Types of tooth movement, bodily or tipping, do not affect the displacement of the tooth's center of resistance but do affect the alveolar bone resorption

Effects of torque overcorrection on mandibular incisor intrusion using clear aligners in the first premolar non-extraction and extraction conditions: a finite element analysis study

BACKGROUND

During intrusion and retraction, the mandibular incisors tend to tip labio-lingually, which might damage the surrounding alveolar bone. This study aimed to investigate the effect of torque overcorrection on the tooth movement and the stress distribution of the periodontal tissues.

METHODS

Mandible and mandibular dentition were reconstructed in the digital software. Three groups were divided: first premolar non-extraction with incisor intrusion (NEI) group, first premolar extraction with incisor intrusion (EI) group, and first premolar extraction with incisor intrusion and retraction (EIR) group. The intrusion amount of 0.25 mm with different torque overcorrection degrees (0°, 1°, 2°, 3°) were sequentially added on the incisors. The biomechanical responses of the teeth and periodontal tissues were calculated in the ANSYS software.

RESULTS

With no overcorrection, the incisors were intruded with lingual tipping, while the canines and premolars were extruded with mesial tipping. The compressive stress was concentrated on the lingual cervical and labial apical areas of the periodontal ligaments (PDLs) and alveolar bone. The incisors in the EIR group showed the most lingual displacement and the highest stress level. When 1°, 1° and 3° overcorrection degrees were added in the NEI, EI and EIR groups, respectively, the lingual displacement of the incisors decreased to zero and the stress was uniformly distributed on the PDLs and alveolar bone. With the increase of the overcorrection degrees, the incisors tended to tip labially, while the canines and premolars also gradually showed distal tipping tendencies. The compressive stresses were concentrated on the labial cervical and lingual apical areas of the PDLs and alveolar bone.

CONCLUSIONS

During mandibular incisor intrusion, the torque overcorrection design may help reduce the lingual tipping tendencies of the incisors, relieve the compressive stress on the periodontal tissues, and protect the anchorage from the canines and premolars. When the first premolar was extracted, similar overcorrection degrees are required if the incisor retraction was not designed. However, more overcorrection degrees are required if the incisor intrusion and retraction were designed synchronously.

Biomechanical effects of periodontal status on molar sequential distalization with clear aligners: a finite element study

OBJECTIVE

Molar sequential distalization with clear aligners was advantageous. However, the effect of periodontal status on it has yet to be investigated. This study aimed to analyze the influence of the different periodontal states on molar distalization to reduce the adverse mechanical stimulation caused by periodontal states by the different stagings of movement and further explore therapeutic recommendations for clinical practice.

METHODS

To ascertain the initial displacement of dentition and periodontal ligament (PDL) hydrostatic stress, finite element models (FEMs) were developed. These models included the distalization of the second molars (Step A) and the first molar (Step B) in three distinct periodontal conditions (simulating the periodontal state of mild, moderate, and severe periodontitis) and three distinct distances (0.10 mm, 0.18 mm, 0.25 mm).

RESULTS

Periodontal status affected the tooth movement during molar distalization. During the molar distalization with 0.25 mm step distance, the initial displacement of the molar was greater in the model with worse periodontal condition. However, it did not increase the efficiency of tooth movement because the initial displacement is accompanied by tipping. Moreover, the second molar relapse to mesialization for a reaction from the first molar distalization affected efficiency. Fortunately, reducing the step distance could control those undesired tooth movements positively associated with alveolar bone resorption.

LIMITATIONS

The finite element method cannot simulate complex periodontal conditions in clinical practice.

CONCLUSION

To reduce the undesired tipping and relapse, the personalized staging of movement should be designed according to the periodontal condition. Designing 0.18 mm step distance for patients with 1/3 alveolar bone resorption is recommended, whereas patients with 1/2 alveolar bone resorption need 0.1 mm. These recommendations can guide orthodontists in designing effective treatment plans for patients with varying degrees of periodontal disease.

Three-dimensional zone of the centers of resistance of the mandibular incisors and canines: A novel approach by finite element analysis

OBJECTIVES

The distribution and size of the zone of the centres of resistance (ZCR) are critical for accurate orthodontic treatments and minimizing unexpected tooth movements. However, this information remains unclear for mandibular incisors and canines. This study aims to address these gaps in knowledge.

