Photocuring of Dental Polymeric Materials Advantages and Disadvantages

Introduction

Caries dentinum is one of the most wide-spread deseases in mankind. It is a
microbiotic/chemical process affecting the hard tissues of the tooth (enamel, dentin, and
cementum). Etiologically it is multicausal, some dominating factors are microorganisms
(streptococci sanguis and mutans) and different carbohydrates (succrose and glucose)
The caries process is rather complicated, involving chemical, physical, as well as
physiological processes. The resulting defects involve all dental hard tissues and the
therapy is based on the removal of decayed substance and substitution with an inert
material. The demands of such materials are extremely high and until now there is no
known material that can fully replace the natural dental tissues. Amalgam has played an
accepted role in dental therapeutics for more than 100 years, and is still responsible for
over 75% of direct posterior restorations today. The reason for its popularity is:

(i) Ease of manipulation, (placing, contouration, finishing, etc.).
(ii) Excellent mechanical properties (particularly resistance to wear).
(iii) No water absorbtion, and excellent resistance to softening in the oral fluid
environment (eg. plastification).
(iv) Virtually no change in volume on hardening and during thermal exposure.
(v) It has a smooth surface texture and low friction.
(vi) It has an acceptable biocompatibiity, and it causes no extensive wear of the opposing
tooth structure.

The reason for its polpularity also lies in its relatively low cost and a service life of up to
20 years and longer. However the deficiences are:
(i) Poor aesthetics. .
(ii) Slow setting behviour.
(iii) Relatively high thermal conductivity (requiring thermal insulation to ptotect the
underlaying pulp tissue).
(iv)Susceptibiity to corrosion and creep (especially in the early stages of hardening).
(v) Release of mercury, (which is toxic).
(vi) Poor margin adaptability (inability to bind to tooth structure) as it acts only as a
mechanical plug.

Traditional amalgams are alloys of silver (66-73 %), tin (25-29%) copper (6-20%)
zinc (up to 2%), and mercury (up to 3%). Under normal service conditions, amalgam as
well as al dental restorations are covered by a thin film of saliva proteins (pellicle) in the
oral cavity. This film excludes direct contact between filling materials and the oral
mucosa,but constitutes a membrane easily permeable to fluids, ions, and larger
molecules.