Association between root resorption and tooth development: A quantitative clinical study

CDC42-mediated Wnt signaling facilitates odontogenic differentiation of DPCs during tooth root elongation

BACKGROUND

CDC42 is a member of Rho GTPase family, acting as a molecular switch to regulate cytoskeleton organization and junction maturation of epithelium in organ development. Tooth root pattern is a highly complicated and dynamic process that dependens on interaction of epithelium and mesenchyme. However, there is a lack of understanding of the role of CDC42 during tooth root elongation.

METHODS

The dynamic expression of CDC42 was traced during tooth development through immunofluorescence staining. Then we constructed a model of lentivirus or inhibitor mediated Cdc42 knockdown in Herwig's epithelial root sheath (HERS) cells and dental papilla cells (DPCs), respectively. Long-term influence of CDC42 abnormality was assessed via renal capsule transplantation and in situ injection of alveolar socket.

RESULTS

CDC42 displayed a dynamic spatiotemporal pattern, with abundant expression in HERS cells and apical DPCs in developing root. Lentivirus-mediated Cdc42 knockdown in HERS cells didn't disrupt cell junctions as well as epithelium-mesenchyme transition. However, inhibition of CDC42 in DPCs undermined cell proliferation, migration and odontogenic differentiation. Wnt/β-catenin signaling as the downstream target of CDC42 modulated DPCs' odontogenic differentiation. The transplantation and in situ injection experiments verified that loss of CDC42 impeded root extension via inhibiting the proliferation and differentiation of DPCs.

CONCLUSIONS

We innovatively revealed that CDC42 was responsible for guiding root elongation in a mesenchyme-specific manner. Furthermore, CDC42-mediated canonical Wnt signaling regulated odontogenic differentiation of DPCs during root formation.

Under pressure-mechanisms and risk factors for orthodontically induced inflammatory root resorption: a systematic review

BACKGROUND

The application of orthodontic forces causes root resorption of variable severity with potentially severe clinical ramifications.

OBJECTIVE

To systematically review reports on the pathophysiological mechanisms of orthodontically induced inflammatory root resorption (OIIRR) and the associated risk factors based on in vitro, experimental, and in vivo studies.

SEARCH METHODS

We undertook an electronic search of four databases and a separate hand-search.

SELECTION CRITERIA

Studies reporting on the effect of orthodontic forces with/without the addition of potential risk factors on OIIRR, including (1) gene expression in in-vitro studies, the incidence root resorption in (2) animal studies, and (3) human studies.

DATA COLLECTION AND ANALYSIS

Potential hits underwent a two-step selection, data extraction, quality assessment, and systematic appraisal performed by duplicate examiners.

RESULTS

One hundred and eighteen articles met the eligibility criteria. Studies varied considerably in methodology, reporting of results, and variable risk of bias judgements.In summary, the variable evidence identified supports the notion that the application of orthodontic forces leads to (1) characteristic alterations of molecular expression profiles in vitro, (2) an increased rate of OIIRR in animal models, as well as (3) in human studies. Importantly, the additional presence of risk factors such as malocclusion, previous trauma, and medications like corticosteroids increased the severity of OIIRR, whilst other factors decreased its severity, including oral contraceptives, baicalin, and high caffeine.

CONCLUSIONS

Based on the systematically reviewed evidence, OIIRR seems to be an inevitable consequence of the application of orthodontic forces-with different risk factors modifying its severity. Our review has identified several molecular mechanisms that can help explain this link between orthodontic forces and OIIRR. Nevertheless, it must be noted that the available eligible literature was in part significantly confounded by bias and was characterized by substantial methodological heterogeneity, suggesting that the results of this systematic review should be interpreted with caution.

REGISTRATION

PROSPERO (CRD42021243431).

