ISO/DIS 23401-3:2026(en)

ISO/TC 106/SC 2

Secretariat: ANSI

Date: 2025-12-01

Dentistry— Denture lining materials — Part 3: Soft type materials for long-term use

© ISO 2026

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Contents

Foreword iv

Introduction v

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Classification 2

5 Requirements 2

5.1 Shore A hardness, 24 h 2

5.2 Shore A hardness, 30 d 2

5.3 Bond strength 3

5.4 Sorption 3

5.5 Solubility 3

6 Sampling 3

7 Test methods 3

7.1 Ambient conditions for testing 3

7.2 Shore A hardness 3

7.2.1 Apparatus 3

7.2.2 Preparation of test samples 3

7.2.3 Procedure 4

7.2.4 Expression of results 4

7.3 Bond strength 4

7.3.1 Apparatus and materials 4

7.3.2 Preparation of acrylic denture base plates 5

7.3.3 Preparation of test specimens 5

7.3.4 Procedure for tensile testing 5

7.4 Water sorption and solubility 6

7.4.1 Materials 6

7.4.2 Apparatus 7

7.4.3 Preparation of test specimens 8

7.4.4 Procedure 8

7.4.5 Calculation and expression of results 9

8 Requirements for packaging, marking and instructions supplied by manufacturer 9

8.1 Packaging 9

8.2 Marking and manufacturer's instructions for use 9

Bibliography 12

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

ISO draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.

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This document was prepared by Technical Committee ISO/TC 106, Dentistry, Subcommittee SC 2, Prosthodontic materials, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 55, Dentistry, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This first edition of ISO 23401-3 cancels and replaces ISO 10139-2:2016 which has been technically revised.

The main changes compared to the previous edition are as follows:

— a new standard number has been given.

— in the Introduction, an explanation of the purpose of the grouping work has been added.

A list of all parts in the ISO 23401 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

ISO 23401 consists of the following parts, under the general title Dentistry – Denture lining materials.

— ISO 23401-1

— ISO 23401-2: former ISO 10139-1

— ISO 23401-3: former ISO 10139-2

The purpose of denture lining materials is to improve the fit of dentures to the oral mucosa. The materials can reline the denture the same day. Thus, they can be a useful material for the general denture patients and especially for bedridden patients who may have no access to dental surgery.

Denture lining materials are classified in hard type and soft type depending on the hardness of the material. The hard type materials are mainly used when the denture in use no longer fits the morphology of the oral mucosa, while the soft type materials are used for patients who are particularly susceptible to pain in the oral mucosa, and there are two types of materials: short-term materials and long-term materials, depending on the period of use in the mouth.

Soft type denture lining materials for long-term use are classified in this document according to their softness. Although it is not claimed that any particular level of softness is superior to another, this classification is intended to assist clinicians because clinicians will have more information with which to make an informed choice.

On the other hand, denture lining materials intended for chairside use are widely used in clinical practice. Therefore, ISO 23401-1:2023 was developed and published, which specifies requirements and test methods for chairside denture lining materials for hard type.

Subsequent discussions on the need to develop standards for chairside denture lining materials for soft type resulted in a confirmation and agreement that no new standards would be developed, as these are covered by ISO 10139-1:2018 and ISO 10139-2:2016. Based on this resolution, it was decided to review the title of the standard. Additionally, the possibility of integrating standards for denture lining materials including ISO 10139-1:2018 and ISO 10139-2:2016 will be considered. Specific qualitative and quantitative requirements for freedom from biological hazard are not included in this document, but it is recommended that, in assessing possible biological or toxicological hazards, reference be made to ISO 10993-1 and ISO 7405.

Dentistry — Denture lining materials — Part 3: Soft type materials for long-term use

This document specifies requirements for soft type denture lining materials suitable for long-term use and the test methods to determine compliance with these requirements. This document also specifies requirements for packaging, product marking, and instructions for use provided by the manufacturer. These materials may also be used for maxillofacial prostheses.

