Contemporary Orthodontic Appliances

Outline

Orthodontic appliances have evolved steadily since the development of the specialty, but the pace of change has accelerated significantly in recent years. Technologic advances have brought both improvements in existing appliance systems (for instance, new brackets and wires for the edgewise appliance) and new ways of correcting malocclusion (such as clear aligners formed on stereolithographic models and temporary skeletal anchorage). The improved technology has greatly increased the productivity of orthodontists. Charles Tweed suggested in the 1950s that an orthodontist should not start treatment for more than 50 patients per year because there would not be enough time to manage more than that and achieve quality results. This number has greatly increased since then but so has average treatment quality—and comprehensive orthodontic treatment that cost about the same as a new car at that time now costs far less.

At this point, an orthodontist can use a given appliance system to treat most of his or her patients, but for the best patient care, needs to select among appliance systems to fit the needs of individual patients. Modern removable appliances can do some things better than fixed appliances, and variants within fixed appliance systems do some things better than others. The purpose of this chapter is to provide an overview of modern appliances, and put them in perspective in a way that helps in the choice of the best appliance for specific situations—a goal that extends into the clinical chapters that follow.

Removable Appliances

Removable orthodontic appliances have two immediately apparent advantages: (1) they are fabricated in the laboratory and adjusted extraorally rather than directly in the patient’s mouth, reducing the dentist’s chair time, and (2) they can be removed on socially sensitive occasions if wires on the facial part of the teeth would be visible, or can be made almost invisible if fabricated from clear plastic materials. This makes them (at least initially) more acceptable to adult patients. In addition, removables allow some types of growth guidance treatment to be carried out more readily than is possible with fixed appliances. These advantages for both the patient and the dentist have ensured a continuing interest in removable appliances for both children and adults.

There are also two significant disadvantages: (1) the response to treatment is heavily dependent on patient compliance, since the appliance can be effective only when the patient chooses to wear it, and (2) it is difficult to obtain the two-point contacts on teeth necessary to produce complex tooth movements, which means that the appliance itself may limit the possibilities for treatment. Because of these limitations, removable appliances in children are most useful for the first of two phases of treatment, with fixed appliances used in the second phase; and if removable clear aligners are used in treatment of adults, some fixed attachments (which can be relatively small tooth-colored composites rather than brackets) often must be bonded in order to achieve effective tooth movement. For these reasons, contemporary comprehensive treatment for adolescents almost always requires fixed, nonremovable appliances, and clear aligner therapy for adults is evolving toward the use of a combination of aligners and fixed appliances for the more complex cases.

The Development of Removable Appliances

In the United States, the original removable appliances were rather clumsy combinations of vulcanite bases and precious metal or nickel-silver wires. In the early 1900s, George Crozat developed a removable appliance fabricated entirely of precious metal that consisted of an effective clasp for first molar teeth, heavy gold wires as a framework, and lighter gold fingersprings to produce the desired tooth movement (Figure 10-1). The Crozat appliance attracted a small but devoted following, and as the twenty-first century began, a modified version still was being used for comprehensive treatment by a few practitioners. Its limitation is that, like almost all removables, it produces mostly tipping of teeth. It had little impact on the mainstream of American orthodontic thought and practice, however, which from the beginning was focused on fixed appliances.

FIGURE 10-1 Crozat appliances for the upper and lower arch, showing the transverse connectors that allow lateral expansion. The Crozat clasps on the molars utilize fingers extending into the mesiobuccal and distobuccal undercuts.

For a variety of reasons, development of removable appliances continued in Europe despite their neglect in the United States. There were three major reasons for this trend: (1) Angle’s dogmatic approach to occlusion, with its emphasis on precise positioning of each tooth, had less impact in Europe than in the United States; (2) social welfare systems developed much more rapidly in Europe, which tended to place the emphasis on limited orthodontic treatment for large numbers of people, often delivered by general practitioners rather than orthodontic specialists; and (3) precious metal for fixed appliances was less available in Europe, both as a consequence of the social systems and because the use of precious metal in dentistry was banned in Nazi Germany. This forced German orthodontists to focus on removable appliances that could be made with available materials. (Precision steel attachments were not available until long after World War II; fixed appliances required precious metal.)

