Univ Colorado Practical Exam - Online Preparation!

The University of Colorado School of Dentistry entrance exams will be coming up before you know it! Last year they were on May 2 and May 9, and it will be similar this year. These are the first practical exams for 2010, and there is still time to prepare - but that also means that there is time to do a comprehensive preparation.

This is a good time to take our Online FRT (Fundamentals of Restorative Techniques) program, which is designed to help you prepare for practical examinations.

Check out our dentistCEprogram.com website for a complete description, even including homework assignments that you do at home and send to me so I can evaluate your preparations onto a DVD.

If you can get here, we have 18 day courses early in the year, since people aren't in so much of a last-minute rush, and 9-day programs for those who can't stay out here quite as long. But if you cannot come out even that long - it is highly recommended to take the much less costly online program. If you have done a comprehensive job with the online program - you can even come out for a three-day hands-on, real-time, one-on-one with me to really make sure that you are doing things in the most effective way and safe way - and I will show you how to work more quickly and still get excellent work done.

We offer many ways that you can learn what you need to.

Please don't wait until you get an invitation to a school interview before starting to prepare! First of all, you won't have time to learn what you need to. And, taking the course earlier will definitely help you get the invitation!

February, March and April can be big months for your preparation for these exams - and making sure you know how to do many preparations with precision and confidence, based on a sound knowledge of all principles.

Grading Clinical Examinations

There is always confusion about how clinical examinations are graded. You do a class II amalgam preparation on a patient, for example, and think you have made very few errors and fail, or make many errors and pass, or make a serious error and pass.

We certainly emphasize these issues during our courses - but a lot has to do with the examination itself. There are two distinct ways to grade a clinical procedure - we will call them the "critical error" approach, and the "average error" approach. In the former, the overall grade is given according to the worst thing you did, and in the latter the overall grade is determined by summing the grades in a number of sub-categories, essentially averaging the errors.

I won't here go into the details of deciding between slight and moderate errors, but whether an error is important enough to be considered failing is important.

Let's say you over extend the facial proximal wall AND you underextend the pulpal depth. For the amalgam procedure, if the thickness of amalgam in the isthmus would be inadequate then the lifetime of the restoration is compromised and that is a major, or failing, error. If the facial wall is overextended by .5 mm or so, and the lifetime would not be impacted, then this would be a moderate or still passing error. For some exams the overall grade for the preparation would be failing because there is one major error, but for other exams only the part of the grade associated with internal form is failed, but the outline form category still passes. Overall the preparation could actually pass if other categories had no errors!

We would like to pass the exam, so the "average error" method sounds desirable - but how does Nature grade? In other words, will the preparation pass LIFE? It doesn't really matter how board examiners grade the preparation - what matters is how it will serve the patient. It would be nice if there would be some correspondence. Unfortunately, in the "average error" case there is not - the preparation can pass the exam but the restoration may break and fall out within days. In the "critical error" grading, the preparation will fail the human graders and fail as well in the test of life!

For the now-discontinued California Dental Board Exam - the old Cal Board - the grading was always based on the critical error. The passing rate was somewhat lower than for other exams based on the average error, but the mandate to do better work was paramount.

Interestingly, it is still possible to pass the some board class II procedures even if you damage the adjacent tooth so severely that the pulp is exposed!

Let's work toward having NO errors that are severe enough to compromise the lifetime of the restoration, and then we will deserve to pass our clinical exam and get fairly licensed.

Clinical Exams - Patient Selection

Since the season for clinical licensure exams is starting to come back around again - I thought I would make some comments about patient selection, or lack of selection, as the case may be.

It is important, or critical, to realize that for patient-based exams the choosing of the appropriate patient is much of the exam - you essentially create your own exam. This is reasonable, since the examiners are really checking to see how much dentistry you understand, and the ability to tell what to expect from a certain tooth in a patient is an important clinical skill. In other words, they are grading you on JUDGMENT - and we hope you have good judgment and exercise it, but you must realize also that this can't happen unless you collect data from which you must make that judgment. Many people fall down in the data collection part.

That being said - you are graded largely on your ability to determine that a particular patient case is within your skill range - but what if someone else chooses a patient for you?

If you have someone else choose a patient for you - for example if you get a patient from a patient-finding service - you may not see inside the patient's mouth until the start of the exam. This means that someone else is creating your exam for you! Definitely not the way to go....

There are people that would like to do away with patient-based clinical exams for licensure, and just have typodont and theoretical exercises instead. My main argument against these people is that I have seen thousands of dentists and dental students learn a lot more dentistry as they go through the process of getting ready for a clinical exam, and this would be lost. These examinations are not about how much you know now, but how much you can learn before the exam. Very few U.S. dental school graduates are ready to practice dentistry upon being graduated - but most will reestablish their landmarks and standards and ability to evaluate subtleties in patients as they prepare for these exams - and this takes them toward a more independent patient interaction and understanding.

