The early reparative process of orthodontically induced root resorption in adolescents--location and type of tissue

Gene expression and phosphorylation of ERK and AKT are regulated depending on mechanical force and cell confluence in murine cementoblasts

Cementoblasts, located on the tooth root surface covered with cementum, are considered to have tooth protecting abilities. They prevent tissue damage and secure teeth anchorage inside the periodontal ligament during mechanical stress. However, the involvement of cementoblasts in mechanical compression induced periodontal remodeling needs to be identified and better understood. Here, we investigated the effect of static compressive stimulation, simulating the compression side of orthodontic force and cell confluence on a murine cementoblast cell line (OC/CM). The influence of cell confluence in cementoblast cells was analyzed by MTS assay and immunostaining. Furthermore, mRNA and protein expression were investigated by real-time RT-PCR and western blotting at different confluence grades and after mechanical stimulation. We observed that cementoblast cell proliferation increases with increasing confluence grades, while cell viability decreases in parallel. Gene expression of remodeling markers is regulated by compressive force. In addition, cementoblast confluence plays a crucial role in this regulation. Confluent cementoblasts show a significantly higher basal expression of Bsp, Osterix, Alpl, Vegfa, Mmp9, Tlr2 and Tlr4 compared to sub-confluent cells. After compressive force of 48 h at 60% confluence, an upregulation of Bsp, Osterix, Alpl, Vegf and Mmp9 is observed. In contrast, at high confluence, all analyzed genes were downregulated through mechanical stress. We also proved a regulation of ERK, phospho-ERK and phospho-AKT dependent on compressive force. In summary, our findings provide evidence that cementoblast physiology and metabolism is highly regulated in a cell confluence-dependent manner and by mechanical stimulation.

Selection and validation of reference genes by RT-qPCR for murine cementoblasts in mechanical loading experiments simulating orthodontic forces in vitro

Different structures and cell types of the periodontium respond to orthodontic tooth movement (OTM) individually. Cementoblasts (OC/CM) located in the immediate vicinity of the fibroblasts on the cement have found way to the centre of actual research. Here, we identify and validate possible reference genes for OC/CM cells by RT-qPCR with and without static compressive loading. We investigated the suitability of 3 reference genes in an in vitro model of cementoblast cells using four different algorithms (Normfinder, geNorm, comparative delta-Ct method and BestKeeper) under different confluences and time. Comparable to our previous publications about reference genes in OTM in rats and human periodontal ligament fibroblasts (hPDLF), Rpl22 in murine OC/CM cells appears as the least regulated gene so that it represents the most appropriate reference gene. Furthermore, unlike to the expression of our recommended reference genes, the expression of additionally investigated target genes changes with confluence and under loading compression. Based on our findings for future RT-qPCR analyses in OC/CM cells, Rpl22 or the combination Rpl22/Tbp should be favored as reference gene. According to our results, although many publications propose the use of Gapdh, it does not seem to be the most suitable approach.

Effects of mesenchymal stem cell transfer on orthodontically induced root resorption and orthodontic tooth movement during orthodontic arch expansion protocols: an experimental study in rats

Objectives

The aim was to evaluate the effects of mesenchymal stem cell (MSC) transfer to periodontal ligament (PDL) on the inhibition and/or repair of orthodontically induced root resorption (OIRR) during and after arch expansion and on the orthodontic tooth movement (OTM) rate of the maxillary first molar teeth of rats.

Material and methods

Sixty Wistar rats were divided into three groups as the untreated group, MSC and control injections during the expansion period group (EMSC-EC), and MSC and control injections at the retention period group (RMSC-RC). Fifty grams of orthodontic force was applied to the maxillary first molar teeth of the rats for 14 days in the vestibular direction, and then, 20 days of retention was carried out. MSCs and control injections were performed every 3 days in the EC, RC, EMSC, and RMSC groups. At the end of the experiment, samples were prepared for OTM evaluation, mRNA expression analysis, micro-computed tomography measurements, cementum thickness calculations, and structural examinations.

Results

The amount of OTM in EMSC group was significantly higher than in EC group (P < 0.001). MSC transfer during the expansion and retention periods reduced the number of resorption lacunae, volumetric and linear resorptive measurements, and cyclooxygenase-2 and receptor activator of nuclear factor kappa B ligand (RANKL) mRNA expression levels, and increased the osteoprotegerin (OPG) expression levels, OPG/RANKL ratio, and cementum thickness in the EMSC and RMSC groups.

