The document discusses dental casting investments which are materials used to form molds for casting dental alloys. It describes the key properties investments should have including being easily manipulated, having sufficient strength and stability at high temperatures, and allowing for gas escape. It classifies investments based on processing temperature and binder used, and describes the main components - refractory material, binder, and other chemicals. Gypsum-based and phosphate-bonded investments are commonly used for casting gold alloys. The document discusses factors that influence the investments' setting expansion, hygroscopic expansion, and thermal expansion properties.
Dental Ceramics and Porcelain fused to metal isabel
Dental porcelain (also known as dental ceramic) is a dental material used to create biocompatible lifelike dental restorations, such as crowns, bridges, and veneers.
Dental Ceramics and Porcelain fused to metal isabel
Dental porcelain (also known as dental ceramic) is a dental material used to create biocompatible lifelike dental restorations, such as crowns, bridges, and veneers.
brief description about pressable ceramicsCONTENTS: • Introduction • Definition For Dental Ceramics • Definition For Pressable Ceramics • History • Various All Ceramic Systems • Classification • Pressable Ceramics • History • Generation Of Pressable Ceramics • Cerestore – Development Fabrication Advantage Disadvantage 2
3. IPS Empress - Materials And Composition Special Furnace Fabrication Advantage Disadvantage IPS Empress 2- INDICATION Properties Fabrication Method Advantage Disadvantage IPS Emax Press - Microstructure Composition Properties OPC 3G- Development Indication Properties 3
4. INTRODUCTION There have been significant TECHNOLOGICAL advances in the field of dental ceramics over the last 10 years which have made a corresponding increase in the number of materials available. Improvements in strength, clinical performance, and longevity have made all ceramic restorations more popular and more predictable 4
5. DEFINITION FOR DENTAL CERAMICS⁶ An inorganic compound with non metallic properties typically consisting of oxygen and one or more metallic or semi metallic elements (e.g ;Aluminium, Calcium, Lithium, Mangnesium, Potassium, Sodium, Silicon, Tin , Titanium And Zirconium)that is formulated to produce the whole or part of a ceramic based dental prosthesis 5
6. DEFINITION FOR PRESSABLE CERAMICS ⁶ • A ceramic that can be heated to a specified temperature and forced under pressure to fill a cavity in a refractory mold 6
7. HISTORY OF DENTAL CERAMICS ⁶ • 1789-first porcelain tooth material by a French dentist De Chemant • 1774- mineral paste teeth by Duchateau in England • 1808-terrometallic porcelain teeth by Italian dentist Fonzi • 1817- Planteu introduced porcelain teeth in US • 1837- Ash developed improved version of porcelain teeth 7
8. • 1903 – Dr.Charless introduced ceramic crowns in dentistry he fabricate ceramic crown using platinum foil matrix and high fusing feldspathic porcelain excellent esthetics but low flexural strength resulted in failure • 1965- dental aluminous core Porcelain by Mclean and Huges • 1984- Dicor by Adair and Grossman 8
9. 9
10. VARIOUS ALL CERAMIC SYSTEMS Aluminous core ceramics Slip cast ceramics Heat pressed ceramics Machined ceramics Machined and sintered ceramics Metal reinforced system 10
11. MICROSTRUCTURAL CLASSIFICATION⁵ Category 1: Glass-based systems (mainly silica) Category 2: Glass-based systems (mainly silica) with fillers usually crystalline (typically leucite or a different high-fusing glass) a) Low-to-moderate leucite-
Dental casting investment: A material consisting primarily of an allotrope of silica and a bonding agent. The bonding substance may be gypsum (for use in lower casting temperatures) or phosphates and silica (for use in higher casting temperatures). (GPT 8)
direct filling gold... material aspect, types, condensation, cavity design, modifications. detaied seminar for post gradutes.... any doubts or suggestions contact dr.mb@hotmail.com
An investment is a refractory material that is used to form a mould around a wax pattern.
Following the production of a wax pattern either by direct or indirect method; the next stage in many dental procedures involves the investment of the pattern to form a mould.
A sprue is attached to the pattern and the assembly is located in a casting ring. Investment material is poured around the wax pattern while still in a fluid state.
When the investment sets hard, the wax and sprue former are removed by burning out to leave a mould which can be filled with an alloy or ceramic using a casting technique.
