Dental alloys, and later zirconia, have been used in dentistry as frameworks for many years in making crowns and bridges veneered with ceramic e.g. feldspathic porcelain. Such methods of restoring teeth have been extensively studied both in the laboratory and clinically. Although such substructures have excellent strength there remains a large properties mismatch between these materials and bone or dentine e.g. elasticity. Furthermore, other drawbacks have been documented such as possible allergies, colouring of alloy margins, veneer chipping and excessive wear to opposing natural dentition.
Polyaryletherketone (PAEK) thermoplastic biomaterial polymers such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) have been successfully applied in different medical applications with the latter recently being introduced to dentistry as a restorative material. The material is called Pekkton® ivory (Cendres+Métaux, SA, Switzerland) and is proposed to be used for fabricating both monolithic and bi-layered structures veneered with indirect composite resin.
The manufacturer recommends methods similar to well-established restorations such as alloy and ceramic based crowns which makes it a user friendly material for both dental clinics and laboratories. Furthermore, the material’s properties such as high strength, low elastic modulus close to that of dentine, high temperature, chemical, hydrolysis and wear resistance, makes it a promising material for the replacement of tooth material.
There is little published data about this material and hence the aim of this research was to evaluate the manufacturing process, aesthetic properties, structural integrity and durability of bi-layered crowns made from PEKK based thermoplastic high performance polymer (Pekkton® ivory, Cendres+Métaux, SA) and veneered with indirect light cured composite (Vita VM LC, VITA Zahnfabrik H. Rauter GmbH & Co.KG, DE).
The processing route for Pekkton® ivory is either via milling or hot-pressing and the procedures were compared.
The polymer-based restoration was compared to equivalent zirconia and metal based bi-layered restoration systems veneered with either light cured composite resin or feldspathic porcelain.
Optical properties of each crown system were compared using a UV and visible light spectrophotometer. Structural integrity was compared for each system by testing the fracture resistance of the crowns using a universal testing machine and durability was evaluated by testing the fatigue limit and fatigue life using a fatigue chewing apparatus.
The research hypothesis is that the PEKK polymer as anunderlying substructure material will perform equivalently to metal and zirconia substructures when veneered with light cured composite in the aspects of optical properties, strength and durability.
The outcome of the study established a pressing protocol for PEKK using a standard ceramic pressing furnace where the pressed samples showed no
significant differences in the CIEL*a*b* colour values, hardness or biaxial flexural strength to those samples produced via milling.
There was no significant optical difference between the systems compared, the study found no evidence of difference in the CIEL*a*b* colour value of PEKK, zirconia or metal based samples when veneered with the same composite veneer. However, zirconia based groups displayed greater translucency with the composite veneer and feldspathic porcelain veneer.
The fracture resistance of the PEKK and metal composite veneered crowns showed to be comparable, whereas zirconia based crowns demonstrated significantly lower fracture resistance.
The durability of the PEKK composite veneered crowns showed the highest fatigue limit in comparison to the zirconia and metal composite veneered crowns. Similarly they showed the highest survival rate in the fatigue life assessment under the same cyclic load. Furthermore, the fracture mode was significantly different than observed with the zirconia and metal based crowns.
The conclusion was that this material is promising for use as a restorative material and that clinical evaluation should be undertaken.
