using metals from the platinum mine.

  The company Wonder Wire proposed to coat the arches and brackets with precious metals from the platinum mine (platinum, palladium, rhodium) or tin / nickel alloy or palladium / nickel. (US Patent 5,882,193 of March 16, 1999). The precious metal or alloy is deposited directly on the base metal. The company currently offers the coating of brackets in pure rhodium. It is very expensive but it is possible to place a thin layer of 0.5 p. because of the hardness which is 16 times that of gold (800 HV). Rhodium is much more resistant to corrosion than palladium but its risk of porosity is also higher and in this case, if the deposition is carried out directly on the substrate, galvanic corrosion can be installed.

  The company Ortho Service proposed a process which consisted in coating the brackets with precious metals and then in replacing the metal layer after using the bracket so that the base metal was never attacked. The coating chosen is that used by jewelers to avoid the risk of allergy to nickel, it consists of palladium / nickel 95/5 (95% Palladium, 5% nickel) deposited on Wood nickel or pre-gilding. This coating passes nickel allergy tests while being 10 times harder than gold (500 HV against 250 HV). After each use, the coating is removed at the same time as the composites by the action of a laser beam of high intensity but very short action time (French patent n099 / 11780). This process allows the brackets to be recycled without increasing the risk of rupture by corrosion of the welds.

  The company LMI has proposed coating the orthodontic devices with a layer of pure Palladium or pure rhodium on a layer of gold (French patent n099 / 11837). Pure Palladium has a lower allergic risk than palladium alloyed with nickel. Its hardness is 5 times higher than that of pure gold.

  Therefore it is theoretically possible to replace the 8Ft gold used by the first processes by 2 p. of pure palladium. In practice, it must be taken into account that the corrosion resistance of Palladium to acids present in the mouth is lower than that of gold. The use of rhodium on gold makes it possible to reconcile great hardness and the absence of risk of corrosion in the event of porosity of the rhodium, gold playing the role of a barrier.

  A patent has been filed for the deposition of titanium nitride on orthodontic brackets 40. Titanium nitride is very resistant to corrosion, but its very gray appearance is a drawback which explains why brackets made entirely of titanium have experienced very little diffusion among practitioners.

  To date, no platinum deposit has been proposed because of the higher cost linked to the weight of this metal.

  The colors of the platinum-mine metals are so close to stainless steel that it is impossible for the practitioner to distinguish them. This advantage over gold rejected for its "flashy" aspect poses a major problem when it comes to claiming the absence of allergic risk throughout the treatment.

  Even if the manufacturer performs clinical checks on many patients, there is nothing to confirm with a 100% guarantee that the coating will last the entire treatment for the following reasons: -the duration of the treatment is not known: a orthodontic device can stay in the mouth between one day and three years. Some patients have very aggressive saliva or more or less favorable habits (use of a hard or flexible toothbrush, choice of food or drink).

  -for reasons of cost, and compliance with tolerances, the layer of precious metals is calculated as accurately as possible, which increases the risk that it is not sufficient. -Even if precious metals or titanium nitride are deposited as part of an ISO certified process with rigorous quality control, some parts may not be sufficiently coated in certain places: the deposits are not always homogeneous in thickness especially if the pieces are sharp.

  if the practitioner recycles his brackets the duration of stay of the bracket in the mouth is lengthened without checking that the residual thickness makes it possible to maintain the properties of the bracket during the second stay in the mouth.

  It is therefore desirable that the practitioner can check that the parts are always coated with precious metals during patient control visits to ensure that the claim for protection of the base metal against corrosion and the mechanical properties of the maintenance are maintained. coating if claimed (eg hardness of rhodium to promote sliding of the arc).

  Description of the invention The present invention consists in creating from orthodontic devices of stainless steel new devices coated with at least two layers of precious metals such that a layer situated between the base metal and the upper layer is composed of black rhodium (finely divided metal containing an oxide and a hydride) or ruthenium.

  The advantage of these two metals is very high hardness (> 600 HV), excellent resistance to corrosion by acids and a very different color from the final layer. The price of ruthenium is lower than the price of black rhodium but the lack of use in the medical field requires expensive clinical trials before its use. It is also known that ruthenium oxides are highly toxic. The electrolytic deposition of ruthenium and black rhodium are very close and well known to professionals.

