Enamel chipping in Taï Forest cercopithecids: Implications for diet reconstruction in paleoanthropological contexts.

Antemortem enamel chipping in living and fossil primates is often interpreted as evidence of hard-object feeding (i.e., 'durophagy'). Laboratory analyses of tooth fracture have modeled the theoretical diets and loading conditions that may produce such chips. Previous chipping studies of nonhuman primates tend to combine populations into species samples, despite the fact that species can vary significantly in diet across their ranges. Chipping is yet to be analyzed across population-specific species samples for which long-term dietary data are available. Here, we test the association between enamel chipping and diet in a community of cercopithecid primates inhabiting the Taï Forest, Ivory Coast. We examined fourth premolars and first molars (n = 867) from naturally deceased specimens of Cercocebus atys, Colobus polykomos, Piliocolobus badius,Procolobus verus, and three species of Cercopithecus. We found little support for a predictive relationship between enamel chipping and diet across the entire Taï monkey community. Cercocebus atys, a dedicated hard-object feeder, exhibited the highest frequencies of (1) chipped teeth and (2) chips of large size; however, the other monkey with a significant degree of granivory, Co. polykomos, exhibited the lowest chip frequency. In addition, primates with little evidence of mechanically challenging or hard-food diets-such as Cercopithecus spp., Pi. badius, and Pr. verus-evinced higher chipping frequencies than expected. The equivocal and stochastic nature of enamel chipping in the Taï monkeys suggests nondietary factors contribute significantly to chipping. A negative association between canopy preference and chipping suggests a role of exogenous particles in chip formation, whereby taxa foraging closer to the forest floor encounter more errant particulates during feeding than species foraging in higher strata. We conclude that current enamel chipping models may provide insight into the diets of fossil primates, but only in cases of extreme durophagy. Given the role of nondietary factors in chip formation, our ability to reliably reconstruct a range of diets from a gradient of chipping in fossil taxa is likely weak.

Influence of cavity depth and restoration of non-carious cervical root lesions on strain distribution from various loading sites.

BACKGROUND: We aimed to investigate the load-induced strain variation in teeth with unrestored and resin-based composite restored non-carious cervical lesions (NCCLs). METHODS: Twelve extracted premolars were provided for measuring buccal-side root NCCLs. Strain gauges were fixed at four measuring sites of each tooth, two at the buccal surface and two at the lingual surface. NCCLs were prepared with occlusal margins at the cemento-enamel junction. A static 9-kg load was applied at seven occlusal loading points: buccal cusp tip (BC), inner inclination of the BC, lingual cusp tip (LC), inner inclination of the LC, center of the mesial marginal ridge or distal marginal ridge, and center of the central groove. The strain was detected at each site in teeth with NCCL depths of 0 (control), 0.5, 1.0, and 1.5 mm. Each NCCL was restored using an adhesive composite resin, and the strains were re-measured. RESULTS: The strains at the NCCL occlusal and gingival margins decreased with increasing defect depths, and the effect was significant when the depth of the defect was 1.5 mm. Loading on the buccal and lingual cusps induced prominent strain variation. The strains at all depth distribution recovered to nearly intact conditions when the NCCLs were restored. CONCLUSIONS: NCCLs at 1.5 mm depth are detrimental, but they can be restored using resin composites. CLINICAL SIGNIFICANCE: The existence of NCCLs should not be ignored. The depth of the NCCL may affect the progression of the lesion. Resin composite restoration is an appropriate method for preventing persistent NCCL deterioration.

Validation of contralateral premolars as the substrate for endodontic comparison studies.

