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Disinfection refers to the destruction of pathogenic micro-organisms, rather than sterilization, which is the complete destruction of all microbial form. This practice is carried out using a cold chemical disinfecting solution. However, was not a regular routine procedure until the late 20th century, when the outbreak of AIDS brought up the need for infection control in dental practice, it was then realized that all items exiting in the dental laboratories should be free from pathogenic micro- organisms; for dental impressions that reasonable meant that they should be disinfected before their shift to the laboratory At the moment most dental schools and hospitals as well as an increasing, though still low, number of practitioners and laboratories disinfect their impression before using them for the construction of casts
Contamination of dental impression with saliva and blood from the oral cavity occurs readily in dental clinics. Direct communication between dental clinics and dental laboratories makes contaminated dental impression difficult material to deal with from the cross infection point of view. Impression materials that have been exposed to infected saliva and blood provide a significant source for cross- contaminated. Microorganisms from the oral cavity can stay alive on the impression surface and can be transferred to the stone casts Washing with water or rinsing in running water does not kill the microorganisms in the impression. When taking into consideration products and methods for disinfecting impression, two main factors are important: the anti bacterial efficacy of disinfecting procedures and the effect of these procedures on the dimensional stability of impression material. Disinfection by immersion has been recognized as more effective and reliable than disinfection by spray
Previous publications investigated the interest in impression materials and disinfection started in 1980 and after two decades, it is now considered very vital to disinfect impression materials in dentistry probably due to rise in infections . The research was readily oriented towards two most important areas, which consist of the main requirements for a disinfectant: the efficiency of the disinfecting solution in eliminating the pathogens and the influence of the disinfection treatment on the properties of the impression material
History of irreversible hydrocolloid (alginate)
There is no confirmation as to the origin or history of impression taking in dentistry. Matthaus Purmann(1648-1711), a German surgeon, appears to have discussed making sketches and wax models from which prosthetic appliances were copied. In another case, a German, Philipp Pfaff (1713-1766), a personal dentist to Frederick the Great of Prussia, was the first to explain a technique of taking impression with sealing wax and pouring with Plaster of Paris to construct a cast. In 1820, the French dentist, C.F Delabarre, introduced the first impression tray, but still use heated wax as an impression medium. In 1925, Alphons Poller, an Austrian, invented "Nogacoll", the first of the reversible hydrocolloids based on agar-agar (a vegetable colloid derived from seaweed), but it was not until 1931 that it was applied to dental impression taking, and called "Denticole". Agar softens when heated and when cooled, and can be reused
These thermoset hydrocolloids, which were derived from unique seaweed off the Japanese coast, were used in Western dentistry up until World war two, when they became unavailable. At the end of the nineteenth century, E.C.C Stanford, a chemist from Scotland, noticed that certain brown seaweed (algae) yielded a peculiar mucous extraction .He named it algin. This natural substance was later known as a linear polymer with numerous carboxyl acid group and named anhydro-B-d-mannuronic acid (also called alginic acid). Alginic Acid (Alaginate, a phycocolloid) and most of the inorganic salts are insoluble in water, but the salts obtained with sodium, potassium, and ammonium, are soluble. When agar impression material became in short supply because of World War 2, follow a line of investigation on chemical-set alginates was accelerated to develop an appropriate substitute. The outcome was the present irreversible hydrocolloid, or alginate impression materials. Chemical processing of brown algae native to North American waters yielded new elastic chemical-set materials with an alginate base. The dry alginate powder when mixed with water forms a sol then sets (gels) to form an irreversible hydrocolloid alginate gel. The wide-ranging use of irreversible hydrocolloid far exceeds that of other impression materials available, because it is simple to use, comfortable for the patient, comparatively low-cost, and does not need highly structured equipment.
Dental impression materials:
A mold of the patient's mouth must first be prepared if a duplicate is to be created. That mold is termed an impression. To make an impression, dental personnel put a soft material e.g. (alginate impression materials) in a small mouth-shaped tray and then place it over the patient's teeth and surrounding tissue, and let it to set. The material is then removed from the mouth and used as a mold for making a duplicate. There are many different types of impression to meet specific needs.
