Data Sources and Searches

An electronic search via PubMed, Science Direct, Embase, Scopus, Web of Science, Cochrane Library, LILACS, and Google Scholar was conducted to identify articles appropriate to the inclusion criteria. In addition, a manual search was conducted that included article reference lists, grey literature, and dissertations. The first (FK) and second (NK) authors assessed the retrieved records independently and in duplicate. Although they were not blinded to the identity of the authors or the conclusions of the studies, they used the same method to assess the eligibility of all retrieved records. All controversies were resolved by discussion with the fourth co-author (AIT).

To identify relevant studies, a combination of the Boolean operators AND/OR and MeSH/non-MeSH terms was used. The algorithm selected for the search strategy was (mandibular molars OR lower molars OR impacted molars AND uprighting OR orthodontic uprighting OR conventional biomechanics OR tipping spring OR frictional mechanics OR surgical uprighting OR surgical verticalization OR surgical repositioning). This review follows the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analysis) Statement (Figure 1).^18,19

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Eligibility Criteria

For the systematic review, due to the scarcity of RCTs on this subject, RCTs and Non-RCTs on human patients of any age, gender, ethnicity, or malocclusion evaluating the efficiency of orthodontic and surgical uprighting of mandibular molars were included. There were no language, publication year, or status restrictions. Case reports/series, literature reviews, laboratory studies, and studies on patients with syndromes and/or craniofacial deformities were excluded.

Data Extraction

A customized data collection form was developed and used to collect information from the selected studies. This information included authors, year of publication, study design, treatment method, reason of inclination, sample size, tooth description, molar axial inclination, treatment time, and outcomes. Two authors (FK and NK) extracted all essential data independently in the customized predesigned extraction form. The same two authors double-extracted data for a random sample of 10% of the included studies to assess data reliability. During the extraction process, any disagreements were resolved by consulting a third reviewer (AIT) until a final consensus was reached to provide an independent decision on the conflict.

Quality Analysis

The risk of bias of the included studies in this systematic review was assessed with the Risk Of Bias In Non-randomized Studies of Interventions [ROBINS-I] assessment tool, with the overall risk of bias ranging by low, moderate, or serious. To assess study quality, different quality appraisal tools were used, specifically designed for each type of study. The studies were estimated by confounding bias, bias in the selection of participants, bias in interventions, bias in missing data, bias in outcomes, and bias in reported results.¹⁸ However, a statistical meta-analysis was not possible to perform due to the heterogeneity of the included data.

Summary of Evidence

The current systematic review summarizes evidence from nonrandomized studies concerning the treatment of molar uprighting with orthodontic or surgical treatment. Out of the initial 958 hits from the literature search, the majority of the studies in the literature were case report/series; only six trials (involving 457 mandibular first and second molars) matched the inclusion/exclusion criteria. The six included studies showed certain defects and, based on the criteria, the majority of the articles were judged to be of moderate quality.

Orthodontic Uprighting

A segmental technique was used in three of the studies included.^8,9,11 Fu et al.¹¹ used uprighting springs (pole arm) made from a 0.016 × 0.022-inch titanium molybdenum alloy (TMA) archwire. When the uprighting spring was connected to the anchor teeth and the distal bend was placed between the distal contact and the first molar tube, the spring was activated, creating an uprighting and distal force. The other two studies included did not go into great detail about the segmental approach used.^8,9

In the literature, however, several uprighting orthodontic treatment approaches (segmental or straight wire) have been described, such as uprighting springs, open push coils, prefabricated Sander springs, helical uprighting springs, tip-back cantilevers, and interarch mechanics.^{13,14,15,21–23} In the segmental technique, an anchorage unit is usually required, such as a lingual arch,²⁴ a continuous or segmental rectangular SS wire,^11,21 or skeletal anchorage.²⁵ The uprighting spring could be fabricated from stainless steel),²⁶ TMA archwire, mostly 0.17 × 0.25-inch,^12,13,21,23 or Memory Titanol.^21,22

In the straight-wire technique, nickel–titanium (NiTi) wires, open coil springs, and elastic separators are mostly used.^{14,15,27–29} Lau et al. presented a method using a 0.016–0.022-inch copper-NiTi archwire with a push-coil spring to create space for the eruption of impacted mandibular second molars.¹⁴ Mansour et al. introduced the molar uprighting simplified technique (MUST) in which a NiTi wire was passed through a double tube attached to the second molar and a single tube attached to the first molar, emerging at the distal end through the second molar auxiliary tube and ligated to the premolar.¹⁵ Manosudprasit et al. used a NiTi archwire combined with an open-coil spring between mandibular first and second molars along with vertical elastics to achieve an adequate occlusion.²⁷

