TheOptimalSmile
Operative Dentistry
Operative Dentistry is that portion of the profession which deals with the treatment of missing or malformed portions of teeth caused by tooth decay (caries), trauma, discoloration or unusual development. Typical materials used by the dentist to restore and correct these conditions are silver amalgam, tooth-colored composite resin or resin modified materials, porcelain, gold and other cast restorative materials.
Filling Materials 1- composite 2- Amalgam
The Natural Beauty of Tooth Colored Fillings The public's demand for aesthetic tooth colored (metal free) restorations (fillings) together with the dental profession's desire to preserve as much natural tooth structure as possible has led to the development of special “adhesive” tooth colored restorations. And this demand is not limited to front teeth.
It is now clearly established that a new Biomimetic Approach (bio – life, mimetic – mimicking) to dentistry is possible through the structured use of tooth-like materials such as composite resins and porcelains. Scientific studies and clinical experience have validated their use as both safe and predictable. These changes have significantly impacted upon the way modern dentistry is practiced. Indeed, we may have even entered the so-called “post-amalgam era.” These techniques are also suitable for children's teeth and can incorporate fluoride to reduce decay rates.
This article will review this evolution and the process that has led to the development of materials that bond successfully to the building blocks of the teeth, enamel and dentin. Properly restored teeth not only function and wear normally under biting forces, but also look indistinguishable from natural teeth.
Teeth and Materials — “Biomimetics” — Mimicking Life
Teeth through their unique combination of nature's materials constitute a perfect compromise between strength and resilience. This is interesting because these two materials, enamel and dentin, while in some ways are quite similar are also very different.
Enamel which forms the outer hard shell covering (the crown) of a tooth, is arguably the hardest substance produced by animals in nature. Made of very densely packed crystals of calcium (hydroxyapatite), it is this crystalline structure that provides its hardness, brilliance and translucent properties, as well as its resistance to wear. Once formed, enamel is quite inert since there is no living tissue within it.
Properly restored teeth function and wear normally, appearing indistinguishable from natural teeth.
Figure 1: This illustration identifies
the parts of a tooth.
Most of the properties of enamel are mimicked quite well by dental porcelains. Porcelains are a form of ceramic, inorganic non-metallic materials formed by the action of heat. Dental porcelains are made in many colors and shades; they are manufactured in a powder form corresponding to the primary colors of basic tooth structure which is mixed with water and then placed in an oven for “firing” — hence their ceramic nature. These porcelains when built up in layers can be made to exactly mimic the natural translucency, staining and contours of tooth enamel.
By contrast the inner core of the tooth and root are made of dentin which has a more porous nature, and is similar to bone. Dentin has a tubular structure, microscopic tubes made of a protein called “collagen” on to which calcium crystals are deposited. Through the living dentin, sensation is transmitted via nerve tissue in the pulp, a central chamber in the middle of the tooth.
Dental composite resins are the most common material used for tooth colored adhesive restorations today and have properties similar to dentin. They consist of “resin” – plastic (methacrylate, a commonly used plastic) and “fillers” made of silica (a form of glass). The fillers give the composites wear resistance and translucency (see-through properties).
Bonding — Nature Influencing Art, Art Mimicking Nature
Scientific discovery and ingenuity have led to the successful bonding of composite resins to enamel, now in use for many years. The startling discovery of the nature of the interface (join) between dentin and enamel of teeth, paved the way for the principles employed in adhesive dentistry.
Successful bonding to dentin has required more research and understanding. Ultimately it has been achieved by a process in which the dentin surface is specially “prepared” and then “sealed.” “Immediate Dentin Sealing” (also called “resin coating”) creates an intimate physical and mechanical bond which is not only very strong, but also overcomes the tendency of the composite resin to shrink. Importantly, it also keeps the tooth and therefore you — comfortable. This technique forms the base to which further composite can be added for rebuilding lost tooth structure.
Restorative Dentistry's Challenge — Rebuilding Teeth
The restoration or rebuilding of back teeth from “the ground up” so to speak is dependent upon successful bonding to both enamel and dentin — the foundation of adhesive restorative dentistry. The goal of restorative dentistry is to return all of the destroyed or lost dental tissues of the teeth to full form (shape) and function — allowing biting stresses to pass through them. These adhesive techniques maximize preservation of tooth structure with minimal preparation (drilling) and allow the maintenance of their vitality and natural appearance.
Major advances in this area have also resulted from the study and understanding of how the crowns of teeth actually flex or give under biting force and how dental restorative materials can be used to greatest effect. These newer materials have been developed to actually fuse with natural tooth material and match its behavior, both stabilizing and strengthening the restored tooth thereby reducing the rate of premature failure from fatigue or fracture. They also recreate very natural looking teeth.