The function of an impression material is to accurately record the dimensions of oral tissues and their spatial relationships. The impression gives a negative reproduction of these tissues. A positive reproduction is obtained by pouring dental stone or other suitable material into the impression and allowing it to harden. The positive reproduction is called a model or cast when large areas of the oral tissues are involved or a die when single or multiple tooth preparations are recorded. Impressions may be taken of portions of a tooth, a single tooth, several teeth, a quadrant of the mouth, or an entire dentulous or edentulous arch.
Irreversible hydrocolloid (dental alginate)
Dental alginate is an elastic impression material. It is an irreversible hydrocolloid. A hydrocolloid is a suspension of medium-sized particles in a water-based solution. An irreversible hydrocolloid is one that cannot be softened after setting without damage to material. Other physical properties are that it has the ability to change from a liquid state (sol) to a semi- solid state (gel) but does not have the ability to change from a semi-solid state to liquid state. Alginate is heat-liable and therefore cannot be sterilized. Physical properties which could be affected by the disinfection process are surface roughness, wettability, and dimensional alteration, commonly termed stability and accuracy. The problem of model deviation can lead to incorrect fitting surface, which amounts to loss of time and extra cost to both dental technician and dentist. The skill or expertise of the dental technician could be undermined by poor replica model.
Presently, all dental alginate impression that is used for construction of models must be disinfected before been send to the dental laboratory. However this process could cause a dimensional change in the dental alginate impression materials.
The aim of this dissertation is to investigate any observable changes (contraction or expansion) that may occur in irreversible hydrocolloid (dental alginate) after immersing in disinfectant solution.
Dental irreversible hydrocolloid (alginate) is the most important dental impression material used worldwide in many clinical procedures. On the other hand, alginate is dimensionally unstable and changes its dimensions after removal from the mouth. When stored for more than ten minutes, alginate begins to distort, and after one to three hours (depending on the product and storage condition) cannot be used for many clinical purposes, especially fixed prosthodontics such as crown and bridges.
The conditions required for ideal properties of dental alginate impression, the material used must fulfils certain criteria such as ease of manipulation and reasonable cost, adequate flow properties, appropriate setting time and characteristics, sufficient mechanical strength not to tear or permanently deform during removal, good dimensional accuracy, acceptability to the patient, safety (not toxic or irritating), no significant degradation of properties as a result of disinfection, compatibility with die and cast materials and good keeping qualities "no deterioration of unused material in the dental office"
ISO 1563:1990 specifies the International Standard for dental alginate impression material, but makes no reference to dimensional accuracy or stability.
ISO 4823:1992 the International Standard for dental elastomeric impression materials, does specify a requirement for dimensional accuracy and stability up to 24 hours( linear change must be less than 1.5%), and sets a method for their determination.
Composition irreversible hydrocolloid (dental alginate) impression material:
The formula of the powder component dental alginate is soluble alginate, usually the sodium salt, reacts with the reactor, calcium sulphate, to form insoluble calcium alginate, which form the gel. A retarder, usually sodium phosphate, preferentially reacts with reactor to prevent the initiation of the reaction to enable the dentist time "working time" to insert the impression into the mouth prior to gelation begins. Once the impression is seated in the mouth, and the retarder is completely consumed, an accelerator (usually potassium titanium fluoride) takes over, and ensures the gelation reaction then proceeds swiftly to full set, to allow early removal from the mouth and.
Dental alginates impression materials have high level of particulate filler to organize physical properties, together with viscosity, and which also have an effect on stability. A useful way to construct a more stable gel is to use particles whose surfaces in solution are charged, resulting in electrostatic stabilization. A lot of oxide particles, such as those of silicone and titanium, contain hydroxyl groups that can hydrolyses in aqueous media to form negatively charged oxide groups, which stabilize the suspension.
