flexible dentures ( acetal resin )
TRANSCRIPT
Thermoplastic MaterialsAcetal resin flexible dentures
BYDR.RAMY MOHSEN
Faculty of dentistry Suez canal university
2015
Changes in dental patient’s attitudes and
awareness have been apparent in all aspects of
dentistry, especially aesthetics. This has
increased the demand for not just improved
functional care, but aesthetically functional care.
In removable partial denture fabrication, unsightly
facial clasps have always been a cosmetic
problem .
In such aesthetically demanding situations, various methods to overcome this aesthetic dilemma have included :
-painting of clasps with toothcolored resin
-use of lingually positioned clasps
-use of gingival approaching clasps.
flexible thermoplastic resins were discovered 50 years
back and presently gaining popularity due to improvement
in their physical and mechanical properites.
Research in polymer science has provided us with an
alternative material called “Acetal resin”. Also known as
Polyoxymethylene (POM), thermoflix , acetal resin is
formed by the polymerization of formaldehyde , it’s a
thermoplastic technopolymer with a monomer-free
crystalline structure.
• This material has been shown to have good biocompatibility and this has fostered its use in total hip replacement and as artificial heart valve occluders. It has been used to form a stress-absorbing component in a dental implant system (IMZ).
• Flexible dentures based on acetal resin , began to be used in dentistry in 1971.
• The concept of flexible resins is based on their flexibilty and ability to engage hard and soft tissue for retention.
• Therefore ,for clinical cases such as kennedy’s class I & II, which involves distal extensions , the flexible dentures by engaging severe soft tissue undercuts and clasping the adjacent teeth provides excellent retention .
Technique
• The material is avaliable in two forms as prepackeged cartidges or granular form .
• Thermoplastic resins are manipulated by inection molding technique .
• 1 - Flasking , spruing the pattern.
• 2 - Injection molding technique :
The metallic cartridges containing thermoplastic grains
are heated to plasticize the resin. The cartridges are set
in place into the injecting unit and pressure of 6-8 barrs
is used to force the plasticized resin to fill the mold. the
material is injected under pressure into a mold, without
any chemical reactions. Thermoplastic materials is
melted at tempreatures from 200-250°C .Pressure,
temperature and injecting time are automatically
controlled by the injecting unit.
Why acital resin ?
• Aesthetics :
Thermoflex acetal resin is available in16 tooth colors, comparable to the Vita® Classic Shades , and 3 pink tissue colors.
• Flexibility :
Thermoflex is flexible enough to accommodate even the most complex cases, while providing excellent stability.
Its elastic memory allows the appliance to secure itself into deep undercuts for a rigid,functional hold.
Durability :
• High-abrasion resistance , Low thermal conductance and excellent tensile and shock strength make Thermoflex acetal resin the preferred material for long lasting performance .
• Resistance to organic solvents, oils, alkalis, hot and cold water .
• Non allergenic, non-toxic
• Low modulus of elasticity which allow for its use in larger retentive undercuts than recommended for Cobalt- Chromium alloys . This may be advantageous in clinical situations in which aesthetics or periodontal health are priorities.
• Lighte wight makes patient more comfortable
• High melting point.
Versatility :
• Used alone or in combination with other
materials, Thermoflex acetal resin makes all
types of temporary flexible restorations,
including removable partial dentures and
combination cases with metal or flexible
denture bases such as Lucitone® FRS™.
Indications of flexible materials • Bilateral undercuts
• Allergy to acrylic resin or cobalt-chromium• Patient who don’t want a fixed restoration or metal clasb• Not enough bone for fitting dental implant• Patients with comprised neruo-motor function.
contraindications• Unilateral distal extension• Lower virtical dimensions and closed bite
Another clinical applications • As direct retainers attached to a cobalt-chromium
removable partial denture framework, as well as the supportive components of removable partial dentures.
• Removable partial dentures.
• Post-surgery space maintainers .
• Gingival masks , Provisional crowns and bridges.
• Mouthgards , impression try , opturators.
Disadvantges :• A major drawback is de-bonding of the acrylic
teeth from acetal denture base , acetal does not bond chemically with acrylic resin , so mechanical undercuts are made in each tooth , it can’t be used with patients having low vertical dimensions and closed bite .
• Costly compared to acrylic dentures .
• Difficult to repair ,add teeth to or leline .