The interesting result was that in the 1925 to 1965 era, American orthodontics was based almost exclusively on the use of fixed appliances (partial or complete banding), while fixed appliances were essentially unknown in Europe and all treatment was done with removables, not only for growth guidance but also for tooth movement of all types.

A major part of European removable appliance orthodontics of this period was functional appliances for guidance of growth. A functional appliance by definition is one that changes the posture of the mandible, holding it open or open and forward. Pressures created by stretch of the muscles and soft tissues are transmitted to the dental and skeletal structures, moving teeth and modifying growth. The monobloc developed by Robin in the early 1900s is generally considered the forerunner of all functional appliances, but the activator developed in Norway by Andresen in the 1920s (Figure 10-2) was the first functional appliance to be widely accepted.

FIGURE 10-2 The Activator, a tooth-borne passive appliance, was the first widely used functional appliance. The appliance opens the bite, and the mandible is advanced for Class II correction. A, In the original Andresen activator, angled flutes in the acrylic were used to guide the path of eruption of the posterior teeth, usually so that the molars moved distally in the upper arch and mesially in the lower arch as the teeth erupted and also to expand the dental arches if desired. B, The lingual flanges of an activator are the mechanism to advance the mandible. In this design, the maxillary posterior teeth are prevented from erupting by the acrylic shelf, while the mandibular posterior teeth are free to erupt; thus the appliance will induce a rotation of the occlusal plane, which usually is desirable in functional appliance treatment because it makes it easier to change a Class II to a Class I molar relationship. This appliance also has displacement springs on the upper first molars, which requires the patient to actively maintain the appliance in the proper position. It was once thought that a loosely-fitting appliance contributed to activation of the mandibular musculature, but research has not supported this concept, so modern activators are more likely to incorporate clasps than displacing springs.

Andresen’s activator became the basis of the “Norwegian system” of treatment. Both the appliance system and its theoretical underpinnings were improved and extended elsewhere in Europe, particularly by the German school led by Haupl, who believed that the only stable tooth movement was produced by natural forces and that alterations in function produced by these appliances would give stable corrections of malocclusion. This philosophic approach was diametrically opposite to that espoused by Angle and his followers in the United States, who emphasized fixed appliances to precisely position the teeth and presumed that if they were in ideal occlusion, that would keep them there. These opposing beliefs contributed to the great differences between European and American orthodontics at mid-twentieth century.

In the European approach at that time, removable appliances often were differentiated into “activators,” or functional appliances aimed at modifying growth, and “active plates” aimed at moving teeth. In addition to the functional appliance pioneers, two European orthodontists deserve special mention for their contributions to removable appliance techniques for moving teeth. Martin Schwarz in Vienna developed and publicized a variety of “split plate” appliances, which were effective for expanding the dental arches (Figure 10-3). Philip Adams in Belfast modified the arrowhead clasp favored by Schwarz into the Adams crib, which became the basis for English removable appliances and is still the most effective clasp for orthodontic purposes (Figure 10-4).

FIGURE 10-3 A removable appliance of the “Schwarz plate” design used a jackscrew to separate the parts of the acrylic plate and expand the dental arch. They can be used in the maxillary or mandibular dental arch—this one is being used to expand across the lower incisors to provide more space for the crowded teeth. Although the force system created by turning a screw is far from ideal, plates of this type can be effective in producing small amounts of tooth movement.

FIGURE 10-4 Clinical adjustments of an Adams clasp. A, Tightening the clasp by bending it gingivally at the point where the wire emerges from the baseplate. This is the usual adjustment for a clasp that has become loose after repeated insertions and removals of an appliance. B, Adjustment of the clasp by bending the retentive points inward. This alternative method of tightening a clasp is particularly useful during the initial fitting of an appliance.

