Angiotensin(1-7) attenuates tooth movement and regulates alveolar bone response during orthodontic force application in experimental animal model

BACKGROUND

Renin-angiotensin system and its ACE2/Ang(1-7)/Mas receptor axis regulates skeletal response to multiple physiological and pathological conditions. Recent research suggested a vital role of Ang(1-7) in regulating alveolar bone metabolism and remodeling. In this context, this study evaluated the effects of the Ang(1-7)/Mas receptor axis on orthodontic tooth movement (OTM) and the alveolar bone response to mechanical load.

METHODS

A coil spring was placed between the right maxillary first molar and the anterior tooth of Wistar rats to apply bidirectional mechanical force. Ang(1-7) with or without a specific Mas receptor antagonist (A779) was infused using subcutaneous osmotic pumps (200 and 400 ng/kg/min: respectively). Animals were killed after 5 and 14 days from the OTM procedure after the clinical evaluation of tooth movement and mobility. Morphometric analysis of alveolar bone structure was conducted using micro-CT and the histological picture was evaluated after H&E staining. Moreover, collagen fiber distribution was assessed using Picro-Sirius red stain. In addition, bone samples were collected from the pressure and tension sites around the anterior tooth for gene expression analysis.

RESULTS

Ang(1-7) infusion suppressed the tooth movement and mobility after 14 days of the orthodontic force application. Additionally, Ang(1-7) infusion preserved the morphometric and histological structure of the alveolar bone at pressure and tension sides. These effects were abolished by adding A779 infusion. Collagen fiber distribution was dysregulated mainly by the A779 Mas receptor blockage. Ang(1-7) affected the bone formation, remodeling- and vascularity-related genes in the pressure and tension sides, suggesting a prominent suppression of osteoclastogenesis. Ang(1-7) also improved osteoblasts-related genes on the tension side, whereas the osteoclasts-related genes were augmented by A779 on the pressure side.

CONCLUSION

Collectively, the activation of Ang(1-7)/Mas receptor axis appears to hinder tooth movement and regulates alveolar bone remodeling in response to mechanical force.

On-Bone Fixation of Free Gingival Graft Induces an Osteoinductive Effect in Human Alveolar Bone

We examined alveolar bone samples in the area of on-bone fixation of a free gingival graft performed during surgery in patients aged 37-55 years with a diagnosis of secondary partial adentia of the upper and lower jaws. Six months after fixation of the graft in the alveolar bone, foci of neoosteogenesis were found in the contact zone. They were characterized by the appearance of appositional lines, cords of basophilic osteoblasts, and growing osteons. An immunohistochemical study revealed an increase in the number of CD44⁺, CD29⁺, and osteocalcin+ cells in the layer of the outer circumferential lamellae, primary osteons, and the lining of the Haversian canals. TGF-β1⁺ cells were located in the intertrabecular reticular tissue and wall of microvessels. The results indicate activation of mesenchymal stem cells in the area of localization of the graft and differentiating osteoblasts. The observed osteoinductive effect of free gingival graft is associated with its participation in reorganization in MSC and induction of morphogenetic molecules.

The Glycoprotein/Cytokine Erythropoietin Promotes Rapid Alveolar Ridge Regeneration In Vivo by Promoting New Bone Extracellular Matrix Deposition in Conjunction with Coupled Angiogenesis/Osteogenesis

The loss of bone following tooth extraction poses a significant clinical problem for maxillofacial esthetics, function, and future implant placement. In the present study, the efficacy of an erythropoietin-impregnated collagen scaffold as an alveolar ridge augmentation material versus a conventional collagen scaffold and a BioOss inorganic bovine bone xenograft was examined. The collagen/Erythropoietin (EPO) scaffold exhibited significantly more rapid and complete osseous regeneration of the alveolar defect when compared to bone xenograft and the collagen membrane alone. The new EPO induced extracellular matrix was rich in Collagen I, Collagen III, Fibronectin (Fn) and E-cadherin, and featured significantly increased levels of the osteogenic transcription factors Runt-related transcription factor 2 (Runx2) and Osterix (Osx). Histomorphometric evaluation revealed a significant two-fold increase in the number of capillaries between the EPO and the BioOss group. Moreover, there was a highly significant 3.5-fold higher level of vascular endothelial growth factor (VEGF) in the collagen/EPO-treated group compared to controls. The significant effect of EPO on VEGF, FN, and RUNX2 upregulation was confirmed in vitro, and VEGF pathway analysis using VEGF inhibitors confirmed that EPO modulated extracellular matrix protein expression through VEGF even in the absence of blood vessels. Together, these data demonstrate the effectiveness of an EPO-impregnated collagen scaffold for bone regeneration as it induces rapid matrix production and osseoinduction adjacent to new capillaries via VEGF.

Complement 3 mediates periodontal destruction in patients with type 2 diabetes by regulating macrophage polarization in periodontal tissues

OBJECTIVES

Diabetes aggravates the risk and severity of periodontitis, but the specific mechanism remains confused. Complement 3 (C3) is closely related to complications of type 2 diabetes (T2DM). In the present study, we concentrated on whether C3 mediates the development of periodontitis in T2DM.

