Impression Materials

EDENTULOUS IMPRESSIONS

ZOE impression paste and impression plaster
ADV Examples of mucostatic impression materials, do not compress the tissue during seating of tray. Ideal material for taking impression of Edentulous structures.
Disadv Are inelastic, cannot be removed past undercuts without fracturing or distorting.

Solution Use very fluid, light body elastomeric impression materials

ELASTOMERIC IMPRESSION MATERIALS
a) Polysulfide, byproduct water. Custom trays recommended for impression making to reduce quantity of material and hence dimensional changes. Lowest viscosity and so one of the least stiff allowing it to be removed from undercut areas with minimum stress
b)Condensation silicone, byproduct ethyl alchohol
c)Additional silicone/ Polyvinyl Siloxanes. No reaction byproduct but reaction between moisture and residual hydride polymers can lead to production of hydrogen gas which can result in pinpoint voids in gypsum if casts are poured soon after removal from mouth. So wait an hour.
Sulphur in latex/vinyl gloves inhibit the setting of this material. Touching the tooth with gloved finger can inhibit the setting of impression material in critical area producing major distortion
d) Polyether

PUTTY refers to high viscosity materials which are highly filled so that less polymer is present and there is less polymerization shrinkage.

IMPRESSION MAKING
Longer the impression material remains in the mouth, less the distortion on removal
I) Multiple Mix technique
a)LIGHT body material- used with syringe and placed directly on hard and soft tissues
b)HEAVY body material- used in tray to support light body material

II) Monophase or Single Viscosity technique : MEDIUM Viscosity materials are used. Single mix is made and part of it is placed in syringe and part on tray. When the medium viscosity material is pushed through the syringe the viscosity decreases (pseudoplastic property). Material in tray retains its medium viscosity and when seated forces the syringed material past critical areas.

III) Putty Wash Technique:
a) Two step technique: Make a preliminary impression with thick putty material in a stock tray using thin polyethylene sheet as a spacer for light body material. This makes a custom tray in which light body material can be used to make a final wash impression. Some light body material can be placed directly onto the preparation.

b)Single step technique: Light body material is syringed in place and unset putty is seated in a tray and then in mouth. Disadv is that the higher viscosity material may displace the lighter material and the critical areas may be reproduced in putty rather than lighter material and the required detail may not be captured in the material.

Both these techniques have distortion as their problem. Inadequate space for light body or distortion of set putty can cause problems.

POURING THE CAST
a) Two or three dies can easily be constructed as these materials are dimensionally stable. Each successive die will be less accurate than the first.
b)The time interval between the impression pours should be less than 30 mins.
c)Polyvinysiloxane materials are hydrophobic which make it difficult to wet the surface by gypsum forming slurry. Use the surfactant spray to form a bubble free cast.

WORKING AND SETTING TIME
Store or Mix the material on cool slab to increase the working time and then the setting time is decreased in mouth at high temp. Working and setting time decrease as viscosity increases.

DIMENSIONAL STABILITY
Polysulfides and Condensation silicones lose reaction byproducts, water and alcohol respectively, so for maximum accuracy, pour these impressions within 30 mins.
Additional silicone and Polyether can be stored from 24 hours to 1 week.

DISINFECTION
Condensation silicones, Polysulfides and Additional silicones can be disinfected with any EPA disinfectant.
Polyethers are suseptible to dimensional changes if immersed for longer than 10 mins due to absorption of water and leaching of water soluble plasticizer.
Long immersion time with Polyvinylsiloxanes may cause the surfactant to leach out rendering the material less hydrophilic and hence difficult to pour.
Rinse and dry the impression after 10 mins of immersion in disinfectant.
EDENTULOUS IMPRESSIONS

ZOE impression paste and impression plaster
ADV Examples of mucostatic impression materials, do not compress the tissue during seating of tray. Ideal material for taking impression of Edentulous structures.
Disadv Are inelastic, cannot be removed past undercuts without fracturing or distorting.

