Response of human pulpal tissue to orthodontic extrusive applications

Leveling the curve of Spee using different sized archwires: a randomized clinical trial of blood flow changes

OBJECTIVES

To compare blood flow (BF) changes of teeth subjected to orthodontic forces during curve of Spee (COS) leveling using different archwires (AW).

MATERIAL AND METHODS

Thirty subjects with COS > 5 mm were randomly assigned (1:1:1) into three groups based on the AW used: group 1: 0.017 × 0.025-inch stainless-steel (SS)AW, group 2: 0.019 × 0.025-inch SSAW, and group 3: 0.021 × 0.025-inch β-titanium (TMA)AW. In the 3 groups, a 5 mm-depth reverse COS was placed in the AWs. A laser Doppler flowmeter was used to measure BF at different time intervals (T0-T4).

RESULTS

In the 3 AWs group, BF of all measured teeth was reduced 20 min after force application. Afterwards, the BF values started to increase until the baseline values were almost restored within 1 week. Differences in BF changes between the extrusion and intrusion subgroups were observed within groups 1 and 3 during the first 20 min of force application (P < 0.05). Similar BF changes were recorded using the 3 different AWs. BF changes were associated with tooth type and the amount of COS depth change.

CONCLUSIONS

During CoS leveling, similar BF changes were recorded using the 3 different AWs. Tooth type and the amount of COS depth change were associated with BF changes within the first 20 min of force application. Greater BF reduction was found in premolars compared to incisors during the first 20 min of AW placement.

CLINICAL RELEVANCE

It is important to select a type of applied forces that minimally affect the BF. Intrusive forces appeared to have lower negative effects on the BF of teeth during COS leveling.

TRIAL REGISTRATION

ClinicalTrial.gov (# NCT04549948).

Adverse effects of orthodontic forces on dental pulp. Appearance and character. A systematic review

OBJECTIVE

To comprehensively assess recent data on the effects of orthodontic forces on the dental pulp and to critically evaluate, whether any of the changes are permanent.

MATERIALS AND METHODS

Articles published between 2/2009 and 2/2022 were searched electronically on the PubMed, EMBASE and SCOPUS databases. The initial search retrieved 780 publications and, applying the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 33 relevant articles were identified. Twenty articles fulfilled the requirements for high (n = 1) or moderate (n = 19) methodological quality and were included. All assessments were made independently by three researchers.

RESULTS

Orthodontic forces appeared to cause a reduction in pulpal blood flow and a reduction in tooth sensibility, as indicated by increased response thresholds and increased amounts of negative responses to tooth sensibility tests. In addition, there were increases in the expression or activity levels of enzymes and neuropeptides associated with hypoxia and inflammation. Fibrotic tissue formation in the pulp was also reported.

CONCLUSIONS

Except for some histological and morphological alterations, the observed pulpal changes were in most cases only temporary, appearing within days of initiating the treatment and usually lasting for weeks. There were no clear signs of permanent damage.

Pulp blood flow changes in maxillary and mandibular anterior teeth after orthodontic retraction: a prospective study

Background

Previous studies of pulpal blood flow (PBF) changes in anterior teeth have been limited in the early phase of orthodontic treatment; less is known about the blood supply of anterior teeth in bimaxillary protrusion patients after orthodontic retraction.

Methods

Fifty bimaxillary protrusion patients (25 orthodontic patients ready for debonding and 25 non-orthodontic patients) were selected as study participants. The PBF of maxillary and mandibular anterior teeth were measured using laser Doppler flowmetry. For orthodontic patients, the PBF was measured at 1 day (T1), 1 month (T2), and 3 months (T3) after fixed appliance removal. Non-orthodontic patient PBF was measured as a control. Cone-beam computed tomography (CBCT) examinations before and after orthodontic treatment were performed for orthodontic patients to measure the root resorption. The anterior teeth in orthodontic group were further divided into subgroups according to root resorption and patient age.

Results

At T1 and T3, PBF changes did not differ significantly between the orthodontic and non-orthodontic groups. Maxillary lateral incisor, maxillary central incisor, and mandibular lateral incisor PBFs at T2 were significantly higher in the orthodontic group (P = 0.048, P = 0.04, and P = 0.021). No significant difference in PBF was found between the root resorption and non-resorption subgroups at any time point. Adolescent patients showed a higher PBF in the maxillary lateral incisor at T2 (12.23 ± 3.48) relative to that at T1 (9.10 ± 3.76) and T3 (9.81 ± 2.80) with statistically significant difference (P = 0.020).