MATERIALS AND METHODS

Levels of C3 in blood and gingival crevicular fluid (GCF) of patients were measured first. A C3-knockout diabetic mouse model was established, real-time PCR, Western blotting and histological investigation were performed to evaluate the progress of periodontitis. Microcomputed tomography (micro-CT) and TRAP staining were performed to detect alveolar bone resorption. Immunofluorescence was performed to detect polarization of macrophages.

RESULTS

Our data showed that C3 levels were elevated in the blood and GCF of T2DM patients compared with non-diabetic individuals. Increased C3 was closely related to the upregulation of inflammatory cytokines including interleukin (IL)-1, IL-6 and tumour necrosis factor-alpha (TNF-α), as well as the decline of the bone volume density (BMD) and bone volume over total volume (BV/TV) of the alveolar bones in diabetic mice. The deletion of C3 inhibited inflammatory cytokines and rescued the decreased BMD and BV/TV of the alveolar bones. C3-mediated polarization of macrophages was responsible for the damage.

CONCLUSION

T2DM-related upregulation of C3 contributes to the development of periodontitis by promoting macrophages M1 polarization and inhibiting M2 polarization, triggering a pro-inflammatory effect on periodontal tissues.

Extracellular matrix composition during bone regeneration in the human dental alveolar socket

Within the dental alveolar socket, the sequence of events following tooth extraction involves deposition of a provisional connective tissue matrix that is later replaced by woven bone and eventually by lamellar bone. Bone regeneration within the dental alveolar socket is unique since the space occupied by the root(s) of a tooth does not originally contain any bone. However, extracellular matrix composition of the healing alveolar socket has not previously been investigated. Here, alveolar bone biopsies representing early (7-46 months, < 4y) and late (48-60 months; 4-5y) healing periods were investigated using Raman spectroscopy, X-ray micro-computed tomography and backscattered electron scanning electron microscopy. Partially or completely edentulous individuals and those with a smoking habit were not excluded. Between < 4y and 4-5y, mineral crystallinity and bone mineral density increase, phenylalanine, proline/hydroxyproline, and bone surface-to-volume ratio decrease, while the carbonate-to-phosphate ratio, the mineral-to-matrix ratio, and the collagen crosslink ratio remain relatively unchanged. Observed exclusively at 4-5y, hypermineralised osteocyte lacunae contain spherical and rhomboidal mineral nodules. Spearman correlation analysis reveals several significant, high (ρ = 0.7-0.9; p ≤ 0.01) and moderate (ρ = 0.5-0.7; p ≤ 0.01) correlations. Mineral crystallinity and proline/hydroxyproline, the carbonate-to-phosphate ratio and phenylalanine, mineral crystallinity and bone surface-to-volume ratio, the carbonate-to-phosphate ratio and bone surface-to-volume ratio, proline/hydroxyproline and bone mineral density, and bone mineral density and bone surface-to-volume ratio are negatively correlated. Mineral crystallinity and bone mineral density, and proline/hydroxyproline and bone surface-to-volume ratio are positively correlated. Although bone regeneration in the dental alveolar socket follows typical bone healing patterns, the compositional and microstructural patterns reveal mature bone at <4y with indications of better mechanical competence at 4-5y.

Mineralized nanofiber segments coupled with calcium-binding BMP-2 peptides for alveolar bone regeneration

Bone loss around tooth extraction sites can occur, thus making future placement of dental implants difficult. Alveolar bone regeneration can be guided by the application of a nanofibrous bone graft coupled with osteoinductive proteins/peptides, following tooth loss or tooth extraction. In the present study, we demonstrate the potential of mineralized nanofiber segments coupled with calcium-binding bone morphogenetic protein 2 (BMP-2) mimicking peptides for periodontal bone regeneration. Thin electrospun nanofiber membranes of PLGA-collagen-gelatin (2:1:1 wt ratios) were mineralized in 10× modified simulated body fluid (10× mSBF) and cryocut to segments of 20 µm. For predetermined weights of the mineralized nanofiber segments, it was possible to load various amounts of heptaglutamate E7-domain-conjugated BMP-2 peptide. Mineralized short fiber grafts (2 mg), with and without E7-BMP-2 peptides, were implanted into 2 mm × 2 mm (diameter × depth) critical-sized socket defects created in rat maxillae, following extraction of the first molar teeth. A sustained release profile of E7-BMP-2 from the mineralized nanofiber segments was recorded over 4 weeks. X-ray microcomputed tomography (µ-CT) analysis of peptide-loaded nanofiber graft filled defects revealed ∼3 times greater new bone volume and bone mineral density over 4 weeks in comparison to unfilled control defects. Further, histopathology data confirmed the formation of greater new osseous tissue in the BMP2 peptide-loaded, mineralized nanofiber segment group than that of fibrous connective tissue in the unfilled defect group. Altogether, the mineralized nanofiber segments coupled with E7-BMP-2 peptides may be an effective treatment option for alveolar bone loss and defects. STATEMENT OF SIGNIFICANCE: With the high incidence of dental implants/fixtures for missing teeth, the success of the surgical procedures in restorative dentistry is dictated by the quality and quantity of the supporting alveolar bone. To address the problem of alveolar bone loss and defects due to tumor, periodontitis, or even postextraction remodeling, the present study is the first report on the application of mineralized nanofiber fragments coupled with calcium-binding osteoinductive BMP-2 peptides as a synthetic graft material for oral bone regeneration. The ease of fabrication and application of cryocut mineralized nanofiber fragments as maxillofacial bone defect fillers present a promising alternative to the current dental bone graft formulations. Furthermore, the nanofiber segments may also be utilized for several biomedical applications including hemostasis, soft tissue engineering, and wound healing.

