In majority of orthodontic cases, routine treatment protocol has been applied. In few special cases rather than conventional protocol, we need to choose different treatment mechanics. The “segmental mechanics” is very efficient in case of anterior crowding with deep overbite cases and flared incisors.1 This study describes a modified three-piece base arch for simultaneous deep bite correction and en masse retraction. In case of severe anterior crowding, increased overbite, and horizontal growth pattern, the treatment with full arch alignment stage directly is difficult.2 Since uprighting of incisors often lengthens the crown vertically and increases the amount of overbite,3 the use of segmental mechanics can be taken to get satisfactory results.1,4,5


The present case report showcases the treatment results and biomechanics involved for en masse retraction and intrusion of anterior teeth using a modified three-piece base arch.


An 18-year-old male patient in permanent dentition presented with the chief complaint of crowded, overlapping, and forwardly placed anterior teeth. He had a class II Division 1 subdivision malocclusion (Figs 1 to 5). The mandibular midline had shifted 2 mm to the right of the facial midline (Fig. 2). Cephalometric analysis indicated a prognathic maxilla and normal mandible with upper and lower incisor flaring. Patient had a horizontal growth pattern and a reduced lower anterior facial height (Table 1). The overjet was 4.5 mm, and the overbite was 40%. A class I molar relation on the right side and a class II molar relation on left side was diagnosed as a class II division 1 subdivision case. A class II canine relation was present on the right side (Fig. 1).

Following a comprehensive clinical and database analysis, we devised a treatment plan involving extraction of the upper first premolars, lower left first premolar, and lower right second premolar to achieve a symmetrical buccal occlusion, midline correspondence, appropriate overjet, and adequate retraction of the flared upper and lower incisors. Asymmetric extraction also helped achieve a class I canine and molar relation on the subdivision side.

Fig. 1:

Pretreatment intraoral right lateral view

Fig. 2:

Pretreatment intraoral frontal view

Fig. 3:

Pretreatment intraoral left lateral view

Fig. 4:

Pretreatment intraoral maxillary occlusal view

Fig. 5:

Pretreatment intraoral mandibular occlusal view


Table 1: Pre-post Treatment Cephalometric Values

Angle of convexity4 °
Wits AO/BO2 mm2 mm
Jarabak's ratio70.7%72.32%
LAFH59 mm61 mm
Gonial angle120°121°
Base plane ang.15°16°
U1 to NA angle40°25°
U1 to NA linear9 mm4 mm
U1 to FH130°118°
U1 to SN126°113°
L1 to NB angle40°26°
L1 to NB linear8 mm4 mm
Interincisal angle96°124°
Nasolabial angle99°105°
“S” line to upper lip2 mm−1 mm
“S” line to lower lip4 mm0 mm
Lower lip to E-line3 mm1 mm


Full-arch 0.022″ appliances were bonded, and leveling and alignment were carried out with continuous 0.016″ heat-activated nickel titanium archwire (Fig. 6). Laceback and bendback were used. All the second molars were banded to increase the anchorage value of posteriors. This was followed by a 0.019″ × 0.025″ heat-activated nickel titanium wire (Fig. 7). Once the arches were aligned, a segmental approach was used to retract the anterior segment en masse. A different approach was used in upper as well as lower arch. A modified three-piece base arch was used in the upper arch.

Anterior Segment

The rigid anterior segment consisted of a 0.021″ × 0.025″ stainless steel wire placed into the brackets of the incisors and canines bilaterally and stepped up gingivally distal to the canine brackets. The wire was then again bent to 90° slightly below the center of resistance. The angled posterior segment allows the intrusive and retraction force to pass through the center of resistance such that a complete bodily movement of the incisors could be achieved. The posterior extensions were adapted such that no soft tissue impingement was created (Figs 8 to 10).

Fig. 6:

Continuous 0.016″ heat-activated nickel titanium archwire

Fig. 7:

0.019″ × 0.025″ heat-activated nickel titanium wire

Fig. 8:

Modified three-piece base arch - right lateral view

Fig. 9:

Modified three-piece base arch - left lateral view

Fig. 10:

Modified three-piece base arch - frontal view


Posterior Segment

The posterior segments were consolidated bilaterally from first premolar to second molar using a passive stabilizing 0.021″ × 0.025″ stainless steel wire (Figs 8 to 10).

The Intrusion Spring

The bilateral intrusion spring were made of 0.017″ × 0.025″ t itanium molybdenum alloy (TMA) wire. The tip back bends were incorporated mesial to the auxiliary tube on the maxillary first molars and the springs were inserted into the tube. The hooks which place an intrusion force on the anterior extension were engaged on the posterior extension of the anterior segment at a point distal to canine (Figs 8 to 10).

Distal Force Component (Elastic Chain)

An elastic chain is extended bilaterally from the molar hook to the posterior hook of the anterior segment. This small distal force directs the intrusive force so its line of action of force passes through the center of resistance of the anterior segment. A tip back moment is generated on the posterior segment. The anterior segment was retracted as a result of small tip back moment created. En masse retraction was competed in 6 months (Figs 8 to 10).

