Treatment of Bimaxillary Protrusion by Distalization of Maxillary and Mandibular Dentitions with Extra Alveolar Bonescrews

 Introduction

Bimaxillary protrusion is characterized by a convex lower facial profile, protruding lips, and proclined anterior teeth. The majority of individuals with bimaxillary projection seek therapy from orthodontics or orthopedics in order to reduce the protrusion, enhance their facial profile, and ultimately improve their facial aesthetics.¹ Teeth extractions during orthodontic interventions have long been a topic of discussion. In borderline instances, it is still uncertain either to extract or retract premolars.² The objective of every orthodontic procedure is to achieve the intended movement of teeth while minimizing the amount of unwanted side effects.³

In a straight, pleasant profile, orthodontic therapy with premolar extraction may cause the profile to flatten, making the patient appear five to ten years older than their actual age.⁴

Positive outcomes with regard to anchoring have been attained ever since skeletal anchorage specifically, orthodontic mini-implants have been incorporated into orthodontists' treatment plans. Miniscrews are classified into inter-radicular (IR) and extra-radicular (ER) types. 

Nonetheless, a number of significant issues with IR miniscrews exist, including a high failure rate, obstruction of tooth movement and contact with the roots of other teeth.^5-7

The best location for the en-masse retraction of the entire dentition seems to be the extra radicular implan- tation of mini-implants or miniplates.

Several publications suggest that the mandibular buccal shelf region and infrazygomatic crest have the perfect bone quality for stable screw insertion.⁴ This does not interfere with dental roots and can tolerate the force needed for distalization.

This case report describes the successful treatment of bimaxillary protrusion using extra-alveolar miniscrews placed in the infra-zygomatic crest of the maxilla and the buccal shelf region of the mandible.

Case Presentation

A 21-year-old woman presented with a chief complaint of forwardly placed front teeth. She was not willing for extraction of any healthy teeth other than the third molars. Extra-oral examination of the patient revealed a convex profile, competent lips, posterior divergence, a reduced nasolabial angle of 75 degrees, and a complex smile with 70% incisal exposure (Figure 1-a). 

The intraoral examination showed proclination of upper and lower anterior teeth with mild crowding in both the arches. The molar relationship was Class I bilaterally, while the canine relationship was end-on bilaterally, with a 4-mm overjet and a normal overbite (Figure 1-b). The lower midline was shifted 3 mm to the left. All third molars were present, with the mandibular left third molar being horizontally impacted.

Lateral cephalogram and orthopantomogram (Figure 1-c, d) showed the presence of all the teeth. Her mandibular right third molar showed mesioangular impaction and mandibular left 3rd molar was horizo- ntally impacted. The cephalometric analysis presented a Class II skeletal pattern (ANB, 5; Wits appraisal, 7 mm) with reduced mandibular plane angle (SN-GoGn, 21 degree). The incisors in both the upper and lower arches were proclined (U1-SN, 114 degrees; IMPA, 112 degrees), and the inter-incisal angle (102 degrees) was increased (Table 1). A diagnosis of Angles Class I malocclusion on a Class II skeletal base, with horizontal growth pattern, bimaxillary dentoalveolar protrusion and crowding in upper and lower arches was derived.

Treatment Objectives

1. To correct proclination of maxillary and mandibular anterior teeth, which was the patient’s chief complaint.

2. Correction of mandibular and maxillary anterior crowding.

3. To achieve Class 1 canine relation and maintain Class 1 molar relationship.

4. To correct lower midline shift.

5. Creation of an ideal overbite and overjet.

6. Improvement of facial profile and consequently the esthetics.

Treatment Alternatives

In this case, extraction of the four second premolars would have been the best course of action to address the anterior proclination. Considering that the patient denied extraction of any teeth other than third molars, distalization of maxillary and mandibular dentitions with miniscrews was planned.