Conclusion

For bimaxillary protrusion patients with four premolars extraction, PBF in the maxillary anterior teeth increased transiently after orthodontic appliance removal and then returned to non-orthodontic levels 3 months later. This effect was more pronounced in adolescents. The PBF of anterior teeth after orthodontic retraction may not be influenced by root resorption.

Association between Periodontitis and Pulp Calcifications: Radiological Study

Objective

The presence of intrapulpal calcifications is one of the effects reported as a consequence of periodontal pathology. Although the impact of the pulp pathology on the periodontium is obvious, the contrary remains unclear and controversial. This study was conducted in order to better understand this fact and establish a potential association between periodontitis and intrapulpal calcifications and then to determine the factors associated with their occurrence.

Materials and Methods

To investigate the issue, a retrospective radiological study using periapical preoperative radiographics assessed 332 teeth taken from the records of 79 patients who received treatment for periodontitis. In the second part of the study, 81 of the sample with intact dental crowns presenting an attachment loss were compared to their contralateral with intact dental crowns without any attachment loss. The study of the association between periodontitis and intrapulpal calcifications and the factors associated with their occurrence was performed by the Chi squared and Fisher's exact tests. The significance level was set at 0.05.

Results

The results indicated that 251 (75.6%) teeth had an attachment loss while 102 (30.7%) had intrapulpal calcification. Among the 206 (62%) teeth with intact crown, only 6 (1.8%) showed calcification in the pulp cavity and 20 (6%) showed calcification in the root canals, with a statistically significant difference (p < 0.005) compared to teeth with restorations and caries. For the 32 (19.7%) teeth with coronary calcification, 18 (22.2%) presented an attachment loss versus 14 (17.2%) without attachment loss; the difference was not statistically significant (p=0.6). Similarly, only 13 (16%) of a total of 22 (13.5%) teeth with root canal calcification had attachment loss versus 9 (11.1%) without attachment loss. This difference was not statistically significant (p=0.5).

Conclusion

This radiographic study revealed no association between the presence of periodontitis and the occurrence of intrapulpal calcifications. Although intrapulpal calcifications were present in some teeth with loss of attachment, they were not necessarily the consequence of periodontal disease.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells (MSCs) have attracted intense interest in the field of dental tissue regeneration. Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures. MSCs possess distinct inherent properties of self-renewal, immunomodulation, proangiogenic potential, and multilineage potency, as well as being readily available and easy to culture. However, major issues, including poor engraftment and low survival rates in vivo, remain to be resolved before large-scale application is feasible in clinical treatments. Thus, some recent investigations have sought ways to optimize MSC functions in vitro and in vivo. Currently, priming culture conditions, pretreatment with mechanical and physical stimuli, preconditioning with cytokines and growth factors, and genetic modification of MSCs are considered to be the main strategies; all of which could contribute to improving MSC efficacy in dental regenerative medicine. Research in this field has made tremendous progress and continues to gather interest and stimulate innovation. In this review, we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration, antiapoptotic effect, proangiogenic potential, and regenerative properties. Challenges in current approaches associated with MSC modification and possible future solutions are also indicated. We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

Effect of orthodontic force on dental pulp histomorphology and tissue factor expression

OBJECTIVES

To evaluate the effects of orthodontic force on histomorphology and tissue factor expression in the dental pulp.

MATERIALS AND METHODS

Two reviewers comprehensively and systematically searched the literature in the following databases: Latin American and Caribbean Health Sciences, Embase, Cochrane, PubMed, Scopus, Web of Science, and Grey literature (Google Scholar, OpenGrey, and ProQuest) up to September 2020. According to the Population, Intervention, Comparison, Outcomes, Studies criteria, randomized clinical trials (RCTs) and observational studies that evaluated the effects of orthodontic force on dental pulp were included. Case series/reports, laboratory-based or animal studies, reviews, and studies that did not investigate the association between orthodontic force and pulpal changes were excluded. Newcastle-Ottawa Scale and Cochrane risk-of-bias tool were used to assess the risk of bias. The overall certainty level was evaluated with the Grading of Recommendations Assessment, Development and Evaluation tool.

