A patient with bimaxillary protrusion was treated by the extraction of four premolars and four compromised first molars: a case report

The first permanent molars play an important role in the development of the dental occlusion¹ but are more prone to caries compared to other permanent teeth.^2,3 In the absence of adequate oral hygiene, caries often leads to the extensive loss of tooth structure, or even tooth loss.⁴ Orthodontists are increasingly encountering patients presenting with missing or severely decayed first molars. The treatment alternatives for these patients are involved and differ from cases requiring conventional orthodontic extractions.⁵ If the dentist chooses to keep the diseased molars and remove healthy wisdom teeth, it goes against the principle of “removing bad teeth and keeping good teeth”. Moreover, additional treatment for the compromised teeth is required following orthodontic intervention. Further treatment might include dental restorations, root canal treatments, and crown replacements, which is not conducive to long-term oral health and poses challenges in achieving sustained treatment stability.⁶ First molar extractions have rarely been a viable treatment option because the first molar is regarded as “the keystone of the occlusion”.⁷ Generally, orthodontic cases involving the extraction of the first permanent molars are more technically demanding compared with conventional premolar extraction cases or non-extraction treatment. Molar extraction is associated with many well-recognised challenges, including extended treatment times, anchorage management, and the control of the molars during space closure.⁸

There is little difference between the first, second or third molars in relation to bite force.⁹ In addition, while normal masticatory force constitutes only a third of maximum bite force, the periodontal ligament is able to withstand a considerably heavy load. Even in cases in which the second molar moves mesially to replace a missing first molar, the normal chewing force remains well within the threshold of the maximum bite force that a healthy second molar can withstand. This forms a solid theoretical foundation for the extraction of molars in orthodontic treatment. Seddon et al.¹⁰ believed that, in cases in which patients had severe decay, large surface fillings, or periapical disease, the removal of a diseased first molar could be a preferred choice. However, numerous clinical and radiographic factors must be carefully evaluated and include the level of crowding, the presenting malocclusion, and the stage of dental development, all of which are worthy of consideration and may impact clinical management.¹¹ In addition, orthodontists should possess the expertise to deal with impacted third molars and master the skills required for uprighting and aligning these teeth. This ensures that the third molars can better replace the second molars, establish an appropriate proximal relationship, and obtain normal occlusal function.^9,12,13

To obtain a harmonious nasolabial-mental relationship, a common treatment approach for patients with a bimaxillary protrusion involves extracting four premolars followed by the retraction of the anterior teeth. However, in cases in which the first molars are severely affected by caries or previously extracted, orthodontic treatment can be performed by the removal of four premolars and four first molars. The following case presentation illustrates that, if the indications are strictly followed, anchorage is judiciously applied, and clinical procedures are conducted with precision, a satisfactory patient outcome can be obtained in difficult cases involving the extraction of first molars.

Diagnosis and aetiology

A young male, 15 years old, visited the Department of Stomatology at the Second Affiliated Hospital of Guangzhou Medical University in China with the chief complaints of malaligned dentitions and a convex profile. The patient was physically healthy without significant medical, dental, family, nor social histories.

Pretreatment facial photographs (Figure 1) showed a symmetrical face, with a slightly increased vertical facial height. The patient exhibited a decreased nasolabial angle, a convex facial profile and a retrusive chin which deviated slightly to the right side. The temporomandibular joints (TMJs) were asymptomatic.

Figure 1.

The patient’s oral hygiene was poor which affected the gingival margins resulting in inflammation. An intraoral examination revealed a fully erupted permanent dentition except for the four third molars. The arches displayed a narrow V-shaped form, and both exhibited moderate crowding. The dental midlines did not align with the facial midline indicated by a 2 mm left deviation in the upper midline and a 1 mm right deviation in the lower midline. There was a mild bilateral crossbite involving the second premolars with obvious displacement. Also, distal proximal caries was noted in tooth 25, and tooth 16 displayed extensive caries. In the lower arch, large restorations were seen on the occlusal surface of tooth 46, while the roots of tooth 36 were retained (Figure 1).

