March 1, 2005
by Janice Goodman, DDS
For your caries susceptible patients, there is now a more vigorous standard of care than scale, prophy and fluoride. Dr. Gerard Chiche (Toronto Academy of Cosmetic Dentistry) and Dr. Kenneth Shay (Toronto Crown and Bridge Study Club-Geriatric Dentistry) both gave similar check lists:
1. Diagnose the etiology of the problem, i.e. medical history, medications and diet. Salivary pH and flow are measurable, (caries check); remove carious colonies (decay) and seal well.
2. Prescribe chlorhexidine 0.12% for its antimicrobial effect. (Optional, depending on your personal feelings about mouthwashes.)
3. Xylitol lozenges or gum–three sticks a day. Xylitol has been demonstrated to specifically inhibit Strep Mutans bacteria (which causes decay) and encourage remineralization. (A web site founded specifically for dentists and their patients to get xylitol products at discount bulk prices is www.xylitolsolutions.com) (Trident gum is too low a concentration to be as effective as the products found in health food stores or xylitol solutions.com.)
Neutral NaF is the fluoride of choice these days for caries prevention. Prevident plus (t.i.d.) -1.1% is one of the name brands.
5. Remineralize with calcium and phosphate toothpastes. There are a number of brand names that are available. (Recalcident, MI paste, Tooth Moouse, Healozone contains calcium, zinc and fluoride.)
6. Place F varnish (e.g. Duraflor) on cervical and/or interproximal areas at recalls.
Tip: If you’re still using an old-fashioned halogen curing light and want to shorten curing time, consider just changing the tip. Kerr sells a turbo tip that can do this (approx. US$200).
LEDs have the advantage of faster cure and are often cordless and highly ergonomic. Keep your old halogen light around if you’re not sure if a material, such as Biscover, will cure with your LED unit. Try curing a drop with the LED of a new product outside the mouth to establish if it fully sets.
This month’s article on curing lights by Dr. Scott Dudley goes through a number of these points. Also, Denmat has little discs that you can use to check curing times of different materials and lights. Ultralume by Ultradent is the only LED that claims it cures all products, apparently because it has two wavelengths. This particular light has a chord and is not as ergonomically designed as some of the other LEDs though. Kerr has the most popular selling LED unit to date, partly because of its association with Demetron and the convenience of the unit.
At curing times of 3-5 seconds, the ARC lights (e.g. Saphire by Denmat) are state-of-the-art and I did not find set difficulties while I was demo-ing one. The light is extremely bright and I have had a hygienist refuse to use it because the few times she was in the room without eye protection she noticed her eyes were adversely affected. It is also a fairly large unit and has a thick chord. The three-second cure is a big luxury. There is a new player in the arena. Swiss Master (EMS) is a high-speed halogen unit that cures in three seconds ($$). It is water-cooled and has a chord.
All lights will cure easily through enamel, but did you know that you cannot cure through dentine? Studies show that very little curing light passes through dentine, so don’t assume that you can cure through a tooth. Also keep in mind that ceramic thickness and shade can affect curing times.
Tip: If you have resin particles on your curing tip you may be cutting curing efficiency by up to 50 percent. If you wrap a two-inch square piece of Saran Wrap around the tip you will loose 10 percent efficiency but avoid the previous scenario and have a more hygienic situation. Clean the tips that have cured material by flicking the material with a scalpel blade occasionally.
SELF ETCHING RESIN CEMENTS
These self-etching cements are all the rage; they are self-etching to dentine, are easy to use, and are great at preventing post-op sensitivity. Note that if you are cementing to enamel, you should still consider doing the etch step or you may not get the bond strength that you were hoping for. You have a number of choices in this arena — 3M’s Unicem was the first: it has a good track record, the capsules have stingy quantities and the mix requires unique mixers and an amalgam triturator. Be sitting down when you price this product out. Kerr has recently introduced Maxcem; Pulpdent distributes Embrace wet bond universal cement.
