I.  Orthodontic Materials

The specialty of orthodontics seeks to align teeth in their most esthetic and functional position. Orthodontists use a variety of materials and devices. Some are the same materials used in other areas of dentistry; others are unique to orthodontics. Orthodontists use devices called appliances to move teeth and to affect growth of the maxilla and mandible. Orthodontists use both fixed and removable appliances. The most common fixed orthodontic appliance consists of brackets, wires, and bands, as shown in Figures 13.1 and 13.2. An orthodontic retainer is a removable appliance and is shown in Figure 13.3.

A.  Materials Similar to Those Commonly Used in General Dentistry

1.  Impression Materials and Gypsum Products

Impression materials used in orthodontics are the same as those discussed in Chapter 8, Impression Materials. Alginate is the most commonly used impression material because orthodontic appliances do not require the precision of a cast restoration. Orthodontists use dental stone to pour casts for the construction of appliances. Orthodontic stone is used for study models. It is not as strong as dental stone because this facilitates model trimming. Whiteners are added to orthodontic stone to improve the appearance of study models. Opital (digital) impressions are becoming common in orthodontics. This digital information is interfaced with digital radiographs and treatment planning software.

2.  Bonding Materials and Composites

The same bonding materials used in restorative dentistry are used by orthodontists to bond appliances to teeth. Both light-cure and chemical-cure composites are used. Generally, orthodontists use only acid-etched enamel for bonding because no dentin is available. Use of dental bonding primers improves bonding if contamination of the etched surface is a problem.

Nearly all composite products are strong enough for use in orthodontics when bonding to anterior and premolar teeth. Strength of the bonding material is not a problem, but adhesion is. A macrofilled composite has the advantage in that when fixed appliances are removed at the end of treatment (debonding), it is much easier to locate residual composite bonding material. Macrofilled composites are rough and turn gray when the composite material is abraded with a metal instrument. The filler particles in macrofilled composites are harder than the metal of the instrument; hence, they abrade the instrument and turn gray. General dentists and dental hygienists have spent significant time and effort removing orthodontic bonding material left on teeth after orthodontic treatment. Debonding of orthodontic brackets is presented in Chapter 32.

3.  Acrylic Resins

The acrylic resins used to construct orthodontic appliances are the same chemically activated materials discussed in Chapter 11, Removable Prostheses and Acrylic Resins. The adolescent patients seen by orthodontists have encouraged the use of colors that stand out rather than match oral tissues. At times, acrylic orthodontic appliances do not blend in with the oral environment but are a fashion statement. Red, green, orange, and even sparkle colors are common.

B.  Wires

Wires are used in orthodontics as springs and stabilizers. Many wires are bought preformed to match an ideal arch form from the manufacturer. Others are bent by the orthodontist to the desired arch form. Wires are attached to the patient’s teeth with brackets, ligatures, tubes, and bands. Elastic deformation of the wire (bending) is used to apply force to the teeth, much like with a spring. The force applied by wires pushes, pulls, or rotates teeth into the proper position, as shown in Figure 13.4.

Many metals have been used for orthodontic wires. Stainless steel is the most common. Nickel–titanium wires are also popular because they can store more energy for tooth movement than can other wires. Wires are manufactured in a variety of shapes and cross-section sizes. As the size of the wire increases, so does the stiffness of the wire and the force it can apply. Some wires are round; others are rectangular, square, or even several wires braided together.

C.  Brackets, Bands, and Tubes

1.  Brackets

A bracket is a device that is attached to teeth, holds the archwire in place, and is used to transfer the forces of wires, springs, and elastics (rubber bands) to the teeth. A variety of materials is used to make orthodontic brackets, as shown in Figures 13.1, 13.2, and 13.4. Historically, stainless steel has been the most widely used material. A metal mesh is attached to the back of metal brackets. The undercuts of the mesh lock in the bonding material and attach the bracket to acid-etched enamel with composite resin material. Metal brackets have excellent mechanical properties, but they suffer from poor esthetics. They are relatively easy to bond to and remove from teeth.

Other materials used to make brackets are polymers, such as polycarbonate resin, and ceramic materials, such as aluminum oxide. Polymers tend to be too weak for this use, as they are subject to creep over time. Some manufacturers have added a metal reinforcement to the bracket slot to improve the strength and stiffness of polycarbonate brackets. Ceramic brackets have had mechanical problems as well. Although strong in compression, ceramic brackets are quite brittle. Bracket fracture during treatment has been a problem. On the other hand, the high compressive strength of ceramic brackets has made them difficult to remove from teeth. Many innovations and improvements have been made to both polymeric and ceramic brackets because the esthetic appearance of these brackets is commonly demanded by patients. Bonding polymeric and ceramic brackets to teeth is more technique sensitive than is bonding metal brackets. If directions are followed, success is common.

