Exploring biological mechanisms in orthodontic tooth movement: Bridging the gap between basic research experiments and clinical applications - A comprehensive review.

OBJECTIVES: The molecular mechanisms behind orthodontic tooth movements (OTM) were investigated by clarifying the role of chemical messengers released by cells. METHODS: Using the Cochrane library, Google scholar, and PubMed databases, a literature search was conducted, and studies published from 1984 to 2024 were considered. RESULTS: Both bone growth and remodeling may occur when a tooth is subjected to mechanical stress. These chemicals have a significant effect on the stimulation and regulation of osteoblasts, osteoclasts, and osteocytes during alveolar bone remodeling. This regulation can take place in pathological conditions, such as periodontal diseases, or during OTM alone. This comprehensive review outlines key molecular mechanisms underlying OTM and explores various clinical assumptions associated with specific molecules and their functional domains during this process. Furthermore, clinical applications of certain molecules such as relaxin, prostaglandin E (PGE), and interleukin-1ß (IL-1ß) in accelerating OTM have been reported. Our findings underscore the existing gap between OTM clinical applications and basic research investigations. CONCLUSION: A comprehensive understanding of orthodontic treatment is enriched by insights into biological systems. We reported the activation of osteoblasts, osteoclast precursor cells, osteoclasts, and osteocytes in response to mechanical stress, leading to targeted cellular and molecular interventions and facilitating rapid and regulated alveolar bone remodeling during tooth movement. Despite the shortcomings of clinical studies in accelerating OTM, this review highlights the crucial role of biological agents in this process and advocates for prioritizing high-quality human studies in future research to gain further insights from clinical trials.

A cone-beam computed tomography study of hyoid bone position and airway volume in subjects with obstructive and nonobstructive adenotonsillar hypertrophy.

OBJECTIVES: To investigate hyoid bone position and airway volume in subjects with adenoid hypertrophy, tonsillar hypertrophy, and adenotonsillar hypertrophy compared to subjects with nonobstructive adenoids or tonsils and to assess the correlation between hyoid bone and airway parameters. MATERIALS AND METHODS: A total of 121 subjects were grouped based on adenoid or tonsillar hypertrophy into four groups, as follows: (1) control group (C-group), (2) adenoid hypertrophy group (AH-group), (3) adenotonsillar hypertrophy group (ATH-group), and (4) tonsillar hypertrophy group (TH-group). Hyoid bone position and airway volumes were measured. The Kruskal-Wallis test was used for intergroup comparison, followed by pairwise comparison using the Mann-Whitney U-test. Bivariate correlation was conducted using Spearman correlation coefficients. Multiple linear regression was performed to create a model for airway volume based on hyoid bone predictive variables. RESULTS: No significant difference was found between subjects with isolated adenoid or tonsillar hypertrophy compared to the C-group. However, the ATH-group exhibited a significantly decreased hyoid bone vertical distance (HV), total airway volume (TA volume), and retroglossal airway volume (RG volume) compared to the C-group. HV and age had a high potential in terms of explaining the RG volume, whereas the TA volume and retropalatal airway volume (RP volume) models were not as successful as the RG volume counterpart. CONCLUSIONS: Subjects in ATH-group were characterized by an elevated hyoid bone position and constricted TA volume and RG volume compared to those in the C-group. HV and age were predictor variables that best explained retroglossal airway volume.

A quantitative three-dimensional comparative study of alveolar bone changes and apical root resorption between clear aligners and fixed orthodontic appliances.

BACKGROUND: This study aimed to evaluate and compare the alveolar bone changes and to investigate the prevalence and severity of orthodontically induced inflammatory root resorption (OIIRR) of maxillary incisors in patients who received treatment with clear aligners (CA) versus conventional fixed appliances (FA), using cone-beam computed tomography (CBCT). METHODS: One hundred sixty maxillary incisors from 40 patients with similar baseline characteristics based on the American Board of Orthodontics discrepancy index scores were divided into the CA and FA groups. The dentoalveolar quantitative changes were analyzed using pre- (T0) and post-treatment (T1) CBCT. The measured parameters included alveolar bone thickness (ABT), alveolar bone height (ABH), root length (OIIRR), and maxillary incisor inclinations. RESULTS: Post-treatment, the average palatal and total ABT significantly decreased in central and lateral incisors in the FA group. In contrast, the CA group's average labial ABT of the lateral incisors decreased considerably. Regarding the ABH, both groups showed significant labial and palatal marginal bone resorption. In both groups, root lengths significantly decreased after treatment (p < 0.005). The inter-group comparison revealed that ABT and root length had significantly decreased in the FA group compared to the CA group, while the ABH showed no significant difference between the two groups. The mean absolute reductions of ABT and OIIRR in the CA group were significantly less (- 0.01 ± 0.89 and 0.31 ± 0.42) than those in the FA group (0.20 ± 0.82 and 0.68 ± 0.97), respectively. CONCLUSIONS: CA and FA treatments appear to cause a significant ABT reduction and a statistically significant increased OIIRR in the maxillary incisor region, with a greater extent expected with FA treatment. However, the increased OIIRR values in the majority of both groups' cases were not clinically significant. Both treatment modalities resulted in a significant ABH reduction, with the highest found in the labial side of lateral incisors in the CA group.