AIM: To use micro-CT technology and metrology software to validate the use of contralateral premolars as samples in endodontic comparison studies by comparing them before and after canal instrumentation with one instrumentation system. Furthermore, to determine whether contralateral premolar roots (CPRs) will yield non-significantly different outcomes regarding shaping ability (volume), degree of twisting and three-dimensional shape changes. The null-hypothesis (H0 ) is that there are no differences between the CPRs pre- or post-instrumentation. METHODOLOGY: Twenty-eight extracted human contralateral premolars (n = 44 contralateral roots) from 12 donor patients were scanned with microcomputed tomography before and after instrumentation. Root canal lengths (RCLs) were measured visually using a dental-operating microscope, electronic apex locator and micro-CT scans. Data were analysed statistically for differences between pre- and post-instrumentation. RESULTS: Instrumentation increased the volume of the canals significantly (P < 0.05). Degree of twisting for a majority (83%) of the contralateral roots pairs did not change significantly (P > 0.05). There was no significant difference (P > 0.05) in the shape deviation analysis between contralateral pairs. There was no significant difference (P > 0.05) for RCL between the contralateral pairs for any of the three endometric methods. CONCLUSION: Contralateral premolar root canals were associated with similar changes in terms of volume, three-dimensional shape and degree of twisting from pre- to post-instrumentation. There was no difference between the CPR pairs pre- and post-instrumentation, and the study validates contralateral premolars as samples for root canal comparison studies. The null-hypothesis (H0 ) could not be rejected.

The evaluation of the transport medium for extracted premolars prior to cryopreservation: a systematic literature review.

Prior to cryopreservation, a tooth is transported from a contaminated oral environment to the tooth bank. Our objective was to identify all studies reporting or investigating a transport protocol prior to the cryopreservation of teeth, in terms of decontamination of the subjects. The systematic literature search (1970-2017) was based on MEDLINE via PubMed, Web of Science and the Cochrane Library. The reference lists of the included studies and the Science Citation Index were used for hand searching (snowballing). Only studies reporting the transport conditions of the transplant were included. Language restrictions for English, Dutch or French were applied. The search led to 14 eligible studies. Almost all studies were laboratory studies, so the methodological quality of evidence was low. The majority of the included studies was performed by only five different research groups and the number of subjects varied between 1 and 120 teeth. In general, the teeth were stored in a tissue culture medium supplemented with fetal calf serum and/or different combinations of antibiotics and/or antimycotics. The teeth were transported cooled (4 °C) or at room temperature, for a period of time not exceeding 24 h. Only three studies reported the irrigation of the teeth with phosphate buffered saline prior to the transport. The optimisation of the decontamination during transport was investigated in three studies (from 1971, 1980 and 1982). It was concluded that the literature on this topic is scarce, and the decontamination protocol for teeth, prior to cryopreservation has not been validated recently.

Analysis of masticatory muscle coordination during unilateral single-tooth clenching using muscle functional magnetic resonance imaging.

In a previous study, we used muscle functional magnetic resonance imaging to show that the anterior movement of the occlusal point increased the activity of the superior head of the ipsilateral lateral pterygoid muscle (ipsilateral SHLP) during unilateral single-tooth clenching. The purpose of this study was to verify the hypothesis that the increased activity of the ipsilateral SHLP described above serves to antagonise the occlusal force acting on the condyle. In total, 9 healthy volunteers were requested to perform left unilateral clenching at the first molar or first premolar region for 1 minute at 20% or 40% maximum voluntary clenching force. Changes in the mean proton transverse relaxation time (∆T2) were examined from the magnetic resonance images obtained before and after each clenching act as an index of the activity in all masticatory muscles. Correlation analyses of the mean ΔT2 for each volume of interest were performed with the first molar or premolar clenches to analyse the correlation between the activities in each muscle. A statistically significant correlation was exhibited between the ipsilateral temporal and ipsilateral SHLP (r = .651, P = .003) during first premolar clenching. However, no significant correlations were observed in the ipsilateral SHLP during first molar clenching. The results of this study suggest that the ipsilateral SHLP may contribute to the pulling of the mandibular condyle forward against the occlusal force generated by the ipsilateral temporal muscle.

Effect of Two Remineralizing Agents on Initial Caries-like Lesions in Young Permanent Teeth: An in Vitro Study.

