Radiographic Features of Mandibular Second Molars with Eruption Disturbances: A Retrospective Study.

We aimed to establish the characteristics and potential etiological risk factors of eruption disturbances in mandibular second molars (MM2). We retrospectively enrolled patients with eruption disturbances in MM2. A total of 143 MM2 with eruption disturbances from 112 patients (mean age 17.45 ± 6.35) were included in this study. Panoramic radiographs were employed to determine the risk factor, angulation type, impaction depth, tooth development stage, and associated pathology. The novel classification method of MM2 was based on impaction depth and angulation. Of 143 MM2, 137 and 6 were diagnosed with impaction and retention, respectively. Insufficient space was the most frequent risk factor for eruption disturbances. There were no significant differences between retention and impaction regarding sex, age, or side. The most frequent impaction type was Type I. The most frequent angulation of impacted MM2 was mesioangular. Impacted MM2 with shallower depth were more frequently associated with the presence of first molar undercut. Impaction types did not differ according to age, side, development stage, or distance from the MM1 distal surface to the anterior border of the ramus. Dentigerous cysts were associated with earlier MM2 development stages and greater MM2 depth. In conclusion, MM2 impaction types differed according to the risk factor, angulation type, MM1 undercut, and presence of cysts. Early MM2 development stage and greater MM2 depth were risk factors for MM2 eruption disturbances with cysts.

Characteristics of Spatial Changes in Molars and Alveolar Bone Resorption among Patients with Loss of Mandibular First Molars: A CBCT-Based Morphometric Study.

OBJECTIVES: To investigate the characteristics of spatial changes in molars and alveolar bone resorption among patients with loss of mandibular first molars. METHODS: A total of 42 CBCT scans of patients with missing mandibular first molars (3 males, 33 females) and 42 CBCT scans of control subjects without loss of mandibular first molars (9 males, 27 females) were evaluated in this cross-sectional study. All images were standardized using the mandibular posterior tooth plane with Invivo software. The following indices regarding alveolar bone morphology were measured, including alveolar bone height, bone width, mesiodistal and buccolingual angulation of molars, overeruption of maxillary first molars, bone defects, and the capability of molar mesialization. RESULTS: The vertical alveolar bone height in the missing group was reduced by 1.42 ± 0.70 mm, 1.31 ± 0.68, and 1.46 ± 0.85 mm on the buccal, middle, and lingual side, respectively (no differences among the three sides; p > 0.05). Alveolar bone width was reduced the greatest at the buccal CEJ level and the least at the lingual apex level. Mandibular second molar mesial tipping (with mean of the mesiodistal angulation = 57.47 ± 10.34°) and lingual tipping (with mean of the buccolingual angulation = 71.75 ± 8.34°) were observed. The mesial and distal cusps of maxillary first molars were extruded by 1.37 mm and 0.85 mm, respectively. Buccal and lingual defects of alveolar bone occurred at the CEJ, mid-root, and apex levels. Through 3D simulation, the second molar cannot be successfully mesialized into the missing tooth position, and the difference between the available and required distances for mesialization was the greatest at the CEJ level. The duration of tooth loss was significantly correlated with the mesio-distal angulation (R = -0.726, p < 0.001), buccal-lingual angulation (R = -0.528, p < 0.001) and the extrusion of the maxillary first molar (R = -0.334, p < 0.05). CONCLUSION: Both vertical and horizontal resorption of alveolar bone occurred. Mandibular second molars exhibit mesial and lingual tipping. Lingual root torque and uprighting of the second molars are needed for the success of molar protraction. Bone augmentation is indicated for severely resorbed alveolar bone.

The effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners: A finite-element study.

INTRODUCTION: The objective of this study was to analyze the effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners. METHODS: Models including a maxillary dentition without first premolars, maxilla, periodontal ligaments, attachments, and aligners were constructed and imported to finite-element software. Two groups of models were created: (1) without canine attachment and (2) with canine attachment. Overtreatment degrees (0°, 1°, 2°, 3°, 4°, and 5°) were applied for both groups. RESULTS: Clear aligner therapy caused lingual tipping and extrusion of incisors, distal tipping and extrusion of canines, and mesial tipping and intrusion of posterior teeth, which was more significant with canine attachments except for second premolars. Aligner overtreatment produced palatal root torquing and intrusion of incisors, distal tipping of canines, and mesial tipping of second premolars, with more significant in the condition with canine attachments. With canine attachments, 1.2° overtreatment could cause bodily retraction of central incisors. Without overtreatment, stress was concentrated on apical and cervical area of both labial and lingual surfaces of periodontal ligaments. The stress value was higher with canine attachments. However, when overtreatment was added, the stress was distributed more evenly. CONCLUSIONS: Clear aligner therapy produced lingual tipping and extrusion of incisors during anterior retraction. Overtreatment can achieve incisor intrusion and palatal root torquing, and the effect could be augmented by adding attachments on canines, which required more anchorage from posterior teeth. Appropriate overtreatment with placing attachments on canines should be designed to ensure bodily retraction and the least root resorption.

Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners.

