Friday, 28 September 2012

Medical History Questionnaire -Information to give to the dentist


Medical History Questionnaire


Full Name*
Address*



Home Phone*
Work Phone
Mobile Phone
Email*
Date of Birth    (MM/DD/YYYY)*
Health Insurance*

Who referred you to our office?*
When was your last dental visit?*
What has been your concern with previous dental visits?*



Are you being treated for a medical condition?*




Who is your doctor?*



Are you taking any medications or supplements at present, both prescribed or
over the counter? (Please List)*

Do you have, or have you ever had, any of the following medical conditions?
(Hold down Ctl & click to pick multiple conditions)


Additional Information

Please list all known allergies*

Do you smoke?* Yes No

For females, are you pregnant or undergoing fertility treatment? Yes No


Dental Emergencies


Dental Emergencies

How to cope with dental emergencies

Do you know what to do if you were faced with an alarming dental emergency?
What would you do if your tooth fell out, became chipped or split into half? Could you cope with a serious bite to your tongue that involved blood spurting everywhere? What if you broke your jaw or had an object seriously stuck between your gums?


The reality is most people wouldn’t have a clue how to react when faced with such instances and this unknowingness can cause them serious pain and the possibility of losing a tooth. Your best bet is to follow these medical emergencies tips and phone your dentist if it necessary.


·         Bitten tongue
Ouch! If you accidently bit your tongue or lip, clean the area pronto with a piece of cotton or mouth wash. If swelling starts, it’s time to compress a frozen ice pack over the affected area. In more serious instances, uncontrolled bleeding can occur which means you should get to the nearest dental practice or hospital; especially if stitches are required.

·         Obstructed gums
If an annoying piece of food or object happens to be jammed between your teeth, it’s best to try to gently remove it with dental floss. Don’t ever attempt to use a sharp object (such as a toothpick, pin or tweezers), as you risk cutting soft gum tissue. If you have no luck in dislodging the obstruction, contact your dentist.

·         Broken Jaw
Swelling, pain, numbness in the lower lip, oral bleeding and bruises on your chin are all tell-tale signs of a broken jaw. If you feel like you have fractured or injured your jaw in some way, immediately apply a frozen ice pack against the area. This will control further swelling while you make your way to the nearest hospital. Do take pain killers if needed, but avoid aspirin which will instigate bleeding.

·         Damaged tooth
Having a broken or chipped tooth means you need to rinse your mouth out with warm, salty water to kill any germs. Be sure to avoid swallowing any broken remaining parts of your teeth. Apply a frozen ice pack on the affected area if you’re experiencing pain and contact your dentist. If you’ ve cracked a tooth, it’s not as serious if it’s small. 

Do contact your dentist however, as an appropriate diagnosis and filling will be required to treat the cracked tooth.

Thursday, 27 September 2012

Teething - Teething and Eruption


Teething - Teething and Eruption



What is teething?


  • Teething is the final stage of the eruption process.

  • It is during this time that the teeth of infants cut through the gum and become visible in the mouth.

  • The baby will eventually have ten teeth in each jaw, making a total of twenty teeth in the mouth.

             

 Teething "cutting through"                                                                      






                                                               1 year later




What is eruption?


  • Eruption is the process during which teeth grow through bone and push through the gum into the mouth.



Permanent tooth
growing under baby tooth 



 



What are the signs of teething?

  • The main signs of teething are:
    • The gum over the erupting tooth can be swollen and red.
    • A spot of blood may be found where the tooth "cuts" through the gum.
    • The cheek on the side of the erupting tooth can appear flushed.
    • There may be more dribbling than usual.
    • The baby has the need to bite on a hard object.
    • General irritability.
    • Disturbed sleeping patterns.
    • Diarrhoea and fever do not necessarily accompany teething.






Red swollen gum  over 

erupting tooth










How to comfort a teething baby

  • Gently massage the gum with a clean finger.
  • A dummy (pacifier) may have a soothing effect.
  • The baby's need to bite on something hard can be satisfied with a teething ring or a sugar-free rusk.
  • A sugar-free

The Facts About Fillings


The Facts About Fillings


The durability of any dental restoration is influenced not only by the material it is made
from but also by the dentist’s technique when placing the restoration. 

Other factors include the supporting materials used in the procedure and the patient’s cooperation during the procedure.