RESULTS

26 observational studies and five RCTs were included. A detailed qualitative analysis of articles showed a wide range of samples and applied methodologies concerning impact of orthodontic force on the dental pulp. The application of orthodontic force seems to promote several pulpal histomorphological changes, including tissue architecture, cell pattern, angiogenesis, hard tissue deposition, inflammation, and alteration of the expression levels of 14 tissue factors.

CONCLUSIONS

Although the included articles suggest that orthodontic forces may promote histomorphological changes in the dental pulp, due to the very low-level of evidence obtained, there could be no well-supported conclusion that these effects are actually due to orthodontic movement. Further studies with larger samples and improved methods are needed to support more robust conclusions.

Pulp volume changes after piezocision-assisted tooth movement: a randomized clinical trial

Background

Orthodontic treatment may result in undesirable side effects, such as root resorption and a decrease in the size of the pulp tissue which could be associated with the duration of the orthodontic treatment. Piezocision-assisted tooth movement was introduced as a minimally invasive surgical procedure to shorten orthodontic treatment time. This prospective randomized clinical trial was aimed to compare the pulp volume changes of maxillary anterior teeth after en-masse retraction with or without piezocision-assisted orthodontics.

Methods

Patients who required orthodontic treatment with bilateral maxillary first premolar extractions and en-masse retraction were recruited. Patients were randomly divided into extraction with piezocision, or only extraction, serving as controls. Pulp volume and root length changes of the maxillary six anterior teeth were measured and compared between the two groups using a 3-Dimensional analytical software. Paired and independent sample t-tests were used to compare within and between groups. Bivariate correlation was done between the mean change in pulp volume and its corresponding root length. The significance level was set at α = 0.05.

Results

A total of 23 patients were included, 12 in the piezocision, and 11 in the control group. At the end of the en-masse retraction phase, (mean = 122.74 ± 3.06 days) pulp volume was significantly decreased in all six anterior teeth in both groups (P < 0.01). The decrease in pulp volume was not statistically different between both groups, (P > 0.05). There was a statistically significant but moderate correlation only between the pulp volume change of the right canine and its root length, r = 0.44, P = 0.034.

Conclusions

The effect of piezocision-assisted orthodontic tooth movement on the pulp volume was comparable to the conventional orthodontic treatment. The degree of change in pulp volume does not appear to be related to the amount of root resorption.

Trial registration NCT03180151. Registered December 25, 2016, retrospectively registered, https://clinicaltrials.gov/ct2/show/record/NCT03180151.

Human Dental Pulp Tissue during Orthodontic Tooth Movement: An Immunofluorescence Study

The orthodontic tooth movement is the last step of several biological processes that take place after the application of external forces. During this process, dental pulp tissue is subjected to structural and protein expression modifications in order to maintain their integrity and functional morphology. The purpose of the present work was to perform an in vivo study, evaluating protein expression modifications in the human dental pulp of patients that have undergone orthodontic tooth movement due to pre-calibrated light force application for 30 days. Dental pulp samples were extracted from molars and premolars of the control group and after 7 and 30 days of treatment; the samples were then processed for immunofluorescence reactions using antibodies against fibronectin, collagen I and vascular endothelial growth factor (VEGF). Our results show that, after 7 days of treatment, all tested proteins change their pattern expression and will reset after 30 days. These data demonstrate that the dental pulp does not involve any irreversible iatrogenic alterations, supporting the efficacy and safety of using pre-calibrated force application to induce orthodontic tooth movement in clinical practice.