Treatment Progress

Both the arches were bonded with 0.022” MBT prescription brackets. Initial leveling and alignment were achieved with 0.014-in and 0.016-in nickel-titanium  arch wires in both the arches. Once leveling was com- plete, 0.019 × 0.025″ stainless steel arch wires were used as a working wire in which distalization of both dentitions was achieved, using infra-zygomatic bone screws (Fav anchor 2 x 12mm) in the infra-zygomatic crest region (IZC), in-between the first and second maxillary molars extraradicularly. Fav anchor (2 x 12mm) screws were then placed in the buccal shelf region in between the first and second maxillary molars. For the purpose of distalizing the maxillary dentition, elastics with initial force of 1.5 and 2.5 N were placed from the miniscrews' neck to the crimpable hooks situated between the canines and lateral incisors (Figure 2) and the interval between the visits was set at four weeks. The distalization process lasted for approximately 10 months. Without interfering with the tooth roots, full-arch distalization of both the arches was achieved by means of extra-radicular, infra zygomatic and buccal shelf bone screws.

 Treatment Results

 The post-treatment records indicated that the goals of the treatment were successfully met. The facial photo- graphs showed significant improvements in the patient’s facial profile and esthetics (Figure 3-a). The anterior proclination had reduced, the crowding was corrected, and the optimal overbite and overjet were achieved. The Class I canine relation was achieved and Class I molar relationship was maintained (Figure 3-b).

Post treatment orthopantamograph showed root parallelism (Figure 3-c). Cephalometric superimposition revealed that maxillary molars were distalized by about 3 mm, maxillary incisors retracted by 6 mm, and mandibular incisors by 5 mm. Both the lower and upper lips retracted by 2 and 1 mm, respectively, falling within the normal range with respect to the E-line (Figure 4).

Discussion

Most patients receiving orthodontic treatment prioritize their facial esthetics, and if their protrusion is not severe, they often refuse to extract their upper and lower teeth. Patients who have bimaxillary protrusion typically have strong oral function due to their Class I relationship of canine and molar connections. The primary reason a patient seeks therapy is to improve facial esthetics. The chief complaint of the patient and the clinical diagnosis are taken into consideration while formulating a treatment plan. The facial changes resulting from the treatment were directly linked to the planned skeletal and dentoalveolar adjustments that were set as treatment objectives for the patient. The primary objective for pursuing orthodontic treatment was to improve facial aesthetics.

Adult molar distalization was once believed to be challenging without causing the incisors and premolars shift forward.^6,7 Round tripping is no longer a concern, as miniscrews enable distalization of the whole arch while simultaneously retracting incisors. It has been shown that the central region of the premolar roots is where the maxillary dentition's center of resistance is situated. Research has indicated that in individuals with bimaxillary protrusion, extraction of the maxillary or mandibular first premolars can effectively reduce dental and soft tissue protrusion.¹

Lower molar intrusion occurs when miniscrews are positioned in the buccal shelf area and force is delivered in a distal direction.⁸ Because the distalization force from the buccal shelf miniscrews crosses the mandibular dental arch's center of resistance, it causes the arch to rotate counterclockwise.^9,10

The space needed to retract incisors in cases of mild to moderate bimaxillary protrusion is smaller than that of a premolar, which might lead to an inefficient use of extraction space.¹¹ Aside from third molars, some individuals do not agree to have healthy teeth extracted because their protrusion is not as extreme as in our case.

In our patient, two miniscrews were placed in the IZC region and two miniscrews in buccal shelf region between the 1st and 2nd molars in both the arches and distalization was achieved in a year.

To distalize the dentitions, temporary anchoring devices (TADs) must be inserted in a suitable position. To avoid interfering with dental mobility, they are best placed in locations where the cortical bone layer is rather thick and at a distance from the tooth roots. The extraradicular site can be infrazygomatic crest in the maxilla, the buccal tent region, and the retromolar area in the mandible.^10.12 Successful distalization of the dentitions using TADs is dependent on two key variables, in addition to a suitable implant location. The TADs' survival becomes vital as they can perform optimally only when they are steady. Miniplates were originally believed to be better than miniscrews or mini-implants up until now.¹³

The study's therapeutic goals were achieved with appropriate overjet and overbite as well as satisfactory facial aesthetics.

Conclusion

This case report demonstrates an innovative approach for addressing bimaxillary dentoalveolar protrusion using miniscrews, avoiding the extraction of any healthy premolars. The method involved en-masse distalization of both the upper and lower arches through the use of extra-alveolar bone screws, rather than relying on extraction and traction. The outcome included an appealing smile, a natural lip seal, and a well-balanced facial profile.

Conflicts of Interest

Nil