WO2007029278A1

WO2007029278A1 - An apparatus for the photo-polymerisation of composite materials, in particular for dental applications

Info

Publication number: WO2007029278A1
Application number: PCT/IT2006/000646
Authority: WO
Inventors: Roberto De Santis; Luigi Ambrosio; Luigi Nicolais
Original assignee: Cnr Consiglio Nazionale Delle Ricerche
Priority date: 2005-09-07
Filing date: 2006-09-07
Publication date: 2007-03-15
Also published as: EP1922016A1; ITRM20050459A1

Abstract

An apparatus for the photo-polymerisation of composite materials, in particular for dental applications, comprising emitter means (10) for generating at least one electromagnetic radiation (20) and irradiating a material to be polymerised, and a control unit (30) for regulating the power irradiated by the emitter means (10), in such a way that said irradiated power has a profile comprising a first segment (2) of polymerisation that is substantially growing or constant over time, and a second segment (3) of thermal control, subsequent in time and contiguous to the first, and having at least one portion (3a) decreasing over time with finite derivative.

Description

An apparatus for the photo-polymerisation of composite materials, in particular for dental applications

Technical Field

The present invention relates to an apparatus for the photo-polymerisation of composite materials, in particular for dental applications.

Background Art

As is well known, composite materials and the photo-activated polymerisation thereof are widely used in dentistry, and in particular for the reconstruction of teeth.

Photo-polymerisation takes place in at least two successive phases: a light curing phase (LCP) and a phase in which the material is not irradiated (DRP - dark curing phase).

The radiation sources (e.g. filament, semiconductor, plasma, voltaic arc sources, etc.) are powered by ramp electrical signals, followed by intervals with constant power and/or by pulses, which control said sources modulating their power output.

In this way, the composite material is to irradiated with a quantity of power sufficient to obtain the desired polymerisation in the shortest possible time, to limit simultaneously the discomfort caused to the patient undergoing the treatment.

However, if the duration of the operation is reduced excessively (i.e., irradiating the material with the required energy for a very short time interval), the so-called polymerisation contraction undergoes a corresponding acceleration, thereby compromising the integrity of the cellular tissues and of the interfaces between the various materials (synthetic and natural).

Every photo-polymerisation process causes a reduction in the volume of the composite material used, and this reduction takes place the faster, the shorter the time interval over which the necessary energy is irradiated. Clearly, an excessively rapid reduction in the dimensions of the material applied to the patient's oral cavity can cause problems at the surfaces of mutual engagement between the material and the patient's dental tissues, thereby reducing the quality and reliability of the dental reconstruction thus achieved.

It should also be noted that photo-polymerisation is an exothermal reaction, and hence it causes a significant rise in the temperature of the natural and synthetic tissues subjected to irradiation. Once the heating phase is complete, the composite material undergoes a further volumetric contraction (this time, thermal in nature), which further reduces the dimensions.

Since, typically, the interruption in the delivery of power by the irradiating source takes place very sharply and suddenly (i.e. following a substantially step-like profile), the polymerised material is cooled in equally sharp and sudden fashion; this causes a rapid decrease in the dimensions of the portion of material used, further compromising the integrity and quality of the dental reconstruction work performed.

Figures Ia-If show that the contraction of the composite material, in percentage terms, is the greater the quicker the cooling of said material at the end of the polymerisation phase.

Moreover, comparing the duration of each process (100 seconds for Figures Ia and Id, 40 seconds for Figures Ib and Ie, 20 seconds for Figures Ic and If), it is apparent that the volumetric contraction is the greater, the faster the polymerisation phase is executed.

Disclosure of Invention

An object of the present invention is to provide an apparatus for the photo- polymerisation of composite materials, in particular for dental applications, that reaches an optimal trade-off between duration of the treatment and slowness of the volumetric contraction of the composite material, thereby limiting both the discomfort caused to the patient undergoing the treatment, and the aforesaid problems caused by excessively rapid reductions in the dimensions of the composite material elements used.