Dental Pulp Stem Cell Mechanoresponsiveness: Effects of Mechanical Stimuli on Dental Pulp Stem Cell Behavior

Dental pulp is known to be an accessible and important source of multipotent mesenchymal progenitor cells termed dental pulp stem cells (DPSCs). DPSCs can differentiate into odontoblast-like cells and maintain pulp homeostasis by the formation of new dentin which protects the underlying pulp. DPSCs similar to other mesenchymal stem cells (MSCs) reside in a niche, a complex microenvironment consisting of an extracellular matrix, other local cell types and biochemical stimuli that influence the decision between stem cell (SC) self-renewal and differentiation. In addition to biochemical factors, mechanical factors are increasingly recognized as key regulators in DPSC behavior and function. Thus, microenvironments can significantly influence the role and differentiation of DPSCs through a combination of factors which are biochemical, biomechanical and biophysical in nature. Under in vitro conditions, it has been shown that DPSCs are sensitive to different types of force, such as uniaxial mechanical stretch, cyclic tensile strain, pulsating fluid flow, low-intensity pulsed ultrasound as well as being responsive to biomechanical cues presented in the form of micro- and nano-scale surface topographies. To understand how DPSCs sense and respond to the mechanics of their microenvironments, it is essential to determine how these cells convert mechanical and physical stimuli into function, including lineage specification. This review therefore covers some aspects of DPSC mechanoresponsivity with an emphasis on the factors that influence their behavior. An in-depth understanding of the physical environment that influence DPSC fate is necessary to improve the outcome of their therapeutic application for tissue regeneration.

Effect of cyclic uniaxial compressive stress on human dental pulp cells in vitro

PURPOSE

Teeth are exposed to various forces during functional and parafunctional movements. These processes inevitably affect the dental pulp, and the mechanism of these influences has been the subject of many previous studies using different apparatuses and obtaining different results. In this study, we aimed to investigate the effects of compressive stress on the proliferation and differentiation of human dental pulp cells (hDPCs).

MATERIALS AND METHODS

A four-point bending strain system was adopted to apply low-density cyclic uniaxial compressive stress (2000 microstrain, 0.5 Hz) to hDPCs for 1.5, 3, 6, 12, and 24 h. The cell cycle progression and mRNA expression of differentiation-related genes (BMP2, ALP, DMP1, DSPP, COL I) were then examined to investigate the proliferation and differentiation of hDPCs.

RESULTS

The results showed that cyclic compressive stress changed the morphology of hDPCs after 12 and 24 h of mechanical loading; cell cycle progression was promoted, especially in the 24-h group (p < 0.05). The expression of BMP2 was significantly upregulated after 3 and 6 h of mechanical loading but declined in the 12- and 24-h groups, whereas the expression levels of DMP1 and DSPP were significantly upregulated in the 12- and 24-h loading groups (p < 0.05).

CONCLUSIONS

Dental pulp cells were sensitive to compressive stress, especially after 12 and 24 h of applied force. Proliferation and odontogenic differentiation were significantly promoted in this in vitro model.

Impact of hypofunctional occlusion on upper and lower molars after cessation of root development in adult mice

Background

Hypofunctional occlusion is known to lead to changes in the length of roots over time. The mechanisms that drive such changes, however, are poorly understood, with most studies concentrating on juvenile rats prior to the arrest of root development. In this article, we investigated the response of the upper and lower first molar roots to lack of occlusion concentrating on time-points after the development of the roots has ceased using the mouse as a model. Mouse molar roots finish development at weaning, much earlier than rat molars, and display a similar pattern of roots in the lower and upper jaw to humans.

Methods

Hypofunctional occlusion was achieved in adult mice at 5 and 9 weeks of age by flattening the cusps of the upper first molar. Mice were then sacrificed after 6 and 2 weeks, respectively, along with control littermates. microCT was used to measure root length, alveolar bone height, and the amount of tooth eruption, followed by sectioning to understand the mechanisms behind the changes at the histological level.

Results

In the lower first molar, the response to hypofunctional occlusion was characterized by elongation of both the mesial root and its surrounding alveolar bone, while the distal root was unaffected. In contrast, the response of the upper first molar was characterized by over-eruption of the mesial side of the tooth without any significant change in the alveolar bone or root length. From histologic sections, it was clear that increased deposition of cellular cementum played an important role in the changes that occurred in the lower mesial root.

Conclusions

In a mouse model, upper and lower molars responded differently to hypofunctional occlusion, with adult mice showing a different response to that previously reported for juvenile rats, highlighting the importance of considering age and tooth position in cases of hypofunction.