Conclusions

MSC transfer to PDL during expansion increased the amount of OTM. Injection of MSC during the retention period was found to be slightly more effective in prevention and/or repair of OIRR than MSC transfer during the expansion period.

Physical properties of root cementum: Part 27. Effect of low-level laser therapy on the repair of orthodontically induced inflammatory root resorption: A double-blind, split-mouth, randomized controlled clinical trial

INTRODUCTION

The purpose of this 2-arm-parallel split-mouth trial was to investigate the effect of low-level laser therapy (LLLT) on the repair of orthodontically induced inflammatory root resorption (OIIRR).

METHODS

Twenty patients were included in this study, with 1 side randomly assigned to receive LLLT, and the other side served as a sham. Eligibility criteria included need for bilateral maxillary first premolar extractions as part of fixed appliance treatment. OIIRR was generated by applying 150 g of buccal tipping force on the maxillary first premolars for 4 weeks. After the active force was removed, the teeth were retained for 6 weeks. LLLT commenced with weekly laser applications using a continuous beam 660-nm, 75-mW aluminum-gallium-indium-phosphorus laser with 1/e² spot size of 0.260 cm², power density of 0.245 W/cm², and fluence of 3.6 J/cm². Contact application was used at 8 points buccally and palatally above the mucosa over each tooth root for 15 seconds with a total treatment time of 2 minutes. After 6 weeks, the maxillary first premolars were extracted and scanned with microcomputed tomography for primary outcome OIIRR calculations. Subgroup analysis included assessment per root surface, per vertical third, and sites of heaviest compressive forces (buccal-cervical and palato-apical). Randomization was generated using www.randomization.com, and allocation was concealed in sequentially numbered, opaque, sealed envelopes. Blinding was used for treatment and outcome assessments. Two-tailed paired t tests were used to determine whether there were any statistically significant differences in total crater volumes of the laser vs the sham treated teeth.

RESULTS

Total crater volumes were 0.746 mm³ for the laser treated teeth and 0.779 mm³ for the sham. There was a mean difference of 0.033 ± 0.39 mm³ (95% CI, -0.21 to 0.148 mm³) greater resorption crater volume in the sham group compared with the laser group; this was not statistically significant (P = 0.705). No harm was observed.

CONCLUSIONS

No significant difference was found between LLLT and sham control groups in OIIRR repair.

Comparison of 4 and 6 weeks of rest period for repair of root resorption

Background

The study was designed to evaluate and compare the rest periods of 4 and 6 weeks for healing of orthodontically induced root resorption craters.

Methods

The study was conducted with a split-mouth design, with the right and left mandibular first premolars of 14 subjects serving as the two groups of the study. The right premolars constituted group A and the left ones, group B. Intrusive force was applied on these teeth for a period of 6 weeks, followed by retaining the teeth for 4 weeks (group A) and 6 weeks (group B) as rest periods before extraction. The extracted teeth were prepared for histologic examination with haematoxylin and eosin staining and studied under a light microscope. The histological sections were scored based on the level of repair (none, partial, functional, or anatomic) seen in the deepest craters in the apical third region of the roots. The mean values of the scores in the two groups were compared using Mann-Whitney U test.

Results

All the teeth showed healing in their deepest craters. The teeth in group A showed partial repair more frequently (84.6%), with the remaining (15.4%) showing functional repair. The teeth in group B showed anatomic repair more frequently (60%), with the remaining (40%) showing functional repair. The mean level of repair was higher in group B (2.6 ± 0.5) as opposed to that in group A (1.15 ± 0.37). The difference between these values was of very high significance (P < 0.05).

Conclusions

Longer rest period of 6 weeks showed more advanced healing than a shorter rest period of 4 weeks. Six weeks of rest period is adequate only for the functional repair of resorption craters.

Interventions for the management of external root resorption

BACKGROUND

External root resorption is a pathological process, which tends to occur following a wide range of mechanical or chemical stimuli such as infection, pressure, trauma or orthodontic tooth movement. Although it is predominantly detected by radiography, in some cases root resorption may be identified by clinical symptoms such as pain, swelling and mobility of the tooth. Treatment alternatives are case-dependent and aim to address the cause of the resorption and aid the regeneration of the resorptive lesion.

