The effect of orthodontic tooth movement on the sensitivity of dental pulp: A systematic review and meta-analysis

The role of the endogenous opioid system in modulating orthodontic-induced neurogenic inflammation of the dental pulp: A comprehensive review of the literature

BACKGROUND

Orthodontic forces may lead to neurogenic inflammation in the dental pulp by triggering the release of somatosensory neuropeptides such as Substance P (SP), Calcitonin gene-related peptide (CGRP) and Neurokinin A (NKA). In the vast majority of patients, acute symptoms are not triggered, probably due to the control of the neurogenic inflammatory process exerted by endogenous opioid systems.

OBJECTIVE

This review aimed to assess the cellular and molecular mechanisms through which the endogenous opioid system modulates the orthodontic-induced neurogenic inflammation of the dental pulp and to identify potential mechanisms for endogenous control of pulp pain.

METHODS

A literature search was conducted in the databases Pubmed, ISI Web of Science and Scopus to find relevant studies using the keywords: "orthodontic movement," "opioids" and "neurogenic inflammation." Following the PRISMA and Amstar recommendations, studies were selected for the literature review.

RESULTS

After removing duplicated and irrelevant articles, and those that does not meet the inclusion criteria, 38 articles were selected and classified according to the opioid peptides analysed in relation to orthodontic movement and dental pulp.

DISCUSSION

Both peripheral and central pathways, via endogenous opioid systems such as somatostatin (SST), dynorphin, β-endorphin, methionine enkephalin, endocannabinoids and anti-inflammatory cytokines, modulate the neurogenic inflammation elicited by orthodontic movements. The bradykinin and monoaminergic systems also appear to display regulatory effects on pain response. These control mechanisms, however, may be insufficient in cases where severe orthodontic forces are applied, thus leading to asymptomatic irreversible pulpitis or necrosis.

CONCLUSION

The opioid system regulates neurogenic pulpal inflammation and pain at the level of the central and peripheral nervous systems by releasing endogenous substances, including SST, opioid peptides, endocannabinoids and anti-inflammatory cytokines.

Reliability of electric pulp test and thermal pulp test for assessing pulpal response in patients undergoing orthodontic treatment - A systematic review

OBJECTIVE

To assess the reliability of pulp sensibility tests in patients undergoing orthodontic treatment.

BACKGROUND

The orthodontic force may cause transient changes in pulp vasculature leading to alteration in its response threshold. This may vary with the type, duration and magnitude of forces used. Thus, it is imperative to monitor the pulp sensibility and vitality of teeth during the course of orthodontic treatment.

MATERIAL AND METHODS

Sources: PubMed, Web of Science, Embase, Scopus, Cochrane Central Register of Controlled trials, ClinicalTrials.gov, Clinical Trials Registry-India and OpenGrey. Randomized clinical trials and/or observational studies evaluating the pulp sensibility response of patients undergoing orthodontic treatment were included. Study characteristics, sample characteristics, methodology details, outcome assessment, and main results were recorded in excel sheet. The Newcastle-Ottawa scale (NOS) was used to assess risk of bias (ROB). Certainty of evidence was evaluated using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) tool.

RESULTS

Thirteen observational studies were included. Total number of participants who underwent orthodontic treatment was 2956 (average age 17.53±3.81 years). The type and duration of orthodontic force was variable in the different studies. The pulp sensibility response was assessed using either Electric pulp test (EPT), or Thermal pulp test (TPT), or both. Pulp response threshold increased after application of orthodontic force, with number of negative responses peaking at about 2-3 months. Most of the studies presented with a high ROB. The certainty of evidence was considered low.

CONCLUSIONS

Based on limited comparative data, TPT was considered more reliable than EPT and that the pulp response threshold increased after application of orthodontic force, peaking at about two or three months. PROSPERO database (CRD42022307390).

Evaluation of pulpal blood flow during orthodontic space closure: Prospective clinical trial

INTRODUCTION

Orthodontic tooth movement (OTM) is a biological process that can affect the vascularization of the dental pulp. The forces exerted on the teeth may increase periapical pressure that could compress the arterioles, which in turn affects pulpal blood flow (PBF). The study aimed to investigate how OTM affects PBF during orthodontic space closure.

METHODS

A total of 22 adolescent participants who required orthodontic space closure in mandibular posterior sectors were enrolled in a prospective clinical study. The same sliding mechanics, wires, and active elements were used. Patients were observed before OTM, after leveling before space closure, and at the 4th, 7th, 21st, and 28th during active space closure. PBF was measured with laser Doppler (LD) flowmetry. Dental models were obtained with an intraoral scanner.

