Patent Application
20200054416
The present invention relates to the technical field of dental medical systems and methods implemented by endodontic handpieces. More particularly, the present invention is related to methods and systems involving endodontic files with super-elastic characteristics.
A handpiece for endodontic treatments is basically composed by a motor unit including a motor or turbine having a rotatable motor shaft and a file coupling unit removably coupled to the motor unit and provided with a head to which the file is removably fixed and coupled, the head rotating the file upon rotation or reciprocation or oscillation of the motor shaft.
Development of handpieces and drilling techniques has seen the migration into these endodontic instruments of new technologies and materials such as superelastic materials. Indeed, endodontic files made of materials based on super-elastic alloys (e.g. Nickel-Titanium—NiTi) are an important part of the root canal instrumentarium.
For instance, the NiTi (namely Nitinol) is a near equiatomic intermetallic of nickel and titanium capable of exhibiting superelastic behaviour due to a stress-induced phase transformation, or shape-memory due to a temperature-induced phase transformation.
The NiTi alloy exists in two different crystal phases, martensite and austenite, which are temperature dependent. When martensitic NiTi is heated, it begins to change to austenite, and once converted to austenite, the alloy will have completed its shape-memory transformation and will display its superelastic characteristics. The temperature at which this phenomenon is complete is called the austenite finish temperature (Af). We will assume Af as a trasition temperature T in the following.
The introduction of these new materials permitted to use more flexible files in order to reduce the risk of intracanal fracture of the endodontic file.
Nevertheless, none of these solutions permits neither to improve the drilling technique in such a way to reach all parts of the root canal under treatment, especially in case of particular root canal configurations, nor to completely exclude the existing risk of intracanal fracture.
As a matter of fact, present files are suggested to be single-use due to the metal fatigue accumulation.
Therefore, the aim of the proposed invention is to avoid the drawbacks of the traditional NiTi alloy, namely separation and distortion of instruments, and of the traditional drilling techniques, developing a method for controlling the flexibility and stiffness of an endodontic super-elastic file and the device implementing said method.
The proposed solution permits to adapt the flexibility of each file at the single clinical case to reduce the main problem, namely the risk of intracanal fracture of the file.
Moreover, the invention permits to improve the quality of the treatment in particular in severely or abruptly curved and narrow root canals with respect to the traditional endodontic techniques.
Another advantage offered by the proposed invention is the possibility to safely use the same endodontic file in a greater number of treatments, with a reduced risk of intracanal fracture.
Further advantages will be more clear from the detailed description of the invention.
Since a common mechanical endodontic file is made of materials based on super-elastic alloys having a transition temperature T, we developed a method for controlling the flexibility and stiffness of such file during the intracanal treatment, according to the independent claim 1.
The first step of the method consists in the selection of a specific file, having a transition temperature T, among a set of super-elastic files with shape-memory characteristics and transition temperatures T comprised in a specific range between T1 and T2.
The selection is carried out by empirical measures of T, such as the well-known differential scanning calorimetry (DSC) already used for orthodontic wires [Ref.-1] or, alternatively, exploiting the well-established correlation between the fatigue resistance and the flexibility of the files under thermomechanical treatment [Ref.-2].
Before the shaping operation starts, the selected file is at the starting temperature TS which can be the room temperature (20° C.) or the intracanal temperature (e.g. 35-36° C.), or is regulated to a specific value.
The next step of the method consists in adjusting the temperature of the file in order to modify its stiffness and making it more flexible or stiffer exploiting the super-elastic characteristics during the intracanal treatment. The temperature of the file may be adjusted thanks to a dedicated heating and cooling system which is managed by a control unit (CU) and a heat regulator (32), to an adjusted temperature Ta>T in order to make it hard and stiff, and Ta<T in order to make it soft and flexible. During the shaping operation the torque is measured and the adjusted temperature Ta is calculated according to a specific torque-temperature relationship. In the simplest cases the torque-temperature relationship can be a standard polynomial or exponential or a negative power function, but also other functions and complex combinations between them are possible.
Both the starting temperature TS of the file and the torque-temperature relationship are initially set by the clinician according to the needs of the treatment, i.e. the root canal configuration. The temperature adjustment of the file can be operated either while the file is rotating (if the torque varies slowly respect to a given curve and is below a predetermined threshold) or during a stop period (until the file reaches the new temperature or up to a predetermined time limit set by the user).
This result is achievable and reproducible thanks to the selection of a file with a well-known transition temperature T, performed in the first step of the method, provided that the torque is constantly monitored and the temperature of the file is kept under control during the treatment.
It has to be stressed that the control of the temperature is crucial for the outcome of the method and to prevent possible undesired effects.
Indeed, since it is not clear how much heat is produced by friction of a file on the root canal wall during the shaping, it's not possible to exploit straightforwardly such heat in order to modify the flexibility of the file and to obtain a precise and well-controlled technical effect.
For instance, if the heat produced during the drilling operation leads to a temperature rise lower than 1.5° C. it could be insufficient to change the crystal phases of the super-elastic alloy from. On the other hand, if the temperature rise is higher than 1.5° C. it could make the file stiffer during the intracanal shaping, especially when the file has a transition temperature around the intracanal temperature, even when more flexibility is needed because of the severe canal curvature and shape.
In both cases the drilling heat could lead to undesired and uncontrolled effects on the file, which can be prevented keeping under control the temperature of the file.
Moreover, in some cases the stress-induced phase transformation to martensitic state occurring during the intracanal shaping represents a drawback for the outcome of the treatment. The proposed invention permits to counteract this effect with a thermal-induced phase transformation to austenitic state by a controlled temperature adjustment of the file.