Functional appliances were introduced into American orthodontics in the 1960s through the influence of orthodontic faculty members with a background in Europe (of whom Egil Harvold was prominent) and later from personal contact by a number of American orthodontists with their European counterparts. (Fixed appliances spread to Europe at the same time through similar personal contacts.) A major boost to functional appliance treatment in the United States came from the publication of animal experiment results in the 1970s showing that skeletal changes really could be produced by posturing the mandible to a new position and holding out the possibility that true stimulation of mandibular growth could be achieved (see Chapter 8). Although some of the enthusiasm for functional appliance treatment caused by the favorable animal experiments has faded in the light of less impressive results from clinical trials and retrospective clinical studies (see Chapter 13), functional appliances have achieved a major place in contemporary growth modification treatment.

At this point, the dichotomy between European and American orthodontics has largely disappeared. European-style removable appliances, particularly for growth modification during first-stage mixed dentition treatment, have become widely used in the United States and other countries, while fixed appliances have largely replaced removables for comprehensive treatment in Europe and elsewhere throughout the world.

Modern removable appliance therapy consists largely of the use of (1) various types of functional appliances for growth guidance in adolescents and, less frequently, in children; (2) active plates for tooth movement, used primarily in preadolescents; and (3) clear plastic aligners for tooth movement in adults. The focus of this part of the chapter, accordingly, is on the characteristics of the appliances used for these purposes, especially clear aligner therapy (CAT) for comprehensive treatment in adults and older adolescents. Clinical use of removable appliances in mixed dentition treatment is covered in Chapters 11 and 13, and the application of clear aligner therapy to specific problems in adults is discussed in Chapter 18.

Functional Appliances for Growth Modification

The design and fabrication of many types of functional appliances are covered in detail in a text devoted to the subject.¹ The goal here is to put these devices in a contemporary perspective. All are used for growth modification in preadolescents and adolescents, and all are fabricated from a construction bite that advances the mandible in Class II patients and rotates it downward in Class III patients. Bite blocks for anterior teeth are used in short-face/deep-bite patients, and bite blocks for posterior teeth are used in long-face/open-bite patients.

Functional appliances are understood best when viewed as falling into one of four broad categories:

1 Passive Tooth-Borne

These appliances have no intrinsic force-generating capacity from springs or screws and depend only on soft tissue stretch and muscular activity to produce treatment effects. In current use, the bionator (Figure 10-5), twin block (Figure 10-6), and Herbst appliances (Figure 10-7) are examples of passive tooth-borne appliances. The bionator is always removable, the twin block usually is removable but can be fixed, and the Herbst appliance usually is fixed but can be made to be removable.

FIGURE 10-5 The bionator design, which removes much of the bulk of the activator, can include posterior facets or acrylic occlusal stops to control the amount or direction of tooth eruption. Note that for this patient who is biting into the bionator so that the mandible is advanced, the lower incisors are capped with acrylic to prevent them from erupting and control their tendency to tip facially. Usually the lower posterior teeth are free to erupt while eruption of the upper posterior teeth is impeded by an acrylic shelf across them. For this patient, the upper teeth are being allowed to erupt while eruption of the lower teeth is impeded.

FIGURE 10-6 The twin-block appliance consists of individual maxillary and mandibular plates with ramps that guide the mandible forward when the patient closes down. The maxillary plate incorporates tubes for attachment of a headgear and often includes an expansion screw.

FIGURE 10-7 A to D, The Herbst appliance is the only fixed functional appliance. It uses a pin and tube apparatus to hold the mandible in an advanced position and is quite compatible with the presence of a fixed appliance on anterior teeth (but also can be used with bonded or removable splints). Note that for this patient the pin and tube attaches to steel crowns on the molars, which are sturdier than molar bands, and extensions from the lower crowns are bonded to the lower premolars. E, The MARA appliance is a Herbst variant that can be used with a complete fixed appliance but also holds the mandible in a forward position full-time. It is less bulky and more comfortable for the patient but may have more of a Class II elastics effect.