OBJECTIVES

To evaluate the effectiveness of any interventions that can be used in the management of external root resorption in permanent teeth.

SEARCH METHODS

The following electronic databases were searched: the Cochrane Oral Health Group Trials Register (to 14 October 2015), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2015, Issue 9), MEDLINE via OVID (1946 to 14 October 2015) and EMBASE via OVID (1980 to 14 October 2015). We searched the US National Institutes of Health Trials Register (http://clinicaltrials.gov) and the WHO Clinical Trials Registry Platform for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases.

SELECTION CRITERIA

We included randomised controlled trials of permanent teeth with any type of external root resorption, which has been confirmed by clinical and radiological examination, comparing one type of intervention (root canal medications and canal filling, splinting or extraction of teeth or the surgical removal of any relevant pathology) with another, or with placebo or no treatment.

DATA COLLECTION AND ANALYSIS

Two review authors screened search records independently. Full papers were obtained for potentially relevant trials. If data had been extracted, the statistical guidelines set out in the Cochrane Handbook would have been followed.

MAIN RESULTS

No randomised controlled trials that met the inclusion criteria were identified. However, we identified one ongoing study that is potentially relevant to this review and will be assessed when it is published.

AUTHORS' CONCLUSIONS

We were unable to identify any reports of randomised controlled trials regarding the efficacy of different interventions for the management of external root resorption. In view of the lack of reliable evidence on this topic, clinicians must decide on the most appropriate means of managing this condition according to their clinical experience with regard to patient-related factors. There is a need for well designed and conducted clinical trials on this topic, which conform to the CONSORT statement (www.consort-statement.org/).

Potential role of high mobility group box protein 1 and intermittent PTH (1-34) in periodontal tissue repair following orthodontic tooth movement in rats

OBJECTIVES

Recent studies indicate that high mobility group box protein 1 (HMGB1) can be released by necrotic and damaged cells and functions as an alarmin that is recognized by the innate immune system. Little is known about the role of HMGB1 within the periodontal ligament (PDL). Therefore, we examined HMGB1 expression by PDL cells in vitro and compared the findings to an in vivo model of orthodontically induced tooth root resorption. In addition, we addressed the question of whether a potentially anabolic intermittent administration of parathyroid hormone (iPTH) would modulate the expression of HMGB1.

MATERIALS AND METHODS

In confluent PDL cell cultures, HMGB1 messenger RNA (mRNA) expression was quantified by real-time polymerase chain reaction. In a rat model comprising 25 animals, mechanical loading for 5 days was followed by administration of either iPTH (1-34) systemically or sham injections for up to 56 days. HMGB1 expression was determined by means of immunohistochemistry and histomorphometry.

RESULTS

The in vitro experiments revealed an inhibitory effect of iPTH on basal HMGB1 mRNA expression in confluent PDL cells. In vivo, the mechanical force-induced enhanced HMGB1 protein expression declined time dependently. Intermittent PTH further inhibited HMGB1 expression. The significantly higher basal HMGB1 protein expression in the former compression side was followed by a more pronounced time- and iPTH-dependent decline in the same area.

CONCLUSIONS

These data indicate a major role for HMGB1 in the regulation of PDL wound healing following mechanical load-induced tissue injury.

CLINICAL RELEVANCE

The findings point to the potential benefit of iPTH in the attempt to support these immune-associated reparative processes.

Histologic evaluation of root-surface healing after root contact or approximation during placement of mini-implants

INTRODUCTION

Placement of mini-implants carries with it the risk of iatrogenic damage to the adjacent root surfaces. The aims of this study were to assess the type of trauma incurred on tooth roots after contact or approximation with mini-implants during placement, and to observe and analyze the healing responses via histologic analysis.

METHODS

Four male minipigs were used as experimental subjects. Twenty mini-implants (1.6 × 8 mm) were implanted in each minipig into the buccal sides of all 4 quadrants between the roots of teeth so that contact or approximation between the mini-implant and root surface occurred, with the aid of dental fluoroscopy. All mini-implants on the left side of the mouth were left in situ, and all mini-implants on the right side were removed immediately after placement. The minipigs were killed at 4-week intervals up to week 16, and histologic sections were made.