AIM: To compare the effect of nano-hydroxyapatite (9000 ppm F) and casein phosphopeptide-amorphous calcium phosphate fluoride (900 ppm F) pastes on initial enamel carious lesions of young permanent teeth. MATERIALS AND METHODS: Sixty extracted young premolars with a standardized window on enamel were immersed in a demineralizing solution for 48 hours to produce subsurface enamel lesions. They were divided into three groups according to remineralizing agents (n = 20) group I: nano-hydroxyapatite paste; group II: casein phosphopeptide-amorphous calcium phosphate fluoride paste; and group III: control (without an agent). The enamel surface microhardness (SMH) was measured at baseline, after the incipient enamel lesion, and after treatment. Additional twenty young premolars were selected and prepared as mentioned above for surface morphology evaluation by scanning electron microscope (SEM). RESULTS: No significant difference was found in mean surface microhardness in teeth treated with nano-hydroxyapatite paste and those treated with casein phosphopeptide-amorphous calcium phosphate fluoride p = 0.26. SEM showed improvement in surface defects of demineralized enamel in the two test groups. CONCLUSION: Nano-hydroxyapatite and casein phosphopeptide-amorphous calcium phosphate fluoride pastes were effec -tive in rehardening the initial enamel caries lesions in young permanent teeth. CLINICAL SIGNIFICANCE: The best strategy for caries management is to focus on the methods of improving the reminer-alization process with the aid of the remineralizing agents. The current study compared the remineralizing effect of two remineralizing agents. Within the limitations of the study, both remineralizing agents were effective for remineralization of early caries-like lesions.

Interrelationships Between Morphometric, Densitometric, and Mechanical Properties of Teeth in 5-Month-Old Polish Merino Sheep.

Interrelationships between morphological, densitometric, and mechanical properties of deciduous mandibular teeth (incisors, canine, second premolar) were investigated. To perform morphometric, densitometric, and mechanical analyses, teeth were obtained from 5-month-old sheep. Measurements of mean volumetric tooth mineral density and total tooth volume were performed using quantitative computed tomography. Microcomputed tomography was used to measure total enamel volume, volumetric enamel mineral density, total dentin volume, and volumetric dentin mineral density. Maximum elastic strength and ultimate force of teeth were determined using 3-point bending and compression tests. Pearson correlation coefficients were determined between all investigated variables. Mutual dependence was observed between morphological and mechanical properties of the investigated teeth. The highest number of positive correlations of the investigated parameters was stated in first incisor indicating its superior predictive value of tooth quality and masticatory organ function in sheep. Positive correlations of the volumetric dentin mineral density in second premolar with final body weight may indicate predictive value of this parameter in relation with growth rate in sheep. Evaluation of deciduous tooth properties may prove helpful for breeding selection and further reproduction of sheep possessing favorable traits of teeth and better masticatory organ function, leading to improved performance and economic efficiency of the flock.

The Effect of Composite Thickness on the Stress Distribution Pattern of Restored Premolar Teeth with Cusp Reduction.

PURPOSE: Different thicknesses of restorative material can alter the stress distribution pattern in remaining tooth structure. The assumption is that a thicker composite restoration will induce a higher fracture resistance. Therefore, the present study evaluated the effect of composite thickness on stress distribution in a restored premolar with cusp reduction. MATERIALS AND METHODS: A 3D solid model of a maxillary second premolar was prepared and meshed. MOD cavities were designed with different cusp reduction thicknesses (0, 0.5, 1, 1.5, 2.5 mm). Cavities were restored with Valux Plus composite. They were loaded with 200 N force on the occlusal surface in the direction of the long axis. Von Mises stresses were evaluated with Abaqus software. RESULTS: Stress increased from occlusal to gingival and was maximum in the cervical region. The stressed area in the palatal cusp was more than that of the buccal cusp. Increasing the thickness of composite altered the shear stress to compressive stress in the occlusal area of the teeth. CONCLUSION: The model with 2.5 mm cusp reduction exhibited the most even stress distribution.

[Regeneration of dental pulp tissue using pulpal autologous mesenchymal stem cells and platelet-rich plasma]. / Regeneratsiia pul'py zuba s ispol'zovaniem autologichnykh mezenkhimal'nykh stvolovykh kletok pul'py i obogashchennoi trombotsitami plazmy.

