Field of invention

This invention regards waxes that can be directly applied to the oral cavity during the preparation phase for fixed and/or combined crowns or dental bridges.

Prior art

Fixed prosthesis work is carried out on stumped teeth (reduced in size) or on implanted posts (endosseus implants).

The professional makes two impressions. - the first involves the dental arch on which the fixed prosthesis work will be carried out (in materials such as polyvinyl siloxanes or polyethers)

- the second involves the antagonist dental arch (in materials such as alginate)

The two impressions that arrive at the dental technician's laboratory are filled with plaster and then mounted on an articulator. Wax is used to model the missing teeth and the teeth on the stumps, thus creating the definitive shape of the article, and then a silicone template is made which will used to model the metal framework which supports the cosmetic material.

The silicone template is used to obtain the exact shape of the tooth, since the metal framework must be shaped so that a layer of cosmetic material can be applied to it which is as evenly thick as possible all over the surface.

The thickness of the cosmetic material will determine the appearance and the colour of the tooth.

Several problems may arise during this phase, as there are many parameters to take into consideration, such as for example the proportions of the occlusion of the arches, the correct sizes and the shapes of the teeth.

In the prior art, in order to check these parameters, resin is applied to the metal framework using the mask produced previously; the model of the tooth produced in this way is then tried out on the patient in the so-called "metal test", in other words a test to see how precise the metal framework is. The weak point of this procedure lies in the fact that most of the work has already been carried out and, if the metal test shows that the tooth being tested does not fulfil all the necessary requirements, all the work has to be started again.

Therefore, it was felt that there was the need to devise a system that would make it possible to avoid the aforementioned drawbacks, which would also conveniently reduce the time need for workmanship and as a result, the associated costs. Summary of the invention The Applicant has unexpectedly found that it is possible to avoid the aforementioned drawbacks by using, during the preparation phase of fixed and/or combined crowns or dental bridges on both natural stumps and implanted posts, waxes that can be applied to the patient's mouth and then be functionalized. These waxes have the following characteristics: Q solidification point between 60 and 90 ⁰ C, measured according to standard

ASTM D938, α needle penetration measured according to standard ASTM D1321 between 8 and 20 dmm (tenths of mm), □ kinematic viscosity measured at 99°C according to standard ASTM D445 between 6 and 20 mm ² /s.

These waxes can be used specifically for preparing models of teeth for tests in the patient's mouth, without using the bridge or the tooth in metal with resin supports. Therefore, a further objective of this invention is a model for a test in the mouth, using the aforementioned waxes. Description of the figures

Figures 1-4 show phase (a) in the preparation of crowns and dental bridges with the traditional technique, using waxes according to this invention. Figures 5 and 6 show phase (d) in the preparation of crowns and dental bridges with the traditional technique, using waxes according to this invention. Figures 7 and 8 show phase (e1) in the preparation of crowns and dental bridges with the traditional technique.

Figures 9 and 10 show phase (e2) in the preparation of crowns and dental bridges with the traditional technique, using waxes according to this invention. Figures 11-16 show phase (e3) in the preparation of crowns and dental bridges with the traditional technique, using waxes according to this invention.

Figures 17-21 show phase (a ¹ ) in the preparation of crowns and dental bridges according to the PRESS OVER technique, using waxes according to this

invention.

Detailed description of the invention

In this description :

□ polymerization means hardening following the reticulation of the resin, α shelled teeth are defined as the teeth that will be subject to prosthesis, α functionalization of the waxes means the testing of the masticatory, aesthetic and phonetic functions carried out directly on the teeth modelled in wax, before starting work on the definitive models.