METHODS

Finite element models of four incisors and canines from four individuals were created. Four centres of resistance (CRs) under four orthodontic directions (0° ∼ 45° ∼ 90° ∼ 135° to the sagittal plane in the horizontal plane) were assessed by a novel method. The height of the CRs was normalized to a percentage of the long axis, and the offsets were expressed as a distance value after normalization. The ZCR was obtained by fitting a 90% confidence sphere of the CR distribution. Validation was conducted to find the perturbations when the positions out of the zone were applied.

RESULTS

The maximum variation of CR in the heights under four directions was 5.17% and 3.70% for the incisors and canines, respectively. The maximum offset between the CR and long axis was 0.14mm in incisors and 0.99mm in canines. The height of the zone in the incisor and canine was 57.75% and 59.72%, and the radius of the zone was 0.60mm and 0.65mm, respectively. The force-acting point outside the zone produced a large rotation, which was unexpected.

CONCLUSIONS

The ZCR of mandibular incisors located slightly lower than that of canines, but they were almost the same size. The ZCR was recommended as the "gold reference" for orthodontics to reduce unexpected movement.

Measurement of the root surface area in rat molars through three-dimensional modeling

OBJECTIVES

Rats are used as animal models for basic and applied research related to orthodontic tooth movement (OTM). The magnitude of mechanical force in OTM rat models mainly depends on the supporting capability of the periodontal ligament (PDL), which is highly associated with the root surface area (RSA). But the size of rat RSA remains unknown, which is the reason why there are still debates on the magnitude of mechanical force in OTM rat models. This study aimed to explore a method for measuring the RSA in rat molars.

DESIGN

The maxillary and mandibular samples of rats were scanned by Micro-CT to generate three-dimensional (3D) images, followed by 3D reconstruction of every molar through Mimics Medical 21.0. Geomagic Wrap 2021 and Unigraphics NX 12.0 were utilized to smooth teeth surface and mark the cementoenamel junction (CEJ). Finally, the RSA in rat molars was measured.

RESULTS

The results showed that for the six-, eight-, or ten-week-old rats, the average RSA of maxillary first, second, and third molars was 25.90 ± 2.29 mm2, 15.92 ± 2.14 mm2, and 10.34 ± 1.94 mm2. The RSA of mandibular first, second, and third molars was 27.03 ± 2.63 mm2, 17.16 ± 1.61 mm2, and 11.39 ± 2.13 mm2.

CONCLUSIONS

Through 3D modelling, we provided data of rat RSA, and observed the trend of increasing RSA mean values with age. These data are pivotal for determining the magnitude of mechanical force required to move rat molars, especially when conducting research related to OTM using rat models.

Cantilever-aided bodily protraction of a mandibular molar with clear aligner: A finite element analysis

OBJECTIVE

To analyse the biomechanics of molar protraction through clear aligner therapy (CAT) with and without a buccal cantilever.

METHODS

Models were composed of mandible, lower dentition, periodontal ligaments, attachments, a buccal cantilever, and clear aligner. Four groups were designed: (1) control (aligner only), (2) aligner+buccal cantilever with buccal class II traction, (3) aligner+buccal cantilever with buccal class II and lingual class II tractions, (4) aligner+buccal cantilever with buccal horizontal traction named buccal class I, buccal class II, and lingual class II tractions.

RESULTS

CAT alone caused mesial tipping, lingual tipping, and intrusion of mandibular second molar. Adding the buccal cantilever on the mandibular second molar with 100-g buccal class II traction was effective in preventing the mesial tipping of mandibular second molar, but resulted in a greater lingual tipping tendency. Further addition of lingual class II traction prevented aforementioned lingual tipping and bodily protraction was achieved in sagittal dimension, while buccal tipping was present. Bodily protraction without buccolingual tipping was achieved through clear aligner, buccal class II, lingual class II, and buccal class I tractions, and the stress concentrated on the alveolar bone was reduced.

CONCLUSION

CAT produced mesial tipping, lingual tipping, and intrusion of mandibular molar during protraction. The incorporation of the buccal cantilever into the clear aligner improves the biomechanical effect of molar protraction. Bodily molar protraction can be achieved with a judicious combination of buccal class II, lingual class II and buccal class I tractions with clear aligner and buccal cantilever.