How Modern Dentistry Mimics Nature
Choosing which material to restore or rebuild teeth is a critical one based on scientific understanding and the experience and clinical judgment of your dentist.
Proper tooth restoration is a lot more than just filling holes. It is a unique art applied with scientific understanding. It is the shapes and location of the back teeth, the “premolars and molars” that allow their specialized function — chewing and breaking down food. A tooth's internal shape and structure is the guide to how it must be rebuilt in order to be successfully restored. Older restorative concepts were based on the development of excessively strong and stiff materials (such as gold alloys) unable to yield and therefore contributed to failures of the remaining tooth substance around restorations (e.g. decay or cracking). Newer concepts tend to get away from the “stronger and stiffer is better” concept, and rather have moved towards safety principles using materials that mimick the properties of natural tooth structure.
Matching the Behavior of Teeth
Immediate Dentin Sealing — involves the formation of a resin coating which both seals and protects the dentin surface against bacterial leakage and sensitivity. Most importantly it keeps the tooth and you the patient comfortable. This is also the first layer of a sandwich-like structure known as a “hybrid layer” (resin coating) to which composite resin is bonded to rebuild tooth structure.
Dentin Build-up — following its sealing the dentin forming the core of the tooth can be rebuilt with composite resin, adding small layers at a time to fill voids or “undercuts.”
A disadvantage of the older amalgam (silver looking fillings) is that they require a special shape called “undercuts” to be cut into the tooth to hold them in. However, this can involve removal of healthy tooth structure. Too much undercutting can undermine and weaken a tooth resulting in less resistance under biting forces possibly leading to fatigue fractures and cracked tooth syndromes.
Direct, Semi-Direct or Indirect Restorations
Sounds like the way some people talk. “Direct, Semi-Direct and Indirect” all describe the techniques by which restorative materials are incorporated into the repair process.
They involve both the method and timing of events in the placement of aesthetic adhesive restorations in posterior (back) teeth today. Deciding which restorative material to use is driven by many factors, the most important of which are how much natural healthy tooth structure remains, its location and the many properties of the different restorative materials available today.
Start by Being Direct — smaller amounts of tooth structure can be replaced directly into small cavities which have resulted from decay. These are direct (or “chairside”) techniques carried out in a single treatment visit using composite resins [Figure 2]. The direct technique is used for preventive as well as relatively conservative situations. Adding the material in small increments allows it to set in the mouth utilizing special lights. This allows complete setting of each increment and overcomes the problem of the shrinkage tendency. The dentist's artistry can create absolute tooth-like replicas — you'll never know the teeth have fillings.
A Semi-Direct Technique — is necessary when a larger volume of tooth structure has to be replaced [Fig 3]. A similar layering technique is used, but the newly formed restoration can be removed and set or “cured” outside the mouth [Fig 4]. This compensates for the shrinkage of the larger volume of material and improves its strength and wear resistance. It is then finally bonded to the tooth [Fig 5].
Another technique for semi-direct restorations is the CAD/CAM (Computer Assisted Design/Computer Assisted Milling) technique for manufacturing “inlays.” This new and quite sophisticated technology allows “chairside” fabrication of restorations of harder and more durable composite or porcelain materials.
Indirect Techniques — are indicated where extensive tooth structure needs to be replaced. Essentially there is not enough tooth left to put a filling into, rather a restoration must be manufactured to replace most of the crown (the visible tooth). This may especially involve the cusps of teeth — the little peaks or points of the back teeth, and necessitates the use of stronger materials to compensate for this more extreme enamel loss.
Indirect techniques are used because the restorations can neither be made directly to the teeth, nor can they be placed the same day. Often aesthetics and dynamic occlusion (biting relations) are issues of primary concern in these situations. The skill of a dental laboratory technician is required to fabricate these more complicated porcelain restorations [Figures 6-10].
The Finale
Today's “Composite Resins” and “Porcelains” allow restorations encompassing moderate loss of tooth structure, but are also able to treat more perilous situations in which more significant amounts of natural tooth material have been lost. Unlike metal alloys, these newer materials bond directly to the remaining enamel and dentin of which the teeth themselves are made, both stabilizing and strengthening them. This has resulted in considerable improvements in tooth restoration; from a biologic aspect — preserving more natural tooth structure; an economic aspect — these newer materials are both more conservative and cheaper; and an aesthetic aspect — resulting in very natural looking teeth.
