All About Dental Restorations
All About Dental Restorations
by Gary M. Verigin, DDS, CTN
If you’re like most of our incoming clients, you’ve probably read a lot about the dangers of mercury amalgam fillings. You also may have read about the systemic problems that can stem from root canals and dental implants. Maybe you suspect that many of your current health problems are due to one or more of these situations.
If your suspicions turn out to be true – and this is something that can be proved only through clinical examination and testing – solving the problem isn’t just a matter of removing the offending elements and replacing them with composites. If replacement is called for, it’s important to make sure that the materials you choose for your restorations are biochemically compatible. If they aren’t, your health situation may not improve. It could even worsen.
Fortunately, when it comes to dental materials, you have a lot of options. And the more you know about them, the more able you are to make an informed decision and realize your preferred health future.
The ABCs of Composites
Several dozen companies manufacture this tooth-colored material. Direct composites can be done in a single office visit. Indirect composites, on the other hand, are created by a dental laboratory, and two office visits are needed to complete the procedure.
All composites contain the materials listed below.
|Monomers:||The liquid portion of the composite usually consists of dimethacrylate (BIS-GMA) and/or urethane diacrylate. Because these elements are difunctional, they cross-link to provide an insoluble polymer matrix. (A polymer is a chemical compound that consists of repeating structural units.)|
|Fillers:||Generally composed of quartz, borosilicate and silicone dioxide or barium glass, fillers increase surface hardness while reducing thermal expansion, water absorption and polymerization shrinkage. (Polymerization refers to the hardening process of composites through two or more molecules combining into larger molecules.)|
|Surface Treatments:||Fillers are treated with a vinyl silicate that acts as a link between the inorganic filler and the organic polymer matrix.|
|Catalysts:||An organic peroxide, such as benzyl peroxide, produces radicals to start the polymerization process. In visible light systems, diketone activators are used.|
|Accelerators:||An aromatic tertiary amine or similar compound chemically reduces the half-life of the organic peroxide at mouth temperature.|
|Inhibitors:||Usually, these are provided by some form of quinine that increases shelf-life by preventing spontaneous polymerization.|
|Methacrylic Acid:||This increases the initial rate of polymerization. Its concentration is kept low, as excess results in poor wet-strength.|
|Colloidal Silica:||Pyrolitic silicic acid is used as a strengthener. It also eliminates the need for larger ceramic filler particles.|
|Pigments:||Coloring is provided by cadmium, chromium, cobalt and/or iron salts.|
Composite restorative materials were developed to be used instead of toxic mercury amalgams (so-called “silver” fillings). Composite is tooth-colored and can be made to seem nearly invisible. It is much more technique-sensitive than dental amalgam, but if properly placed and treated, it is just as durable.
Although the procedure can be done in a single office visit, composites take longer to insert than amalgam because the material must be carefully layered in increments no thicker than three millimeters. After each layer, a curing light is used to polymerize (harden) the composite material. The light can only be of a certain intensity so as not to overheat the delicate tissues of the pulpal complex (the nerves, vessels and other interior structures of each tooth.) This material has excellent characteristics for small fillings in particular.
|Before: Tooth #5, in the middle, shows no external decay. But digital x-rays revealed inter-proximal decay on each side.|
|During: Partial drilling of tooth #5 reveals the interior decay.|
|During: The opposite side of tooth #5 has been drilled, revealing additional decay.|
|During: Tooth #5 is now prepared, ready for the composite material to be bonded to it.|
|After: The composite has been placed and polymerized on tooth #5. Note how the filling has been shaped to simulate the original tooth surface and is indistinguishable from the natural teeth.|
The monomer is not a linear molecule. It has more than two double bonds. Once the hardening process begins, the bonds open as they become polymerized and form highly cross-linked molecules. These double bonds do not move around, so the composite is very strong and insoluble. This type of restoration is highly impervious to chemicals in foods, as well as saliva.
Direct composites do have a shortcoming: durability and longevity. When they fail, it is almost always due to fracture or breakage, as shown:
|Two teeth with composites, the rightmost showing obvious breakage. The one on the left is starting to break down on several edges, where the filling meets the tooth’s margin. As a result, these fillings had become sensitive to cold and the pressure of chewing.|
These teeth had originally been repaired with mercury amalgam when the client was a teenager. About eight years later, due to leaking and breakage, they were replaced with second generation mercury fillings. Eventually, they were replaced with direct composite material, which lasted another six or seven years. When the composites fractured, the client chose to have the fourth generation restorations made of gold – onlays made of 89% gold and 9% platinum.
|The failing composites now replaced with gold onlays.|
The gold restorations here are six years old, yet look as good as on the day they were placed.