According to this invention the waxes are preferably used in the following operative phases in the preparation of crowns or dental bridges, a) Before beginning rehabilitative work in the mouth of a patient, the dentist takes two impressions in alginate of the antagonist arches; these impressions will be filled with plaster in the dental technician's laboratory, to recreate two models for the upper arch and two models for the lower arch, called "study models" or "preliminary treatment models". These two models will be used for a diagnostic modelling, in other words an initial rehabilitation study to present to the patient (see Figures 1-4). b) after having decided which treatment to carry out, the dentist asks the dental technician's laboratory to prepare the provisional shelled teeth which are polymerized on the models obtained previously during stage (a), c) the provisional shells are then made in the following way:

(c1) a silicone template is applied to the teeth that are to undergo prosthesis, (c2) the next stage is to shave down into stumps the plaster reproduction of the teeth that are to undergo prosthesis and (c3) with the help of the silicone template prepared in (d), the teeth are polymerized with resin on the aforementioned stumps prepared in (c2), and are then perfected and polished. d) once the provisional shelled teeth have been removed from the model, the silicone template is placed into position, into which the wax, the subject of this invention, is poured in a liquid state; once the wax has solidified and cooled, it is extracted from the mask and archived with the aforementioned preliminary treatment models obtained in (a), and the provisional shelled teeth obtained in (b)

are repositioned on the plaster mould; said shelled teeth must be assessed by the dentist for the cementing which follows (see figures 5 and 6) e) next, further provisional teeth are prepared, called "second provisionals" or "last provisionals"; these are made based on the stumps previously prepared by the dentist in the patient's mouth, according to the following procedures

(e1) two alginate impressions are taken of the teeth that have been shaved down into stumps; the impressions are then developed in plaster at the laboratory, and the plaster casts obtained in this way are mounted on an articulator with the help of a centric wax and a facial arch (see figures 7 and 8). (e2) the blue wax that we had previously archived is placed on the plaster stumps, and we perfect the modelling and send it to the dental clinic for testing, (see figures 9 and 10),

(e3) the dentist will position the wax on the stumps in the patient's mouth and will carry out all checks, including aesthetics, shape, volume, inclinations, phonetics, mastication, height of the teeth that we have modelled; any necessary modifications are made directly at the dental clinic, since wax is a material that can be easily manipulated; another check is made in the mouth to verify whether the results are satisfactory for the dentist, if so the wax model returns to the dental technician's laboratory and is used to carry out the polymerization process of the second provisional teeth (see figures 11-16).

(e4) the next step is to construct the silicone template on the wax, according to the present invention the wax is removed from the stumps and is once again archived with the preliminary treatment models; (e5) the provisional teeth are then polymerized on the silicone template, and lastly they are perfected and polished, and are sent to the clinic to be cemented in the mouth. Wax modified in this way has all the characteristics that are required in the definitive article and also has a further advantage in that, during the test in the mouth, it allows the dentist to correct any errors in the preparation of the stumps (crookedness, inclination, length). Having already decided what the final height of the prosthesis will be, allows a resin rest or gig (mastication guide) to be prepared in the laboratory; this will be used for further mounting of casts on the articulators. This will allow us to proceed

safely with the construction of the prosthesis.

The use of the wax according to this invention is also of interest with the PRESS OVER and PRESSABLE CERAMIC SYSTEM technique, in which the cosmetic material, in other words the ceramic, is not modelled by hand and fired on the metal framework but instead is die-cast in a special oven with the lost wax technique.

With this technique, the wax according to this invention can be used in the following way: (a ¹ ) after having tested the wax in the mouth as described in (e), the "master" models are made, on which the prosthesis work will be carried out. After having prepared the stumps, the functionalized diagnostic wax casts according to this invention are positioned and the silicone templates are arranged, to be used to prepare the metal framework. The masks will then be used for the shaping, over the bridge of the teeth, which will simply be performed by pouring liquid wax into the mask. Once the waxes according to this invention have cooled, they allow a modelling over the metal to be achieved which has an identical shape and size to that tested in the mouth and judged to be optimal by the dentist (see figures 17- 21). (b') the wax according to this invention is poured over the metal into the silicone template, and when the wax has solidified the silicone template is removed, thus obtaining teeth with an identical shape to those tried in the mouth and judged to be optimal by the dentist.