A Graded Multifunctional Hybrid Scaffold with Superparamagnetic Ability for Periodontal Regeneration

The regeneration of dental tissues is a still an unmet clinical need; in fact, no therapies have been completely successful in regenerating dental tissue complexes such as periodontium, which is also due to the lack of scaffolds that are able to guide and direct cell fate towards the reconstruction of different mineralized and non-mineralized dental tissues. In this respect, the present work develops a novel multifunctional hybrid scaffold recapitulating the different features of alveolar bone, periodontal ligament, and cementum by integrating the biomineralization process, and tape casting and electrospinning techniques. The scaffold is endowed with a superparamagnetic ability, thanks to the use of a biocompatible, bioactive superparamagnetic apatite phase, as a mineral component that is able to promote osteogenesis and to be activated by remote magnetic signals. The periodontal scaffold was obtained by engineering three different layers, recapitulating the relevant compositional and microstructural features of the target tissues, into a monolithic multifunctional graded device. Physico-chemical, morphological, and ultrastructural analyses, in association with preliminary in vitro investigations carried out with mesenchymal stem cells, confirm that the final scaffold exhibits a good mimicry of the periodontal tissue complex, with excellent cytocompatibility and cell viability, making it very promising for regenerative applications in dentistry.

Relationship Between Orthodontic Force Applied by Monoblock and Salivary Levels of Alkaline Phosphatase and Lactate Dehydrogenase Enzymes

AIM

The current study was aimed to determine the relationship between the orthodontic force applied by monobloc and the salivary level of alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) enzymes, considering the time factor after insertion of the appliance and whether there is a correlation between these enzymes.

MATERIALS AND METHODS

A sample of 28 growing patients requiring orthodontic treatment with myofunctional appliance (Monoblock) was taken for the current study with an age range 9 to 12 years,all patients had Angle's class II division 1 mal-occlusion with no or mild crowding, the sample was selected using simple random sampling. Only 16 subjects (10 males and 6 females) were included who follow certain inclusion criteria. Unstimulated saliva was collected from the patients before monoblock insertion, then 1 hour after insertion, followed by 14 days and 28 days. Salivary levels of ALP and LDH were measured using a spectrophotometer and compared with the base line.

RESULTS

The results revealed that ALP and LDH levels increased with increasing time after monoblock insertion, and there was the statistically insignificant difference after 1-hour post-insertion for ALP enzyme level, but highly significant after 14 and 28 days. While for LDH level,there was the statistically significant difference after 1-hour post-insertion, but highly significant difference after 14 and 28 days post-insertion. In this regard to the relation between salivary ALP and LDH enzymes levels at different time intervals, showed that there were no significant correlations between the enzymes using Pearson's correlation test.

CONCLUSION

The ALP and LDH salivary enzymes activity is affected by mechanical forces generated by monobloc activator and these enzymes activities can also be increased during the rapid growth phase of childhood such as late infancy and early puberty where the age of subjects was selected in the current study.

CLINICAL SIGNIFICANCE

The determination of ALP and LDH salivary enzymes activities during the skeletal maturity is crucial for the success of myofunctional monobloc treatment; therefore, saliva can be used as a noninvasive diagnostic tool for determination of chemical biomarkers for detection of bone remodeling process during myofunctional monoblock treatment Keywords: Alkaline phosphatase (ALP), Lactate dehydrogenase (LDH), Monoblock, Orthodontic force, Salivary levels.

Biology of teeth and implants: The external environment, biology of structures, and clinical aspects

For the past several thousand years, until development of the titanium dental implant, only a few missing teeth were replaced successfully in a very small number of individuals. Nowadays, placement of dental implants has become sufficiently commonplace that there is a need to interchange information between what we know about periodontal health and disease and what we know about health and disease involving dental implants. This review discusses the similarities and differences between teeth and dental implants with regards to anatomy, biology, physiology, and pathologic processes. The concept of biologic width is discussed in the context of interaction of periodontal and peri-implant tissues with microbial products produced by periodontal biofilms. The periodontal microbiome is discussed as networks of organisms interacting not only with periodontal and peri-implant tissues, but also with each other as networks of competing organisms. Overall, the transfer of biologic knowledge from what we know about peri-implantitis and what we know about periodontitis should help to develop new directions for biologic understanding about both health and disease of teeth and dental implants.