Age-related changes of dental pulp tissue after experimental tooth movement in rats

It is generally accepted that the effect of orthodontic tooth movement on the dental pulp in adolescents is reversible and that it has no long-lasting effect on pulpal physiology. However, it is not clear yet if the same conclusion is also valid for adult subjects. Thus, in two groups of rats, aged 6 and 40 weeks respectively, 3 molars at one side of the maxilla were moved together in a mesial direction with a standardized orthodontic appliance delivering a force of 10 cN. The contralateral side served as a control. Parasagittal histological sections were prepared after tooth movement for 1, 2, 4, 8, and 12 weeks. The pulp tissue was characterized for the different groups, with special emphasis on cell density, inflammatory cells, vascularity, and odontoblasts. Dimensions of dentin and the pulpal horns was determined and related with the duration of orthodontic force application and age ware evaluated. We found that neither in young nor in adult rats, force application led to long-lasting or irreversible changes in pulpal tissues. Dimensional variables showed significant age-related changes. In conclusion, orthodontic tooth movement per se has no long-lasting or irreversible effect on pulpal tissues, neither in the young nor in the adult animals.

Influence of orthodontic forces on human dental pulp: a systematic review

AIM

The aim of the present study was to systematically review the influence of orthodontic force on human dental pulp.

METHODS AND RESULTS

The addressed focused question was "Do orthodontic forces affect the human dental pulp?" which was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a specific question was constructed according to the PICO (Participants, Interventions, Control, Outcomes) principle. Databases were explored from 1952 up to and including August 2014 using different combinations of the following keywords: "orthodontic force"; "dental pulp"; "reaction" and "tooth movement". Literature reviews, letters to the editor, commentaries and case-reports were excluded. Thirty studies were included. Six studies assessed the effect of orthodontic forces on pulpal blood flow and 20 studies investigated the pulpal cellular responses to orthodontic forces. In 4 studies, pulpal responses to orthodontic forces were compared between previously traumatized- and non-traumatized teeth.

CONCLUSIONS

There is insufficient scientific validation regarding the association between orthodontic forces and human dental pulp. However, a history of dental trauma maybe considered a risk factor for loss of pulp vitality during orthodontic treatment.

Prevalence of coronal pulp stones and its relation with systemic disorders in northern Indian central punjabi population

Aim. To estimate the prevalence of coronal pulp stones in the molar teeth of dental outpatients of Sunam, Sangrur district, Punjab, India, to report any association between occurrence of pulp stones with age, gender, dental arch, side, and dental status and to find out correlation between pulp stones with dental and systemic diseases. Materials and Methods. 500 routine dental outpatients within age group of 18–67 years were involved in the study. Molar bitewing of left and right side of each patient was taken with XCP bitewing instrument and size 2 film. The presence or absence of pulp stones was recorded. Chi-square analysis was used to record the prevalence of pulp stones and to compare it with demographic and systemic factors. Results. Overall prevalence of pulp stones was 41.8%. Pulp stones were significantly higher in maxilla (11.59%) than mandible (6.54%), left side than right side, and first molar than other molars. Higher numbers of pulp stones were recorded in patients with cardiovascular disease (38.89%) than with cholelithiasis and renal lithiasis. Conclusion. Pulp stones were higher in maxillary arch than mandibular arch and in females than males. Cardiovascular patients had higher number of pulp stones than other groups.

Effect of low level laser therapy on dental pulp during orthodontic movement

AIM: To validate the protocol described here to be used in future clinical trials related to the effect of laser therapy on dental pulp.

METHODS: Histologically treated samples from eight human healthy premolar teeth obtained from the middle root level were distributed in four groups: group 1 (G1) absolute control; group 2 (G2) only laser irradiation; group 3 (G3) exposed only to orthodontics; and group 4 (G4) treated with orthodontics and laser. Laser treatment was performed at 830 nm wavelength, 100 mW (energy 80 J/cm², 2.2 J), for 22 s in the vestibular surface and 22 s in the palatal surface, 1 mm away from the dental root mucosa. Three staining methods were performed: hematoxylin-eosin (HE), Masson’s Trichrome method and Gomori’s method.