2 Active Tooth-Borne

These are largely modifications of activator and bionator designs that include expansion screws or springs to move teeth. This produces tooth movement that often replaces jaw growth modification with camouflage tooth movement. For this reason, active tooth-borne appliances have little or no place in modern orthodontics and now are used much less than previously.

3 Tissue-Borne

The Frankel appliance (which Frankel called the function regulator) is the only tissue-borne functional appliance (Figure 10-8). Insofar as possible, contact of the appliance with the teeth is avoided. Much of the appliance is located in the vestibule, holding the lips and cheeks away from the dentition. This makes it an arch expansion appliance in addition to its effects on jaw growth because the arches tend to expand when lip and cheek pressure is removed.

FIGURE 10-8 The Frankel appliance, shown here sitting on the lower cast, is the only functional appliance that is primarily tissue-borne rather than tooth-borne. The large buccal shields and lip pads reduce cheek and lip pressure on the dentition and provide the expansion of the maxillary arch that usually is needed as part of Class II correction; the lingual pad dictates the mandibular position. The appliance looks bulky, but for the most part, it is restricted to the buccal vestibule, and therefore it interferes less with speech and is more compatible with 24-hour wear than most other functional designs.

4 Hybrid

Hybrid functionals are composed of components that are common to functional appliances but are combined to meet a specific need, often in the treatment of jaw asymmetry (Figure 10-9). The components of functional appliances are shown in Table 10-1. They can be combined as needed for individual patients.

TABLE 10-1

Functional Appliance Components

FIGURE 10-9 A hybrid functional appliance consists of the components of one type of functional on one side and components of another type on the other. For a child with a facial asymmetry, an appliance of the type shown here can be effective in improving both the vertical and a-p aspects of the problem. Note that the teeth are free to erupt on the left side (which requires a lingual as well as a buccal shield), while a bite block impedes eruption on the other. The bite is taken to bring the jaw to the midline, advancing the deficient side (here, the left) more than the other. (From Proffit WR, White RP, Sarver DM. Contemporary Treatment of Dentofacial Deformity. St. Louis: Mosby; 2003.)

Functional appliances are used primarily in late preadolescent children and during the adolescent growth spurt. They are discussed in more detail in Chapter 13.

Removable Appliances for Tooth Movement in Children

Tooth movement with removable appliances in children almost always falls into one of two major categories: (1) arch expansion, in which groups of teeth are moved to expand the arch perimeter, and (2) repositioning of individual teeth within the arch.

Active Plates for Arch Expansion

The framework of an active plate is a baseplate that serves as a base in which screws or springs are embedded and to which clasps are attached. The active element usually is a jackscrew placed so that it holds the parts of the plate together (see Figure 10-3). Opening the screw with a key then separates the sections of the plate. The screw offers the advantage that the amount of movement can be controlled, and the baseplate remains rigid despite being cut into two parts. The disadvantage is that the force system is very different from the ideal one for moving teeth. Rather than providing a light but continuous force, activation of the screw produces a heavy force that decays rapidly. Activating the screw too rapidly results in the appliance being progressively displaced away from the teeth rather than the arch being expanded as desired.

Removable Appliances with Springs for Tooth Movement

In contrast to the heavy, rapidly decaying forces produced by a screw, nearly optimum light continuous forces can be produced by springs in a removable appliance. Like the edges of an active plate, however, these springs contact the tooth surface at only one point, and it is difficult to use them for anything but tipping tooth movements (although this is theoretically possible) (Figure 10-10). The guideline for tooth movement with a spring from a removable appliance therefore is that this approach should be used only when a few millimeters of tipping movement is acceptable.