[Evaluation of root resorption after surgical orthodontic treatment of skeletal Class Ⅲ malocclusion by three-dimensional volumetric measurement with cone-beam CT]

OBJECTIVE

To explore the method of measuring root volume with cone-beam computed tomography (CBCT) three-dimensional reconstruction technology, and to study root length and root volume of upper and lower central incisors in patients with skeletal Class Ⅲ malocclusion treated by surgical orthodontic treatment.

METHODS

Twenty patients with skeletal Class Ⅲ malocclusion undergoing surgical orthodontic treatment were selected. CBCT data at three time points, before decompensation treatment (T0), after decompensation treatment (before orthognathic surgery, T1), and the end of post-operative orthodontic treatment (T2) were collected. Three-dimensional reconstruction technology was used to measure the root length and root volume of the upper and lower central incisors (including total root volume, cervical root and apical root), calculate the percentage of reduction volume, and measure the distance of tooth movement after orthodontic treatment. Data were statistically analyzed by SPSS 20.0 software. Least significant difference (LSD) method was used for pair comparison between the groups subject to normal distribution, and non-parametric test was used for comparison between the groups not subject to normal distribution. The differences of root length and root volume of upper and lower incisors were compared, and the characteristics of root absorption were analyzed.

RESULTS

Root length and root volume of the upper and lower central incisors were reduced during the surgical orthodontic treatment (P < 0.05) in cases. Both the root volume of cervical root and apical root were significantly reduced (P < 0.05), the reduction of apical root was more significant. The percentage of root volume reduction of the upper central incisor was (30.51±23.23)%, and lower central incisor (23.24±11.96)%. Compared with the upper central incisor, the root volume reduction amount and percentage of the lower central incisor were smaller, and apical root volume reduction of the upper central incisor was greater than that of the lower central incisor, which was statistically significant (P < 0.05). During pre-surgical orthodontic treatment, maxillary central incisor palatal moving was in a controlled tipping manner, and the mandibular central incisor tipped labially.

CONCLUSION

In patients with skeletal Class Ⅲ malocclusion, root length and total root volume of upper and lower central incisors decreased during surgical orthodontic treatment. Root volume measurement indicated that the cervical root also had root resorption. The difference in root resorption of the upper and lower central incisors might be related to the distance and direction of teeth movement. CBCT three-dimensional reconstruction will compensate for the limitation of root length measurement in evaluating root resorption.

Wnt5a-Ror2 signaling mediates root resorption

INTRODUCTION

This study aimed to investigate the role of wingless-type MMTV integration site family member 5a (Wnt5a)-receptor tyrosine kinase-like orphan receptor 2 (Ror2) signaling in root resorption.

METHODS

The messenger RNA (mRNA) expression of Wnt5a, Ror2, and RANKL in periodontal ligament cells (PDLCs) under compression force (CF) with or without Ror2 small interfering RNA (siRNA) were measured by quantitative reverse transcription-polymerase chain reaction, and these proteins released into culture supernatants were measured using enzyme-linked immunosorbent assay. Then these PDLC-conditioned media under CF with or without Ror2 siRNA were used to culture osteoclast precursors to detect osteoclastogenesis effects via tartrate-resistant acid phosphatase staining. In in vivo studies, the odontoclast number and the root resorption volume under excessive CF with or without Ror2 siRNA were investigated by tartrate-resistant acid phosphatase immunohistochemical staining and microcomputed tomography. The protein levels for Wnt5a, Ror2, and receptor activator of nuclear factor-kappa B ligand (RANKL) in the periodontal ligament tissues were also detected using immunohistochemical staining. Finally, the odontoclast number, root resorption volume, and the mRNA and protein expressions were compared between immature and mature teeth.

RESULTS

The mRNA production and protein release level of Wnt5a, Ror2, and RANKL increased after CF, whereas they were significantly downregulated with Ror2 siRNA. The osteoclast number increased treating with culture medium from PDLC applying CF, but the increase was inhibited after adding Ror2 siRNA. In the animal model, the odontoclast number and root resorption volume significantly increased in the CF group but decreased in the CF with the Ror2 siRNA group. The protein levels of Wnt5a, Ror2, and RANKL in periodontal ligament were upregulated under excessive CF, and the pathway was inhibited with Ror2 siRNA. In the immature tooth group, the odontoclast number, root resorption volume, and the mRNA and protein expressions of Wnt5a-Ror2 signaling were reduced.

