Radiological assessment of periodontal ligament space visibility on third molars for forensic age assessment - a comparison study of three different staging scales.

Various staging scales have been proposed for the assessment of the visibility of the periodontal ligament space of mandibular third molars on dental panoramic radiographs (PANs) for forensic age assessment in living individuals. However, up to now, there has been no systematic comparison between these staging scales available. We directly compared the 2010 staging scale proposed by Olze et al. with the 2017 staging by Lucas et al. and the 2020 staging by Guo et al. in a German study population. We evaluated 233 PANs from 115 females and 118 males aged 20.0 to 40.9 years using three independent examiners, with one examiner conducting two assessments. We examined the correlation between age and stage, as well as the inter- and intra-rater reliabilities. While the point estimates for the correlation coefficient and the reliability measures were lowest for the Guo scale and highest for the Olze scale, confidence intervals showed a large overlap, particularly for the scales of Olze et al. and Lucas et al. The correlation coefficients between stage and age were consistently lower in females than in males across all methods. In summary, we showed that the staging scales of Olze et al. and Lucas et al. were very similar. The Olze method showed higher point estimates across all analyses, and because there are more reference data available for this method, we argue that it should be preferred as the method of choice for further studies in the field. However, Guo method could be considered for instances, in which the inter-radicular periodontal ligament is not evaluable.

Effects of different patterns of movement for correcting a deep curve of Spee with clear aligners on the anterior teeth: a finite element analysis.

OBJECTIVE: To analyse the anterior teeth effects of clear aligners on five different patterns of mandibular molar movement and to define the most effective configuration to be implemented with clear aligners through finite element analysis. METHODS: A three-dimensional mandibular model with a deep overbite in the mandible was constructed using cone beam computerized tomography (CBCT) data. The model included the mandibular dentition, mandibular periodontal ligaments, attachments, and aligners. Five models were created: (1) configuration A: second molar distalization (0.25 mm); (2) configuration B: second molar distalization (0.25 mm), first molar extrusion (0.15 mm); (3) configuration C: second molar distalization (0.25 mmm), first and second premolar extrusion(0.15 mm); (4) configuration D: second molar distalization (0.25 mm), first molar and first/second premolar extrusion(0.15 mm); and (5) configuration E: second molar distalization (0.25 mm), first molar and first/second premolar extrusion (0.15 mm), first molar and first/second premolar expansion (0.15 mm). RESULTS: In all configurations, the anterior teeth exhibited labial tipping and the mandibular central incisor of configuration E showed the highest labial tipping. Configuration E demonstrated a relatively minor impact on mandibular molars distalization compared with configuration A. Configuration A showed the highest distal displacement value, and configuration E produced the lowest displacement value. Configuration E caused the highest periodontal ligament (PDL) pressure of the central and lateral incisors. The differences in the canines between configurations C and D,were not significant, and the stress distribution differed among the five groups. CONCLUSIONS: All patterns utilizing clear aligners facilitated mandibular molar distalization. Extruding the premolars and second molar distalization at the same time had little impact on second molar distalization; When expansion and extrusion were simultaneously performed during the distalization of mandibular molars, our prime consideration was the alveolar bone on the labial side of the anterior teeth to prevent the occurrence of gingival recession, dehiscence, and fenestration. Due to the lack of consideration for periodontal tissues in this study, clinical protocols should be designed based on the periodontal status of the mandibular anterior teeth.

Effectiveness of different intrusion modes of maxillary anterior teeth with mini-implants in clear aligner treatment: a three-dimensional finite element analysis.