FIGURE 10-10 Diagrammatic representation of the spring assembly necessary for bodily retraction of a canine with a removable appliance. The spring on the mesial of the canine exerts a heavier force than the distal spring, leaving a net force to move the canine distally, while the couple necessary for control of root position is created by the opposing action of the two springs. Although bodily movement with a removable appliance is theoretically possible with spring arrangements of this type, the spring adjustments and clasp arrangements become too complex for practical clinical use. A fixed appliance is necessary for efficient bodily tooth movement.

Because these appliances are used primarily for minor tooth movement in children, they are discussed in more detail in Chapters 11 and 12.

Clear Aligner Therapy

Development of Clear Aligners

The use of clear aligners in orthodontic treatment for adults became possible as vacuum-formed clear thermoplastic sheets were introduced into orthodontics in the 1980s. These “suck-down” materials were used initially as retainers and still are important for this purpose (see Chapter 17). It became apparent rather quickly, however, that if teeth were reset slightly and the vacuum-formed sheet was made to fit the reset teeth, a tooth moving device rather than a retainer would be the result. The device now could be, and quickly was, called an “aligner” because the typical use was to bring mildly displaced teeth back into alignment, as, for instance, when mild irregularity of maxillary or mandibular incisors occurred in an orthodontic patient after retainers were discontinued.

Only small amounts of tooth movement are possible with a single aligner, however, because of the stiffness of the plastic material. To obtain more than minor changes, it was necessary either to reshape the aligner or make a new one on a new cast with the teeth reset to a greater degree. Because the suck-down material is softened and becomes moldable when heated, it would be possible to alter the shape of an aligner with a heated instrument,² and in an attempt to extend the use of aligners, a special heated pliers for this type of reshaping was offered as a way to avoid the cost and complexity of having to make multiple new aligners (Figure 10-11). This still allowed only minor tooth movement, and skill was required to obtain just the right amount of change in the aligner. A major limitation is that the plastic can only be stretched a maximum of about 3 mm (in 1 mm increments) before it becomes too thin to exert force. More recently, hard plastic bumps that snap into a hole in the aligner have been used to modify it for further tooth movement, which has the advantage that the plastic of the aligner is not stretched and thinned.³

FIGURE 10-11 A pliers heated to the correct temperature (which must be checked) can be used to create a divot in an aligner to increase the amount of movement of a selected tooth without having to make a totally new aligner. A, Heating the special pliers. B, Checking the temperature. C, Creating a divot in the aligner, in this case to increase movement of one maxillary central incisor. D, The modified aligner in place, with increased pressure against the central incisor.

Despite these improvements, reshaped aligners are not a practical way to manage orthodontic problems that require movement of more than a few teeth. It became clear that a sequence of several aligners, made on a series of casts with some teeth reset in small increments (not more than 1 mm) to a new position, would be needed to correct even mild malalignment. Although a sequence of modified dental casts can be produced by hand and a short sequence of two to five aligners made from these casts works for minor tooth movement, this is prohibitively time consuming and difficult if more than a few aligners are required.

In the late 1990s, a new company, Align Technology, obtained venture capital to computerize the process of producing a sequence of casts with incremental changes on which aligners could be fabricated. The current approach (illustrated in more detail later) is to scan a patient’s teeth with an intraoral scanner that combines laser and optical scanning to create a digital model, make a series of incremental changes on the digital model, and produce a matching series of stereolithographic casts for aligner fabrication. With careful planning, this would result in a sequence of aligners that could correct more complex problems. From the beginning, it was recognized that since growth changes could not be predicted, the method would be useful only for treatment of adults or adolescents in whom growth modification was not needed, but these are the patients most interested in making an orthodontic appliance invisible or minimally visible.