CONCLUSIONS

Wnt5a-Ror2 signaling in PDLCs enhanced by excessive CF could promote RANKL release and induce precursor differentiation, partly leading to increased odontoclast activity and ultimate root resorption. The less resorption of the immature tooth may be due to odontoclastogenesis inhibition by decreased expression of Wnt5a-Ror2 signaling.

Orthodontic root resorption

External apical root resorption (EARR) is one of the most frequently reported iatrogenic side effects of orthodontic movement. Nevertheless, no robust and unequivocal scientific evidence is yet available in the literature regarding the clinical and biological factors that trigger EARR. The purpose of the present position paper is to provide clinicians, residents, and investigators a summary of our current understanding about root resorption caused by orthodontic tooth movement, based on up-to-date available scientific evidence. Morphological, structural, biomechanical, and biological differences account for predisposing the apical third to EARR compared to other root surfaces during orthodontic treatment. In addition, a relevant number of patient and treatment-related factors increase risk of EARR. The main patient-related factors are reviewed and discussed: genetic factors, tooth anatomy, demographic factors, malocclusion factors, previous endodontic treatment, medical history, short root anomaly. Similarly, the influence of treatment-related factors are analyzed with regard to the effect of: biomechanical factors, type of orthodontic appliance, adjunctive therapies to accelerate tooth movement, early treatment, maxillary expansion, teeth extractions, the duration of treatment and the amount of apical displacement. Clinical management of EARR from pre-treatment records to the monitoring strategy as well as recommendations for the post orthodontic-treatment period are presented as a guide for the clinician. Despite years of studies, we still do not fully understand EARR, but the future is promising. True three-dimensional imaging with higher resolution and low radiation, and predictive tools towards an earlier detection without radiographs, will mark future developments in the field of EARR in orthodontics.

An Assessment of the Effects of Orthodontic Treatment after Apexification of Traumatized Immature Permanent Teeth: A Retrospective Study

INTRODUCTION

Root resorption may occur in traumatized necrotic teeth that have undergone apexification after orthodontic treatment. This study examined the effects of orthodontic treatment on the outcome of apexification.

METHODS

This retrospective study included 36 children presenting with anterior permanent traumatized teeth with immature roots who were treated by apexification and root canal treatment. The orthodontic group consisted of 17 children with 24 teeth that were subjected to orthodontic treatment after apexification. The control group consisted of 19 children with 21 teeth that underwent only apexification without orthodontic treatment. Almost half of the teeth in both groups underwent apexification with calcium hydroxide, whereas the other half were treated with mineral trioxide aggregate. The effects of sex, stage of root development, and apexification material on the outcomes of apexification were analyzed and compared between the 2 groups.

RESULTS

Apexification was successful in 88% of cases after at least 5 years of follow-up. Neither apexification technique nor sex had a significant effect on treatment outcome. The stage of root development had a positive effect on outcome, although it was not statistically significant. Some root resorption (average = 0.3 mm) was observed after orthodontic treatment, whereas teeth that underwent apexification without orthodontic treatment exhibited some root elongation (average = 0.1 mm). This difference was highly significant.

CONCLUSIONS

Minor root resorption was observed in the orthodontic group compared with a minor increase in root length in the control group. Orthodontic movement of immature traumatized teeth after apexification appears to be safe.

X-linked hypophosphatemic rickets: Orthodontic considerations and management. A case report

X-linked hypophosphatemic rickets (XLH) is a rare condition affecting bone metabolism. It has characteristic dental features such as poorly mineralised dentine, spontaneous abscess formation in the absence of caries and taurodontism. There are limited published data about patients with this condition undergoing orthodontic treatment, and there is no clear guideline on the suitability of orthodontic treatment in this cohort. We present a case report of a patient with XLH with a confirmed PHEX gene mutation undergoing orthodontic treatment and clinical recommendations to support treatment.