Regeneration of pulp and dentin could be important in operative dentistry as a method to save teeth. Currently cell population from dental pulp of deciduous and permanent teeth of humans and laboratory animals are isolated and characterized. The paper presents a study on pulp regeneration using autologous mesenchymal stromal cells from pulp of molars in combination with fibrin clot, transplanted in pulp chamber of miniature pigs after pulp removal. The results proved that transplantation of autologous multipotent stromal cells of dental pulp in combination with autologous platelet-rich plasma in pulp chamber of miniature pigs after pulp removal leads to pulp restoration and reparative dentinogenesis with dentinal bridge formation on the 30th day. However, the completion of regeneration also results in a decrease in the pulp chamber volume due to the neodentin bedding. Tissue regeneration of dental pulp by direct pulp capping in the absence of inflammatory processes is a promising direction of the use of cellular technologies.

Quantitative sensory testing of dentinal sensitivity in healthy humans.

OBJECTIVE: The study was to provide information on quantitative sensory testing (QST) of normal teeth to establish a sensory profile and investigate the possible gender and regional differences. MATERIALS AND METHODS: A modified QST protocol was applied on both left and right upper-jaw incisors and pre-molar sof 14 healthy men and 14 age-matched healthy women (18-25 years). Mechanical stimulus sensitivity (MSS), cold detection threshold (CDT), cold pain threshold (CPT), warm detection threshold (WDT), heat pain threshold (HPT), electrical detection threshold (EDT) and electrical pain threshold (EPT) were determined from the four teeth (labial side of incisor and buccal side of the first premolar). The QST parameters were analysed by ANOVA. RESULTS: The applied mechanical or thermal stimuli did not evoke any pain sensation. A normal tooth did not seem to be able to distinguish between the warm or cold stimuli applied. No significant differences were found between genders (p > 0.099) or teeth (p > 0.053) regarding mechanical and thermal stimuli. The EDT and EPT were significantly higher in the pre-molar compared with incisor (p < 0.002) without gender differences (p > 0.573). CONCLUSION: The established methods and results provided important information on diagnosis and treatment evaluation of dentinal hypersensitivity.

Effect of material variation on the biomechanical behaviour of orthodontic fixed appliances: a finite element analysis.

INTRODUCTION: Biomechanical analysis of orthodontic tooth movement is complex, as many different tissues and appliance components are involved. The aim of this finite element study was to assess the relative effect of material alteration of the various components of the orthodontic appliance on the biomechanical behaviour of tooth movement. METHODS: A three-dimensional finite element solid model was constructed. The model consisted of a canine, a first, and a second premolar, including the surrounding tooth-supporting structures and fixed appliances. The materials of the orthodontic appliances were alternated between: (1) composite resin or resin-modified glass ionomer cement for the adhesive, (2) steel, titanium, ceramic, or plastic for the bracket, and (3) ß-titanium or steel for the wire. After vertical activation of the first premolar by 0.5mm in occlusal direction, stress and strain calculations were performed at the periodontal ligament and the orthodontic appliance. RESULTS: The finite element analysis indicated that strains developed at the periodontal ligament were mainly influenced by the orthodontic wire (up to +63 per cent), followed by the bracket (up to +44 per cent) and the adhesive (up to +4 per cent). As far as developed stresses at the orthodontic appliance are concerned, wire material had the greatest influence (up to +155 per cent), followed by bracket material (up to +148 per cent) and adhesive material (up to +8 per cent). LIMITATIONS: The results of this in silico study need to be validated by in vivo studies before they can be extrapolated to clinical practice. CONCLUSION: According to the results of this finite element study, all components of the orthodontic fixed appliance, including wire, bracket, and adhesive, seem to influence, to some extent, the biomechanics of tooth movement.

Ideal orthodontic alignment load relationships based on periodontal ligament stress.

OBJECTIVES: To test the hypothesis that periodontal ligament (PDL) stress relationships that yield resistance numbers representing load proportions between different teeth depend on alignment load type. MATERIALS AND METHODS: Finite element models of all teeth, except the third molars, were produced. Four different types of loads were applied, and the third principal stresses of different teeth in standardized areas of most compression were calculated. Based on these results, resistance numbers, representing the load proportions for each tooth derived from PDL stress, were determined. RESULTS: The third principal stress values for typical alignment loads in the areas of most stress were very different for different load types for each tooth. Differences in resistance numbers between teeth also varied with different loads. CONCLUSION: Resistance numbers, that is, load proportion numbers between teeth to achieve similar stress at the compressive PDL zone, depend on the type of applied load.