RESULTS: The pulp histology parameters were evaluated and the results classified in to 3 parts: an inflammatory response, soft tissue response (dental pulp) and hard tissue response (dentin and predentin). There was no inflammation (chronic or acute) in any of the evaluated groups. The zones of pulp necrosis were found in one premolar of G3 and in one of G4; in groups G2 and G4 there was higher angiogenesis than in the other two groups. G4 group presented the highest level of vascularization. A reduced nerve density was observed in G3. A G2 specimen showed increased nerve density. A higher rate of calcification was observed in G1 compared to G2. Denticles, either real or false, were observed in G1, G2 and G3. Sclerosis of dentin and focal dentin loss was observed among all the groups. Secondary dentin was present in one sample in G1 and G2. A necrosis zone was found in one sample of G3 and G4. No differences between groups were observed in the odontoblast irregularity layer but the layer was wider in the group treated with laser only. A notable difference was detected in reduction of the cell-free layer between the groups G1 and G4. The findings in pulp tissue favor its adaptative response against dental movement induced by orthodontics. No definitive conclusions may be derived as this is a pilot study.

CONCLUSION: The protocol described here was shown to be an effective method to evaluate changes in dental pulp submitted to low level laser in teeth under orthodontic movement.

Mechanical stretch increases the proliferation while inhibiting the osteogenic differentiation in dental pulp stem cells

Dental pulp stem cells (DPSCs), which can differentiate into several types of cells, are subjected to mechanical stress by jaw movement and occlusal forces. In this study, we evaluated how the uniaxial mechanical stretch influences proliferation and differentiation of DPSCs. DPSCs were isolated and cultured from male Sprague-Dawley rats. Cultured DPSCs were identified by surface markers and the differentiation capabilities as adipocytes or osteoblasts. To examine the response to mechanical stress, uniaxial stretch was exposed to cultured DPSCs. We evaluated the impact of stretch on the intracellular signaling, proliferation, osteogenic differentiation, and gene expressions of DPSCs. Stretch increased the phosphorylation of Akt, ERK1/2, and p38 MAP kinase as well as the proliferation of DPSCs. The stretch-induced proliferation of DPSCs was abolished by the inhibition of the ERK pathway. On the other hand, stretch significantly decreased the osteogenic differentiation of DPSCs, but did not affect the adipogenic differentiation. We also confirmed mRNA expressions of osteocalcin and osteopontin were significantly suppressed by stretch. In conclusion, uniaxial stretch increased the proliferation of DPSCs, while suppressing osteogenic differentiation. These results suggest a crucial role of mechanical stretch in the preservation of DPSCs in dentin. Furthermore, mechanical stretch may be a useful tool for increasing the quantity of DPSCs in vitro for regenerative medicine.

Association between dental pulp stones and calcifying nanoparticles

The etiology of dental pulp stones, one type of extraskeletal calcification disease, remains elusive to date. Calcifying nanoparticles (CNPs), formerly referred to as nanobacteria, were reported to be one etiological factor in a number of extraskeletal calcification diseases. We hypothesized that CNPs are involved in the calcification of the dental pulp tissue, and therefore investigated the link between CNPs and dental pulp stones. Sixty-five freshly collected dental pulp stones, each from a different patient, were analyzed. Thirteen of the pulp stones were examined for the existence of CNPs in situ by immunohistochemical staining (IHS), indirect immunofluorescence staining (IIFS), and transmission electron microscope (TEM). The remaining 52 pulp stones were used for isolation and cultivation of CNPs; the cultured CNPs were identified and confirmed via their shape and growth characteristics. Among the dental pulp stones examined in situ, 84.6% of the tissue samples staines positive for CNPs antigen by IHS; the corresponding rate by IIFS was 92.3 %. In 88.2% of the cultured samples, CNPs were isolated and cultivated successfully. The CNPs were visible under TEM as 200–400 nm diameter spherical particles surrounded by a compact crust. CNPs could be detected and isolated from a high percentage of dental pulp stones, suggesting that CNPs might play an important role in the calcification of dental pulp.

Evaluation of the interaction between calcifying nanoparticles and human dental pulp cells: a preliminary investigation

Calcifying nanoparticles (CNPs, previously called nanobacteria) are self-propagating, cultivable macromolecular complexes. Their extraordinary characteristic is that they can aggregate carbonate apatite on their envelope from soluble calcium and phosphorus at physiologic concentrations and display cytotoxic effects on murine and human fibroblast cell lines. The question arises whether CNPs contribute to the degeneration of pulp tissue and thus result in clinically significant human dental pulp stones as nidies. This study evaluates CNPs’ effects upon human dental pulp cells (HDPCs, the host cells in pulp tissue). We observed the ultrastructural variation of HDPCs attacked by CNPs. The spatial relationship of HDPCs and CNPs after coculture was also identified by immunofluroscence staining. Furthermore, it was verified by MTT viability assay that CNPs isolated from dental pulp stones exerted cytotoxic effect on HDPCs. Therefore, it could be concluded that the existence of CNPs might interfere with the normal physiologic function of the cells, and that might lead to dental pulp calcification. Elucidation of the cytotoxic characteristics of CNPs may offer a new perspective for understanding the etiology of human dental pulp stones.

