**5. Selection of the appropriate (effective) biomechanical approach**

After selection of the proper approach to reach the impacted tooth, an appropriate biome‐ chanical approach should be selected. A proper biomechanical system is capable of protecting periodontium and avoiding any unwanted tooth movement or root damage of the adjacent teeth.

#### **a. Anchorage preparation (Direct vs. Indirect)**

tooth #23 by means of Seifi Twin Screws (STS) for protecting other teeth from early unwanted

Soft tissue covering hard palate is called masticatory mucosa and it consists of keratinized stratified squamous epithelium. Since palate is covered with keratinized mucosa or attached gingiva, problems with alveolar mucosa are not applied to this part of operational area. If the bulge of impacted canine is obvious from palatal aspect, cuspid tooth should be located superficial and accessible after soft tissue removal plus precautious removal of covering bone. Patient G.H. (Figure 8), had not canine bulge of left side on facial aspect (top row-left and middle slides) but it was seen on the palatal aspect clinically (top row-right slide) and also in CBCT (bottom- left and middle). Uncovering the tooth and bonding through a small window can be hectic (control of vascular bleeding, plasma fluid exudation, and even next week granulation tissue bleeding) and a palatal flap may help in achievement an isolated and dry environment for the bonding and open or close eruption technique. Again sufficient bone removal is recommended without damage to the tooth root because PDL is interface for tooth movement and enamel of crown

Figure 7. Upper right central incisor is positioned horizontally. Apically positioned flap is not indicated in the present situation

**Figure 7.** Upper right central incisor is positioned horizontally. An apically positioned flap is not indicated in the present situation and a closed eruption surgical approach may be used. Thin overlying bone can be removed with a periosteal elevator instead of rotary instrument (burs) and bonding performed in an isolated dry environment (top row). After wound healing, tooth 11 can be pulled towards the dental arch by means of absolute anchorage (miniscrews) or after bonding upper dental arch (continuous wire). In this case, an orthodontic attachment was bonded in the lingual fossa of tooth 11 and ligature wire was placed out of the flap for biomechanical extrusive forces (bottom

ordered closed eruption surgical approach. Thin overlying bone can be removed with periosteal elevator instead of rotary instrument (burs) and bonding performed in isolated dry environment (top row). After wound healing, tooth 11 can be pulled toward dental arch by means of absolute anchorage (Mini-screws) or after bonding upper dental arch (continuous wire). In the present condition, orthodontic attachment was bonded in lingual fossa of tooth 11 and ligature wire was placed out of flap for

alveolar bone. It should be planned to preserve an adequate apico-coronal height of keratinized gingiva (2-3 mm), especially in the presence of thin gingival biotype (transparency of the periodontal probe through gingival margin). In some cases impacted teeth are superficial and coronal or near mucogingival junction, in these circumstances, an apically positioned flap or open approach is indicated but author suggest minimum apical repositioning of the flap that equals the amount needed for bonding of orthodontic bracket in proper position for avoiding future apical migration of gingival margin. Uneven gingival contours can be corrected by cosmetic periodontal plastic surgery (laser, scalpel, or radiosurgery) if adequate soft tissue exist. Uncontrolled

When impacted teeth may have facial (labial or buccal) approach, and the position of tooth is deep; best technique is closed eruption. In the afore mentioned situation, an apically positioned flap will not be stable and rebound of soft tissue may happen

During the tooth exposure, care should be given to protect root surface, for example; by avoiding the usage of sharp or rotary instrument if possible because bone and unerupted tooth are color matched and any damage to root leads to periodontal ligament breakdown, increased risk of ankylosis, and increased risk for future bone and gingival recession (deleterious effects to periodontal health and esthetics). Thin layers of bone can be removed by periosteal elevator or similar instruments e.g. curette to

tipping toward labial/buccal can produce gingival/bone recession plus a long clinical crown that should be avoided.

(not reintrusion of tooth) in addition to unwanted exposed parts of the bone that should be covered by flap (Figure 7).

has not potential for participating in bone remodeling and consequent tooth movement. Absolute anchorage was used for eruption of tooth #23 by means of Seifi Twin Screws (STS) for protecting other teeth from early unwanted orthodontic forces (Figure 8).

Figure 8. Patient G.H. with an impacted tooth #23, underwent a surgical uncovering of palatal left canine (mirror image after surgery-bottom right). An absolute anchorage by combination of two miniscrew and a cantilever helical loop (Seifi Twin screws/STS) was used for forced eruption or extrusion of impacted canine without exerting unwanted orthodontic force to the

**Figure 8.** Patient with an impacted tooth #23 underwent a surgical uncovering of a palatal left canine (mirror image after surgery-bottom right). An absolute anchorage by combination of two miniscrews and a cantilever helical loop (Seifi Twin Screws/STS) was used for forced eruption or extrusion of impacted canine without exerting unwanted or‐ thodontic force to the adjacent teeth. Miniscrews were covered by composites for better performance of springs and

4‐ Selection of the appropriate (efficient) biomechanical approach

After selection of proper approach to reach the impacted tooth, an appropriate biomechanical approach should be selected. A proper biomechanic system is capable of protecting periodontium and avoiding any unwanted tooth movement or root damage of

