Anatomical limitations and factors influencing molar distalization

Long-term stability of maxillary molar distalization in the treatment of Angle Class II malocclusion: A systematic review and meta-analysis

OBJECTIVES

This study aimed to evaluate the long-term skeletal and dental stability following maxillary molar distalization for Angle Class II malocclusion and to explore potential relapse-related factors.

METHODS

A systematic search of twelve electronic databases and six manual sources was conducted. After data extraction and risk of bias assessment, meta-analyses using random-effects models were performed. Heterogeneity was explored through subgroup analyses and sensitivity analyses. The certainty of evidence was rated using the GRADE approach.

RESULTS

9 non-randomized clinical trials involving 223 Class II malocclusion patients were included. Meta-analyses of 5 skeletal and 9 dental treatment effects were conducted. While skeletal changes were minimal and not statistically significant, significant mesial relapse of the first molar (1.80 mm, p = 0.002, I2 = 90%) and the second molar (3.19 mm, p = 0.007, I2 = 93%) was observed. Besides, the first molar showed notable extrusion (1.18 mm, p = 0.002, I2 = 85%) and mesial inclination (1.46°, p = 0.004, I2 = 18%). Subgroup analyses identified a significant age-related effect on vertical changes of the first molar, with greater extrusion in younger patients (≤ 18 years). The certainty of evidence was rated low to very low.

CONCLUSIONS

Over a mean follow-up of 4.2 years, skeletal changes were minimal, while maxillary molars showed significant mesial relapse. The first molar also exhibited measurable extrusion and mesial inclination, with younger patients showing greater vertical changes. However, these findings were based on low to very low certainty of evidence due to non-randomized study designs and high heterogeneity, warranting cautious interpretation and further validation.

CLINICAL RELEVANCE

Identifying long-term relapse patterns and patient-related factors after maxillary molar distalization can help orthodontists optimize treatment planning, select appropriate cases, and develop individualized retention strategies to improve long-term stability.

Expert consensus on the clinical strategies for orthodontic treatment with clear aligners

Clear aligner treatment is a novel technique in current orthodontic practice. Distinct from traditional fixed orthodontic appliances, clear aligners have different material features and biomechanical characteristics and treatment efficiencies, presenting new clinical challenges. Therefore, a comprehensive and systematic description of the key clinical aspects of clear aligner treatment is essential to enhance treatment efficacy and facilitate the advancement and wide adoption of this new technique. This expert consensus discusses case selection and grading of treatment difficulty, principle of clear aligner therapy, clinical procedures and potential complications, which are crucial to the clinical success of clear aligner treatment.

How accurate is predicted root movement achieved in four first-premolar extraction cases with Invisalign?

OBJECTIVES

This study aims to compare the achieved and predicted root movements in adults after four first-premolar extractions and Invisalign treatment.

MATERIALS AND METHODS

Thirty-three consecutive adults (22 Class I, 9 Cusp-to-cusp Class II and 2 Cusp-to-cusp Class III) from a single clinical division who completed the first series of aligners after premolar extractions were included in this retrospective study. A pretreatment cone-beam computed tomography model was registered onto the pretreatment surface-scanned dental model (SSDM) to locate the pretreatment root apices of the whole dentition. These were copied and transferred to the predicted and achieved post-treatment SSDMs to acquire the locations of the predicted and achieved post-treatment root apices. The differences between predicted and achieved root movements (DPARMs) were tested using the paired t-test or Wilcoxon signed rank test.

RESULTS

In the anteroposterior direction, posterior root movements of maxillary and mandibular anterior teeth were poorly achieved (3.24-5.74 mm DPARMs, p < .05). In the vertical direction, roots of maxillary anterior teeth achieved greater intrusion (0.70-0.93 mm DPARMs, p < .05), while those of mandibular incisors achieved less intrusion (0.57-0.65 mm DPARMs, p < .05) than predicted. In the mediolateral direction, lateral incisor roots did not move distally (-0.65 to -0.96 mm DPARMs, p < .05), while those of canines did not move buccally, compared with the prediction (-0.75 mm DPARMs, p < .05).

CONCLUSIONS

In the four first-premolar extraction treatments with Invisalign, root movements were not achieved as predicted, particularly for anterior teeth in the anteroposterior direction.