One of the problems with having so many repeated procedures on each tooth is that it can injure a tooth’s pulpal complex. This can lead to post-treatment sensitivity. In the worst case scenario, the pain can be bad enough to warrant a root canal or surgical removal of the tooth.
The main reason direct composites are prone to breakage is that they are not fully polymerized. In any composite, a certain percentage of monomers are not converted to double bonds. Chemists tell us that some monomer systems are only 55% converted, while others are as high as 65% converted. The remaining 35 to 45% consists of open-ended molecules. In general, the higher the conversion rate, the more shrinkage of the composite.
Because the polymerization of a direct composite is never total, the unhardened portion remains unstable. When you chew or grind on its surface,outgassing occurs. Pressure releases potentially toxic chemical elements from the unstable portion – just as chewing or grinding on amalgam fillings releases mercury vapor. This is why it is so important to make sure that the composite material chosen is biochemically suited to your physical make-up. If inappropriate, there could be additional toxic effects on the body. So before deciding to use any restorative material, it is vital that the client take a blood serum test to determine the suitability of any proposed materials. Those who are especially sensitive to environmental toxins should also be given an electro-dermal screening to verify and refine the results of the blood test.
After the tooth has been etched with a dilute acid, an adhesive is bonded to it. The composite is placed and likewise bonded. The restoration is then light-cured at increments about two millimeters thick. This light-curing hardens the composite.
But one more question should be asked: how do such composites affect the surrounding oral tissues?
Mark Latta is a dentist and researcher at Creighton University Dental School who has studied the effects of the growth of mesenchymal fibroblasts on composite resin material. He writes,
Many factors affect the completeness of cure of composite resins. If under polymerized due to inadequate light energy or because of the depth of the resin, the biological compatibility of the material may be compromised. This could have ramifications, for example in the gingival tissue area adjacent to a Class II composite resin restoration. The purpose of the study was to evaluate PDL fibroblasts (PL) growth on specimens of fully polymerized and deliberately under polymerized composite resin. Filtek A110 (breast tissue from laboratory mice) was exposed to various curing conditions identifying fully converted and 50% converted composite resin specimens using attenuated total reflective FTTR. 2-millimeter thick specimens were placed inside 5 millimeter glass tubing and polymerized either fully (FP) or to 50% double bond conversion.
Confluent monomers of PDL fibroblasts were trypinized and re-suspended to a concentration of 1.5 x 10 x 4 cells/ml in Dulbecco’s modified Eagles medium. The resin specimens were placed in 24 well tissue culture plates and overlaid with 1 millimeter of the cell suspension. Controls were also concurrently as positive controls. The PDL’s were allowed to attach and were harvested at 2, 4, 6, 8 and 24 hours and 7 days. After washing off unattached cells, the resin specimens were fixed and stained. Cell counts were recorded for 4 x 2 mm x 2 area on specimens of each condition at each time period. Data was recorded as a percentage of cell counts compared to the control cultures and analyzed using a sign rank test.
2hr 4hr 6hr 8hr 24hr 7 days 50% Polymerization 42.6% 55.9% 47.9% 35.1% 33.1% 7.4% Full Polymerization 57.3% 76.0% 75.6% 75.8% 94.9% 99.4%
There were significant differences in cell attachment between the FP (fully polymerized) and 50% group (<0.05). After 7 days PDL attachment was equal to the control for the FP resin (p>0.05). PDL fibroblasts growth and attachment at seven days is equal to a control surface. Under polymerizing the resin inhibits PDL growth and attachment.
What this tells us is that direct-cured composites are not as inert as many first thought. Because the directly placed composite material is not hardened completely, about 60% of it will negatively affect the regeneration of the delicate periodontal tissues it touches. Totally uncured composites, as previously reported in the literature, may produced allergological-immunological activity, spurring the body to create antigens that could affect the body adversely over the long haul. It appears, then, that fully polymerized indirect composites are nearly always the best choice of direct restorations.