 In contrast to dental implants, orthodontic miniscrews are loaded immediately, and most authors suggest the use of light forces early on.(12) Only a few studies, mostly on animals, have dealt with the investigation of tissue reaction to immediate loading of miniscrew implants. Miniscrew implants can be immediate loaded (there is no need for a waiting period for osseointegration, in contrast to orthodontic implants), reducing the total treatment time. There is no need for complicated clinical and laboratory procedures (i.e., fabrication of acrylic splints by taking imprints with additional implant copying systems to accurately transfer

Direct anchorage screws are useful when prognosis of the eruption (impacted tooth) is questionable. If the impacted tooth is ankylosed, by applying force from a continuous arch, dental arch could be deflected toward ankylosed tooth (sometimes creating open bites) but an absolute anchorage could be a valuable tool to determine the sensitive stage of tooth eruption without endangering the adjacent anchored teeth (Figure 8). Direct anchorage can be used for anterior retraction in protrusion cases or non-extraction treatment of the Class III malocclusions (retraction of lower anterior sextant) and cases who has midline shift toward previous extraction sites (Figure 9). Protraction of upper dentition is possible by using miniscrews in anterior part of facial portion or palatal part. Better results in protraction of upper dentition can be expected by using miniscrews in combination with miniplates. In some situations transpalatal arch (TPA) is used for eruption of impacted teeth as a direct anchorage unit that its resistance to displacement depends on the number of teeth and the root surface area of them (Figure 10). Following force application, some mobility or movement of teeth will be noticeable and in X-ray examination, disappearance of lamina dura plus widening of PDL will be evident; these are sequel of force dispersion in the dental anchorage units. In maximum anchorage cases (Group A), mesial movement of posterior teeth (protraction) should be less than 25% of extraction site, in moderate anchorage

adjacent teeth. Miniscrews were covered by composites for better performance of spring and sustained stability.

a‐ Anchorage preparation (Direct Vs Indirect)

the implant position to cast models) to facilitate safe and precise implant insertion.(13)

orthodontic forces (Figure 8).

biomechanical extrusive forces (Bottom row).

and

row).

reach coronal part of tooth (Figure 7).

78 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

the adjacent teeth.

sustained stability.

In contrast to dental implants, orthodontic miniscrews are loaded immediately, and most authors suggest the use of light forces early on.[12] Only a few studies, mostly on animals, have dealt with the investigation of tissue reaction to immediate loading of miniscrew implants. Miniscrew implants can be immediate loaded (there is no need for a waiting period for osseointegration, in contrast to orthodontic implants), reducing the total treatment time. There is no need for complicated clinical and laboratory procedures (i.e., fabrication of acrylic splints by taking imprints with additional implant copying systems to accurately transfer the implant position to cast models) to facilitate safe and precise implant insertion.[13]

Direct anchorage screws are useful when prognosis of the eruption (impacted tooth) is questionable. If the impacted tooth is ankylosed, by applying force from a continuous arch, the dental arch could be deflected towards the ankylosed tooth (sometimes creating open bites); but, an absolute anchorage could be a valuable tool to determine the sensitive stage of tooth eruption without endangering the adjacent anchored teeth (Figure 8). Direct anchorage can be used for anterior retraction in protrusion cases or non-extraction treatment of the Class III malocclusions (retraction of lower anterior sextant) and cases who have midline shift toward previous extraction sites (Figure 9). cases (Group B), posterior protraction is almost equal to anterior retraction, and in minimum anchorage cases (Group C), posterior protraction is more than 75% of the extraction site. Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which orthodontic force is placed. Locations for indirect anchors include retromolar, buccal vestibule, and midpalatal (Figure 11). As they are not destined for restoration or any functional use after serving as anchor units, all indirect-anchor devices are explanted at some time after the completion of orthodontics. Consequently, all indirect-anchor devices, be they endosseous implants or mini-screws, must be considered TADs.(14)

Figure 9. Patient M.T. had Class III open bite with midline deviation toward left side, a prvious extraction site. A miniscrew was inserted in retromolar area of right side for midline correction and meanwhile retraction of anterior teeth to correct class III relationship and establishment of proper overjet and overbite. **Figure 9.** Patient with Class III open bite with midline deviation towards the left side, a prvious extraction site. A min‐ iscrew was inserted in the right retromolar area for midline correction ; meanwhile retraction of anterior teeth to cor‐ rect class III relationship and establishment of proper overjet and overbite was done.

Protraction of the upper dentition is possible by using miniscrews in anterior or palatal parts. Better results in protraction of the upper dentition can be expected by using miniscrews in combination with miniplates. In some situations transpalatal arch (TPA) is used for eruption of impacted teeth as a direct anchorage unit; resistance to displacement depends on the number of teeth and the root surface area (Figure 10).

Figure 10. Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resist against reactive forces produced by traction force on the impacted upper right

canine.

relationship and establishment of proper overjet and overbite.

posterior protraction is more than 75% of the extraction site.

mini-screws, must be considered TADs.(14)

inserted in retromolar area of right side for midline correction and meanwhile retraction of anterior teeth to correct class III

Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which

cases (Group B), posterior protraction is almost equal to anterior retraction, and in minimum anchorage cases (Group C),

Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which orthodontic force is placed. Locations for indirect anchors include retromolar, buccal vestibule, and midpalatal (Figure 11). As they are not destined for restoration or any functional use after serving as anchor units, all indirect-anchor devices are explanted at some time after the completion of orthodontics. Consequently, all indirect-anchor devices, be they endosseous implants or

Figure 10. Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resist against reactive forces produced by traction force on the impacted upper right canine. **Figure 10.** Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resists reactive forces produced by traction force on the im‐ pacted upper right canine.