Indian Dental Academy: will be one of the most relevant and exciting
training center with best faculty and flexible training programs
for dental professionals who wish to advance in their dental
practice,Offers certified courses in Dental
implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic
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VR與AR技術於醫療領域的可能性及案例分析 (VR & AR Technologies in Medical Applications)宇軒 黃
【跨 X 創 產業小聚】#6
VR技術引爆超世代教學革新:從醫療與教育出發
VR and AR Technologies in Medical Applications
據美國研究機構報告,AR/VR的醫療健康市場到2020年將達25.4億美元,主要來自模擬訓練及康復治療。在未來的健康醫療教育融入虛擬及擴增實境應用中,又可以達到什麼境界?
brief description about pressable ceramicsCONTENTS: • Introduction • Definition For Dental Ceramics • Definition For Pressable Ceramics • History • Various All Ceramic Systems • Classification • Pressable Ceramics • History • Generation Of Pressable Ceramics • Cerestore – Development Fabrication Advantage Disadvantage 2
3. IPS Empress - Materials And Composition Special Furnace Fabrication Advantage Disadvantage IPS Empress 2- INDICATION Properties Fabrication Method Advantage Disadvantage IPS Emax Press - Microstructure Composition Properties OPC 3G- Development Indication Properties 3
4. INTRODUCTION There have been significant TECHNOLOGICAL advances in the field of dental ceramics over the last 10 years which have made a corresponding increase in the number of materials available. Improvements in strength, clinical performance, and longevity have made all ceramic restorations more popular and more predictable 4
5. DEFINITION FOR DENTAL CERAMICS⁶ An inorganic compound with non metallic properties typically consisting of oxygen and one or more metallic or semi metallic elements (e.g ;Aluminium, Calcium, Lithium, Mangnesium, Potassium, Sodium, Silicon, Tin , Titanium And Zirconium)that is formulated to produce the whole or part of a ceramic based dental prosthesis 5
6. DEFINITION FOR PRESSABLE CERAMICS ⁶ • A ceramic that can be heated to a specified temperature and forced under pressure to fill a cavity in a refractory mold 6
7. HISTORY OF DENTAL CERAMICS ⁶ • 1789-first porcelain tooth material by a French dentist De Chemant • 1774- mineral paste teeth by Duchateau in England • 1808-terrometallic porcelain teeth by Italian dentist Fonzi • 1817- Planteu introduced porcelain teeth in US • 1837- Ash developed improved version of porcelain teeth 7
8. • 1903 – Dr.Charless introduced ceramic crowns in dentistry he fabricate ceramic crown using platinum foil matrix and high fusing feldspathic porcelain excellent esthetics but low flexural strength resulted in failure • 1965- dental aluminous core Porcelain by Mclean and Huges • 1984- Dicor by Adair and Grossman 8
9. 9
10. VARIOUS ALL CERAMIC SYSTEMS Aluminous core ceramics Slip cast ceramics Heat pressed ceramics Machined ceramics Machined and sintered ceramics Metal reinforced system 10
11. MICROSTRUCTURAL CLASSIFICATION⁵ Category 1: Glass-based systems (mainly silica) Category 2: Glass-based systems (mainly silica) with fillers usually crystalline (typically leucite or a different high-fusing glass) a) Low-to-moderate leucite-
Dental casting investment: A material consisting primarily of an allotrope of silica and a bonding agent. The bonding substance may be gypsum (for use in lower casting temperatures) or phosphates and silica (for use in higher casting temperatures). (GPT 8)
direct filling gold... material aspect, types, condensation, cavity design, modifications. detaied seminar for post gradutes.... any doubts or suggestions contact dr.mb@hotmail.com
An investment is a refractory material that is used to form a mould around a wax pattern.
Following the production of a wax pattern either by direct or indirect method; the next stage in many dental procedures involves the investment of the pattern to form a mould.
A sprue is attached to the pattern and the assembly is located in a casting ring. Investment material is poured around the wax pattern while still in a fluid state.
When the investment sets hard, the wax and sprue former are removed by burning out to leave a mould which can be filled with an alloy or ceramic using a casting technique.
Indian Dental Academy: will be one of the most relevant and exciting
training center with best faculty and flexible training programs
for dental professionals who wish to advance in their dental
practice,Offers certified courses in Dental
implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic
Dentistry, Periodontics and General Dentistry.
VR與AR技術於醫療領域的可能性及案例分析 (VR & AR Technologies in Medical Applications)宇軒 黃
【跨 X 創 產業小聚】#6
VR技術引爆超世代教學革新:從醫療與教育出發
VR and AR Technologies in Medical Applications
據美國研究機構報告,AR/VR的醫療健康市場到2020年將達25.4億美元,主要來自模擬訓練及康復治療。在未來的健康醫療教育融入虛擬及擴增實境應用中,又可以達到什麼境界?