Reference points to evaluate changes in the upper lip after labial incisor movement between tipping and translation in crowding patients: A retrospective study

Objective

This study aimed to compare the changes of reference points on the labial surface of upper incisors (U1) to upper lip (UL) after U1 labial movement between a translation group (TSL) and tipping group (TIP). Correlations between changes in U1 and UL were determined.

Methods

Lateral cephalometric radiographs were selected and divided into TSL and TIP groups by pre- and post-treatment superimpositions. Skeletal, dental, and soft tissue of pre- and post-treatment and variables were evaluated. Independent t-test and Mann-Whitney U test were applied for the statistical analysis between TSL and TIP. Spearman's correlation coefficients and multiple linear regression analysis were used to verify the association between lip profile changes and other variables in TSL and TIP group separately.

Results

After U1 labial movement, the incisal edge (LaU1e), middle (LaU1m), and cervical (LaU1c) points of TSL moved evenly labially, whereas the TIP group had incisal edge that moved greater labially than the middle and cervical points. UL moved more labially in TSL (0.87-1.05 mm) than the TIP (0.31-0.41 mm). UL changes to the E-line in TSL showed significant positive correlations to all three LaU1(e, m, c)-SnTV changes. In the TIP group, only a positive correlation presented for the LaU1m-SnTV and LaU1c-SnTV changes. Nevertheless, Multiple linear regression analysis indicated the unfeasibility of predicting the upper lip changing.

Conclusion

LaU1e in TSL and TIP moved almost equally labially but less labially in TIP at the middle and cervical points. The UL moved more labially in TSL than TIP. Rather than using the incisal edge to estimate upper lip changes, it would be better to use the middle and cervical points of U1, which coincide with Labrale superioris (Ls).

Mandibular molar protraction: A comparison between fixed functional appliances and temporary anchorage devices

INTRODUCTION

This study aimed to compare the efficiency of temporary anchorage devices (TADs) and fixed functional appliances (FFAs) for mandibular molar protraction.

METHODS

Orthodontic records of 1050 consecutively treated patients with molar protraction were screened. Thirty-six records (22 females and 14 males; mean age, 17.4 years) were divided into two groups: TAD (21 subjects with 25 edentulous spaces) and FFA (15 subjects with 24 edentulous spaces). The primary outcome measure was the efficiency of protraction [magnitude and time required for protraction (rate) and anchor loss (AL)]. The secondary outcomes involved measuring the type of tooth movement (TOTM), external apical root resorption (EARR), alveolar bone height change (ABHC), alveolar bone width change (ABWC) and appliance failure.

RESULTS

The rate of tooth movement was significantly higher for FFAs (0.83 ± 0.35 mm/month) versus TADs (0.49 ± 0.2 mm/month) (P = .005). Total treatment duration was less for FFAs (34.78 ± 8.1 months) versus TADs (47.72 ± 13.94 months) (P = .002). TOTM was similar for both (P = .909). EARR was 1.42 ± 1.38 mm for TAD and 1.25 ± 0.88 mm for FFA (P = .81). ABHC increased in the FFA group (1.01 ± 3.62 mm) and decreased for the TAD group (0.68 ± 1.66 mm). ABWC increased for both TAD (1.81 ± 1.73 mm) and FFA (1.75 ± 1.35 mm). The failure rate was 50% for FFAs and 33% for TADs.

CONCLUSIONS

Both systems provided translation of lower molars with comparable anchorage control. However, FFAs were more efficient than TADs for lower molar protraction.

Three-dimensional finite element analysis of the optimal mechanical design for maximum inward movement of the anterior teeth with clear aligners

This study aims to refine clinical designs within clear aligner therapy, exploring the appropriate ratio of anterior tooth retraction to intrusion under maximum anchorage. Using a three-dimensional finite element model and evaluating 19 load scenarios with first premolar extraction, the research identifies the optimal force angle for anterior tooth retraction as 45 to 55°. For clinical planning, it is recommended to design a retraction of 0.19 mm combined with an intrusion of 0.16 mm to achieve anterior tooth retraction. This investigation is crucial for enhancing understanding of biomechanical principles in clear aligner orthodontics, offering significant insights for effective treatments.