The Three-Dimensional Investigation of the Radiographic Boundary of Mandibular Full-Arch Distalization in Different Facial Patterns

OBJECTIVE

Mandibular full-arch distalization (MFD) is a popular approach, particularly in non-extraction cases. However, we still cannot confirm whether facial patterns affect the amount of limits. This study aimed to determine the anatomical MFD limits in patients with different facial patterns.

STUDY DESIGN

Using computed tomography (CT), the shortest distances from the mandibular second molar to the inner cortex of the mandibular lingual surface and from the lower central incisor to the inner cortex of the lingual mandibular symphysis were measured in 60 samples (30 patients). The available distalization space in both regions was compared between groups with different facial patterns.

RESULTS

The available space in symphysis was more critical than that in retromolar area: the shortest distances to the inner cortex of the lingual mandibular symphysis at root levels 8 mm apical to the cementoenamel junction of the incisor were 1.28, 1.60, and 3.48 mm in the high-, normal-, and low-angle groups, respectively.

CONCLUSIONS

Facial patterns affected the MFD capacity, and the thickness of the lingual mandibular symphysis was the most critical anatomic limit encountered. Practitioners should always pay attention to the possible impacts from facial patterns, especially in the treatment of high-angle cases.

Influence of the maxillary third molars and the surrounding cortical plate during maxillary tooth movement with TADS- A CBCT Study

OBJECTIVE

To determine the influence of the presence/absence of third molars and intact/loss of cortical plate of the maxillary tuberosity on the amount of distal movement of the maxillary first permanent molar during distal movement of the maxillary dentition with mini-implants.

MATERIALS AND METHODS

Thirty six maxillary tuberosity sites were evaluated in eighteen young adult patients. The distal movement of the entire maxillary dentition was performed with mini-implants with 200 g of distalising force applied from the mini-implant placed in the maxillary posterior buccal region to attachments placed on the arch wire between the maxillary lateral incisor and canine bilaterally. The distal movement of the maxillary first permanent molars was measured on lateral cephalograms. The maxillary tuberosity sites with intact cortical plate due to congenitally missing third molars or atraumatic extraction of third molars (G1), partial loss of cortical plate due to surgical removal of third molars (G2), fully erupted third molars (G4), third molars located at (G3), and below the cementoenamel junction (G5) were evaluated with cone beam computed tomography. One way Anova and Fisher LSD test was done.

RESULTS

The order of greater to lesser amount of distal movement of the maxillary first permanent molar depending on the integrity of maxillary of tuberosity was partial loss of cortical plate, third molars at the cementoenamel junction, third molars below the cementoenamel junction, intact cortical plate and fully erupted third molars.

CONCLUSION

The integrity of the cortical plate and the relative position of the maxillary third molar to the second molar influence the amount of distal movement of the maxillary first permanent molar during distal movement of the maxillary teeth with TADS.

CLINICAL RELEVANCE

The amount of distal movement of the maxillary dentition appears to depend on the presence or absence of the third molars and the condition of the cortical plate in the region of the maxillary tuberosity and thereby greatly influence the outcome of treatment.

Boundary of mandibular molar distalization in orthodontic treatment: A systematic review and meta-analysis

To explore the mandibular retromolar space length (MRSL), initial root-inner cortex contact percentage (IRCCP), and the various factors that influence mandibular molar distalization. Searches were undertaken in PubMed, EMBASE, Web of Science, Cochrane Library, Scopus, and grey literature (Google Scholar and OpenGrey) for eligible cross-sectional observational studies measuring the MRSL and IRCCP in healthy adult patients. The risk of bias and evidence quality were evaluated using the Joanna Briggs Institute's checklist and GRADE framework. Thirteen studies involving 1169 patients were included for qualitative synthesis. Seven of these studies were eligible for quantitative analysis. Meta-analysis showed that the mean MRSL at the subfurcation-6 mm plane in Asian normodivergent cases was 3.78 mm (95% confidence interval [CI]: 2.81-4.35; I2 = 79.7%) for skeletal Class-I malocclusions, 3.02 mm (95% CI: 2.10-3.94; I2 = 62.5%) for Class-II, and 4.43 mm (95% CI: 3.14-5.73; I2 = 75.1%) for Class-III. The mean MRSL at the sub-cementoenamel junction (CEJ)-10 mm plane for Asian, Class-I, normodivergent cases was 3.28 mm (95% CI: 2.44-4.12; I2 = 68.9%). The mean IRCCP for Asian, Class-I, normodivergent cases was 27.2% (95% CI: 0.22-0.32; I2 = 0%). In Asian normodivergent cases, MRSL ranges from 3.28 to 4.43 mm with a 27.2% IRCCP for Class-I. Cone-beam computed tomography imaging is recommended for measuring the MRSL in the apex region particularly before molar distalization. Factors influencing MRSL and IRCCP include different races, skeletal patterns, facial types, and third-molar status.

