1. a highly investigated field in current medical research

1. Introduction

Development
of new biodegradable metal implants is a highly investigated field in current
medical research work, since resorption of implants would redundantize a second
intervention. The first use of magnesium as an orthopedic biomaterial was
introduced in the beginning of 20th century 1. Unfortunately those magnesium alloys showed a rapid
corrosion rate and therefore early implant failure. Ever since there have been
many efforts creating special magnesium alloys to decrease this rate 1. AZ91D as one example already shows a good corrosion
resistance. It is said to show 43 times lower corrosion rates, than the daily
allowance of human body magnesium intake, but on the other hand could cause
neurotoxicity 2,
3.

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Magnesium
is a promising biodegradable metal for new implants, since its mechanical and
physical properties resemble the human bone concerning its density, stability
and modulus of elasticity 1,
4. Therefore it is less
likely to lead to stress shielding effects, which are observed in current used alloys
4,
5. Earlier studies
already investigated the good mechanical and corrosion properties of Mg-Ca-Zn
alloys 5-7, plus its components
are just natural occurring elements, which have important metabolism functions 8-10.

Former
reports described beneficial effects to bone strength, growth, callus forming without
inflammatory side effects nearby the implant, which supports fracture healing 1,
4, 11, 12. The daily intake of
Magnesium in adults is around 300-400mg and surplus ones are harmless and can
be easily eliminated with the urine 5,
13, 14.

These
aspects and no need for secondary interventions through resorption makes it the
ideal implant for future maxillofacial surgeries.

 

Yet positive
effects are limited by the physiological blood or plasma environment, which tends
to hydrogen evolution and alkalization through rapid corrosion due to high
chloride amounts 15,
16. This may lead to
delayed healing and necrosis of the tissue through hydrogen bubble forming and
local alkalization 17,
18. Other studies show no
adverse effects of bubble forming 12. Nevertheless, in
order to solve these issues, the decrease of the corrosions rate e.g. by
special alloys seems to be a promising step 6,
17. So far many alloys or
pure magnesium systems show a relatively high corrosion rate, which limits
their clinical application 7.

 

Implants
in oral and maxillofacial surgery have to deal with different environmental
properties through saliva exposure, which contains less chloride amounts than
blood serum and is therefore most likely to resemble lower corrosion rates. 3,
7, 15, 19.

Studies investigating this aspect were finished after 5 days without
respecting longer lasting effects and wound closure 3, 10. Physiological this
occurs on day 4 -14 20 and leads to serum like environmental conditions and therefore altered
corrosion rates. This study investigates on those changing conditions after
wound closure, by using a Hank’s salt solution, which simulates physiological
pH and isotonic salt concentration. The impact of prior saliva exposure on the
corrosion rate after wound closure is unknown and needs to be solved before
application

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