¶ Chapter 9 — ORTHODONTICS
Reference Edition
This chapter is part of the Air Force Dental Laboratory Manual (2005) – Digitally Restored Edition.
This edition preserves the original publication while correcting OCR errors, restoring formatting, reconstructing damaged tables where necessary, and improving digital readability.
The technical content has not been rewritten, modernized, expanded, or altered.
It is provided as a professional reference. Modern instructional material is published separately throughout DentalTechnology.org.
¶ Section 9A — Types of Orthodontic Appliances
¶ 9.1. Introduction
9.1.1. Orthodontic appliances may be removable, fixed, or a combination of both. Most of the time, an appliance can be classified as fixed or removable depending on its anchorage. (A patient cannot remove a fixed appliance.) Fixed appliances are generally anchored by metal bands cemented to anchoring teeth. A large group of removable orthodontic appliances get anchorage from acrylic resin denture bases retained by wrought wire clasps. The focus of our interest in this Chapter is on simple fixed and removable orthodontic appliances made by dental technicians in the laboratory. The devices described are capable of performing limited, minor tooth movements and holding functions. They do not compare to the highly complex systems of bands and wires assembled by orthodontists in a patient’s mouth.
9.1.2. Fixed and removable appliances are further classified as active or passive. Active devices are designed to move teeth into a more esthetic and functional alignment in a dental arch. Movement results from forces exerted by spring wire attachments or rubber bands. These spring wire attachments, or rubber bands, have to be “anchored” to stable dentition to make other teeth that are not as firmly anchored change position. One definition of a passive appliance is that it holds or maintains teeth in the positions they already occupy. The concept of anchorage is just as important for passive orthodontic appliances as it is for active devices. A passive appliance’s anchorage must be more resistant to movement than the teeth the appliance is supposed to stabilize.
¶ Section 9B — Orthodontic Materials
¶ 9.2. Orthodontic Wires
9.2.1. Orthodontic appliances rely heavily on stainless steel wires to passively hold or actively move teeth. The 18-8 and Elgiloy® are two types of stainless steel wire frequently used. Both are chrome-nickel-iron alloys. Elgiloy® contains substantial amounts of cobalt and molybdenum, and it is supposed to be more resistant to breakage when bent at sharp angles.
9.2.2. The wires are manufactured by being drawn through dies and are supplied in wrought condition. They are available in round, rectangular, and square cross-sections and in various states of springiness. Besides the purchase options already mentioned, orthodontic wires come in a series of graduated sizes, generally measured in thousandths of an inch.
9.2.3. The wires used for the kinds of appliances made in military dental laboratories are ordinarily very springy and round in cross-section. The wire sizes for common holding, moving, and clasping applications vary from .014 to .036 inch. NOTE: When selecting wire of proper size and temper, it is better to use wire that is too large and too soft rather than wire that is too small and too highly tempered.
¶ 9.3. Orthodontic Bands
9.3.1. Orthodontic bands are most often made of stainless steel alloys. Molar bands are 0.005 inch (0.127 mm) thick and 0.180 to 0.250 inch (4.6 to 6.3 mm) wide. Premolar and anterior band materials are 0.003 to 0.004 inch (0.076 mm to 0.100 mm) thick and from 0.13 to 0.18 inch (3.3 to 4.55 mm) wide. The width selected is determined by the height of the clinical crown and the position the band is going to occupy on the tooth.
9.3.2. The use of bands is most often associated with fixed orthodontic appliances. Laboratory made, fixed orthodontic appliances are assembled on casts. Normally, the bands are first placed or fitted onto the necessary teeth by the dentist; then a pickup impression is made. The subsequent cast then has the bands firmly positioned in the correct locations for the appliance to be fabricated. Various attachments and wires can be soldered or welded to bands for purposes of holding or moving teeth.
9.3.3. The finished fixed appliance is then cemented into the patient’s mouth. The most commonly used bands are prefabricated bands (stainless steel). Prefabricated bands are preformed to fit maxillary and mandibular teeth. They come closed and do not require soldering or spot-welding to close them. The bands are available in a full range of sizes and are easily adapted to fit almost any tooth’s circumference (Figure 9.1).
Figure 9.1. Prefabricated Band.
¶ 9.4. Preformed Crowns
Preformed crowns are made of stainless steel. They come in a variety of sizes and shapes to fit almost any tooth in a dental arch. Like orthodontic bands, the use of preformed crowns is also associated with fixed orthodontics appliances. Attachments and wires are fastened to the crowns to form the appliances. The decision to use a preformed crown rather than a band usually depends on whether the natural tooth requires restoration or not. If the natural tooth is badly broken down, a preformed stainless steel crown would probably be used to cover the tooth and retard its deterioration.
¶ 9.5. Attachments for Bands and Crowns
Hooks, eyelets, tubes, brackets, and other attachments may be soldered or welded to bands and crowns to enable the appliance to serve many purposes (Figure 9.2). Most of the time these attachments are chosen from prefabricated, commercially available stocks.