The material for indirect composites unites an advanced, high-strength fiber substructure with an aesthetic overlay of revolutionary low-wear and stain-resistant polymer-glass ceramic (polyceram) material. Metal-free, it possesses flexural strength. This material is classified as a CEROMER, which stands for CERamic Optimized PolyMER.
Taking two visits to complete, the procedure begins in the dental office. The tooth is mechanically prepared and impressions are taken. A temporary restoration is made, fitted to the tooth and cemented in place. The impressions are sent to a laboratory where specialists fabricate the restoration.
Indirect composites are virtually 99% polymerized. They are made of a highly reinforced, homogenous microfill material with radiopaque additives. They are light-cured at high-intensity, cured in high-heat furnaces and pressure-cured with a vacuum pump and pressure bowl for maximum strength. The result? Outstanding permanent aesthetic restorations.
|Before: Mercury-silver amalgam fillings in the upper left posterior of the mouth, with a porcelain-fused-to-gold full crown on the 2nd bicuspid. The client wanted no metal in her mouth.|
|During: All mercury has been safely removed.|
|After: Sculpture inlays, onlays and a full crown bonded to the prepared teeth. “Sculpture” is a brand of indirect composite material.|
|After: A side view of the same restorations. Note how in both views, the restorations are indistinguishable from the natural teeth.|
Indirect composites are even more durable than direct composites because of their greater density. Tooth structure is preserved and reinforced. And since the material is compatible with one’s natural teeth, there is less wear on the opposing teeth. The marginal integrity is enhanced, and there is minimal chair-side polymerization shrinkage. Moreover, they are very smooth, having a self-polishing surface. Since they are made on a laboratory bench and articulator, the technicians can take longer to make them, but because of this, more fine details, such as contour in all five surfaces of the tooth, can be incorporated. For true cosmetic results, a variety of tooth shades are available. The technicians can also refine the occlusal anatomy to provide a greater control of function and aesthetics to create a more optimal bite with the opposing tooth or teeth.
The long-range economy of this type of restoration is obvious.
In the Phase II office visit, the temporary restoration is removed and the laboratory restoration is placed on the tooth preparation. With a direct composite, it can be difficult to create just the right bite; the client is still numb, unable to feel all the teeth coming together. This is not an issue with indirect composites. Because the client is not anesthetized, we can refine the bite to exact detail. In fact, the occlusion often can be improved from what the person had originally.
Once the occlusion and the adjacent contacts have been properly refined, the client is anesthetized. The restoration is then bonded to the tooth using dual-cure-suitable composite cement.
Yet for all the strength and durability of indirect composites, there are superior materials.
Gold, Porcelain and Ceramic Restorations
Sometimes, gold remains the restorative material of choice because of its durability and biocompatibility. The chief features of this type of restoration:
- All restorations take two appointments: one for preparation and one for fitting the restoration.
- Gold alloys offer the greatest durability of any compatible dental restorative material.
- Gold alloy is a tough material. There is no possibility of it cracking.
- Gold alloy’s surface hardness is very similar to natural enamel, so it does not cause unwanted wear or abrasion.
- Gold can be mixed with many different metals, which give the final alloy different properties of hardness and color.
- The restorations are well tolerated by the gingival tissues.
- Deformations will not cause rupturing, as they will to ceramic materials.
- Alloys are ductile, rather than glass- or resin-based.
|Before: Mercury silver amalgams on the lower right posterior.|
|After: The lower right posterior restorations. Once the mercury was safely removed, high noble 89% gold inlays were placed in each of the teeth.|
|After: A side view showing the completed restorations.|
Porcelain Fused to Gold
Porcelain fused to metal restorations are often used in the back of the mouth because of their strength. They stand up better to the increased force of chewing. When decay has invaded the root structures and is hidden below the gum tissues, the chamfer-style margins, when fabricated in gold, offer a more precise and superior fit than the shoulder margins used for composite and porcelain full-crown restorations.
On the other hand, slightly more tooth structure must be removed to accommodate for the metal substructure and allow for the proper porcelain thickness. If the dentist does not remove enough, the result is an oversized crown. In such a case, if the technician tries to build a correctly sized crown, the optical qualities of the porcelain will be sacrificed somewhat because staining will be needed to enhance the surface appearance. Generally, this comes at the expense of translucency and other optical qualities.