Following force application, some mobility or movement of teeth will be noticeable and on Xray examination, disappearance of the lamina dura plus widening of PDL will be evident; these are sequel of force dispersion in the dental anchorage units. In maximum anchorage cases (Group A), mesial movement of posterior teeth (protraction) should be less than 25% of the extraction site, in moderate anchorage cases (Group B), posterior protraction is almost equal to anterior retraction, and in minimum anchorage cases (Group C), posterior protraction is more than 75% of the extraction site. Figure 9. Patient M.T. had Class III open bite with midline deviation toward left side, a prvious extraction site. A miniscrew was inserted in retromolar area of right side for midline correction and meanwhile retraction of anterior teeth to correct class III relationship and establishment of proper overjet and overbite.

Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which orthodontic force is placed. Locations for indirect anchors include retromolar, buccal vestibule, and midpalatal areas (Figure 11). As they are not destined for restoration or any functional use after serving as anchor units, all indirect-anchor devices are explanted at some time after the completion of orthodontics. Consequently, all indirect-anchor devices, be they endosseous implants or mini-screws, must be considered TADs.[14] Figure 10. Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resist against reactive forces produced by traction force on the impacted upper right canine.

**Figure 11.** Miniscrews as an indirect anchorage resist against vertical pull of elastics for open bite closure. In the present condition eruption of lower anterior teeth has a major role for establishment of proper overbite. Vertical move‐ ment of the maxillary dentition is controlled by ligating both upper canines to miniscrews as indirect anchorage.

#### **b. Force application**

cases (Group B), posterior protraction is almost equal to anterior retraction, and in minimum anchorage cases (Group C),

Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which orthodontic force is placed. Locations for indirect anchors include retromolar, buccal vestibule, and midpalatal (Figure 11). As they are not destined for restoration or any functional use after serving as anchor units, all indirect-anchor devices are explanted at some time after the completion of orthodontics. Consequently, all indirect-anchor devices, be they endosseous implants or

Figure 9. Patient M.T. had Class III open bite with midline deviation toward left side, a prvious extraction site. A miniscrew was inserted in retromolar area of right side for midline correction and meanwhile retraction of anterior teeth to correct class III

cases (Group B), posterior protraction is almost equal to anterior retraction, and in minimum anchorage cases (Group C),

Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which orthodontic force is placed. Locations for indirect anchors include retromolar, buccal vestibule, and midpalatal (Figure 11). As they are not destined for restoration or any functional use after serving as anchor units, all indirect-anchor devices are explanted at some time after the completion of orthodontics. Consequently, all indirect-anchor devices, be they endosseous implants or

Figure 10. Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resist against reactive forces produced by traction force on the impacted upper right

**Figure 10.** Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resists reactive forces produced by traction force on the im‐

Following force application, some mobility or movement of teeth will be noticeable and on Xray examination, disappearance of the lamina dura plus widening of PDL will be evident; these are sequel of force dispersion in the dental anchorage units. In maximum anchorage cases (Group A), mesial movement of posterior teeth (protraction) should be less than 25% of the extraction site, in moderate anchorage cases (Group B), posterior protraction is almost equal to anterior retraction, and in minimum anchorage cases (Group C), posterior protraction is

Figure 9. Patient M.T. had Class III open bite with midline deviation toward left side, a prvious extraction site. A miniscrew was inserted in retromolar area of right side for midline correction and meanwhile retraction of anterior teeth to correct class III

Indirect anchorage miniscrew stabilizes dental units, which in turn serve as the anchor units, and opens absolute anchor possibilities that can be even more flexible than direct-anchor setups. Indirect-anchor setups will entail an implant, or TAD, placed in a non-dental location, which is then used to stabilize teeth, rendering them as indirect absolute anchors, on which orthodontic force is placed. Locations for indirect anchors include retromolar, buccal vestibule, and midpalatal areas (Figure 11). As they are not destined for restoration or any functional use after serving as anchor units, all indirect-anchor devices are explanted at some time after the completion of orthodontics. Consequently, all indirect-anchor devices, be they endosseous

Figure 10. Transpalatal arch (TPA) has served as indirect anchorage (contributing role of root surface area of upper first molars) in addition to a full size rectangulet wire that resist against reactive forces produced by traction force on the impacted upper right

**Figure 11.** Miniscrews as an indirect anchorage resist against vertical pull of elastics for open bite closure. In the present condition eruption of lower anterior teeth has a major role for establishment of proper overbite. Vertical move‐ ment of the maxillary dentition is controlled by ligating both upper canines to miniscrews as indirect anchorage.

posterior protraction is more than 75% of the extraction site.

relationship and establishment of proper overjet and overbite.