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
dental Investment materials/ orthodontic course by indian dental academyIndian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
dental Investments 1/ orthodontic course by indian dental academyIndian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
Investment materials developed in the first half of the twentieth century, to give clinically acceptable dental castings. But
Wrongly, many assume that dental casting investment materials have reached a level of development that makes them completely fit for purpose and that the technology is stable.
This is not the case. Casting titanium and it’s requirement for increased precision have given new challenges
Silica exists in 22 different condensed phases. Five of these are amorphous, and 17 are crystalline; the latter are the polymorphs of silica.
Of this group, only one phase, low-temperature quartz, is thermodynamically stable at normal temperature and pressure. Two more, tridymite and low-temperature cristobalite, exist under normal atmospheric conditions as metastable (but actually long-lived) phases
In the investment powder, the binder is calcium sulfate hemihydrate. When the investment sets, the silica is unaffected; the hemihydrate binder combines with water to form dihydrate (gypsum).The set investment consists of fine particles of silica embedded in gypsum crystals.
When this material is heated to the temperatures required for complete dehydration and sufficiently high to ensure complete castings, it shrinks
considerably and occasionally fractures.
The thermal expansion curves of the three common forms of gypsum products are shown in Figure. All forms shrink considerably after dehydration between 200" C and 400" C . A slight expansion takes place between 400" C and approximately 700, and a large contraction then occurs This shrinkage is most likely caused by decomposition and the release of sulfur gases, such as sulfur dioxide. This decomposition not only causes shrinkage but also contaminates the castings with the sulfides of the non-noble alloying elements, such as silver and copper.
Thus it is imperative that gypsum investments not be heated above 700" C (1292" F). However, for gypsum products containing carbon, the maximum temperature should be 650" C (1202" F). In this way, proper fit and uncontaminated alloys are obtained.
Description :
The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and
offering a wide range of dental certified courses in different formats.for more details please visit
www.indiandentalacademy.com
Description :
The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and
offering a wide range of dental certified courses in different formats.for more details please visit
www.indiandentalacademy.com
dental Investment material/ orthodontic course by indian dental academyIndian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
Dental Investments / orthodontic course by indian dental academyIndian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and
offering a wide range of dental certified courses in different formats.for more details please visit
www.indiandentalacademy.com
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Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
micro teaching on communication m.sc nursing.pdfAnurag Sharma
Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
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Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
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Prix Galien International 2024 Forum ProgramLevi Shapiro
June 20, 2024, Prix Galien International and Jerusalem Ethics Forum in ROME. Detailed agenda including panels:
- ADVANCES IN CARDIOLOGY: A NEW PARADIGM IS COMING
- WOMEN’S HEALTH: FERTILITY PRESERVATION
- WHAT’S NEW IN THE TREATMENT OF INFECTIOUS,
ONCOLOGICAL AND INFLAMMATORY SKIN DISEASES?
- ARTIFICIAL INTELLIGENCE AND ETHICS
- GENE THERAPY
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- ETHICAL CHALLENGES IN LIFE SCIENCES
- Prix Galien International Awards Ceremony
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
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NVBDCP.pptx Nation vector borne disease control programSapna Thakur
NVBDCP was launched in 2003-2004 . Vector-Borne Disease: Disease that results from an infection transmitted to humans and other animals by blood-feeding arthropods, such as mosquitoes, ticks, and fleas. Examples of vector-borne diseases include Dengue fever, West Nile Virus, Lyme disease, and malaria.
NVBDCP.pptx Nation vector borne disease control program
Investment materials
1. PRESENTED BY Dr EKTA GARG
MDS 1st YEAR
DEPARTMENT OF
CONSERVATIVE DENTISTRY &
ENDODONTICS
2. An investment can be
described as a
material which is
suitable for forming a
mold into which a
metal or alloy is
appropriately cast.
The procedure for
forming the mold is
described as
3. Easily Manipulated – not only should it be possible to mix & manipulate the
mass readily & to paint the wax pattern easily, but the investment should also
harden within a short time.
Sufficient strength at room temperature – To permit ease in handling &
provide enough strength at higher temperature to withstand the impact force of
the molten metal.
Stability at higher temperature – Investment must not decompose to give off
gases that could damage the surface of the alloy.