Angulations of Anterior Teeth With Reference to the Alveolar Bone Measured by CBCT in a Chinese Population.

OBJECTIVE: To analyze angulations of anterior teeth with reference to the alveolar bone. METHODS: Cone-beam computed tomographic (CBCT) images of 105 participants were taken with the same machine (ProMax 3D Max CBCT), showing the intact anterior teeth. The angulations formed between the long axis of the anterior teeth and the alveolus were measured using cross-sectional images. The thicknesses of alveolar bone on different area of root surfaces were also measured. RESULTS: Maxillary anterior teeth were found to be close to the buccal alveolar surface in apical level with the angulations referred to alveolar bone in center incisor, lateral incisor, and canine were 17.65 ± 6.8, 18.79 ± 7.4, and 23.82 ± 6.96 degrees, respectively. Means of angulations of mandibular anterior teeth were less than 8 degree. The thicknesses of buccal bone at mid-root level in 77% to 90% maxillary anterior teeth were less than 1 mm. The determinations provided high intrarater/interrater reliability. CONCLUSIONS: The application of CBCT is reliable for a complete calculation of angulations and thicknesses in a Chinese Han population. As a result, adequate planning combined with image examination preoperatively would contribute to a favorable outcome.

Cytokine measurements in gingival crevicular fluid and periodontal ligament: Are they correlated?

INTRODUCTION: Mechanical stress can induce molecular changes in gingival crevicular fluid (GCF) and the periodontal ligament (PDL). It is still not clear whether changes in the PDL and GCF are linked. In this study, we aimed to analyze the expression of cytokines in GCF and PDL after mechanical stress. METHODS: Twenty-three healthy patients were included. The experimental group consisted of premolars subjected to a force of 0.980 N for 1, 3, 7, 14, 21, or 28 days. The contralateral teeth were the controls. GCF and PDL samples were collected at the same time points for analysis of cytokines using the cytometric bead array. RESULTS: Interleukin (IL)-6 (IL-6) production was significantly elevated in the PDL on day 1 after force application. Significantly strong positive correlations between GCF and PDL in experimental group were seen on days 3 (interferon-gamma), 7 (IL-10), 14 (IL-17A), and 28 (IL-17A, tumor necrosis factor-alpha), and significantly strong negative correlation were seen on days 14 (interferon-gamma) and 21 (IL-2, IL-10). CONCLUSIONS: Different patterns of IL-6 expression were seen in the PDL and GCF after mechanical stress. Despite occasional correlations between GCF and PDL, the molecular contributions of the PDL to the GCF changes could not be clearly defined by our model.

Morphometric, densitometric and mechanical properties of mandibular deciduous teeth in 5-month-old Polish Merino sheep.

BACKGROUND: Caries, enamel hypoplasia, molar incisor hipomineralization, amylogenesis imperfecta, dentine dysplasia, hypophosphatasia and other dental disorders lead to tooth mineralization disturbances and structural abnormalities, decreasing masticatory organ functions. Dental disorders in sheep can lead to premature slaughter before they have attained final stage of their reproductive life and induce economic loss due to high flock replacement costs. Growth rate, health status and meat quality of sheep depends on tooth properties and quality determining in large extent efficiency of the masticatory apparatus and initial food break up. Considering lack of basic anatomical and physiological data on teeth properties in sheep, the aim of the study was to evaluate morphometric, densitometric and mechanical traits of deciduous mandibular incisor, canine and the second premolar obtained at the slaughter age of 5 months of life. RESULTS: The obtained results have shown the highest values of weight, total tooth volume, enamel volume and dentine volume in second premolar. Morphometric and mechanical parameters of incisors reached the highest values in first incisor and decreased gradually in second and third incisor, and in canine. Densitometric measurements have not revealed significant differences of the volumetric tooth mineral density in hard dental tissues between the investigated teeth. CONCLUSIONS: In conclusion, proposed methodological approach is noninvasive since the deciduous teeth undergo physiological replacement with permanent teeth. Deciduous teeth can be easy collected for analyses from large animal population and may reflect mineral status and metabolism resulting from postnatal growth and development of the whole flock. In individual cases, evaluation of properties of deciduous teeth may serve for breeding selection and further reproduction of sheep possessing favorable traits of teeth and better masticatory system functions.

