January 1, 2012
by Carla Cohn, DDS
Years ago, a father came into my offce with his young son. The boy had rampant decay involving multiple surfaces on all of his primary molars. To make matters more complex, the child had behavioural issues – as we seem to see more and more frequently these days. ADHD and sensory perception disorder made it impossible for this young man to sit for any length of time for treatment, never mind the four appointments necessary to complete treatment on all of his molars. I recommended that he be seen in the operating room, under general anaesthetic. We discussed the treatment required at the preliminary consultation, including the stainless steel crowns that would be necessary to repair his devastated mouth. Treatment was agreed upon, an informed consent was completed and signed and a date was set for treatment in the operating room. The day came for treatment to be completed and I placed eight stainless steel crowns on all of his primary molars. Beautiful, durable, technically perfect stainless steel crowns. Or so I thought! As the child was rousing from his anaethesia, his dad was distraught. He hated the look of the stainless steel crowns. They were, his words exactly, “the ugliest things he had ever seen” and that “all his child had going for him was his smile, and now that was ruined.” In his father’s opinion, it was preferable to have a mouth full of brown decayed teeth than stainless steel. I was horri¿ed at his reaction. After all, full coverage was the recommended treatment. I thought that I had no other options available. But, I was wrong. What I perceived to be ideal treatment at that time was far from ideal.
The “triangle” of agreement when treating children relies in part on the parents and theirwants and needs. If we aren’t listening to the parents in our practice, we are failing. In no way am I suggesting that parents dictate treatment, however their wishes must be taken into the equation. The professional must always remain the professional. Surprisingly, or not, in a recent study on parental attitude on restorative materials, it was found that “many paediatric dentists acquiesce to parents’ wishes when challenged about the material with which they have chosen to restore a posterior primary tooth.” An astonishing 43% of paediatric dentists when confronted by the parents accepted their preference even when it was contrary to their clinical judgement. When considering the restoration of posterior primary teeth, the parents’ chief concern is aesthetics.1 But it isn’t solely the adults who have opinions on treatment, it is the children as well. Both children and their parents prefer tooth coloured restorations.2
How many times have you had the parents in your practice urge you to place a tooth coloured flling instead of an amalgam or a stainless steel crown? How many times have you known that a flling won’t stand the test of time and that this child will be back with a broken tooth? The failure rate of a class II composite restoration is high, 62% in one study when assessed at six years post-op. Stainless steel/nickel chrome crowns provide the most durable restoration, often surviving until the tooth exfoliates.3
According to the clinical guidelines for the American Academy of Pediatric Dentistry, full coverage is indicated in any of the following circumstances:
1) children at high risk with anterior and / or posterior decay,
2) children with extensive decay,
3) large lesions or multiple surface lesions,
4) pulpally treated teeth and
5) children requiring general anaesthesia.4
Preformed metal crowns, ie. stainless steel / nickel chrome crowns, outperform intracoronal restorations in terms of longevity.5-7 They are reliable and durable. But aesthetics are clearly lacking. Statistics show that when full coverage is required, it is most commonly the frst primary molars.8 As the mandibular first primary molars are the most visible, this is the area with the highest concern for aesthetics, besides the anterior teeth.9 When full coverage is required, stainless steel crowns are most certainly the gold standard of treatment in many aspects. But, it is evident that there is a need and desire for an aesthetic full coverage option.
What are the options for full coverage besides stainless steel crowns? The ideal requirements are: durability, ease of placement and aesthetics. Pre-veneered stainless steel crowns (PVSSC) provide full coverage, are durable, easy to place and are aesthetic. Pre-veneered stainless steel crowns are stainless steel / nickel chromes crown that has an aesthetic facing, mechanically and/or chemically bonded. PVSSC were introduced in the early 1990s. They were initially developed for anterior teeth, but later developed for primary molars.10 Some of the PVSSC for posterior primary molars on the market are Nusmile Primary Crowns (Houston, TX), Kinder Krowns (St. Louis Park, MN), and Cheng Crowns (Exton, PA).
PVSSC come with inherent advantages and disadvantages as described in the following table. The most common concern is the retention of the aesthetic facing. The facings can be prone to fracture and in some cases complete loss.11-13 Over the years since their introduction the facings have become more resistant and fracture and loss are less of a problem. Repair of the facing is possible but it is suggested that the crown be replaced should the facings fracture.14 Fracture resistance investigations showed that the crowns should be able to resist occlusal forces over short clinical periods, however long term loading and fatigue failures must be taken into account.15
The clinical outcomes for PVSSC, specifically Nusmile crowns, are promising.16 Another recently published study gave excellent reports on longevity and durability.17 Failure rates are low and parental satisfaction studies have been positive.18
Another concern of the PVSSC is the limited crimpability of the crowns. Crimping of the metal portion will weaken the aesthetic facing and may lead to premature failure. Instead care must be taken to have as close a fit as possible in order to eliminate the need for crimping and to minimize the reliance on the strength of the cement.
Preparation for placement of a PVSSC requires more aggressive tooth reduction to allow for the thickness of the crown due to the aesthetic facing. It has been suggested by some that pulpal therapy will be required more frequently because of this, however in my clinical experiences, I have found this not to be the case.
Finally the shape of the PVSSC is not alterable and in cases in which there is a loss of space, usually due to caries, the crown cannot be “squeezed” mesio-distally. Careful case selection is necessary to avoid difficulties.
Knowing all of the advantages and disadvantages, it is imperative to have these discussions with the parents prior to treatment. Informed consent is crucial, as it is in any treatment we deliver.
Placement of a posterior pre-veneered stainless steel crown has proven to be simple. The first step is to size the tooth and estimate the crown size needed. This is best done prior to tooth preparation. It was determined that a steam technique of sterilization is suitable and can be used to successfully sterilize the crowns.19 However, although the crowns can be sterilized, it is best to minimize exposure to the stress of sterilization on the facing. As with a traditional stainless steel crown preparation, occlusal reduction is the first step in preparation. The bulk of the material must be taken into account and so a minimum of 2mm of occlusal reduction must be accomplished. This can be done with a high speed tapered diamond, football diamond or with a simple straight fissure carbide bur as seen in Figure 2. Next circumferential reduction is completed. Again a tapered diamond or a tapered carbide bur may be used. Care must be taken to remove enough tooth structure to allow for the bulk of the crown. Preparation should be a feather edge and extend slightly subgingivally as in Figure 3. Caries removal and pulpal therap
y, if necessary, are completed after preparation for the crown. Upon try-in, the crown should fit passively with no resistance to the fully seated position. Occlusion must be checked as a “high” restoration would lead to premature fracture of the facing. Cementation with a glass ionomer is the cement of choice.
The following clinical photos demonstrate the preparation and placement of a posterior pre- veneered stainless steel crown.
The demand for aesthetics is increasing at a rate that is in line with our “on line” society. We must be prepared to offer alternatives to our patients. Without compromising strength and requirement for full coverage, pre veneered stainless steel crowns are a most viable aesthetic option. The simple truth is, if you do not offer an aesthetic alternative for full coverage you are missing an integral part of your armamentarium. We must be able to hear and react to the wants and needs of our parents and our patients. OH
Dr. Cohn maintains a private practice at Kid’s Dental and at Western Surgery Centre, in Winnipeg. She is a clinical instructor, part-time, in the department of Preventive Sciences at the University of Manitoba. Dr. Cohn lectures internationally on children’s dentistry for the general practitioner. She can be reached at email@example.com
Oral Health welcomes this original article.
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