Vibration paradox in orthodontics: Anabolic and catabolic effects

Vibration in the form of High Frequency Acceleration (HFA) is anabolic on the craniofacial skeleton in the absence of inflammation. Orthodontic forces trigger an inflammation-dependent catabolic cascade that is crucial for tooth movement. It is unknown what effect HFA has on alveolar bone if applied during orthodontic treatment. The objectives of this study are to examine the effect of HFA on the rate of tooth movement and alveolar bone, and determine the mechanism by which HFA affects tooth movement. Adult Sprague Dawley rats were divided to control, orthodontic force alone (OTM), and different experimental groups that received the same orthodontic forces and different HFA regimens. Orthodontic tooth movement was assessed when HFA parameters, frequency, acceleration, duration of exposure, and direct or indirect application were varied. We found that HFA treatment significantly enhanced the inflammation-dependent catabolic cascade during orthodontic tooth movement. HFA treatment increased inflammatory mediators and osteoclastogenesis, and decreased alveolar bone density during orthodontic tooth movement. Each of the HFA variables produced significant changes in the rate of tooth movement and the effect was PDL-dependent. This is the first report that HFA enhances inflammation-dependent catabolic cascades in bone. The clinical implications of our study are highly significant, as HFA can be utilized to enhance the rate of orthodontic tooth movement during the catabolic phase of treatment and subsequently be utilized to enhance retention during the anabolic remodeling phase after orthodontic forces are removed.

Osteopontin regulates dentin and alveolar bone development and mineralization

The periodontal complex is essential for tooth attachment and function and includes the mineralized tissues, cementum and alveolar bone, separated by the unmineralized periodontal ligament (PDL). To gain insights into factors regulating cementum-PDL and bone-PDL borders and protecting against ectopic calcification within the PDL, we employed a proteomic approach to analyze PDL tissue from progressive ankylosis knock-out (Ank^-/-) mice, featuring reduced PP_i, rapid cementogenesis, and excessive acellular cementum. Using this approach, we identified the matrix protein osteopontin (Spp1/OPN) as an elevated factor of interest in Ank^-/- mouse molar PDL. We studied the role of OPN in dental and periodontal development and function. During tooth development in wild-type (WT) mice, Spp1 mRNA was transiently expressed by cementoblasts and strongly by alveolar bone osteoblasts. Developmental analysis from 14 to 240days postnatal (dpn) indicated normal histological structures in Spp1^-/- comparable to WT control mice. Microcomputed tomography (micro-CT) analysis at 30 and 90dpn revealed significantly increased volumes and tissue mineral densities of Spp1^-/- mouse dentin and alveolar bone, while pulp and PDL volumes were decreased and tissue densities were increased. However, acellular cementum growth was unaltered in Spp1^-/- mice. Quantitative PCR of periodontal-derived mRNA failed to identify potential local compensators influencing cementum in Spp1^-/- vs. WT mice at 26dpn. We genetically deleted Spp1 on the Ank^-/- mouse background to determine whether increased Spp1/OPN was regulating periodontal tissues when the PDL space is challenged by hypercementosis in Ank^-/- mice. Ank^-/-; Spp1^-/- double deficient mice did not exhibit greater hypercementosis than that in Ank^-/- mice. Based on these data, we conclude that OPN has a non-redundant role regulating formation and mineralization of dentin and bone, influences tissue properties of PDL and pulp, but does not control acellular cementum apposition. These findings may inform therapies targeted at controlling soft tissue calcification.

Maxillary expansion in an animal model with light, continuous force

OBJECTIVES

Maxillary constriction is routinely addressed with rapid maxillary expansion (RME). However, the heavy forces delivered by most RME appliances to expand the palate may lead to deleterious effects on the teeth and supporting tissues. The objective of this study was to explore a more physiologic maxillary expansion with light continuous force.

MATERIALS AND METHODS

Twenty 6-week-old Sprague-Dawley rats were equally divided into experimental (EXPT) and control (CTRL) groups. A custom-fabricated archwire expansion appliance made from 0.014-inch copper-nickel-titanium wire was activated 5 mm and bonded to the maxillary molar segments of animals in the EXPT group for 21 days. The force applied to each maxillary segment was 5 cN. Microfocus x-ray computed tomography and histological analyses were used to compare the tooth movement and bone morphology in the midpalatal suture and buccal aspect of the alveolar process between the EXPT and CTRL groups. Descriptive statistics (mean ± standard error of the mean) and nonparametric statistical tests were used to compare the outcomes across groups.

RESULTS

Compared to the CTRL group, there was a statistically significant increase in buccal tooth movement and expansion of the midpalatal suture in the EXPT group. There was no difference in the bone morphologic parameters between groups. The mineral apposition rate was increased on the buccal surface of the alveolar process in the EXPT group.

CONCLUSIONS

Application of light, continuous force resulted in maxillary osseous expansion due to bilateral sutural apposition and buccal drift of the alveolar processes. This animal experiment provides a more physiologic basis for maxillary expansion.

The effects of dentoalveolar distraction extraction on alveolar ridge preservation: Cone-beam computed tomography and X-ray analysis in canine model

OBJECTIVE

This study aims to evaluate the effect of dentoalveolar distraction extraction (DDE) on site preservation, and to evaluate how the technique keeps the height and width of alveolar bones to a greater extent.