80 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

posterior protraction is more than 75% of the extraction site.

canine.

canine.

pacted upper right canine.

mini-screws, must be considered TADs.(14)

more than 75% of the extraction site.

relationship and establishment of proper overjet and overbite.

implants or mini-screws, must be considered TADs.[14]

mini-screws, must be considered TADs.(14)

After anchorage preparation, a pivotal phase of treatment begins i.e. force application for eruption of the impacted tooth into the dental arch. Any root damage to the impacted tooth is not acceptable e.g. ligating ligature wire around the cervical part of the tooth may destroy PDL and have a deleterious effect on periodontal health of the future leveled/aligned tooth. In addition, the author does not prefer enamel drilling for canine traction (EDCT) over accessory bonding for canine traction (ABCT) i.e. bonding orthodontic attachment for loading because of its inherent characteristics in enamel destruction. A clean, etched surface of enamel is a prerequisite for successful bonding but before force application, a recheck of bonded attach‐ ment by manual traction is a prerequisite for wound closure. Figure 11. Miniscrews as an indirect anchorage resist against vertical pull of elastics for open bite closure. In the present condition eruption of lower anterior teeth has a major role for establishment of proper overbite. Vertical movement of the maxillary dentition is controlled by ligating both upper canines to miniscrews as indirect anchorage. b‐ Force application

Description of tooth movement for an impacted tooth is intricate and difficult. Only 3 dimensional analysis that contains information on both rotation and translation of the tooth movement has potential to evaluate and explain the nature of the exact movement. However, coordinate systems are used in orthodontics for better understanding of clinicians. Application of force to the center of resistance of a rigid body can produce translation without rotation. If the vector of the force is out of the center of resistance (CRes), according to its distance to the CRes it can produce a moment of the force (MF) with an expression of rotation for free-bodies or rotation tendency for teeth. In Figure 12, a 100 gram force plus 1000 g mm of moment equals the 100 gram force applied to the bracket with 10 mm distance. By addition of counterbalancing moment (MC) i.e. insertion of rectangular archwire in the bracket slot and its engagement to the walls, the bracket system will act like the system in the green box of Figure 12 (the green box is hypothetical) and depending on the proportion of MC/MF, a controlled tipping (0<MC/ MF<1), translation or bodily movement (MC/MF=1), and torque (MC/MF>1) can be produced. The relationship between the orthodontic force and counterbalancing moment is also ex‐ pressed in the "moment to force ratio" or M/F ratio. M/F ratio 1 to 7 produce controlled tipping; ratios of 8 to 10 (according to root length) produce bodily movement, and ratios greater than root length produce root torque movement. After anchorage preparation, a pivotal phase of treatment begins i.e. force application for erupting the impacted tooth to the dental arch. Any root damage to the impacted tooth is not accepted e.g. ligating ligature wire around the cervical part of the tooth may destroy PDL and have deleterious effect on periodontal health of future leveled/aligned tooth. In addition, author do not prefer enamel drilling for canine traction (EDCT) over accessory bonding for canine traction (ABCT) i.e. bonding orthodontic attachment for loading because of its inherent characteristics in enamel destruction. A clean, etched surface of enamel is prerequisite for successful bonding but before force application; a recheck of bonded attachment by manual traction is prerequisite for wound closure. Description of tooth movement for an impacted tooth is intricate and difficult. Only 3-dimensional analysis that contain information on both rotations and translation of the tooth movement, has potential to evaluate and explain the nature of the exact movement. However, coordinate systems are used in orthodontic for better understanding of the clinicians. Application of force to the center of resistance of a rigid body can produce translation without rotation. If the vector of the force is out of the center of resistance (CRes), according to its distance to the CRes; it can produce a moment of the force (MF) with an expression of rotation for free-bodies or rotation tendency for teeth. In figure 12, 100 gram force plus 1000 g.mm of moment equals the 100 gram force applied to the bracket with 10 mm distance. By addition of counterbalancing moment (MC) i.e. insertion of rectangular archwire in the bracket slot and its engagement to the walls, the bracket system will act like system in green box of figure 12 (green box is hypothetical and cannot happen in clinics) and depending on the proportion of MC/MF; a controlled tipping (0<MC/MF<1), Translation or Bodily movement (MC/MF=1), and Torque (MC/MF>1) can be produced. The relationship between the orthodontic force and counterbalancing moment is also expressed in the "moment to force ratio" or M/F ratio. M/F ratio 1 to 7 would produce controlled tipping, ratios of 8 to 10 (according to root length) produce bodily movement, and ratios greater than root length produce root torque movement.

Figure 12. Application of force to the bracket without any tools to exert moment (like round wire in bracket or labial bow in removable appliances) produce a type of "Uncontrolled tipping" movement (slide A). In this type of movement, the center of rotation (red circle) is near the center of resistance (blue circle). The similar or equivalent force system can be produced by exerting force (100 g) plus moment (100x10=1000 g.mm) to the center of resistance (green box- slide C). If 100 g force is applied to bracket (slide A) and a counterbalancing moment (MC) is produced by rectangular wire (slide C) but less than 1000 g.mm; it can move the center of rotation to near apical area and create a type of "Controlled tipping" (slide B) type of movement. **Figure 12.** Application of force to the bracket without any tools to exert moment (like round wire in bracket or labial bow in removable appliances) produce a type of "uncontrolled tipping" movement (slide A). In this type of move‐ ment, the center of rotation (red circle) is near the center of resistance (blue circle). The similar or equivalent force sys‐ tem can be produced by exerting force (100 g) plus moment (100x10=1000 g mm) to the center of resistance (green boxslide C). If 100 g force is applied to the bracket (slide A) and a counterbalancing moment (MC) is produced by rectangular wire (slide C) but less than 1000 g mm, it can move the center of rotation near to the apical area and create a type of "controlled tipping" (slide B) type of movement.