Early-stage periodontal ligament compression predicts orthodontically induced root resorption in rats

OBJECTIVES

To determine the effect of orthodontic pressure on periodontal ligament (PDL) compression in rats and assess correlation between PDL compression and orthodontically induced root resorption (OIRR).

MATERIALS AND METHODS

Eight female Wistar rats aged 10 weeks underwent surgery to place 2 mini-screws at the center of the palatal plate. 25 cN coil springs connecting the maxillary first molars and mini-screws were applied bilaterally to generate mesial force. Maxillary first molars were assigned to undergo either bodily or tipping movements. Micro-computed tomography (μCT) scans were taken on days 0, 3, 7, and 14, and histological sections were taken on day 14. OIRR was measured from histological sections, and the corresponding PDL compression ratio was quantified using μCT images.

RESULTS

The PDL was compressed by approximately 76% in tipping movement and 55% in bodily movement after 3 days, and by approximately 47% in bodily and tipping movements after 7 days of orthodontic force application. The extent of OIRR in tipping movement was significantly greater than that in bodily movement. A strong positive correlation between OIRR and PDL compression ratio was observed on day 3; however, no correlation was observed on day 7.

CONCLUSIONS

A strong correlation between PDL compression ratio and OIRR was observed at an early stage after the application of orthodontic force regardless of the tooth movement type (bodily or tipping), implying the importance of early stage PDL compression in the induction of OIRR.

Alveolar bone loss and root resorption in mesialized second molars in mandibular first molar extraction cases as compared to contralateral non-extraction side in young adults: A retrospective cross-sectional study

INTRODUCTION

The alveolar bone loss (ABL) and external apical root resorption (EARR) depict the safety of mesialization of mandibular second molars into the extraction space of mandibular first molars. The aim of this study was to evaluate the ABL and EARR after closure of mandibular first molar extraction space by mesialization of second molar on extraction side (ES) as compared to the contralateral non-extraction side (NES).

MATERIAL AND METHODS

A retrospective cross-sectional study was carried out using the pre and posttreatment orthodontic records of young adults with complete set of permanent dentitions treated with extraction of unilateral mandibular first molar and non-extraction treatment on the contralateral side. All patients underwent mini-implant supported mesialization of second molar on ES. The ABL and EARR of second molar on ES and contralateral NES were measured on digital orthopantomograms. The ABL and EARR of second molars on ES and contralateral NES were compared using independent sample t-test.

RESULTS

A total of 36 subjects (14 males and 22 females) were included in the study. The mean treatment duration for molar mesialization was 28.75±8.05months. The mean crown and root movements of mandibular second molar on ES were 10.94±1.25mm and 9.04mm±1.14mm, as compared to 0.91±1.01mm and 0.77±0.83mm on contralateral NES, respectively. The mean ABL and EARR at mandibular second molar were found to be significantly greater on the ES than the contralateral NES (P<0.001 and<0.05, respectively). A total of seven patients (19.4%) experienced ABL≥1mm on ES as compared to none in the contralateral NES. EARR of>2mm of at least one root was found in seven patients (19.4%) in ES as compared to four (11%) in contralateral NES.

CONCLUSION

There was small but statistically significant difference in the ABL and EARR of mesialized mandibular second molar at first molar ES as compared to the contralateral NES. For majority of patients this difference was small but few isolated cases experienced severe ABL and EARR.

Effect of piezocision-assisted lower second molar protraction on periodontal tissues, alveolar bone height, and lower second molar root resorption

OBJECTIVES

To assess the effect of piezocision on periodontal tissues and alveolar bone height and to detect lower second molar root resorption in piezocision-assisted mandibular second molar protraction compared to no-piezocision molar protraction.

MATERIALS AND METHODS

Twenty-one subjects (four males, 17 females, aged 22.43 ± 2.83 years) who presented with bilateral extraction of lower first molars were included. The patients were divided into two groups; Group 1: Piezocision-assisted molar protraction (right or left side of subjects) in which piezocision was performed immediately before lower second molar protraction and, Group 2: No-piezocision molar protraction in which lower second molar protraction was not surgically assisted. Plaque index (PI), gingival index (GI), periodontal pocket depth (PPD), width of keratinized gingiva (WKG), gingival recession (GR), lower second molar mesial root resorption, alveolar bone height, and mandibular bone height were recorded at T1 (immediately before molar protraction) and at T2 (after second molar space closure).