(c ¹ ) then, using the lost wax fusion technique, the wax is replaced with pressure- cast ceramic in a special oven. The waxes to be used according to the present invention are those that are habitually used in dental mechanics, such as those of a natural type for example, including mineral waxes and in particular paraffin waxes, vegetable waxes and waxes of animal-origin, or synthetic waxes. In any case, the critical element that is necessary for these waxes to be directly used in the patient's mouth is that they have a melting temperature, penetration and kinematic viscosity within the aforementioned recommended intervals. Preferably, the waxes that are the object of this invention should have needle penetration measured according to standard

ASTM D1321 included between 9 and 14 dmm (tenths of mm), kinematic viscosity measured at 99°C according to standard ASTM D445 between 7 and 15 mm ² /s. Even more preferable is that the waxes that are the object of this invention should present almost no shrinkage or contraction following solidification. Almost no shrinkage following solidification means a contraction in volume following solidification that is lower than 11%, preferably lower than 5%, and even more preferably lower than 2%.

Preferably, the waxes that fit the abovementioned requirements are waxes that contain paraffinic hydrocarbons. Even more preferably, these waxes should contain at least two of the following hydrocarbons C26H54, C27H56, C28H58, C ₂ CjH ₆ O, C ₃₀ H ₆₂ , C ₃ - ₁ H ₆₄ each at concentrations higher than 10% by weight of the total weight of the hydrocarbons, and the total concentration of these hydrocarbons compared to the total weight of said hydrocarbons should be between 45 and 65% by weight out of the total weight of hydrocarbons contained in the wax, and moreover, the principal hydrocarbon should be C29H ₆ 0.

A particularly favourable embodiment of wax to use according to this invention is wax (2) containing C ₂₆ H ₅ 4, C27H ₅₆ , C ₂₈ H58, C29H60, each in concentrations of over 10% and the total concentration of these hydrocarbons is around 47% of the total weight of hydrocarbons contained in the wax. Another particularly favourable embodiment to use according to this invention is wax (2A) containing C ₂₇ H5 ₆ , C28H58, C29H60, C3 ₀ H ₆ 2 in concentrations of over 10%, where the total concentration of said hydrocarbons is 46% of the total hydrocarbons contained in the wax. Another preferred embodiment is wax (3) which contains C27H56, C28H58, C ₂ gH6o , C ₃ oH ₆ 2 , C ₃₁ H64 each in a concentration of over 10% by weight, and concentrated so that the total concentration of these hydrocarbons is around 62% of the total weight of hydrocarbons in the wax.

The preferred waxes to be used according to this invention are in turn preferably obtained by blending at least two of the aforementioned waxes: Wax (A) containing hydrocarbons C26H54, C27H56, C28H58, C ₂ 9H6o, C30H62 C31H64 each at a concentration higher than 10% by weight and so that the total concentration is around 71% of the total weight of hydrocarbons in the wax, this

wax is available on the market under the trade name ELASTODIP. Wax (B), in which the hydrocarbons, each of which are present in amounts higher than 10% by weight out of the total weight of hydrocarbons, are C ₂₈ H ₅₈ , 029H ₆₀ , C30H62 , C3iH ₆₄ ,C32H66, and are present in amounts totalling around 70% of the total weight of the hydrocarbons; this wax is available on the market under the trade name Solidus 84.

Wax (C) in which the hydrocarbons, each present in quantities higher than 10%, are C27H ₅₆ , C28H5 ₈ , C ₂ E)H ₆ O, and the total concentration of said hydrocarbons compared to the total amount of hydrocarbons in the wax is around 35%. This wax is available on the market under the name Coming's.

However, the Applicant has found that none of these commercial waxes can be used alone for the purposes of this invention, as it is not possible to obtain with them wax models of teeth that can be directly applied to the mouth. Even more favourably, the waxes to use according to this invention should be prepared by blending wax (A) with at least one of the abovementioned waxes (B) and (C).

In a particularly favourable embodiment, the waxes to use according to this invention are prepared by blending wax (A) with wax (C) in the following ponderal ratios comprised between 1 :6 and 1 :2. This class includes, for example, wax (2) obtained by blending wax (A) and wax (C) in ponderal ratios of 1 :6 and wax (2A) obtained by blending wax (A) and wax (C) in ponderal ratios of 1 :2. In another embodiment that is particularly favourable, the waxes to use according to this invention are obtained by blending wax (A) in quantities between 55 and 20% of the total weight of the blend, wax (B) in quantities between 20 and 45% of the total weight of the wax, and finally wax (C) in ratios between 40 and 60% by weight of the total weight of the blend. This class includes, for example, wax (3), which is obtained by mixing wax (A) in a quantity of around 15%, with wax (C) in a quantity of around 42% and wax (B) in the same percentage amount as (C). The Applicant has also found that other waxes also meet the aforementioned requirements.