BACKGROUND: The intrusion of maxillary anterior teeth is often required and there are various intrusion modes with mini-implants in clear aligner treatment. The objective of this study was to evaluate the effectiveness of maxillary anterior teeth intrusion with different intrusion modes, aiming to provide references for precise and safe intrusion movements in clinical practice. METHODS: Cone-beam computed tomography and intraoral optical scanning data of a patient were collected. Finite element models of the maxilla, maxillary dentition, periodontal ligaments (PDLs), clear aligner (CA), attachments, and mini-implants were established. Different intrusion modes of the maxillary anterior teeth were simulated by changing the mini-implant site (between central incisors, between central and lateral incisor, between lateral incisor and canine), loading site (between central incisors, on central incisor, between central and lateral incisor, between lateral incisor and canine), and loading mode (labial loading and labiolingual loading). Ten conditions were generated and intrusive forces of 100 g were applied totally. Then displacement tendency of the maxillary anterior teeth and CA, and stress of the PDLs were analyzed. RESULTS: For the central incisor under condition L14 and for the canine under conditions L11, L13, L23, and L33, the intrusion amount was negative. Under other conditions, the intrusion amount was positive. The labiolingual angulation of maxillary anterior teeth exhibited positive changes under all conditions, with greater changes under linguoincisal loading. The mesiodistal angulation of canine exhibited positive changes under labial loading, while negative changes under linguoincisal loading except for condition L14. CONCLUSIONS: The intrusion amount, labiolingual and mesiodistal angulations of the maxillary anterior teeth were affected by the mini-implant site, loading site, and loading mode. Labial and linguoincisal loading may have opposite effects on the intrusion amount of maxillary anterior teeth and the mesiodistal angulation of canine. The labiolingual angulation of the maxillary incisors would increase under all intrusion modes, with greater increases under linguoincisal loading.

Using machine learning to determine age over 16 based on development of third molar and periodontal ligament of second molar.

BACKGROUND: Having a reliable and feasible method to estimate whether an individual has reached 16 years of age would greatly benefit forensic analysis. The study of age using dental information has matured recently. In addition, machine learning (ML) is gradually being applied for dental age estimation. AIM: The purpose of this study was to evaluate the development of the third molar using the Demirjian method (Demirjian3M), measure the development index of the third molar (I3M) using the method by Cameriere, and assess the periodontal ligament development of the second molar (PL2M). This study aimed to predict whether Chinese adolescents have reached the age of criminal responsibility (16 years) by combining the above measurements with ML techniques. SUBJECTS & METHODS: A total of 665 Chinese adolescents aged between 12 and 20 years were recruited for this study. The development of the second and third molars was evaluated by taking orthopantomographs. ML algorithms, including random forests (RF), decision trees (DT), support vector machines (SVM), K-nearest neighbours (KNN), Bernoulli Naive Bayes (BNB), and logistic regression (LR), were used for training and testing to determine the dental age. This is the first study to combine ML with an evaluation of periodontal ligament and tooth development to predict whether individuals are over 16 years of age. RESULTS AND CONCLUSIONS: The study showed that SVM had the highest Bayesian posterior probability at 0.917 and a Youden index of 0.752. This finding provides an important reference for forensic identification, and the combination of traditional methods and ML is expected to improve the accuracy of age determination for this population, which is of substantial significance for criminal litigation.

Functional Adaptation of LPS-affected Dentoalveolar Fibrous Joints in Rats.