RESULTS

In the piezocision-assisted molar protraction group, significant changes were detected in the WKG (P < .001), GR (P < .05), and the mandibular bone height (P < .001). Compared to the no-piezocision group, piezocision-assisted molar protraction resulted in an increased WKG (P < .001) and less second molar mesial root resorption (P < .01).

CONCLUSIONS

Piezocision does not have any detrimental effect on the periodontium and produces less root resorption.

Periodontal and Orthodontic Synergy in the Management of Stage IV Periodontitis: Challenges, Indications and Limits

This retrospective study described the clinical and radiographic long-term outcomes of combined periodontal and orthodontic treatment (OT) with fixed appliances in patients with Stage IV periodontitis and pathologic tooth migration (PTM) in the anterior sextants. OT was performed in either one or both arches, using tooth-supported or skeletal anchorage, following completion of active periodontal treatment and accurate planning of tooth movement biomechanics. Twenty-nine patients were identified and retrospectively examined when presenting for a supportive periodontal care (SPC) appointment. The mean SPC duration was 8.9 years (range 5 to 12 years). All anterior-migrated teeth showed statistically significant periodontal improvement compared to baseline values and stable radiographic bone levels at the final follow-up. Residual probing depths were 2.9 ± 0.5 mm at the end of active periodontal treatment, and they remained stable at the completion of OT (2.9 ± 0.6 mm) and at the last follow-up visit (2.8 ± 0.5 mm). These findings suggest that OT is a safe and effective treatment in improving the long-term prognosis of teeth with PTM in Stage IV periodontitis provided that periodontal health has been re-established and maintained with individualized SPC sessions.

Detailed Correlation between Central Incisor Movement and Alveolar Bone Resorption in Adults with Orthodontic Premolar Extraction Treatment: A Retrospective Cohort CBCT Study

Background: This study aims to explore the detailed correlation between the movement of maxillary and mandibular central incisors and alveolar bone resorption in adults who had orthodontic premolar extraction treatment. Methods: A total of 63 adult patients (mean age, 24.41 years) who received orthodontic treatment with the extraction of four first premolars were included in this study. CBCT images were obtained before and after treatment. Three-dimensional evaluations of the movement of 252 central incisors (126 maxillary and 126 mandibular incisors) and alveolar bone changes were conducted. Four points were used to describe the incisor movement: C (cusp point), R (root apex point), M (mid-point of root neck), and L (labial cementoenamel junction point). The thickness of labial and palatal alveolar bone was assessed at the crestal, mid-root, and apical levels of incisors. The results were analyzed with Spearman’s correlation and multilinear regression. Results: Matching the measurements of central incisor movement and alveolar bone resorption, significant correlations could be observed. For maxillary central incisors, the labial alveolar bone resorption at the crestal level was correlated with the movement of Point L (r = 0.290, p < 0.05), and the labial alveolar bone resorption at the apical level was correlated with Point M (r = 0.387, p < 0.05). For mandibular central incisors, the labial alveolar bone resorption at the apical level was correlated with the movement of Point M (r = 0.493, p < 0.05) and R (r = 0.498, p < 0.01); the palatal alveolar bone resorption at the mid-root level with Point M (r = -0.170, p < 0.01); and the palatal alveolar bone resorption at the apical level with Point R (r = 0.177, p < 0.01). Conclusions: This study investigated the concrete correlations between central incisor movement and alveolar bone resorption in adults after orthodontic treatment with premolar extraction. It is potentially helpful for orthodontists to have a relatively accurate prediction of alveolar bone resorption based on the specific movements of central incisors and to reduce the risk of alveolar bone resorption by better adjusting the three-dimensional movement types of incisors.

Alveolar bone changes after molar protraction in young adults with missing mandibular second premolars or first molars

OBJECTIVES

To assess the changes in alveolar bone of the mandibular second molars following molar protraction and investigate the factors associated with the alveolar bone changes.

MATERIALS AND METHODS

Cone-beam computed tomography of 29 patients (mean age 22.0 ± 4.2 years) who had missing mandibular premolars or first molars and underwent molar protraction were reviewed. Alveolar bone level was measured as the distance from the cementoenamel junction at six points, buccal, lingual, mesiobuccal (MB), mesiolingual (ML), distobuccal (DB), and distolingual (DL), of the second molars at pretreatment (T0) and after molar protraction (T1). Factors associated with alveolar bone changes at the distal and mesial of the second molars were assessed.

