June 2009, Volume 5, Issue 6
Published by AEGIS Communications
Some Considerations for Treatment Planning the Veneer Modality
“I think if we can achieve the esthetic results we want with a veneer and keep our preparations primarily in enamel, veneers are far better alternatives than crowns,” believes Terry Donovan, DDS. “On the other hand, if the teeth are worn to a certain extent, sometimes we have to use crowns, and often we use a combination of crowns and some veneers, and which tooth receives what type of restoration depends on how much structure is left, as well as tooth position.”
Such determinations, however, are predicated on the comprehensive examination that includes conversations with the patient about his or her goals and what they are willing to accept in terms of compromise (eg, esthetics) in order to preserve as much tooth structure as possible, explains Dino S. Javaheri, DDS. Some patients want perfection, so their expectations must be reviewed before treatment planning, he says.
“With veneers, whether minimal prep, no-prep, or conventional, it really is all about case selection,” Javaheri says. “It’s definitely not a one-size-fits-all that will cover every patient. Treatment planning has to be very case-specific.”
Esthetic and Smile Design Considerations
Once clinicians have an understanding of what the patient hopes to achieve with veneers, it’s important to evaluate the midline position of the teeth, Javaheri says. If the midline is off and no tooth structure will be removed, then the laboratory can’t change that, he explains. So, if it’s off before, and you do no prep, it’s going to be off afterward as well.
He adds that lip fullness is another important consideration. If the patient has a thin lip and porcelain is added, he or she could feel like they’re scraping their teeth against their lip. If somebody has a very thick lip, they won’t notice additional porcelain or that the teeth have been built out, Javaheri says.
“With any veneer case, the incisal edge position is very important, but it is especially so with no-prep cases because we’re moving it forward,” Javaheri elaborates. “Additionally, when we alter the incisal edge position, it could affect the patient’s speech.”
Functional and Masticatory Considerations
“As with all restorative dentistry, the management of occlusal factors is extremely important. It is important to create an angle of guidance that does not create premature loading of the teeth during function,” explains Betsy Bakeman, DDS. “The greater the degree of structural and functional compromises presented in the pre-operative situation, the greater the degree to which these parameters must be managed.”
Tooth Size, Shape, and Color Considerations
What’s important about the tooth size and shape lies primarily with the widths of the teeth, Javaheri says. If dentists are just adding porcelain and they’re not reducing any tooth structure in between the teeth, they limit what the laboratory can do to change the size of teeth.
“If we have the two central incisors that are being restored and one is 1 mm larger than the other one, it will still be 1 mm larger than the other one afterwards if it is not prepared,” Javaheri explains.
There is no one technique of anything that works for every patient, explains Ed McLaren, DDS. When it comes to veneers, many times clinicians need to slightly lingualize teeth for the final esthetic result. This requires some preparations, he says.
Two other important esthetic considerations that will determine if a veneer can be prep-less, McLaren says, are:
- Is it going to be additive (ie, do you want to increase the volume of the tooth esthetically)?
- Is the shade of the tooth going to change? Note that you need 0.2 mm thickness of veneer for each shade grouping change (ie, A1 to A0 is one group; A2 to A0 would be two groups).
“The reality is that we have certain physical and anatomical limitations within which we can work and have something that, number one, looks good, but even more importantly, remains in what we call the confines of physiologic contours of the crowns,” explains Donovan. “Teeth are made to be shaped a certain way, and if we don’t prepare the tooth, then we’re simply adding on to it.”
Answering the earlier question of whether the case is additive and to what extent, or not, determines the need for preparation. Adding porcelain to the labial surface, or to the incisal edge, could result in over-contouring, Donovan says. As a result, most of the time in most patients, clinicians need to provide very specific preparations that allow for veneers that look good within the confines of physiologic contours, he believes.
According to Bakeman, situations that can accept additive-only protocols typically call for thin veneers to control bulk and minimize over-contouring. Thin veneers take advantage of the optical properties of the underlying tooth structure and, as a result, can be highly esthetic, she says. That of course requires the underlying tooth structure to be of an acceptable range and need minimal, if any, shift in color. The need to change color requires greater room for a variety of porcelains to facilitate a significant color shift.
“Certainly the design of the preparation is important. However, the most important factor to consider is the preservation of enamel. More extensive preparations have an effect on the flexure of the tooth, which can in turn have an influence in adhesive failures,” Bakeman says. “Studies have demonstrated that adhesive failures, which in their early phases are not detected clinically, are quickly followed by catastrophic failures of the porcelain. While it may appear that the porcelain fractured and that was followed by an adhesive failure, the reverse is more likely to be true.”
“The preparation of a virgin tooth is part of an overall treatment plan, and that doesn’t come into play too many times in my geographical area,” observes Michael R. Sesemann, DDS. “When it does, I’ve utilized on incisors both the overlap chamfer design and a butt joint coming off of the incisal edge, and both work really well with the incisors.”
With canines, what influences his preparation design is the presence of significant previous dentistry, Sesemann says. When there are a number of Class 3 composites on anterior teeth or various areas of erosion or attrition, those factor into the preparation design when treatment planning and diagnosing a particular restorative solution, he says.