Thursday, May 5, 2011

More questions and answers

Question: Why are Class III cases with open bite tendencies so difficult for beginners to treat?

Class III open bites are difficult for anyone, not just beginners. In these cases you have two problems that are tough to control. With Class III’s, you are at the mercy of mandibular growth. This growth accelerates during the growth spurt which means the Class III often worsens. In other words growth works against your treatment. Often Class III elastics are effective in correcting mild to moderate Class III problems. However, any inter-arch mechanics (in high angled patients, because muscle strength in these patients is usually not strong enough to resist the vertical component of force resulting from these mechanics) can make the high angled problem worse. Since virtually every published study involving facial aesthetics show that excessive face height leads to the most unattractive faces, it is important to minimize increases in face height in patients who already have long faces.
In these cases, extractions are sometimes effective. Extractions and space closure are effective in limiting increases in the vertical dimension and in many cases can actually reduce the anterior facial height. However, as this happens, the mandible rotates into a more closed position and, because the mandible opens and closes on an arc, it also moves forward, which worsens the Class III. So you see, most of what you can do in these cases have consequences that worsen other aspects of the malocclusion. There are no easy answers. This is why they are so difficult.

Question: One of my patients has a deep bite and bad oral hygiene. Every month he comes in, brackets are missing. Is it the bracket positioning that is responsible for the bonding failures? What do you suggest?

The bracket positioning is the least of your worries. Orthodontic bonding failures occur more in poor cooperators than in good cooperators. Poor cooperation is the major problem. My advice: either the patient improves his oral hygiene or you remove the braces. Don't tolerate this stuff. The patient and family are not upholding their end of the contract. The worst thing that can happen in an orthodontic case is decalcification due to bad hygiene. This problem will make any malocclusion look mild in comparison. Don't allow the possibility of decalcification to rear its ugly head. It's either clean teeth or no braces. It is just that simple. Do not compromise.

Question: I am a little confused about the shaping of arch wires. Is the upper wire 3mm longer than lower? What arch wire shape do you usually buy? There are so many sizes (for example wide, narrow, natural) that I am not sure which ones should I buy. Should I use the same arch form for nitinol wires as I do for stainless steel wires?

When coordinating arch wires, it is the width of the wire we are altering. The length simply depends on the total amount of wire needed to engage all the brackets. We have no control over this as it just depends on the total arch length. When buying wire, buy upper and lower broad arch forms for both stainless steel and nitinol. The original arch form of the stainless steel wire is less important than nitinol, because you will be shaping all stainless steel wires based on the pre-treatment arch form. Since the more flimsy (scientific term: low load-deflection rate) nitinol wire does not, due to its lack of stiffness, affect arch width as much as stiffer (high load deflection rate) wires like stainless steel, we do not routinely reshape nitinol wire (because of its flexibility it is hard to do anyway) and simply use the broad arch form in both the upper and lower arches.

Question: Do you prefer to use standard size brackets or minis?

I actually like the standard size brackets. Larger (wider) brackets result in better rotation control. Additionally, standard brackets have more surface area on the bonding pad which results in greater bond strength. Many doctors prefer the mini brackets because they are more aesthetic, but I don’t think the aesthetics of mini stainless steel brackets are that much different than the standard sized brackets.

Question: In extraction cases, what teeth do you usually extract?

If there is minimal lower arch crowding with a Class II tendency, I tend to extract upper 4’s and lower 5's. In this situation, reciprocal space closure results in more forward lower molar movement than forward upper molar movement. This moves the molars closer to a Class I relationship. In cases that are close to a full cusp Class II with minimal lower arch crowding, I often extract only upper 1st bicuspids and finish the case with Class II molars. If the case is Class I and extractions are necessary, four 1st bicuspid extractions is usually my treatment of choice.

Question: I am starting a case that has anterior spacing in both the upper and lower arches. How are these cases best started? Should I use 6-6 chain right from the start in 016 Niti wire? Or do I wait until later in the wire sequence?

For a case with spacing, it is usually prudent to progress into stiffer wires before initiating space closure. Always get the bite open to the desired level before initiating space closure. Additionally, you want the teeth to be sliding on a rigid arch wire so side effects of space closure are minimal. If the wire is too flimsy the chain can collapse the lateral segments, which results in a lot of tipping that you may not want. So wait to begin space closure. When you finally start space closure, if you want to reduce anterior torque, use round wire (020ss is my choice) when you close the spaces. If maintaining torque is a concern, wait until you are in 019X025 stainless steel (rectangular wire) before initiating space closure. The advantage of space closure on rectangular wire is the amount of control it provides but, because of the friction created due to the relatively full slot (there is not a lot of “slop” with 019X025 wire in an 022 slot), space closure may be inhibited. This is frustrating. Frictional forces are much less when closing space on 020 stainless steel, but this advantage is offset by the disadvantage of lack of control that is a result of the wire not filling the slot to a significant degree.
Many practitioners prefer to close space on round wire due to ease of space closure. For me, it depends on the torque of the anterior teeth. If torque is excessive, round is OK. If not, be careful. It is not easy to regain lost torque. Also, de-torqued anterior teeth (as the teeth de-torque the incisal edges rotate lingually) are often esthetically and functionally inferior to properly torqued teeth.

Question: I am treating a 10 year old boy with a 2x4 set-up on both upper and lower arches. His pretreatment overbite was 8mm. I'm intruding lower anterior teeth with a tip back set-up. Should I also intrude the upper anteriors?

It depends. My decision to intrude the upper anterior teeth is based on the amount of gingival display. If he has a smile that is too gummy, use tip back bends to intrude the upper anteriors. If his smile line is OK, just intrude the lowers.


Gina Milo said...

I am treating two girls, who apparently have the same problem, mild to moderate class II, division II, not very pronounced deep bite. I have already alingned the upper and lower arches, corrected the midline discrepancy, and all is left are the elastics. I thought to create a reverse curve of Spee at the lower arch OR an accentuated Spee at the upper one, just to open the bite a little more and to counteract the tendency the elastics have on the vertical dimension. The question is, on which arch should I work? Is there a rule for that? And what is the rationale, so that I can use your information rightfully on my next cases?

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