Dental materials: 1988 literature review

A comparative evaluation of impact strength of conventionally heat cured and high impact heat cured polymethyl methacrylate denture base resins: an in vitro study

The denture bases made by using polymethyl methacrylates of Acrylic resin family have excellent physical properties, simple to process and easy to reline, rebase and repair. One of the inherent disadvantages of this material is the liability to break during function. The strength assessment of acrylic resins have been made generally by transverse defection tests.

AIM

To evaluate the impact strength valves of certain brands of commercially available denture base resins and suggest their suitability.

MATERIALS AND METHODS

The denture bases we made using polymethyl methacrylates of acrylic resin family because they have excellent physical properties, simple to process and easy to reline and rebase. Six commercial brands of polymethyl meth- acrylate, namely Stellon (DPI-India), Acralyn-H (Asian Acrylate, India), Trevalon (Dentsply-England), Lucitone 199 (Dentsply/ York division), Acralyn-H (Super Unbreakable), Trevalon HI (Dentsply, Detray division, England) were tested by breaking them using Analog Pendulum (ASTM D 256).

RESULTS

From the entire study the maximum impact strength was reported for Acralyn-H super unbreakable (Asian Acrylates, India) 62.19 joules.

CONCLUSION

All the analysis led to conclusion that there is basic change in material composition within and among the different groups of denture base resins.

CLINICAL IMPLICATIONS

The complete dentures made using denture base resins with high impact strength valves (e.g. Acralyn-H super unbreakable) will be more durable and can be used by the patient for considerable period of time, i.e. beyond 4 to 5 years.

Current materials and techniques for direct restorations in posterior teeth. Part 1: Silver amalgam

This paper, the first of two reviewing materials and techniques for direct intracoronal restorations in posterior teeth, deals with the use of silver amalgam. Based on a consensus view on appropriate applications and contraindications for silver amalgam, the toxicity of amalgam and competing materials, financial implications and international legislation, consideration is given to the continued use of this material. It is concluded that silver amalgam still has a place in everyday practice, albeit restricted in comparison to its former use. Amalgam should only be used where it offers clear advantages over other materials. This requirement for use of silver amalgam will continue until true substitutes are developed and evaluated, alternative materials are optimised and dentists are fully trained in the use of adhesive techniques.

The characteristics and performance of dentine bonding agents

Several attempts have been made to synthesise dentine bonding systems, but low bonding strength, increased variance, toxicity and poor hydrolytic stability were some of the disadvantages excluding them from being widely approved. However, many dentine bonding systems are considered to be biocompatible and have become commercially available. These adhesives are thought to have one or two bifunctional agents where one part of the molecule is intended to bond to the inorganic part of the dentine (calcium ions of the apatite), or to the organic part of the dentine (amino and hydroxy groups of the collagen), and the methacrylate part of the molecule is intended to copolymerise with the restorative resin. This review demonstrates that further work is needed to achieve the synthesis of novel dentine bonding agents which bond chemically to dentine by strong covalent bonds, and which are hydrolytically durable and non-toxic to the oral environment.