Teeth under a Microscope-Enamel

Dental Enamel is the outer part of a tooth; the part you see. It coveres the tooth like a thick eggshell. In baby teeth, it is quite thin. In permanent teeth, it is thicker, roughly 1-2mm. It is very hard. Under a microscope the enamel "rods" are arranged kind of like a stack of lumber with the surface being the ends of the stack. These rods have sort of a keyhole shape in crossection.

In order for a composite filling, sealant or other bonded material to adhere to the enamel, the surface is "etched". This is usually done by applying 37% phosphoric acid solution for about 15-20 seconds and then rinsed off. (No the acid does not hurt. In fact, you can touch it for a good while and nothing will happen. It's acid, but not that strong). The etchant removes inorganic material and parts of the enamel rods whose ends are exposed by demineralization. Yes, if you put an egg into vinegar it will eventually demineralize the eggshell. Same thing here, but a much shorter time, stronger acid and it's only the microscopic surface that is demineralized. This etching produces multiple areas for bonding material to mechanically adhere to the enamel surface. Visually the tooth has a frosted appearance. It's sort of like sandblasting or priming the surface. Bonding agent is then applied, flowing down into this rougher surface. Once curing occurs, this locks into the undercuts, and bonds the material to the tooth.

Unetched Enamel:











Etched Enamel:












Dentin can also be etched, but the bond strength is less than with the enamel. It is much more organic with dental tubules evident on microscopic view. Newer bonding agents bond to enamel and dentin. You can see from these photos how the surface is primed for bonding.
Etched Dentin:



















Here is a good slide show on enamel: Enamel Histology
A good summary of the status of enamel and dentin bonding: JADA Article

Now, is the histology of enamel different with enamel flourosis? with hypoplasia? Basically, yes. That would be whole other post.

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Silver Fillings (Amalgam)

I don't want a silver filling! I hear this from time to time in the office. What are silver fillings (amalgam fillings)? They are sometimes called amalgam because they have a few different things in them amalgamated together to form something new.


Just so you know we do not do amalgam silver fillings anymore in our office and have not for many years. This mainly was a factor of the improvement in the strength and durability of white fillings and patient demand. We have found that the ability of the stonger newer composite white fillings that bond to the tooth (strengthening it) and the cosmetic benefits make it a very desirable restorative material.

Amalgam consists of a powder of ground up mainly silver and copper and some other metals mixed with a little drop of mercury. You shake it all together (amalgamate). After a few seconds of "trituration" the thing is kind of maleable and putty like. It is placed into the cavity preperation and initially hardens in a few minutes. It is very important to note that there is basically no murcury coming out of a silver filling once it is amalgamated. They are quite safe as determined by extensive scientific clinical studies-(See links below.)
Silver fillings were very common in the past and were the standard of care, and still are, because they hold up quite well to biting forces. If a dentist is still doing silver fillings, that is still an acceptable method of treatment. There are a few drawbacks to "silver" fillings: 1. They do not bond to the tooth, they basically just fill the cavity. 2. They are silver so there is a cosmetic concern. Now, how many people are looking at your back teeth trying to see in there? If you know them that well, it probably does not matter what your teeth look like. Still, we are all concerned with appearance and want the most cosmetic solution available. 3. thermal conductivity is better/lower with white fillings.








































See the ADA sites here for more scientific reviewed studies on this sometimes controversial subject:
ADA site on dental filling options
ADA Summary of safety of Amalgam study April 19th issue JADA 2006

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Dental Curing Lights

What is that blue light you are shining in my child's mouth? Dentists are very gadget oriented. We love the newest gizmos some of which are valuable to our clinical practice and some which are not. One of the advances in modern dentistry is the advent of light cured composite restorative materials (in other words-white fillings). The filling material starts out like a putty like substance you place and contour into the cavity preperation. You shine this blue looking curing light onto the material. This causes a polymerization reaction and makes the material get as hard as a rock (harder really) in just a few seconds.


The light is not an ultraviolet light or a laser. Originally, they were a really bright projector bulbs with a loud cooling fan, cords and everything. Now the newer ones are wireless LED's which do not produce much heat. The light travels down a fiberoptic glass bundle to the tooth. (That's the curved rod looking thing). I think most of the cost of the things is making the fiber-optics. They also have reduced the curing times by adjusting the frequency of the light to match the chemical in the material that initiates the reaction-roughly 470nm. Curing times used to be about 40 seconds. The most recent one claims a 5 second cure. That seems a little too short for me, but we will see. They make the thing beep every 10 seconds or so as a timer, so you might hear a mysterious "beep" noise while in the dental office. For all this fancy technology, I tell the kids it's a flashlight, (which it pretty much is).