An additional purpose of the present invention is to make available an apparatus for the photo-polymerisation of composite materials, in particular for dental applications, that allows the execution of high-power photo-polymerisation processes without compromising the integrity of the cell tissues and of the interfaces between the (natural and synthetic) surfaces involved in the treatment. These and other objects are substantially achieved by an apparatus for the photo- polymerisation of composite materials, in particular for dental applications, as described in the appended claims.

Additional characteristics and advantages shall be more readily apparent from the detailed description of a preferred, but not exclusive embodiment of the apparatus according to the invention.

Description of the Drawings

Said description is provided with reference to the accompanying figures, also provided purely by way of non limiting example, in which:

- Figures Ia-If show the profiles over time of the temperature and percent of volumetric contraction of a composite material in different operative conditions;

- Figure 2 shows a circuit that can be used in the apparatus according to the invention; - Figure 3 schematically shows an embodiment of a part of the apparatus according to the invention;

- Figure 4 shows a schematic diagram of a circuit that can be used in the apparatus according to the invention;

- Figure 5 shows an apparatus according to the invention; - Figures 6a-6f show possible power profiles which may be generated by the apparatus according to the invention;

- Figure 7 shows a general diagram of a power profile generated by the apparatus according to the invention.

Description of the Illustrative Embodiment

With reference to the accompanying figures, the number 1 globally designates an apparatus for the photo-polymerisation of composite materials, in particular for dental applications.

The apparatus 1 comprises first of all emitter means 10, for generating at least one electromagnetic radiation 20 and irradiate a material to polymerise.

In particular, the emitter means 10 can comprise at least one main source of electromagnetic radiation 11 for generating an electromagnetic radiation preferably having wavelength between 400nni and 500 nm.

The material to be polymerised can be a composite material; in particular, said material can be appropriately positioned in the oral cavity of a patient, on whom a dental treatment, e.g. a dental reconstruction, is to be performed. BY way of example, said material to be polymerised can be Enamel Plus

(Micerium Spa) or any composite for dental cavities comprising camphorquinone as the photo-active element.

The apparatus 1 further comprises a control unit 30, associated to the emitter means 10 to regulate at least the power irradiated thereby. Advantageously, through the control unit 30 an irradiate power profile can be obtained that enables to optimise the quality/duration ratio of the polymerisation process.

As mentioned above, it is important that the process not have excessive time duration (to limit the discomfort caused to the patient), but it is also necessary for the natural and artificial tissues involved not to undergo excessively rapid volumetric contractions (due both to polymerisation, and to the consequent thermal dynamics), in order not to cause fractures or faulty adherence in the various surfaces.

Preferably the irradiated power profile of the apparatus 1 is defined as follows (Figure 7).

The profile comprises first of all a first segment 2, in which power reaches the peak necessary to obtain the polymerisation of the predefined material; in this first segment 2, the profile is substantially growing or constant.

Typically, the first segment can be constituted by a ramp, followed by an interval in which the profile remains substantially constant.

The profile further comprises a second segment 3, subsequent to the first segment 2 and contiguous in time to the first segment 2; in other words, between the first and the second segment 2, 3 there is no break and there are no substantially interruptions of irradiation on the material to be polymerised/already polymerised between the first and the second segment 2, 3.

During the second segment 3, the irradiation is not aimed at the polymerisation of the composite material, since said polymerisation was obtained during the first segment

2; the irradiation of the second segment 3 is aimed at the thermal control of the polymerised material. To prevent the polymerised material from cooling too suddenly, with the second segment 3 heat is supplied to the material itself, so that the latter cools gradually and the problems described above do not emerge.

The second segment 3 has at least one portion 3a decreasing over time with finite derivative; in other words, the power irradiated by the emitter means 10 in the second segment 3 decreases progressively, at least in the portion 3a, in order to obtain the gradual cooling of the polymerised material. Preferably, the slope of the portion 3a can range between 50m W/s and 500mW/s.