If clinical exams for licensure in the U.S. were run by their providing you with a patient and asking you to do a certain procedure, you can bet that the hew and cry would be stentorious objecting to this exam format. And yet, if you pay someone to find a patient for you, often this is exactly what you are subjecting yourself to.

But even under these circumstances, your skills at looking at a tooth and deciding what needs to be done and what to watch out for while doing the preparation and restoration, and what are the dangerous aspects of each case, will be paramount in determining your success.

Over the last 10 years we have recorded thousands of patient evaluations involving discussion of prospective patient cases and working through what to expect from each - would they be a reasonable board case or not - would they be an acceptable board case or not.

Now a selected set of these evaluations is available for you ONLINE. Check out dentistCEprogram.com for information about our offering!

Whether you are looking for patients yourself, or using one provided by someone else, you need to know that you are looking at and how it will relate to your skill level. Most people looking at a maxillary first premolar DO don't notice several common situations that can make their lives very miserable indeed. Learn to look, learn to see - only this gives you the opportunity to use good judgment!

Typodont Equilibration

For those who are taking Advanced Standing Entrance (practical) exams, during the on campus interviews, it is going to be a really good idea for you to be aware of what it takes to get a typodont in shape. That means that the proximal contacts are there and passive and the occlusion is reasonable and stable. I discussed in another post the difference between Columbia and Kilgore tpodonts, but didn't really get into how to make each of them good enough for an exam.

While the practical exams are mostly over for this year, the first one for 2010 will probably be in May - at least the Colorado exam was in early May this year, and this comes pretty fast. Those who didn't apply during this season or who are planning to apply next year, should start figuring out some of the issues right away - and one is control of the typodont.

In the next few months I will make a new videotape of typodont equilibration and put it on our DDSeClass.com website, so you can sign up and see how it is done. But there is no definite rule, except the same one that works in the patient's mouth - figure out what the problems are and then invent something that will fix them!

There is, however, a reasonably systematic approach to adjusting a typodont. I will go through some of it here and leave the rest of the details for the eClass. First, I will point out that the other day I equilibrated a student's typodont for the USC exam, and it was really a mess. The typodont was Columbia and only about 2-3 years old, but the teeth I have, which are newly manufactured, did not fit well at all. The problem is that when you put the teeth into the socket and look through the hole in the bottom of the typodont base, the screw hole in the tooth doesn't line up. In this instance the hole in the base must be enlarged so the screw will enter the tooth passively and not break the tooth.

Provided the holes all line up, we need first to tighten all of the screws on the typodont, so that if they are tightened later during equilibration, nothing changes. Also it will prevent rotation, which is a big problem on the anterior teeth. Then I will take out all of the second premolars and the maxillary lateral incisors. At this point I check to see how passive the contact is between the molars in all four quadrants. I also check to see how the contacts are anterior to the removed teeth. Also we need to know if there is room to put the second premolar back in the socket. Sometimes there is more than enough room, and sometimes, like the newer Columbia typodonts, there is not enough room. Then we have to decide which way to move the teeth anterior and posterior to the missing tooth so that there is just the right amount of space to return the premolar, and so that there are good contacts in the anterior and posterior regions, and they are passive contacts.

Sometimes a lot of tilting of the teeth is involved. Sometimes all of the proximal contacts in the anterior and posterior segments are fine, but there is not enough room to return the second premolar. In this case, the second premolar is usually recontoured to fit the space that is available.

I will describe here some techniques for tilting teeth, but I will save the occlusal adjustment for another posting.

If you wish to tilt a premolar mesially or distally, it is usually possible to cut the bottom of the tooth at an angle, so when the screw is tightened, the tooth will tilt accordingly. Sometimes the tooth won't tile because the head of the screw sits on the base in a bad way, so we recut the surface of the base where the head tightens at an angle. For molars it is generally best to take a small piece of aluminum foil (I generally use a strip from the edge of a scalpel blade package) and place it under the tooth, on one side or another. You can also use foil to raise a tooth into occlusion, or to raise AND tilt a tooth at the same time, by using different thicknesses of foil in two different locations. The scalpel foil can be folded a number of times to get different thicknesses. Sometimes I've had to use 5 layers on one side of a tooth and 7 layers on another to get it raised into occlusion, but without the facial cusp (say) too close to the opposing tooth surface.

When we get back into prime practical exam preparation "season" we'll be going over more of these things more carefully and I'll be answering more questions.

It is also relevant that typodont equilibration is important in some Regional Clinical Licensure Examinations, like the CRDTS, but a lot of people don't realize it due to the way the exam is graded.