Uniaxial cyclic tensile stretch inhibits osteogenic and odontogenic differentiation of human dental pulp stem cells

As the most important organs of occlusion, teeth are subjected to a variety of mechanical stresses. These stresses are transmitted into the dental pulp tissue and affect the dental pulp stem cells. In this study, human dental pulp stem cells were isolated from human impacted third molars and their multilineage differentiation abilities were tested. Human dental pulp stem cells were then exposed to cyclic tensile stretch. The results showed that the cyclic tensile stretch inhibited the expression of osteogenic marker genes and proteins such as BMP-2, OCN and ALP. Simultaneously, odontogenic marker genes and proteins such as DSPP, DSP and BSP were also inhibited by the mechanical stress. It was concluded that cyclic tensile stretch inhibits the osteogenic and odontogenic differentiation of dental pulp stem cells.

MMP-2, MMP-9, and iNOS expression in human dental pulp subjected to orthodontic traction

OBJECTIVE

To test the hypothesis that some metalloproteinases (MMP-2, MMP-9) and inducible nitric oxide synthetase (iNOS) enzymes in dental pulp samples do not vary when subjected to orthodontic treatment.

MATERIALS AND METHODS

Human dental pulps were taken from male and female patients (N=10; age 10-14 years). A straight wire technique was used with nickel-titanium or steel archwires. The increase of pressure applied on teeth was gradual. Five patients were subjected to premolar extractions after 14 months of treatment and one after 24 months. Samples were Bouin-fixed, paraffin-embedded, and afterwards processed for immunohistochemistry using anti-MMP-2, anti-MMP-9, and anti-iNOS antibodies.

RESULTS

A reduction of MMP-2, MMP-9, and iNOS expression occurred in treated samples. This became more evident with increased treatment time.

CONCLUSION

The hypothesis is rejected. The reduction of expression of those proteins revealed a time-dependent relationship.

Mechanical stress promotes odontoblastic differentiation via the heme oxygenase-1 pathway in human dental pulp cell line

AIMS

Although heme oxygenase-1 (HO-1) is involved in osteoblastic differentiation, the HO-1- and odontoblastic differentiation-inducing effects of mechanical stress (MS) have not been clarified in human dental pulp cells (HDPCs). In this study, we examined the effects of MS on the odontoblastic differentiation of immortalized HDPCs and on the primary intracellular signaling pathways, including the HO-1 pathway, implicated in this differentiation.

MAIN METHODS

A Flexercell strain unit was used to generate cyclic tensile strain in HDPCs. Expressions of mRNAs encoding HO-1 and HDPC differentiation markers, such as osteopontin (OPN), bone sialoprotein (BSP), dentin sialophosphoprotein (DSPP), and dentin matrix-protein-1 (DMP-1), were evaluated using the reverse transcription-polymerase chain reaction. Expression of the NF-E2-related transcription factor 2 (Nrf2) protein was analyzed by Western blotting.

KEY FINDINGS

MS significantly increased the expression of HO-1, OPN, BSP, DSPP, and DMP-1 mRNAs in HDPCs. HO-1 silencing and inhibitors of HO-1, p38 MAPK, ERK, phosphoinositide 3-kinase, and nuclear factor-kappaB (NF-kappaB) all attenuated MS-stimulated differentiation. The MS-induced nuclear translocation of Nrf2 was suppressed by inhibitors of PI3K and NF-kappaB.

SIGNIFICANCE

Collectively, these results provide the first evidence that MS stimulates odontoblastic differentiation of HDPCs via modulation of the Nrf2-mediated HO-1 pathway.

Prevalence of dental anomalies in various malocclusions

INTRODUCTION

The purpose of this study was to evaluate the prevalence of dental anomalies in different orthodontic malocclusions.