This new approach was introduced with television publicity for “Invisalign” that was designed to create consumer interest in this new approach. The early days of Invisalign treatment were wrought with problems because staging of treatment, optimal rates of tooth movement, and indications for use of attachments on the teeth had not been worked out, and initial professional acceptance of the method was spotty. The technique has matured, however, as clinical evaluation has clarified the best sequence of steps in treatment and the amount of tooth movement in steps that should be attempted, and as the use of tooth-colored shapes bonded to the teeth has improved the appliance’s grip on the teeth and ability to move them. Although remarkably little has been published about the outcomes of Invisalign treatment, there is no doubt now that for many adults, complex malocclusions can be successfully treated in this way (see Chapter 18). As patents expire or are challenged successfully, it is likely that competitive companies will offer sequenced aligners based on modifications of the current techniques.

Invisalign Production Process

Steps in Preparing the Aligners: Diagnostic records for CAT are not different from those for any other type of orthodontic treatment, but for Invisalign sequenced aligners, an intraoral optical scan (which also records the initial set of the patient’s bite) or PVS (polyvinyl siloxane) impressions and a bite registration (maximum intercuspation) are obtained. The scan or impressions and photographs are submitted to the company along with the doctor’s initial instructions. The production process begins when the intraoral scan or impressions are used to create an accurate three-dimensional (3-D) digital model of each dental arch (Figure 10-12). These records are transferred electronically to a digital treatment facility (presently in Costa Rica).

FIGURE 10-12 A, The first step in the production of a series of aligners using Invisalign’s computer technology is a CT scan of the impressions submitted by the doctor. The impressions are placed in a container before going into the CT scanner. B, This produces a three-dimensionally accurate digital image that is transmitted to a technology facility consisting entirely of computer work stations. C, In this view, the seated technician is conferring with one of the orthodontic advisors as the digital dental arches are displayed on the computer screen. D, Using the company’s proprietary software, virtual tooth movement in three dimensions can be created and staged as desired.

At the digital treatment facility, the teeth are digitally sectioned and cleaned up (obvious artifacts removed), the dental arches are related to each other, gingiva is added, movement is staged following the doctor’s instructions, and this preliminary plan is placed online for the doctor’s review as a “ClinCheck.” After the doctor is satisfied with the planned sequence of aligners, the set of digital models for a patient is transferred to a cast production facility, where a stereolithographic model for each step is fabricated (Figure 10-13). A clear plastic aligner is formed over each model, and the set of aligners is sent directly to the doctor.

FIGURE 10-13 After the sequence of treatment steps has been adjusted if desired and approved by the doctor, who can access the digital models electronically after the preliminary treatment sequence has been put together, the models are used to fabricate a sequence of stereolithographic (SL) casts and a sequence of aligners are formed over the casts. A, SL casts emerging from the production machine. B, Close-up of a single SL cast. C, SL cast and the aligner formed from it.

Clinician’s Role in ClinCheck: With experience, doctors tend to be more specific in their initial prescription of what they want, but the sequence of steps and the amount of movement between steps is specified by algorithms built into the Treat software if this is not spelled out in detail in the prescription. In essence, when the ClinCheck is posted for the doctor to examine, the computer technician has sent a draft treatment plan for review (Figure 10-14). The software used by the computer technicians has default scenarios for different types of malocclusions and default rates of tooth movement. These defaults are satisfactory for simpler cases but not for the more complex ones.

FIGURE 10-14 A, The Invisalign Clincheck form, as modified by the doctor, shows where bonded attachments are to be placed, the steps in the treatment sequence, and the amount of tooth movement at each step. For this patient, bonded attachments are to be placed as shown in the frontal and maxillary occlusal views. B, Bonded attachments on the facial surface of the teeth (same patient as the Clincheck form) are made of clear plastic in a variety of shapes. These are necessary to produce rotation or extrusion and facilitate other types of tooth movement. C and D, It is possible to bond a button on the lingual side of a tooth that is proving difficult to rotate and use a rubber band to rotate it along with the aligner.