Figure 2: An example of a “direct” composite restoration (right) replacing an older, failing silver filling (left). Courtesy of the CDA journa
Figure 3: A photograph of two molar teeth with old silver fillings that are being replaced.
Figure 4: These fillings represent examples of a “semi-direct” composite technique finished outside of the mouth.
Figure 5: A photograph showing the beauty of the “semi-direct” technique restoring the molar teeth to their original appearance.
Figure 6: A failing gold restoration.
Figure 8: Immediate dentin sealing after decay removal.
Figure 7: Decay found underneath the gold filling.
Figure 9: A dental laboratory fabricated “indirect” restoration.
Figure 10: The final restoration showing a beautiful result.
What is a Composite Resin (White Filling)?
A composite filling is a tooth-colored plastic and glass mixture used to restore decayed teeth. Composites are also used for cosmetic improvements of the smile by changing the color of the teeth or reshaping disfigured teeth.
How is a composite placed?
Following preparation, the dentist places the composite in layers, typically using a light specialized to harden each layer. When the process is finished, the dentist will shape the composite to fit the tooth. The dentist then polishes the composite to prevent staining and early wear.
What is the cost?
Prices vary, but composites can cost up to two times the price of a silver filling. Most dental insurance plans cover the cost of the composite up to the price of a silver filling, with the patient paying the difference. As composites continue to improve, insurance companies are more likely to increase their coverage of composites.
What are the advantages of composites?
Aesthetics are the main advantage of composites, since dentists can blend shades to create a color nearly identical to that of the actual tooth. Composites bond to the tooth to support the remaining tooth structure, which helps to prevent breakage and insulate the tooth from excessive temperature changes.
What are the disadvantages?
After receiving a composite, a patient may experience postoperative sensitivity. Also, the shade of the composite can change slightly if the patient drinks tea, coffee or other staining foods. The dentist can put a clear plastic coating over the composite to prevent the color from changing if a patient is particularly concerned about tooth color. Composites tend to wear out sooner than silver fillings in larger cavities, although they hold up as well in small cavities.
What is Dental Amalgam (Silver Fillings)?
Most people recognize dental amalgams as silver fillings. Dental amalgam is a mixture of mercury, silver, tin and copper. Mercury, which makes up about 50 percent of the compound, is used to bind the metals together and to provide a strong, hard, durable filling. After years of research, mercury has been found to be the only element that will bind these metals together in such a way that can be easily manipulated into a tooth cavity. See More Click Here .
Is mercury in dental amalgam safe?
Mercury in dental amalgam is not poisonous. When mercury is combined with other materials in dental amalgam, its chemical nature changes, so it is essentially harmless. The amount of mercury released in the mouth under the pressure of chewing and grinding is extremely small and no cause for alarm. In fact, it is less than what patients are exposed to in food, air and water.
Ongoing scientific studies conducted over the past 100 years continue to prove that amalgam is not harmful. Claims of diseases caused by mercury in amalgam are anecdotal, as are claims of miraculous cures achieved by removing amalgam. These claims have not been proven scientifically.
Why do dentists use dental amalgam?
Dental amalgam has withstood the test of time, which is why it is the material of choice. It has a 150-year proven track record and is still one of the safest, durable and least expensive materials used to a fill a cavity. It is estimated that more than 1 billion amalgam restorations (fillings) are placed annually. Dentists use dental amalgam because it is easier to work with than other alternatives. Some patients prefer dental amalgam to other alternatives because of its safety, cost-effectiveness and ability to be placed in the tooth cavity quickly.
Why don't dentists use alternatives to amalgam?
Alternatives to amalgam, such as cast gold restorations, porcelain and composite resins are more costly. Gold and porcelain restorations take longer to make and can require two dental appointments. Composite resins, or white fillings, are aesthetically appealing but require a longer time to place the restoration. It should also be known that these materials, with the exception of gold, are not as durable as amalgam.
What about patients allergic to mercury?
The incidence of allergy to mercury is far less than one percent of the population. People suspected of having an allergy to mercury should be tested by qualified physicians, and, when necessary, seek appropriate alternatives. Should patients have amalgam removed? No. To do so, without need, would result in unnecessary expense and potential injury to teeth.
Are dental staff occupationally exposed?
Dentists use premixed capsules, which reduce the chance of mercury spills. And newer, more advanced dental amalgams are containing smaller amounts of mercury than before. An interesting factor can be brought into this: Because dental staff are exposed to mercury more often, one would expect dental personnel to have higher rates of neurological diseases, such as multiple sclerosis. They, in fact, do not.
What are other sources of mercury?
Mercury can be found in air, food and water. We are exposed to higher levels of mercury from these sources than from a mouthful of amalgam