Anatomical factors of the maxillary tuberosity that influence molar distalization

Objective

To examine the areas of the maxillary tuberosity (MT) (coronal, apical, width, and height) with respect to the presence or absence of the third molar to establish possible anatomical limitations for molar distalization.

Methods

A total of 277 tuberosities were evaluated through sagittal computed tomography (CT) images, divided for measurement into coronal (free of bone), apical (area of influence of the maxillary sinus), and tuberosity (bony area) zones, and stratified by the presence or absence of the third molar, sex, and two age subgroups. Mann-Whitney U test was used to compare the groups considering the third molar.

Results

The medians of the width and height of the tuberosity decreased significantly in the absence of the third molar (P < 0.001). The apical area also showed differences, with negative values in the absence of the third molar and positive values in the presence of the third molar (P < 0.001). However, no differences were observed for the coronal area (P > 0.05).

Conclusions

In the absence of the third molar, the size of the MT, represented by its width and height, was smaller and negative values (decrease) were observed for the maxillary sinus. The sagittal CT provides useful information regarding the amount of bone tissue available for distalization and relationship of the second molar with respect to the maxillary sinus, which allows individualizing each case in relation to the amount and type of movement expected.

Vertical Control in Molar Distalization by Clear Aligners: A Systematic Review and Meta-Analysis

Background: Molar distalization is used to correct molar relationships or to create space for mild anterior crowding. However, whether clear aligners can provide proper vertical control with the sequential distalization strategy has been highly debated. Thus, the current study aimed to systematically review the amount of dentoskeletal changes in the vertical dimension that results from sequential molar distalization in clear aligner therapy without temporary anchorage devices (TADs). Methods: Registered with PROSPERO (CRD42023447211), relevant original studies were screened from seven databases and supplemented by a manual search by two investigators independently. Articles were screened against inclusion and exclusion criteria, and a risk of bias assessment was conducted for each included article. Relevant data were extracted from the included articles and meta-analysis was performed using RStudio. Results: Eleven articles (nine for maxillary distalization and two for mandibular distalization) were selected for the final review. All studies have a high or medium risk of bias. For maxillary molar distalization, the meta-analysis revealed 0.26 mm [0.23 mm, 0.29 mm] of maxillary first molar intrusion based on post-distalization dental model analysis, as well as 0.50 mm [-0.78 mm, 1.78 mm] of maxillary first molar intrusion and 0.60 mm [-0.42 mm, 1.62 mm] of maxillary second molar intrusion based on post-treatment lateral cephalometric analysis. Skeletally, there was a -0.33° [-0.67°, 0.02°] change in the SN-GoGn angle, -0.23° [-0.30°, 0.75°] change in the SN-MP angle, and 0.09° [-0.83°, 1.01°] change in the PP-GoGn angle based on post-treatment lateral cephalometric analysis. There was insufficient data for meta-analysis for mandibular molar distalization. Conclusions: No significant changes in vertical dimension were observed, both dentally and skeletally, after maxillary molar distalization with a sequential distalization strategy. However, further studies on this topic are needed due to the high risk of bias in the currently available studies.

Combined distalization and lingual cortex remodeling during mandibular growth for facial profile improvement: a case report

Borderline crowding poses a challenge in deciding whether or not to prescribe premolar extraction. This case report describes the two-phase nonextraction orthodontic treatment of an 11-year-old girl with a hyperdivergent skeletal Class I pattern exhibiting anterior crowding and moderate lip protrusion. The initial phase of treatment included maxillary and mandibular expansion to correct the transverse discrepancy as an early intervention. Subsequently, comprehensive treatment was initiated at the age of 13 years, with fully erupted permanent second molars and growth potential remaining. Phase II treatment involved a second round of maxillary expansion, followed by simultaneous bimaxillary total arch intrusive distalization, using interradicular, temporary skeletal anchorage devices to correct dental crowding and improve the facial profile. Although the limited retromolar space posed a challenge to mandibular tooth distalization, gradual bone remodeling was observed in the lingual cortex of the mandibular body, enabling sufficient orthodontic tooth movement without noticeable side effects. After 4 years 3 months of treatment, her dental crowding was relieved, with significant improvement in the facial profile and proper occlusion. The treatment outcomes remained stable 2 years 4 months after retention.