The length of time a restoration will last depends upon your dental hygiene, home care,
and diet and chewing habits.



Dental Materials Fact Sheet

What About the Safety of Filling Materials?

Patient health and the safety of dental treatments are the primary goals of  dental professionals and our PORUR TOOTH Centre.

The purpose of this fact sheet is to provide you with information concerning the risks and benefits
of all the dental materials used in the restoration (filling) of teeth.

 Your dentist wishes to provide this fact sheet to every new patient and all patients of record only once before beginning any dental filling procedure. As the patient or parent/guardian, you are strongly encouraged
to discuss with your dentist the facts presented concerning the filling materials being considered for your particular treatment.


Allergic Reactions to Dental Materials

Components in dental fillings may have side effects or cause allergic reactions, just like other materials we may come in contact with in our daily lives. The risks of such reactions are very low for all types of filling materials.

Such reactions can be caused by specific components of the filling materials such as mercury, nickel, chromium, and/or beryllium alloys. 

Usually, an allergy will reveal itself as a skin rash and is easily reversed when the individual is not in contact with the material.

There are no documented cases of allergic reactions to composite resin, glass ionomer, resin ionomer, or porcelain. 

However, there have been rare allergic responses reported with dental amalgam, porcelain fused to metal, gold alloys, and nickel or cobalt-chrome alloys.

If you suffer from allergies, discuss these potential problems with your dentist before a filling material is chosen.


*******************************************************************************

Dental Materials – Advantages & Disadvantages

                                                                                                                            

PORCELAIN FUSED  TO METAL

This type of porcelain is a glasslike material that is “enameled” on top of metal shells.  It is tooth colored and is used for crowns and fixed bridges.

Advantages

Good resistance to further
decay if the restoration fits well
Very durable, due to metal
substructure

The material does not cause
tooth sensitivity

Resists leakage because it can
be shaped for a very accurate fit

Disadvantages

• More tooth must be removed
  (than for porcelain) for the metal substructure

• Higher cost because it requires
  at least two office visits and
  laboratory services

GOLD ALLOY

Gold alloy is a gold-colored mixture of gold, copper, and other metals and is used mainly for crowns and fixed bridges and some partial denture frameworks.

Advantages

Good resistance to further
decay if the restoration fits well

Excellent durability; does not
fracture under stress

Does not corrode in the mouth

Minimal amount of tooth needs
to be removed

Wears well; does not cause
excessive wear to opposing teeth

Resists leakage because it can
be shaped for a very accurate fit

Disadvantages

• Is not tooth colored; alloy is yellow

• Conducts heat and cold; may irritate sensitive teeth

• High cost; requires at least two

   office visits and laboratory

PORCELAIN  (CERAMIC)

Porcelain is a glass-like material  formed into fillings or crowns using models of the prepared teeth. 
The material is toothcolored and is used in inlays, veneers, crowns and fixed bridges.

Advantages

❤ Very little tooth needs to be
removed for use as a veneer;
more tooth needs to be removed for a crown because its
strength is related to its bulk(size)

❤ Good resistance to further
decay if the restoration fits well

❤ Is resistant to surface wear but
can cause some  wear on opposing teeth

❤ Resists leakage because it can
be shaped for a very accurate fit.

❤ The material does not cause
tooth sensitivity

Disadvantages

• Material is brittle and can break
under biting forces

• May not be recommended for
molar teeth

• Higher cost because it requires
at least two office visits and laboratory services

NICKEL OR COBALT CHROME ALLOYS

Nickel or cobalt-chrome alloys are mixtures of nickel and chromium. 
They are a dark silver metal color and are used for crowns and fixed bridges and most partial denture frameworks.


Advantages

❤ Good resistance to further
decay if the restoration fits well

❤ Excellent durability; does not
fracture under stress

❤ Does not corrode in the mouth

❤ Minimal amount of tooth needs
to be removed

❤ Resists leakage because it can
be shaped for a very accurate fit.

Disadvantages

• Is not tooth colored; alloy is a
dark silver metal color

• Conducts heat and cold; may
irritate sensitive teeth

• Can be abrasive to opposing
teeth

• High cost; requires at least two
office visits and laboratory services.

• Slightly higher wear to opposing teeth 


GLASS IONOMER CEMENT

Glass ionomer cement is a selfhardening mixture of glass and organic acid. 
t is tooth-colored and varies in translucency.  