The preparation of irreversible hydrocolloid (alginate) impression material should be prepare by taking a proportion and mix material carefully, center filled tray over arch prior to compressing over teeth and work gently and distract patient at some stage in impression procedure. Then leave in mouth for one minute beyond set. Break suction prior to attempting impression taking away from mouth. Then gently remove set impression with a single continuous pull. After that, clean and disinfect impression before pouring making sure that alginate impressions maintain appropriate humidity until impression is poured. Finally, position the impression on flat surface tray side down.
The impressions which are cast are utilized to construct a multitude of different appliance such as study model and working model. This working model can be to construct such as orthodontic appliances, splints, bleaching tray and mouth guards.
The advantages of irreversible hydrocolloid (dental alginate) impression material:
reasonably priced (inexpensive)
Easy to use
Comparatively accurate at recording the size and shape of mouth structures
Used once and sets by a chemical reaction
High elastic recovery.
The disadvantages of irreversible hydrocolloid (dental alginate) impression material:
Reacts irreversibly with water to form a gel
Has a thick, pasty consistency that possibly will reason gagging
Can be unsuccessful to record anatomy or be weakened by incorporation of air in mix
Has poor compressive and tensile strength
Can act in response with the environment to gain or lose water.
The problems that can caused dimensional instability of irreversible hydrocolloid (dental alginate) impression materials:
Dental alginates, like all hydrocolloids, tend to distort with time, as moisture is lost (water) by (evaporation and syneresis) or gain by (imbibition) water, and thereby expand or contract (Miller, 1975). If irreversible hydrocolloid impression materials (dental alginate) expand or contract, the particular prosthesis made on the model produce will not fit in the mouth (Coleman et al., 1979). Even when stored under condition of 100% humidity (to prevent dehydration), dental alginate impression will contract (more slowly), indicating that other processes other than dehydration, including polymerization and syneresis are involved (Miller, 1975). Ideally, dental alginate impression materials should be poured immediately, before these factors can distort the impression materials. However, an unrelated factor, like the (elastic deformation) of dental alginate, or the temporary distortion when it is withdrawn from undercut, prevent immediate pour. This is because it takes time (ten minutes) for the deformed dental alginate to recover from the original proportions of the impression before removal from the mouth .Therefore; the best results are obtained when dental alginate impression materials are poured after 10 minutes to avoid distortion from initial expansion or elastic deformation before one hour.
A practical clinical interest from the point of view of possible imbibitions is that modern 'accepted best practice' procedures required disinfection by immersion of dental impression in water-based disinfectant in order to reduce the risk of transmitting communicable diseases to dental laboratory. Fortunately, many workers have shown that, because the immersion times required to achieve sterility are relatively short, the dimensional changes resulting from disinfection were insignificant but nevertheless, worth reducing. Also, mixing techniques "mechanical versus hand mixing" have been investigated for their effect on dimensional stability, with results confirming there is no significant clinical difference.
In a study conducted by Taylor et al., (2002), the aims of this study was to investigate the effect of disinfection procedures (Perform® and sodium hypochlorite) on the dimensional accuracy and surface quality of four irreversible hydrocolloid impression materials and the resultant gypsum casts. The antibacterial efficacy of the procedures was also studied. Dimensional accuracy was determined from the mean percentage deviation of six measurements taken from casts made from disinfected impressions compared with corresponding measurements from the master model and controls. Statistical analysis of data was determined by analysis of variance. Surface quality was determined using a stainless steel test block in accordance with ISO 1563. The dimensional accuracy of the impression materials tested were of a comparable standard following disinfection. The surface quality of casts taken from Blueprint Cremix impressions were unaffected by the disinfection procedures. The remaining impression materials studied showed greater surface deterioration on casts following disinfection with sodium hypochlorite than immersion in Perform®. All disinfection procedures selected proved appropriate for antibacterial purposes.
