Plastic dentures hit the dentistry market

An increasing number of plastics companies are looking to develop products for the dental market. Amongst them is Dens3000, a Germany-based firm, which manufactures two-component PMMA teeth for dentures.

Dens3000 teeth, which the company says closely resemble natural human teeth in shape and structure, are made by injection moulding biocompatible and monomer-free "Densomid" modified PMMA plastic layers - comprising a core material and an outer "enamel" layer - of different hardness and colour.

According to patents covering the artificial tooth design, the core material can be a thermoplastic filled with siliceous glass, quartz and hydroxylapatite, as well as injection-mouldable polymer-bound ceramics.

Dens3000 says that as the thermoplastic tooth comes directly out of the injection mould and does not require further working, it is "highly cost-effective", costing five to ten times less than artificial teeth produced by the conventional thermosetting plastic ram extrusion method.

The 0.1-0.73g teeth are moulded with 2.5-5.6g shot weights in four 8-cavity moulds, in a cycle time of 22-30 seconds. A full denture set has 28 teeth chosen from 144 samples in 16 different shades, three sizes and various shapes.

The original developer, medical physicist Dr Reinhard Lohse, says: "I wanted to introduce a high-quality yet inexpensive plastic tooth onto the market and so make dentures that appeal to China and eastern European countries, where cost is an important issue."

Aside from cost benefits, Lohse says the PMMA teeth "are also not prone to plaque or crack formation".

Dens3000 teeth have a useful life of around five to ten years. Design features include a "finger", modelled on the human tooth root that stabilises the denture base, while an external palatal/lingual slot at the tooth base and a "retention bore", with integrated undercut, strengthen the denture base to "previously unattainable levels", he says.

Lohse further developed the tooth in partnership with the IWK materials technology and plastics processing institute at Kaiserslautern University, and the Regensburg and Homburg (Saar) university hospitals. After developing production tools and prototypes, Lohse set up the Dens3000 company in 2006.

The teeth are injection moulded on four electric-drive 150-tonne clamp-ing force Arburg Allrounder 520A machines, each equipped with two size 70 injection units. Earlier this year, Arburg said Dens3000 is expected to "shortly" reach full production capacity of 20 million teeth per year.

Dens3000 is also setting up a production site in China, according to the Protonia-IT foundation.

Initial Chinese production is ex-pected to amount to around 40 million teeth per year, with start-up scheduled for October 2011. The project contract is being managed by the DCTA German-Chinese technology exchange foundation.

Plastic materials are also making inroads in dental implants. Here, NT_Trading is using medical grade Vestakeep I PEEK from Evonik to make Dentokeep semi-finished implants, substituting titanium and cobalt-chromium metals. The material provides high implant elasticity and a similar flexing behaviour as bone, making the implants more comfortable for the patient.

Marc Knebel, medical implants sales and marketing manager at Evonik, says injection moulding already substitutes machined semi-finished parts when volumes are sufficiently high, cutting implant production costs.

Knebel adds that since 1999 PEEK has become the most important substitute material for titanium in orthopaedic, cardiovascular and spinal implants, a trend partly driven by the material's high resistance to gamma rays, transparency to x-rays and biocompatibility.