Download A Brief resume of the intended work: Need for the study Recent

A Brief resume of the intended work:
Need for the study
Recent focus on the potential for cross contamination between dental patients and
dental personnel's emphasizes the need for sterile techniques. One common dental
procedure that may cause cross-contamination, especially between patients and dental
personnel's is the making of impression and potential exists for contamination of gypsum
casts that are secured from those impressions.
Microorganisms have been recovered from dental casts under various experimental
and environmental conditions. Therefore disinfecting stone casts should be a part of the
infection control regimen of the dental office and dental laboratory.
The potential for cross-contamination with stone casts is especially prevalent in
prosthodontics because of multiple opportunities for the transfer of infectious agents from
saliva to casts. There fore these casts should be disinfected after each clinical and
laboratory procedures.
Sterilization and disinfection of impressions will probably sacrifice the
dimensional accuracy of the impression due to heat and / or time lapse. A more practical
approach would be, to clean the impression of visible contaminants, such as saliva, make
the stone cast and then disinfect the cast .
Since conventional autoclaving of the cast could easily damage the surface of the
dental stone, and gas sterilization is costly and time consuming , and immersion of the
cast in chemical disinfectant could lead to dissolution of sufficient amount of gypsum to
cause measurable reduction in dimensions of the cast and decrease in the compressive
strength of the dental stone, microwave oven disinfection might provide a convenient
solution.
Review of literature
An invitro and invivo study conducted on high level microwave disinfection of
dental gypsum cast revealed that there was a striking reduction of bacteria on the casts
after 5 minutes of microwave oven irradiation in an ordinary household microwave oven
set at 900 wattage1.
A study was conducted to determine if gypsum casts were potential source of
microbial cross-contamination and it was concluded that high potential exists for
contamination of gypsum casts that were secured from impression and gypsum casts were
source of cross-contamination between patients and dental personnel's2.
A study on microwave sterilization showed that fungi, viruses, and aerobic & anerobic
bacteria including spore formers can easily be killed in a conventional microwave oven
with proper modification and sterilization can be accomplished if the items to be
sterilized are rotated in 3 dimensional manner throughout the microwave cavity3.
A study conducted on microwave oven irradiation of contaminated dental casts
revealed that 20 minutes irradiation of 45 minutes and 24 hours set cast exhibited less
growth of bacillus subtilis and serratia marcescens 4.
Objective of the study
To test whether microwave oven irradiation can disinfect gypsum casts
effectively.
To compare effectiveness of microwave oven disinfection with that of chemical
disinfection of dental gypsum cast.
B Materials and methods:
Source of data.
This invitro study is carried out in Department of Prosthodontic, A.B.Shetty Memorial
Institute of Dental sciences, Deralakatte,Mangalore & Department of Microbiology,
K.S.Hegde Medical Academy, Deralakatte, Mangalore. (No objection certificate will be
taken and enclosed).
Method of collection of data (including sampling procedure ,if any)
Procedure:
80 casts will be made out of standardized study mold using typeIII dental stone
and sterile water. Out of 80 casts 40 casts will be contaminated with 1 ml test suspension
of staphylococcus aureus and other 40 casts will be contaminated with 1 ml test
suspension of Pseudomonas aeruginosa.
Out of the 40 casts contaminated with staphylococcus aureus 20 casts will be
disinfected with microwave oven at 2,450 MHz , 900 wattage for 5 minutes and other 20
casts will be disinfected with 0.5% sodium hypochlorite at Ph 10 by immersion method
for 10 minutes. Out of 20 casts in each group, 10 will be used as experimental group and
other 10 will be used as control group.
Same procedure will be followed for 40 casts contaminated with Pseudomonas
aeruginosa.
All casts will then be submerged in bactotryptic soy broth (TSB) and incubated
aerobically at 37 degree centigrade for 6 hours. TSB dilutions will be prepared from
cultures of each disinfected and undisinfected casts. These dilutions will be inoculated
on tryptone soy agar (TSA) plates and incubated aerobically at 37 0 C for 18 hours. After
incubation of TSA plates , the colony forming units per ml for each cast will be
calculated.
Through out the study all laboratory and bacteriologic procedures will be carried
out in aseptic condition . A standard barrier technique will be used with sterile gloves and
face masks. The study mold, spatulas, mixing bowls will be disinfected with 70% ethanol
before each use.
Statistical method:
The results will be analysed using students t test.
Does the study contain any investigation or intervention to be conducted on
patients or other human beings or animals?
No
Has ethical clearance been obtained from your institution ?
Yes (Ethical Clearance letter Enclosed)
C List of references:
1) Berg E, Nielsen O, Skaug N. High level microwave disinfection of dental casts. Int J
Prosthodont 2005;18:520-525.
2) Leung RA, Schonfeld SE. Gypsum casts as a potential source of microbial crosscontamination. J Prosthet Dent 1983;49:210-211.
3) Rohrer MD, Bulard RA. Microwave sterilization. J Am Dent Assoc 1985;110:194198.
4) Davis DR , Curtis DA, White JM. Microwave irradiation of contaminated
dental casts. Quintessence Int 1989;20:583-585.
5) Kohn WG, Collins AS, Clevland JL,et al. Centers for disease control in
dental health care settings -2003. MMWR Recomm Rep 2003;52:1-61.