This document is not applicable to hard type denture lining materials or soft type denture lining materials for short-term use.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 1942, Dentistry — Vocabulary

ISO 3696:1987, Water for analytical laboratory use — Specification and test methods

ISO 6344‑3, Coated abrasives — Determination and designation of grain size distribution — Part 3: Microgrit sizes P240 to P5000

ISO 48‑4, Rubber, vulcanized or thermoplastic — Determination of hardness — Part 4: Indentation hardness by durometer method (Shore hardness)

ISO 8601‑1, Date and time — Representations for information interchange — Part 1: Basic rules

ISO 20795‑1, Dentistry — Base polymers — Part 1: Denture base polymers

For the purposes of this document, the terms and definitions given in ISO 1942, ISO 20795-1 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1

denture lining material

denture base lining material

dental material designed to be used on the intaglio surface of a denture base to modify its adaptation to soft tissues

[SOURCE: ISO 1942:2020, 3.3.5.1, modified — A preferred term has been added.]

3.2

soft type denture lining material

denture lining material (3.1) bonded to the intaglio surface of a denture base to reduce trauma to the supporting tissues

Note 1 to entry: Cured soft type denture lining material is softer than cured denture base material.

[SOURCE: ISO 23401-2:20xx, 3.2, modified — Note 2 to entry has been deleted.]

3.3

long-term use

use for a period of more than 30 d

Soft type denture lining materials for long-term use are classified into the following types according to Shore A hardness of 24 h specimens (5.1) as determined in accordance with 7.2:

— Type A: soft;

— Type B: extra soft.

When 24 h test specimens are subjected to a 5 s Shore A hardness test in accordance with 7.2.3.2, the material shall conform to the requirements for the relevant type as shown in Table 1. For a material to be classified as a particular type, the mean Shore A hardness for at least two of the three specimens shall conform to the requirements for that type, as specified in Table 1. If the results for two or more specimens are greater than 50, the material shall be deemed not to conform to this document.

Table 1 — Shore A hardness, 24 h – 5 s

When 30 d test specimens are subjected to a 5 s Shore A hardness test in accordance with 7.2.3.3, the material shall conform to the requirements for the relevant type as shown in Table 2 for at least two of the three specimens. If the results for two or more specimens are greater than 55 for Type A materials or greater than 35 for Type B materials, the material shall be deemed not to conform to this document.

Table 2 — Shore A hardness, 30 d – 5 s

The bond strength of the lining material to denture base shall be at least 1,0 MPa for eight out of 10 tested specimens for Type A materials and at least 0,5 MPa for eight out of ten tested specimens for Type B materials when tested in accordance with 7.3.

The increase in mass per volume (water sorption) shall not exceed 20 µg/mm³ for at least four out of five tested specimens when the processed lining material is tested in accordance with 7.4.

The loss in mass per volume (water solubility) shall not exceed 3 µg/mm³ for at least four out of five tested specimens when the processed lining material is tested in accordance with 7.4.

If the loss in mass per volume (water solubility) does exceed 3 µg/mm³ for at least two out of five tested specimens when the processed lining material is tested in accordance with 7.4, the manufacturer of the material shall state the amount and the nature of the soluble components in the material.

The test sample shall consist of a retail package, or packages, from the same batch and containing enough material to carry out the specified tests, plus an allowance for any repeat tests, if necessary.

Conduct all tests at (23 ± 2) °C and relative humidity of 30 % to 70 % unless otherwise stated.

7.2.1.1 Mould, suitable for producing test specimens of at least 35 mm diameter and at least 6 mm thick, constructed using a smooth metal or polymer disc as a template. A mould release agent, e.g. Polytetrafluoroethylene (PTFE) spray, may be used to avoid the adherence of material.