¶ 9.6. Acrylic Resin
Autopolymerizing resin is an integral part of many kinds of removable orthodontic appliances. The plastic becomes the resistance or anchorage portion of the appliance against which other elements of the device act to move or hold teeth. Orthodontic self-curing resins are usually molded by the sprinkle-on method. Because the polymer powder is exceptionally fine, the polymer mass stays where it is put when wet down with monomer. Autopolymerizing orthodontic resin is dense after it cures. As a result, the plastic is nonporous, cleans well, and is strong.
¶ 9.7. Solder
The joining of stainless steel surfaces is usually accomplished by spot-welding or silver soldering. Although the corrosion resistance of silver solders is low compared to gold solders, it is acceptable. Silver solders melt at about 1150 oF; gold solders fuse at around 1400 oF. Temperatures in excess of 1250 oF cause stainless steel wire to soften and lose its springiness.
¶ 9.8. Soldering Flux
Silver soldering requires using a fluoride flux. The bond between stainless steel and silver solder is a mechanical one. Besides ridding the stainless steel of its oxide layer, a fluoride flux etches the metal so that solder will bond to it better.
Figure 9.2. Band and Crown Attachments.
¶ Section 9C — Orthodontic Techniques
¶ 9.9. Instruments
Instruments used are as indicated in Figure 9.3 and as follows:
Figure 9.3. Basic Instruments.
9.9.1. Wire cutter (Figure 9.3-A)
9.9.2. Bird beak pliers (Figure 9.3-B), 5 inches. This is a universal application type of pliers for making acute or gradual bends. Adequate loops are also possible.
9.9.3. Three-prong wire bending pliers (Figure 9.3-C), 4 3/4 inches. These pliers can make abrupt bends between 0 and 90 degrees without nicking the wire.
9.9.4. Young-loop bending pliers (Figure 9.3-D), Rocky Mountain, #1 -47. These pliers are used for consistently accurate bending of uniform curves as required for canine loops, helical loops, etc.
9.9.5. Arch former (Figure 9.3-E)
This is a convenient template for making the primary curve in a labial bow.
¶ 9.10. Method of Bending Wire
9.10.1. Gradual bends in orthodontic wire are made with the fingers. Acute bends require the use of pliers as well. The pliers should be regarded as a vise to hold the wire while it is being bent.
9.10.2. Before bending the wire, position the wire on the working cast and mark where the bend should be made with a wax pencil. Hold the wire in the pliers with one hand and bend it downward over a beak of the pliers with the free hand.
9.10.3. Never bend round wire over a sharp-edged beak. Instead, bend it over the rounded beak of the pliers so that the wire does not become nicked.
9.10.4. Before making the next bend, place the wire back on the working cast and check the bend just made. Try to keep all bends at right angles to the long axis of the wire so the torque will be incorporated into the wire and all bends will be in the same plane.
9.10.5. When bending short sections of wire, such as a spring or a clasp, start with the more critical areas (usually toothborne areas)
Then bend the easier sections. (This does not apply to a labial bow or helical spring.)
9.10.6. When making a complex series of bends, such as used in a labial bow or helical spring, begin in the center of the wire and work to either end.
¶ 9.11. Wire-Bending
Consider the following paragraphs as an exercise in wire-bending and take the time to practice making the different bends, using short pieces of orthodontic wire. A few of the more common wire-bending maneuvers are as follows:
9.11.1. Closed-End Loop.
9.11.1.1. Used as the mechanical retention portion of orthodontic wires that are anchored in acrylic. One way to retain the wire in the acrylic is to use a large closed-end loop.
9.11.1.2. To fabricate a closed-end loop, first place the bird beak pliers with the working end facing you and the square beak pointing up. Then firmly grasp the end of a piece of wire with the pliers. The size of the loop will depend on where you place the wire in the jaws of the pliers. The smallest loop is made near the very tip end; the larger loops are made as you move the wire closer to the hinge. Hold the pliers in position and turn the wire around the beak of the pliers (Figure 9.4). With the pliers held still, bend the wire back at a 45-degree angle to complete the closed-end loop.
9.11.2. Zigzag Bend.
9.11.2.1. This is another type of wire-bending maneuver that is used for mechanical retention in the acrylic resin.
9.11.2.2. To fabricate the zigzag bend, start with the three-prong pliers facing you and the middle prong facing up. Firmly grasp the wire. Squeeze the wire to make a slight bend in the wire. Reposition the pliers so the middle prong faces down. Make another bend. Repeat these procedures until you reach the desired length of pattern (Figure 9.5).
Figure 9.4. Closed-End Loop.
Figure 9.5. Zigzag Bend.
9.11.3. Right-Angle Bend.
9.11.3.1. Many times, when making a clasp or spring, the direction of the wire must change abruptly. This is another one of the many uses for three-prong pliers.
9.11.3.2. With the working end of the three-prong pliers facing up, grasp the wire. Squeeze the pliers with one hand and apply finger pressure to the wire with the other until a 90-degree angle has formed (Figure 9.6).
9.11.4. Semicircular Bend.
9.11.4.1. A way of making short springs do the work of long springs is to include spiral loops or multiple bends in their design (paragraph 9.17.1)
The semicircular bend is one such method.