Theoretical efficacy of preventive measures for pathologic fracture after surgical removal of mandibular lesions based on a three-dimensional finite element analysis.

PURPOSE: Pathologic fracture of the mandible after removal of a lesion historically has been a clinical problem. The present study aimed to evaluate mandibular strength after removal of a lesion and to illustrate the theoretical efficacy of preventive measures against pathologic fracture based on a 3-dimensional finite element (FE) analysis. MATERIALS AND METHODS: A computed tomographic (CT)-based FE model of the mandible of a patient with a dentigerous cyst including a third molar was constructed. Using this model, the decrease of mandibular strength after virtual removal of the lesion was analyzed. The effect of the decrease of occlusal force and reinforcement by a miniplate was analyzed using a simple FE model of the mandible. Based on these analyses, removal of the cyst with the third molar was performed with a decrease of occlusal force and reinforcement by a miniplate. The validity of these procedures was analyzed using a CT-based FE model constructed after surgery. RESULTS: The von Mises stress in a CT-based FE model after virtual removal of the cyst with the third molar was markedly greater than that in the original FE model. In the analysis using a simple FE model, the stress around the fenestrated area was decreased after premolar loading compared with that after molar loading. In addition, miniplate placement around the fenestrated area markedly decreased the stress. Based on these results, the cast crowns of the first and second molars were removed and the fenestrated area of the mandible was reinforced with a 1.5-mm locking miniplate in the actual surgery. The von Mises stress in the fenestrated area was decreased and primarily borne by the miniplate in the analysis of a CT-based FE model constructed after surgery. CONCLUSION: The present study illustrated the theoretical efficacy of plate application for the decrease of stress on the mandible after surgical removal of a cyst including a third molar based on a simulation by FE analysis.

Effects of post core materials on stress distribution in the restoration of mandibular second premolars: a finite element analysis.

STATEMENT OF PROBLEM: Previous studies have not resolved the question as to which post and core combination optimizes the stress distribution within the post restoration and tooth. PURPOSE: The purpose of this study was to determine which post and core combination provides the most favorable stress distribution upon loading. MATERIAL AND METHODS: Three-dimensional models of teeth were created with the Ansys program to simulate different materials used for post and cores (Ti, NiCr, AuPd, zirconia, zirconia post/composite resin core, glass fiber post/composite resin core, and carbon fiber post/composite resin core) and metal ceramic crowns (nickel chromium alloy [Group NiCr] and gold palladium alloy [Group AuPd]). A force of 400 N was applied to the occlusal surface, and von Mises equivalent stress values were calculated. RESULTS: Carbon fiber post/composite resin core/metal ceramic crowns with NiCr alloy core had the highest stress values in the weakened root, tooth/post interface, and post. NiCr post/NiCr core/metal ceramic crowns with NiCr alloy core had the lowest stress values in the weakened root and post. The zirconia post and core had the lowest stress value in the tooth/post interface. CONCLUSIONS: A post material with a high elastic modulus led to lower stress in the weakened root (approximately 6%) and tooth/post interface (approximately 12%) and to higher stress in the post (approximately 5 times). A composite resin core led to higher stress in the weakened root (approximately 11% to 17%) and lower deformation in the tooth/post interface (approximately 17.5%) and post materials (approximately 24%). Group AuPd resulted in lower stress in the root and high stress in the post (approximately 4.5% to 7%) and affected the amount of deformation in posts with a composite resin core.

Influence of occlusal contact and cusp inclination on the biomechanical character of a maxillary premolar: a finite element analysis.