RESULTS

When mini-implants were left in situ, the root surface was mostly resorbed away from the mini-implant thread. Partial repair started at 8 weeks. When the mini-implant thread was left touching the root, there was no normal healing response. If the mini-implant was placed less than 1 mm from the periodontal ligament, resorption was evident on the root surface. Abnormal healing responses were seen when the pulp tissue was ruptured, mostly through osteodentin formation. In all instances after mini-implant removal immediately after placement, varying degrees of cementum repair was observed.

CONCLUSIONS

Immediate removal of the mini-implant leads to cementum repair, whereas leaving the mini-implant in place will cause either a delay in repair or no repair. Placing mini-implants less than 1 mm from the root surface causes root-surface resorption.

Interventions for the management of external root resorption

BACKGROUND

External root resorption is a pathological process which tends to occur following a wide range of mechanical or chemical stimuli such as infection, pressure, trauma or orthodontic tooth movement. Although it is predominantly detected by radiography, in some cases, root resorption may be identified by clinical symptoms i.e. pain, swelling and mobility of the tooth. Treatment alternatives are case-dependant and aim at the removal of the cause and the regeneration of the resorptive lesion.

OBJECTIVES

To evaluate the effectiveness of any interventions that can be used in the management of external root resorption in permanent teeth.

SEARCH STRATEGY

We searched the following databases in April 2010: The Cochrane Oral Health Group's Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 3); MEDLINE (via OVID) (1950 to April 2010); and EMBASE (via OVID) (1980 to April 2010). We also searched two regional bibliographic databases (IndMED and Iranmedex) and handsearched five Iranian dental journals using free text terms appropriate for this review.

SELECTION CRITERIA

Randomised controlled trials comparing any type of intervention including root canal medications and canal filling, splinting or extraction of teeth or the surgical removal of any relevant pathology with each other, or placebo or no treatment applied to permanent teeth with any type of external root resorption which had been confirmed by clinical and radiological examination.

DATA COLLECTION AND ANALYSIS

Two review authors conducted screening of studies in duplicate and independently. The Cochrane Collaboration statistical guidelines were to be followed.

MAIN RESULTS

66 trials were identified in our searches none of which matched our inclusion criteria. However, we identified one ongoing study which is potentially relevant to this review and will be assessed when it is published.

AUTHORS' CONCLUSIONS

We were unable to identify any reports of randomised controlled trials regarding the efficacy of different interventions for the management of external root resorption. In view of the lack of any high level evidence on this topic, it is suggested that clinicians decide on the most appropriate means of managing this condition according to their clinical experience with regard to patient related factors. Future research should consist of robust clinical trials which conform to the CONSORT statement (www.consort-statement.org/).

Comparisons of the effects of systemic administration of L-thyroxine and doxycycline on orthodontically induced root resorption in rats

The aim of this study was to histologically evaluate and compare the effects of the systemic administration of L-thyroxine (TX) and doxycycline (DX) on orthodontically induced root resorption, Twenty-eight male 50- to 60-day-old Wistar rats were used. Seven rats served as the baseline control. Seven animals received TX (20 μg/kg bodyweight/day) and seven DX (1.2 mg/kg bodyweight/day), by means of a mini-osmotic pump implanted subcutaneously. Seven rats were separated as a sham, in order to evaluate the pure effect of the surgical procedure on the animals' health. Tooth movement (TM) was achieved with a continuous force of 50 g by placing Elgiloy coil springs between the right maxillary first molar and incisors for 14 days. The animals were sacrificed and specimens containing the appliance and maxillary tooth-bearing segments were processed for light microscopy. The surface area of root resorption lacunae was measured histomorphometrically using digital photomicrographs. To evaluate the resorptive changes on the molar root surface of each group, scanning electron microscopy (SEM) examinations were also carried out. Statistical evaluation of root resorption percentages was performed using Kruskal-Wallis analysis of variance test. Multiple comparisons were determined by the Student-Newman-Keuls method. The level of significance was set at P < 0.05. Histomorphometric analysis of root resorption, expressed as a percentage, showed that the average relative root resorption affecting the maxillary molars on the TM side was 0.32 ± 0.25 in the TX and 0.26 ± 0.06 in the DX groups and 2.19 ± 0.86 in the control. Statistically significant inhibition of root resorption was determined both in the TX and DX groups (P < 0.001) on the TM side. There was no statistically significant difference in relative root resorption between the TX and DX groups. Systemic administration of TX and DX demonstrated similar effects on root resorption in rats and may have inhibitory effects on orthodontically induced resorptive activity.