If the margins facing the outside of the tooth are not made as a “shoulder/butt margin” preparation but as a combined margin of gold and porcelain, restorations made from low-noble alloys will exhibit a “black line margin”: the metal substructure shows through the thin gingival area surrounding the tooth and restoration. This can be minimized by using a very thin high-noble gold margin. It can be done in the further reaches of the dental arch, where it is less conspicuous when the person smiles or talks.
The typical gold alloy used in such restorations is 88.4% gold and 9.5% platinum. These are mixed with 1% or less of manganese, zinc, indium and iridium.
|Before: Tooth preparations, 2nd lower bicuspid, 1st and 2nd molars. The roots of each tooth were very sensitive to temperature changes, sweets and brushing. Note the stained dentin from mercury amalgams.|
|After: A side view showing the completed restorations.|
Although porcelain fused to gold restorations are used mainly on the molars, we sometimes use them on the front teeth. For incisors, cuspids and bicuspids, though, all-porcelain or ceramic, non-metallic crowns are preferable.
Porcelain and Ceramics
All porcelain restorations are classified as indirect restorations, and in many ways, they are similar to indirect composites. Both offer
- Beauty and the reproduction of almost any shade of tooth in one’s mouth.
- Outstanding durability.
- Excellent smoothness, a self-polishing surface and virtually no irritation to the gums.
- Enhanced contours and occlusal anatomy for a better bite.
- Preservation and reinforcement of tooth structure.
- The appearance and feel of healthy, attractive teeth, even in the most demanding cases.
- The formation of a lasting bond that reinforces the tooth from every angle, as opposed to the mere filling of a tooth.
- Excellent biocompatibility.
- A close marginal seal, enhanced by the restoration’s bond with moist dentin and enamel.
However, if you consider the individual components of porcelain, you will note some significant differences between porcelain and composites, as well.
- Porcelain restorations appear even more natural due to an absence of core material. As a result, they have enhanced optical properties such as light transmission and illumination, vitality, translucency and surface brilliance. Reflection of porcelain closely mimics that of natural tooth structures.
- Porcelain restorations are made of an all-ceramic system based on glass that contains nucleating agents. In a multi-stage process, controlled crystallization is used to produce leucite crystals, each measuring a few microns, in the glass matrix. The semi-finished product of leucite-reinforced ceramic powder is pressed and vacuumed into ingots and sintered. Technicians press restorations from these basic components.
- Porcelain – though its characteristics are in the range of natural enamel – is harder than most tooth structure, so bruxing or grinding teeth will cause adverse wear against the opposing teeth. Yet it’s not as tough as composite, so breakage is a possibility. Any breakage that does occur, however, is minimal.
- Porcelain restorations usually have less shock-absorbing capability than composites, but this matters only with implants.
|Before: Gum recession due to trauma from the parafunctional habit of clenching. The teeth are discolored because the dentin on the exposed tooth roots is porous and easily subject to staining.|
|After: The six front teeth have been restored with Empress porcelain crowns.|
Increasingly, we are relying on ceramic restorations made with CAD-CAM technology. “CAD-CAM” stands for Computer-Aided Design and Computer-Aided Manufacture. They are the cutting edge in restorative dental technology.
Bridges and crowns are made from a ceramic core built up with porcelain, while inlays and onlays may be fully-milled blocks of ceramic material. These materials are some of the strongest yet made. Even better, they are extremely biocompatible and aesthetically superior. They are reportedly as durable as gold and fit as well, blending in cosmetically with all the surrounding teeth. They let us create ideal conditions in the mouth: one that contains no metals at all. And no metals in the mouth means no adverse oral batteries or galvanic currents can be created by the restorations.
|Before: Mercury silver amalgams in the lower right quadrant.|
|During: All mercury has been safely removed.|
|After: Fully milled CAD-CAM inlays bonded to each prepared tooth. Compare to the previous composite photos and note the greater brightness and reflection of these restorations.|
As you can see, CAD-CAM restorations blend perfectly with the adjacent teeth. They are nearly invisible – even when viewed through magnifying lenses. Moreover, the surfaces feel just like those of your tooth before it got damaged. Biofilm also has a much harder time clinging to these restorations than to natural teeth, let alone toxic mercury fillings or direct composite resin fillings.
Dental ceramics manufacturers seemingly never sit back and let time go on without further research. And we can be sure that the lab we use will be right up-to-date as well. Thanks to the fine team at Creative Arts in Sacramento, we can provide you with the best possible restorations to fix damaged teeth, made with the most biologically inert dental materials ever introduced to the profession.