Glass ionomer is usually used for -
    - small fillings, 
    - cementing metal and porcelain/metal crowns, liners,and 
    - temporary restorations.

Advantages

❤ Reasonably good esthetics

❤ May provide some help against
decay because it releases fluoride

❤ Minimal amount of tooth needs
   to be removed and it bonds well to
   both the enamel and the dentin beneath the enamel

❤ Material has low incidence of
producing tooth  sensitivity

❤ Usually completed in one dental visit

Disadvantages

• Cost is very similar to composite resin 
(which costs more than amalgam)

• Limited use because it is not
recommended for biting surfaces in permanent teeth

• As it ages, this material may become rough and could
increase the accumulation of  plaque and chance of periodontal disease

• Does not wear well; tends to
crack over time and can be dislodged


RESIN-IONOMER CEMENT

Resin ionomer cement is a mixture of glass and resin polymer and organic acid that hardens with exposure to a blue light used in the dental office. 

It is tooth colored but more translucent than glass ionomer cement. 

It is most often used for small fillings,
cementing metal and porcelain metal crowns and liners.

Advantages

❤ Very good esthetics

❤ May provide some help against
decay because  it releases
fluoride

❤ Minimal amount of tooth needs
to be removed  and it bonds well to both the enamel 
and the dentin beneath the enamel

❤ Good for non-biting surfaces

❤ May be used for short-term
primary teeth restorations

❤ May hold up better than glass
ionomer but not as well as
composite

❤ Good resistance to leakage

❤ Material has low incidence of
producing tooth sensitivity

❤ Usually completed in one dental
visit

Disadvantages

• Cost is very similar to composite resin
 (which costs more than amalgam)

• Limited use because it is not recommended to restore the biting surfaces of adults

• Wears faster than composite and amalgam


DENTAL AMALGAM FILLINGS


Dental amalgam is a self-hardening mixture of silver-tin-copper alloy powder and liquid mercury and is sometimes referred to as silver fillings because of its color.

 It is often used as a filling material and replacement for broken teeth.

Advantages

❤ Durable; long lasting

❤ Wears well; holds up well to the forces of biting

❤ Relatively inexpensive

❤ Generally completed in one visit

❤ Self-sealing; minimal-to-no shrinkage and resists leakage

❤ Resistance to further decay is high, but can be difficult to find in early stages

❤ Frequency of repair and replacement is low


Disadvantages

• Refer to “What About the Safety of Filling Materials”

• Gray colored, not tooth colored

• May darken as it corrodes; may stain teeth over time

• Requires removal of some healthy tooth

• In larger amalgam fillings, the remaining tooth may weaken and fracture

• Because metal can conduct hot and cold temperatures, there may be temporary sensitivity to hot and cold.

• Contact with other metals may cause occasional, minute electrical flow




COMPOSITE RESIN FILLINGS

Composite fillings are a mixture of powdered glass and plastic resin, sometimes referred to as white, plastic, or tooth-colored fillings.   

It is used for fillings, inlays, veneers, partial and complete crowns, or to repair portions of broken teeth.

Advantages

❤ Strong and durable

❤ Tooth colored

❤ Single visit for fillings

❤ Resists breaking

❤ Maximum amount of tooth preserved

❤ Small risk of leakage if bonded only to enamel

❤ Does not corrode

❤ Generally holds up well to the forces of biting depending on product used

❤ Resistance to further decay is moderate  and easy to find

❤ Frequency of repair or replacement is low to moderate

Disadvantages

• Refer to “What About the Safety of  Filling Materials”

• Moderate occurrence of tooth sensitivity;  sensitive to dentist’s method of application

• Costs more than dental amalgam

• Material shrinks when hardened and could lead to further decay and/or temperature sensitivity

• Requires more than one visit for inlays, veneers, and crowns

• May wear faster than dental enamel

• May leak over time when bonded beneath the layer of enamel 





Toxicity of Dental Materials


Dental Amalgam

Mercury in its elemental form is  known to cause reproductive toxicity. 

Mercury may harm the developing brain of a child or fetus.

Dental amalgam is created by mixing elemental mercury (43-54%) and an alloy powder (46-57%) composed mainly of silver, tin, and copper. 

