Surgery – Truss – Pad
Patent
1994-03-31
1995-06-27
Manuel, George
Surgery
Truss
Pad
A61B 800
Patent
active
054271053
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a measuring procedure for the thickness of the mucous membrane of an alveolar process. Dentists require a measurement of the thickness of the mucous membrane in order, before implantation of screw cores, e.g. titanium screw cores, in an alveolar process, to be able to determine the actual thickness of the alveolar process in order for certainty to exist that enough bone material is present for a durable implant. According to the state of the art, the thickness of the mucous membrane is determined with a penetrating body (needle); for this purpose the mucous membrane is pierced and one determines what path the needle covers until it encounters the alveolar process. This procedure is not only painful but also entails the risk of an infection.
From EP-A 0 353 209 a device is known for the inspection of teeth by ultrasound with which the teeth to be tested are scanned by an array of ultrasonic oscillators. Between the array and the gum a front-running body is arranged which may consist essentially of water or the like.
U.S. Pat. No. 4,603,702 shows a circuit which can be used for measuring how long a patient is exposed to ultrasound. The circuit can distinguish whether an ultrasonic oscillator is coupled to a patient or to air. The sound exposure time is measured as long as the ultrasonic oscillator is coupled to the patient.
The invention has the objective of devising a measuring procedure which can be operated without damaging the mucous membrane.
The procedure according to the invention operates with ultrasound according to the pulse-echo procedure, also called the pulse-reflection method. For ultrasonic measuring procedures in general, reference is made to the German book: J. Krautkramer and H. Krautkramer, "Material testing with ultrasound", 4th ed., Springer Verlag. The ultrasonic oscillator arranged in the probe housing of the measuring device periodically emits ultrasonic pulses which pass through the probe tip and enter the mucous membrane from its coupling surface. The pulses are reflected at the transition (interface) between mucous membrane and alveolar process surface. The thickness of the mucous membrane is determined from the travel time of the sound by using the known velocity of sound (about 1500 m/s).
A qualitatively good coupling of the coupling surface with the mucous membrane is achieved according to the invention by manufacturing the probe tip from a material which has acoustic impedance similar to that of the mucous membrane. This is a tissue and therefore, in ultrasound, has essentially the same properties as water. If the probe tip is in good contact with the mucous membrane, no or only a small jump (sound hardness jump) on the coupling surface/mucous membrane surface interface occurs in the acoustic impedance with the result that practically no sound is reflected there. The criterion of low or absent sound reflection at the transition between coupling surface and mucous membrane is utilized in order to distinguish between good and poor couplings. A measurement is performed only if the coupling is good, therefore if the echo from the coupling surface/mucous membrane surface interface is below a threshold value.
In order to make certain that the echo from the coupling surface is normally present, this echo is registered during the calibration phase in which the coupling surface is free and in contact only with air. It must display only a certain amplitude. In this case not only one echo, i.e., preferably the first echo of the coupling surface is registered during the calibration phase and evaluated, but also a subsequent, preferably the second, echo from the coupling surface is also evaluated. During the calibration phase the coupling surface should be totally free; it may not be covered with water droplets or dirt but rather exposed exclusively to air. However, if it is coated or covered in any way, then this is manifested in the fact that the ratio from two consecutive echoes is changed. The ratio of two echoes is therefore, according to the invention, used to
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Bonenkamp Heiko
Knapp Gerd
Pollock Benedikt
Volkmann Klaus
Krautkramer GmbH & Co.
Manuel George
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