INTRODUCTION: The functional interplay between cementum of the root and alveolar bone of the socket is tuned by a uniquely positioned 70-80 µm wide fibrous and lubricious ligament in a dentoalveolar joint (DAJ). In this study, structural and biomechanical properties of the DAJ, periodontal ligament space (PDL-space also known as the joint space), alveolar bone of the socket, and cementum of the tooth root that govern the biomechanics of a lipopolysaccharide (LPS)-affected DAJ were mapped both in space and time. METHODS: The hemi-maxillae from 20 rats (4 control at 6 weeks of age, 4 control and 4 LPS-affected at 12 weeks of age, 4 control and 4 LPS-affected at 16 weeks of age) were investigated using a hybrid technique; micro-X-ray computed tomography (5 µm resolution) in combination with biomechanical testing in situ. Temporal variations in bone and cementum volume fractions were evaluated. Trends in mineral apposition rates (MAR) in additional six Sprague Dawley rats (3 controls, 3 LPS-affected) were revealed by transforming spatial fluorochrome signals to functional growth rates (linearity factor - RW) of bone, dentin, and cementum using a fast Fourier transform on fluorochrome signals from 100-µm hemi-maxillae sections. RESULTS: An overall change in LPS-affected DAJ biomechanics (a 2.5-4.5X increase in tooth displacement and 2X tooth rotation at 6 weeks, no increase in displacement and a 7X increase in rotation at 12 weeks; 27% increase in bone effective strain at 6 weeks and 11% at 12 weeks relative to control) was associated with structural changes in the coronal regions of the DAJ (15% increase in PDL-space from 0 to 6 weeks but only 5% from 6 to 12 weeks compared to control). A significant increase (p < 0.05) in PDL-space between ligated and age-matched control was observed. The bone fraction of ligated at 12 weeks was significantly lower than its age-matched control, and no significant differences (p > 0.05) between groups were observed at 6 weeks. Cementum in the apical regions grew faster but nonlinearly (11% and 20% increase in cementum fraction (CF) at 6 and 12 weeks) compared to control. Alveolar bone revealed site-specific nonlinear growth with an overall increase in MAR (108.5 µm/week to 126.7 µm/week after LPS treatment) compared to dentin (28.3 µm/week in control vs. 26.1 µm/week in LPS-affected) and cementum (126.5 µm/week in control vs. 119.9 µm/week in LPS-affected). A significant increase in CF (p < 0.05) in ligated specimens was observed at 6 weeks of age. CONCLUSIONS: Anatomy-specific responses of cementum and bone to the mechano-chemo stimuli, and their collective temporal contribution to observed changes in PDL-space were perpetuated by altered tooth movement. Data highlight the "resilience" of DAJ function through the predominance of nonlinear growth response of cementum, changes in PDL-space, and bone architecture. Despite the significant differences in bone and cementum architectures, data provided insights into the reactionary effects of cementum as a built-in compensatory mechanism to reestablish functional competence of the DAJ. The spatial shifts in architectures of alveolar bone and cementum, and consequently ligament space, highlight adaptations farther away from the site of insult, which also is another novel insight from this study. These adaptations when correlated within the context of joint function (biomechanics) illustrate that they are indeed necessary to sustain DAJ function albeit being pathological.

Overall stress in periodontal ligament under orthodontic movement during a periodontal breakdown.

INTRODUCTION: This research aimed to assess qualitatively and quantitatively the overall stress in the periodontal ligament during gradual periodontal breakdown (0-8 mm) under orthodontic movements. Correlations between the applied forces, the level of bone loss, the decrease of force magnitude, and the increase of stress were also assessed. METHODS: On the basis of cone-beam computed tomography examinations (voxel size, 0.075 mm), nine 3-dimensional models of a mandibular second premolar with intact periodontium were created and then individually subjected to various levels of horizontal bone loss. Orthodontic forces (intrusion at 0.2 N; extrusion, rotation, and tipping at 0.6 N; translation at 1.2 N) were applied on the brackets. Finite elements analysis was performed, and von Mises (VM) stresses were quantitatively and qualitatively determined. RESULTS: Rotation and translation induced the highest stress apically and cervically, whereas intrusion determined the lowest. Apical stress was lower than cervical stress. In intact periodontium, VM stress was under maximum hydrostatic pressure (MHP) and maximum tolerable stress (MTS). In reduced periodontium, VM stress was lower apically than MHP, whereas cervically, the rotation, translation, and tipping exceeded MHP. CONCLUSIONS: A force of 1.2 N seemed safe to be used in the intact periodontium. Forces higher than 0.6 N could produce stresses exceeding MHP and MTS endangering the reduced periodontium. VM stress failure criterion (despite its limited use) seemed to be more adequate for accurate quantitative results. An overall correlation between the applied force, VM stress increase, and periodontal breakdown applicable to all 5 movements could not be established. This was possible only for individual movements.

The effects of different types of periodontal ligament material models on stresses computed using finite element models.