This has caused discussion about the risks of mercury in dental amalgam. Such mercury is emitted in minute
amounts as vapor.

Some concerns have been raised regarding possible toxicity. Scientific research continues on the safety of
dental amalgam. There is scant evidence that the health of the vast majority of people with amalgam is compromised.

The Food and Drug Administration (FDA) and other public health organizations have investigated the safety of amalgam used in dental fillings. The conclusion: no valid scientific evidence has shown that amalgams cause harm to patients with dental restorations, except in rare cases of allergy. 

The World Health Organization reached a similar conclusion stating, “Amalgam restorations are safe and cost effective.”

A diversity of opinions exists regarding the safety of dental amalgams. Questions have been raised about its safety in pregnant women, children, and diabetics. However, scientific evidence and research literature in peer-reviewed scientific journals suggest that otherwise healthy women, children, and diabetics are not at an increased risk from dental amalgams in their mouths.

The FDA places no restrictions on the use of dental amalgam.


Composite Resin

Some Composite Resins include Crystalline Silica, which is  known  to cause cancer.

It is always a good idea to discuss any dental treatment thoroughly with your dentist.



Wednesday, 26 September 2012

Impacted Teeth


Impacted Teeth



 What is an impacted tooth?


An impacted tooth is one that is prevented from growing (erupting) into its correct or normal position. It is usually wedged against another tooth below the gum.

 What causes a tooth to become impacted?



There a many factors that influence the growth pattern of a tooth:

  • The size of the jaw may be too small to allow the tooth to erupt into its correct position.
  • Neighbouring teeth that are out of their normal position, may obstruct the growth path of a tooth, and cause it to become impacted.
  • A layer of bone or a hard cover of gum over the tooth, can also affect the growth process.
  • A tooth may become impacted if it grows in an abnormal direction and position.



Click to enlarge



Which teeth are most likely to become impacted?


  • The teeth most commonly impacted are the 

  • wisdom teeth, and the eye teeth.




What are the signs and symptoms  associated 



with an  impacted tooth?



The signs and symptoms of an impacted tooth are:

Severe pain can be caused by the impacted tooth exerting pressure on other teeth, and on nerves around it.

A partially erupted wisdom tooth may have a flap of gum over it.

Food can become trapped between the tooth and the gum. This can cause a severe infection around the tooth.
This is called a peri-coronitis, and it can be very painful.
It may be painful to open your mouth or to chew.

Temporary relief can be provided by taking an analgesic, and possibly an antibiotic.


There may be no symptoms from a dormant impacted tooth for many years.

A deeply impacted tooth is not visible except on X-ray.






What is the treatment for an impacted wisdom tooth?



  • When an impacted tooth causes pain, or adversely affects the tooth it has impacted against, it will usually be extracted:
  • The tooth blocking the way of the wisdom tooth can be extracted, thereby creating space for the impacted tooth to grow into.
  • When a wisdom tooth is impacted, the opposing wisdom tooth in the other jaw may not be.
  • The normal wisdom tooth will continue to grow after reaching its normal position if there is no opposite tooth for it to chew against. This is termed over-eruption.
  • In these circumstances it may be wise to extract this tooth before it reaches the gum in the opposite jaw.

Over erupted upper tooth


What is the treatment for an impacted eye-tooth (canine)?

Since eye-teeth are very important for dental aesthetics and facial appearance, techniques have been developed to correct their positions.

The gum is cut open to expose the tooth.
The orthodontist attaches a bracket to the tooth, and begins the process of moving it into position with the use of wires, elastics and often the extraction of teeth.

These techniques are generally successful but they do take time.






Dental x-ray


Dental x-ray


A dental x-ray is a picture of the inside of a tooth and bone.



 viewing and interpretation


  • How to read or interpret an X-ray:

  • Soft objects appear black, solid objects are white on x-ray.

  • What you see as grey/black on x-ray:
    • Decay.
    • Abscess.
    • Nerves and blood vessels (the pulp).
    • Gum in the spaces between teeth.
  • What you see as white/cream on x-ray:
    • The enamel.
    • Metal fillings and crowns will be white.
    • The dentine appears as a creamy white colour.

  • Bone has a mottled grey and white appearance. It has a fine white line at its margin around the teeth.


