Resin 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.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.

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


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