A cast analysis revealed Class I canine and molar relationships on the left side and Class II relationships on the right, accompanied by a 6.0 mm overjet and a 3.6 mm overbite. The anterior Bolton ratios (77.2%) were compatible. Moderate crowding (8 mm in the upper arch, 7 mm in the lower arch), a 4.8mm depth in the curve of Spee, and V-shaped arch forms were observed. The maxillary arch was transversely deficient, which created bilateral buccal crossbite relationships involving the second premolars. In addition, the transverse widths of the maxilla (canine: 31.6 mm, first premolar: 31.1 mm and first molar: 45.1 mm) and the widths of the mandible (canine: 24.9 mm, first premolar: 27.8 mm and first molar: 40.8 mm) were noted.

A panoramic radiograph revealed complete dentitions and the presence of the developing third molars. Tooth 46 had undergone root canal treatment, while carious lesions were evident in the crowns of the upper first molars. Additionally, tooth 36 presented extensive loss of tooth structure. No other apparent pathology was observed (Figures 2 and 3). A cephalometric analysis revealed a skeletal Class I relationship (ANB = 3.4) with a slightly increased mandibular plane angle reflecting a vertical facial pattern (SN-MP = 37.8°; FMA = 31.7°; Kaxis angle = 68.6°). The upper incisors were significantly proclined at 118.7° (U1-NA = 11.2mm), while the lower incisors maintained a normal inclination of 91.4° (L1-NB = 10.5mm), resulting in an interincisal angle of 111.7° (Figures 2 and 3 and Table I). A soft tissue analysis revealed a convex profile (UL-E: 4.0mm; LL-E: 7.8mm) (Table I).

Figure 2.

Figure 3.

Table I.

Cephalometric analysis

	Chinese norm	Pre-treatment	Post-treatment
SNA (°)	82.8 ± 4.0	80.6	80.1
SNB (°)	80.1 ± 3.9	77.2	77.6
ANB (°)	2.7 ± 2.0	3.4	2.5
NA-PA (°)	6.0 ± 4.4	7.5	4.7
FMA (°)	31.3 ± 5.0	31.7	31.9
SN-MP (°)	31.1 ± 5.6	37.8	38.3
U1-SN (°)	105.7 ± 6.3	118.7	107.4
U1-NA (mm)	5.1 ± 2.4	11.2	3.0
L1-MP (°)	92.6 ± 7.0	91.4	85.5
L1-NB (mm)	6.7 ± 2.1	10.5	4.0
Interincisal angle (°)	125.4 ± 7.9	111.7	127.5
Y-axis angle (°)	65.8 ± 4.2	68.6	64.3
Overbite (mm)	0-3.0	3.6	0.8
Overjet (mm)	0-3.0	6.0	1.9
Upper lip to E-line (mm)	-1.0 ± 2.0	4.0	-1.4
Lower lip to E-line (mm)	0.0 ± 2.0	7.8	-0.2

The patient was diagnosed with a hyperdivergent skeletal Class I and a dental Class II malocclusion, together with a convex profile and upper incisors which were significantly proclined. Additionally, the patient exhibited strain in the mentalis muscle upon forcible lip closure.

Treatment progress

After extracting the four premolars and four first molars, standard straightwire brackets with an MBT prescription (0.022-inch slot; Xingchen 3B Dental Instrument & Material Co., Ltd, Hangzhou, China) were bonded to the upper and the lower arches. Sequentially, 0.014, 0.016, 0.018 and 0.020- inch Nickel-Titanium (NiTi) wires were inserted to align the dentition. Lacebacks were placed in all four quadrants, gradually establishing the cuspfossa relationship of the premolars and a Class I relationship of the canines (Figure 4).

Figure 4.

After 8 months, 0.019 × 0.025-inch NiTi wires were inserted in both arches to continue alignment. The application of a reverse-curve in the wires aimed to level both dentitions and correct the deep overbite.

Subsequently, the extraction spaces were closed using continuous light forces via power chains (American Orthodontics, Sheboygan, WI, USA) on 0.019 × 0.025-inch stainless steel (SS) wires. With appropriate Class II intermaxillary traction (size: 1/4 inch, Force: 3.5oz; Ormco Corp. CA, USA), the lower second molars moved mesially, facilitating the eruption of the third molars (Figure 5).

Figure 5.