Illustration of x-ray showing  tooth parts and bone


Click to enlarge




                                                            Abscess above root
                                                                 (the dark area)


Click to enlarge




IMPACTED TOOTH



Click to enlarge


Click to enlarge


Digital x-ray imaging




  • When computer technology is applied to the taking of x-rays, it allows the image to be made, stored, retrieved and transmitted to another site in a digital form:

  • The images may be enlarged permitting better diagnosis.

  • They can easily be stored in the computer or printed on paper.

  • The system is thought to considerably reduce exposure to radiation.

  • The use of digital x-ray imaging is increasing rapidly.

  • The processing of x-ray films with developing solutions will become a thing of the past.


Intra-oral computer camera



  • This is a specialised camera system:
  • A thin instrument is moved around the mouth to take the photographs:

  • The picture can immediately be viewed on a computer screen.

  • The picture can be stored for future reference or comparison.

  • Problems can be shown to the patient.

  • The results of treatment can be shown.

  • When cosmetic changes are planned, patients may preview the results before the treatment is decided.

  • This system is increasingly being used for patient education and cosmetic dentistry.
































Dental Anatomy - for all ages.


Dental Anatomy - for students of all ages.





A) Tooth Root -
That portion of a tooth that is embedded in the jawbone. Individual types of teeth characteristically have 1, 2, or 3 roots. Individual roots can be distinct or fused with others.
B) Tooth Crown -
That portion of a tooth that lies above the gum line, and when you look in someone's mouth, the part of their teeth that you see. This is also that part of a tooth that is covered with dental enamel.
C) Tooth Neck -
The area where a tooth's root and crown meet. It's found in the same general area as where a tooth's gum line lies.
D) Enamel -
The white, calcified tissue that covers the crown portion of a tooth. It's the hardest (most mineralized) tissue found in the human body.
E) Dentin -
A calcified tissue that is harder than bone but less mineralized than tooth enamel. Most a tooth's hard internal structure is composed of dentin.


F) Cementum -
A very thin layer of calcified tissue that covers the surface of a tooth's root. The fibers of one side of a tooth's periodontal ligament are anchored in this layer.
G) Dental Pulp -
The soft tissue that lies within the hollow chamber found inside each tooth. It's composed of blood vessels, nerve fibers and connective tissue. Informally, it's often referred to simply as a tooth's "nerve."
H) Alveolar Bone -
That aspect of the jawbone that encases and anchors the roots of teeth. The portion of the jaw where tooth sockets are located.
I) Gingiva -
The oral skin tissue that surrounds the teeth and covers the surface of the jawbones. It is also referred to as gum tissue.
J) Periodontal Ligament -
That tissue that occupies the space between a tooth's root and the bone that surrounds it. It firmly binds the tooth in place within its socket.
K) Pulp Chamber -
The hollow space that lies within the center of a tooth's crown. It is filled with the tooth's pulp tissue.






Tooth Names and Positions.


A. Baby Teeth
Tooth NamesPositions
Front Teeth:
A. Central incisor
B. Lateral incisor
C. Canine or eye tooth
Click to enlarge
Upper Teeth
Back Teeth:
D. First molar
E. Second molar
Click to enlarge
Lower Teeth


A. Permanent Teeth
Tooth NamesPositions
Front Teeth:
1. Central incisor
2. Lateral incisor
3. Canine or eye tooth
Click to enlarge
Upper Teeth
Back Teeth:
4. First premolar
5. Second premolar
6. First Molar
7. Second Molar
8. Third Molar Or Wisdom Tooth
Click to enlarge
Lower Teeth



 The Jaws and Jaw Joints (Temporomandibular Joints / TMJ)


  • The temporomandibular joints are the two jaw joints, one at each side of the face
    • Movement of the lower jaw is made possible by this joint.
    • The upper jaw is called the maxilla and is joined to the temporal bone.
    • The lower jaw is called the mandible or mandibular bone.
    • The term "temporomandibular" refers to the connection between these two bones.
    • Chewing and speech would not be possible without this joint.
Click to enlarge