Kilgore Typodonts

Just a few notes here with respect to the Kilgore versus the Columbia typodonts. Depending on which school you apply to, the practical exam at the interview could involve one or the other, and either could be on a manikin or hand-held. The USC exam that was just held yesterday involved hand-held typodonts - which is actually more complicated for some procedures and a lot less realistic, of course. But if you can do the preparations well in the manikin, you know exactly what to look for as you do the work hand-held - just practice a little.

BUT, the Kilgore and Columbia typodonts are significantly different in several important ways. The nature of the ideal preparations, of course, does not change, but the sensitivity of each typodont to any overextension or carelessness in margin placement is very different.

Mostly, we are looking at Kilgore typodonts for the Northern California schools, but there are others as well. Be sure to ask what typodont they are expecting you to use, and if you supply your own or not. Remember that ALL typodonts have problems with positioning of teeth so that there is good proximal contact, or at least some, and it is not ACTIVE, and that there is good occlusion, with solid vertical stops for posterior preparations.

But you must be aware that for the Kilgore typodont the proximal contacts are positioned much farther toward the facial than for Columbia, and the occlusogingival width of the contact is very small, typically, for the Kilgore. This means that the box for a class II is shifted to the facial with respect to the isthmus, and that very little gingival extension is required to get gingival clearance. In fact, if you are not careful about your pulpal depth, you may have gingival clearance before even making the box!

For the Kilgore, it is generally easier to cut a crown preparation through the proximal contact area without coming too near the adjacent tooth, because the gingival embrasures are so large, but the preparations tend to be shorter than for Columbia, because of the smaller clinical crown. This makes over reduction of the marginal ridges a more serious problem, due to the short resultant walls and limited retention.

For the Columbia, active proximal contacts is a continuing problem - necessitating adjustment of the bottom of the tooth at an angle, recutting the seat of the screw on the back of the base, or placing aluminum foil under one side or the other of the bottom of the tooth, mostly molars in this case. If the adjacent tooth shifts while cutting a class II box, it can cause real problems. To say nothing of the very large contacts occlusogingivally for Columbia, often requiring very deep boxes to get gingival clearance. The newer Columbia typodonts use a different plastic for the base than they used to - exchanging Melamine for, I think, Nylon. This new base does not lend itself well to the adjustments that are necessary to get teeth to fit with only passive proximal contact.

A few days ago I equilibrated an older typodont - only 2 years old - and had to replace most of the teeth with new ones. Normally this would cause difficulties, having to adjust ALL proximal contacts in a sequential fashion, but in this case it was doubly complex, because almost all of the teeth did not fit the screw holes in the base. That is, when you look at the bottom of the tooth through the screw hole in the base, the hole in the tooth is not centered, often points so that the screw will hit the side of the hole in the base (hence tipping the tooth), or the screw will not even go into the tooth. In this case I had to recut the holes in the base in all of these cases - if that were not done and the screw could be tightened into the tooth, the tooth would almost always break. Some of you might have had this problem before - but it is becoming more frequent with Columbia typodonts recently!

If you read this post and find the subject of typodont equilibration important for you now or in the future, with a little encouragement I will make a videotape of the procedure for a couple of typodonts so that you can see some of the techniques that are necessary. Realistically, most students that see how complex this can be, elect to have me do it for them if they are to take their own typodont to an exam. If you use a typodont supplied to you by the school, know at least enough to check it and see if it will make your life more complicated because they did not equilibrate it well enough!

Class II and Class III Composite - Posting #9

Some comments should well be made about composite preparations as they may be found on entrance exams - so far I only know of one that gives the class III and that is U Mich - see another posting. For the USC exam it could well be that the case descriptions that they give you would call for either a composite or amalgam class II filling, and you should know what the criteria are for either. But you should also know how to do them. There are some significant issues that one comes across with these preparations, and, it must be known, that not all examination entities agree on the ideal preparation designs.

For example, the class III composite preparation. Know, first of all, that if you are preparing a typodont tooth, you must have a clear picture of where the decay WOULD be. It's pretty much the same as for a class II, the decay is at the gingival portion of the contact area, but here we enter from a completely different direction. Now there is some question about how much of the contact needs to be involved. In reality, typically, very little of the contact is involved. The incisal margin is generally in contact with the adjacent tooth, but it is not placed too far into the contact - if it is IN contact, that is far enough incisally.

The facial extension is another issue - both for clinical exams and manikin exams. For the patients it is easy to see how far the facial margin will have to be extended, because the surface decalcification is generally found into the facial embrasure, at least far enough so that the facial clearance will allow a bevel to remove the last of it. For a typodont, various approaches may be mandated as to how far the facial margin is extended - there could be the directions "don't break facial contact" - which tells you exactly nothing. Generally, I council my students to extend the facial wall, angled outward, until there is just enough clearance facially so that a facial bevel can be placed all the way to the incisal wall. This most closely duplicates what we commonly find in patients.