The correct M/F ratio should be obtained for bringing the impacted tooth to the dental arch but it is important to maintain the ratio for a constant center of rotation. By using rectangular loop (R-loop) in a cantilever spring, load-deflection rate will be decreased i.e. make the spring more flexible (relative to straight wire), and the configuration of the spring leads to a better maintenance of M/F ratio for a constant center of rotation. Segmented R-loop has long range of action with minimal force decrease during tooth movement and acceptable control of force magnitude. If the spring is distorted by the patient, cantilever

Treating a clinical case of a maxillary canine in infralabioversion by means of the straight archwire technique used to level the tooth is a harmful procedure for adjacent teeth. Canine extrusion would occur regardless of the type of bracket, whether conventional or self-ligating, however, it would be followed by undesired intrusion and moments on the lateral incisor and first premolar (figure 14). Many authors believe that these side effects would be solved with intermaxillary rubber bands, arch bends or wire progression. Conversely, with the aid of the segmented arch technique (SAT) and after preparation of the anchorage unit, only the canine is extracted by a cantilever or a rectangular loop (Figure 14). Differently from the conventional techniques, which normally use an arch made of one single alloy, connecting all brackets and adjacent tubes; the SAT uses arch segments connected

spring do not fail safely, and it can significantly move the tooth in an unwanted direction (Figure 13).

Alloy (TMA).

4 mm

The correct M/F ratio should be obtained for bringing the impacted tooth into the dental arch but it is important to maintain the ratio for a constant center of rotation. By using rectangular loop (R-loop) in a cantilever spring, load-deflection rate will be decreased i.e. make the spring more flexible (relative to straight wire), and the configuration of the spring leads to a better maintenance of M/F ratio for a constant center of rotation. Segmented R-loop has long range action with minimal force decrease during tooth movement and acceptable control of force magnitude. If the spring is distorted by the patient, it can significantly move the tooth in an unwanted direction (Figure 13). to each other, but not necessarily connected to brackets and adjacent tubes. This allows a combination of wires made of different alloys, dimensions and hardness to be used. Rigid and thick archwires can connect groups of teeth into anchorage units, whereas flexible archwires are used to exert forces between these units. (15)

Figure 13. A straight wire is used in (A) to erupt the bicuspid. When the wire is bent (blue line) and engaged in bracket, root apex tend to go to distal, in next yellow line position, root is upright and moment drops off, and in red line position; roots tends to go to the mesial while the crown is depressed. With this configuration, several center of rotation exists and constancy of the moment to force ratio is affected (inconsistent force system). Slide B demonstrates preactivated rectangular loop (R-loop) which provides constant control of M/F ratio. R-loop is made from 0.018x0.025 inch Stainless Steel or 0.017x0.025 inch Titanium Molybdenum **Figure 13.** A straight wire is used in (A) to erupt the bicuspid. When the wire is bent (blue line) and engaged in the bracket, the root apex tends to go to distal, in the next yellow line position, the root is upright and moment drops off, and in red line position; roots tends to go to the mesial while the crown is depressed. With this configuration, several centers of rotation exist and constancy of the moment to force ratio is affected (inconsistent force system). Slide B dem‐ onstrates preactivated rectangular loop (R-loop) which provides constant control of M/F ratio. The R-loop is made from 0.018x0.025 inch Stainless Steel or 0.017x0.025 inch Titanium Molybdenum Alloy (TMA).

Treating a clinical case of a maxillary canine in infralabioversion by means of the straight archwire technique used to level the tooth is a harmful procedure for adjacent teeth. Canine extrusion would occur regardless of the type of bracket, whether conventional or self-ligating; however, it would be followed by undesired intrusion and moment on the lateral incisor and first premolar (Figure 14). Many authors believe that these side effects can be solved with intermaxillary rubber bands, arch bends or wire progression. Conversely, with the aid of the segmented arch technique (SAT) and after preparation of the anchorage unit, only the canine is extracted by a cantilever or a rectangular loop (Figure 14).

30 gr Differently from the conventional techniques, which normally use an archwire made of one single alloy, connecting all brackets and adjacent tubes, the SAT uses arch segments connected to each other, but not necessarily connected to brackets and adjacent tubes. This allows a combination of wires made of different alloys, dimensions and hardness to be used. Rigid and thick archwires can connect groups of teeth to anchorage units, whereas flexible archwires are used to exert forces between these units. [15]

Figure 14. Top-left) Continuous arch wire (NiTi or CuNiTi) or straight archwire technique can be used to level the impacted canine/high buccal canine (infralabioversion canine) but canine extrusion would be followed by intrusive force and positive and negative moments on first premolar and lateral incisor. A lingual moment is created for upper canine that will lead it to the dental arch. Top-right) with the cantilever mechanics or segmented arch technique (SAT), a cantilever rectangular spring is inserted into a rectangular tube and tied to one point on the other side to produce "determinate one-couple system". Bottom-left) Sectional cantilever spring is used to extrude the impacted canine (force 30 grams, and distance between canine and first molar, presumably, about 20 mm). Extrusive force on canine (30 grams) will produce 30 gram intrusive force on upper first molar plus 600 g.mm moment (M=Fxd=30x20=600) to create distal root movement (blue arrow). The moment would be created by a couple (molar tube, presumably, 4 mm in length) with 150 grams force (600/4=150g) upward on the mesial end of the tube and 150 grams downwards on the distal end. Bottom-right) the abovementioned force system from the occlusal view. Consider the moment created by the rectangular archwire in molar tube (torque) and moment on canine. If center of resistance of the canine tooth is, presumably, about 5 mm lingual to the bonded button on the crown, a 150 g.mm (30x5=150g.mm) moment rotates the