Solution Use very fluid, light body elastomeric impression materials

ELASTOMERIC IMPRESSION MATERIALS
a) Polysulfide, byproduct water. Custom trays recommended for impression making to reduce quantity of material and hence dimensional changes. Lowest viscosity and so one of the least stiff allowing it to be removed from undercut areas with minimum stress
b)Condensation silicone, byproduct ethyl alchohol
c)Additional silicone/ Polyvinyl Siloxanes. No reaction byproduct but reaction between moisture and residual hydride polymers can lead to production of hydrogen gas which can result in pinpoint voids in gypsum if casts are poured soon after removal from mouth. So wait an hour.
Sulphur in latex/vinyl gloves inhibit the setting of this material. Touching the tooth with gloved finger can inhibit the setting of impression material in critical area producing major distortion
d) Polyether

PUTTY refers to high viscosity materials which are highly filled so that less polymer is present and there is less polymerization shrinkage.

IMPRESSION MAKING
Longer the impression material remains in the mouth, less the distortion on removal
I) Multiple Mix technique
a)LIGHT body material- used with syringe and placed directly on hard and soft tissues
b)HEAVY body material- used in tray to support light body material

II) Monophase or Single Viscosity technique : MEDIUM Viscosity materials are used. Single mix is made and part of it is placed in syringe and part on tray. When the medium viscosity material is pushed through the syringe the viscosity decreases (pseudoplastic property). Material in tray retains its medium viscosity and when seated forces the syringed material past critical areas.

III) Putty Wash Technique:
a) Two step technique: Make a preliminary impression with thick putty material in a stock tray using thin polyethylene sheet as a spacer for light body material. This makes a custom tray in which light body material can be used to make a final wash impression. Some light body material can be placed directly onto the preparation.

b)Single step technique: Light body material is syringed in place and unset putty is seated in a tray and then in mouth. Disadv is that the higher viscosity material may displace the lighter material and the critical areas may be reproduced in putty rather than lighter material and the required detail may not be captured in the material.

Both these techniques have distortion as their problem. Inadequate space for light body or distortion of set putty can cause problems.

POURING THE CAST
a) Two or three dies can easily be constructed as these materials are dimensionally stable. Each successive die will be less accurate than the first.
b)The time interval between the impression pours should be less than 30 mins.
c)Polyvinysiloxane materials are hydrophobic which make it difficult to wet the surface by gypsum forming slurry. Use the surfactant spray to form a bubble free cast.

WORKING AND SETTING TIME
Store or Mix the material on cool slab to increase the working time and then the setting time is decreased in mouth at high temp. Working and setting time decrease as viscosity increases.

DIMENSIONAL STABILITY
Polysulfides and Condensation silicones lose reaction byproducts, water and alcohol respectively, so for maximum accuracy, pour these impressions within 30 mins.
Additional silicone and Polyether can be stored from 24 hours to 1 week.

DISINFECTION
Condensation silicones, Polysulfides and Additional silicones can be disinfected with any EPA disinfectant.
Polyethers are suseptible to dimensional changes if immersed for longer than 10 mins due to absorption of water and leaching of water soluble plasticizer.
Long immersion time with Polyvinylsiloxanes may cause the surfactant to leach out rendering the material less hydrophilic and hence difficult to pour.
Rinse and dry the impression after 10 mins of immersion in disinfectant.

Polysulfide (Coe-Flex,Permlastic)
Advantages High tear resistant,Modest Cost
Disadvantages Long working time,Requires custom tray,Odor,Pour within 1 hour,Stains clothes

Vinyl Polysiloxane (Aquasil,Express/Imprint/Imprint II,Extrude,Polysil)
Advantages One material,Easily seen margins,Pour repeatedly,Stable delay pour
Disadvantages Hydrophobic,No flow If sulcus moist,Low tear strength,High cost,Difficult to pour cast


Polyether (Impergum,Permadyne)
Advantages Fast setting,Least hydrophobic,Easily seen margins,Good stability,Delay pour
Disadvantages Stiff, high modulus, Bitter taste, Needs to block undercuts,Absorbs water,Leaches components,High Cost.

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Fluoride Causes Cavities

Like most drugs, fluoride causes what it purports to cure.

