Causes of Tooth Damage
While many things can damage teeth, in general, they fall into two categories – damage from chemicals (acid) and damage from friction (abrasion). The most common type of chemical breakdown is tooth decay, which is the result of demineralization of the tooth by acid producing bacteria. However, there are other important sources of damaging acid, including acid reflux disease and acidic foods or beverages (see “Causes of Worn Teeth” article).
The hardest and most abrasive thing most teeth come in contact with is not the foods we eat, but rather the opposing teeth with which they come in contact. Damage from friction between teeth is most commonly the result of biomechanical issues (see “Dental Biomechanical Harmony – the Key to Predictable Dental Comfort, Health, and Esthetics” and “Biomechanical Disharmony – Problems, Evaluation, and Treatment”). These are usually the result of either biomechanical disharmony or tooth grinding (bruxism) which damage the functioning surfaces of the teeth – the chewing surfaces of back teeth and inside, outside, and biting edges of front teeth. In both cases, the wear or breakage of tooth structure is a result of the friction generated by the rubbing together of opposing teeth.
Another important cause of frictional damage is what is referred to as “toothpaste abrasion”. In a recently completed study, it was shown that, contrary to what was previously believed, tooth brushing alone (without toothpaste) could not damage tooth structure – regardless of how soft or firm the bristles were and regardless of the brushing technique. However, when toothpaste was added, damage became possible. It was discovered that when a “scrubbing” tooth brushing method was used with any combination of toothbrush and toothpaste types, teeth were damaged. In addition, contrary to what was expected, it was discovered that whether a soft bristle brush with a low abrasion toothpaste was used or a stiff bristle brush with a more abrasive toothpaste was used, the amount and type of damage was about the same – a notch-like defect near the gum line, most frequently on the cheek side of the tooth (see “Toothpaste Abrasion” article).
Restoring Damaged Teeth
The appropriate type of restoration depends upon a number of factors. Foremost are the amount and part of the tooth that are damaged. However, the position of the tooth (front vs. back), the importance of appearance, and a need to restore biomechanical harmony or function are also important considerations. The following is a list of different restoration types and typical applications for each.
Amalgam (silver) fillings:
Amalgam has been used to fill teeth since 1826. It has many excellent physical properties and has saved countless millions of teeth. However, because of toxicity concerns and the development of bonded composite, Dr. Hegyi has not placed mercury containing amalgam fillings since 1983.
Bonded composite fillings have replaced amalgam fillings in this and many other dental practices. Dental composites are made of synthetic resins with coloring agents and glass-like filler particles to increase strength. When the structural integrity of a tooth is still intact, tooth colored composite fillings that are bonded to the tooth may provide many years of functional and esthetic service. However, all fillings (even bonded composite) weaken a tooth, leaving it more susceptible to breaking or cracking. Therefore, when a tooth has a large defect or the structural integrity of the tooth is compromised, bonded composite fillings (or any other variety of fillings) are not a good choice. Both the filling itself and tooth are at risk. The filling is likely to fracture or leak (resulting in decay under the filling) and the tooth is at risk of fracturing or cracking. Either of these may lead to the need for root canal treatment or tooth loss. When the structural integrity of a tooth is compromised, a tooth strengthening restoration should be placed.
When there is a significant loss of tooth structure or the tooth is at risk of fracture, a crown may be the best treatment. Crowns are the most common type of tooth strengthening restorations used. They surround the entire tooth, all the way to the gum line, adding strength and holding it together – similar to how the rings of a barrel hold it together. Crown types include all-metal (usually gold), metal with a covering of ceramic, and all-ceramic varieties. These varieties possess significant differences in strength, appearance, and the amount of tooth structure that must be removed in order to use them. Therefore, the requirements of each patient and each individual tooth must be considered when choosing the best crown type. There is not one type of crown that is the best for every situation. However, with the ceramics that are now available, in most cases, some variety of metal-free tooth-colored all-ceramic crown is the best choice.