Should there be a bevel on the class III margins? All the textbooks say yes. Regional clinical board exams, even for patient-based procedures, generally state that bevels are optional! What does this mean? It really means that you need to decide whether to place a bevel or not. I can picture situations where, just for retention, a bevel would be an absolute clinical requirement. And in all other cases I would still place a bevel for good marginal bonding, good esthetic gradient, and to allow a more conservative preparation that still removes all of the surface decalcification. But be careful about local beliefs here.

For the class II composite preparation it is clear that there should be a gingival bevel - and yet it is rarely done in practice. I sometimes think that the lack of requirements for a bevel on clinical board exams is more a reflection of what the examiners do in their practice - as opposed to what the schools teach. I admit, I have not been in any regional board calibration meetings for years, and never got the chance to ask this question, but that could be it. What will you choose to do in your practice? Personally, I won't place a class II composite when I do not have gingival enamel to bond to, and I will always take that extra 30 seconds to place the bevel - why not?

The other interesting thing about the class II composite preparation is the proximal wall exit angles. If they are flared - i.e. the angle of tooth structure is obtuse, the end of the enamel rods is exposed by the wall itself and no proximal wall bevel is necessary. On the other hand, a more conservative preparation can be made by underextending facially and lingually and then removing the last of the decalcification with the bevel. On the other hand, in the dental community, the burs that are most commonly used for class II preparations are too large to permit a conservative class II preparation anyway - whether amalgam or composite.

So we basically do the class II composite preparation just as we do the amalgam - the same technique exactly, but we flare the proximal walls a little, and bevel the gingival margin. The isthmus width can be smaller, the "axial depth" can be smaller, but otherwise it is the same in most respects.

I'd like to hear about what experiences you might have observing dentistry in the U.S. in the area of composite preparations. Many of my students are dental assistants, and they always have something interesting to say about how dentistry is practiced in their office. Generally, not how it is taught!

Univ of Michigan Entrance Exam

I recently heard from a student who came back from the Univ Michigan practical exam. They were pretty upset with the way the exam was conducted. I'll repeat some of what she said - but this is second hand and should be taken lightly until confirmed. She said that the typodonts were supported by a vertical rod, not a horizontal rod and ball joint as we usually have in manikins, AND that they weren't supplied with mirrors. If this is accurate, then I don't think I could do a decent job on any preparations, nor could anyone else. All of the preparations were on maxillary teeth, including an MOD amalgam preparation. AND they were required to do amalgam fillings. I didn't think that any school was requiring the filling - I have said that I miss teaching that part for these exams (I do it all the time for our clinical courses), because it is something that few people do well at all. On the other hand, most people never had time to even do the filling. Apparently the hand instruments that they supplied were dull.

Now, how much of this is literally true I don't know, but it certainly wouldn't seem to test a candidate's skills in clinical dentistry as well as I think they could have done.

If you are going to apply in 2010 to this school - better call ahead and see if the same thing will be done then. There are other details about the exam that were told to me, and if you are interested just post a comment and I'll fill you in.

Gold Onlays - Posting #8

Color me old fashioned, but there are times where the choice between a PFM and an onlay preparation in a patient's mouth is difficult. Into this mix we have to add the Cerec/full ceramic crown also. Speaking as a dentist to a dentist, when you walk into your dentist's office with a broken cusp, are you thinking gold onlay, ceramic onlay or full ceramic crown? Naturally, the most conservative possible, with the best margins and that people don't see a lot of gold in your mouth?

I, myself, have lots of crowns - several full and partial gold veneers, several PFMs and a Cerec molar onlay. I frequently ask my students after they have studied with me for a week or two how many crowns I have and how many lower crowns do I have with occlusal gold. They never have any idea, because, conversationally, it really doesn't show for me. I guess I don't yawn in public or scream a lot either. But for many people it really doesn't make any difference whether they have gold on the occlusal or not, especially in the upper arch. But often, as dentists, we make patients think it will make a difference. Many dentists do this because they aren't confident in being able to do conservative gold preparations, like the onlay, or because they have a Cerec unit and the monthly "nut" must be covered.

But, for whatever the reason, the gold onlay can be a very useful preparation and most dentists these days don't really understand it. My dental practice was in an area where there were many older patients, so most of the crowns I did were gold, because, even if the facial surface were prepared, it didn't make much difference to them. I could always restore the tooth with an absolute minimum of removed tooth structure, generally using just what was already missing for retention of the occlusal restoration, replacing one or more cusps. The principles that we learn from 3/4 crowns, inlays and onlays will allow design of preparations that are very conservative, even though they may not have names! I used to have a die from a patient case that I passed around in my classes and defied students to figure out what kind of preparation it was. It is lost now, but as I recall it replaced only the ML cusp on a maxillary molar, had both a box and groove for retention and axial reduction only on part of the lingual surface with a chamfer margin. Now, realistically, one can do the same restoration with adhesive technology - using porcelain - but the reduction would have to be much more. Don't forget that adhesive technology can be used with GOLD as well, but it is of little advantage since we can get good retention generally for this material with less reduction.