5 mm

30 gr

5 mm

to each other, but not necessarily connected to brackets and adjacent tubes. This allows a combination of wires made of different alloys, dimensions and hardness to be used. Rigid and thick archwires can connect groups of teeth into anchorage units, whereas

Figure 13. A straight wire is used in (A) to erupt the bicuspid. When the wire is bent (blue line) and engaged in bracket, root apex tend to go to distal, in next yellow line position, root is upright and moment drops off, and in red line position; roots tends to go to the mesial while the crown is depressed. With this configuration, several center of rotation exists and constancy of the moment

A <sup>B</sup>

flexible archwires are used to exert forces between these units. (15)

Alloy (TMA).

The correct M/F ratio should be obtained for bringing the impacted tooth into the dental arch but it is important to maintain the ratio for a constant center of rotation. By using rectangular loop (R-loop) in a cantilever spring, load-deflection rate will be decreased i.e. make the spring more flexible (relative to straight wire), and the configuration of the spring leads to a better maintenance of M/F ratio for a constant center of rotation. Segmented R-loop has long range action with minimal force decrease during tooth movement and acceptable control of force magnitude. If the spring is distorted by the patient, it can significantly move the tooth in an

**Figure 13.** A straight wire is used in (A) to erupt the bicuspid. When the wire is bent (blue line) and engaged in the bracket, the root apex tends to go to distal, in the next yellow line position, the root is upright and moment drops off, and in red line position; roots tends to go to the mesial while the crown is depressed. With this configuration, several centers of rotation exist and constancy of the moment to force ratio is affected (inconsistent force system). Slide B dem‐ onstrates preactivated rectangular loop (R-loop) which provides constant control of M/F ratio. The R-loop is made

Treating a clinical case of a maxillary canine in infralabioversion by means of the straight archwire technique used to level the tooth is a harmful procedure for adjacent teeth. Canine extrusion would occur regardless of the type of bracket, whether conventional or self-ligating; however, it would be followed by undesired intrusion and moment on the lateral incisor and first premolar (Figure 14). Many authors believe that these side effects can be solved with intermaxillary rubber bands, arch bends or wire progression. Conversely, with the aid of the segmented arch technique (SAT) and after preparation of the anchorage unit, only the canine

Differently from the conventional techniques, which normally use an archwire made of one single alloy, connecting all brackets and adjacent tubes, the SAT uses arch segments connected to each other, but not necessarily connected to brackets and adjacent tubes. This allows a combination of wires made of different alloys, dimensions and hardness to be used. Rigid and thick archwires can connect groups of teeth to anchorage units, whereas flexible archwires are

from 0.018x0.025 inch Stainless Steel or 0.017x0.025 inch Titanium Molybdenum Alloy (TMA).

is extracted by a cantilever or a rectangular loop (Figure 14).

used to exert forces between these units. [15]

Figure 14. Top-left) Continuous arch wire (NiTi or CuNiTi) or straight archwire technique can be used to level the impacted canine/high buccal canine (infralabioversion canine) but canine extrusion would be followed by intrusive force and positive and negative moments on first premolar and lateral incisor. A lingual moment is created for upper canine that will lead it to the dental arch. Top-right) with the cantilever mechanics or segmented arch technique (SAT), a cantilever rectangular spring is inserted into a rectangular tube and tied to one point on the other side to produce "determinate one-couple system". Bottom-left) Sectional cantilever spring is used to extrude the impacted canine (force 30 grams, and distance between canine and first molar, presumably, about 20 mm). Extrusive force on canine (30 grams) will produce 30 gram intrusive force on upper first molar plus 600 g.mm moment (M=Fxd=30x20=600) to create distal root movement (blue arrow). The moment would be created by a couple (molar tube, presumably, 4 mm in length) with 150 grams force (600/4=150g) upward on the mesial end of the tube and 150 grams downwards on the distal end. Bottom-right) the abovementioned force system from the occlusal view. Consider the moment created by the rectangular archwire in molar tube (torque) and moment on canine. If center of resistance of the canine tooth is, presumably, about 5 mm lingual to the bonded button on the crown, a 150 g.mm (30x5=150g.mm) moment rotates the

30 gr

5 mm

30 gr

5 mm

unwanted direction (Figure 13).

82 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

A B

flexible archwires are used to exert forces between these units. (15)

Alloy (TMA).