Fig. 11:

Continuous arch wire in lower arch after achieving a class I molar relation

Fig. 12:

Continuous arch wire – left lateral view


For the lower arch, a modified intrusion and retraction utility arch was used, which consisted of incisors and canine made of 0.017″ × 0.025″ TMA wire. The utility arch was inserted in the auxiliary tube of the first molars bilaterally. Posterior segment consisted of segments from second premolar to second molar on the left side (Fig. 10) and from first premolar to second molar on the right side (Fig. 8). The curve of Spee was corrected by the tip back moment from the utility arch. An e-chain was used from lower right first molar to first premolar to convert the subdivision side to class I molar relation before retraction. After achieving a class I molar on the subdivision side, a continuous arch wire with friction mechanics was used to complete the case (Figs 11 and 12).


Absolute intrusion, relative intrusion, and extrusion of posterior teeth are the three methods used for deep overbite correction. Relative intrusion is achieved by preventing the eruption of the lower incisor while ramal growth provides vertical space into which the posterior teeth erupt, whereas in extrusion of the posterior teeth mandible rotates down and back in the absence of growth.6 As a general rule, extrusion is undesirable, while relative intrusion is acceptable during growing stage and absolute intrusion in nongrowing stage.6 Bite opening with molar eruption is usually desired in low angle cases with deep overbite, whereas in high angle cases with a deep overbite, bite opening should be carried out with upper and lower anterior teeth intrusion.7 Clinically, intrusion is a difficult movement to achieve, and it requires three-dimensional controls. Intrusion mechanics basically depend on the initial inclination of the incisor. Clinically, pure bodily intrusion is difficulty owing to the complexity of the movement. A slight change in the relationship of the line of action of the force with the center of resistance can change the type of movement.8 If the forces pass anterior to the center of resistance of the incisor protrude, it can be prevented with a light chain elastic.7 Leveling by intrusion can be accomplished with continuous archwire that bypasses the premolar and segmented archwire with auxiliary depressing arch.6

The key to successful retraction and intrusion is light continuous force directed through the center of resistance of the anterior segment.3 The low force also helps in minimizing root resorption. Approximately, 10 gm of force per tooth is used for intrusion. The reactionary molar distal tipping and extrusion may occur due to intrusive force in anterior segment.6,7,9 The molar extrusion rotates the mandible downward and backward, which results in an increase of lower anterior facial height and worsening of the incisor lip relationship and soft tissue profile. The occlusal forces normally can compensate for this bite opening because low angle individuals have relatively strong chewing muscles. So, in our case, modified three-piece base arch was selected for intrusion and retraction of upper anterior teeth. The cephalometric superimpositions revealed mild restraint in the growth of maxilla and a slight increase in the downward and forward advancement of the mandible (Fig. 13). The maxillary first molars were slightly extruded and moved mesially. The maxillary incisors were translated palatally and intruded. The mandibular molars were slightly extruded and mesially moved. The mandibular incisors were moved bodily and intruded. The end treatment results showed class I molar and canine relation, ideal overjet and overbite (Figs 14 to 18), competent lips, and decreased incisal display at rest and smile. The postoperative orthopantogram reveals parallel roots without any significant root resorption of upper anterior teeth (Fig. 19). The postoperative cephalometric values reveal mild restriction in the growth of maxilla, maintaining the mandibular plane angle, decreased interincisal angle, and decreased protrusion of lips (Table 1). Comparing the pretreatment extraoral photographs (Figs 20 to 24) with posttreatment extraoral photographs (Figs 25 to 29), a significant improvement was seen in smile line, smile arc, lip competency, and profile.

Fig. 13:

Pretreatment and posttreatment superimposition

Fig. 14:

Posttreatment intraoral right lateral view

Fig. 15:

Posttreatment intraoral left lateral view

Fig. 16:

Posttreatment intraoral frontal view

Fig. 17:

Posttreatment intraoral maxillary occlusal view

Fig. 18:

Posttreatment intraoral mandibular occlusal view



Simultaneous retraction and intrusion with three-piece base arch proves to be an efficient treatment mechanics in terms of time. Unlike the traditional three-piece base arch where a staged retraction in two stages was done, the modified base arch for en masse retraction does not require the canines to be retracted first. Also, since canines receive an intrusion force along with incisor, the roots are placed more in the cancellous bone and the interference from lower canine in the class II side is avoided. This accelerates the en masse retraction.

Fig. 19:

Posttreatment orthopantomogram

Fig. 20:

Pretreatment extraoral frontal view

Fig. 21:

Pretreatment extraoral frontal smile view

Fig. 22:

Pretreatment extraoral oblique view

Fig. 23:

Pretreatment extraoral oblique smile view

Fig. 24:

Pretreatment extraoral right lateral profile view



A careful combination of treatment planning and biomechanics to correct deep overbite and proclined incisors can help to achieve a desirable esthetic result. The modified three-piece base arch is effective in controlled translation and intrusion of anteriors and would be a preferable mechanotherapy in low angle case with deep bite, proclined anteriors, and class II canine relationship.

Fig. 25:

Posttreatment extraoral frontal view

Fig. 26:

Posttreatment extraoral frontal smile view

Fig. 27:

Posttreatment extraoral oblique view

Fig. 28:

Posttreatment extraoral oblique smile view

Fig. 29:

Posttreatment extraoral right lateral profile view

Conflicts of interest

Source of support: Nil

Conflict of interest: None