Molar distalization in orthodontics: a bibliometric analysis

OBJECTIVES

The study endeavors to undertake a bibliometric analysis on molar distalization, with the objective of illuminating its evolutionary trajectory, current status, and prognosticating future research hotspots and trends.

MATERIAL AND METHODS

A comprehensive exploration of the literature on molar distalization was carried out by conducting a search in the Web of Science (WOS) core database of the University of Hong Kong Electronic Library. The search for topic terms employed included "molar distalization," "molar distalisation," "move molar distally," "molar distal movement," and "molar backwards." The search results were subsequently subjected to meticulous analysis using CiteSpace software. This analysis encompassed various facets such as the citation count; the geographical distribution of the countries, institutions, and journals responsible for publishing the articles; the distribution of the authors; the utilization of keywords within the articles; and the analysis of references.

RESULTS

A total of 516 articles were included in the analysis. The top 5 countries in terms of the number of published papers were the United States (USA), South Korea, Turkey, Italy, and Germany, and the top 5 institutions in terms of the number of published papers were Kyung Hee University, A.T. Still University of Health Sciences, Catholic University of Korea, Seoul St. Mary's Hospital, and Universidade de Sao Paulo. The top 5 authors in terms of the number of published papers were Park, Kook, Bayome, Janson, and Lee. There was little cooperation overall. The top 3 journals in terms of the most published related articles were all orthodontic-related journals. After molar distalization and anchorage, the most frequently used keywords were distalization, movement, and pendulum appliance. Kinzinger GSM is the most frequently cited author in references, and one of his articles also has the highest centrality score in references.

CONCLUSIONS

As the tides of time shift and scholars display an ever-growing dedication to unraveling the intricacies of this therapeutic modality, the realm of molar distalization has undergone notable advancements in technology. Initially, the traditional appliance suffered from aesthetic drawbacks and discomfort. However, contemporary iterations of the appliance have transcended these limitations, boasting enhanced elegance and convenience while concurrently elevating their efficacy. Nevertheless, limitations of current appliances, including their durability and propensity for recurrence post-treatment, continue to necessitate further advancement. Hence, the ongoing scientific inquiry aims to delve deeper into refining treatment modalities and fabricating cutting-edge appliances within this realm.

CLINICAL RELEVANCE

This study holds the potential to significantly enhance the ability of orthodontists to devise treatment protocols and offer state-of-the-art clinical recommendations, thereby empowering them to deliver advanced and refined orthodontic interventions.

Mandibular Posterior Anatomic Limit for Distalization in Patients With Various Patterns of Third Molar Impactions: A Three-Dimensional Cone Beam CT (CBCT) Study

AIM

The aim was to compare and evaluate the variation in the mandible's posterior anatomic limits (MPAL) stratified by different third molar impaction patterns utilizing cone-beam CT (CBCT) in individuals with skeletal Class III malocclusion.

METHODOLOGY

The sample consisted of CBCT records of 80 samples of Class III patients categorized based on the pattern of their third molar impaction. The shortest linear distances from the distal root of the second mandibular molar to the inner cortex of the mandibular body were measured at the crown level, at the cementoenamel junction (CEJ), and at the depths of 4, 6, and 8mm from the CEJ, all parallel to the posterior occlusal line. The MPAL of the four groups were compared. The Shapiro-Wilk test for normality was performed. The Kruskal-Wallis test was performed to compare the MPAL distances between the groups.

RESULTS

Significant differences were noted between the four groups at every level. MPAL distances decreased towards apex in all the groups and was least at the 8mm root level. The greatest MPAL distances were noted in the no-impaction group followed by the horizontal. At 8mm, the MPAL were 4.2+/-1.3 in Group 3 (Control), 3.3+/-0.9 in Group 1 and 2.7+/-0.05 mm in Group 2. Though the amount of space available for distalization was greatest for the mesioangular group at the crown level, it was least at the 8mm level compared to other groups.

CONCLUSION

MPAL distances were shortest at the root level in Class III patients who had mesioangularly impacted third molars and care should be taken before attempting distalization in them.