The other misconception about gold onlays is that the preparations are more difficult than for the PFM. I have done very few gold onlays where I had to make the boxes for retention in areas where there were NOT previous restorations. In other words, almost always, there is a restoration with boxes already on the tooth and these areas can be readily used, in most circumstances, for retention of the gold restoration. You need but to make the boxes DRAW, put on some bevels and a couple other refinements, and you are ready to take the impression - AND the impression is much easier than for the PFM!

So, at the very least, we owe it to our patients to know this restoration - and occasionally it will make our lives much easier too. But, of course, to be fair, for a badly broken down tooth, we may not have enough tooth structure left for an onlay or even a traditional crown of any sort, without a major buildup first. These days, the buildup/crown combination is rarely used, since we can often prepare the remaining tooth structure for an adhesive porcelain restoration without removing much more structure. So, realistically, as usual, there are occasions where either type of restoration may be the most appropriate - don't be one sided!

By the way - another important issue that we should cover in more detail is porcelain abrasivity. I have studied this in the lab extensively, and don't miss a chance to study it in patient's mouth also. When a traditional PFM with occlusal porcelain is in the mouth for some time, a couple of years or even less, you can feel that the surface is quite rough. There are reasons for this which I won't go into here unless I get a specific question about it. I have a Cerec crown on #30 that was placed about 9 months ago, and I just checked it with an explorer and it is much smoother in the grooves than at the cusp tips, where it wears against the opposing teeth. It should be theoretically possible for the Cerec crown procelain to be less abrasive, but I'm pessimistic in practice. The abrasivity of porcelain crowns in certain patients can be a major factor in ruling them out.

For the MOD gold onlay, where there are boxes on both the mesial and distal sides, there are pretty well circumscribed preparations designs that work quite well. The most important aspect is the depth of the boxes gingivally, because this is where the retention comes from, and also, depending on the gingival recession, we might not be able to get a good impression of the gingival margin if there is not enough gingival clearance to allow passage of the set impression material. As indicated before, often the boxes are already there, but they need to be made to diverge occlusally in the faciolingual direction and converge axially, in order to have draw, AND we may need to deepen them gingivally.

When working with a tooth with a prior amalgam restoration, or even MOD composite, it is often found that this preparation was done with a great deal of faciolingual convergence. Maybe this was done to remove decalcification at the F and L proximal margins near the gingival floor, but more often it is done out of careless on the part of the operator, or because they were taught that way. It only takes a degree or two of convergence to retain amalgam, not the 30 degrees that I often see, when it is absolutely unnecessary. Also, with this much convergence, in order to convert the direct restoration prep into an indirect prep we have to make it DIVERGE, and this will increase the faciolingual size of the box, often too much to be practical. In this case we might have no choice but for full coverage or extracoronal retention.

Again - I encourage you to read through these postings and be stimulated by the topics I have presented and bring up questions that occur to you. In this blog I am only dealing with those issues that relate to preparations that may show up on advanced standing admissions practical exams - but there are many dental topics that are widely misunderstood and would be fun to discuss as well. If you are interested in the general subject of cast gold restorations, I will refer you to the best place for this - and it is not dental schools any more. Try the Richard V. Tucker Cast Gold Study clubs. They have a website now, and many study clubs throughout the world.

Partial Veneer Crowns - Posting #7

One can expect partial veneer crown preparations on some school practical examinations - notably USC, for their case-based exam it is sometimes most appropriate to do this type of crown preparation.

There are many times in dental practice that, even if you start off thinking that you are going to do a full gold crown on a patient, you end up doing a partial veneer crown, for example a 3/4 crown, without even knowing it!

For example - and I use this example in my classes all the time - you are doing a FGC on #18 and it is the most distal tooth in the arch, and the gingival level is very high on the distal side. The patient may be in their 20s and they have had very little attachment loss and the tissue is high on that side. Now, you proceed as normal to do the occlusal reduction for the FGC and the occlusal surface of the preparation is, on the distal side, already at the gingival level, and you haven't done the axial reduction on that side of the tooth! So you have no retentive wall on the distal. Presuming that you have three retentive axial walls out of a possible four, you are doing a 3/4 crown, like it or not. Now, how do we get some resistance form for mesial tipping? Place grooves on the buccal and lingual. Then make sure that the margins are smooth and continuous gingival to the grooves, and up onto the distal margin which is just outside the marginal ridge, insure that the gold at the distal margin will not be too thin, and you have a 90 degree rotated 3/4 crown!