OBJECTIVES: To analyze the biomechanical system of anterior retraction with clear aligner therapy (CAT) with and without an anterior mini-screw and elastics. MATERIALS AND METHODS: Models including a maxillary dentition (without first premolars), maxilla, periodontal ligaments (PDLs), attachments, and aligners were constructed and imported to finite element software. Three model groups were created: (1) control (CAT alone), (2) labial elastics (CAT with elastics between the anterior mini-screw and buttons on central incisors), and (3) linguoincisal elastics (CAT with elastics between the anterior mini-screw and precision cuts on the lingual sides of the aligner). Elastic forces (0-300 g, in 50 g increments) were applied. RESULTS: CAT alone caused lingual tipping and extrusion of the incisors. Labial elastics caused palatal root torquing and intrusion and mesial tipping of the central incisors, while linguoincisal elastics produced palatal root torquing and intrusion of both central and lateral incisors. Second premolars were intruded in all three groups, with less intrusion in the linguoincisal elastics group. For the control group, stress was concentrated on both labial and lingual root surfaces, alveolar ridge, and cervical and apical PDLs. Stress was more concentrated in the labial elastics group and less concentrated in the linguoincisal elastics group. CONCLUSIONS: CAT produced lingual tipping and extrusion of incisors during anterior retraction. Anterior mini-screws and elastics can achieve incisor intrusion and palatal root torquing. Linguoincisal elastics are superior to labial elastics with a lower likelihood of buccal open bite. Root resorption and alveolar defects may occur in CAT, more likely for labial elastics and less likely for linguoincisal elastics.

Retrograde nerve growth factor signaling modulates tooth mechanical hyperalgesia induced by orthodontic tooth movement via acid-sensing ion channel 3.

Orthodontic tooth movement elicits alveolar bone remodeling and orofacial pain that is manifested by tooth mechanical hyperalgesia. Nerve growth factor (NGF) is upregulated in periodontium and may modulate tooth mechanical hyperalgesia. The objectives were to examine the role of NGF in tooth mechanical hyperalgesia and to elucidate the underlying mechanisms. Tooth mechanical hyperalgesia was induced by ligating closed coil springs between incisors and molars in Sprague-Dawley rats. Retrograde labeling was performed by periodontal administration of fluor-conjugated NGF and the detection of fluorescence in trigeminal ganglia (TG). Lentivirus vectors carrying NGF shRNA were employed to knockdown the expression of NGF in TG. The administration of agonists, antagonists, and virus vectors into TG and periodontium was conducted. Tooth mechanical hyperalgesia was examined through the threshold of biting withdrawal. Our results revealed that tooth movement elicited tooth mechanical hyperalgesia that could be alleviated by NGF neutralizing antibody and that NGF was upregulated in periodontium (mainly in periodontal fibroblasts) and TG. Retrograde labeling revealed that periodontal NGF was retrogradely transported to TG after day 1. Acid-sensing ion channel 3 (ASIC3) and NGF were co-expressed in trigeminal neurons and the percentage of co-expression was significantly higher following tooth movement. The administration of NGF and NGF neutralizing antibody into TG could upregulate and downregulate the expression of ASIC3 in TG, respectively. NGF aggravated tooth mechanical hyperalgesia that could be alleviated by ASIC3 antagonist (APETx2). Moreover, NGF neutralizing antibody mitigated tooth mechanical hyperalgesia that could be recapitulated by ASIC3 agonist (GMQ). NGF-based gene therapy abolished tooth mechanical hyperalgesia and downregulated ASIC3 expression. Taken together, in response to force stimuli, periodontal fibroblasts upregulated the expressions of NGF that was retrogradely transported to TG, where NGF elicited tooth mechanical hyperalgesia through upregulating ASIC3. NGF-based gene therapy is a viable method in alleviating tooth-movement-induced mechanical hyperalgesia.

Is platelet-rich plasma able to accelerate orthodontic tooth movement?

Objectives To examine whether periodontal injection of platelet-rich plasma (PRP) could accelerate orthodontic tooth movement.Methods A split-mouth randomised controlled clinical trial was conducted among 16 female participants. Canines were retracted on 0.017 x 0.025-inch stainless steel archwires through closed-coil springs attached on first molars with mini-screws for anchorage preservation. The intervention side received PRP + CaCl2 solution and the control side CaCl2 only. Intraligamental injections were performed during the canine retraction period every three weeks (zero, three and six weeks). The rate of canine retraction was assessed through superimposition of digital models every month for a total of four months. Assessment of associated pain was conducted by questionnaire.Results During the four-month period, a faster rate of canine retraction was detected on the intervention side only for the first month. Following cessation of PRP injections, the rate of canine retraction on the intervention side was initially slower than and then similar to that on the control side. An increase of pain was reported on both sides.Conclusions PRP could accelerate orthodontic tooth movement in the short term with no prolonged effects.

m6A regulator-mediated RNA methylation modification patterns are involved in immune microenvironment regulation of periodontitis.