Sufficient Expansion – Enough to compensate for shrinkage of the wax
pattern & metal that takes place during the casting procedure.
4. Porosity – Porous enough to permit the air & other gases in the mold cavity to escape
easily during the casting procedure.
Smooth surface – Fine details & margins on the casting.
Ease of Divestment – The investment should break away readily from the surface
of the metal & should not react chemically with it.
Inexpensive
Not be bio hazardous
Reasonable setting time
Long shelf life
6. Refractory material: Usually a form of silicon dioxide, such as
quartz, tridymite, cristobalite or a mixture of these.
Binder material: Common binder used for dental casting gold
alloy is α calcium sulphate hemihydrate, phosphates and ethyl
silicate.
Other Chemicals: Such as sodium chloride, boric acid
potassium sulphate, graphite, copper powder or magnesium
oxide.
7. • Phosphate
bonded
• Silicate bonded
High
temperature
casting
investment
• Gypsum bonded
Low
temperature
casting
investment
CLASSIFICATION
1. Based on processing temperature :-
8. 2. Based on type of
Binder Used
Gypsum bonded
investment
Type I
Type II
Type III
Phosphate bonded
investments
Ethyl silicate
Bonded
investments
9. 3. BASED ON TYPE OF REFRACTORY USED
a.) Silica -
quartz
cristobalite
b.) Magnesium oxide
c.) Zirconia based investments
10. The Gypsum based materials represent
the type traditionally used for
conventional casting of gold alloy inlays,
onlays, crowns, & fixed partial dentures
(FPDs).
11. ADA specification No. 2 for casting investments for dental gold
alloys encompasses three types of investments.
Type I: Employed for the casting of inlays or crowns when the
alloy casting shrinkage compensation is accomplished principally
by thermal expansion of the investment.
Type II: Investments are also used for the casting of inlays or
crowns, but the major mode of compensation is by the hygroscopic
expansion of the investment.
Type III: Used in the fabrication of partial dentures with gold
alloys.
12. Quartz or Cristobalite – Allotropic
forms of silica [ 55 – 75 % ]
alpha– hemihydrate – provides strength and
rigidity serves as a binder [ 25 – 35 %]
Chemical modifiers – 5 %
13. The α-hemihydrate form of gypsum is generally the
binder for investments used in casting gold
containing alloys with melting ranges below
1000°C.
When this material is heated to the temperature
required for complete dehydration and sufficiently
high to ensure complete castings, it shrinks
considerably and frequently fractures.
15. Silica (SiO2) is added to provide a refractory component
during the heating of the investment and to regulate the
thermal expansion.
During the heating, the investment is expected to
expand thermally to compensate partially or totally for
the casting shrinkage of the gold alloy.
If proper forms of silica are employed in the investment,
the contraction of gypsum during heating can be
eliminated and changed to an expansion.
16. Thermal expansion of
four forms of silica
Quartz 575°c
Cristobalite b/w
200°c & 270°c
Tridymite two
inversions occur at
117°c & 163°c
18. Modifying agents, coloring matter, & reducing agents,
such as carbon & powdered copper.
Reducing agents provide a nonoxidizing atmosphere in
the mold when gold alloy is cast.
Some of the added modifiers, such as boric acid, and Na
chloride, not only regulate the setting expansion and the
setting time, but they also prevent most of the shrinkage
of gypsum when it is heated above 300°C.
19. According to ADA specification No. 2 for dental inlay
casting investment, the setting time should not be
shorter than 5 minutes nor longer than 25 minutes.
Usually, the modern inlay investments set initially in 9
to 18 minutes.
Sufficient time should be allowed for mixing and
investing the pattern before the investment sets.
20. The purpose of setting expansion is to aid in enlarging the mold
to compensate partially for the casting shrinkage of the gold.
ADA specification No. 2 for Type I investment permits a
maximum setting expansion ‘in air’ of only 0.6%.
The setting expansion of such modern investment is
approximately 0.4%. It can be regulated by retarders and
accelerators.
A mixture of silica and gypsum hemihydrate results in setting
expansion greater than that of the gypsum products when it is
used alone.
21. Setting expansion is influenced by the exothermic heat
transferred to the pattern.
Variables other than the exothermic heat of reaction also
influence the effective setting expansion.
• As the investment sets, it essentially gains sufficient
strength to produce a dimensional change in the wax
pattern & mold cavity as setting expansion occurs.
• Also, the softer the wax, the greater the effective setting
expansion, because the softer wax is more readily moved
by the expanding investment.