Monday, 24 September 2012

WHAT PARENTS SHOULD KNOW ABOUT BABIES' TEETH

Kids' Fluoride Needs
===============

So how much fluoride do kids need? In general, kids under the age of 6 months do not need fluoride supplements. 
WE RECOMMEND THAT YOUR BABY'S FIRST VISIT TO THE DENTIST SHOULD BE AT THE AGE OF 6MONTHS.
Your child's 6-month checkup offers a great chance to discuss fluoride supplementation with your doctor.
 If you live in a nonfluoridated area, your doctor or dentist may prescribe fluoride drops, tablets, or vitamins after your baby is 6 months old.
The experts recommend that these fluoride supplements be given daily to kids between the ages of 6 months and 16 years.
 The dosage depends on how much fluoride naturally occurs in the water and the child's age. Only kids living in nonfluoridated areas or those who drink only nonfluoridated bottled water should receive supplements.
What about toothpastes, mouth rinses, and other products that contain fluoride? Here are a few tips:
·         Kids under 2 years old should not use fluoride toothpaste unless instructed to by a dentist or health professional.
·         Kids over age 2 should use an approved fluoride-containing toothpaste. 
     Kids younger than 6 may swallow too much toothpaste while brushing, so we recommend  SUPERVISED BRUSHING and children should be taught to spit, not swallow, toothpaste.
·         Kids should use only a pea-sized amount of toothpaste.
·         Kids under age 6 should never use fluoride-containing mouth rinses. 
    However, older kids at high risk for tooth decay may benefit from using them. Your dentist can talk with you about risk factors such as a family history of dental disease, recent periodontal surgery or disease, or a physical impediment to brushing regularly and thoroughly.
Your family dentist or pediatric dentist (one who specializes in the care of children's teeth) is a great resource for information about dental care and fluoride needs. 
A dentist can help you understand more about how fluoride affects the teeth, and once all of your child's primary teeth have come in, may recommend regular topical fluoride during routine dental visits.
Overexposure to Fluoride
If some fluoride is good, why isn't more fluoride better? As with most medications, including vitamins and mineral supplements, too much can be harmful. Most kids get the right amount of fluoride through a combination of fluoridated toothpaste and fluoridated water or supplements.
Too much fluoride before 8 years of age, a time when teeth are developing, can cause enamel fluorosis, a discoloration or mottling of the permanent teeth. For most, the changes are subtle. In one study, 94% of identified fluorosis cases were very mild to mild. Most cases are due to inappropriate use of fluoride-containing dental products, including toothpaste and mouth rinses. Sometimes kids take daily fluoride supplements but may be getting adequate fluoride from other sources, which also puts them at risk.
If naturally occurring fluoride levels exceed the optimal levels used in community fluoridation programs (0.7 to 1.2 ppm), putting kids under 8 years old will be at risk for severe enamel fluorosis. So in communities where natural fluoride levels are greater than 2 ppm, parents should give kids water from other sources.
We should also recognize that infants need less fluoride than older kids and adults. Some infants may be getting too much fluoride in the water used to reconstitute infant formula. If you're concerned that your infant may be getting too much fluoride, talk with your doctor or dentist, who may recommend ready-to-feed formula or formula reconstituted with fluoride-free or low-fluoride water.
REMEMBER-
PERMISSIBLE FLUORIDE  IN WATER - AVOID FLUORIDE TOOTHPASTE FOR CHILDREN < 8 YRS OLD.
FLUORIDE LEVEL HIGH IN WATER    - AVOID  AND USE BOTTLED WATER.
NO / LOW FLUORIDE IN WATER       - FLUORIDE SUPPLEMENTS ESSENTIAL.

Very rarely, fluoride toxicity can occur when large amounts of fluoride are ingested during a short period of time. Kids under age 6 account for more than 80% of reports of suspected overingestion. Although outcomes are generally not serious, fluoride toxicity sends several hundred children to emergency rooms each year.
Symptoms of fluoride toxicity may include nausea, diarrhea, vomiting, abdominal pain, increased salivation, or increased thirst. Symptoms begin 30 minutes after ingestion and can last up to 24 hours. If you suspect your child may have eaten a substantial amount of a fluoridated product or supplement, call 108 or avail immediate medical attention .
Be sure to keep toothpaste, supplements, mouth rinses, and other fluoride-containing products out of kids' reach or in a locked cabinet. You should also supervise your young child's toothbrushing sessions to prevent swallowing of toothpaste or other fluoridated products.
If you have any questions about your water's fluoride content, the fluoridated products your child uses, or whether your child is receiving too much or too little fluoride, talk to your doctor or dentist.