RESULTS

Mean alveolar bone changes ranged from -1.2 mm (bone apposition) to 0.8 mm (bone resorption). The presence of a third molar impaction at T0 (P < .001), third molar angulation at T0 (P < .001), and Nolla's stage of third molar at T0 (P = .005) were significantly associated with alveolar bone level changes distal to the second molars. Treatment duration (P = .028) was significantly associated with alveolar bone level changes mesial to the second molar.

CONCLUSIONS

Patients with impacted third molars, third molars at an earlier stage of development, and mesially angulated third molars at pretreatment may have less alveolar bone resorption distal to the second molars following protraction. Patients with increased treatment time may have reduced alveolar bone resorption mesial to the second molars.

Efficiency and side effects of a novel method for maxillary central root torque (a horizontal box loop of round wire) in comparison with the conventional rectangular wire: A finite element study

INTRODUCTION

Applying root torque using conventional methods (rectangular wire) has side effects such as inverse and destructive forces, undesirable torque on adjacent teeth, heavy forces that are limited in range and duration, and needing too many sessions. We introduce a new method (a horizontal box loop [HBL]) that is designed to reduce many of these side effects; we tested its efficiency and side effects using finite element analysis.

METHODS

An HBL was created from a 0.018-in round stainless steel archwire, in the form of an equilateral triangle of 7 mm sides, for the permanent maxillary left central incisor. As a control, a SS rectangular wire (19 × 25-in) was used. First, a pilot simulation was performed to standardize the torque in both models as 31.099 N mm. The extent of twisting by the rectangular wire, of which the same amount of moment would be applied, was estimated at 28.282°. The main study evaluated the effects of the 31.099 N.mm moments applied by both models to the left central incisor on stresses, dental movements (buccolingually, mesiodistally, and extrusive or intrusive), and intercanine or intermolar widths.

RESULTS

Under standardized conditions, the HBL causes a greater palatal root torque of the central incisor than the rectangular wire. The HBL does not apply reverse root torque on adjacent teeth, whereas the rectangular wire causes reverse root torque in neighboring teeth. The HBL also causes less extrusion and expansion in the molar area than does the rectangular wire. The HBL increases intercanine width, whereas the rectangular wire might not change it.

CONCLUSIONS

HBL of round wire seems an appropriate appliance and hence its clinical assessment is recommended.

Three-dimensional assessment of two different canine retraction techniques: a randomized split-mouth clinical trial

Introduction

The aim of this split-mouth trial was to compare power-arm sliding (PAS) and direct sliding (DS) canine retraction mechanics in terms of speed, rotation, angulation, and anchorage loss.

Methods

Thirty-six class II division 1 patients (20 females, 16 males; mean age, 16.94 ± 3.23) requiring upper first premolar extraction were included in the study. Miniscrews were used as anchorage units, and a retraction force of 150 gr was applied from the power arm on one side and from the bracket on the opposite side by using elastomeric chains. Randomization was achieved by block randomization with a 1:1 allocation ratio either to the right or the left with allocations concealed in opaque, sealed envelopes. Digital models were acquired using an intraoral scanner at the beginning of the retraction (T0), the first month (T1), the second month (T2), and the third month (T3). Before the scans, the archwire was removed, and custom metal jigs were inserted into the vertical slot of the canine brackets to evaluate the canine angulation. The digital models of each patient were separately superimposed with the local best-fit algorithm, and the retraction rate, angulation, rotation, and anchorage loss were measured. The digital measurements were performed using the Geomagic Control X software.

Results

The DS technique’s total retraction rate was higher than that of the PAS technique (2.09 and 1.57, respectively, p = .002). There was, however, no significant difference between the two techniques in terms of angulation, rotation, and anchorage loss. A negative correlation was observed between the retraction rate and age, but it was not statistically significant. No significant difference was observed between the retraction rates of female and male participants in either retraction technique.

Conclusions

For both orthodontists and patients, the DS technique is simpler and more convenient; thus, it is the preferred method for canine retraction.

Trial registration

The trial was not registered.