METHODS

12 beagle dogs, randomly divided into three groups (DDE group, NH group, BOG group), were used. In the dogs of three groups, the root of the left or right third mandibular premolars were respectively extracted by three methods namely, DDE, traditional extraction with natural healing, and traditional extraction with Bio-Oss bone dust implanted and guided bone regeneration (GBR). Cone-beam computed tomography (CBCT) scans and X-rays were taken immediately and three months after the tooth extraction. The height and width of the alveolar ridges were compared among different groups.

RESULTS

Three months after tooth extraction, at the 1 mm level below the alveolar ridge crest, the amount and degree of buccal alveolar ridge width resorption in DDE group were significantly lower than that of NH and BOG group (P < 0.05). At the 2 mm and 3 mm level below the alveolar ridge crest, the amount and degree of buccal alveolar ridge width resorption in DDE group and BOG had no significant difference, and both were significant lower than that of NH group (P < 0.05). The height resorption of alveolar ridge in DDE group was significantly lower than NH and BOG groups (P < 0.05), while NH and BOG group had no statistically significant.

CONCLUSIONS

To a greater extent, the alveolar ridge preservation through DDE could preserve the height and width of alveolar ridge crest.

Computer-assisted system on mandibular canal detection

BACKGROUND

A dentist always checks a patient by using panoramic radiography (PR) initially. The measurement of the minimal distance (MD) between the alveolar crest and the mandibular canal (MC) superior border is critically important before the dental implant surgery, extraction of 3rd molar teeth or any surgery in the posterior area of minimal distance (MD). However, the image of MC is not always clear to identify.

OBJECTIVE

A software is needed for training dentists as well as a tool of demonstration to patients in clinics precisely and quickly. Moreover, it should be able to calculate the MD between the alveolar crest and the MC superior border before dental implant.

METHODS

A computer-aided software system to semi-automatically detect the MC and mental foramen (MF) in the PR with minimal human interference is proposed.

RESULTS

The result shows that the averaged relative error (RE) is 1.83% with a standard deviation of 2.31%.

CONCLUSION

The results show that the proposed algorithm is able to detect the MC superior and inferior borders. This system has the potential to train young clinicians and to replace the manual work in measuring the MD between the alveolar crest and the MC superior border with a minimal human intervention.

A Step-by-Step Description of PDL-Mediated Ridge Preservation for Immediate Implant Rehabilitation in the Esthetic Region

The aim of this study was to present in detail the clinical steps of the root-membrane technique. This technique combines the benefits of conventional root submergence via intentional maintenance of a root fragment for ridge preservation with those of immediate implant placement for functional rehabilitation of the treated site. A case study of a tooth diagnosed with a horizontal root fracture is used to illustrate this technique step by step. The clinical application of the root-membrane technique not only allowed for immediate placement in a site with compromised buccal plate but also facilitated excellent clinical stability of soft tissue contours during the 3 years of follow-up.

Distraction Osteogenesis May Promote Periodontal Bone Regeneration

Distraction osteogenesis has numerous applications in the treatment of conditions affecting the dentofacial complex, from midface advancement to orthodontic tooth movement produced by transversal distraction of the periodontal ligament. The purpose of this study was to test the hypothesis that periodontium can be consistently distracted toward the tooth crown to promote periodontal bone regeneration. After the surgical production of periodontal defects in maxillary canines of 5 mongrel dogs, periodontal bone distraction was performed. Light microscopy was used for histopathological and morphometric analysis. Periodontal bone regeneration occurred in all animals. Periodontal bone regeneration in the distraction sites (Mean ± SD: 5.45 ± 2.01 mm) differed from that in control sites (0.008 ± 0.67 mm; p < 0.0001). Periodontal bone distraction resulted in periodontal bone regeneration. This finding may establish periodontal bone distraction as a new treatment alternative for periodontal defects.

Reactive Soft Tissue Preservation in Maxillary Large Bone Defects

PURPOSE

Granulation tissue containing reactive soft tissue with potential multipotent stem cells can help socket healing following extraction. The aim of this study was to assess bone healing of maxillary large bone defects while maintaining reactive soft tissue.

MATERIALS AND METHODS

A total of 32 patients presenting large bone defects were selected for this prospective study. Eight patients (Group A) presented with large bone defects but an intact buccal cortical plate, while 24 patients (Group B) presented with large bone defects lacking a buccal cortical plate. Teeth were extracted, and reactive soft tissue was left in the defects. Bone volume was assessed through cone beam computed tomography (CBCT) both before tooth extraction and at 4 months. A histomorphometric evaluation was performed.

RESULTS

CBCT and cylinder bone cores were obtained for histology and histomorphometry analysis. At 4 months after tooth extraction, CBCT showed bone volume preservation and bone formation and no statistically significant difference in bone volume before and after tooth extraction in group A. However, in group B, over the same time period, a statistically significant increase (P < .01) of vertical bone volume was reported. Biopsy specimens showed the presence of vital bone in the defects 4 months later.

CONCLUSION

Reactive soft tissue left in large bone defects after tooth extraction may support a significant bone volume gain and vital bone formation.

The Influence of Bone Quality on the Biomechanical Behavior of a Tooth-Implant Fixed Partial Denture: A Three-Dimensional Finite Element Analysis

PURPOSE

The purpose of this study was to evaluate whether or not bone quality has an effect on the biomechanical behavior of a tooth connected to an implant, when a rigid and a nonrigid attachment are used.