Within this group of all-ceramic crown types, there are also significant differences in appearance, strength, and the amount of tooth structure removal required. One noteworthy variety is the all-zirconia crown. Zirconia has a remarkable combination of high strength, high biocompatibility, excellent fit accuracy, very low frictional wear of opposing teeth, and good esthetics. This combination of desirable properties has never existed before in dentistry. In addition, because of their strength, they require very little tooth reduction (approximately 1 mm – less than ½ of other tooth colored crown types), making them the most minimally invasive variety of crown available. As a result they are revolutionizing when and how crowns are used in dentistry. Although their visual qualities may not make them the best choice for esthetically critical front teeth, their tremendous fracture resistance and minimal tooth reduction requirements make them an excellent choice for most back teeth.
When the esthetic requirements are higher than all-zirconia crowns can provide, there are more esthetic varieties of ceramics to choose from. Again, these ceramics are also going to vary in both appearance and strength, so there is not one variety that is the best choice for every situation. However, when both visual and biomechanical requirements are considered, each of them has a place where it is the best choice (see “Esthetic vs. Cosmetic Dental Treatment”). It is for this reason that this practice and Dr. Hegyi use only a dedicated laboratory that is able to produce all crown (or Onlay or Veneer) types – with the finest combination of strength, esthetics, and precision possible.
Onlays are very similar to crowns in that they cover the entire chewing surface of the back teeth and add strength and fracture resistance to the tooth. They can also be made out of the same material types. How they differ is in the extent to which they cover the sides of the teeth. As described above, crowns cover the tooth all the way to the gum line. Onlays on the other hand only extend as far as is necessary to cover defective tooth structure and add needed strength to the tooth.
In many cases, even when a tooth is badly damaged or weakened, much of the sides of the tooth are healthy. In this situation, an onlay may be the best, most conservative treatment. The advantage of the onlay here is that since it does not involve as much of the tooth, the amount of tooth structure that must be removed to place it is also reduced. Compared to a crown, the onlay is a less invasive and slightly less costly treatment option.
Veneers are often believed to be a purely cosmetic treatment – only for improving the appearance of the front teeth. They are also often believed to only involve the front surface of the teeth and of being very much different than crowns. While these statements may be true in some cases, in most cases they are not. The following are some important facts about veneers including their composition, properties, and proper applications.
Composite vs. Ceramic Veneers:
Veneers may be made of either dental composite or ceramic. While many practices offer only ceramic veneers, we believe there is currently a place for both composite and ceramic types. Composite veneers were the first type of veneers. Their use began when the technology for bonding tooth colored composite materials to teeth was developed in the mid 1970’s. Dr. Hegyi first began creating composite veneers when he graduated from dental school in 1978. One of the reasons he believes there is still a place for composite veneers today is because they continue to be some of the most beautiful restorations possible. In addition, they are also the most conservative, least invasive means of making many esthetic and functional corrections to teeth.
To better understand why they are the least invasive restoration possible, it is helpful to think of a tooth in terms of its qualities of structural integrity, appearance, and function. Next, think in terms of the existing status of each of these qualities – and furthermore, consider the status of each of these qualities for each part of each tooth. The existing condition for any part may be Defective, Excessive, Deficient, or Acceptable. Examples of Defective tooth structure could be areas of decay or stain. Excessive tooth structure could be a portion of a tooth that is either unattractively too long or interfering with healthy function (see “Dental Biomechanical Harmony – the Key to Predictable Dental Comfort, Health, and Esthetics” and “Biomechanical Disharmony – Problems, Evaluation, and Treatment”). Deficient tooth structure could be areas of a tooth where material needs to be added in order to make it look or function better (e.g. teeth that are esthetically too short or narrow, or teeth that need to be added to in order to function properly with the opposing teeth). Acceptable tooth structure is all tooth structure that is esthetically, functionally, and structurally acceptable.