22. One of the methods for expanding the casting mold to compensate
for the casting shrinkage of the gold alloy.
Occurs when the gypsum product is allowed to set when placed in
contact with water.
Greater in magnitude than normal setting expansion
ADA specification No. 2 for Type II investments requires a
minimum setting expansion in water of 1.2% while the maximum
allowed is 2.2%.
23.
24. Factors influencing hygroscopic expansion-
a. Effect of composition-
The magnitude of setting expansion of a dental
investment is generally proportional to the silica content
of the investment.
• Finer the particle size of silica greater the
expansion.
• α-hemihydrate will produce a greater expansion
than β-hemihydrate.
25. b. Effect of water:powder ratio:
The highest the W:P ratio of the original investment
water mixture, the less the hygroscopic setting
expansion.
c. Effect of spatulation:
With most investments, as the mixing time is reduced,
the hygroscopic expansion is decreased.
26. d. Shelf life of the investment:
Older the investment, the lower its hygroscopic
expansion.
e. Effect of time of immersion:
The greatest amount of hygroscopic setting expansion is
observed if the immersion takes place before the initial
set.
27. f. Effect of the amount of water added:
The magnitude of hygroscopic expansion is in direct proportion to
the amount of water added during the setting period until a
maximum expansion occurs, no further expansion is evident
regardless of any amount of water added.
Expansion can be detected when water is poured into a vessel
containing only small, smooth quartz particles. The water is drawn
between the particles by capillary action and thus causes the particle
to separate, creating an expansion.
28. The effect is not
permanent after the water is
evaporated, unless a binder is
present.
The greater the amount of
the silica or the inert filler,
the more easily the added
water can diffuse through the
setting material and the
greater is the expansion.
29. The thermal expansion of a gypsum bonded investment is
directly related to the amount of silica present and to the type of
silica employed. A considerable amount of quartz is necessary to
counterbalance the contraction of gypsum during heating.
The contraction of the gypsum is entirely balanced when the
quartz content is increased to 75%.
The investments containing cristobalite expand earlier and to a
greater extent than those containing quartz.
30. The desirable magnitude of the thermal expansion of a
dental investment depends on its use.
If hygroscopic expansion is to be used to compensate
for the contraction of the gold alloy, as for the Type II
investment. ADA specification No. 2 requires that the
thermal expansion be between 0% and 0.6% at 500°C.
31. However, for Type I investment, which rely principally
on thermal expansion for compensation, the thermal
expansion must be not less than 1% nor greater than 1.6%.
Another desirable feature of an inlay investment is that
its maximum thermal expansion be attained at a
temperature not higher than 700°C. Thus when a thermal
expansion technique is employed, the maximum mold
temperature for casting of gold alloy should be less than
700°C.
32.
33. Factors affecting thermal expansion-
a. Effect of Water:Powder ratio
The magnitude of thermal expansion
is related to the amount of solids
present. Therefore it is apparent that
the more water that is used in mixing
the investments, the less is the
thermal expansion that is achieved
during subsequent heating.
34. b. Effect of chemical modifiers:
The addition of small amounts of sodium, potassium, or
lithium chlorides to the investment eliminates the
contraction caused by the gypsum and increases the
expansion without the presence of an excessive amount
of silica.
35. c. Thermal contraction/cooling
of investment:
When the investment is cooled from
700˚c, its contraction follows the expansion
curve during the inversion of the beta-
quartz or beta crytobalite to its stable alpha
form at room temperature.
On cooling – investment shows overall
contraction as compared to its dimensions
before heating .
On reheating – does not expand to its
previous level – also it can cause cracks &
affect quality of casting .
36. d. Strength:
According to ADA specification No. 2, the compressive
strength for an inlay investment should not be less than
2.4Mpa tested 2 hours after setting.
Heating the investment to 700°C may increase or
decrease the strength as much as 65%, depending on the
composition. The greatest reduction in strength on heating
is found in investments containing sodium chloride.
37. Other gypsum investment considerations:
Fineness:- Finer the investment, the smaller are the surface
irregularities on the casting.
Porosity:- More gypsum crystals present in the set
investment,
less porosity.
More uniform the particle size, greater is its porosity.
Storage:- The investment should be stored in airtight &
moisture
proof containers.
38.
39. As suggested by Skinner (1963) “The definite advan
type of investment is that there is less chance for c
alloy during casting and hence could be the investmen
The present trend is towards the use of less expens
Alloys, most of which require phosphate investments.