STATEMENT OF PROBLEM: Restoring teeth with large amounts of dentin loss is challenging, especially for posterior teeth with high cusps. However, strategies for reducing the lateral forces are based on clinical experience instead of than scientific evidence. PURPOSE: The purpose of this study was to analyze the biomechanical characteristics of maxillary premolars with different ferrule configurations and to investigate the influence of occlusal contact and cusp inclination on stress distribution with the finite element method. MATERIAL AND METHODS: Five numerical casts of a maxillary premolar were generated; each adopted 1 of the 5 coronal dentin configurations: i (access cavity with 4-mm dentin height) and ii to v (2-mm complete ferrule, 2-mm facial ferrule, 2-mm palatal ferrule, 2-mm proximal ferrule, and restored with a post and core, respectively). Both gold-alloy and glass-fiber posts were modeled. An oblique load of 200 N was applied to the top, middle, and bottom of the 45-degree facial cusps. The cusp inclination was remodeled to 60 degrees, followed by the application of a 200-N load to the top. The values of the maximum principal stress and von Mises stress were calculated to assess overload risk. RESULTS: When the top of 45-degree facial cusps was loaded, the maximum local stress concentration on dentin was found in teeth with a facial ferrule and restored with a gold-alloy post. When the middle of 45-degree facial cusps were loaded, the principal stresses of teeth with a complete ferrule, palatal ferrule, and proximal ferrule were similar to those of the access cavity teeth. In contrast, the principal stress of a tooth with a facial ferrule was close to that of the access cavity tooth after remodeling the facial inclination to 60 degrees. CONCLUSIONS: Maxillary premolars with only facial dentin remaining show higher local stress on root dentin. Altering the loading position and reducing the facial cusp inclination can reduce local stresses.

The time-dependent biomechanical behaviour of the periodontal ligament--an in vitro experimental study in minipig mandibular two-rooted premolars.

The aim of the present work was to evaluate the biomechanical behaviour of the periodontal ligament (PDL) with respect to force development with different controlled loading velocities. For this purpose, an in vitro experimental study was performed on 18 minipig jaw segments. Displacements with variable increasing loading time were applied to one premolar crown of each jaw segment into the linguobuccal direction through a force sensor provided by a specialized biomechanical set-up. The predefined displacement values to be achieved were 0.1 and 0.2 mm. Each of the given displacement increments was applied on the specimens with a linear displacement increase employing the following time spans: 5, 10, 20, 30, 60, 120, 300, 450, and 600 seconds. Force values were measured during load application to register force/displacement diagrams and after the maximum displacement was reached force decay was monitored for a period of 600 seconds. Force/time curves for each tooth were plotted according to the data obtained. Diagrams of the maximum force values obtained from these plots and the force at the end of each measurement were extracted for all teeth. Forces at the point when maximum displacement was reached ranged from 0.5 to 2.5 N for the 0.1 mm activation and showed extreme variation with the specimens. The factor of volume and surface area of the individual roots were evaluated and found not to be responsible for these deviations. A comparable behaviour was recorded for the 0.2 mm deflection, however, on a higher force level. The results show that the force development at different displacement velocities is complex and dominated by the PDL biomechanical characteristics.

A histomorphometric and radiographic study of replanted human premolars.

SUMMARY OBJECTIVES: The purpose of this study was to investigate time-related dental tissue reactions to tooth replantation in mature and immature human premolars by histomorphometric and radiographic methods. MATERIAL AND METHODS: Sixty premolars were extracted, immediately replanted (T0), and left without intervention for 1, 2, 3, 6, 12, and 24 weeks before re-extraction (T1). Periapical radiographs were taken at T0 and T1 in all groups except for the 24 week group. Paraffin-embedded teeth were sectioned buccolingually at 5 µm, stained with haematoxylin-eosin, and prepared for histological analysis. Root resorption, tertiary dentine, and root and crown length were recorded and compared on both radiographs and paraffin sections. RESULTS: Initial degeneration of the odontoblast layer and disturbance of vasculature and normal architecture of the pulp were seen in both mature and immature teeth within the first 3 weeks. Revascularization and tertiary dentine formation was visible on histological sections in immature teeth at 6 weeks. After 24 weeks, most immature teeth had pulps partly or completely obliterated. Abundant tertiary dentine observed on histological slides was not easily seen on periapical radiographs. Likewise, surface root resorption found in both immature and mature teeth was not visible on the radiographs up to 6 weeks after replantation. CONCLUSION: Within the limits of this study it can be concluded that the dental pulp of immature teeth has the ability to regenerate and produce tertiary dentine after replantation. Root resorptions and tertiary dentine seen on histological sections are not visible on corresponding radiographs 6 and 12 weeks after replantation.