For complex treatment, the doctor must customize the plan in terms of the amount and location of interproximal reduction of teeth (if any) that is to be done (Figure 10-15), the sequence of tooth movement steps, the rate of tooth movement with each subsequent aligner (often reducing the amount of movement at critical points), and the extent to which bonded shapes are to be used to increase the aligner’s grip on the teeth.

FIGURE 10-15 The Invisalign reproximation form (same patient as Figure 10-14), specifying how much enamel is to be removed from teeth and when in the sequence of aligners the reproximation will be done. For this patient, the upper incisors are to be reduced slightly in width to facilitate their alignment.

Considerations in Clinical Use of Clear Aligners: Although Invisalign is over a decade old, only a few studies of the outcomes of Invisalign treatment have been published in refereed professional journals.⁴ A recent prospective study used Invisalign’s software to evaluate the accuracy with which planned changes were accomplished, using the ratio of achieved to predicted change, and found that the highest accuracy (47%) was achieved during lingual constriction of the dental arches and the lowest (18%) for extrusion of maxillary incisors.⁴ Based on the existing studies and comments from experienced users, it seems clear now that Invisalign (and clear aligners more generally) do some things well and others not so well (Box 10-1). The limitations should be kept in mind when CAT is considered.

Several other considerations in the use of sequential aligners include the following:

• The use of attachments that are bonded to selected teeth greatly extends the possible tooth movement with aligners. In general, significant root movement (as in the closure of extraction sites) is almost impossible without the use of attachments, as is closure of open bites by elongation of incisor teeth; with attachments, both are possible (see Figures 18-40 and 18-41). Even with attachments, significant rotation of rounded teeth (canines and premolars) is difficult. It is possible to bond a button to a rotated tooth so that a rubber band can be used to rotate it while an aligner is being worn (see Figure 10-14). There is an increasing trend toward a combination approach to complex treatment, using a short phase of partial fixed appliances or auxiliaries in addition to the sequence of aligners.

• Interproximal enamel reduction (IPR) to obtain space for aligning crowded teeth often is part of the treatment plan. If IPR is planned, removal of interproximal enamel in the canine-premolar region to provide space can be used in addition to reduction in the width of incisors. The amount of interproximal reduction is part of the doctor’s prescription (see Figure 10-15).

• Patients must be monitored carefully to verify that tooth movement is tracking with the series of aligners (i.e., that all teeth are seated completely in the aligner after it has been worn for the specified period of time). If the teeth are not tracking, there are several possibilities: not enough wear of the aligners by the patient, insufficient interproximal reduction, insufficient crown height or shape to allow a grip on the tooth or teeth to be moved, wrong type or position of bonded attachments, or movement created in ClinCheck that is too fast to be possible biologically. A refinement or midcourse correction, with a new intraoral scan or PVS impressions and revision of the treatment plan, often is necessary in treatment of complex problems.

• Aligners cover the teeth like a bleaching tray, and they can be used to bleach during treatment (unless the patient has bonded attachments on the anterior teeth). If this is done, it is important to remember that tooth movement causes transient pulpitis and so does bleaching. The combination of the two procedures can lead to significant tooth sensitivity. This can be controlled by increasing the intervals between bleaching sessions, but bleaching usually is better deferred until the retention stage.

The clinical use of clear aligners in adjunctive and comprehensive treatment is discussed in greater detail in Chapter 18.

Fixed Appliances

Contemporary fixed appliances are predominantly variations of the edgewise appliance system. The only current fixed appliance system that does not use rectangular archwires in a rectangular slot is the Begg appliance, and practitioners using it have shown renewed interest in rectangular archwires at the finishing stage as the original Begg appliance has morphed into the Tip-Edge appliance. The focus in this and the succeeding chapters therefore is almost entirely on the contemporary edgewise appliance, with occasional reference to the modified Begg technique.