SELF-ETCH BONDING RESINS
Like the self-etch cements mentioned above, these products are touted as superior at preventing post-op sensitivity, especially when used after 30 seconds of Gluma or a resin modified glass ionomer liner (e.g. Vitrebond by 3M or Fuji lining LC by GC). There are a lot of these products and there is quite a variation in cost. Be aware that it might cost you $1.00 or more for each drop and some are half the price of others. The bond to enamel, again, is not as strong as the multi-step ‘old faithfuls’.
PREP MODIFICATIONS FOR SCANNED RESTORATIONS
There are now about 10 different scanning machines that all scan a prep either by using optics or tactile means. Both systems are slightly flawed in that they cannot pick up sharp lines or angles as well as lipping, troughing or feather edges. Therefore, if you are doing a restoration that will be scanned, make sure that it is as smooth as possible and that the margins are not right angle shoulders, or feather edged or sharpely concave. These features are very well illustrated in the free handout on the Lava Crown prep from 3M.
Tip: To get super smooth preparations without going through a refinement stage, try the new G Force* burs from Garrison Dental. The diamonds particles are small sized and quite uniform, which is responsible for this smoothness. Brasseler and Axis Dental have burs made by a similar manufacturing system also.
Tip: Double Scan Technique –courtesy of DSG Laboratory. One of the reasons for porcelain fractures on Procera, Cercon, and Lava type crowns was due to unsupported porcelain because of a unithick underlying core. Now that this weakness has been recognized, some labs are adopting a new technique, which allows the core to be thicker in areas so that the overlying thickness of the porcelain above the core can be more even. This is accomplished by first scanning the prep, then waxing up the core to an ideal thickness and then scanning the wax up. The core is then cut to both scan dimensions and will be more ideal for the longevity of the porcelain that will be placed over the core.
If you need to improve your impressions, Klausz Dental Lab has a well illustrated trouble-shooting guide and CD.
ACQUIRING CR 🙁
If you’re doing major restorative cases and are not sure you’re actually capturing CR for the lab, try this technique, as described by Gary Alex. Use the patient’s NTI appliance if they have one or you can order “Pankey Deprogrammers” (Pankey Inst.). Roughen the resin a bit, add bonding resin and place resin to guide the incisors to one spot (red compound will work for this also). Then just add bite impression material to the discluded posterior areas and have the patient bite at this stabilized position. Dr. John Kois also describes a technique using a Hawley device that has acrylic build-up behind the maxillary centrals to accomplish the same results. This Hawley appliance is also great to use to do adjustments to remove interferences as it just discludes the teeth by the smallest leeway, so it’s easy to find first points of contact.
I have modified an Essix appliance, first described by Dr. John Sheridan, which is like a bite plane with no posterior teeth with a ramp behind the anterior teeth made with a Hilliard ramping plier (Raintree Essix carries these). This works in a similar fashion as Dr. Kois’s but can be made in minutes in the offic
e and costs under a toonie to produce.
In the very least, make sure that the patient’s teeth are slightly discluded to prevent the teeth from reprogramming the musculature on the way to CR, when taking a bite and where you are trying avoid CO. Jerry Tully a New Orleans dentist has also written about the “stop technique” to acquire CR in a bite.
Dr. Nassar Barghi had a lot to say about silane when he came to town recently, some of which I’d like to share here. First, Dr. Barghi claims that silane is only good for six months after a bottle is opened although when I asked 3M, they assured me that, with their research, their silane is still good for more than a year. To get fresher silane, you can use a two-part system (e.g. Mirage), which is good for one week after mixing and you can be assured that your silane is good.
Also, silane is better as a thin mono layer so paint a stingy coating on rather than a thick drop–similar to applying contact cement or Crazy Glue. The best time to silinate porcelain is immediately after etching it. Make sure you know if the lab etches and/or silinates their porcelain, so that there are no misunderstandings which may lead to failures.
When you polish resins, you are removing some of the silane that surrounds the particles. Silinating the polished resin surface before adding more resin will enhance the resin-resin bond if it is a thin layer.
Cojet by 3M is a silinating product that works in your microetcher and is not very expensive.