Therefore, it has been developed a dedicated apparatus in order to implement the above-mentioned method which allows to keep under control the stiffness and flexibility of a selected endodontic file, avoiding all those possible drawbacks occurring during the intracanal shaping.
The apparatus, according to claims 5, consists in an endodontic handpiece comprising an endodontic file made of a super-elastic alloy based material which has been selected in order to have a desired transition temperature T among a set of endodontic files with transition temperature T in the range between T1 and T2, said apparatus including a heating and cooling system designed to adjust the temperature of the file before and during the intracanal shaping.
In addition to the heating and cooling system, that is the fundamental part of the apparatus, there is a control system comprising a heat regulator (32) and a programmable Control Unit (CU) able to acquire data coming from the motor and from other parts of the apparatus and to operate settings on the heat regulator (32) according to mathematical relationships between torque, or motor speed, and temperature.
Therefore, not only can the CU decrease or stop and reverse rotation once the set torque limit has been reached, but also it can change the temperature of the file and consequently adjust its stiffness and flexibility. The CU can be either part of the handpiece or an external device connected to the handpiece with proper cablings, and could be switched to a manual mode so as to calculate and display the temperature, leaving the clinician free to make manual settings.
Many types of handpieces comprising piping and nozzles to spread coolant fluids on the teeth have been already produced, but only with the aim to reduce the tooth temperature in order to avoid the possible thermal irritation of teeth resulting from the heat produced by friction during dental treatment procedures, such as the removal of tooth structures during the canal preparation. Despite the fact that, according to some studies [Ref.-3], the heat produced during the tooth preparation with low- and high-speed handpieces seems to increase the intrapulpar temperature of 1.8° C. and 1.4° C. respectively, it is still not clear how much heat is actually produced by friction of a file on the root wall during the shaping operation. Furthermore, in some cases the cooling of the canal, especially a straight and narrow canal, could be a drawback considering that the sum of the effects of the stress-induced transition and the temperature-induced transition to martensitic state increases the risk of fracture by torsion. Therefore the file should be heated in the case of a straight and constricted canal in order to be stiffer and should be cooled near the curvature, not near the tip, in the case of the curved canal to be more flexible. This result is obtained by the proposed invention with the heating and cooling system which induces a temperature variation mainly near the larger portion of the file so as to obtain a temperature gradient up to the tip of the file, possibly leaving the heat produced by friction on the tip to counteract the stress-induced transition to the martensitic state. More conveniently the invention permits to heat a selected file having T>35° C. up to its austenitic phase and consequently cool it down, near the curvature, below the transition temperature during the shaping operation. On the other hand, in the case of a straight and narrow canal, a file preferably selected to be in austenitic phase at intracanal temperature, can be entirely heated and stiffened, as well as a martensitic file at intracanal temperature is selected.
In a first embodiment (
A possible alternative to the first embodiment (
In both cases the fluids are pumped either by an internal pump or an external one (not shown in the figures) and the flow is managed by a flow control means (35), e.g. buttons onto the handpiece, or by external commands (e.g. pedals).
In a second embodiment (
A possible alternative for the second embodiment is realized including an inner rotary portion in the electrical heating system (23) comprising a set of bearings in order to keep in contact said electrical heating system (23) with the neck portion (21) of the file (20), even placing the electrical heating system (23) near or inside the rotary portion (34) (the rotatable shaft, inside the head of the handpiece).
In a third embodiment (
In all the embodiments the electrical heating means are powered by dedicated external wirings (31) from an external power system, but it is not excluded the possibility to include in the handpiece an internal power source, such as a dedicated power battery (33), whereas the electrical current and the produced heat can be regulated by the heat regulator (32).
The temperature of the file is measured in the same way, i.e. by the probe or termocouple (15), but in the second and third embodiment it could be calculated from the electric current flowing inside the electrical heating system and from the power absorption of the power laser diode, which could be measured in a simple way.
Furthermore, the probe (15) and the display (16) could be either powered by the power battery (33) independently from the power circuit of the heating system, or they could be all included in the same power circuit, powered by the battery (33) or by an external power system.
The three embodiments could be also properly combined in such a way to obtain an apparatus with mixed heating and cooling systems so as to implement the method in claims 1-4.
A non-limiting example of a combined or mixed heating and cooling system is a fluid containment chamber (25), preferably made of metal, composed by an outer sealed cylinder filled with the fluid which is provided by the pipes (11), and an inner cylinder coupled to the outer one by bearings and being in contact with the file (20). Besides, the outer part of the containment chamber (25) could be surrounded by an electrical heating system (23). In this case the fluid can flow at low temperature so that the file is kept to a temperature lower than its transition temperature T, but it can also be heated by the electrical heating system (23) keeping the fluid at rest inside the containment chamber (25), and consequently cooled down allowing the fluid to flow also switching off the electrical heating system (23), if necessary. Moreover, the probe (15), or even a second probe, could also be placed inside the containment chamber (25) in order to measure the temperature of the fluid and of the file (when the thermal equilibrium is reached).
In a possible alternative to the previous example of mixed heating and cooling system, the cooling system is the fluid containment chamber (25) (both types, with or without bearings and rotary part, are possible) whereas the heating system is the electrical heating system (23), so that they are two independent systems which can be either separated or contiguous each other along the central axis of the file.
In each embodiment we can consider, as non-limiting examples, the following cases:
In this case the file may take both advantages being cooled and heated, representing the ideal situation in which the clinician may adjust such parameters in a well-controlled way in order to reach the optimal adaptation to each different clinical case.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017000027275 | Mar 2017 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IT2018/000028 | 2/28/2018 | WO | 00 |
