Lid-opening Test
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Lid-opening test
General information
The lid-opening test is a specialised technological method of materials testing used to characterise the dimensional stability of medical implants (see: implant testing). It was developed in the 1990s [1–3] and has been used to evaluate the material and deformation behaviour of voice prostheses [4].
A voice prosthesis (also known as a voice button) is used for vocal rehabilitation in patients who have had their larynx removed for medical reasons.
Various polymer testing methods are available for characterising the material properties; however, these do not provide specific information on component behaviour, i.e. valve resistance or the resistance of the flange during the removal and insertion of the prosthesis. As a physical testing method, the recording of pressure flow-resistance curves can be used, whereas for the mechanical characterisation of the hardness of the surface and the creep behaviour (see: creep plastics) of the materials used for shunt valves, instrumented microhardness measurement is suitable [1].
To assess the resistance of the valve or valve flap, the following technological test methods were developed: the
- prosthesis pull-through test and the
- lid-opening test.
Diagram of the lid-opening test test
Figure 1 shows a schematic representation of the lid-opening test and a corresponding typical load–deformation (extension) diagram.
| Fig. 1: | Lid-opening test for voice prostheses (valve flaps) (a) and schematic load–deformation (extension) diagram (b) (Fmax – maximum load) |
In the lid-opening test, the flap of the fixed prosthesis is deflected centrally using a pin with a diameter of 4 to 5 mm, and the load-deformation behaviour is recorded using a universal testing machine at a crosshead speed of 2 mm min-1. The parameters of interest here are the maximum load achieved and the rise of the curve in the initial range, which serves as a measure of stiffness in Nmm-1.
A characterisation of the performance under various loads using technological tests allows conclusions to be drawn regarding the usability (e.g. design strength with regard to replaceability) and service life (e.g. flap function) of the voice prostheses.
Lid-opening test, voice prosthesis
Valve prostheses, commonly referred to internationally as “voice prostheses”, have been in use since the 1980s and are implanted as functional devices in patients without a larynx to facilitate vocal rehabilitation.
A voice prosthesis enables rapid vocal rehabilitation [5]. The prosthesis generates the voice only indirectly by allowing airflow to cause vibrations in the muscles and mucosa at the entrance to the oesophagus. It is actually a pharyngo-tracheal shunt valve, i.e. it allows air to flow into the oesophagus or the lower pharynx when there is excess pressure in the trachea, but its valve action prevents saliva and food from passing from the oesophageal side into the trachea. A key feature of its functionality is the flawless valve function; failure of this necessitates replacement of the prosthesis. There are a number of products on the market that differ mainly in the design of the valve. The material of choice is silicone rubber. Polyurethane has also been tested as a material.
The laryngeal prosthesis is subject to medial forces during use. The voice prosthesis is in contact, via its shaft, with the tissue lymph of the non-epithelialised shunt between the trachea and pharynx. It is designed to remain mobile within the shunt so that it can be easily removed in the event of malfunction. Its valve-bearing side is in constant contact with saliva and thus also with the oral flora. Biocorrosion is particularly likely to occur here.
To determine how sensitive different mechanical testing methods are to variations in the materials used in voice prostheses, microhardness tests, creep tests and specially developed technological procedures for characterising dimensional stability were carried out on various prostheses made of silicone rubber, silicone rubber blends and polyurethane (voice prostheses ‘Halle’ and a reference voice prosthesis ‘Provox’) microhardeness tests, creep tests and specially developed technological methods for characterising dimensional stability were carried out [1].
| Fig. 2: | Lid-opening test for selected prosthetic materials [6] |
The results demonstrated that, using the determined mechanical measurement variables and the material values, it is possible to distinguish between and evaluate the voice prostheses in terms of material behaviour.
The lid-opening test proves to be a sensitive test method that can be used to good effect. In this test, a pin is used to deflect the valve flap of the fixed prosthesis centrally. The measured variable of interest is the maximum load and the rise of the curve in the initial range, which serves as a measure of stiffness. Figure 2 shows the maximum load for the three selected prosthesis materials: polyurethane (1), silicone rubber (2) and a silicone rubber blend (3) [6].
From Fig. 2, it can be seen from the maximum loads that the three implant materials examined exhibit significantly different behaviour in this technical test. In the lid-opening test, the lowest forces are recorded for the PUR elastomer, which is certainly positive for valve extension but does not guarantee a secure fit of the prosthesis.
Since the values for lid-opening with the silicone rubber compound are almost identical to those for the silicone rubber, the silicone rubber compound therefore represents the best compromise solution for practical clinical application.
See also
References
| [1] | Bierögel, C., Bethge, I, Grellmann, W., Haberland, E.: Deformation behaviour of voice prostheses – Sensitivity of mechanical test methods. In: Grellmann, W., Seidler, S. (Eds.): Deformation and Fracture Behaviour of Polymers. Springer, Berlin Heidelberg (2001) pp. 471–478 (ISBN 978-3-540-41247-2; e-Book (2013): ISBN 978-3-662-04556-5; see AMK-Library under A 7); https://doi.org/10.1007/978-3-662-04556-5 |
| [2] | Zwanzig, I., Haberland, E.-J., Bierögel, C., Grellmann, W.: Werkstoff- und Deformationsverhalten von funktionellen Prothesen im pharyngo-trachealen Bereich. In: Proceedings Polymerwerkstoffe ’96, Merseburg, September 18–20, 1996, pp. 494–497 |
| [3] | Bierögel, C.: Implant testing. In: Grellmann, W.], Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 624–634 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22) |
| [4] | Haberland, E.-J., Neumann, G., Löbe, L. P., Voigt, K. (1990): Stimmprothese. Patentschrift Nr. DD 275183 A1, Aktenzeichen WP A 61 F, 17.01.1990 |
| [5] | Haberland, E.-J., Berghaus, A., Füting, M., Bethge, I., Grellmann, W.: Material parameters and ESEM characterization of functional ENT prostheses during ongoing degradation. In: Grellmann, W., Seidler, S. (Eds.): Deformation and Fracture Behaviour of Polymers. Springer, Berlin Heidelberg (2001) pp. 451–460 (ISBN 978-3-540-41247-2; e-Book (2013): ISBN 978-3-662-04556-5; see AMK-Library under A 7); https://doi.org/10.1007/978-3-662-04556-5 |
| [6] | Bierögel, C.: Testing the application behaviour of pharyngotracheal voice prostheses. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2025) 3rd Edition, pp. 629–632 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22) |