Figures 6a-6f show some examples of how the second segment 3 can be shaped; the y-axis represents irradiated power on the material, whilst the x-axis represents time.

In a first embodiment (Figure 8a), the emitter means 10 comprise a single main electromagnetic radiation source 11, whereby a power whose profile is defined by the first and by the second segment 2, 3 is irradiated to the predefined material. In a second embodiment (Figure 8b), the emitter means 10 can comprise both a main source 11, and an auxiliary source 12 of electromagnetic radiation; in this case, the main source 11 generates a radiation whose power profile is defined by the first segment 2, whilst the auxiliary source 12 generates a radiation whose power profile is defined by the second segment 3. In other words, in the second embodiment, the main source 11 is employed substantially for polymerisation only, whilst the auxiliary source 12 is used to control the gradual cooling of the polymerised material.

In practice, the main source 11 (in both embodiments) and the auxiliary source 12 can be, for example, LED, halogen, plasma sources, etc. In general, the main source 11 and the auxiliary source 12 emit electromagnetic radiation having different wavelengths; for example, the main source 11 can emit radiation between 400nm and 500nm, whilst the auxiliary source can emit radiation between 600nm and 700nm. The control unit 30 can constructed in different ways.

The control unit 30 can, for example, regulate the profile of the power delivered by the emitter means 10 according a pre-set program stored in a memory 31 associated to the control unit 30 (Figure 9a); in other words, the desired power profile is set a priori, and the emitter means 10 are appropriately regulated according to a pre-set program to obtain said profile.

In particular, the pre-set program can pertain to the second segment 3 of the profile of the irradiated power.

A circuit that can be used in this case is shown in Figure 2: this circuit comprises a switch 110, preferably of the reed type, an RC set constituted by the resistor 120 and by the capacitor 130, and a controlled electronic device 140 (preferably a transistor); the emitter means 10 are connected in series to the controlled device 140, and in particular they are connected to the terminals 15, so the energy accumulated in the capacitor 130 can be gradually transferred to the emitter means 10, and the power irradiated to the material is regulated correspondingly.

Alternatively, the control unit 30 can be connected to a temperature sensor 40

(Figure 9b), whose function is to measure the temperature of the material to be polymerised/already polymerised; in this way, the control unit 30 can regulate the cooling of said material, as a function of the temperature detected by the sensor 40, defining in real time at least the profile of the second segment 3.

Figure 4 shows an exemplifying diagram of a circuit that can be used in this case: the temperature T of the emitter means 10 is measured by the sensor 40, and a comparator node (e.g. a subtractor node) compares this measurement with one or more pre-set values VP. The difference signal is transmitted to a regulating block PID (Proportional - Integral - Derivative) which appropriately drives the electronic device 140 by means of a command signal 24.

In an additional, substantially mechanical alternative, the control unit 30 comprises a shutter 32 of the electromagnetic radiation generated by the emitter means

10; said shutter 32 can comprise a screening element, not transparent to the radiation generated by the emitter means, which is interposed between said means and the material M (Figure 3).

By means of said screening element, at least part of the radiation emitted by the emitter means 10 is blocked (e.g., absorbed or reflected), such a way as to regulate the incident power on the material. By moving the screening element to different operative positions, it is then possible progressively to reduce the power irradiated on the material and gradually to regulate the cooling thereof. Preferably, the shutter 32 can comprise diaphragm means, which can be driven between a plurality of operative conditions, each corresponding to a respective power which is made to impact on the material. Advantageously, the control unit 30 can be provided with an activation module 33, operatively connected to the shutter 32 to activate it.

In particular, the activation module 33 can be connected to the diaphragm means to drive them between their operative conditions. Thanks to the activation module 33, a profile defined at least by the second segment 3 is imposed by means of the shutter 32 on the power impacting the material. Figure 5 shows the outer structure that can be assumed by the apparatus 1.