Protocol

The protocol was not published before the trial commencement.

Factors associated with alveolar bone depth mesial to the mandibular third molars after orthodontic protraction

INTRODUCTION

The objective of this research was to study the factors associated with the alveolar bone depth mesial to the mandibular third molars (M8) after the mandibular second (M7) and third molars were protracted into the space of the mandibular first molars (M6), which were newly extracted for orthodontic treatment or extracted more than 1 year before treatment.

METHODS

This retrospective study included 57 adult patients (mean age 23.40 ± 4.40 years) in whom M6 were newly extracted for orthodontic treatment or extracted more than 1 year before treatment. The alveolar bone depth mesial to M8 was measured on posttreatment panoramic radiographs. The vertical, horizontal, and angular changes of M8 were measured on both pre- and posttreatment panoramic radiographs. Linear correlation and regression analyses were conducted to explore the factors associated with the alveolar bone depth mesial to M8.

RESULTS

The alveolar bone conditions of M6 (R= -0.391, P <0.001) and the vertical movement directions of M8 (R= -0.433, P <0.001) were significant factors associated with the alveolar bone depth mesial to M8 after orthodontic protraction.

CONCLUSIONS

Without considering the pretreatment periodontal status of M8, patients with M6 extracted exceeding 1 year before treatment and with M8 extruded after orthodontic protraction may exhibit deeper alveolar bone depth mesial to M8.

Orthodontic Tooth Movement Studied by Finite Element Analysis: an Update. What Can We Learn from These Simulations?

PURPOSE OF REVIEW

To produce an updated overview of the use of finite element (FE) analysis for analyzing orthodontic tooth movement (OTM). Different levels of simulation complexity, including material properties and level of morphological representation of the alveolar complex, will be presented and evaluated, and the limitations will be discussed.

RECENT FINDINGS

Complex formulations of the PDL have been proposed, which might be able to correctly predict the behavior of the PDL both when chewing forces and orthodontic forces are simulated in FE models. The recent findings do not corroborate the simplified view of the classical OTM theories. The use of complex and biologically coherent FE models can help understanding the mechanisms leading to OTM as well as predicting the risk of root resorption related to specific force systems and magnitudes.

Stress distribution and deformation in six tie wings Orthodontic bracket during simulated tipping - A finite element analysis

BACKGROUND AND OBJECTIVES

Four tie wings brackets are widely used in orthodontics, while the Six Tie Wings Brackets (STWB) are recently emerging in fixed orthodontic appliances due to their claim for less friction and thus faster teeth movement. The aim of this work was to evaluate the stress distribution and deformation during simulated mesio-distal tipping forces in Stainless Steel (SS) six tie wings orthodontic bracket using Finite Element Analysis (FEA).

METHODS

A six tie wings bracket (Synergy®, RMO, USA) dimensions were measured using the Vision system and a 3D model of the bracket was constructed. A Finite Element (FE) model was developed and mesio-distal tipping forces of 1.22 N to 1.96 N (125 to 200 gm) in increments were applied on the gingival and incisal slot walls. The stress distribution and deformation were recorded at specific points in the bracket and analyzed.

RESULTS

The maximum deformation and stress distribution for the mesial and distal tipping forces of 1.96 N were recorded as 0.137 µm and 10.60 MPa respectively. The stress concentration was more at the junction of the slot wall and the slot base. For mesial tipping,the deformation was more on the disto-incisal and mesio-gingival tie wings. Similarly, for distal tipping the deformation was more on the mesio-incisal and disto-gingival tie wings. The mid-tie wings showed minimal deformation during both distal and mesial tipping.

CONCLUSIONS

Our study visualized both the mesial and distal tipping forces induced stress distribution in the bracket tie wing-slot junctions. The deformation was present maximum in the mesio-incisal and disto-incisal tie wings and minimal in the mid-tie wings. Clinicians should be aware of this behavior of STWB in making decisions to alter the tipping forces in the archwire to compensate for the tie wing deformation in refining the teeth position.

Three-dimensional nonlinear prediction of tooth movement from the force system and root morphology

OBJECTIVES

To determine the different impact of moment-to-force ratio (M:F) variation for each tooth and spatial plane and to develop a mathematical model to predict the orthodontic movement for every tooth.

