Physical properties of root cementum: Part 6. A comparative quantitative analysis of the mineral composition of human premolar cementum after the application of orthodontic forces

Physical properties of root cementum: Part 28. Effects of high and low water fluoridation on orthodontic root resorption: A microcomputed tomography study

INTRODUCTION

Transient inflammatory surface resorption, referred to as orthodontic induced inflammatory root resorption (OIIRR), is an iatrogenic consequence of orthodontic tooth movement. Systemic fluoride has been associated with a reduction of OIIRR. This study aimed to investigate the effects of water fluoridation levels on OIIRR in a clinically applicable human orthodontic model.

METHODS

Twenty-eight patients who required bilateral maxillary first premolar extraction as part of orthodontic treatment were selected from 2 cities with high and low water fluoridation of ≥2 ppm and ≤0.05 ppm, respectively. Patients were separated into high fluoride (HF) and low fluoride (LF) groups on the basis of water fluoridation levels. Bilateral maxillary first premolar teeth were subjected to 150 g of buccal tipping forces for 12 weeks with reactivation every 4 weeks. Teeth were extracted at the end of 12 weeks. Root resorption crater volume was determined using microcomputed tomography and 3-dimensional reconstruction.

RESULTS

HF group showed significantly less mean root resorption volume on the palatal root surface when compared with the LF group (P = 0.025). This difference was specifically displayed at palatal apical regions (P = 0.041). When root resorption volumes from the zones of orthodontic pressure (buccal cervical, palatal apical) were combined, the mean difference between HF and LF groups was statistically significant (P = 0.045).

CONCLUSIONS

Findings of the present study indicated a positive correlation between water fluoridation and the reduction of OIIRR, especially at the zones of orthodontic pressure, using a clinically relevant human orthodontic model.

The past and present research at the University of Sydney’s Discipline of Orthodontics

The University of Sydney’s Discipline of Orthodontics has been actively pursuing research in the areas of root resorption, sleep apnea, magnets in orthodontics, implants, acceleration of orthodontic tooth movement (OTM), and remote monitoring (RM). Our research has shed light on many specific factors that influence orthodontically induced inflammatory root resorption (OIIRR). We also explored the effects of some of the most discussed acceleration interventions on OTM and OIIRR, such as vibration, micro-osteoperforations, piezocision, low-level laser therapy, light emitting diode, light amplification by stimulated emission of radiation, and pharmacological substances. Further, we have researched into maximizing orthopedic treatment outcomes of maxillary deficient children with use of intraoral force application with utilization of miniscrew-assisted rapid palatal expander. We are currently trialing use of RM to facilitate orthodontic services in the public dental clinics.

Relationship between root resorption and individual variation in the calcium/phosphorous ratio of cementum

INTRODUCTION

The purpose of this study was to investigate whether individual variation in the hardness and chemical composition of the cementum in the root apex affects the degree of root resorption.

METHODS

In a previous study, we evaluated the Vickers hardness scale of 50 extracted teeth. For this study, we classified the 50 extracted teeth into soft, moderate, and hard groups according to the Vickers hardness scale. Then, we randomly selected 7 teeth from each group and measured the resorbed areas of the apical cementum in vitro using human osteoclast precursor cells. We also investigated the calcium/phosphorous (Ca/P) and magnesium/calcium ratios of these 21 extracted teeth using energy-dispersive x-ray microanalysis studies to determine the chemical composition of the cementum in the root apex.

RESULTS

In the pit formation assay, the resorbed area in the soft group showed a greater extent than it did in the moderate and hard groups (P < 0.01). A correlation was noted between the Vickers hardness and the resorbed area of the cementum in the root apex (r = -0.714; P < 0.01). The Ca/P ratios in the soft and moderate groups were lower than the ratio in the hard group (P < 0.01 and P < 0.05, respectively). A correlation was noted between the Vickers hardness and the Ca/P ratio of the cementum in the root apex (r = 0.741; P < 0.01).

CONCLUSIONS

These results suggest that the hardness and Ca/P ratio of the cementum may be involved in root resorption caused by orthodontic forces.