The apparatus 1 can comprise a housing body 100, preferably having the shape of a pistol, the housing body 100 has a front area 102, preferably with cone frustum shape, in which the aforementioned emitter means 10 can be housed.

The housing body 100 also has a rear area 103, whereat can be positioned cooling means (not shown) to cool the emitter means 10.

The housing body 100 also has a handle 105, to enable a user to grip the apparatus 1 and perform the photo-polymerisation operation where it is required.

At the handle 105 can be provided an activation element 106 (e.g. a switch) to activate the apparatus 1 at the time when the polymerisation is to be performed. Through a cable 107, the housing body 100 and its content can be connected to a central unit 110; the latter can contain, for example, the control unit 30 (in particular in the embodiment in which the latter is electronic and not mechanical).

In addition to the above, the apparatus 1 can further comprise conveying means F (e.g. an optical fibre), to correctly route the radiation generated by the emitter means 10 on the composite material.

The invention achieves important advantages.

First of all, the apparatus enables to optimise the duration/quality ratio of the photo-polymerisation process, allowing to perform operations that are sufficiently rapid and at the same time sufficiently reliable. Moreover, the apparatus according to the invention enables to exploit the benefits deriving from high-power polymerisation processes without compromising the quality and integrity of the irradiated materials.

Claims

1. Apparatus for the photo-polymerisation of composite materials, in particular for dental applications, comprising: - emitter means(lθ), for generating at least one electromagnetic radiation (20) and irradiate a material to polymerise;

- a control unit (30) associated to said emitter means (10) to regulate the power irradiated thereby; characterised in that said control unit (30) imposes to said irradiated power a profile comprising:

- a first segment (2) where polymerisation is substantially growing or constant over time;

- a second segment (3) of temperature control, subsequent in time to the first one and having at least one portion (3 a) that decreases over time with finite derivative, said first and second segment being contiguous in time.

2. Apparatus as claimed in claim 1 characterised in that said emitter means (10) comprise a main source of electromagnetic radiation (11), preferably having wavelength between 400 run and 500 nm, said main electromagnetic radiation having a power profile defined by said first and second segment (2, 3).

3. Apparatus as claimed in claim 1, characterised in that said emitter means (10) comprise:

- a main source of electromagnetic radiation (11), preferably having wavelength between 400nm and 500nm, said main radiation having a power profile defined by said first polymerisation segment (2); - an auxiliary source of electromagnetic radiation (12), preferably having wavelength between 600nm and 700nm, said auxiliary radiation having a power profile defined by said second segment (3).

4. Apparatus as claimed in claim 3 characterised in that said main source (11) and said auxiliary source (12) emit electromagnetic radiation with mutually different wavelengths.

5. Apparatus as claimed in any of the previous claims, characterised in that said control unit (30) imposes to the delivered power a profile defined by said second segment (3) according to a program pre-set in a memory (31) associated to said control unit (30).

6. An apparatus as claimed in any of the claims 1 through 4, characterised in that it further comprises at least one temperature sensor (40), to measure a temperature of at least said material.

7. Apparatus as claimed in claim 6, characterised in that said control unit (30) is connected to said sensor (40) to define at least the profile of said second segment (3) according to the temperature measured by said sensor (40).

8. Apparatus as claimed in claim 1 characterised in that said control unit (30) comprises a shutter of electromagnetic radiation (32) interposed between said emitter means (10) and said material to be polymerised to regulate said irradiate power over time.

9. Apparatus as claimed in claim 8, characterised in that said shutter (32) comprises diaphragm means, preferably able to be driven between a plurality of operative conditions, each corresponding to a different power irradiated to said material.

10. Apparatus as claimed in claim 8 or 9, characterised in that said control unit (30) comprises an activation module (33) to activate said shutter (32), and preferably to drive said diaphragm between said operative conditions, to impose to said irradiated power a profile defined by at least said second segment (3).