Physical properties of root cementum: Part 13. Repair of root resorption 4 and 8 weeks after the application of continuous light and heavy forces for 4 weeks: a microcomputed-tomography study

INTRODUCTION

The reparative process of root absorption begins in the periodontium when orthodontic force is discontinued or reduced below a certain level. Our aim was to evaluate cementum repair at 4 and 8 weeks of retention after 4 weeks of continuous light and heavy orthodontic forces. The effects of age, tooth movement, and fluoride exposure were also investigated.

METHODS

Forty patients were recruited and divided into 4 groups of 10. The maxillary first premolars were loaded with either light (25 g) or heavy (225 g) orthodontic force. After 4 weeks of loading, the maxillary left first premolars were extracted as the positive control group, and the maxillary right first premolars were placed in retention for 4 or 8 more weeks before extraction; these were the experimental groups. The extracted teeth were studied with microcomputed tomography. To assess cementum repair, volumetric changes of the resorption craters were measured with specially designed computer software. Tooth movement was also measured on study casts taken before and after the extractions.

RESULTS

Root resorption continued for 4 weeks after orthodontic force ceased. The resorptive activity was more pronounced from heavy forces. Passive retention after 4 weeks of light force had the least root resorption crater volume (cube root scale). The total amount of the cementum repaired did not depend on magnitude of orthodontic force or retention time within our parameters (P >0.05). This might indicate concurrence of resorption and repair during passive retention. Most repair seemed to occur after 4 weeks of passive retention following the 4 weeks of heavy forces. The volume of root resorption craters positively depended on tooth movement (P = 0.02) and negatively correlated with chronologic age (P <0.01).

CONCLUSIONS

Although there was no significant difference in the amounts of repair between groups, root resorption continued for 4 weeks after orthodontic force stopped. Resorptive activity was more pronounced after the heavy forces. The reparative processes were different between the light and heavy forces, with marked individual variations. Repair seemed to become steady after 4 weeks of passive retention following 4 weeks of light force application, whereas most repair occurred after 4 weeks of passive retention following 4 weeks of heavy force application. Root resorption crater volume positively depended on tooth movement and negatively correlated with chronologic age.

Cellular and extracellular factors in early root resorption repair in the rat

The aim of this study was to investigate the role of extracellular matrix components, such as collagen type I, fibronectin, and osteopontin (OPN) during cementum repair following experimentally induced tooth movement, and to characterize the cells taking part in the regenerative process. The upper right first molars were moved mesially in 21 three-month-old male Wistar rats using a coil spring with a force of 0.5 N. After 9 days, the appliance was removed and the animals were killed in groups of three immediately after withdrawal of the force and 5, 7, 10, 12, 14, and 17 days later. Three rats served as non-experimental control animals. The maxillae were prepared and processed for histological analysis. Together with the disappearance of the multinucleated odontoclasts from the resorption lacunae, signs of repair were visible 5 days after the release of the orthodontic force. The first signs of cementum repair were seen on day 10. The newly produced cementum was of the acellular extrinsic fibre type (AEFC) and reattachment was achieved with the principal periodontal ligament (PDL) fibres orientated almost perpendicular to the root surface. The initial interface formed between the old and new cementum, as well as the new AEFC, was characterized by a strong immunoreaction with OPN and collagen I antibody, but only a weak immunoreaction with the fibronectin antibody. Only a small number of mononuclear cells, which were involved in the repair process, showed a positive immunoreaction with the osteoblastic lineage markers runt-related transcription factor 2 and osteocalcin. These same cells stained sparsely with muscle segment homeobox homologue 2, but not with the E11 antibody. Thus, most of the cells associated with this reparative activity on the surface of the lacunae were differentiated PDL cells of the fibroblastic phenotype. Cells with a defined osteoblastic phenotype seemed to be of minor importance in this repair process.

Physical properties of root cementum: Part 9. Effect of systemic fluoride intake on root resorption in rats

INTRODUCTION

Orthodontically induced inflammatory root resorption is a common complication in orthodontic treatment. Fluoride has been reported to have a beneficial effect against root resorption in dental traumatology. The effect of fluoride on orthodontically induced inflammatory root resorption has not been investigated. This study was undertaken to investigate the effect of fluoride on the incidence of root resorption.