MATERIALS AND METHODS

Models of fixed partial dentures supported by a tooth and an implant were developed. These models were then imported into finite element analysis software to study the impact of forces on different types of attachments (rigid vs nonrigid) and bones (types 1 to 4). Each fixed partial denture was subjected to a vertical load of 200 N on the premolars and 230 N on the molar. The materials were considered linear, isotropic, and homogenous. Eight different scenarios were tested. The von Mises criterion was used to display the stress in five structures: fastening screw, implant, attachment, cortical, and trabecular bone. The displacements of the tooth and the implant were also examined.

RESULTS

The calculated maximum observed stress values differed among the simulated scenarios. The biggest values of stress concentrations were observed at the lingual cervical areas, the implant-cortical bone interface, the implant-crown interface, the butt-joint contact of the implant-abutment screw, and the apical parts of the tooth and implant. The main difference between the rigid and nonrigid connection was observed between the natural tooth retainer and the pontic. In the rigid connection, the movement of the natural tooth retainer was smooth. In the nonrigid connection, the attachment exhibited a partial buccal displacement. Von Mises stresses among the different tested structures ranged between 24 and 840 MPa.

CONCLUSION

The quality of the bone and the rigidity of the connection between a natural tooth and an implant influence both the generated stresses and the displacement of the tooth and the implant. The highest stresses for the implant-trabecular bone interface, the neck of the implant, and the fastening screw were observed in type 3 bone when a rigid connection was used. The lowest stresses for the implant-cortical bone interface, the neck of the implant, and the connector were registered in type 1 bone, when a rigid connection was used. The smallest tooth and implant displacement was observed in type 1 bone, when a rigid connection was used, while the biggest tooth and implant displacement was registered in type 4 bone when a nonrigid connection was used.

Alveolar dimensional changes relevant to implant placement after minimally traumatic tooth extraction with primary closure

The purpose of this study is to evaluate the dimensional changes that occur in the alveolar ridge after minimally traumatic tooth extraction by means of computed tomography (CT), with special focus on the portion of bone supporting the gingival zenith. Twenty subjects with indication for singlerooted tooth extraction and preserved alveolar walls were selected for this study. After a minimally traumatic extraction, two CT scans were performed; the first within 24 hours postextraction (TC1) and the second 6 months (TC2) later. A radiographic guide with a radiopaque marker was used to obtain references that enabled accurate measurements over time, in both vertical and horizontal directions. The bone crest immediately apical to the gingival zenith was identified and termed "osseous zenith". The displacement of the osseous zenith in horizontal and vertical direction was analyzed and correlated with several alveolar anatomical variables with the aim of identifying possible predictors for bone remodeling. Dimensional changes that occur in postextraction sockets within a 6month period showed significant vertical and horizontal displacement of the osseous zenith (p<0.001). Mean vertical resorption was 2.1 ± 1.7 mm, with a median of 1.9 mm and a range of 0.2 to 7.5 mm. Mean horizontal resorption was 1.8 ± 0.8 mm with a median of 1.7 mm and a range of 0.6 to 4.4 mm. However, no correlation was found between the width of the facial alveolar crest and the displacement of the osseous zenith. The results of the present study showed that if the width of the facial crest at the apicalcoronal midpoint is less than 0.7 mm, a high degree of displacement of the osseous zenith (> 3 mm) should be expected. The present study suggests that the width of the alveolar crest at its midlevel, rather than crestal width, may be correlated with the displacement of the osseous zenith.

Critical buccal bone dimensions along implants

The buccal bone plate is a component of the alveolar process tightly related to the tooth it supports. A plethora of physiological and pathological events can induce its remodeling. Understanding this remodeling process and its extent is of major importance for the practitioner as it can affect the functional and esthetic outcome of implant surgery at the involved sites. Bone remodeling and resorption of the buccal bone plate are inevitable after tooth loss or extraction. To limit resorption, several ridge-preservation techniques of varying efficacy have been described. Bone resorption is equally found to occur upon implant placement and is thought to be a result of the surgical trauma inflicted as well as an adaptation process of the tissues to the new foreign body. Because of the implications of bone resorption on the soft-tissue levels and the general esthetic outcome, it is of primary importance for the practitioner to be able to evaluate the hard tissues and the inherent resorption risks in an effort to optimize the treatment strategies. Based on limited short-term data, the present general opinion advises the need for a 2-mm-thick buccal bone plate in order to avoid vertical bone resorption.

[Behavior of the periodontium during leveling of the mandibular incisors: what precautions are needed?]

Since the position of the mandibular incisors is one of the keys to successful treatment, most orthodontic treatments focus on control but take no special precautions regarding the periodontal environment. Can we trust the lateral headfilm alone when evaluating such slender quantities of bone surrounding the mandibular incisors? What is the true bone situation prior to treatment and above all, following alignment, leveling and uprighting of the incisors? We performed a prospective 3-year study on 50 patients to assess the periodontal behavior of the mandibular incisors following a leveling phase by means of a clinical approach using periodontal and radiologic probing based on measurements of bone thickness obtained by cone beam. The bone loss observed was not inconsiderable given the thinness of the initial bone. In the face of this clinical situation, we need to adapt our treatment by performing a pre-orthodontic periodontal check-up and by supplementing the diagnosis with 3D examinations for at-risk patients and by checking the incisal axes during the leveling phase. The advent of cone beam has provided us with a valuable tool making it possible to individualize orthodontic treatment and view the posttreatment bone environment and root positions.