Dentists tell us that drinking “optimal” levels of fluoridated water - 1 part per million or 1 milligram fluoride per liter (quart) - each day, reduces tooth decay without serious side effects. While this dental dogma has never been proven scientifically, research shows, above optimal fluoride levels causes tooth decay and most Americans get more fluoride then they need.

The severe outward sign of fluoride overdose is dental fluorosis - yellow, brown or black stained and/or pitted teeth. Cavities increase in people with severe fluorosis according to a dentistry textbook entitled, “Dentistry, Dental Practice and the Community,” by Burt and Eklund.

This phenomenon has been demonstrated in the United States from National Institute of Dentistry and Craniofacial Research studies in seven communities in northern Illinois. The results of the dental decay examinations, related to fluoride concentrations in drinking water, form a J-shaped curve. With increasing fluoride levels, cavity experience diminishes to a certain point and then starts to rise again, the authors report.

These data suggest that the true relationship between water fluoride levels and dental decay is the J-shaped curve, with the turning point in the J being something between 3 and 4 times the optimal level, they write.

Additionally, protein-calorie malnutrition, iodine deficiency and excessive fluoride increase susceptibility to dental caries, according to the U.S. Surgeon General's first ever Oral Health Report.

The problem is that children already receive above optimum doses of fluoride even without drinking fluoridated water. By 1974 samples of duplicate meals indicated more than ten times as much fluoride as had been found thirty years earlier – and this study didn't factor in fluoride content of snack foods.

Excess fluoride may be contributing to the growing tooth decay problem in the U.S. Even though U.S. children are fluoride saturated from water, air, foods, beverages and dental products, the surgeon general reports that tooth decay is still a major problem and an epidemic in our poor and minority populations. The Centers for Disease Control reports that up to 48% of school children sport dental fluorosis - 4% is severe.

Children from the African country of Uganda have less tooth decay than American children even though most Ugandan children don’t use fluoride toothpaste or even a toothbrush to clean their teeth. In fact, Ugandan children who drink high fluoride water have more tooth decay than their equals in low fluoride districts, according to “Clinical Oral Investigations."

A different paper, presented at a June 2001 meeting of the International Association of Dental Research by Louw, et al, shows the same unexpected results with a different African population. Children drinking 3.0 mg/L water fluoride have more cavities than children drinking .19 and .48 mg/L fluoride.

Americans drink fluoridated water, use fluoridated toothpaste, eat foods and beverages made with fluoridated water, along with fluoride pesticide residues on produce and grains. Fluoride supplements, mouthrinses, treatments, varnishes, and other fluoridated dental products are used profusely in the U.S. And fluoride is a major industrial air pollutant. Fluoride is also a component of many drugs, in teflon and sulfuryl fluoride has replaced methyl bromide as a post-harves fumigant.

The big difference between American and Ugandan children is diet. The basic Ugandan diet is composed of complex carbohydrates, e.g., cooking banana, cassava, potatoes, maize and sorghum eaten at regular meals. About 80% of the children reported no between-meal intake of sugar containing items.

In American, black children have the highest rates and severity of dental fluorosis and have among the highest rates of tooth decay.

Fluoride is neither a nutrient nor essential. Fluorosed teeth contain more fluoride and less calcium than normal teeth, according to A. K. Susheela, Ph.D., Director, Fluorosis Research and Rural Development Foundation, in “A Treatise on Fluorosis.”

Research on about 400,000 Indian children by Teotia and Teotia, indicate that cavities are caused by high fluoride and low dietary calcium intakes, separately and through their interactions.

One would think dentists would be campaigning to have calcium placed in the drinking water but then they might lose the financial support they enjoy from fluoride manufacturers of toothpastes and other dental materials. When dentists endorse fluoride, people buy it.

Dentists report they are seeing more tooth decay among their soda drinking patients despite full fluoride “protection.” Ironically, many soft drinks and juices contain “optimal” fluoride levels because fluoridated tap water is used to make them.

And a study in the Journal of “Contemporary Dental Practice” shows that, among people who drink fluoridated water and use fluoride toothpaste, tooth decay still progresses after snacking on cola, apple juice or sweetened yogurt between meals. However, cavities remineralized (partially reversed) when snacks were whole milk, skim milk, 2% milk, cheddar cheese, plain yogurt and chocolate milk or no snacks at all.