The main thing about partial veneer crowns, including the 3/4 and the 7/8 is that they allow, many times, a much more conservative preparation than would be necessary for the PFM. The PFM will allow retention, in principle, more easily, since we are preparing the entire facial surface and extending deep subgingivally - but often we should be thinking about the wisdom of this when a lot of the lingual part of the tooth is broken off - does it make sense to cut off most of the buccal part of the tooth?

In general, we need to keep in mind that a 3/4 or 7/8 crown can be done, and many times can be done more easily than a PFM or full ceramic crown, and certainly more conservatively, and with less hazard to the opposing teeth and with much better margins. Then, for an individual patient, we can decide what makes the most sense, esthetically and otherwise. If all you know how to do is a PFM your practice will be limited, to be sure. We have a variety of model typodonts that are available, and one does have a 7/8 crown on a maxillary premolar! Even this can be the most appropriate restoration in certain circumstances.

If you have any questions about how grooves and flares are made, or whether the standard textbook groove design is really necessary for retention, or if other, easier methods may work, just post a comment on this section and I'll be happy to discuss these things.

We are close to having our Fundamental Restorative Techniques course on-line! This will enable you to see exactly how many of the restorative preparations are done and hear a lot of discussion of the use of different designs.

Porcelain-fused-to-metal Crowns - Posting #6

Ceramometal crowns require careful attention to the desired form of the final crown, especially for the anterior teeth, and the thickness of porcelain required for adequate esthetics, especially for older patients, where the enamel is more transparent.

The key to the preparation is the facial reduction, which is frequently done incorrectly, so that the lab tech must either overcontour the facial surface of the crown, or make the porcelain thin so that it has a poor appearance.

The evaluation of the facial reduction requires that you check the axial reduction at the gingival margin, AND check the taper in relation to the adjacent teeth whose contours the crown will be designed to match.

In order to evaluate the facial axial reduction at the gingival margin, you can do it without caring about the margin form. For example, if you use a horizontal shoulder, an angled shoulder, or a shoulder-bevel (no longer desirable for anterior teeth in the esthetic zone), you can see the axial reduction (horizontal distance from the gingival margin to the axial wall) by looking gingivally down the facial wall and measuring the apparent width of the shoulder from this viewing direction. This viewing direction cancels out the effect of angulation so you get the actual axial reduction automatically. We'd like to get approximately a 1.0 mm axial reduction uniformly from the mesial to distal facial embrasures.

From the gingival shoulder to the incisal edge, we need to make certain that the angulation is correct on the facial surface. You can guarantee that this will be appropriate by comparing the facial taper to that of the middle third of another adjacent tooth, that the crown will match. This should be the angle of the facial reduction for the gingival 2/3 of the surface to the shoulder. The incisal 1/3 will typically have another angle, matching that of the incisal 1/3 of the comparison tooth - referred to as a secondary plane, recognizing that the curved surface of the facial contour will require two planes for uniform axial reduction from gingival to incisal.

The most common error in PFM preparations is to allow the shoulder to remain horizontal into the proximal embrasures, mesially and distally. The problem is that this margin will sometimes be in enamel, and if it is the enamel will be undermined due to the natural incisal divergence of the enamel contours at the margin. Often I have seen preparations done by students in patients that, after removal of the provisional crown, before cementation of the permanent restoration, the gingival enamel was found to be chipped and broken, leaving deficient margins in these areas. It is always best to angle the shoulder gingivally with the end of a shoulder diamond so that the EXTERNAL angles of porcelain AND the enamel are closer to 90 degrees!

The esthetics of shoulder-bevel margins are not acceptable for anterior teeth these days, because of inadequate gingival placement or thin tissue biotype to which dentists don't pay enough attention. For posterior PFMs out of the esthetic zone, the shoulder-bevel can be a nice approach for the facial reduction.

We can discuss other types of porcelain crowns, including full ceramic crowns and CAD/CAM crowns. There are advantages and disadvantages to each, and they can be subtle. How one does a FCC prep on a typodont can be a challenge and I can go into this in detail.

For comments or questions about any of these issues, I will love to have you reply to this posting and I'll answer or discuss anything that concerns you. Be sure to check out our programs at www.dentistCEprogram.com

Full Gold Crowns - Posting #5

Full gold crown preparations are done to conserve as much tooth structure as possible, provide the best adaptation at the margins (second only to what is possible with exposed margins on inlays, onlays, etc), antagonize the pulp chamber to the minimal extent, and be the most kind to the opposing teeth, particularly when there is a loss of anterior guidance and parafunctional habits create posterior attrition in group function.

While many dentists are quite aggressive about occlusal reduction, for younger patients this can be a really bad idea with the proximity of the pulp and the gingival limitations on crown height and thus retention and resistance form. So the circumstances need to be studied with some care to see how conservative you really need to be, but, in general, a more strategic approach to the crown preparation will require little if any additional time, and yet allow total control of the reduction and/or clearance of the occlusal reduction.