INTRODUCTION: Finite element (FE) method has been used to calculate stress in the periodontal ligament (PDL), which is crucial in orthodontic tooth movement. The stress depends on the PDL material property, which varies significantly in previous studies. This study aimed to determine the effects of different PDL properties on stress in PDL using FE analysis. METHODS: A 3-dimensional FE model was created consisting of a maxillary canine, its surrounding PDL, and alveolar bone obtained from cone-beam computed tomography scans. One Newton of intrusion force was applied vertically to the crown. Then, the hydrostatic stress and the von Mises stress in the PDL were computed using different PDL material properties, including linear elastic, viscoelastic, hyperelastic, and fiber matrix. Young's modulus (E), used previously from 0.01 to 1000 MPa, and 3 Poisson's ratios, 0.28, 0.45, and 0.49, were simulated for the linear elastic model. RESULTS: The FE analyses showed consistent patterns of stress distribution. The high stresses are mostly concentrated at the apical area, except for the linear elastic models with high E (E >15 MPa). However, the magnitude varied significantly from -14.77 to -127.58 kPa among the analyzed patients. The E-stress relationship was not linear. The Poisson's ratio did not affect the stress distribution but significantly influenced the stress value. The hydrostatic stress varied from -14.61 to -95.48 kPa. CONCLUSIONS: Different PDL material properties in the FE modeling of dentition do not alter the stress distributions. However, the magnitudes of the stress significantly differ among the patients with the tested material properties.

Individualization of the three-piece base arch mechanics according to various periodontal support levels: A finite element analysis.

INTRODUCTION: The orthodontic correction of periodontally compromised dentitions constitutes a huge challenge in the clinical practice of adult orthodontics. The biological and physical distinct features of these conditions require a carefully designed mechanical plan for the successful treatment of these complex cases. SETTING AND SAMPLE POPULATION: A segment of a human maxilla containing the central and lateral incisors, obtained from autopsy, was scanned with microcomputed tomography, and a finite element (FE) model was generated to represent an intact periodontal dentition. Based on this model, three additional models simulating a mild, moderate and severe bone alveolar loss were created as well. MATERIALS AND METHODS: Two loading scenarios for the application of intrusive and retraction mechanics with a three-piece base arch appliance were evaluated in a series of FE analyses. The tooth displacements and strains in the periodontal ligament (PDL) were calculated and compared for the four FE models. RESULTS: The periodontal reduced dentitions exhibited a similar axis of resistance for intrusive mechanics, but the axis of resistance for retraction movements was significantly dependent on the degree of alveolar bone loss. The tooth displacements and PDL loads were higher in the reduced dentitions for both intrusive and retraction mechanics. CONCLUSIONS: A reduction in the force levels applied to periodontal reduced dentitions is indicated, and a customized selection of appropriate points of force application is needed according to the specific amount of alveolar bone loss.

Nonuniformity in ligaments is a structural strategy for optimizing functionality.

Ligaments serve as compliant connectors between hard tissues. In that role, they function under various load regimes and directions. The 3D structure of ligaments is considered to form as a uniform entity that changes due to function. The periodontal ligament (PDL) connects the tooth to the bone and sustains different types of loads in various directions. Using the PDL as a model, employing a fabricated motorized setup in a microCT, we demonstrate that the fibrous network structure within the PDL is not uniform, even before the tooth becomes functional. Utilizing morphological automated segmentation methods, directionality analysis, as well as second harmonic generation imaging, we find high correlation between blood vessel distribution and fiber density. We also show a structural feature in a form of a dense collar around the neck of the tooth as well as a preferred direction of the fibrous network. Finally, we show that the PDL develops as a nonuniform structure, with an architecture designed to sustain specific types of load in designated areas. Based on these findings, we propose that ligaments in general should be regarded as nonuniform entities, structured already at developmental stages for optimal functioning under variable load regimes.

Numerical simulation of optimal range of rotational moment for the mandibular lateral incisor, canine and first premolar based on biomechanical responses of periodontal ligaments: a case study.