Electromyographic activities of the jaw and facial muscles in subjects with different vertical skeletal patterns and breathing modes.

BACKGROUND: Mouth breathing (MB) can affect morphological changes in the craniofacial structures, electromyography is widely used for quantitative analysis of muscle function. OBJECTIVE: The aim was to evaluate the electromyographic (EMG) activities of the anterior temporalis (TA), masseter muscle (MM), orbicularis oris superior (OOS) and mentalis muscle (MT) in children with different vertical skeletal patterns and breathing modes during rest and various functional mandibular movements. METHODS: BioEMG III was used to measure the variations in EMG activities of TA, MM, OOS, and MT in 185 subjects aged 6-12 years during continuous clenching, rest, maximal intercuspation, lips closed lightly and swallowing. RESULTS: The results of logistic regression analysis showed that the model with vertical skeletal patterns as the dependent variable was ineffective (p = .106), while the model with breathing modes as the dependent variable was effective (p = .000). When considering both vertical skeletal patterns and breathing modes, the following significant differences were found. (1) In the normal-angle group, the EMG ratio in OOS with lips closed lightly of MB was significantly higher than NB (p = .005). (2) In the low-angle group, EMG ratios in TA and MM during the swallowing of MB were significantly lower than NB (p = .020, p = .040, respectively). (3) In the high-angle group, EMG ratios of MB were significantly higher in MT during continuous clenching, rest, lips closed lightly and swallowing (p = .038, p = .036, p = .005, p = .028, respectively), and OOS with lips closed lightly compared to NB (p = .005). CONCLUSION: Breathing modes and vertical skeletal patterns interacted to alter maxillofacial EMG activities, with breathing modes having a greater effect.

Analysis of maxillary arch morphology and its relationship with upper airway in mouth breathing subjects with different sagittal growth patterns.

OBJECTIVE: This three-dimensional cone beam computed tomography(CBCT) study assessed pharyngeal airway and maxillary arch in mouth breathing subjects with different skeletal classifications and analyzed the factors associated with the upper airway morphological variations in mouth breathing (MB) and nasal breathing (NB) subjects. METHODS: One hundred and five subjects (52 MB and 53 NB children), divided into three skeletal groups: Class I (1° ≤ ANB° ≤ 5°), Class II (ANB° >5°), and Class III (ANB°<1°). An independent t-test and one-way ANOVA test were utilized in the group analysis of normal distributed data. The linear multiple regression test was applied to create a model for the airway volumes based on the maxillary arch parameters in different skeletal groups. RESULTS: In three skeletal groups, NB individuals had greater oropharyngeal airway volume (OPV) and total pharyngeal airway volume (TPV) than MB. Maxillary arch parameters of intermolar width (IMW), intercanine width (ICW), and maxillary width of canines (MWC) were larger in NB participants than in MB subjects. In the MB group, we discovered that Class II individuals had lower NPV (nasopharyngeal airway volume) than Class I and Class III. MWC was lower in Class II subjects compared to Class I and Class III in both the NB and MB groups. CONCLUSION: NB individuals had greater pharyngeal airway and maxillary arch parameters than MB subjects. Our model equation revealed that the inter-molar width (IMW) and palatal area (PA) parameters were the strongest predictors of total pharyngeal airway volume (TPV) in the skeletal Class II and Class I groups.

A Study of the Facial Soft Tissue Morphology in Nasal- and Mouth-Breathing Patients.