9.11.4.2. Perform this maneuver in a similar manner to the one used with the closed-end loop, except place the bird beak pliers in the center of the wire. Hold the wire still while you gradually bend it downward until the semicircle is complete (Figure 9.7)
9.11.5. Helical Bend.
9.11.5.1. The helical bend, like the semicircular bend, is used in making springs. This is the preferred method of increasing the “spring action” to wire because the helix produces a lighter force over a longer period of time.
Figure 9.6. Right-Angle Bend.
Figure 9.7. Semicircular Bend.
9.11.5.2. Begin by making a semicircular bend in a piece of wire. Reverse the position of the wire within the loop so the working end is facing up and the square end faces down. Bend the wire around until a circle is formed (Figure 9.8). Again, invert the pliers 180 degrees and turn the wire until the helix is complete. A helical bend can be made by using either the bird beak pliers or the Young’s loop bending pliers.
Figure 9.8. Helical Bend.
9.11.6. Deflection Bend.
9.11.6.1. You may have occasion to use this bend where the wire is needed to contact an isolated tooth or clear the opposing occlusion.
9.11.6.2. Grasp a piece of wire with the bird beak pliers and bend one end of the wire slightly downward against the round beak. With the pliers held firmly, bend the other end of wire slightly upward until the two angles formed are equal (Figure 9.9).
Figure 9.9. Deflection Bend.
9.11.7. Smooth-Curve Bend.
9.11.7.1. This bend is used primarily to adapt orthodontic wire to soft tissue and teeth.
9.11.7.2. Grasp the wire at the point where you want to start the curve. The wire should be close to the hinge to make the largest curve possible. Slowly apply finger pressure around the beak of the pliers and, if necessary, reposition the pliers as you go (Figure 9.10).
Figure 9.10. Smooth-Curve Bend.
¶ 9.12. Sprinkle-On Technique for Fabricating Removable Appliance Anchorage
Removable appliance anchorage in the form of a resin denture base is easily made with autopolymerizing orthodontic resin. The procedures for fabricating an acrylic resin base from self-curing orthodontic resin are indicated in Figure 9.11 and as follows:
9.12.1. Survey the cast and block out lingual tooth and tissue undercuts that would prevent placement of the appliance. The presence of some lingual tooth undercut is desirable. Carve blockout wax back 1 to 2 mm gingival to the survey line. Round off any wax ledges created.
9.12.2. Place the working cast in a saturated calcium SDS to remove the air from the cast. Blow off excess water. Air left in the cast could result in air pockets between the resin base and the cast during curing.
9.12.3. Paint the area of the cast to be covered by acrylic with tinfoil substitute and let it dry.
9.12.4. Secure all springs, guards, bows, and clasps with sticky wax. Do not place wax on the loops that will retain them in the resin. Ensure loops are approximately 0.5 mm off the surface of the cast.
9.12.5. Cover the active portion of all springs with wax to prevent entrapping them in hardened resin. Later, when the wax is removed, the spring will have space to function.
9.12.6. Apply alternate portions of powder and liquid to the desired thickness. To better control the resin, do about a third of the total area at a time. As soon as the surface sheen disappears, add acrylic resin to another third (and so forth). To avoid unnecessary finishing, apply the resin in an even layer, 2 to 3 mm thick.
Figure 9.11. Sprinkle-On Technique for Removable Orthodontic Appliance Anchorage.
9.12.7. After the surface sheen dulls, place the appliance upside down in a pressure pot containing 110 oF water. Placing the cast upside down minimizes porosity caused by air escaping from the cast. Apply 15 psi for 10 minutes as per manufacturer’s directions to ensure a dense, well-cured appliance.
9.12.8. When the resin has set, remove the cast from the pressure pot and check the acrylic for flaws. If the cast is satisfactory, remove the appliance from the cast, being careful to avoid distortion. Shape and polish the base as you would the resin base areas of a removable denture. Be careful not to nick the wires or distort them.
9.12.9. After finishing and polishing, the acrylic base rests against soft tissue and the lingual surfaces of the teeth. However, if the appliance is an active one and a tooth is going to be moved, space must be provided between the tooth and the base to allow that movement. The dentist usually creates such a space with the patient present.
¶ 9.13. Fixed Appliance Anchorage
In most cases, depending on the preferences of an individual dentist, you will not have to adapt bands or crowns for fixed orthodontic appliances. The dentist will have done that part of the procedure at chairside in the patient’s mouth. The dentist then makes an impression with the band or crown in place. After the impression is removed from the mouth, the dentist seats the band or crown in the impression and sends the assembly to the laboratory. The impression is poured in dental stone. When the cast is separated from the impression, the band or crown will occupy the same position on the dental stone tooth as it did in the mouth. You can now finish the appliance on the cast in terms of attaching wires, tubes, hooks, etc.