In the literature, uprighting time differed widely. Mangusson and Kjellberg observed that the uprighting treatment time lasted 8.3 months (range: 1–20 months).⁸ Fu found that males had a mean uprighting period of 3.62 ± 0.71 months and females had a mean uprighting period of 3.54 ± 0.56 months. The period of uprighting was related to the depth of impaction: the more deeply, horizontally, or distally impacted, the initial uprighting period was longer. However according to case studies, the average uprighting treatment time ranged from 2 weeks to 15 months.^7,21,28,29

Surgical Uprighting

Five of the included studies used surgical uprighting.^8,9,16,17,20 Surgical uprighting incorporates luxation of the impacted tooth. Additionally, a small amount of buccal crest bone is removed from around the crown prior to luxation to ensure that the cementoenamel junction and root surfaces remain covered. The tooth then tips superiorly and distally until the occlusal surface is approximately level with the occlusal plane and the molar is rotated on its root apices and repositioned within its socket to preserve the apical vessels.^{8–10,16,17,20} In case of excessive tooth mobility, a buccal wire of approximately 0.5-mm diameter from the first to the second molar can be used for immediate stabilization. This wire should be left in place for about 4 weeks. Prophylactic antibiotics could be given to all patients prior to surgery and continued for 24 hours.¹⁶ In addition, though root formation appears to occur subsequently in cases of incomplete root formation, it is inconsistent and unpredictable. This could be caused by trauma to the apical vessels or the Hertwig's sheath.³⁰

The mean angle change achieved in the study by Pogrel was 23.5 ± 16.1° (P < .001) and the mean distal bone level of the adjacent first molar was 3.41 ± 1.52 mm preoperatively and 1.45 ± 0.54 mm postoperatively (42.5% improvement, P < .001).¹⁶

Success Rate

According to Mangusson and Kjellberg, orthodontic uprighting had a success rate of 42%, while surgical uprighting was 50%.⁸ The sample of lower mandibular molars, however, was significantly reduced, so the findings should be considered cautiously.

Orthodontic uprighting seemed to have 100% success rate in the studies of Kenrad et al. and Fu et al.^9,11 However, surgical uprighting showed a lower success rate, but was still clinically favorable. Out of the 350 molars, 338 were successfully uprighted (96.75%).^9,8,16,17,20 The remaining 12 molars had to be extracted due to subsequent submerging and root resorption/infection around the uprighted tooth, which developed into osteitis and root fracture.^17,16,20

According to La Monaca, orthodontic and surgical uprighting had a 100% success rate, but when surgical-orthodontic uprighting were combined, the success rate was significantly lower (34/48 molars, 70.8%).³¹

Third Molar Extraction

Third molar extraction enables the creation of a corticomedullar void distal to the second molar, which reduces the treatment time.³² Additionally, although third molar extraction is useful to obtain more space for luxation, it is not always considered necessary.³¹ Its presence may create a wedge effect against the second molar to improve the immediate postoperative stability of the uprighted position. Also, the third molar may be used as a future replacement if the second molar ultimately requires extraction.

According to Padwa, the posterior eruption space was not influenced by third molar retention or extraction. However, due to the inability of the second molar to be uprighted, the third molar was extracted in 50% of the study cases.¹⁷

Complications

Orthodontic uprighting complications include hypertrophy of the mucosa and poor oral hygiene.³³ Surgical uprighting was associated with complications such as pulpal calcification, misalignment, infection/abscess in three molars, increased (more than 5 mm) periodontal pocketing, root fracture, and nonvital indication on electric pulp test. None of the teeth that were found to be nonvital on electric pulp testing were symptomatic, implying that radiographic pulpal changes do not predict clinical failure.^16,17 In addition, Padwa et al. found that, while 47.3% of postoperative radiographic findings were abnormal, none of the patients experienced pain, swelling, or other symptoms during the average follow-up period.¹⁷

Strengths and Limitations

This systematic review had several strengths, including its comprehensive literature search, the exclusion of case reports/series, and the transparent provision of all data. This systematic review is the first that included a risk of bias of previous clinical trials suggesting orthodontic and/or surgical uprighting as an effective treatment option for impacted mandibular molars. The current review confirmed the recommendation for both techniques. However, surgical uprighting may be more associated with some complications.

According to the quality analysis of the included studies, the majority were judged to be of moderate quality. The most serious shortcomings were the Non-RCT design^{8,9,11,16,17,20} and missing data along with the bias of retrospective studies. Additionally, in the absence of comparable measurement results, the lack of confounders like age of intervention, sex, or a standard method used to assess molar angulation precluded conducting a proper meta-analysis and reporting bias that were initially planned. Therefore, the results of this systematic review should be used in conjunction with sound clinical judgment. The treatment of lower molar uprighting with nonsurgical and surgical methods has yet to be adequately addressed in the literature.

Due to the inclusion of a few, small, nonrandomized trials in the absence of RCTs, the efficacy of treatment options is only moderately documented. Well-controlled RCTs on the effectiveness of different orthodontic techniques for mandibular molar uprighting and comparison with surgical uprighting are needed in the future to assess the costs and side effects of the interventions.