Physical properties of root cementum: Part 19. Comparison of the amounts of root resorption between the right and left first premolars after application of buccally directed heavy orthodontic tipping forces

INTRODUCTION

Previous studies have used the right and left sides of the same jaw to compare different force levels, types of movement, and durations of forces. However, the amounts of root resorption have not been compared between the right and left sides after applying the same amount of force. The aims of the study were to quantitatively compare the volumes of the root resorption lacunae between the right and left first premolars to determine whether 1 side can serve as a control to the other and to compare the volumes of root resorption lacunae of the first premolars between the maxilla and the mandible.

METHODS

Forty-four first premolars, orthodontically indicated for extraction from 11 patients (left and right maxillary and mandibular first premolars from each) were moved buccally by using beta-titanium-molybdenum alloy 0.017 × 0.025-in cantilever springs with continuous heavy (225 g) force. After the experimental period, the teeth were extracted under a strict protocol to prevent root cementum damage and then analyzed by using a microcomputed tomography scan x-ray system (1172; SkyScan, Aartselaar, Belgium) and specially designed software (Convex Hull 2D, University of Sydney, Sydney, Australia) for direct volumetric measurements.

RESULTS

There were no statistically significant differences in the mean cube root volumes of root resorption craters between the right and left sides (P = 0.18) or between the maxillary and mandibular jaws (P = 0.10). There was also no statistical significance for the interception (P = 0.41), which indicated that the jaw and the side had independent effects.

CONCLUSIONS

The amount of root resorption on the left and right sides of the jaw were similar in both the maxilla and the mandible. Therefore, for future root resorption studies, it is justifiable to use the split-mouth technique so that teeth from 1 side of the jaw can serve as the controls.

Analysis of orthodontically induced root resorption using micro-computed tomography (Micro-CT)

OBJECTIVE

To establish a protocol for assessing orthodontically induced tooth root resorption (OITRR) in human premolars using micro-computed tomography.

MATERIALS AND METHODS

Ten extracted maxillary first premolars were obtained from eight healthy adolescent patients; five of these premolars were extracted before any orthodontic movement was applied to them, and the other five premolars were involved in nonextraction orthodontic treatment for 1 year before treatment plan modification lead to extraction treatment. Using reconstructed scanned images, we measured several key resorption lacunae parameters, including the number, volume, and depth on each surface, as well as its extension coronoapically.

RESULTS

Orthodontic treatment resulted in a significantly greater tooth root resorption lacunae volume, number, maximum depth, and coronoapical extension as well as in areas of dentin demineralization subjacent to the resorption lacunae than in normal premolars.

CONCLUSIONS

We have established a protocol to evaluate OITRR quantitatively and have provided a method to predict further resorption based on dentine demineralization.

Periodontal Ligament Hydrostatic Pressure with Areas of Root Resorption after Application of a Continuous Torque Moment

Objective: To evaluate the risk of root resorption, individual finite element models (FEMs) of extracted human maxillary first premolars were created, and the distribution of the hydrostatic pressure in the periodontal ligament (PDL) of these models was simulated.

Materials and Methods: A continuous lingual torque of 3 Nmm and 6 Nmm respectively was applied in vivo to the aforementioned teeth. After extraction, FEMs of these double-rooted teeth were created based on high-resolution microcomputed tomographics (micro CT, voxel size: 35 microns). This high volumetric resolution made the recognition of very small resorption lacunae possible. Scanning electron micrographs of the root surfaces were created as well. This enabled the investigation of advantages and disadvantages of the different imaging techniques from the viewpoint of the examination of root resorption. Using the FEMs, the same loading conditions as applied in vivo were simulated.

Results: The results of clinical examination and simulations were compared using the identical roots of the teeth. The regions that showed increased hydrostatic pressure (&gt;0.0047 MPa) correlated well with the locations of root resorption for each tooth. Increased torque resulted in increased high-pressure areas and increased magnitudes of hydrostatic pressure, correlating with the experiments.

Conclusion: If hydrostatic pressure exceeds typical human capillary blood pressure in the PDL, the risk of root resorption increases.