9.13.1. Soldering. Soldering is defined as the process of joining two pieces of metal by using a third piece of metal whose melting range is lower than those of the two being joined. Orthodontic soldering is most often accomplished using a handheld butane torch. However, orthodontic soldering can be carried out with a Hanau alcohol torch, specially designed orthodontic soldering burner (blowpipe), or gas-air torch with an orthodontic tip. Most of the procedures consist of soldering stainless steel parts together with silver solder.
9.13.2. Soldering Requirements. Six rules must be observed for successful soldering:
9.13.2.1. The surfaces of the metals to be joined must be clean and as free from oxides as possible.
9.13.2.2. The parts to be joined should be accurately related as follows.
9.13.2.2.1. For wire to wire, use a soldering jig (Figure 9.12)
Figure 9.12. Soldering Jig.
9.13.2.2.2. For wire to band or crown, seat the band or crown on a dental stone cast. Adapt the wire to the cast according to the dentist’s prescription. What remains is to solder the wire to the band or crown. Hold the wire immobile with wet tissue molded to the cast or a small amount of stone laid over the wires adjacent to both sides of the area to be soldered. This not only helps to secure the wires, but also helps to protect the cast from unnecessary heat damage from the torch. Another similar method is to relate the wire to the band or crown with investment material (Figure 9.13).
9.13.2.3. The parts to be joined should be in contact with each other. (EXCEPTION: The major exception to this rule is that the soldering techniques used in fixed partial denture construction require a slight space between the parts to be joined.)
9.13.2.4. The soldering of stainless steel requires a fluoride paste flux. Paste flux is easy to place and confine to the exact area where it is needed. It etches the surfaces of the steel and improves bonding. When metals are heated, they acquire a strong affinity for oxygen in the air. Unless provision is made for preventing significant oxidation, an oxide film will develop on the stainless steel and form a barrier between the solder and the metal. When this happens, the solder may ball up and fail to flow. If it does flow, it might not make a strong joint. The flux will protect the surface of the metal by preventing the formation of oxide or by removing any oxide that forms.
Figure 9.13. Soldering a Cantilever Loop to a Band.
9.13.2.5. The joint being soldered must be able to be reached by the flame (accessible)
It must also be visible so that the progress of the soldering operation can be observed.
9.13.2.6. Use the reducing part of the flame and perform the soldering procedure quickly. The assembly must be preheated. Only a slight amount of additional heat will be needed to make the solder flow. Do not solder with the tip or outer zone of the flame. When this part of the flame is applied to metal surfaces, oxidation occurs, requiring the application of additional flux. Instead, move inward from the tip of the flame to its reducing zone. Remove the flame from the assembly as soon as the solder flows into the joint. Overheating causes weak joints. Soldering is best done in subdued light. The appearance of the metal and the appearance of the solder are harder to observe in a bright light.
9.13.3. Soldering Method.
9.13.3.1. Lay out all materials for maximum convenience and quick availability.
9.13.3.2. Relate the parts to be soldered.
9.13.3.3. Make sure the parts are clean and in contact.
9.13.3.4. Apply flux.
9.13.3.5. Using the reducing part of a flame, heat the two pieces to be joined and observe the action of the fluoride flux. The flux will bubble up and then melt. As the flux melts, it will take on the appearance of liquid glass. Begin to concentrate the flame on the larger of the two pieces. Apply fluxed solder at the proposed place of union. The solder should flow smoothly and promptly. Remove the flame immediately.
9.13.3.6. Take the appliance off the cast. Finish and polish it.
¶ 9.14. Spot-Welding
Spot-welding is the process of joining two pieces of metal by using a machine that generates high voltage electric current. The parts to be joined are held together by electrodes. As the electric current passes through the work, resistance builds, heat is generated, metal melts, and a union of the parts occurs. A true weld is formed, and no solder or flux is used. This technique is used only on stainless steel alloys and is less commonly used in most soldering procedures (Figure 9.14).
Figure 9.14. Electric Spot-Welder.
¶ Section 9D — Removable Orthodontic Appliances
¶ 9.15. Parts of an Appliance
Removable orthodontic appliances are composed of three distinct parts:
9.15.1. Effecting Mechanism. The first part is a device or mechanism that moves teeth into new positions or holds teeth in existing position. These mechanisms consist of active or passive bows along with springs, screws, or rubber bands that mostly have active orthodontic functions.
9.15.2. Anchorage. Anchorage for removable orthodontic appliances consists of an autopolymerizing resin base formed to fit both the palate and lingual surfaces of teeth in the maxillary arch, or the lingual aspect of the alveolar process and teeth in the mandibular arch. The effecting mechanism is embedded in the anchorage. Since the anchorage is built to have a great deal of resistance to movement, the effecting mechanism has a solid base from which to push, pull, or hold.
9.15.3. Retention. Retention is accomplished by various popular forms of wrought wire clasps embedded in anchorage and adapted to existing natural teeth. The purpose of the clasps is to maintain the anchorage in place. The Hawley retainer was the forerunner of the variety of removable appliances presently in use. Most are modifications of the Hawley principle.
¶ 9.16. Hawley Retainer
See Figures 9.15 and 9.16 and as follows:
9.16.1. Effecting Mechanism (Labial Bow)
The method of bending the bow is shown in Figure 9.17. The bow is composed of a bow portion and bilateral canine loops. Wire sizes are .030 to .032 inches.
