Dental Devices continued
by Tim B Hunter, MD, MSc and Rick Light, DDS
Mandible and Maxilla: Dental and Facial Implant Devices
General dentists, prosthodontists, periodontists, orthodontists, and oral surgeons use restorative and reconstructive prosthetic devices manufactured from alloplastic materials, acrylics, ceramics, porcelains, and metals (elemental and alloys) (figures: dental and mandibular devices). In dentistry, most alloys contain varying combinations of gold, platinum, palladium, silver, cobalt, aluminum, copper, chromium, zinc, and mercury. Except for aluminum, all metals and metal alloys used in dentistry are radiopaque.
Dental amalgam consist of an alloy of
two or more metals. It is intensely
radiopaque and is composed primarily of mercury (>50%) (figure: mandibular fractures; figure: miscellaneous dental devices). The leading secondary element is silver,
followed by trace elements that may include copper,
tin, and zinc. These trace elements are used
to aid against expansion and corrosion. Dental amalgam is used to fill in bony defects caused by dental caries.
recently, dental amalgams enjoyed universal acceptance.
Concern has been expressed about potential
mercury toxicity through systemic absorption of the mercury from the
scientific evidence that dental mercury
amalgam presents a danger remains elusive,
the much-heated debate within the dental profession
continues. In light of the alleged risk to the
medical and dental health of patients as well the
high probability of an unsatisfactory aesthetic outcome
with its use, the future of dental amalgam is uncertain.
Acrylic polymers are especially suited for a wide variety of dental applications (Phillips, 1991; Stafne, 1985). Acrylics are relatively inexpensive and well tolerated by the body. They may be easily fabricated to any desired size, shape, and color. The relative ease with which they can be colored allows an acrylic prosthesis to have not only functional value but an appealing “natural” look for such items as dentures, orthodontic appliances, oral orthopedic appliances, bite guards, temporary or definitive restorations, crowns, bridges, and cosmetic veneers. Dental acrylics are usually radiolucent. To avoid their being misconstrued as dental pathologic lesions radiopaque fillers are added to the acrylics (figure: zicornia crown and acrylics; figure: dental overview).
Fillers often add strength to composite acrylic resins. The aesthetic value of adding fillers to color composite restorations for an ideal match with natural tooth dentin or enamel is complemented by the ability of these fillers to enhance resistance to destructive masticatory forces. As a result, this type of dental restoration provides a formidable challenge to the dominant position once held by amalgam alloys in restorative dentistry. Aesthetics and strength make composite acrylic resins the restoration medium for the radiographic detection and diagnosis of dental disorders.
Removable denture prosthetic devices with chromium alloy, resin acrylic
bases and teeth, or porcelain teeth provide an economical alternative for the partially edentulous
individual. In addition, a semipermanent appliance can provide long-term temporomandibular joint stability
for patients suffering from masticatory-related temporomandibular disease or craniofacial
pain. Although acrylics are, to varying degrees, radiolucent, the metal framework is intensely
radiopaque (figure: removable partial denture; figure: temporomandibular prosthesis; figure: dental implants, bridgework, acrylic teeth).
Porcelain dental materials are stronger and more opaque than acrylic materials. Their radiopacity is similar to that of natural tooth enamel (figure: root canal fillings and porcelain teeth; figure: cubic zirconia and acrylics). Unfortunately, they are much more brittle. Dental porcelains are widely used and like composite acrylics, may be altered in color to conform to the “natural” look of dentin or enamel. They have become an integral component to crowns, bridges, veneers, and dentures. To compensate for their brittleness in crown restorations and fixed partial dentures, dental porcelains have been used with an underlying substructure of metal alloys, such as gold, palladium, or nickel and beryllium. For fixed partial dentures, metal alloys have been necessary to acquire the strength needed to span edentulous areas (figure: removable partial denture).
The latest generation of reinforced composites, soft porcelains, and ceramic substructures has dynamically changed the options available for both the doctor and the patient. Lucite-reinforced composites and soft porcelains are now directly bonded to the tooth with resin bonding agents that are almost totally resistant to the effects of washout from fluids within the oral cavity. Ceramic substructures, such as cubic zirconia (zirconium oxide), allow for permanent fixation with cements. They have the strength once provided by metal alloys while meeting the modern aesthetic and cosmetic demands of patients (figure: zirconia crown and acrylics).
Ceramic substructures have totally replaced all metals and metal alloys for fillings, inlays, onlays, cosmetic veneers, crowns, and fixed partial dentures (bridges). The synergy of ceramic composites or porcelains with bonding resins has yielded dental devices with such a look and feel that they are virtually indistinguishable from natural human teeth clinically or radiographically.
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Root Canal Treatment
The term "root canal" is sometimes considered as a synonym for "torture," probably because it can be an unpleasant procedure used for severe dental disease. Root canal treatment is designed to repair and save a badly diseased tooth which is decayed and infected (figure: root canal). There is often a periodontal abscess around the root(s) of the tooth. Anatomically, a root canal is the natural cavity in the center of a tooth with a soft area, the pulp chamber or root pulp containing vascular connective tissue and the tooth's nerve.