4 mm

Figure 13. A straight wire is used in (A) to erupt the bicuspid. When the wire is bent (blue line) and engaged in bracket, root apex tend to go to distal, in next yellow line position, root is upright and moment drops off, and in red line position; roots tends to go to the mesial while the crown is depressed. With this configuration, several center of rotation exists and constancy of the moment to force ratio is affected (inconsistent force system). Slide B demonstrates preactivated rectangular loop (R-loop) which provides constant control of M/F ratio. R-loop is made from 0.018x0.025 inch Stainless Steel or 0.017x0.025 inch Titanium Molybdenum Figure 14. Top-left) Continuous arch wire (NiTi or CuNiTi) or straight archwire technique can be used to level the impacted canine/high buccal canine (infralabioversion canine) but canine extrusion would be followed by intrusive force and positive and negative moments on first premolar and lateral incisor. A lingual moment is created for upper canine that will lead it to the dental arch. Top-right) with the cantilever mechanics or segmented arch technique (SAT), a cantilever rectangular spring is inserted into a rectangular tube and tied to one point on the other side to produce "determinate one-couple system". Bottom-left) Sectional cantilever spring is used to extrude the impacted canine (force 30 grams, and distance between canine and first molar, presumably, about 20 mm). Extrusive force on canine (30 grams) will produce 30 gram intrusive force on upper first molar plus 600 g.mm moment (M=Fxd=30x20=600) to create distal root movement (blue arrow). The moment would be created by a couple (molar tube, presumably, 4 mm in length) with 150 grams force (600/4=150g) upward on the mesial end of the tube and 150 grams downwards on the distal end. Bottom-right) the abovementioned force system from the occlusal view. Consider the moment created by the rectangular archwire in molar tube (torque) and moment on canine. If center of resistance of the canine tooth is, presumably, about 5 mm lingual to the bonded button on the crown, a 150 g.mm (30x5=150g.mm) moment rotates the **Figure 14.** Top-left) Continuous arch wire (NiTi or CuNiTi) or straight archwire technique can be used to level the im‐ pacted canine/high buccal canine (infralabioversion canine); but canine extrusion would be followed by intrusive force and positive and negative moment on the first premolar and lateral incisor. A lingual moment is created for the upper canine that will lead it to the dental arch. Top-right) with the cantilever mechanics or segmented arch technique (SAT), a cantilever rectangular spring is inserted into a rectangular tube and tied to one point on the other side to produce "determinate one-couple system". Bottom-left) Sectional cantilever spring is used to extrude the impacted canine (force 30 grams, and distance between canine and first molar, presumably, about 20 mm). Extrusive force on canine (30 grams) will produce 30 gram intrusive force on upper first molar plus 600 g mm moment (M=Fxd=30x20=600) to create distal root movement (blue arrow). The moment may be created by a couple (molar tube, presumably, 4 mm in length) with 150 grams force (600/4=150g) upward on the mesial end of the tube and 150 grams downwards on the distal end. Bottom-right) the abovementioned force system from the occlusal view. Consider the moment created by the rectangu‐ lar archwire in molar tube (torque) and moment on the canine. If center of resistance of the canine tooth is, presuma‐ bly, about 5 mm lingual to the bonded button on the crown, a 150 g mm (30x5=150g.mm) moment rotates the tooth lingually. At the first molar, if the center of resistance is 5 mm lingual to the tube, a 30 g intrusive force can create 150 g mm moment to rotate it buccally. If the center of resistance of the impacted canine is, presumably, 10 mm palatal to the buccal surface of the first molar, activation of spring to tie to the canine, can twist it and create 300 g mm (30x10=300g mm) moment to rotate the molar crown palatally. The result at the molar is a net 150 g mm (300 g mm palatal – 150 g mm buccal =150 g mm palatal) palatal crown torque. (Bracket type and existence of continuous archwire of the model are not related to the biomechanical explanations.)

#### **5.1. Biomechanical alternatives for forced tooth eruption**

The orthodontist should avoid mechanics that draw the tooth labially, which could produce a bony dehiscence and accelerated migration of the labial gingival margin, resulting in labial recession. A "Ballista" loop is a simple, convenient, unobtrusive method of applying a vertical vector of force to a labially impacted tooth to erupt the crown into the center of the alveolus. When the canine crown is displaced mesially and lies over the root of the permanent lateral ‐Biomechanical alternatives for tooth forced eruption

explanations.)

incisor, an apically positioned flap is the appropriate surgical uncovering technique. Exposure of the crown facilitates attachment of an elastomeric chain directed toward the center of the edentulous alveolar ridge to gradually guide the canine crown into the dental arch. [16] A "Vertical spring" bent into 0.14 inch stainless steel wire that faces downward before activation is another alternative. It can be activated by pushing the vertical legs toward the impacted canine. This kind of round wire has the benefit of increased length and springiness but needs some kind of anti-rotation bent for avoiding rotation of round wire inside bracket slot that neutralizes the activity of the spring. Another alternative is an "Overlaid Auxiliary NiTi wire" on the rectangular stabilizing arch. These auxiliary arch wires are very efficient to bring an impacted tooth into dental arch. "Cantilever springs" can be used, either soldered to a heavy base arch or from auxiliary tube on the first molar. Some have used headgear tube plus an antirotation bend on wire and a helix around main arch wire for forced eruption of impacted teeth. vertical legs toward the impacted canine. This kind of round wires have the benefit of increased length and springiness but they need some kind of anti-rotation bent for avoiding rotation of round wire inside bracket slot that neutralizes the activity of the spring. Another alternative is an "Overlaid Auxiliary NiTi wire" on the rectangular stabilizing arch. These auxiliary arch wires are very efficient method to bring an impacted tooth into dental arch. "Cantilever springs" can be used, either soldered to a heavy base arch or from auxiliary tube on the first molar. Some clinician have used headgear tube plus an anti-rotation bend on wire and a helix around main arch wire for forced eruption of impacted teeth. ‐Molar uprighting in impacted cases Dental arch with aligned teeth and heavy main archwire can serve as an anchorage unit to be used for uprighting posterior second or third molar teeth by a NiTi or sectional Stainless Steel wire incorporating loops e.g. T-loop. Absolute anchorages i.e. miniscrews or titanium miniplates are other alternatives for distalizing or uprighting impacted molar teeth (Figure 15). Molar uprighting is generally associated with extrusion of antagonist teeth, reduction in edentulous space, bone dehiscence in the mesial surface of tipped molars, gingival recession of tipped molars, early contact in centric relation and occlusal interference on excursion of the mandible. With regard to integrated planning, clinicians must decide whether the tooth subject to uprighting will undergo movement for space closure, opening of space for prosthetic rehabilitation or implant placement. Mesial movement of molars may be rendered difficult due to the following: alveolar bone resorption resulting from tooth loss, which causes the molar mesial bone to become too thin; unfavorable root morphology for movement of lower molars; greater mandibular bone density in