9.16.1.1. Bow. Use an arch-forming template to develop the arch’s initial ideal curvature. Then adapt the bow to the rotations and inclinations of individual teeth by bending the wire with the fingers or with the help of the pliers. Start in the center and move towards one side. Bend the other half keeping the wire parallel to the occlusal plane. For best results, be sure the wire contacts the teeth in the middle thirds of the crowns’ facial surfaces.
9.16.1.2. Canine Loop (Vertical Loop)
At about the mesial third of the canine on one side, make a 90-degree bend in the wire toward the gingiva. Next, use wire bending pliers to bend the closing portion of the loop (Figure 9.18). Make the loop long enough to clear the gingival crest, but not so long that it dips into the bottom of the buccal sulcus. The loop’s distal upright should descend vertically to the bucco-occlusal embrasure between the canine and first premolar.
Figure 9.15. Hawley Retainer—Occlusal View Showing Anchorage and Clasps.
Figure 9.16. Hawley Retainer—Facial View Showing Labial Bow.
9.16.1.3. Adapting the Wire into the Palatal Area. Bend the wire into the occlusal embrasure and adapt it to the embrasure as closely as possible. Be certain the wire does not interfere with the occlusion. Shape the remaining wire to the lingual embrasure and extend the wire onto the palate. End the bow with an angled bend or loop for retention in the resin base. The palatal part of the bow should be elevated about 1/2 mm off the cast’s surface so it will become firmly embedded in the resin of the anchorage. NOTE: Repeat the canine loop and palatal adaptation steps for the other side of the bow.
9.16.2. Retention. The common clasp forms used for retaining removable orthodontic appliances are the circumferential, Adams, and ball. They are custom bent from wrought wire (Figure 9.19) as follows:
9.16.2.1. Circumferential Clasp. The circumferential clasp comes out of an occlusal embrasure area, is adapted to the facial surface of the tooth, and engages a mesial or distal zone of undercut opposite the embrasure of origin. Wire sizes are .028 to .030 inches. It is also common for a circumferential clasp to pass distal to the terminal abutment in a quadrant on the way to a mesiofacial zone of undercut.
Figure 9.17. Bending a Labial Bow.
Figure 9.18. Canine (Vertical) Loop.
Figure 9.19. Wrought Wire Clasp Types—Circumferential (A), Adams (B), and Ball (C).
9.16.2.2. Adams Clasp. The Adams clasp is the most retentive of the wrought wire clasps and is probably the most popular. Wire sizes are .022 to .025 inches. The method of bending this clasp is shown in Figure 9.20. The bending sequence for the Adams clasp is as follows:
Figure 9.20. Bending an Adams Clasp.
9.16.2.2.1. Make a 90-degree bend about 1 1/2 inches from the end of the wire. Lay the wire against the tooth, measure the mesiodistal width, and make another 90-degree bend that parallels the first.
9.16.2.2.2. With a pair of pliers, bend each leg back up to form a loop. Adjust the legs so they fall in the interproximal areas and fit snugly against the tooth. The horizontal part of the wire should cross the middle third of the tooth with no contact. Mark the height of the occlusal embrasure on each leg with a grease pencil.
9.16.2.2.3. Bend each leg into its respective occlusal embrasure and make the wire touch the occlusal aspect of the contact area. The wires should not interfere with the occlusion. Be sure the horizontal bar of the clasp still crosses the middle third of the tooth with no contact.
9.16.2.2.4. Cut off the excess wire and contour the remainder to the palate, ending with an angled bend or loop to provide retention in the acrylic base. Leave about ½ mm space between the cast and the wire.
9.16.2.2.5. Adjust the loops previously adapted to the buccoproximal areas to fit well against the tooth’s surface.
9.16.2.3. Ball Clasp. This clasp is usually prefabricated and is available in diameters of 0.024 inch (0.6 mm), 0.028 inch (0.7 mm), or 0.040 inch (1.0 mm). It is bent sufficiently to spring into mesio or distofacial undercuts. The ball size increases with an increase in wire size.
9.16.3. Anchorage.
9.16.3.1. Block out lingual undercuts on the cast as previously described. Paint the cast with tinfoil substitute. Seal the bow and clasp in place with sticky wax. Develop the resin base, using the “sprinkle-on” method. Place the appliance in a pressure pot to cure. Finish and polish it.
9.16.3.2. If the dentist is going to use the retainer as a passive appliance, leave the resin in contact with the lingual surfaces of the anterior teeth. If the appliance is going to be activated by modifying the bow or closing the canine loops, cut the resin back out of contact with the anteriors to allow their movement. An activated labial bow moves teeth lingually.
¶ 9.17. Modifications of the Hawley Retainer
Most of the modifications of the Hawley principle are designed as active appliances. The effecting mechanisms consist of various springs, rubber band systems, screws, and ramps instead of or in addition to a conventional labial bow. Passive retainers sometimes require the use of clear acrylic shields added on the labial bow. This not only gives the wire additional occlusal-gingival stability, but also helps eliminate unwanted tooth rotation in anterior teeth.