MATERIALS AND METHODS

Two full sets of teeth were obtained combining cone-beam computed tomography (CBCT) and optical scans for two patients. Subsequently, a finite element analysis was performed for 510 different force systems for each tooth to evaluate the centers of rotation.

RESULTS

The center of CROT locations were analyzed, showing that the M:F effect was related to the spatial plane on which the moment was applied, to the force direction, and to the tooth morphology. The tooth dimensions on each plane were mathematically used to derive their influence on the tooth movement.

CONCLUSION

This study established the basis for an orthodontist to determine how the teeth move and their axes of resistance, depending on their morphology alone. The movement is controlled by a parameter (k), which depends on tooth dimensions and force system features. The k for a tooth can be calculated using a CBCT and a specific set of covariates.

Effect of Magnet Position on Tipping and Bodily Tooth Movement in Magnetic Force-Driven Orthodontics

The goal of our study is to launch magnetic force-driven orthodontics. This continuous study investigated the influence of magnet position on tipping and bodily tooth movement, using 3D printing technology and digital analysis. Orthodontic typodont models (TMs) for space-closure were 3D printed to mimic maxillary central incisors. Nd-Fe-B magnets were placed in the middle third (Model-M), and the cervical third (Model-C), of the tooth. TMs, before and after movement, were digitally scanned and superimposed. The 3D digital coordinates (X, Y, and Z axes), and rotations (yaw, pitch, and roll) of the tooth crown and root, were calculated and compared between the two magnet position settings. Model-M showed higher rates of movement, but more rotation than Model-C (p < 0.01). The root apex of Model-M moved in the opposite direction of the crown (R = −0.29), indicating tipping movement. In contrast, the crown and root apex moved in the same direction (R = 0.56) in Model-C, indicating bodily movement. These patterns were confirmed in a typodont model of a moderate crowding case. The results validated that modifying the magnet position increased the amount of bodily tooth movement, and decreased rotation/tipping in an ex vivo setting.

Change in alveolar bone level of mandibular second and third molars after second molar protraction into missing first molar or second premolar space

Objective

To investigate the factors associated with the change in alveolar bone level of mandibular second and third molars after second molar protraction into the space of the missing first molar (L6) or second premolar (LE).

Methods

Fifty-one patients in whom space of the missing L6 or LE was treated with second molar protraction (13 males, 38 females, mean age 19.6 ± 4.7 years) from 2003 to 2015 were included. The alveolar bone level and position and angulation of the mandibular second and third molars were measured in panoramic radiographs at pre-treatment (T1), and after the alignment of the third molars following second molar protraction (T2). Factors associated with alveolar bone loss on the distal aspect of the mandibular second molars were assessed using linear regression analysis.

Results

Age at T1 (P < 0.001) and third molar angulation at T1 (P = 0.002) were significant factors for the prediction of alveolar bone level distal to the second molars.

Limitation

This study used two-dimensional panoramic radiographs, and we could observe only the interproximal bone level.

Conclusions

After second molar protraction into the missing first molar or second premolar space, mandibular second molars may exhibit alveolar bone resorption in the distal root in older patients and in those with mesially tilted third molars before treatment.

Pulp analysis of teeth submitted to different types of forces: a histological study in rats

Objective:

The purpose of this study was to histologically evaluate pulp and dentin under induced tooth movement (ITM) with different types of forces.

Material and Methods:

The maxillary right first molars of rats were submitted to movement with continuous (CF), continuous interrupted (CIF) and intermittent (IF) forces during 5, 7 and 9 days with nickel-titanium (NiTi) closed-coil springs exerting 50cN force magnitude. The groups were histologically evaluated as for cellularity pattern, presence of dystrophic, hemodynamic alterations in the pulp as well dentin alterations. The main observed alterations were related to hemodynamic pulp characteristics, such as presence of thrombosis, vascular congestion and hemorrhages. The hemodynamic alterations were statistically evaluated by Shapiro-Wilk normality test and analysis of variance by the Kruskall-Wallis test.

Results:

There was no significant differences observed between groups in the different types of applied forces and duration of ITM (vascular congestion, p=1.000; hemorrhage, p=0.305; thrombosis, p=1.000).

Conclusions:

Pulp tissue alterations resulting from ITM were limited to hemodynamic events, without progressing to irreversible degeneration, regardless of the type of force applied.