In another study by (Jagger et al., 2004), the dimensional accuracy of two model materials; dental stone and plaster of Paris, reproduced from three commonly used impression materials: alginate, polyether and addition-cured silicone were retained by their adhesives in acrylic resin trays and exposed to four disinfectant solutions was evaluated. Ninety casts were used to investigate the effect of the four disinfectants on the dimensional accuracy of alginate, polyether and addition-cured silicone impression material. For each impression material 30 impressions were taken, half were poured in dental stone and half in plaster of Paris. The disinfectants used were Dimenol, Perform-ID, MD-520, and Haz-tabs. Measurements were carried out using a High Precision Reflex Microscope. For the alginate impressions only those disinfected by 5-minute immersion in Haz-tabs solution and in full-strength MD 520 were not adversely affected by the disinfection treatment. All polyether impressions subjected to immersion disinfection exhibited a clinically acceptable expansion. Disinfected addition-cured silicone impressions produced very accurate stone casts. Those disinfected by spraying with fill-strength Dimenol produced casts that were very similar to those left as controls, but those treated by immersion disinfection exhibited negligible and clinically acceptable expansion. The results of the studied demonstrated that the various disinfection treatments had different effects on the impression materials. It is important that an appropriate disinfectant is used for each type of impression material.
Jagger et al., 2007, furthermore investigated and evaluated the dimensional accuracy and dimensional stability of a model dental stone, reproduced from five commonly used impression materials (Aquasil soft putty/Aquasil Ultra LV; Aquasil Monophase; Aquasil Ultra Heavy; Impregum F and Provil putty/ Provil Light CD wash) were retained by their adhesives in acrylic resin trays and exposed to three disinfectant solutions (Perform ID; Haz-Tabs and MD 520). Two hundred models were used to investigate the effect of the three disinfectants on the dimensional accuracy of the five impression materials. Five impressions were taken for each impression material for each disinfection treatment group. Measurements were carried out using a High Precision Reflex Microscope. All materials demonstrated a percentage change in dimensions when subjected to no disinfection when this was compared to the brass master die in which all materials demonstrated a percentage change in dimensional stability when subjected to the different disinfection procedures. The results demonstrated that for all of the materials investigated, the changes in dimensional stability were small in the order of microns. These changes may however be of clinical significance for procedures requiring a high degree of accuracy, for example fixed prosthodontics. The materials respond differently depending on the disinfectant used and it may therefore be appropriate that manufacturers recommend the use of particular disinfectants for their products in order to ensure optimum dimensional accuracy and stability.
Amin et al., (2009), evaluated the effect of disinfecting impression materials on dimensional accuracy and surface quality of the result casts. Impressions of a steel die was constructed according to ANSI/ADA specification No.18 were made with each of alginate, additional cured silicone, condensation cured silicone and zinc oxide eugenol paste, and disinfected consequently by each of 0.2% chlorhexidine gluconate, 1% sodium hypochlorite, 2% gluteraldehyde for 5 minutes, and 0.5% sodium hypochlorite for 10 minutes. Dimensions of the disinfected impressions and their resultant casts were measured using a computerized digital caliper, and the dimensional changes were calculated. Reproduction of detail and surface quality of the resultant casts were assessed by grading casts surfaces according to a specific scoring system. 0.5% sodium hypochlorite was found to produce the least dimensional changes in all the impression materials. Corsodyl produced the maximum changes in both alginate and zinc-oxide eugenol while addition-cured silicon was most affected by Gluteraldehyde and condensation-cured silicon was most affected by Hexana. The dimensional changes, however, were minimal and clinically insignificant. Addition-cured silicon showed the best surface quality and dimensional stability followed by condensation-cured silicon. Alginate and zinc-oxide eugenol had poorer surface quality and were affected to a higher extent by the disinfection procedures. The results were comparable with the standard specifications for dimensional stability. Recommendations were made for the use of 10 minutes immersion in 0.5% sodium hypochlorite as the most appropriate disinfection protocol to the investigated impression materials.