A root canal procedure cleans the nerve root and pulp from the tooth. An access hole is drilled into the tooth to permit drainage of infected material and removal of the pulp and nerve by suction and by the use of root canal files. The sides of the root are scraped and cleaned. The debris is flushed away by water or a weak sodium hypochlorite solution. Medication may be placed inside the tooth as well. The tooth may be sealed the same day or later. The interior of the tooth is usually filled at the next appointment with a sealer paste and gutta-percha, a resinous filling material. A filling or a dental crown is then used to permanently seal the access hole in the top of the tooth and restore the tooth's biting function and natural appearance.
While root canal procedures have a somewhat troubled reputation, they are often not painful, because the tooth's nerve may already be dead. In most circumstances, root canals have a very high success rate (WebMD).
Facial Implant Devices
Metals and metal alloys may be used for implant devices whether in the maxilla, the mandible, or
the temporomandibular joint connecting the two (figure: temporomandibular prosthesis; figure: dental implants, bridgework, acrylic teeth; figure: subperiosteal dental implant; figure: dental implant crown; figure: Zimmer metal implant; figure: permanent mandibular retainer). In addition, metals are used in oral facial reconstruction. Metal and metal alloys, such as stainless steel, cobalt-chromium-molybdenum
alloy, titanium, and titanium-aluminum-vanadium alloy, are the foundation for either subperiosteal, transosteal, or endosseous types of implant devices and are intensely opaque on radiographs. Precision in their placement is critical, and for this reason, CT may be used as an adjunct to the surgical procedure.
A new form of metal composition known as enhancing oseo-integration or trabecular metal consists of a metallic substrate surrounding interconnecting pores. Because it is 80% porous yet with a very high strength to weight ratio, it does not require a solid metal structure, allowing for a two to three-fold enhancement of bone in-growth. One such product is the Zimmer Trabecular Metal Implant (figure: Zimmer metal implant). According to the manufacture (Zimmer), "...elemental tantalum is deposited onto a substrate, creating a textured surface topography...one atom at a time." This composition is conducive to direct bone apposition (both on-growth and in-growth). This provides strength and corrosion resistance with biocompatibility.
Ceramics offer excellent biocompatibility and are often combined with metals and metal alloys in the construction of oral facial devices. A popular
ceramic is hydroxyapatite, a bioactive-type material that contains calcium, phosphate, and
hydroxyl ions [Ca10(PO4)6(OH)2]. Another popular ceramic form is bioactive glass made
from silicon, calcium, sodium, and phosphorus (Bioglass, Biogran, PerioGlas, and
Nova Bone are particular forms of bioactive glass).
Nova Bone is used by orthopedic surgeons in procedures such as spinal fusion, revision arthroplasty, and for filling in bony defects. In dentistry, it is used by oral surgeons for craniofacial and maxillofacial surgery. Perioglas and Biogran are used primarily in the treatment of periodontal defects caused by periodontal disease. In general, ceramics have a crystalline form with a specific lattice configuration that may be fused to natural bone or to a metallic substructure. This combination provides strength and durability with an exceptional bonding mechanism both to the metal and to bone. Ceramics are also beneficial for bony bonding without an underlying metal or metal alloy substructure being present.
Bioactive ceramics are useful for augmenting alveolar ridges defects or for filling
in other mandibular or maxillary bony defects. The granular forms of certain ceramics allow for their easy placement into osseous defects. Hydroxyapatite and Bioglass are negatively charged. This negative charge results in their ability
to stimulate the production of new bone where bone has been lost from disease or surgical removal. Ceramics are an excellent substitute for natural bone, acting as a stimulant and
scaffold for the production of new bone. Bioactive ceramics also have a radiopacity similar to that of
dense bone, allowing for their easy visualization on radiographic studies.
Autograft or allograft bone may also be used for facial and mandibular reconstructions in extreme cases, such facial or mandibular tumors (figure: mandibular reconstruction).
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Dentures (also generally known as false teeth) are removable replacements for missing teeth and surrounding tissues. There are complete and partial dentures. Complete dentures are for replacement of all the teeth, and partial dentures are used for replacing lost teeth when some of the natural teeth remain.
Conventional dentures are placed after the teeth have been removed and the gum healed. They are usually placed in the mouth 8-12 weeks after teeth removal. Dentures are very common and often visible on head, neck, or cervical spine radiographs (figure: dentures).
Immediate dentures are another type of complete dentures. They are made prior to removal of the teeth and placed immediately after tooth removal. This spares the patient from going without teeth during the healing period, but bones and gums shrink during the healing period. This requires adjustment of the immediate dentures during the healing process. Immediate dentures are usually considered a temporary solution until the placement of the more common conventional dentures after complete gum healing.
Removable partial dentures or bridges are artificial replacement teeth attached to a plastic base and a metal framework that holds the denture in the mouth. Partial dentures are used when natural teeth remain in the upper or lower jaw. A fixed bridge is a denture that remains in place permanently. It replaces one or more crowns on the teeth on either side of the missing tooth or teeth. Artificial teeth are attached to the bridge to fill up the space of the missing teeth. The bridge is permanently cemented into place.
Single dental implants or permanent tooth implants permanently replace a missing tooth with a prosthetic tooth that is cosmetically and functionally very similar to the lost tooth. They can sometimes replace dentures and support cemented fixed bridges. Dental implants and associated fixed bridges closely resemble natural teeth, but they are very expensive and usually require considerable surgical preparation prior to their placement and integration into the upper or lower jaw.
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Dental and Mandibular Devices
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