METHODS

Thirty-two female 8-week-old Wistar rats were separated into 4 groups. Two groups (6 rats per group) were controls; they did not undergo orthodontic tooth movement. The other 2 groups (10 rats per group) had orthodontic tooth movement consisting of activated 100-g closing nickel-titanium coils (NiTi 10-000-06, GAC International, Bohemia, NY) connecting the mandibular first molar to the incisors. Fluoridated water (100 ppm) was given ad libitum to 1 control and 1 experimental group. The other 2 groups received deionized water. After 2 weeks, the animals were killed, and the samples were harvested. Resorption craters were scanned with a Micro CT (SkyScan 1072, Aartselaar, Belgium). Software analysis of the scanned samples provided a volumetric measurement of the resorption craters on the mandibular molar cementum surface.

RESULTS

Resorption sites were found in the control samples, especially on the distal surfaces; this could be attributed to normal physiological tooth drift. Resorption sites were significantly (P <.05) increased in the groups receiving orthodontic tooth movement.

CONCLUSIONS

Fluoride reduces the size of resorption craters, but the effect is variable and not statistically significant (P >.05).

Physical properties of root cementum: Part 8. Volumetric analysis of root resorption craters after application of controlled intrusive light and heavy orthodontic forces: A microcomputed tomography scan study

INTRODUCTION

Intrusion is a critical type of orthodontic tooth movement in relation to external root resorption. Our aims in this prospective randomized clinical trial were to quantify, 3 dimensionally, the amount of root resorption when controlled light and heavy intrusive forces were applied to human premolars and to establish the sites where root resorption is more prevalent.

METHODS

Fifty-four maxillary first premolars, orthodontically indicated for extraction from 27 patients (left and right maxillary first premolars from each), were intruded for 28 days with buccal and palatal beta-titanium-molybdenum alloy 0.017 x 0.025-in cantilever springs. The patients were randomly divided into 3 groups, and various levels of force were used: group 1, heavy force (225 g) on 1 side and control force (0 g) on the contralateral side; group 2, light force (25 g) on 1 side and control force (0 g) on the contralateral side; group 3, light force (25 g) on 1 side and heavy force (225 g) on the contralateral side. After the experimental period, the teeth were extracted under a strict protocol to prevent root surface damage and analyzed by using a microcomputed tomography scan x-ray system (SkyScan-1072, Skyscan, Aartselaar, Belgium) and specially designed software for direct volumetric measurements.

RESULTS

The volume of the root resorption craters after intrusion was found to be directly proportional to the magnitude of the intrusive force applied. The results showed that the control group had fewer and smaller root resorption craters, the light force group had more and larger root resorption craters than the control group, and the heavy force group had the most and the largest root resorption craters of all groups. A trend of linear increase in the volume of the root resorption craters was observed from control to light to heavy groups, and these differences were statistically significant. The mean volumes of the resorption craters in the light and heavy force groups were 2 and 4 times greater than in the control groups, respectively. The mesial and distal surfaces had the greatest resorption volume, with no statistically significant difference between the 2 surfaces.

Insulin-like growth factor system components in the periodontium during tooth root resorption and early repair processes in the rat

There is evidence that growth factors, such as the insulin-like growth factors (IGFs), are involved in biological and pathological processes in oro-dento-facial tissues. To investigate their roles in tooth movement, root resorption, and repair, the occurrence of components of the IGF system, including the ligands IGF-I and -II, the IGF receptor 1 (IGF1R) and six IGF-binding proteins (IGFBP-1 to -6), was investigated by immunohistochemistry on sections from rat maxillae where the first molar had been moved mesially by means of an orthodontic appliance for 9 d to induce root resorption. After force deactivation on day 0, early repair was studied after a further 5, 7, 10, 12, 14, and 17 d. The immunostaining pattern in the periodontal ligament, cementum, and bone of control animals showed similarities known from studies in human teeth. Increased immunostaining for nearly all components in pressure sides and resorption lacunae indicated an involvement in resorption processes and clastic activities. During early stages of repair, the occurrence of several components (e.g. IGF-II, IGFBP-5 or -6) within lacunae and in cementoblasts showed an involvement in the resorption-repair sequence, which is considered to be a coupling process as known from bone.