Twelve months later, after the eruption of the four wisdom teeth, buccal tubes designed for the first molars were bonded to the buccal surfaces of the third molars and 0.016-inch NiTi wires were inserted to upright and align those teeth (Figure 6).

Figure 6.

After 35 months, 0.019 × 0.025-inch SS wires incorporating reverse-curves were used to close the remaining extraction spaces through continuous light forces and sliding mechanics. Additionally, Class II intermaxillary traction was applied on the right side to aid in centerline correction. The anterior teeth were adjusted to achieve a normal overbite and overjet, and the molars achieved bilateral Class I relationships (Figure 7).

Figure 7.

After 44 months, space closure and centerline adjustment were proceeding through asymmetric traction. Individual brackets were repositioned, and 0.016-inch NiTi wires were utilised for detailed adjustments (Figure 8).

Figure 8.

Active treatment was completed in 48 months. Following debonding, modified Hawley retainers were inserted into the upper and lower arches for long-term retention.

Treatment results

The patient’s chief complaints (malaligned dentition and a convex profile) were resolved. Post-treatment facial photographs (Figure 9) showed a significant reduction in facial convexity, achieving a balanced appearance in the nose—lip—chin relationship (Figure 9). The midline deviation was essentially corrected, aligning the midline of the maxillary and mandibular incisors with the facial midline. The intraoral examination demonstrated that the extraction spaces were completely closed. All third molars were upright and aligned, establishing bilateral canine and the right molar in Class I relationships, while the left molar exhibited a slight Class III relationship. The anterior teeth also achieved a normal occlusal relationship with proper overbite and overjet.

Figure 9.

The post-treatment panoramic radiograph (Figure 10A) showed good root parallelism, except for teeth 33 and 43, for which the roots exhibited a slight distal inclination. Despite the considerable retraction of the incisors and long-distance movement of the molars, no significant root resorption nor alveolar bone loss was observed. The cephalometric analysis (Figure 10B and Table I) showed retraction of the upper incisors (U1-SN = 107.4°; U1-NA = 3.0mm) and decreased lower incisor proclination to a slight lingual inclination (L1-MP = 85.5°; L1- NB = 4.0mm) (Figure 10B). Cephalometric superimposition revealed extensive movement of the anterior and posterior teeth, along with a significant reduction in lip protrusion (UL-E: -1.4mm; LL-E: -0.2mm) (Figure 11). The ANB angle (ANB = 2.5°) showed that the skeletal Class I relationship was maintained after treatment and the mandibular plane angle (SN-MP = 38.3°) revealed no significant changes (Table I).

Figure 10.

Figure 11.

The 5-year follow-up facial and intraoral photographs showed optimal stability with a good maintenance of overbite, alignment and the occlusal relationship (Figure 12).

Figure 12.

The patient presented with a convex profile and lip incompetence involving mentalis strain before treatment. Typically, the extraction of the first premolars would be recommended, coupled with extensive retraction of the anterior teeth to optimise the facial profile and improve lip function. However, given that the four first molars were compromised and exhibited a poor long-term prognosis, and considering the well-developed nature of all wisdom teeth, a strategic decision was made to extract the compromised molars. This approach was chosen to minimise the need for subsequent tooth restorative treatments. In addition, tooth 26 was extracted to facilitate the adjustment of the left molar relationship. However, a challenge arose as the first molars were positioned posteriorly in the dental arch, which was not conducive for adequate retraction of the anterior teeth.¹⁴ Also, it was anticipated that allocating space for incisor retraction might result in insufficient retromolar space for the mandibular third molars.¹⁵ This complex scenario required careful consideration to address the molar relationship and ensure sufficient space for the planned orthodontic adjustments. Therefore, the final option was to remove four premolars and the four first molars, leading to the extraction of two posterior teeth in each of the four quadrants. This plan presented an evident and considerable challenge. The literature extensively explores various facets of molar extraction, and describes the facial profile, control of overbite, the distal movement of the dentition, the eruption of the third molars, the stability of the lower incisors, the functional occlusion, TMJ disorders, and treatment duration as contributing factors.^16,17 In clinical practice, there is a prevailing tendency for many clinicians to avoid first molar extractions. This hesitancy often stems from the belief that such a treatment approach is inherently more intricate, demanding, and time-consuming.⁸ Contrary to the trend reported by European and American scholars, Asai¹⁸ and other researchers hold the viewpoint that Japanese patients, with severe crowding and convex profiles, may need the extraction of molars in addition to premolars.