OBJECTIVES: The objective of this study was to investigate the optimal range of rotational moment for the mandibular lateral incisor, canine and first premolar to determine tooth movements during orthodontic treatment using hydrostatic stress and logarithmic strain on the periodontal ligament (PDL) as indicators by numerical simulations. MATERIAL AND METHODS: Teeth, PDL and alveolar bone numerical models were constructed as analytical objects based on computed tomography (CT) images. Teeth were assumed to be rigid bodies, and rotational moments ranging from 1.0 to 4.0 Nmm were exerted on the crowns. PDL was defined as a hyperelastic-viscoelastic material with a uniform thickness of 0.25 mm. The alveolar bone model was constructed using a non-uniform material with varied mechanical properties determined based on Hounsfield unit (HU) values calculated using CT images, and its bottom was fixed completely. The optimal range values of PDL compressive and tensile stress were set as 0.47-12.8 and 18.8-51.2 kPa, respectively, whereas that of PDL logarithmic strain was set as 0.15-0.3%. RESULTS: The rotational tendency of PDL was around the long axis of teeth when loaded. The optimal range values of rotational moment for the mandibular lateral incisor, canine and first premolar were 2.2-2.3, 3.0-3.1 and 2.8-2.9 Nmm, respectively, referring to the biomechanical responses of loaded PDL. Primarily, the optimal range of rotational moment was quadratically dependent on the area of PDL internal surface (i.e. area of PDL internal surface was used to indicate PDL size), as described by the fitting formula. CONCLUSIONS: Biomechanical responses of PDL can be used to estimate the optimal range of rotational moment for teeth. These rotational moments were not consistent for all teeth, as demonstrated by numerical simulations. CLINICAL RELEVANCE: The quantitative relationship between the area of PDL internal surface and the optimal orthodontic moment can help orthodontists to determine a more reasonable moment and further optimise clinical treatment.

Biomechanical analysis of occlusal modes on the periodontal ligament while orthodontic force applied.

OBJECTIVE: The study objective was to investigate four common occlusal modes by using the finite element (FE) method and to conduct a biomechanical analysis of the periodontal ligament (PDL) and surrounding bone when orthodontic force is applied. MATERIALS AND METHODS: A complete mandibular FE model including teeth and the PDL was established on the basis of cone-beam computed tomography images of an artificial mandible. In the FE model, the left and right mandibular first premolars were not modeled because both canines required distal movement. In addition, four occlusal modes were simulated: incisal clench (INC), intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function (RGF). The effects of these four occlusal modes on the von Mises stress and strain of the canine PDLs and bone were analyzed. RESULTS: Occlusal mode strongly influenced the distribution and value of von Mises strain in the canine PDLs. The maximum von Mises strain values on the canine PDLs were 0.396, 1.811, 0.398, and 1.121 for INC, ICP, RMOL, and RGF, respectively. The four occlusal modes had smaller effects on strain distribution in the cortical bone, cancellous bone, and miniscrews. CONCLUSION: Occlusal mode strongly influenced von Mises strain on the canine PDLs when orthodontic force was applied. CLINICAL RELEVANCE: When an FE model is used to analyze the biomechanical behavior of orthodontic treatments, the effect of muscle forces caused by occlusion must be considered.

Compressive stress in periodontal ligament under orthodontic movements during periodontal breakdown.

INTRODUCTION: This analysis aimed to assess quantitatively and qualitatively the compressive stress (S3) in periodontal ligament in a gradual periodontal breakdown (0-8 mm) under orthodontic movements. Correlations between the applied forces, the level of bone resorption, the decrease of force magnitude, and S3 increase were also conducted. METHODS: On the basis of cone-beam computed tomography examinations (voxel size, 0.075 mm), nine 3-dimensional models of the second mandibular premolar with intact periodontium were created and then individually subjected to various levels of horizontal bone loss. Orthodontic forces (intrusion: 0.2 N; extrusion, rotation, tipping: 0.6 N; translation: 1.2 N) were applied on the brackets. Finite elements analysis was performed, and S3 stresses were quantitatively and qualitatively determined. RESULTS: Translation and rotation induced the highest stress apically and cervically, whereas intrusion determined the lowest. Apical stress was lower than cervical stress. In intact periodontium, only intrusion and extrusion exhibited S3 stresses lower (apically and cervically) than maximum hydrostatic pressure (MHP) and maximum tolerable stress (MTS). In reduced periodontium, S3 stress (except for intrusion) exceeded MHP and MTS. CONCLUSIONS: In reduced periodontium, forces of 0.2 N seems safe to be used. Forces of 0.6-1.2 N may produce stresses exceeding both MTS and MHP, endangering the periodontium. S3 failure criterion (despite its widely use) seems not to be adequate for accurate quantitative results when evaluating the stress in the periodontal ligament while remaining adequate for qualitative results. An overall correlation between the applied force, S3 increase, and periodontal breakdown applicable to all 5 movements could not be established-this was possible only for sole movements.