A study by Semensato et al., (2009), investigated a quantitative evaluation of the antimicrobial efficacy of eight different disinfection procedures for irreversible hydrocolloid impressions and the dimensional changes induced by them. Samples were collected immediately after impressions, after the disinfection procedures and over casts and analyzed for bacterial growth. Control, enzyme solutions, acetic acid and ultraviolet irradiation samples showed bacterial growth. Chlorhexidine and 1% sodium hypochlorite presented adequate antimicrobial activity, while 2% sodium hypochlorite solution showed the best results. Dimensional changes were similar to those of the controls in all the tested agents. The results indicated 2% hypochlorite was the most appropriate disinfectant tested.
Materials and Methods
The aim of this project is to evaluate dimensional stability of irreversible hydrocolloid (dental alginate) impression material before immersion in disinfectant solution and after immersion in disinfectant solution in different time.
The materials which were used according to the instruction of respective manufactures are presented in table 1.
Dental alginate impression materials(fast setting) 500g
Disinfectant tablets (HAZ-TABS) 2.5g
Demonized water 1 litter
Instrument and equipment
digital weight scale
The procedure of experiment
The dental alginates were mixed according to manufactures' instruction 8g of powder to 17.5 ml of water (23- or+ 2 C degree/73.5 F - or + 3.5F degree), a standard hand mixing bowl and spatula for 30 second.
The dental alginates were dispended onto the silicon mould (30 second) and kept in bath tray (filled warm water 38+ or- 1 C degree measured by using digital thermometer) for 60 second.
The dental alginates samples were removed and measured the width, the length and the height from three different points.
All dental alginates samples were immersed in disinfectant solution for 5 minute, 30 minute 60 minute and 120 minute.
Heraeus Kulzer,LLC300 Heraeus Way South Bend, The Netherlands
17.5 ml of water /
8 g of powder
Guest Medical, Eden bridge, Kent, U K
1 liter of water/
Table1: The materials which were used according to the instruction of respective manufactures
The results of this dissertation are to illustrate if any observable changes (contraction or expansion) that may occur in irreversible hydrocolloid (dental alginate) after immersion in disinfectant solution. Sixteen rectangular samples (n=16) were prepared from silicon mould. Eight irreversible hydrocolloid (dental alginate) samples were measured before immersed in disinfectant solution and the samples were immersed in disinfectant solution for ten minutes, thirty minutes, one hour and two hours. The other eight dental alginate samples were measured at the same time but in a humid environment then comparison were then made.
One way analysis of variance (ANOVA) was utilized to determine differences between the dimensions of alginate impression materials after immersion in disinfectant solution (P<0.05). Tukey's standardized range test was used to discern accuracy differences among the combined variables. Statistical analyses revealed no significant differences for the dimensions in all samples except in sample 4(height P=0.001) and 7(length P=0.008 and height 0.014) in groups which immersion in disinfection and samples 1(width P=0.003), 4(width P=0.011) and 6(length P=0.003and height P=0.001) relative humidity.
Figure 1: shows the mean width (mm) of samples in groups A, B, C, D and E (immersion in disinfection at different time). Group A as a control group. Group B all samples contract apart from sample 1and minor change in sample 2.Group C all samples are decreased again comparing with group A except sample 1but it is decreased comparing with group B and sample 7 almost the same as in group B. in addition sample 8 slightly expands comparing with group B . Group D sample 7 increased about 0.58mm from control group and slightly increases in samples 6 and 8 but all samples are decreased. Group E samples 1 and 3 almost the same as a control group and samples 2, 6, 7 and 8 are increased but samples 4 and 6 are decreased.
Figure 2: shows the mean length (mm) of samples in groups A, B, C, D and E (immersion in disinfection at different time). Group A as a control group. Group B
Figure 3: shows the mean height (mm) of samples in groups A, B, C, D and E (immersion in disinfection at different time).
Figure 4: shows the mean width (mm) of samples in groups F, G, H, I and J (humid environment at different time).
Figure 5: shows the mean length (mm) of samples in groups F, G, H, I and J (humid environment at different time).
Figure 6: shows the mean height (mm) of samples in groups F, G, H, I and J (humid environment at different time).