In the present case, except for the extraction of the first molars on both sides of the maxilla, teeth 14 and 25 were also extracted to facilitate midline adjustment. In addition, the decision to remove tooth 25 instead of 24 was guided by the compromised condition of tooth 25 and its position on the palatal side of the dental arch. Choosing to remove tooth 24 might have led to a further narrowing of the upper dental arch. However, following the extraction of teeth 25 and 26, a substantial extraction space of nearly 15 mm was created. This presented potential challenges, including the difficulty in closing the gap, the risk of mesial inclination of the molars or mesial lingual torsion, challenges in obtaining anchorage, the possibility of atrophy of alveolar bone, and an extended treatment duration.¹⁹ However, clinical studies have determined that it is feasible to use light forces to close the extraction space on a stainless steel rectangular wire after fully aligning the dentition without excessive absorption of the alveolar ridge.²⁰ A 0.019 × 0.025-inch SS arch wire, complemented by a reverse-curve, was used to support extraction space closure by continuous light forces and sliding mechanics. Additionally, appropriate Class II traction may also be employed as part of the treatment strategy.

The extraction space was substantial and asymmetric, requiring significant mesial movement of the molars during the retraction of the anterior teeth. This introduced a notable challenge in anchorage management, particularly in the mandibular arch. The implementation of precise biomechanical design is essential for successfully closing the extraction space and establishing a stable occlusal relationship.²¹

When retracting the anterior teeth, attention should be paid to torque control, especially of the lower incisors. To avoid the risk of lingual inclination and potential complications related to bone dehiscence and fenestration, the strategic use of 0.019 × 0.025- inch SS arch wires, complemented by the incorporation of reverse-curves in the wire, proved to be helpful.

In the assessment of the unerupted third molars, a thorough examination of their size, positions and anticipated eruption directions is imperative.²² Due to the mesial movement of the second molar, the third molar would likely erupt forward and upward.^23,24 When the crown is exposed, some clinicians suggest that bonding small and low-profile buccal tubes with 10° lingual crown torque designed for second molars could be necessary, which would provide enhanced control and help prevent lingual roll.^8,22 However, buccal tubes designed for the first molars were chosen, which was more conducive to the required mesial bodily molar movement. In addition, the third molars often exhibit irregular occlusal surface morphology, necessitating the reshaping of cusps during or after treatment to achieve an optimal functional occlusion.

Root resorption has long been a concern for orthodontists.^25–27 To avoid this, it is crucial to employ light forces and promptly address any occlusal trauma. Unlike the anterior region, the cortical bone of the posterior teeth is distributed on both the buccal and lingual sides. This distribution reduces the probability of contact with the cortical bone during mesiodistal movement. Therefore, compared with the anterior teeth, the posterior teeth are less susceptible to root resorption.²⁸

The treatment duration tends to be prolonged when molars are extracted, especially for individuals awaiting the eruption of the third molars.²² This aspect is important and should be communicated to the patient at the start of treatment. Moreover, the patient’s active co-operation in the treatment process is essential, including diligent adherence to the prescribed hours and the specific types of elastics as directed by the clinician.

Finally, the extraction spaces were successfully closed during treatment. The post-treatment panoramic radiograph showed normal morphological structure of the roots, periodontal tissues and alveolar bone of the molars. The patient reported no symptoms of discomfort and expressed satisfaction with the treatment results. The 5-year follow-up facial and intraoral photographs showed a commendable improvement of the occlusion, demonstrating better stability compared to the relationship following the active treatment period (Figure 12).

The present case report illustrates that, with precise diagnosis, a critical overview of treatment and exemplary patient compliance, a favourable orthodontic result is achievable following the extraction of four premolars and four additional first molars. Not only were the carious teeth removed, but also the upper and lower anterior teeth were retracted to enhance the profile. Notably, all extraction spaces were effectively closed during treatment. This approach harmoniously aligned with the concept of personalised planning of orthodontic extraction treatment. Consequently, combined with the specific conditions and needs of patients, the extraction of significantly compromised teeth to facilitate orthodontic treatment proves to be a feasible and effective treatment plan.