Complete or partial denture bases are made of hard acrylic-plastic-resin. The bone and soft tissues underneath a denture respond to the pressure of use by resorbing. These hard denture materials retain their relative shape over time, but the underlying tissues do not. These dentures rest on the soft tissue which over time will eventually change (both the soft external tissue and bone underneath) and then the prosthesis will require either a replacement prosthesis or a reline of the hard material in the space created by that change. There are many types of relines and their purposes, as well as their method of application, are different depending on the reason they are used.
Generally there are two types of relines: 1) Chairside application (applied and processed directly to the prosthesis at the appointment) and 2) Laboratory processed (the prosthesis is sent out to the laboratory for indirect processing).
Chairside direct processing is necessary for many reasons, but generally the materials are limited to shorter lives because they are processed/cured either in the mouth or in combination by application in the mouth and under limited pressure and heat for very short times in the office laboratory.
Laboratory processed relines require an impression of the underlying tissue and sending the prosthesis out to a laboratory to have the impression material removed and replaced with a processed reline. This laboratory processed reline can be either soft or hard (most usually hard) and normally results in an excellent fit in a much denser and nicely finished base.
Tissue Conditioner: This is a soft reline material that is used to facilitate healing of the tissue under a prosthesis, like a complete or removable partial denture. These are used for many reasons, which include:
This material is very soft and comforting to the tissue. It is initially very soft and then gradually loses this softness and becomes harder with time. This helps condition the tissue and assists in healing. Due to the nature of the material it is intended for short term use, typically 1 to 2 weeks, but up to 3 weeks in some cases. Since it cannot be brushed and cleaned like a typical hard denture base it will collect more bacteria and fungi as time goes on and must be replaced.
Soft Liner: Sometimes a more definitive soft liner for a denture can be used for longer term care. Soft liners are a tougher and more resilient material than a tissue conditioner. However, soft liners will collect more bacteria and fungi than a hard liner, so even these are recommended for short times, but can function satisfactorily for 6 months or even a year in some cases. It really depends on the type of soft liner and how it was processed (through a chairside application or laboratory process). The most common soft liner is used to bridge the time from the discontinuence of a tissue conditioner until a definitive hard liner can be placed. However, all long term, laboratory processed, soft liners will last less time than hard liners, typically 2 to 3 years. Long term soft liners have several disadvantages:
Hard Liner: Hard liners may be placed chairside or laboratory processed. The hard liner is basically the same as the original processed hard acrylic plastic the denture was originally made from. The laboratory processed hard liner is preferred for many reasons, but mainly because the liners perform like the original denture materials over time. The chairside liners are adequate and can perform well, but as indicated above, are more porous and do not provide the exact fit of the laboratory processed liner.
Over the counter reline materials and adhesives: Over the counter reline materials should not be used as the tissues do not get a proper fit and they do not promote healing. In fact, the tissues continue to get abused and they may cause significant damage to the underlying tissues even though they may feel like they provide temporary relief. There is also an increased risk of infection because adhesives are very hard to remove from tissues. Use of these materials are discouraged. Adhesives may be necessary for short term use, but only when directed by your dentist/Prosthodontist. Since adhesives are very hard to completely remove from the soft tissues (and the denture) and tend to collect bacteria and yeast, they can cause even further problems with your denture(s). Ill fitting dentures need to be evaluated, diagnosed, and treated by a dentist/Prosthodontist.
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