Analytical methodology to measure periodontal bone morphometry following orthodontic tooth movement in mice.

INTRODUCTION: Basic research in orthodontics is commonly conducted in rodents. However, experimental studies on orthodontic tooth movement (OTM) lack a standard method to examine OTM and periodontal changes. This study describes a unifying protocol for the analysis of OTM and associated bone microarchitectural changes in mice using microcomputed tomography (µCT). METHODS: Mice (10 animals/group) were divided into control and OTM groups. OTM was generated by anchoring a nickel-titanium closed-coil spring to the upper incisors to pull the upper left first molar. A third group of TNFα -/- mice was added since these are known to have slower OTM. Using µCT, we implemented and tested a number of methods to measure OTM distance and examine 3D bone morphometric parameters associated with OTM in mice. RESULTS: In total, we tested five methods to measure the OTM distance in mice. The results indicated that measuring the intermolar diastema, and assessing tooth movement relative to the anterior root of the zygomatic arch, displayed the lowest standard deviation and enabled optimal detection of intergroup differences. We also developed two protocols for µCT analysis of the periradicular bone that yielded no false-positive results. Our results revealed that including the width of the periodontal ligament rather than excluding it from the region of interest in mice detected more statistically significant differences in the morphometric parameters between the OTM and control sides and between WT and TNFα -/- mice despite more subtle differences. CONCLUSIONS: We, therefore, propose new guidelines for a standardized µCT-based method to analyse OTM and the extent of the periradicular bone structural changes in mice.

Dental age estimation based on the radiographic visibility of the periodontal ligament in the lower third molars: application of a new stage classification.

The purpose of the present study was to test whether a new stage classification based on radiographic visibility of the periodontal ligament in lower third molars in a Chinese population can be used for the 18- and 21-year thresholds. A total of 1300 orthopantomograms, including equal numbers of northern Chinese males and females evenly distributed between the ages of 15 and 40 years, were analyzed. The stages were defined according to the visibility of periodontal ligament for the outer parts of lower third molar roots because the visibility status of the periodontal ligament between the roots of lower third molars is none valuable in many Chinese individuals. Stage 0 was first achieved at the age of 17.05 years in males and 17.46 years in females. The earliest appearance of stage 1 was 17.47 years in males and 17.86 years in females. Stage 2 was first observed in males at the age of 21.43 years and in females at the age of 21.96 years. The onset of stage 3 was first observed at the age of 25.83 years in males and 23.14 years in females. Compared with the stage classification of Olze et al., which also considers the mesial parts of the roots, the number of assessable cases could be significantly increased. Therefore, our novel approach is effective for age estimation in the Chinese population.

Cystathionine gamma-lyase aggravates periodontal damage in traumatic occlusion mouse models.

BACKGROUND AND OBJECTIVE: Though impacts of traumatic occlusion (TO) on periodontal tissues and roles of cystathionine γ-lyase (Cth) gene in the regulation of bone homeostasis have been studied by many, no consensus has been reached so far on whether TO deteriorates the periodontium and precise roles of Cth in occlusal trauma. Therefore, this study aims to investigate the impacts of TO on periodontal tissues and the involvement of Cth gene. METHODS: Eighty C57BL/6 wild-type (WT) mice and Cth knockout (Cth-/- ) mice, 8 weeks old, were used in this study. The TO model was established using composite resin bonding on the left maxillary molar for one, two, and three weeks, respectively. Morphological and histological changes in the periodontium were assessed by micro-computed tomography (micro-CT), hematoxylin and eosin (H&E) staining, and tartrate-resistant acid phosphatase (TRAP) staining. Osteoclast-related genes were analyzed by real-time polymerase chain reaction (qPCR). RESULTS: It was found that decreased alveolar bone height, expanded bone resorption area, and increased width of periodontal ligament (PDL) occurred in TO models, accompanied by an increased number of osteoclasts in a time-dependent manner by micro-CT and histological staining. Osteoclast-related genes including Ctsk, Mmp9, Rank, Trap, and Rankl/Opg were also up-regulated after one week of modeling. The up-regulated expressions of Cth gene and its protein CTH were observed in TO mouse models. After 1, 2, or 3 weeks of modeling, WT mice showed more severe alveolar bone resorption, wider PDL, higher osteoclast count, and higher levels of osteoclast-related genes Ctsk, Rank, and Rankl/Opg than Cth-/- mice. CONCLUSION: TO causes a reduction in alveolar bone height and PDL morphological disorder with their severity increases in a time-dependent manner. Cth aggravates periodontal damage caused by TO.