The rapid growth in use of metal
ceramic restorations and a higher melting
point alloys have resulted in an increased
use of “phosphate bonded investment.”
41. Filler: silica, in the form of cristobalite, quartz, or a mixture of
the two and in the concentration of approximately 80%.
• The purpose of this filler is to provide high temperature thermal
shock resistance (refractoriness) and a high thermal expansion.
The binder: consists of magnesium oxide and a phosphate
(Monoammonium phosphate).
42. Colloidal silica liquid suspensions are available for use with the phosphate
bonded investments in place of water. For base metal alloys, a 33% dilution of the
colloidal silica is required.
Carbon is often added to the powder to produce clean castings, and facilitate the
‘divesting’ of the casting from the mold.
Water
Exhibit less SE
Hygroscopic expansion
negligible
Colloidal silica
- Exhibit higher SE – useful as
shrinkage more in base metal alloys
.
Can expand hygroscopically
Strength of investment more
43. Setting Reaction
The chemical reaction for the binder system that
causes the investment to set and harden is
NH4H2PO4 + MgO + 5H2O NH4 MgPO4 6H2O
44. MgO+NH4H2PO4+ 5H2O
(NH4MgPO4 .6H2O)n Room Temperature
MgO
NH4H2PO4 Colloidal-type particles
H2O
Prolonged setting at 25°c
or dehydration at 50°c
(NH4MgPO4 .6H2O)n
Dehydrated at 160°c
(NH4MgPO4 .H2O)n
Heated from 300-650°c
(Mg2P2O7)n
Noncrystalline polymeric phase
Mg2P2O7
Heated above 1040°c
Mg3 (P2O4) 2
On heating the binder undergoes the
following thermal reactions :
45. When phosphate bonded investments are mixed with water they
exhibit a shrinkage within essentially the same temperature range
as gypsum bonded investments i.e. 200°c-400°c
This contraction is practically eliminated when a colloidal silica
solution replaces the water.
The early thermal shrinkage of phosphate investments is
associated with the decomposition of the binder, magnesium
ammonium phosphate and is accompanied by the evolution of
ammonia, which is readily apparent by its odor.
Setting and Thermal Expansion
46. Influence of liquid concentration
on setting & thermal expansion.
Thermal expansion of the investment
when mixed with water as compared
to special liquid.
47. Phosphate investments are markedly affected by
temperature. The warmer the mix, the faster it sets.
The setting reaction itself gives off heat, and this
further accelerates the rate of setting. The more
efficient the mixing better the casting in terms of
smoothness and accuracy.
The ideal technique is to mix, as long as possible, yet
have enough time for investing. Mechanical mixing under
vacuum is preferred.
49. HYL SILICATE bonded investments are being us
nstruction of the high fusing base metal partial d
alloys.
e investments are losing popularity because of th
mplicated and time consuming procedures involve
The silica is used as the binder
h may be derived from ethyl silicate or sodium sil
50. POWDER LIQUID It’s a mixture of
Powder – refractory particles of silica , MgO & other
oxides .
For these systems – 2 or more liquids – reacted together
– before being mixed with powder .
51. The REACTION
The silica is first formed by the hydrolysis of ethyl
silicate in the presence of hydrochloric acid, ethyl
alcohol & water. The reaction can be expressed as:
Si (OC2H5) + 4H2O HCl Si(OH)4 + 4C2H5OH
52. Because a polymerized form of ethyl silicate is used, a
colloidal sol of polysilicic acids is expected instead of the
simpler silicic acid sol shown in the reaction- Stage
called - HYDROLYSIS
The second stage of reaction – GELATION .
Sol – mixed with quartz or cristobalite + small amount
of MgO to render the mixture alkaline .
Coherent gel of polysilicic acid formed – accompanied
by slight ‘setting shrinkage’.
53. Third stage – DRYING
Soft gel – dried to a temp. below 168 °C .
During drying – Gel loses alcohol & water – to form
hard concentrated gel of silica particles – tightly
packed together .
Volumetric contraction accompanies drying – “ green
shrinkage” .
54. Process of ethyl silicate-bonded investment is a little
more complicated than that of phosphate type in that care
must be exercised during handling & burnout because
inflammable alcohol is given off.
This type of investment can be heated between 1090°c
and 1180°c and is compatible with the higher fusing
alloys. Its low setting expansion minimizes distortion.
Editor's Notes
The latest evidence indicates that palladium does react with carbon a temperature above 1504°C. Thus, if the temperature exceeds this temperature during casting, a carbon free investment should be used