tooth lingually. At the first molar, if the center of resistance is 5 mm lingual to the tube, a 30 g intrusive force can create 150 g.mm moment to rotate it buccally. If the center of resistance of the impacted canine is, presumably, 10 mm palatal to the buccal surface of the first molar, activation of spring to tie to the canine, can twist it and create 300 g.mm (30x10=300g.mm) moment to rotate molar crown palatally. The result at the molar is a net 150 g.mm (300 g.mm palatal – 150 g.mm buccal =150 g.mm palatal) palatal crown torque. (Bracket type and existence of continuous archwire of the model are not related to the biomechanical

The orthodontist should avoid mechanics that draw the tooth labially, which could produce a bony dehiscence and accelerated migration of the labial gingival margin, resulting in labial recession. A "Ballista" loop is a simple, convenient, unobtrusive method of applying a vertical vector of force to a labially impacted tooth to erupt the crown into the center of the alveolus. When

the center of the edentulous alveolar ridge to gradually guide the canine crown into the dental arch.(16) A "Vertical spring" bent into 0.14 inch stainless steel wire that faces downward before activation is another alternative. It can be activated by pushing the

#### **5.2. Molar uprighting in impacted cases** upright tipped molars is considered unfeasible, given that, in these cases, there is a strong tendency towards extrusion of molars, especially due to the short distance between brackets. Additionally, incorporating a T-loop spring into the arch will lead to

A dental arch with aligned teeth and heavy main archwire can serve as an anchorage unit to be used for uprighting posterior second or third molar teeth by a NiTi or sectional Stainless Steel wire incorporating loops e.g. T-loop. Absolute anchorages i.e. miniscrews or titanium miniplates are other alternatives for distalizing or uprighting impacted molar teeth (Figure 15). extrusion of premolars. A cantilever, extended up to the anterior region, may be used to reduce the effects of extrusion on molars. Researches have proved a moment of 1200 gf.mm to be appropriate for molar uprighting. Should a 30-mm cantilever be used, an activation of 40 gf is enough for molar uprighting, in which case 40 gf corresponds to intrusive forces in the anterior region and extrusive forces in the region of molar teeth. Mesocephalic or brachycephalic patients are able to eliminate or reduce this effect of extrusion by their own muscular pattern. (15,17)

relation to the maxilla; and thin buccolingual bone thickness from distal to mesial in the mandibular arch. Using straight wires to

**Figure 15.** T-loops have efficient control on angulation and torque of an inclined tooth (left). An alternative to absolute anchorage can help in uprighting the tilted impacted second or third molars without endangering other teeth as an‐ chorage units that may be affected with orthodontic force and tooth movement or root resorption.

Molar uprighting is generally associated with extrusion of antagonist teeth, reduction in edentulous space, bone dehiscence in the mesial surface of tipped molars, gingival recession of tipped molars, early contact in centric relation and occlusal interference on excursion of the mandible. With regard to integrated planning, clinicians must decide whether the tooth subject to uprighting will undergo movement for space closure, opening of space for prosthetic rehabilitation or implant placement. Mesial movement of molars may be rendered difficult due to the following: alveolar bone resorption resulting from tooth loss, which causes the molar mesial bone to become too thin; unfavorable root morphology for movement of lower molars; greater mandibular bone density in relation to the maxilla; and thin buccolingual bone thickness from distal to mesial in the mandibular arch. Using straight wires to upright tipped molars is considered unfeasible, given that, in these cases, there is a strong tendency towards extrusion of molars, especially due to the short distance between brackets. Additionally, incorporating a T-loop spring into the arch will lead to extrusion of premolars. A cantilever, extended up to the anterior region, may be used to reduce the effects of extrusion on molars. Researchers have proved a moment of 1200 gf.mm to be appropriate for molar uprighting. Should a 30-mm cantilever be used, an activation of 40 gf is enough for molar uprighting, in which case 40 gf corresponds to intrusive forces in the anterior region and extrusive forces in the region of molar teeth. Mesocephalic or brachycephalic patients are able to eliminate or reduce this effect of extrusion by their own muscular pattern. [15, 17]