Effect of photobiomodulation therapy as an adjunct to scaling and root planing in a rat model of ligature-induced periodontitis: a histological and radiographic study.

This study aimed to histologically and radiographically evaluate the effectiveness of low-intensity laser irradiation of different wavelengths (660 or 808 nm) as an adjunct to scaling and root planing in the treatment of experimental periodontitis in rats. Periodontitis was induced by placing a ligature around the mandibular first molar of the rats. In total, 40 Wistar rats were randomly divided into five groups (n = 8 each): control (CG), periodontal disease (PD), scaling and root planing (SRP), SRP + 660 nm laser (GL660) and SRP + 808 nm laser (GL808). Groups with laser use received radiation at 6 points in the first molar. The animals were euthanized at baseline and at 7 and 14 days after the interventions. Mandibles were surgically removed for histomorphometric and radiographic assessment of periodontal tissues. The GL660 group showed lesser bone loss than the PD group (P < 0.05) and greater alveolar bone margin after 14 days, indicating a better long-term treatment response (P < 0.05). These findings suggest that SRP with the 660 nm laser as an adjunct results in more favorable radiographic and histological responses than the 808 nm laser.

Periodontal ligament enhancement in mesio-angulated impaction of third molars after orthodontic tooth movement: A prospective cohort study.

INTRODUCTION: The mesio-angulated impaction of mandibular third molars makes them unsuitable as donor teeth for tooth autotransplantation. However, uprighted molars may be applicable for autotransplantation. This study aimed to determine the amount of periodontal ligament (PDL) on the root surfaces of extracted third molars after an application of uprighting force and to examine the amount of PDL at the tension and compression sites. METHODS: In this prospective cohort study, 15 mesio-angulated mandibular third molars (iM8s) from 15 patients planned for orthodontic extraction, were uprighted using springs connected to miniscrews, whereas 15 nonopposing and fully erupted mandibular third molars from 15 other patients served as controls. The altered angulation was monitored and assessed from panoramic radiographs. All 30 molars, removed by simple extraction, were stained with 0.04% (w/v) toluidine blue to analyze the percentages of stained PDL on the root surfaces. RESULTS: An average period of 3.4 months was necessary to upright the iM8s at a mean rate of 8.3° per month. The mean percentage of stained PDL on the loaded iM8s was significantly greater than that on the unloaded molars (P <0.05). The mean percentages of stained PDL were significantly increased at the cervical and middle thirds and the buccal, mesial, and distal surfaces of the loaded iM8s compared with those of the unloaded molars (P <0.05), whereas the apical third and the lingual surface, corresponding to the compression sites, showed no significant increases. CONCLUSIONS: Orthodontic uprighting leads to significantly increased proliferative PDL on certain radicular portions and surfaces of iM8s, which might be useful for tooth autotransplantation.

Response of the tooth-periodontal ligament-bone complex to load: A microCT study of the minipig molar.