9.17.1. Springs.
9.17.1.1. Overview. Springs produce force when a wire’s attempt to return from a stressed to an unstressed condition is resisted. If a technician makes springs as part of a removable orthodontic appliance, the springs are bent and subsequently positioned on the cast in a passive condition. The dentist activates them before placing the appliance in the patient’s mouth. Springs are supposed to produce gentle pressures over as long a route of travel as possible. Long springs are better able to satisfy these requirements than short ones, but space is almost always at a premium in the mouth. A short spring can be made to have the desirable qualities of a long one by incorporating spiral loops or multiple bends into the spring’s design:
9.17.1.2. Helical Loop Springs.
9.17.1.2.1. The word helical means “having the form of a spiral.” The basic shape of a helical loop spring is shown in Figure 9.21. It consists of three parts: a tag which is embedded in the anchorage; a spiral coil which acts to make the spring behave like a longer one without a coil; and an arm which contacts a tooth and transmits force to it. Figures 9.21-B and 9.21-C show that the route tooth movement takes is largely a function of how the arm is angled.
Figure 9.21. Helical Loop Spring.
9.17.1.2.2. Notice in Figure 9.21 that the tooth moves at a right angle to the initial point of contact of the spring. It is important to note that the tag has to be of sufficient size and bent in a way that holds it in the anchorage and keeps it from twisting in the plastic.
9.17.1.3. Finger Springs.
9.17.1.3.1. Finger springs are generally designed to move teeth either mesially or distally. Wire sizes range between .014 and .032 inches. The versions of this spring made with lighter gauge wire are used on anterior teeth (Figure 9.22). Heavier gauge finger springs can perform tasks like retracting or uprighting a molar that has migrated and closed needed space (Figure 9.23). In Figures 9.22 and 9.23, note that the springs are protected by guards. If it were not for the guards, the springs would be less likely to maintain proper contact with the teeth they are supposed to move.
Figure 9.22. Finger Springs and Guards for Anterior Tooth Movement.
9.17.1.3.2. In the case of the molar-retracting spring (Figure 9.23), the guard also guides the path of the molar as it moves distally. In Figure 9.22, the labial bow acts to steer or guide the path of incisor movement. The bow itself may be either active or passive.
9.17.1.3.3. Guards for springs can be made two different ways. First, as described above, the guard is placed over top of the spring’s arm and guides the path of the tooth and the spring’s arm. In this method the guard and spring arm are not imbedded into the acrylic; only the tag is in the acrylic. Another method is to place the guard under the spring’s arm, block out the arm and guard with wax, and then cover the entire spring with acrylic (Figure 9.24). With this method, the guard guides the path of the spring arm and the acrylic guides the path of the tooth. When blocking out the spring arm and guard with wax, do not build up the wax any thicker than the thickness of the wire and do not blockout the retentive tag.
Figure 9.23. Finger Spring (A) and Guard (B) for Uprighting a Molar.
Figure 9.24. Finger Spring With Guard (Alternate Method).
9.17.1.4. Canine Retractor-Premolar Holder (Figure 9.25)
The finger springs discussed so far are lingually oriented. Although the canine retractor-premolar holder is obviously another style of finger spring, it is classified separately because it is facially oriented with respect to the teeth. Wire sizes are .030 to .032 inches. When the spring is anchored at point “A” in Figure 9.25, the spring will retract the canine. If the spring is anchored just distal to the canine, it can be made to prevent the premolar from drifting forward.
9.17.1.5. “W” Spring (Figure 9.26-A). Although this spring has a helical loop in it, it takes its name from the terminal series of bends that look somewhat like a “W.” Wire sizes are .014 to .020 inches. The “W” spring is mostly used to move teeth facially. Because it rests on inclined tooth surfaces, a guard is constructed over the spring to keep it from sliding along an incline (Figure 9.26-B). Observe the labial bow. It has been bent to stop the central incisor after the tooth has been moved to an acceptable position in the dental arch.
Figure 9.25. Canine Retractor Finger Spring.
Figure 9.26. “W” Spring and Guard.
9.17.1.6. Coffin Spring. As pictured in Figure 9.27, the purpose of this spring is expansion of the posterior segments of the maxillary arch.
9.17.2. “Booties” Plus Elastics (Figure 9.28)
9.17.2.1. The “bootie” takes its name from its appearance. It is simply a rubber band anchoring device. The combination of a rubber band and bilateral booties is sometimes used as a substitute for a labial bow to make teeth contact or to move teeth lingually. Wire sizes are .032 to .036 inches.
9.17.2.2. The tags of the booties pass between the canines and first premolars to become embedded in lingual anchorage. The rubber band functions best when it is situated near the incisal third of the teeth. Bend the booties and position them on the cast accordingly. One disadvantage associated with a rubber band is that it tends to migrate gingivally on teeth that have moderate facial inclinations.
9.17.3. Screws. Some uses for screws are illustrated in Figure 9.29.
Figure 9.27. Coffin Spring for Arch Expansion.