Root Resorption in Relation to Orthodontic Tooth Movement

Root resorption is an undesirable sequela of orthodontic tooth movement. The odontoclasts are responsible for root resorption and the process of hyalinization is known to preceed the orthodontic root resorption. It is found that there are several predisposing factors, therefore an evaluation of these factors should be done by careful examination of personal medical history, severity of malocclusion and dental treatment (if any due to previous history of trauma), anterior crossbite etc. The evaluation becomes an essential factor as it helps the orthodontists in detecting the occurance and severity of the root resorption and thereby plan out the treatment more effectively. Orthodontic tooth movements especially intrusion and other movements like tipping, torque are all known to influence the root resorption, therefore the detection using radiographs and repair of root resorption is of utmost significance as root resorption is a more serious problem from a medicolegal stand point of view. However some studies have shown that the repair process is known to occur after the cessation of orthodontic treatment by the deposition of cementum of cellular type. In the light of orthodontist’s liability of what is basically an unpredictable phenomenon, it is necessary that the speciality define this uncertainity and protect its members against unnecessary and unjustified litigation.

Incidence and severity of root resorption in orthodontically moved premolars in dogs

OBJECTIVES

To study treatment-related factors for external root resorption during orthodontic tooth movement.

DESIGN

An experimental animal study.

SETTING AND SAMPLE POPULATION

Department of Orthodontics and Oral Biology, University Medical Centre Nijmegen, The Netherlands. Twenty-four young adult beagle dogs.

EXPERIMENTAL VARIABLE

Mandibular premolars were bodily moved with continuous or intermittent controlled orthodontic forces of 10, 25, 50, 100, or 200 cN according to standardized protocols. At different points in time histomorphometry was performed to determine the severity of root resorption.

OUTCOME MEASURE

Prevalence of root resorptions, defined as microscopically visible resorption lacunae in the dentin. Severity of resorption was defined by the length, relative length, depth, and surface area of each resorption area.

RESULTS

The incidence of root resorption increased with the duration of force application. After 14-17 weeks of force application root resorption was found at 94% of the root surfaces at pressure sides. The effect of force magnitude on the severity of root resorption was not statistically significant. The severity of root resorption was highly related to the force regimen. Continuous forces caused significantly more severe root resorption than intermittent forces. A strong correlation (0.60 < r < 0.68) was found between the amount of tooth movement and the severity of root resorption.

CONCLUSIONS

Root resorption increases with the duration of force application. The more teeth are displaced, the more root resorption will occur. Intermittent forces cause less severe root resorption than continuous forces, and force magnitude is probably not decisive for root resorption.

Exploring the third dimension in root resorption

OBJECTIVE

To review and investigate the validity of various 2D quantitative measurement techniques, and to explore the third dimension of root resorption.

DESIGN

A review of the literature involving various quantitative evaluation of root resorption.

RESULTS

Quantitative evaluation of resorption using radiographs has proven to be highly inaccurate because of magnification errors and their inability to be readily repeated and reproduced. Studies using histology sections of samples have proven to be laborious and technique sensitive. Inherent parallax errors and loss of material in data transfer have denied the true understanding of this 3D event.

CONCLUSION

With the evolution in computing technology and digital imaging, the vision of evaluating the extent of root resorption in 3D has materialized. It was demonstrated that 3D volumetric quantitative evaluation of root resorption craters was feasible and its accuracy and repeatability was high.

Mechanical stress generated by orthodontic forces on apical root cementum: a finite element model

OBJECTIVES

1) To determine the mechanical stress generated at the root apex during different types of tooth movement using a finite element model of an ideal, human maxillary central incisor. 2) To determine the relationship of thickness of cementum and the magnitude of mechanical stress at the root apex.

DESIGN

Computer simulation.

SETTING AND SAMPLE POPULATION

Not applicable, computer simulation.

EXPERIMENTAL VARIABLES

Tooth and investing tissue layers (enamel, dentin, cementum, pulp, periodontal ligament, and alveolar bone).

OUTCOME MEASURE

Von Mises and maximum principal stresses.

RESULTS

Increasing the apical thickness of cementum increases the amount of mechanical stress.

CONCLUSION

A finite element model incorporating all layers of a human maxillary central incisor has been developed. This model was used to determine the location and magnitude of mechanical stress generated for all regions of the tooth, PDL, and enclosed alveolar bone, when orthodontic forces are applied to the tooth. Mechanical stresses were found to increase at the root apex with increasing thickness of apical cementum.