The role of epigenetic regulation in immunity is emerging, especially for RNA N6-methyladenosine (m6A) modification. However, little is known about the role of m6A in the regulation of the immune microenvironment of periodontitis. Thus, we aim to investigate the impact of m6A modification in periodontitis immune microenvironment. The RNA modification patterns mediated by 23 m6A-regulators were systematically evaluated in 310 periodontitis samples. The impact of m6A modification on immune microenvironment characteristics was explored, including infiltrating immunocytes, immune reaction gene-sets and HLAs (human leukocyte antigen) gene. m6A phenotype-related immune genes were also identified. 17 m6A regulators were dysregulated and a 15-m6A regulator signature can well distinguish periodontitis and control samples. ALKBH5 and FMR1 are closely related to infiltrating monocyte abundance. ELAVL1 and CBLL1 are significant regulators in immune reaction of TNF_Family_Members_Receptors and Cytokine. The expression of HLA-B and HLA-DOA is affected by ALKBH5 and LRPPRC. 3 distinct RNA modification patterns mediated by 23 m6A regulators were identified. They differ from immunocyte abundance, immune reaction and HLA gene. 1631 m6A phenotype-related genes and 70 m6A-mediated immune genes were identified, and the biological functions of these were explored. Our finding demonstrated the m6A modification plays a crucial role in the diversity and complexity of the immune microenvironment of periodontitis.

A comparison of the effects of Forsus appliances with and without temporary anchorage devices for skeletal Class II malocclusion.

OBJECTIVES: To compare the effects of Forsus appliances with and without temporary anchorage devices (TADs) for patients with skeletal Class II malocclusion. MATERIALS AND METHODS: Through a predefined search strategy, electronic searching was conducted in PubMed, Embase, Web of Science, CENTRAL, ProQuest Dissertations & Theses, and SIGLE with no language restrictions. Eligible study selection, data extraction, and evaluation of risk of bias (Cochrane Collaboration tool) were conducted by two authors independently and in duplicate. Any disagreement was solved by discussion or judged by a third reviewer. Statistical pooling, sensitivity analysis, subgroup analysis, and assessment of small-study effects were conducted by using Comprehensive Meta-Analysis and Stata 12.0. Heterogeneity was analyzed for different types of study designs, TADs, and radiographic examinations. RESULTS: Electronic search yielded a total of 256 studies after removing duplicates. Among them, six studies were finally included. All articles were of high quality. The pooled mean differences were -0.27 (95% confidence interval [CI]: -0.59, 0.05) for SNA, 0.58 (95% CI: -0.07, 1.23) for SNB, -0.86 (95% CI: -1.74, -0.03) for ANB, 1.63 (95% CI: 0.46, 2.80) for Co-Po, 0.75 (95% CI: 0.28, 1.23) for SN-MP, -7.56 (95% CI: -11.37, -3.76) for L1-MP, 0.47 (95% CI: -0.98, 1.91) for overjet, 0.39 (95% CI: -0.57, 1.35) for overbite, -1.84 (95% CI: -5.15, 1.47) for SN-OP, and 4.97 (95% CI: -1.22, 11.17) for nasolabial angle. CONCLUSIONS: TADs (especially miniplates) were able to eliminate dental adverse effects of Forsus appliances for correction of skeletal Class II malocclusion.

Identification of immune-related lncRNAs in periodontitis reveals regulation network of gene-lncRNA-pathway-immunocyte.

BACKGROUND: Long noncoding RNAs (lncRNAs), which is essential in regulating multiple biological functions, have been found to have pivotal roles in immune regulation. Since immune reaction and immunocytes are the key part in periodontitis progression, we aim to investigate the underlying lncRNA-immunity regulatory network of periodontitis. METHODS: A series of bioinformatic algorithms were used to identify immune-related lncRNAs in periodontitis. Infiltrating immunocyte were calculated by MCP-count. Pathway activity were estimated by the GSVA. The relationships between immune-related lncRNA and periodontitis features were investigated including immune gene categories, perturbated lncRNAs, immunocytes and pathways. Immune-related periodontitis subtypes were identified by ConsensusClusterPlus algorithm. Immunocytes related gene-lncRNA modules were identified by WGCNA. RESULTS: An integrated algorithm and pipeline to identify immune-related lncRNAs was developed and 1059 immune-related lncRNAs in 14 immune categories were identified, 291 of them were perturbated in periodontitis. An independent validation set verified the robustness of immune-related lncRNAs. A higher proportion of immune-related lncRNAs are correlated with immunocyte infiltration. Pathways associated with immune-related lncRNAs were also revealed. Two distinct immune-related periodontitis subtypes were identified according to perturbated immune-related lncRNAs with different immune and clinical characteristics, in which subtype-1 has a higher infiltrated immunocytes, higher immune reaction scores and more chronic periodontitis samples. Immunocytes and clinical phenotypes matching their gene-lncRNA modules, and their functions were annotated. CONCLUSIONS: Our study systematically investigated periodontitis immune-related lncRNAs and have taken a glimpse of the underlying mechanism of periodontitis from gene-lncRNA-immunocyte networks, which can not only inspire researchers but also help in periodontitis related immune researches.