What is the difference between occlusal reduction and clearance? Most of the time there is no difference. If the particular part of the occlusal surface is originally in occlusion, probably it will be waxed into occlusion, and therefore the amount of reduction is geometrically identical to the amount of clearance between the preparation and the opposing surface. When the original tooth is NOT in occlusion and we want it to be, then we will reduce only to the extent that the clearance is adequate to build the occlusal surface of the gold crown in that area - this may be 1.0 mm or 1.5 mm. On the other hand, if the original tooth surface at some point is not in occlusion and we don't want it to be, we simply reduce it the 1.0 or 1.5 mm to get the thickness of the gold right, and we don't care how much clearance there is at the end. If we stop reducing, say, the ML cusp on a mandibular first molar when there is only 1 mm clearance, it will have little reduction and the cusp will be much higher than original and the patient will feel that it is a very sharp area on the crown.

As far as axial reduction is concerned - the major issues involve appropriate wall form, generally flat until sloping gingivally at the gingival .5 mm or so, axial reduction at the gingival margin approximating .5 mm and appropriate taper and reduction to construct the proximal contacts and F/L surfaces with natural contours. Generally, we can select a particular diamond bur that will accomplish the axial reduction with minimal problems if the tip of the bur is kept at the margin, if the gingival position of the margin is appropriate, and the taper is 10-12 degrees. All three of these criteria can be controlled as long as the operator is looking in the correct direction relative to the surface being prepared.

If you would like to ask some questions about the issues mentioned here, or would like to contribute, or are uncertain about anything, feel free to answer this post - we can get a lively discussion going.

Class II Amalgam Preps - Posting #4

The class II amalgam preparation design is based on the need to remove caries and the need to take into account the physical characteristics of the amalgam material, which should not have an angular bulk at any margin less than 90 degrees. In some areas of certain teeth it may be difficult to avoid an acute angle of amalgam, for example the facial occlusal proximal margin when the contact area is shifted unusually much to the buccal. This also makes it difficult to CARVE the amalgam in that area because the buccal margin is so much higher than the lingual margin in the area of the marginal ridge.

But, generally, we can always get close to a 90 degree angle of amalgam. Remember the material is very hard, but brittle. I had a student in a clinical course back in 1993 who had taken the Cal Board and done an amalgam prep on her daughter - a lower second premolar. She had neglected to extend into the lingual groove for the occlusal outline and was failed because of that. When she brought her daughter into the course it was interesting to see that the amalgam that had been done during the exam had fractured completely through in the isthmus area where the wall was short due to the lack of extension into the lingual groove. We need to adhere pretty well to the principles design for this material in order to do a conservative preparation and restoration that will not compromise the strength of the filling itself.

Remember that the lifetime of an amalgam restoration with todays materials should be a minimum of 50 years, probably 60 or more when the preparaton is done with reasonable precision. There was a study done in Chicago 20 years ago where they recalled many patients who had been given amalgam restorations 50 years earlier and most of these restorations were still there and doing fine! And those were old type materials!

I'd like to hear some discussions under this posting about amalgam preparation design and carving, or anything else you may be confused about for class II restorations. For example, when and where do you think the "reverse curve" should be done?

DMD

Practical Exams - Post #3

At Duggan Dental Studies we are particularly interested in helping dentists gain the level of skill and understanding of dental preparations that is required to give a stand-out performance at any practical examination. Make no mistake about it, as opposed to board examinations, these dental school admissions exams are competitive, and hotly competitive. Within our field we are working toward the equivalent of a 400 meter race. How do you stack up against the competition? Are you doing what it takes to do better than most of the other applicants?

Who are the schools comparing you to? How will you look in comparison to the third year traditional students? What does the average applicant know and what can they do? What will the exam be like? What preps do I need to know? These are all questions that we hear all the time and we can discuss most of these issues in this posting, but also this is a great place to share information you have gathered about various schools and what you observed there.

Feel free to provide any information you have or ask any questions you want. If I don't have the answer readily at my fingertips, I can probably find out, or another viewer may have the answer. Let's share whatever we know and I will make sure that the information gets passed on to the benefit of all.

Having said that these examinations are competitive, I will also say that any dedicated group of people working together can elevate their level of work considerably above the crowd - sometimes my students comprise a large proportion of an entering class at various schools because they tend to all know what they are doing and do well. There are always benefits to working together and not trying to "fly alone" - if you went through the interview process last year and "fell out of the sky", now may be the time to try something different!

Advanced-Standing Schools - Post #2

There are approximately 38 schools in the U.S. that are offering advanced-standing admissions for foreign-trained dentists who have attended or been graduated from a program not accredited by the ADA. Some of these schools admit only one or two to make up for extra space in the class. Some have large programs. Some have programs where the students are merged with the traditional students in lecture classes, preclinical labs and clinical instruction,, and some have independent programs with separate instructors and clinics. Some have practical admissions exams and some do not. Some have "review programs" for various periods of time before you are officially admitted, and some do not, or they are more unofficial.