Evaluation of apical root resorption in Class III patients who received one- or two-phase orthodontic treatment

Objectives:

The aim of this study was to compare the incidence root resorption and dilaceration between the patients with and without previous orthopedic treatment after the fixed orthodontic treatment.

Materials and Methods:

The pre- and post-treatment digitized panoramic films of 40 Class III adult patients meeting the inclusion criteria were selected from patient population of the orthodontic department. Half of the patients were treated with two-phase treatment (orthopedic therapy followed by fixed appliance treatment; Group 1), while the others wore only fixed appliances (Group 2). Root resorption was evaluated from the first molar to the first molar for each arch using the ImageJ software (Bethesda, Maryland, USA). The presence of root dilacerations was also recorded on the pre-treatment panoramic radiographs. Paired samples t-test and Mann– Whitney U-test were used to compare root length.

Results:

Intragroup comparisons for each tooth indicated that the upper and lower incisors, first molars and upper left second premolars presented a significant decrease in Group 1 (P < 0.05). In contrast, in Group 2, a significant decrease in tooth length was found only in the upper incisors (P < 0.05). Intergroup comparisons for root length change indicated statistically significant differences for the lower incisors, upper second premolars, and all first molars except for the upper left molars (P < 0.05). Nevertheless, the prevalence of root dilaceration in Group 1 was higher than that in Group 2.

Conclusion:

Class III patients who received two-phase treatments experienced more root resorption and dilaceration compared with patients who received one-phase treatments. It should be remembered that early orthopedic forces may have potential adverse effects on a dental root in the long-term.

Notch signaling inhibition protects against root resorption in experimental immature tooth movement in rats

INTRODUCTION

This study aimed to build an experimental immature tooth movement model and verify less resorption of incompletely developed roots than those fully developed during the same orthodontic treatment, followed by investigating the cellular and molecular mechanism.

METHODS

The development of Wistar rat tooth was investigated using in vivo microcomputed tomography and hematoxylin and eosin staining to decide the optimal ages of rats for immature tooth and mature tooth groups. The rats in the immature tooth and mature tooth groups were divided into experimental, sham control, and blank control groups. After orthodontic treatment for 3 weeks, the mesial root volume, crown movement distance, neck movement distance, root inclination, and apical distance were measured by microcomputed tomography. The expressions of TRAP, Jagged1, Notch2, IL-6, and RANKL were analyzed by immunohistochemical staining and real-time polymerase chain reaction. The repair of root resorption was also investigated after removing orthodontic force for 3 and 6 weeks.

RESULTS

The root achieved the development stage around 10 weeks, so 4-week-old rats and 10-week-old rats were used in the immature tooth group and mature tooth group, respectively. The volume of root resorption in the experimental immature tooth group was 0.0869 ± 0.0244 mm³, which was less than that in the mature tooth group (0.1218 ± 0.0123 mm³) (P <0.001). Immature tooth movement decreased TRAP-positive odontoclasts on the compression side while having no statistically significant effect on osteoclasts. The protein expression of Jagged1, Notch2, IL-6, and RANKL in the mature tooth group increased significantly compared with the immature tooth group, not only on the compression side but also on the tension sides. The mRNA expression of Jagged1, Notch2, and RANKL was significantly lower in the immature tooth group, whereas the expression of IL-6 had no significance but a strong tendency. The root volume after repairing for 3 weeks was still less than that of blank control, whereas after repairing for 6 weeks, the difference was not statistically significant.

CONCLUSIONS

The experimental immature tooth movement model for the Wistar rat was achieved for the first time. The immature tooth will suffer less root resorption than the mature tooth, which may be due to odontoclastogenesis inhibition by decreased expression of Jagged1/Notch2/IL-6/RANKL signaling.