HAEMA IN BONDING AGENTS
Put one drop of your bonding resin on a glass slab and light cure it–the haema in it causes the yellow hue (the amount of yellow varies greatly amoung available bonding resins). That is the colour that you are adding below your resin restorations each time you apply it. If you use bonding resin to glaze your finished restoration, you are altering the shade that you had matched so nicely by some degree of yellow.
Do not use bonding resin in veneers as it will yellow them also. It is preferable for this reason to use an unfilled resin with no haema or something that is pure BisGma, like Purebond (Bisco), Visarseal or Permaflo. Lately, I have used a Kerr product called Optiguard and I also use Wetting Agent by Ultradent. These also make the best wetting agents on brushes when working with resins. Too much product can weaken surface hardness by reducing the filler ratio, so be careful.
BONDING TO BLEACHED TEETH
I am not sure how long one has to wait after bleaching teeth to get a good bond to enamel. Most of the literature and speakers vary on this detail, but it usually runs between one and six weeks. The reasons you wait are many: hydration of the enamel and increased surface energy are commonly held beliefs. If you don’t have the luxury of waiting, there are a number of techniques to bond to bleached teeth sooner:
1) roughen the surface and bond to it;
2) use vitamin C for eight hours contact time prior to bonding;
3) Allbond 2 pulls the water out and you get back about 90 percent of the bond strength to enamel;
4) Bleach and Bond is a new product that will be available soon.
PREP SHAPES FOR VENEERS
I prefer the most conservative preps when doing veneers (depending on the porcelain choice), but when faced with an end-to end-incisal bite consider taking a lot more off the incisal edge so that the insical can be moved labially hopefully to create incisal guidance and keep the incisal edge thin. Avoid moving the lingual labially as you will weaken the tooth due to biomimetics.
PORCELAIN CHOICE FOR VENEERS
Studies have shown that there is no difference between feldspathic and pressed porcelains as far as in vitro strength performance in the anterior. I usually prefer feldspathic in the anterior because it is so aesthetic and the preps are more conservative.
The newest thought is to have minimal to no die spacer on veneer dies, to have the smallest amount of luting agent (quite different from the two layers of die spacers that I used to ask for).
Use masking dentine porcelain to cover discoloration or dentine. It has one percent tin oxide and can be placed very thin. Do not use resin to cover discoloration under a veneer as it will be much thicker and resin is more translucent. Contact lens porcelain at the margin allows for great blending to tooth for veneers.
If a veneer shows a crack, you don’t have to rush to replace it unless it is unesthetic. The cause is often an internal flaw or bubble in the porcelain and the veneer should remain bonded.
REMOVING CEMENTED CROWNS AND HARD RESTORATIVE MATERIALS
Tip: Save your used fissure burs and with a heavy-duty wire cutter, cut them about one-third of the way down. Try not to angle the cut so that the end remains as perpendicular to the shaft of the bur as possible. I use these ‘modified’ burs to remove crowns and porcelain restorations. You may have to go through a few burs to get a crown off, but they are inexpensive and quite efficient.
SOFT TISSUE MANAGEMENT
The Soft Tissue Trimmer from Axis Dental won’t cost as much as a laser or electrosurg, but, you can charge the same code and it really works, when used for the correct indications.
Tip: use the bur dry-the manufacturer says it is a common error to use the bur with water; it works better dry.
For gingiva that threatens to bleed if you look at it too hard, here’s a tip from Dr. Anthony Mancuso. Apply a drop of trichloracetic acid (very carefully-it is extremely caustic) to the gingival for instant haemostasis, count to two and then wash it with copious amounts of water. You will end up with a transient white area on the gingival where the acid was applied. If you don’t rinse after the application, the acid will eat the tissue…do not miss that step!
Dr. Mancuso suggests purchasing the trichloracetic acid in a pharmacy in crystal form; it is inexpensive. When you use it, take four to five crystals in a glass dampen dish and had a drop of water. Use a mini-brush applicator to apply it and don’t pass it over the patient’s face. That mixture will last for about a week and then should be discarded.
* Not available in Canada, no ISO certification.