Figure 9.28. Bootie Anchorage.
Figure 9.29. Uses for Screws.
9.17.3.1. The appliance pictured in Figure 9.29-A will expand a dental arch as the screw is opened.
9.17.3.2. In Figure 9.29-B, opening the screw should move the four incisors facially.
9.17.3.3. On a more limited basis, the screw arrangement in Figure 9.29-C should move the two teeth anterolaterally.
¶ 9.18. Inclined Plane Appliance
An incisal inclined plane appliance is used to move one or two maxillary teeth in crossbite facially (Figure 9.30). It consists of an acrylic resin ramp with a resin substructure adapted to a minimum of four opposing lower teeth that serve as anchorage. The steeper the ramp, the faster the teeth in crossbite will move. However, the angle the ramp forms with the occlusal plane should not exceed 45 degrees. Also, if the bulk of the appliance is responsible for too much separation between the upper and lower teeth, it can cause extreme discomfort in the masticatory muscles or temporomandibular joints.
Figure 9.30. Inclined Plane Appliance.
¶ Section 9E — Fixed Orthodontic Appliances Made in the Dental Laboratory
¶ 9.19. Space Maintainers
Space maintainers are orthodontic appliances designed to preserve the space created by the premature loss of a tooth. These appliances are purely passive in nature. Fixed space maintainers may be made of preformed stainless steel crown forms or bands with wire projections of the following type:
9.19.1. Quadrant cantilever loopspace maintainers (Figures 9.31 and 9.32)
9.19.2. Lingual archwire space maintainer (Figure 9.33)
9.19.2.1. Lingual archwires are round in cross-section and range from 0.032 to 0.36 inches in diameter (Figure 9.34)
Bend the size wire the dentist specifies to the general shape of the dental arch. Adapt the wire to the linguogingival third of the teeth, just above the gingival margins. The objective is to touch the lingual aspect of all teeth in good alignment without special regard for teeth that are grossly out of position.
9.19.2.2. Solder the ends of the archwire to bands on the first permanent molars. The appliance is more versatile if the archwire carries bilateral vertical loops. The loops are directed toward the floor of the mouth and are situated just anterior to the first permanent molars.
Figure 9.31. Cantilever Loop Space Maintainer (Preformed Crown Retainer).
Figure 9.32. Cantilever Loop Space Maintainer (Band Retainer).
Figure 9.33. Lingual Arch Space Maintainer.
¶ 9.20. Space-Closing or Space-Regaining Appliance
9.20.1. This fixed orthodontic appliance is used with rubber bands to obtain a degree of bodily tooth movement while closing a space (Figure 9.35). The tooth to be moved and the primary anchor tooth are banded. An open-end tube and hook, facing distally, is soldered or welded facial and lingual to the main anchor, banded tooth. Guiding wires are placed into the tubes and welded or soldered to the banded tooth to be moved. Hooks facing mesially are also welded or soldered on the banded tooth to be moved.
9.20.2. Rubber elastics are then placed onto the hooks to obtain movement. When used as a space regaining appliance, no hooks are attached to the bands. Instead, compressed coil springs are threaded onto the guide wires.
Figure 9.34. Wire Sizes for Effecting Mechanisms, Clasp, and Guards.
Wire Sizes for Various Applications (listed in thousandths of an inch)
| Application | Device | Wire Size |
|---|---|---|
| Archwires | Labial Bow | .030-.032 |
| Archwires | Lingual Archwire | .032-.036 |
| Springs | Finger Spring (anterior teeth) | .014-.028 |
| Springs | Finger Spring (posterior teeth) | .025-.032 |
| Springs | W Spring | .014-.020 |
| Springs | Cuspid Retractor-Bicuspid Holder | .030-.032 |
| Springs | Coffin Spring | .032-.036 |
| Clasps | Adams | .022-.025 |
| Clasps | C-Clasp | .028-.030 |
| Clasps | Ball Clasp | .028-.032 |
| Miscellaneous | Spring Guard | .028-.030 |
| Miscellaneous | Booties | .032-.036 |
| Miscellaneous | Space Maintainer Loop | .032-.036 |
Figure 9.35. Space-Closing or Space-Regaining Appliance.
¶ Section 9F — Trimming and Finishing Orthodontic Casts
¶ 9.21. Overview
9.21.1. Orthodontic casts are used as a three-dimensional aid to explain treatment to the patient prior to orthodontic treatment. Orthodontic casts can then be made after treatment is complete to show the amount of change or development that has occurred.
9.21.2. Casts are trimmed and finished differently from removable and fixed prosthetic working casts. The base and sides are trimmed so the heels of the maxillary and mandibular casts can be positioned on a flat surface with the teeth in maximum intercuspation. They can also be turned onto their right or left sides and the teeth will remain in maximum intercuspation (Figure 9.36). NOTE: The angles and height of the orthodontic cast in the following trimming procedures may vary among dentist. However, the order of the steps should remain the same.
Figure 9.36. Trimmed Orthodontic Casts.