7.2.1.2 Water bath, capable of being maintained at (37 ± 1) °C, with water complying with grade 2 of ISO 3696:1987.

7.2.1.3 Shore A hardness equipment, corresponding to ISO 48-4 with a precision of ±1 HS.

7.2.1.4 Timer device, accurate to 0,1 s.

Prepare each test specimen in the mould cavity in accordance with the manufacturer’s instructions. Remove the specimen from the mould (7.2.1.1) and store it in the water bath (7.2.1.2) at (37 ± 1) °C for (24 ± 1) h prior to testing. Prepare the three test specimens.

General

Carry out the test procedure in accordance with 7.2.3.2, 7.2.3.3 and ISO 48-4 on each of the three test specimens. For the measurements, place the specimens on a flat and solid base and lower the Shore A hardness tester (7.2.1.3) gradually onto the surface of the specimen in such a way that the indenter foot just touches the specimen surface. The surface of the specimens and the contact surface of the Shore A hardness tester shall be coplanar. Ensure that the indenter is normal to the specimen surface. Five measurements shall be made for each of the specimens at each testing time. The loading points shall be uniformly distributed on the surface and shall have a distance of at least 5 mm from the edge of the specimen.

Shore A hardness test, 24 h specimen

Remove the specimen from the water bath (7.2.1.2) (24 ± 1 h) after preparation and measure the Shore A hardness immediately. Record the values 5 s after loading, using a timer device (7.2.1.4). Make all recordings within (2 ± 1) min of having removed the specimen from the water bath. Return the specimens to the water bath. Calculate the mean of the five Shore A values for each of the three specimens (results a, b and c).

Return the specimens to the water bath and maintain them in it for an additional 29 d. Change the water every 7 d with water complying with grade 2 of ISO 3696:1987.

Shore A hardness test, 30 d specimen

Remove the specimen from the water bath (7.2.1.2) 29 d ± 6 h after the first testing and measure the Shore A hardness immediately. Record the values 5 s after the loading using a timer device (7.2.1.4). Make all recordings within (2 ± 1) min after having removed the specimen from the water bath. Use fresh loading points and ensure that no measurement is made closer than 2 mm to a previous one. Calculate the mean of the five Shore A values for each of the three specimens (results x, y and z).

Record the test results for each of the three specimens in the format illustrated in Table 3.

Table 3 — Shore A hardness

7.3.1.1 Acrylic denture base material, in accordance with the instruction given in 8.3 g) and complying with ISO 20795-1.

7.3.1.2 Standard metallographic grinding paper, P500 in accordance with ISO 6344-4 (with a median grain size of 30 µm).

7.3.1.3 Water bath, capable of maintaining a constant temperature of (37 ± 1) °C, with water complying with grade 2 of ISO 3696:1987.

7.3.1.4 Collars, made from polyethylene or other non-adhering materials, cut from suitable tubing, with an internal diameter of (10 ± 0,5) mm and a thickness of (3 ± 0,25) mm.

7.3.1.5 Micrometer or calliper, accurate to 0,01 mm and fitted with parallel anvils.

7.3.1.6 Clamp, such as G-cramp or similar.

7.3.1.7 Tensile testing machine, with a vertical set-up, capable of an even displacement of 10 mm/min.

Prepare sufficient plates of the dimension (25 ± 3) mm² and (3 ± 0,5) mm thick of the acrylic denture base material (7.3.1.1) by the method recommended by the manufacturer. Prepare the specimens in gypsum casts using the recommended curing cycle. The plates may be made individually or cut from larger pieces (up to 80 mm × 80 mm).

Maintain the flat surfaces of the plates in plano-parallel configuration while the surfaces are ground (wet) using P500 paper (7.3.1.2) ensuring that the dimensions of the individual plates still conform to the dimensions above. Avoid touching the bonding surface after grinding.

Store the plates for (30 ± 2) d in the water bath (7.3.1.3) at (37 ± 1) °C before use.

Measure the internal diameter of the collar (7.3.1.4) with the micrometer or calliper (7.3.1.5) to a precision of 0,05 mm and use this to calculate the adhesive area, A, in square millimetres.

Use the lining material and the adhesive supplied by the manufacturer according to the instructions for mixing, application and setting.