An acoustic study of multiple lateral consonants in three Central Australian languages

This study presents dental, alveolar, retroflex, and palatal lateral /̪ll ɭ ʎ/ data from three Central Australian languages: Arrernte, Pitjantjatjara, and Warlpiri. Formant results show that the laminal laterals (dental /̪l/ and palatal /ʎ/) have a relatively low F1, presumably due to a high jaw position for these sounds, as well as higher F4. In addition, the palatal /ʎ/ has very high F2. There is relatively little difference in F3 between the four lateral places of articulation. However, the retroflex /ɭ/ appears to have slightly lower F3 and F4 in comparison to the other lateral sounds. Importantly, spectral moment analyses suggest that centre of gravity and standard deviation (first and second spectral moments) are sufficient to characterize the four places of articulation. The retroflex has a concentration of energy at slightly lower frequencies than the alveolar, while the palatal has a concentration of energy at higher frequencies. The dental is characterized by a more even spread of energy. These various results are discussed in light of different acoustic models of lateral production, and the possibility of spectral cues to place of articulation across manners of articulation is considered.

Tissue Reaction and Biomechanics

Tissue reaction to orthodontic force has been a subject of research with the purpose of providing the orthodontists with information necessary for the application of a force system that can generate a maximum of tooth movement and modeling of the alveolar process with a minimum of damage. Traditionally, the studies of bone biological reactions have been distinguishable from those performed by bone biologists. This has led to a controversy regarding both the terminology and perception of the reaction to mechanical perturbation. The present chapter, with its basis in bone biology, surveys the attempts by orthodontists to optimize the tissue reaction and shorten treatment time.

Osteoclastogenesis and Osteogenesis during Tooth Movement

It is a well-known concept that bone remodeling occurs during orthodontic tooth movement. The orthodontic literature is vastly full of information about the changes occurring on the periodontal ligament level. However, changes occurring in the alveolar bone are being elucidated. The purpose of this chapter is to present some of the studies describing the bone changes associated with orthodontic tooth movement. Initiation of osteoclastogenesis requires inflammation in the adjacent area. Tissue biomarker RANKL responds to the compressive forces. Conversely, an increase in osteoprotegrin biomarker causes a decrease in RANKL and inhibits tooth movement. Osteocyte activity during tooth movement is not well understood. Emerging studies are showing the effect of osteocytes on orthodontic tooth movement. Nitric oxide (NO), produced by osteocytes, is an important regulator of bone response to loading and has been shown to mediate osteoclast activity. iNOS (which produces NO) has been shown to mediate inflammation-induced bone resorption on the compression side. Several molecules have been linked to osteogenesis in tooth movement: TGF-β, BSP, BMPs and epidermal growth factor. Osteogenesis on the tension side is not well understood. Studies have shown increase in the expression of Runx2 on the tension side. Additionally, eNOS (produces NO) mediates bone formation on the tension side. The concept of osteoclastogenesis and osteogenesis is being unraveled.

Periodontal Ligament and Alveolar Bone in Health and Adaptation: Tooth Movement

The periodontal ligament (PDL) and alveolar bone are two critical tissues for understanding orthodontic tooth movement. The current literature is replete with descriptive studies of multiple cell types and their matrices in the PDL and alveolar bone, but is deficient with how stem/progenitor cells differentiate into PDL and alveolar bone cells. Can one type of orthodontic force with a specific magnitude and frequency activate osteoblasts, whereas another force type activates osteoclasts? This chapter will discuss the biology of not only mature cells and their matrices in the periodontal ligament and alveolar bone, but also stem/progenitor cells that differentiate into fibroblasts, osteoblasts and osteoclasts. Key advances in tooth movement rely on further understanding of osteoblast and fibroblast differentiation from mesenchymal stem/progenitor cells, and osteoclastogenesis from the hematopoietic/monocyte lineage.

Regional Acceleratory Phenomenon

The regional acceleratory phenomenon (RAP) is a tissue reaction to a noxious stimulus that increases the healing capacities of the affected tissues. It is typical not only of hard tissues such as bone and cartilage, but also of soft tissues. The RAP is characterized by acceleration of the normal cellular activities, as an 'SOS' phenomenon of the body that has to respond to the new perturbation. In the alveolar bone, the RAP is characterized, at a cellular level, by increased activation of the basic multicellular units (BMUs), thereby increasing the remodeling space. At the tissue level, the RAP is characterized by the production of woven bone, with the typical unorganized pattern, that will be reorganized into lamellar bone at a later stage. In the alveolar bone, the RAP occurs typically in the healing process of the alveolar sockets after tooth extraction, in periodontal disease, after surgery and trauma and during orthodontic tooth movement. In relation to orthodontic tooth movement, the RAP can be seen as a tissue response to the mechanical cyclical perturbation that induces the formation of microdamage that has to be removed to avoid their accumulation and the following bone failure. The adaptation to the new orthodontically induced mechanical environment is ensured by an increased activation of the BMU that returns to normal levels after few months.