2.  Bands and Tubes

An orthodontic band encircles the crown of the tooth. Bands were used to attach brackets to teeth before acid etching became available. Brackets were welded to the bands, and the bands were cemented around each tooth. Current orthodontic practice uses bands only on molar teeth because molars require more force to move compared to other teeth.

Orthodontic bands and tubes are made from stainless steel. An orthodontic tube is just that, a tube that allows a wire to slide through it, as shown in Figure 13.2A. Most orthodontic tubes are actually a combination of several tubes, both round and square. An orthodontist may use more than one wire at a time. One wire is used to apply force to one or more teeth, and a second wire is used to stabilize the “anchor” teeth. Orthodontic tubes are welded to bands, and the bands are cemented on molars. The cement of choice is glass ionomer cement (because of fluoride release). At times, tubes are bonded to molars by using acid-etched composites.

D.  Elastics and Ligatures

The term elastic is used in orthodontics for several types of products and thus can be confusing. The “rubber bands” worn by orthodontic patients are used to apply force to teeth. They are called elastics. These rubber bands are changed by the patient several times each day as the force (pull) of the rubber band decays (decreases) over time. They are made from latex rubber and come in a variety of sizes, force levels, and colors.

Other “elastics” are used to secure the archwire into the bracket. These are called elastic ligatures. They look like little rubber donuts and are stretched around the “wings” of the bracket, forcing the wire into the bracket slot. These elastic ligatures are typically made from thermoplastic rubber, such as polyurethane. Other commonly used ligatures are thin, stainless steel wires that are wrapped around the archwire and bracket wings and twisted to secure the archwire in the bracket. The end of the ligature wire is then cut and tucked in around the bracket, tying the wire into the bracket. Both types of ligatures are shown in Figure 13.1.

E.  Retainers

After the teeth are moved into the proper position, the orthodontist removes the bands and brackets. The patient is typically very happy that day. If left alone, however, the teeth would tend to “relapse” or partially return to their original position. To prevent relapse, orthodontists use retainers to keep the teeth in the desired position. There are many kinds of retainers, and many are similar to functional removable orthodontic appliances.

The common retainer for the maxillary arch consists of an acrylic palate with several wire clasps (much like a partial denture framework) and a wire that sits on the labial surface of the teeth. A retainer is shown in Figure 13.3. Sandwiched between the acrylic and the wire, the teeth are held in place.

A common mandibular retainer is a lingual arch. With this type of retainer, a heavy wire sits on the lingual surface of the lower anterior teeth and is bonded to the canines with a mesh pad using composite. A lingual arch retainer is shown in Figure 13.5.

F.  Stainless Steel

Stainless steel devices are common in orthodontics. Stainless steel typically has a significant nickel content (~8%). Many patients are sensitive to nickel, and orthodontists find themselves in a dilemma with these patients. Until recently, many products were only available as nickel-containing, stainless steel products. More and more, however, manufacturers are using stainless steel with little or no nickel or other metals. Titanium is a popular alternative to stainless steel.

G.  Oral Hygiene and the Orthodontic Patient

All orthodontic patients are considered to be at high risk for caries. Oral hygiene is difficult with orthodontic appliances because food debris is retained after every meal. Many orthodontic patients have “white spots” on their teeth when their brackets are removed. These white spots are the visible sign of initial decalcification (caries). Some orthodontic patients develop cavitated lesions. It is critical that the dental hygienist stress the importance of oral hygiene and proper diet to the orthodontic patient. Poor plaque control frequently results in gingival inflammation. Food debris stuck on the wires and brackets is a continuous source of carbohydrate for acidogenic bacteria. The orthodontic patient’s swollen gums quickly heal after the “hardware” is removed, but carious lesions must be restored. It is very frustrating to the general dentist to restore the facial surfaces of anterior teeth in young patients when they know that these carious lesions could have been—and should have been—prevented. Many orthodontists will recommend fluoride rinses and auxiliary oral hygiene aids to their patients in an effort to prevent decay. In addition, orthodontists are using fluoride-releasing bonding materials and fluoride varnish to reduce the patient’s risk of caries.

II.  Endodontic Materials

A.  Endodontics in General

Endodontics is the specialty of dentistry that treats pathology of the pulp and periapical tissues of teeth. Typically, endodontic treatment involves root canal therapy.

1.  Diagnosis

Diagnosis involves determining which tooth, if any, requires root canal therapy. The status of the dental pulp and periapical tissues is important to determine the diagnosis. Occasionally, a patient is certain which tooth is causing the pain; other times, the involved tooth is difficult to identify. The clinician must use diagnostic tests to make a definitive diagnosis. Diagnostic tests include percussion tests (tapping the tooth with the handle of a dental mirror), mobility, reaction to hot and cold stimuli, periodontal probing, electric pulp tests, and radiography. A radiograph of tooth #7 with a periapical radiolucency is shown in Figure 13.6A. Before root canal therapy is performed, the clinician must determine if the tooth can be restored to adequate form and function. This involves examining the tooth’s periodontal health and extent of caries.

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