RESULTS

The LD flow values decreased significantly during the observation period (2-way repeated measures analysis of variance, P <0.001). There was a significant difference in LD flow between tooth categories (2-way repeated measures analysis of variance, P <0.001). During space closure, the most pronounced LD flow reduction was observed in single-rooted teeth closest to the residual space. A higher speed of OTM was associated with a greater decrease in LD flow on day 4 of OTM (Pearson correlation, P = 0.0299).

CONCLUSIONS

Orthodontic space closure reduced PBF; it was lowest in the early stages of space closure and showed a tendency to increase during the first month. Anterior teeth closer to the interdental space that experiences more OTM and teeth that move faster during initial OTM had a higher risk of reduced blood flow.

How does orthodontic tooth movement influence the dental pulp? RNA-sequencing on human premolars

OBJECTIVES

The objective of this study is to analyse the gene expression profile of the dental pulp (DP) of human premolars subjected to 7 and 28 days of orthodontic force (OF) in vivo by using RNA sequencing. The maxillary and mandibular DP were additionally compared.

METHODS

Healthy patients requiring orthodontic premolar extractions were randomly assigned to one of the three groups: control (CG) where no OF was applied, 7 and 28 days, where premolars were extracted either 7 or 28 days after the application of a 50-100 g OF. Total RNA was extracted from the DP and analysed via RNA-seq. Differentially expressed genes (DEGs) were identified using a false discovery rate and fold change threshold of <0.05 and ≥1.5, respectively. Functional analysis was performed.

RESULTS

After 7 days of OF, pulp reaction indicates immune response, hypoxia, DNA damage and epigenetic regulation. After 28 days, cell adhesion, migration, organization and tissue repair are evident. The maxillary and mandibular pulp tissues react differently to OF. The maxilla exhibits minimal alterations, mostly related to immune response at 7 days and tissue repair at 28 days, whereas the mandible shows mostly DNA damage and epigenetic regulation at 7 days and return to the original state at 28 days.

CONCLUSIONS

This study demonstrates that the early reaction of the DP to OF is marked by immune response, hypoxia and DNA damage. In contrast, after 28 days, cell adhesion, migration, organization, tissue repair and dentine formation are observed. Maxillary and mandibular premolars react differently to OF: although the maxilla exhibits minimal alterations at both time points, the mandible mostly shows DNA damage, epigenetic regulation, and immune response at 7 days. These disparities could stem from different blood supplies or the lower maxillary bone density, potentially triggering faster biological changes. Our findings provide insights into the gene regulatory networks modulating DP response to OF.

Effect of orthodontic space closure on dental pulp sensitivity. Prospective clinical trial

BACKGROUND

Orthodontic tooth movement (OTM) is a biological process that can influence the function of the pulp, including its innervation. The excitability of the nerve fibres of the pulp may be altered by forces exerted on the nerve fibres or by reduced blood flow to the pulp. The aim of this clinical study was to evaluate the sensitivity of the dental pulp during levelling and during the phase of space closure, to assess the role of certain controlled risk factors.

METHODS

Twenty-two adolescent participants requiring orthodontic space closure in transcanine sector were enrolled in a prospective clinical study. Patients were observed before OTM, after levelling and 1 month during active space closure. The sensitivity threshold of the pulp was measured using the electric pulp test (EPT). Dental models were obtained using an intraoral scanner, allowing measurement of interdental distances and calculation of OTM speed. The teeth were categorized according to position and tooth type.

RESULTS

The EPT values increased significantly during orthodontic treatment (one-way RM-ANOVA, P = .014). There was a significant difference in EPT values between the tooth categories. Teeth with a single root adjacent to the residual space had the highest EPT thresholds (two-way RM-ANOVA, P < .001; Holm-Sidak, P < .05).

CONCLUSIONS

OTM reduced pulpal sensitivity. Pulpal sensitivity during active space closure was similar to sensitivity during the levelling phase. The pulpal sensitivity of molars was less affected by OTM than that of single-rooted teeth, while teeth closer to the gap had a significantly higher pulpal sensitivity threshold during active OTM.

Abrasion and dental pulp morphological changes in occlusal dysfunction

AIM

The authors set out to assess if the presence and the degree of severity of the abrasion, as a consequence of the occlusal dysfunction, determine further morphological changes in the dental pulp.