We have assembled a spreadsheet for the schools offering advanced-standing admissions, and this includes all information we can get from the schools, from ADEA, from the ADA and from forums where discussions of these programs take place. There are currently 20 categories of information about each school. This can save you a tremendous amount of time as you plan your strategy for admission to these programs. Not all of the information can be current, because the schools change things frequently, and some of the information is just passed on by those who have been to the school. But it is a great starting point. If you would like a copy of this emailed to you, register with this blog.

Otherwise, if you have anything that you have heard or experienced that would be helpful to others reading this posting, please register and respond on this posting #2. If it is confirmed by enough people we will add it to the information in the master spreadsheet.

International Dentists in US - Orientation - Posting#1

International Dentists - Posting #1

This Blog Set is directed specifically to dentists who were graduated overseas and are looking for the opportunity to practice in the U.S. It is estimated that there are approximately 1000 dentists per year who fall into this category. Considering the range of experience and performance on standardized examinations, foreign graduates can hope to enter dental school in the U.S. during the third or junior year.

Admissions to U.S. dental schools with advanced-standing status is extremely competitive – there are approximately 400 places available each year. Performance on National Board Dental Examinations must for many schools be better than the national average of U.S. dental students, proficiency in English must be demonstrated, and for most of the positions a competitive practical examination is required.

At Duggan Dental Studies, our goal is to help in whatever way possible the foreign graduate to successfully navigate the challenges to dental school admissions. Our NBDE I program will be online in coming months – we already have 65 DVDs of recorded and edited material for this exam. Our Fundamentals of Restorative Techniques course has been widely popular to help with the practical examinations. We are about to expand our FRT program to another, 18-day offering, for those who can stay longer and further refine their skills and understanding. Also, international dentists who gain acceptance into an advanced-standing program must be aware that in most schools these are provisional acceptances, dependent upon performance in a “summer review” program. Once “accepted” it is very useful to work on advancing skill levels further, to guarantee excellent progress in these school reviews. If you have already taken one of our FRT programs, our 18-day clinical dentistry review is deal preparations for whatever your admitting school might throw at you – virtually guaranteeing the making of a very favorable impression during your first months.

Most of the foreign graduates that work with me at DDS have never done a crown on a patient before, or very few. Most have never been taught to do preparations with a strategy so that the least tooth structure is removed and the remaining structure is very refined in form. Most have never been taught the rationale for materials selection and for preparation decisions based on the nature of the problem and the characteristics of the available materials. Most have never been taught how to LOOK and what must be SEEN while doing a dental preparation. Most have never been taught how to use a handpiece and bur with the kind of precision that gives pleasure each and every day of your life in dental practice. We make up for all of this with our FRT program.

Posting #1 is for general questions about dentistry in the U.S., dental schools in the U.S., how dental faculty think, what the 4-year traditional students are like, what a teaching career is like, what dental practice is like, and anything else that comes to mind. Other posting threads will cover: #2. Schools with Advanced Standing Programs and their requirements; #3. Practical Examinations at various schools; #4. Detailed questions about class II amalgam preparations; #5. Detailed questions about full gold crown preparations; #6. Detailed questions about porcelain-fused-to-metal crown preparations; #7. Detailed questions about partial veneer crowns – including ¾ and 7/8 crowns; #8. Detailed questions about gold onlays; #9. Detailed questions about class II composite and class III composite restorations.

We will attempt to use these postings both as question-answer sessions with me providing the answers, and also where responders can contribute their own input – perhaps about what particular schools are looking for, what they gave on the last exam, etc. Postings #1, #2, and #3 will often be seen to work like forums.

All questions regarding preparations in the Postings #4 – 9 will be answered in words as completely and well as possible, but some mental image of the preparations will be very helpful. This can either be obtained from a standard textbook on the subject, or from our models with DVDs that are available. These are articulated models with a variety of preparations done in a manikin , using a mirror, and recorded with a loupe-mounted video camera so you can look in the mirror with me! We will also be posting pictures and short videos to further illustrate some of the points made.

We also have an online course which was recorded from a Fundamentals of Restorative Techniques program given a few months ago. All lectures and presentations are presented as well as demonstrations and evaluations and modifications of student work, done with the recording “point-of-view” camera, developed at DDS. We are planning that this online course will be ready for registration before the end of September.

At DDS and its precursor company, Duggan Study Institute, we have trained over 3500 international dentists for various examinations throughout the country. It is likely that no one in the world has worked on as many preparations with students as I have – and I would very much like to add you to the rolls of successful graduates from our programs. We proud of our record over the last 17 years and still get most of our students as referrals from those who have studied with us before.