For example, this category includes waxes obtaining by blending at least 4 of the following waxes in the right way:

D) refined paraffin 52/54 with a melting point measuring according to standard ASTM D87: 51.5-54.0 ⁰ C, kinematic viscosity at 100 ⁰ C according to standard D445 3- 3,5 (mm ² /s), needie penetration measured at 25°C (1/10mm) according to standard ASTM D 1321 : 14-20 dmm (1/10mm), E) CW 82 is a mix of Vybar 103 paraffin wax , microcrystalline wax and a hydrocarbon resin, and has the following characteristics: melting point measured according to standard ASTM D566: 62-64°C, needle penetration measured at 25°C (1/10mm) according to standard ASTM D1321 : 6-8 dmm (1/10mm),

F) Eltene LCS is a blend that includes paraffin and ethylene-vinylacetate copolymers, and has the following characteristics: solidification point measured according to standard ASTMD938: 78-80 ⁰ C, penetration measured according to standard ASTM D1321 6-8 dmm (1/10mm), Brookfield viscosity measured at 150°C 800-900 cps, at 130°C 1400-1450cps, at 120°C 1900-1950 cps.

G) Licowax PE520 non-oxidized polyethylene wax with the following characteristics: drop melting point calculated with standard ASTM D127: 117-

122°C, acid number calculated with standard ASTM D1386: 0 mg/KOH/g, saponification index calculated with standard ASTM D1387 0 mg/KOH/g, density at 20°C calculated with standard ASTM D1505 0,92-0,94 g/cm ³ H) Vybar 103 wax with the following characteristics: softening point calculated according to modified standard ASTM D-36: 68,30-79,40 ⁰ C, Brookfield viscosity at 210°C calculated according to modified standard ASTM D-3236: 250-440cps, needle penetration measured at 77°C with standard ASTM D-1321 : 3-7 dmm, Even more preferably, the waxes according to this invention contain a blend of 4 of the abovementioned waxes. A particularly preferred embodiment of this type is that in which the blend is formed of the aforementioned waxes (D), (E), (F) and (H).

Other preferred embodiments are those that involve the use of blends containing all 5 of the aforementioned waxes. Even more preferably, these blends contain: wax (D) in quantities between 40 and 60% by weight of the total weight of the blend, wax (E) in quantities between 30 and 40% by weight of the total weight of the blend,

wax (F) in quantities between 5 and 20% by weight of the total weight of the blend, wax (G) in quantities between 0 and 8% by weight of the total weight of the blend, wax (H) in quantities between 0.1 and 5% by weight of the total weight of the blend.

Below, for illustrative and non-limitative purposes, some examples are given of waxes obtained through blending wax (A) (Elastodip) with at least one of the waxes (B) (Solidus 84) and (C) (Coming's), as well as some examples of waxes obtained by blending waxes (D) (refined paraffin 52/54), E (CW 82), (F) (Eltene LCS), (G) Licowax PE520, (H) Vybar 103. TABLE 1 - COMPOSITION OF THE WAXES

Waxes 2, 2A, 3 as well as commercial waxes (A), (B) and (C) were analysed with gas chromatography, using elicosane as a solvent, and identified through mass spectrometry.

For each of the abovementioned waxes, the % of the hydrocarburic components within them is given in table form.

TABLE 2 - Hydrocarbon compositions of the waxes to be used according to the present invention and of commercial waxes

TABLE 3 - COMPOSITION OF WAXES

Chemical physical properties of wax 8: solidification point (ASTM D 938): 85-87°C needle penetration (ASTM D1321) 9-10 dmm (1/10mm)

Chemical physical properties of wax (9) Solidification point (ASTM D 938): 60-62 ⁰ C

Needle penetration (ASTM D1321): 10-12 dmm (1/10mm) Kinematic viscosity (ASTM D445), 7.2-8.5 mm ² /s