OBJECTIVES: This study aimed to investigate the 3-dimensional (3D) facial morphology of children with skeletal Class II structure with different breathing patterns. METHODS: The 3dMDFace system (3dMD Inc.) was used to obtain 3D facial images. A total of 65 patients aged 10 to 12 years with skeletal Class II malocclusion (A point-Nasion-B point angle >5°) were grouped by sex into nasal-breathing (NB) and mouth-breathing (MB) participants. A total of 19 measurements, including linear distances, angles, and ratios, were measured. The measurements were compared using independent sample t test and Mann-Whitney U test. Factor analysis and logistic regression were used to test the correlation between facial morphology and different breathing patterns. RESULTS: For male children, the lower lip was longer in the MB group than in the NB group (P < .05). For female children, compared to NB, MB patients had a narrower mandibular width (P < .05), a smaller ratio of mandibular width to face height (MB: 0.99 ± 0.08 vs NB: 1.04 ± 0.09; P < .05), and a larger ratio of lower lip height to lip width (MB: 1.24 ± 0.10 vs NB: 1.19 ± 0.16; P < .05). In both male and female children, MB participants had a more convex nasolabial angle (P < .05) and an increased ratio of the lower part of the face to the upper facial height (male MB: 1.61 ± 0.17 vs male NB: 1.50 ± 0.12; female MB: 1.52 ± 0.10 vs female NB: 1.50 ± 0.20; P < .05). The logistic regression test showed no significant correlation between facial morphology and breathing patterns. CONCLUSIONS: In participants with skeletal Class II pattern, MB children compared with NB children showed different facial morphology in the same sex group. The children with MB showed a more protruded upper lip and increased lower facial height, accounting for a larger proportion of the facial height. However, no significant correlation was found between facial morphology and breathing pattern. Only correlative trends were found.

Three-dimensional evaluation of pharyngeal airway and maxillary arch in mouth and nasal breathing children with skeletal Class I and II.

OBJECTIVE: This study aimed to investigate whether the subjects with mouth breathing (MB) or nasal breathing (NB) with different sagittal skeletal patterns showed different maxillary arch and pharyngeal airway characteristics. METHODS: Cone-beam computed tomography scans from 70 children aged 10 to 12 years with sagittal skeletal Classes I and II were used to measure the pharyngeal airway, maxillary width, palatal area, and height. The independent t-test and the Mann-Whitney U test were used for the intragroup analysis of pharyngeal airway and maxillary arch parameters. RESULTS: In the Skeletal Class I group, nasopharyngeal airway volume (P < 0.01), oropharyngeal airway volume (OPV), and total pharyngeal airway volume (TPV) (all P < 0.001) were significantly greater in subjects with NB than in those with MB. Furthermore, intermolar width, maxillary width at the molars, intercanine width, maxillary width at the canines, and palatal area were significantly larger in subjects with NB than in those with MB (all P < 0.001). In the Skeletal Class II group, OPV, TPV (both P < 0.05) were significantly greater in subjects with NB than in those with MB. No significant differences in pharyngeal airway parameters in the MB group between subjects with Skeletal Class I and those with Skeletal Class II. CONCLUSION: Regardless of sagittal Skeletal Class I or II, the pharyngeal airway and maxillary arch in children with MB differ from those with NB. However, the pharyngeal airway was not significantly different between Skeletal Class I and II in children with MB.

Three-dimensional evaluation of hyoid bone position in nasal and mouth breathing subjects with skeletal Class I, and Class II.

BACKGROUND: This retrospective study investigated the effect of breathing pattern, skeletal class (Class I, Class II), and age on the hyoid bone position (HBP) in normodivergent subjects. METHODS: A total of 126 subjects (61 males, 65 females) aged 7-9 years and 10-12 years were scanned using cone-beam computed tomography (CBCT). All participants were classified according to the anteroposterior skeletal pattern into (Class I, Class II). Each skeletal group was further divided according to the breathing mode into mouth breathers (MB) and nasal breathers (NB). The HBP was measured accordingly. Independent sample t-test and Mann Whitney U test were used to detect significant differences between the groups, and binary logistic regression was used to identify MB predictive indicators. RESULTS: The breathing mode and skeletal class affected the vertical HBP in subjects with 7-9 years, while they affected the anteroposterior HBP in subjects with 10-12 years. Regarding the age effect, hyoid bone was located more anteriorly in the older NB subjects, and hyoid bone was more inferiorly in the older age group. A regression equation of the significant variables was formulated, C3-Me (P: 001, OR: 2.27), and H-EB (P: 0.046, OR: 1.16) were positively correlated with occurrence of MB. CONCLUSION: There were significantly different HBPs among subjects with different anteroposterior skeletal classes, breathing modes, and age cohorts. Moreover, C3-Me, and H-EB were significant predictors and correlated with increased likelihood of being MB subject.