Immediately after removing the acrylic plates from the storage water, dry as recommended by the manufacturer or by using the method described in 7.4.4.2, and apply the adhesive to both surfaces of the acrylic plates that will be involved in bonding, following manufacturer's instructions. Make sure not to touch the adhesive surface.

Apply the prepared (mixed) soft lining material to the adhesive surfaces of the acrylic plates using slight excess while being confined within the collar (7.3.1.4) (see Figure 1). Clamp (7.3.1.6) the plates during setting. Maintain the clamped arrangement at room temperature (23 ± 2) °C, unless curing at a higher temperature is recommended. At 1 h ± 5 min after application of the soft material to the base, place the bonded specimen into the water bath (7.3.1.3) at (37 ± 1) °C for (23 ± 1) h.

Prepare a minimum of 10 test specimens.

Remove the specimen from the water bath and immediately transfer it to a tensile testing machine (7.3.1.7). Fix the specimen in the testing machine in a vertical alignment. Ensure that no torsion forces are made upon the specimen and keep the specimen in vertical alignment during testing. This may be facilitated using sections of a PMMA rod bonded to the acrylic plates with cyanoacrylate cement (see Figure 1). The PMMA rod may be applied just before testing or immediately after making the bond.

Carry out the tensile test at a displacement rate of 10 mm/min. Record the maximum load, F, recorded during debonding.

Repeat the test for a total of 10 specimens and calculate each bond strength, B, (in MPa) according to Formula (1):

(1)

where

F is the maximum load, in Newtons, before debonding;

A is the adhesive area, in square millimetres.

Key

1 test material (lining material)

2 acrylic denture base plates

3 collar

4 PMMA-rods (optional)

^a Direction of the tensile stress.

Figure 1 — Tensile test setup for bond strength measurement

7.4.1.1 Silica gel, freshly dried according to manufacturer’s instructions or at least 300 min at (130 ± 5) °C.

7.4.1.2 Water, complying with grade 2 of ISO 3696:1987.

Dimensions in millimetres

^a Mould depth (0,5 ± 0,1) mm to form specimen.

Figure 2 — Stainless steel mould and cover for specimen preparation for water sorption and solubility

7.4.2.1 Circular stainless steel mould and cover, having the dimensions shown in Figure 2, mounted in gypsum in separate halves of a denture flask.

7.4.2.2 Circular stainless steel ring, with an inner diameter of (50,0 ± 0,1) mm and thickness of (0,5 ± 0,1) mm, and glass plate with dimensions of approximately 100 mm × 80 mm × 6 mm.

7.4.2.3 Unplasticized polymer sheet (polyester, polyethylene, or polypropylene), having a thickness of (50 ± 25) µm to cover the steel mould (7.4.2.1).

7.4.2.4 Micrometer or dial calliper, accurate to 0,01 mm and fitted with parallel anvils.

7.4.2.5 Rack, to keep the specimens parallel and separated.

7.4.2.6 Two desiccators.

7.4.2.7 Oven, maintained at (37 ± 1) °C.

7.4.2.8 Timer, accurate to 1 s.

7.4.2.9 Analytical balance, accurate to 0,1 mg.

7.4.2.10 Polymer-coated tweezers.

7.4.2.11 Towel, clean and dry.

Prepare the material in accordance with the instructions for use specified by the manufacturer. Use either the mould and cover (7.4.2.1) or the steel ring (7.4.2.2) to prepare the specimen. Place the material immediately into the mould (7.4.2.1) or ring (7.4.2.2) with the unplasticized polymer sheets (7.4.2.3) and glass plate (7.4.2.2) to a slight excess, avoiding air inclusions. Place an unplasticized polymer sheet onto the material in the mould or ring and cover this with cover or glass plate. Retain the unplasticized polymer sheets during the processing cycle.

Measure with a micrometer or dial calliper (7.4.2.4) to ensure that each specimen has a diameter of (50 ± 1) mm and a thickness of (0,5 ± 0,1) mm and that the top and bottom surfaces are flat.