¶ 9.22. Procedures
9.22.1. Following disinfection, pour impressions by the one- or two-step method in orthodontic plaster or dental stone as directed by the dentist (Figure 9.37). Technicians generally use rubber base former molds to form the bases of the cast. This provides for the bulk of stone needed for trimming the cast and eliminates a line of demarcation between the impression and base of the cast.
9.22.2. Remove all nodules and excess stone so the casts may be accurately occluded during certain trimming steps.
9.22.3. Place the maxillary cast on the cast trimmer’s table. Stand the cast with its occlusal plane contacting a right angle guide plate. The base of the cast should now be directed toward the trimming wheel. Place a folded, damp paper towel between the guide plate and the stone teeth to reduce the possibility of chipping. Trim the base of the maxillary cast until it is parallel with the occlusal plane and 40 mm in height.
9.22.4. Remove the right angle guide plate and position the maxillary cast on the trimming table so the back of the cast can be trimmed.
9.22.5. Trim the back of the cast perpendicular to the median raphe and 6 mm short of the pterygomaxillary notch. For symmetry of the completed cast to be correct, it is critical for the back to be perpendicular to the median raphe. If it is a class II malocclusion case, more space distally will be needed to prevent overtrimming the mandibular cast when it is in occlusion.
9.22.6. Place the back of the maxillary cast against the angulator guide. Set the angulator guide at 65 degrees (Figure 9.37). Trim one side to the deepest part of the mucobuccal fold. Repeat this step for the other side.
9.22.7. Place the back of the maxillary cast against the angulator guide. Set the angulator guide at 22 degrees. Trim the anterior until you reach the depth of the labial vestibule fold and the cut is from the canine eminence to the midline. Repeat this step on the opposite side. The point of the anterior cuts should fall on an imaginary line that follows the median raphe. Use caution to avoid damaging the anterior teeth during this step.
Figure 9.37. Trimming Orthodontic Casts.
9.22.8. Place the mandibular cast in occlusion with the trimmed maxillary cast. The dentist may have supplied an interocclusal record for this purpose. If an interocclusal record is not provided, extreme care must be taken to avoid breaking teeth. If necessary, trim some plaster from the heels of the mandibular cast to get the upper and lower casts together.
9.22.9. With the casts in occlusion, place the base of the maxillary cast against the right angle guide plate. Trim the base of the mandibular cast until the combined height in occlusion of the casts is 70 mm.
9.22.10. Place the mandibular cast on the trimming table with the maxillary cast in occlusion. Trim the mandibular heel area, using the maxillary cast as a guide. Trim the mandibular cast until the maxillary cast just starts to make contact with the trimming wheel. This should enable the casts to stay in occlusion while on their backs.
9.22.11. Place the back of the mandibular cast against the angulator guide. With the angulation set at 55 degrees, trim one side to the deepest part of the mucobuccal fold. Repeat this for the other side.
9.22.12. Trim the anterior portion of the mandibular cast parallel to its back cut, stopping when you reach the depth of the labial vestibule. Finish the cut by rounding to each canine area. The completed anterior cut should be an evenly rounded symmetrical form that extends from canine to canine area at approximately the deepest part of the labial vestibule fold. Use caution to avoid damaging the anterior teeth during this step.
9.22.13. Place the cast in occlusion with the base of the mandibular cast on the trimming table. Set the angulator guide to 120 degrees. Trim the heel (corners) of both casts until you reach 6 mm from the distobuccal cusp of the most terminal molar. Repeat this step on the opposite side. After completing this step the casts should stay in occlusion while setting on either heel.
9.22.14. After establishing correct height and proper trim, finish all sides of the casts with a fine grit trimming wheel if available.
9.22.15. Rinse the casts under running water. Use a soft toothbrush on the anatomical portion to remove any slurry left from the trimming process. To remove any blobs of material, use a rounded scraper in the mucobuccal fold area and a sharp instrument around the teeth.
9.22.16. Use the finest grained wet-dry sandpaper on a glass slab to remove the cast trimmer marks. Do this under running water, holding the surface of the cast firmly against perfectly flat sandpaper.
9.22.17. Let the cast dry overnight. Fill holes with dry plaster or stone. Add water using a camel hair brush. After the holes are filled, allow the casts to dry thoroughly before stoning or sanding. Use a minimum of water during stoning or sanding. Dip the cast in water and rub dry. Wipe the residue away.
9.22.18. If needed, repeat all of the above to produce an acceptable cast.
9.22.19. After the cast is free of holes and scratches, dry it thoroughly.
9.22.20. Place the patient’s name and the date printed on gummed labels on the base of the maxillary and mandibular casts. If a cast marking machine is available, use it instead.
9.22.21. Place the casts in liquid soap for 30 to 45 minutes. Remove the casts from the soap, and rinse them under running water until all excess soap is removed. Polish the casts with a slightly damp cloth, paper towel, or dry chamois and rub them to a high gloss.
¶ Section 9G — Administrative Information
¶ 9.23. Forms Adopted
DD Forms 1348-6, DoD Single Line Item Requisition System Document; and 2322, Dental Laboratory Work Authorization.
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