An article in “RDH” (Registered Dental Hygienist) reports, “Dr. Carole Palmer, professor of nutrition and preventive dentistry at Tufts University, says, ‘We’re looking at why these things (nutrition in dentistry) have fallen by the wayside. There was a perception, perhaps, that fluoride had resolved the problem (of caries), but that’s far from the truth. A lack of research and funding in nutrition and oral connections has made it difficult to move forward. But nutritional counseling and diet counseling need to be important components of preventive dental care.’”

Like most things American, fluoride is overblown, over-prescribed, and over-used. Along with the expansion of fast food restaurants and American waistlines, fluoride's expansion into the food supply via the water supply is out of control and may be creating instead of curing tooth decay. It's time to stop water fluoridation. Fluoride can't fix a poor diet
Posted by: SallyStride
http://www.granitebaypt.com/detail/93536.html

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Writing a Personal Statement for Dental School

I have personally been through the process of applying to dental schools for an advanced standing program and I know how it feels when it comes to writing a personal statement especially when you have no clue what to write and what exactly they are looking for. When I was in need, somebody helped me and now its my turn to help others. Before I start, the following views are based on the advices/guidance I was given and from my own personal experience in this journey so far but you are the best judge for yourself.

The personal statement is one of the most important aspects of one's application which unfortunately is overlooked by prospective candidates. They are just worried about hitting the deck with scores above 90. A strong and very well written personal statement can make the all the difference. It is your first introduction to the admissions committee that also demonstrates your writing abilities.They are very experienced and they can actually make out a lot about you without actually seeing you just by reading what reflects from it.

A good personal statement should address why or how you became interested in dentistry, your past achievements and your vision of your future goals.You can mention what you can contribute to a given program if you are selected (this is also a potential interview question).

Why you ? Highlight aspects of your life that set you apart from other international dental graduates. Perhaps you have a unique cultural background that
broadens your perspective.Try to emphasize something about yourself that makes you a little different than the “average” applicant (achievements academically, in sports, any research experience, observership or dental assisting experience,any volunteer experience may not only be in dentistry but for any social cause), this will help you to “stand out from the crowd”. Admissions committees will read hundreds of personal statements; you should write in a way that attracts their attention and keeps them interested in what you have to say.

The personal statement should also allude to your professional aspirations. Be as specific as possible without making up goals. If you have a desire to do research,specialize in a particular area, focus on prevention and public health, or become a general practitioner, say what your professional career ideally would entail. You are not locking yourself into a particular career path by doing this. Everyone realizes that goals can change remarkably over the course of time, but being specific gives an idea about how focused you are.Be professional in your choice of words.

It wont be a bad idea to write a general sop which you can send to all the schools.In case you are very particular about some school then you can modify it a little bit to highlight the attributes that particular school is looking for in you. For instance some schools desire the candidates to have leadership qualities. For such schools write something that shows your leadership abilities, if you ever lead a group etc.You may also like to mention why did you come to US or why you selected this school over others.Find out some key points about that particular program and mention them in you sop. This shows that you are really interested in their program and that you actually did your homework.

Represent yourself accurately and positively.Don't be modest about your strengths and avoid mentioning weaker aspects of your application, such as poor TOEFL or NDBE scores.If there happen to be irregularities in your academic record or any other points which might need explanation, you can write about that but keep it brief and try to keep the main focus of your essay on the positive aspects.

Like any other essay a clear introduction, a body and a conclusion are a must. Make sure it is proofread, spell-checked, and grammatically correct.

You can take professional help also. There are agencies that charge you and write a SOP for you but I feel you are the best person to write about yourself. In case someone is writing for you just make sure you know whats written in your sop and review it before going for an interview. They may pick up few questions from it and ask you to elaborate.

Last piece of advice is that please do not make it too long.Be very precise and clear. With hundreds of students applying to these schools each term no one has the time or the patience to read all the junk. A good personal statement according to me is the one which is just about a page long and yet contains all that shows you as a bright and promising candidate. Some schools also mention that the personal statement be written in particular font size. Check for the requirements and modify accordingly.

All the very Best..!!!!

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