Prepare five specimens.

Conditioned specimens

Place the specimens in the rack (7.4.2.5) inside one of the desiccators (7.4.2.6) containing freshly dried silica gel (7.4.1.1). Store the desiccator in the oven (7.4.2.7) at (37 ± 1) °C for (23 ± 1) h and then remove the desiccator from the oven.

Transfer the specimens kept in the rack directly to the second desiccator which has been supplied with freshly dried silica gel. The second desiccator is kept at (23 ± 2) °C. After (60 ± 10) min in the second desiccator, the specimens are ready for weighing.

Use an analytical balance (7.4.2.9) weigh the specimen to an accuracy of 0,1 mg. Keep the desiccator sealed except for the shortest possible period required for removing and replacing specimens. After all the specimens have been weighed, replace the silica gel in the first desiccator with freshly dried gel and place the desiccator in the oven.

Repeat the cycle described until a constant mass, m₁, to be called the “conditioned mass”, is reached, i.e. until the loss in mass of each specimen is not more than 0,2 mg between successive weighings. At this point, measure the diameter and the thickness of each specimen to an accuracy of 0,01 mm. Calculate the volume, V, of each specimen using the mean of three diameter measurements and the mean of five thickness measurements. The thickness measurements are taken in the centre and at four equally spaced locations around the circumference.

Wet specimens

Immerse the conditioned specimens in water (7.4.1.2) at (37 ± 1) °C for 7 d ± 2 h. After this time, remove the discs from the water with polymer-coated tweezers (7.4.2.10), wipe with a clean, dry towel (7.4.2.11) until free from visible moisture, wave in the air for (15 ± 1) s and weigh (60 ± 10) s after removal from the water (to an accuracy of 0,1 mg). Record the mass as m₂.

Reconditioned specimens

After this weighing, recondition the specimens to constant mass in the desiccator as described in 7.4.4.1. Record the mass of the “reconditioned” specimens as m₃.

It is essential that the same conditions be applied as for the first drying process, using the same number of specimens and the freshly dried silica gel in the desiccators.

Water sorption

Calculate the value for the water sorption, W_sp, for each of the five specimens, expressed in micrograms per cubic millimetre (µg/mm³), using Formula (2):

W_sp = (m₂ − m₃) / V (2)

where

m₂ is the mass of the specimen, in micrograms (µg), after immersion in water (see 7.4.4.2);

m₃ is the reconditioned mass of the specimen, in micrograms (µg) (see 7.4.4.3);

V is the volume of the specimen, in cubic millimetres (mm³) (see 7.4.4.1).

Round off the calculated values for water sorption to the nearest microgram per cubic millimetre (µg/mm³).

Water solubility

Calculate the value for the water solubility, W_sl, for each of the five specimens, expressed in micrograms per cubic millimetre (µg/mm³), using the Formula (3):

W_sl = (m₁ − m₃) / V (3)

where

m₁ is the conditioned mass of the specimen, in microgram (µg) (see 7.4.4.1);

m₃ and V are as given in 7.4.5.1.

Round off the values calculated for water solubility to the nearest 0,1 µg/mm³.

The components shall be supplied in sealed immediate containers made of materials which shall neither contaminate nor permit contamination of the contents. The immediate containers shall be packaged so as to prevent damage or leakage during transit and storage.

An outer package may also be used to present the immediate containers as a single unit.

The outer packages and the immediate containers or wrappings of the components shall be clearly marked with the information given in Table 4.

If the size of the immediate container or package is too small to fit the required information, reference shall be made on the outer package to a leaflet inside where the additional information shall be provided.

Instructions for use shall accompany each package and, shall at a minimum include the information given in Table 4.

Table 4 — Requirements for marking and manufacturer’s instruction

Bibliography

[1] ISO 7405, Dentistry — Evaluation of biocompatibility of medical devices used in dentistry

[2] ISO 10993‑1, Biological evaluation of medical devices — Part 1: Requirements and general principles for the evaluation of biological safety within a risk management process