The Development of Contemporary Fixed Appliances

Angle’s Progression to the Edgewise Appliance

Edward Angle’s position as the “father of modern orthodontics” is based not only on his contributions to classification and diagnosis but also on his creativity in developing new orthodontic appliances. With few exceptions, the fixed appliances used in contemporary orthodontics are based on Angle’s designs from the early twentieth century. Angle developed four major appliance systems:

E-Arch: In the late 1800s, a typical orthodontic appliance depended on some sort of rigid framework to which the teeth were tied so that they could be expanded to the arch form dictated by the appliance. Angle’s first appliance, the E-arch, was an improvement on this basic design (Figure 10-16). Bands were placed only on molar teeth, and a heavy labial archwire extended around the arch. The end of the wire was threaded, and a small nut placed on the threaded portion of the arch allowed the archwire to be advanced so that the arch perimeter increased. Individual teeth were simply ligated to this expansion arch. This appliance still could be found in the catalogs of some mail-order orthodontic laboratories as late as the 1980s, perhaps because of its simplicity, and despite the fact that it can deliver only heavy interrupted force.

FIGURE 10-16 Edward Angle’s E-arch from the early 1900s. Ligatures from a heavy labial arch were used to bring malposed teeth to the line of occlusion.

Pin and Tube: The E-arch was capable only of tipping teeth to a new position. It was not able to precisely position any individual tooth. To overcome this difficulty, Angle began placing bands on other teeth and used a vertical tube on each tooth into which a soldered pin from a smaller archwire was placed. With this appliance, tooth movement was accomplished by repositioning the individual pins at each appointment.

An incredible degree of craftsmanship was involved in constructing and adjusting this pin and tube appliance, and although it was theoretically capable of great precision in tooth movement, it proved impractical in clinical use. It is said that only Angle himself and one of his students ever mastered the appliance. The relatively heavy base arch meant that spring qualities were poor, and the problem therefore was compounded because many small adjustments were needed.

Ribbon Arch: Angle’s next appliance modified the tube on each tooth to provide a vertically positioned rectangular slot behind the tube. A ribbon archwire of 10 × 20 gold wire was placed into the vertical slot and held with pins (Figure 10-17). The ribbon arch was an immediate success, primarily because the archwire, unlike any of its predecessors, was small enough to have good spring qualities and therefore was quite efficient in aligning malposed teeth. Although the ribbon arch could be twisted as it was inserted into its slot, the major weakness of the appliance was that it provided relatively poor control of root position. The resiliency of the ribbon archwire simply did not allow generation of the moments necessary to torque roots to a new position.

FIGURE 10-17 Angle’s ribbon arch appliance, introduced about 1910, was well-adapted to bring teeth into alignment but was too flexible to allow precise positioning of roots.

Edgewise: To overcome the deficiencies of the ribbon arch, Angle reoriented the slot from vertical to horizontal and inserted a rectangular wire rotated 90 degrees to the orientation it had with the ribbon arch, thus the name “edgewise” (Figure 10-18). The dimensions of the slot were altered to 22 × 28 mils, and a 22 × 28 precious metal wire was used. These dimensions, arrived at after extensive experimentation, did allow excellent control of crown and root position in all three planes of space.

FIGURE 10-18 A and B, Angle’s edgewise appliance received its name because the archwire was inserted at a 90-degree angle to the plane of insertion of the ribbon arch, which made it wider than it was tall. The rectangular wire could be twisted to create torque (see Figure 10-22). It was tied into a rectangular slot with wire ligatures, making excellent control of root position possible. The original appliance is seen here on a typodont. Note the narrow brackets (double width on the maxillary centrals, which are wider teeth), which were soldered to gold bands. Also note the eyelets soldered on the corners of the bands. These were used for ligature ties to the archwire as needed for rotational control. C and D, Close-up views of a modern edgewise twin bracket with a rectangular archwire in place. The wire is held in the bracket by an elastomeric ligature, here part of a chain of ligatures that also keep spaces closed between the teeth.

After its introduction in 1928, this appliance became the mainstay of multibanded fixed appliance therapy, although the ribbon arch continued in common use for another decade.