Oh, this is a short funny video showing the "flat (dead) battery" feature. Of course, I always dress in a tux in the office:



There are some other cool videos out there for different companies version of these lights, especially if you go deeper into their websites. Ivoclar has a Ivoclar James Bond Theme Video-A License to Cure

Light frequency distribution chart courtesy ADA Professional Products Review Vol. 4 Issue 4 2009.

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A Typical Day in Pediatric Dentistry-Part 2

What does a Pediatric Dentist do? I mean, what do we actually do on a daily basis?

In Part One on this, I described without too many specifics, the flow of a normal day. Here are some more specific cases I seem to see almost every day:



1. Teeth coming in behind baby teeth. Every day, I mean every day, a child (or several children) presents with this.

2. Chipped or Fractured Teeth-Usually after a long weekend kids show up with small or large fractures of their teeth. Some we just smooth and some need a composite buildup to restore.

3. Premed or Sedation Cases. These are usually the longer operative cases of the day. These are children who need conscious sedation for the longer or more complicated work they require-this can be anywhere from one tooth to multiple quadrants of dentistry: white fillings, stainless steel crowns, Pulpotomies, extractions, Space Maintainers.

4. Routine operative dentistry-one or two fillings, one crown, a couple of extractions for orthodontic reasons, etc. on more cooperative patients.

5. Occasionally the tooth ache, Ulcer, or other odd things that need a dentist's eye.

6. Orthodontic adjustments-not too many for me as we have a couple orthodontists that handle most cases. Still, I have a few Crossbite corrections etc.

7. AND--of course the many hygiene examinations we do throughout the day. Hospital Cases on Fridays.

What I do not see on a regular basis is something like that that I saw the other day. A "routine" examination of new patient. Yes, one or two cavities, but an evident large swelling in the mandible the size of a golf ball. X-rays, discussions with the other docs in the practice, and finally a referral to an oral surgeon for followup and likely surgical removal of an obvious tumor. Yes, we do see things like that and need to be prepared and educated to make the right decision. That kind of case makes the whole day much more interesting and rewarding.

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Using a tooth to help the blind




I know this sounds weird, but there is a surgical procedure that uses a tooth implanted in the eye to help some types of blindness. It's called..
Osteo-Odonto-KeratoProsthesis

OOKP:
Osteo=Bone
Odonto=Tooth
Kerato=In this case corneal tissue of the eye
Prothesis=artificial replacement of a body part

Here are a few links:

Opthalmology Report-OOKP in Detail

Here is a CNN Report on this:


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Chidren Grinding Their Teeth

"My child grinds their teeth at night, what should I do?" I get this question all the time. In adults it is often called Bruxism. It seems most preschoolers grind their teeth (at least according to their parents). I also see it a lot of this with babies trying out their new teeth. Bottom line, it is usually not a big concern for baby teeth.Teeth grinding in children seems to be very common. Sometimes, continued grinding (usually at night), can cause abnormal wear of the teeth, sometimes it does not.
When it does, I usually see flattening of the baby teeth almost if you had placed them on a sander. Sometimes it can look like back teeth in the photo here sort of like a bowl shape. Sometimes there are associated factors that might aggrivate the situation like esophegeal reflux causing erosion of the enamel.














What to do? Well, even though it sounds awful and eventually can look funny, there is not much you can do. More importantly, usually there is really no need to do anything. As the enamel wears away the teeth flatten out, the dentin (inside more yellow layer) wears away even faster, sometimes leading to funny looking teeth like in the photo. It does not hurt as the pulp "scars" back out of the way about as fast as the kid grinds away the tooth structure. By the time you would see real problems due to lost tooth struture, the teeth naturally fall out. Very few cases I have ever seen where we needed any kind of restorative treatment or extraction.














What about a night guard? I might consider such a thing in adults who are grinding and doing damage to permanent teeth, that is more of a concern, but in kids-no. You would have to remake the thing so often due to growth and the kid would never wear it. Plus, like I stated, there is no real benefit.
"But the noise is driving me crazy!" First, get your pediatric dentist to take a look to make sure what is going on. If everything is ok, the grinding will likely reduce and most of the time go away by the time the permanent molars settle in around 7 or 8 years of age. Oh, a good set of earplugs for the parents does not hurt.

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