An important fact is that, typically, even when teeth are badly damaged or unattractive, portions of these teeth are still structurally, esthetically, and functionally Acceptable. Composite has the unique quality of being able to restore esthetics and function to teeth by removing only Defective or Excessive tooth structure. All healthy, Acceptable tooth structure is maintained. Any other method of restoring teeth, even ceramic veneers, requires the removal of some Acceptable tooth structure.
If composites can look beautiful and allow the least invasive treatment, then why not make all veneers out of composite? This is because, like most materials, composite also has limitations. The first and most important limitation is their susceptibility to staining or discoloration. While color stability of composite has improved, they will still ultimately discolor in the mouth (becoming yellow or dark). In addition, how quickly this occurs is highly variable from patient to patient. In some patients, they will discolor within a couple years, while in others they may remain unchanged for several years. Unfortunately, it is not possible to predict in which patients discoloration will occur quickly and in which the color will remain stable.
The second weakness of composite is that it is not as strong as many ceramics. Even though composites have become stronger, they are still more susceptible to breakage than most ceramics. Therefore there are limitations to where and how composite can be added to make esthetic or functional corrections (e.g. adding to the biting edge to lengthen a tooth).
Finally, composite is a highly translucent material. When bonded to the tooth, its appearance is affected by the color of the tooth that it covers. Therefore, if it is covering a nicely colored tooth, it will look beautiful and natural– blending in with the visual characteristics of that tooth (a quality referred to as the “chameleon effect”). However, if there is underlying stain or discoloration, the appearance of the composite will be adversely affected. As with all restoration types, there are situations where composite veneers are the best treatment option and others where they are not. Only with many years of experience creating composite veneers combined with a careful and thorough evaluation can Dr. Hegyi determine what results can be realistically expected.
The appearance of composite (or ceramic) veneers can often be determined before treatment with a “mock-up” or “preview”. In this procedure, composite or temporary crown material can be placed on the tooth (but not bonded) for viewing and then removed. However, while this procedure demonstrates the initial shape and shade of the veneer, it does not predict long-term color stability or durability.
Because of the limitations of composite, ceramics are the most common materials used to make veneers in the US. The variety of ceramic types is similar to those used for crowns and onlays. Their color stability, strength, and ability to make esthetic changes with conservative treatment make ceramic veneers the treatment of choice in many situations. There is virtually no esthetic situation involving healthy teeth that can’t be improved with ceramic veneers. Although ceramic veneers require more removal of tooth structure than composite veneers, tooth preparation is still very minimal. This is because the ceramic veneer is bonded to the tooth and only needs to be approximately ½ millimeter (approximately 1/50 of an inch) thick.
Ceramic Veneers vs. Ceramic Crowns
When ceramic veneers were first introduced in the early 1980’s, there were clear distinctions between veneers and crowns (or “Caps”) for front teeth. Early ceramic crowns for front teeth required a very aggressive removal of tooth structure all around the tooth and even under the gum line (the “tooth preparation”). Veneers on the other hand covered only the front surface of the tooth and involved little or no tooth preparation (although the complete lack of tooth preparation usually results in over-sized or bulky looking teeth). In addition, ceramic veneers were done strictly for cosmetic purposes, with no attempt to improve strength or function (see “Dental Biomechanical Harmony – the Key to Predictable Dental Comfort, Health, and Esthetics” and “Biomechanical Disharmony – Problems, Evaluation, and Treatment”). However, today because of advances in materials and technology, and a better understanding of the functional importance of front teeth, differences between all-ceramic crowns and ceramic veneers are not always so clear.
We now understand that in order to achieve ideal esthetics with veneers, as well as improve function, we usually need to involve more than just the front surface of the tooth (see “Esthetic vs. Cosmetic Dental Treatment”). Because of this, tooth preparations for ceramic veneers involve more tooth structure being removed today than they originally did (although they are still very conservative). Conversely, as described above, tooth preparations for modern all-ceramic crowns have become more conservative.
As a result, it is not always clear whether we should call some of these restorations veneers or crowns. However, in the end, what we call it really isn’t important. What is important is that the restoration be done in a way that is esthetically and functionally as ideal as possible, with the least possible removal of healthy tooth structure.