MATERIALS AND METHODS

Study group included teeth dental pulp from 45 cases with occlusal dysfunction, subsequently divided into two subgroups: 24 cases with abrasion (AB) and 21 cases without abrasion (NONAB). The set of morphological parameters of dental pulp were thicknesses of the outer layer, inner layer and entire peripheral pulp zone, the presence of pulpal calcifications and their extent within the dental pulp, the presence of interstitial fibrosis and its extent within the dental pulp and the vascular density (VD) of pulpal capillary network. Tissue samples were fixed in 10% buffered formalin, embedded in paraffin, and sectioned off at 4 μm. Serial slides were stained with Hematoxylin-Eosin (HE), Masson's trichrome (MT) and anti-cluster of differentiation 34 (CD34) antibodies labeled with 3,3'-Diaminobenzidine (DAB) and transformed into virtual slides on which the above-mentioned parameters were studied comparatively with the help of a dedicated in-house software, realized in MATLAB (MathWorks, USA). The numerical values of the assessed parameters were also stratified in classes, thus obtaining score scales for each parameter. Statistical tools used were Lilliefors test, t-test (two-sample assuming equal variances), Mann-Whitney test, Pearson's correlation test, one-way analysis of variance (ANOVA) test and χ² (chi-squared) test.

RESULTS AND DISCUSSIONS

Both peripheral zone (PZ) and its layers individually tended to be thicker in the teeth with abrasion than in those without abrasion. Also, teeth with abrasion tended to develop larger amounts of calcium deposits in their dental pulp than teeth without abrasion. On the other hand, fibrotic tissue in dental pulp had no relationship with the presence or absence of abrasion. PZ as a whole and its layers evolved together in the same way, with a stronger correlation in the group of teeth without abrasion. Deposits of calcium evolved in the opposite direction to both the amount of fibrous tissue and the capillaries density of the dental pulp. Consequently, the amount of fibrous tissue and VD evolved together in the same way, more pronounced in the teeth without abrasion.

CONCLUSIONS

Our preliminary study pointed out that different components of the dental pulp showed slight to moderate changes depending on the degree of abrasion in teeth with occlusal dysfunction.

Orthodontics and Endodontics Clinical Practice Correlation: A Narrative Review

Research on the connection between endodontic therapy and orthodontics is lacking. This overview of the literature synthesizes the findings from the fields of orthodontics and endodontics and explains how they are related. Beginning with the diagnosis, treating the patient at the appropriate time, moving endodontically treated teeth and traumatized teeth, resorbing roots by orthodontic mechanics, and managing traumatized teeth with orthodontic therapy. Multiple electronic databases were utilized including (PubMed, Scopus, Science Direct, and Web of Science) to perform manual literature searches. A total of 31 articles were reviewed and summarized in this paper in keywords like "Endodontically Treated Teeth and Orthodontic Treatment," "Endodontically Treated Tooth and Orthodontic Movement," "Orthodontic Treatment in RCT Teeth," "Root Canal Treatment with Orthodontic Movement," "Trauma with Orthodontic Movement," "Orthodontic and Endodontic." Orthodontic treatment of endodontically treated and traumatized teeth is a subject of controversy. The lack of research on the topic makes it a hard decision to make when to treat these teeth. Especially given that both orthodontic and endodontic treatments have multiple consequences on each other's outcomes. Thus, it is crucial for clinicians to understand how they integrate and have a guideline to refer to during decision-making. Successful orthodontic tooth movement could be carried out immediately after endodontic treatment. However, traumatized teeth need a follow-up period before initiating orthodontic movement, which ranges from three months to 12 months depending on the type of trauma and severity. Careful radiographic and clinical follow-up should be done during the healing period. Collaborative teamwork is important between orthodontists and endodontists for the success of treatment, and to achieve satisfactory outcomes.

Endodontic-orthodontic interactions: a review and treatment recommendations

The literature is replete with articles describing the many and varied interactions between endodontic treatment and orthodontic tooth movement (OTM), often reporting conflicting views and findings, which creates confusion for clinicians. Original research and review articles have described aspects such as apical root resorption and potential pulpal complications of teeth related to OTM. Some interactions are of relatively minor clinical significance, whilst others may have adverse consequences. A history of dental trauma before or during OTM further complicates the interactions. This review re-assesses the historical literature on endodontic-orthodontic interactions in light of more recent research and presents guidelines for managing clinical situations involving both disciplines. © 2023 Australian Dental Association.