One strategy evolved by teeth to avoid irreversible damage is to move and deform under the loads incurred during mastication. A key component in this regard is the periodontal ligament (PDL). The role of the bone underlying the PDL is less well defined. We study the interplay between the PDL and the underlying alveolar bone when loaded in the minipig. Using an Instron loading device we confirmed that the force-displacement curves of the molars and premolars of relatively fresh minipig intact mandibles are similar to those obtained for humans and other animals. We then used this information to obtain 3D images of the teeth before and after loading the tooth in a microCT such that the load applied is in the third linear part of the force displacement curve. We observed that at many locations there is a complimentary topography of the cementum and alveolar bone surface, strongly suggesting an active interplay between the tooth and the bone during mastication. We also observed that the loaded tooth does not come into direct contact with the underlying bone surface. A highly compressed layer of PDL is present between the tooth and the bone. The structure of the bone in the upper furcation region has a unique appearance with little obvious microstructure, abundant pores that have a large size range and at many locations the bone at the PDL interface has a needle-like shape. We conclude that there is a close interaction between the tooth, the PDL and the underlying alveolar bone during mastication. The highly compressed PDL layer that separates the tooth from the bone may fulfill a key shock absorbing function.

Examination of regressive features of third molars for the purpose of age assessment in the living by means of rescaled regression analyses.

The main criterion of dental age assessment in living adolescents and young adults is the evaluation of third molars' mineralization. Concerning forensic age assessment after the completion of third molars' mineralization, apposition of secondary dentine and narrowing of the periodontal membrane as seen as decreasing radiolucent areas in the radiographs for mandibular third molars have already been described as regressive features. The present study examines the combination of both these features for the purpose of age assessment in regression analyses after rescaling the data to make it on the interval scale. To this end, a total of 1245 orthopantomograms was evaluated, taken from 606 females and 639 males in the age group of 15-40 years. The apposition of secondary dentine and narrowing of the periodontal membrane as seen as decreasing radiolucent areas in the radiographs were determined for the lower third molars. The correlation of the features with the chronological age was assessed by means of rescaled regression analyses. Furthermore, regression formulas for age assessment were established. The values of the standard error of estimate ranged between 3.55 and 4.52 years. In general, the rescaled regression of the examined features appears to be suited for forensic age assessment. A limitation of the present study is the comparatively low number of evaluable teeth in the examined age group. Due to an incomplete development or a lack of the mandibular third molars, only a mere half of the respective teeth could be included in the statistical analysis.

Microanatomical changes and biomolecular expression at the PDL-entheses during experimental tooth movement.

The novel aspect of this study was to contextualize the co-localization of biomolecular expression in widened and narrowed periodontal ligament (PDL)-space within a mechanically activated periodontal complex. The PDL is unique as it is the only ligament with both innervation and vascularization. Maxillary molars in 6-week-old male C57BL/6 mice (N = 5) were experimentally translated for 2 weeks using an elastic spacer. Contralateral teeth were used as controls. Mechanical testing of the periodontal complex of a mouse in situ and imaging using X-ray micro-computed tomography (micro-XCT) illustrated deformations within blood vessels (BV) of the PDL. PDL-bone and PDL-cementum entheses at the widened and narrowed PDL-spaces following experimental tooth movement (ETM) illustrated osterix (OSX), bone sialoprotein (BSP), cluster of differentiation 146 (CD146), and protein gene product 9.5 (PGP9.5), indicating active remodeling at these sites. PGP9.5 positive nerve bundles (NBs) were co-localized with multinucleated cells (MCs), Howship's resorption lacunae, and CD146 positive BVs. Association between nerves and MC was complemented by visualizing the proximity of osmium tetroxide stained NBs with the ultrastructure of MCs by performing scanning transmission electron microscopy. Spatial association of NB with BV, and NB with MC, provided insights into the plausible co-activation of NBs to initiate osteoclastic activity. Resorption of mineral occurred as an attempt to restore PDL-space of the load-bearing complex, specifically at the PDL-entheses. Mapping of anatomy-specific structural elements and their association with regenerative molecules by correlating light and electron micrographs provided insights into the use of these extracellular matrix molecules as plausible targets for pharmacological interventions related to tooth movement. Within the realm of tissue regeneration, modulation of load can reverse naturally occurring mineral formation to experimentally induced resorption, and naturally occurring mineral resorption to experimentally induced formation at the enthesial sites to permit tooth translation.