METHODS

Based on pretreatment diagnostic records, 900 orthodontic patients were classified as Class I (n = 358), Class II (n = 325), Class II Division 2 (n = 51), or Class III (n = 166). The occurrence rates of each dental anomaly were calculated as percentages of the total sample. Differences in incidence rates of each dental anomaly by sex and malocclusion were analyzed by using chi-square, Fisher exact, and z tests. The Mann-Whitney U test was used to determine whether there were significant differences in the occurrence of dental anomalies by age.

RESULTS

It was found that 40.3% of patients (n = 363) had at least 1 dental anomaly. Agenesis was the most common (21.6%), followed by dens evaginatus (6.2%), invaginatus (5.0%), pulp stones (4.2%), and impaction (2.9%). No statistically significant correlations were found between dental anomaly and type of malocclusion, with the exception of impaction and short or blunt roots (P <0.01 and P <0.05, respectively). The Mann-Whitney U test indicated no significant difference in dental anomalies by age.

CONCLUSIONS

A remarkably high rate of dental anomalies was recorded in orthodontic patients; therefore, orthodontists should carefully examine pretreatment records for dental anomalies to include their management in the treatment planning.

Pulp stones: a review

Pulp stones are a frequent finding on bitewing and periapical radiographs but receive relatively little attention in textbooks. A review of the literature was therefore performed, initially using the PubMed database and beginning the search with 'pulp calcifications' and 'pulp stones'. Each term provided more than 400 references, many of which related to pulp calcification in general rather than pulp stones, and focussed largely on the problems these changes presented to clinicians. A manual search using references from this source was carried out. Contemporary textbooks in endodontology were also consulted, and an historic perspective gained from a number of older books and references. The factors involved in the development of the pulp stones are largely unknown. Further research may determine the reasons for their formation, but with current endodontic instruments and techniques this is unlikely to alter their relevance to clinicians.

Initial pulp changes during orthodontic movement: histomorphological evaluation

This study evaluated pulp changes in molars of rats submitted to tooth movement by application of a 0.4 N force. Twenty-five adult male Wistar rats (Rattus norvegicus, albinus) were randomly assigned to 5 groups (n=5), being one control group not submitted to force application, and four study groups of 6, 12, 24 and 72 h of force application. The study groups received a 5-mm long nickel-titanium closed coil spring, placed from the right maxillary first molar to the maxillary incisors of each animal. The coil spring was used for mesial inclination of the first molar. After the specific period of tooth movement of each study group, the animals were sacrificed and specimens containing the teeth submitted to movement were processed and stained with hematoxylin and eosin for histological analysis under light microscopy. The results demonstrated alteration of the odontoblastic layer, with hypertrophy of odontoblasts especially at the mesial area of the coronal pulp, edema of the pulp connective tissue in the central area of the pulp, and vascular alteration with accumulation of erythrocytes and leukocytes inside the vessels, especially at the mesial root of the moved teeth. These changes were less remarkable for the 72-h period. Thus, it may be concluded that tooth movement yielded pulpal tissue alterations compatible with an inflammatory process, which are reversible if the aggression is not more intense than the physiological limit of tissue tolerance.

Alkaline phosphatase activity in dental pulp of orthodontically treated teeth

INTRODUCTION

The aim of this study was to examine alkaline phosphatase (ALP) activity in the dental pulp of orthodontically treated teeth.

METHODS

Sixteen healthy subjects (mean age 17.0 +/-1.6 years) who required extraction of 4 first premolars for orthodontic reasons participated. One maxillary first premolar subjected to orthodontic force was the test tooth. The contralateral first premolar, bracketed but not subjected to mechanical stress, was the control tooth. After a week of treatment, the first premolars were extracted and the dental pulp removed from the teeth. ALP activity was determined spectrophotometrically and the results expressed as units/liter per milligram of pulp tissue [U/(L x mg)].

RESULTS

ALP activity was 89 +/- 26 U/(L x mg) in the test teeth and 142 +/- 33 U/(L x mg) in the control teeth. The difference between the groups was statistically significant (P < .01).

CONCLUSIONS

Orthodontic treatment can lead to significant early-phase reduction in ALP activity in human dental pulp tissue.