  The following deposit procedure is given as an example. Variations are possible depending on the composition of the baths. The black rhodium, used in an acid bath can be deposited directly on the base metal according to the processes usually used in electroplating. The upper layer deposited on black rhodium may be composed of an alloy comprising metals traditionally used in the dental field such as nickel (in proportion less than 5%), cobalt in proportion less than 10%, palladium and rhodium. Given the desired properties which are both the formation of a corrosion barrier and the increase in hardness compared to that of stainless steel, the use of an alloy of palla15 dium / nickel 95 / 5, palladium-cobalt 90/10 or 80/20 or palladium / rhodium 95/5 seems to us the most suitable. Likewise, the intermediate layer may consist of black Rhodium deposited on pre-gilding or Wood nickel, these latter two metals not involved in the functionality of the intermediate layer but being only intended to promote its deposition on the substrate and in the case of pre-gilding to constitute an anticorrosion barrier.

  The electrolytic treatment can be carried out as follows from a part comprising possibly welded, polished and deburred steels:-degreasing in an ultrasonic bath in a 50% caustic soda solution heated to 60C for 10 min, rinsing in a bath dead and under running water.

  - soaking the parts in a 5% sulfuric acid bath for 5 minutes.

  -electroplating in a black rhodium bath at 2 g / liter heated to 25 0C with an intensity of 1 A / dm2, rinsing in demineralized bath.

  -electrolytic deposit in a 95/5 palladium-nickel bath with Og / liter chaf30 fé at 30'C with an intensity of 1 A / dm2, rinsing and drying.

  The exposure times determine the thickness of the coatings.

  It is essential to carry out thickness measurements of the deposited layers (X-ray fluorescence) and resistance and porosity tests. The absence of porosity is essential and delicate to obtain with black Rhodium.

  It is possible to deposit the abovementioned coatings on a titanium substrate using an oxalic acid attack in place of sulfuric acid.

  The medical device thus treated can be placed directly in the mouth under the same conditions as an untreated device. On occasion, usual visual visual checks 40 of the device, the practitioner ensures that the protection of the device is ensured by the absence of black spots. If black rhodium appears, the device can be removed. It is important to note that at this stage, protection remains assured. The thickness of black Rhodium must be sufficient so that it cannot be used between two visits to the practitioner. The thicknesses of the wear layers and the intermediate layer are to be determined by the manufacturer according to the use specified by each medical device. The devices thus treated are classified for single use. If reused, the intermediate layer appears and the device must be removed. The manufacturer 1o therefore has better control over the use of the medical device. It can define, within the framework of the certification of medical devices used in dento-facial orthopedics or stomatology, a clear indicator included in the device specifying the need to end its use. This point seems essential to us in order to legally establish the responsibilities of the various parties involved in the event of malfunction of medical devices. As soon as the intermediate layer of black rhodium is destroyed, the manufacturer can release his responsibility.

  Drawing of the invention It is not useful to represent all the orthodontic devices which can be coated by this process. We limit ourselves to the presentation of a crimp hook on a bow. Figure 1 is a front view on the hook, Figure 2 is a section on the hook which shows the type of coating deposited.

  1-ball 2-cylindrical part 3-part fixed on the orthodontic arch 4-base metal 5-intermediate layer 6-upper layer

Claims (5)

  1) Medical device used in dento-facial orthopedics or in stomatology comprising a base metal such as stainless steel covered with two layers of precious metals. It is characterized by the fact that the intermediate layer between the base metal and the upper layer consists of black rhodium (derived from rhodium containing a hydride and an oxide) and that the upper layer is composed of a metal of the mine of platinum, namely palladium, platinum or rhodium.   2) Device according to claim 1 wherein the upper layer consists of an alloy of precious metals from the platinum mine and semi-precious metals such as nickel at a percentage less than 5% or cobalt at a percentage less than 10%.   3) Device according to claim bou 2 wherein the intermediate layer consists of black rhodium on predororium or wood nickel. 4) Device according to claims 1, 2, 3 in which the base metal is titanium. 5) Device according to claims 1, 2, 3, 4 wherein the black rhodium is replaced by ruthenium.