Bone stress and strain modification in diastema closure: 3D analysis using finite element method

The aim of this study was to analyse the stress and strain distribution in the alveolar bone between two central incisors in the process of diastema closure with a constant force. A 3-dimensional computer modeling based on finite element techniques was used for this purpose. A model of an anterior segment of the mandible containing cortical bone, spongy bone, gingivae, PDL and two central incisors with a bracket in the labial surface of each tooth were designed. The von Mises stress and strain was evaluated in alveolar bone along a path of nodes defined in a cresto-apical direction in the midline between two teeth. It was observed that stress and strain of alveolar bone increased in midline with a constant force to close the diastema regardless of the type of movement in gradual steps of diastema closure, however the stress was higher in the tipping movement than the bodily so it can be suggested that a protocol of force system modification should be introduced to compensate for the stress and strain changes caused by the reduced distance to avoid the unwanted stress alteration during the diastema closure.

Intramembranous bone healing process subsequent to tooth extraction in mice: micro-computed tomography, histomorphometric and molecular characterization

Bone tissue has a significant potential for healing, which involves a significant the interplay between bone and immune cells. While fracture healing represents a useful model to investigate endochondral bone healing, intramembranous bone healing models are yet to be developed and characterized. In this study, a micro-computed tomography, histomorphometric and molecular (RealTimePCRarray) characterization of post tooth-extraction alveolar bone healing was performed on C57Bl/6 WT mice. After the initial clot dominance (0h), the development of a provisional immature granulation tissue is evident (7d), characterized by marked cell proliferation, angiogenesis and inflammatory cells infiltration; associated with peaks of growth factors (BMP-2-4-7,TGFβ1,VEGFa), cytokines (TNFα, IL-10), chemokines & receptors (CXCL12, CCL25, CCR5, CXCR4), matrix (Col1a1-2, ITGA4, VTN, MMP1a) and MSCs (CD105, CD106, OCT4, NANOG, CD34, CD146) markers expression. Granulation tissue is sequentially replaced by more mature connective tissue (14d), characterized by inflammatory infiltrate reduction along the increased bone formation, marked expression of matrix remodeling enzymes (MMP-2-9), bone formation/maturation (RUNX2, ALP, DMP1, PHEX, SOST) markers, and chemokines & receptors associated with healing (CCL2, CCL17, CCR2). No evidences of cartilage cells or tissue were observed, strengthening the intramembranous nature of bone healing. Bone microarchitecture analysis supports the evolving healing, with total tissue and bone volumes as trabecular number and thickness showing a progressive increase over time. The extraction socket healing process is considered complete (21d) when the dental socket is filled by trabeculae bone with well-defined medullary canals; it being the expression of mature bone markers prevalent at this period. Our data confirms the intramembranous bone healing nature of the model used, revealing parallels between the gene expression profile and the histomorphometric events and the potential participation of MCSs and immune cells in the healing process, supporting the forthcoming application of the model for the better understanding of the bone healing process.

Overdenture retaining bar stress distribution: a finite-element analysis

OBJECTIVE

Evaluate the stress distribution on the peri-implant bone tissue and prosthetic components of bar-clip retaining systems for overdentures presenting different implant inclinations, vertical misfit and framework material.

MATERIALS AND METHODS

Three-dimensional models of a jaw and an overdenture retained by two implants and a bar-clip attachment were modeled using specific software (SolidWorks 2010). The studied variables were: latero-lateral inclination of one implant (-10°, -5°, 0°, +5°, +10°); vertical misfit on the other implant (50, 100, 200 µm); and framework material (Au type IV, Ag-Pd, Ti cp, Co-Cr). Solid models were imported into mechanical simulation software (ANSYS Workbench 11). All nodes on the bone's external surface were constrained and a displacement was applied to simulate the settling of the framework on the ill-fitted component. Von Mises stress for the prosthetic components and maximum principal stress to the bone tissue were evaluated.

RESULTS

The +10° inclination presented the worst biomechanical behavior, promoting the highest stress values on the bar framework and peri-implant bone tissue. The -5° group presented the lowest stress values on the prosthetic components and the lowest stress value on peri-implant bone tissue was observed in -10°. Increased vertical misfit caused an increase on the stress values in all evaluated structures. Stiffer framework materials caused a considerable stress increase in the framework itself, prosthetic screw of the fitted component and peri-implant bone tissue.

CONCLUSIONS

Inclination of one implant associated with vertical misfit caused a relevant effect on the stress distribution in bar-clip retained overdentures. Different framework materials promoted increased levels of stress in all the evaluated structures.

Comparing the influence of crestal cortical bone and sinus floor cortical bone in posterior maxilla bi-cortical dental implantation: a three-dimensional finite element analysis

OBJECTIVE

This study aimed to compare the influence of alveolar ridge cortical bone and sinus floor cortical bone in sinus areabi-cortical dental implantation by means of 3D finite element analysis.

MATERIALS AND METHODS

Three-dimensional finite element (FE) models in a posterior maxillary region with sinus membrane and the same height of alveolar ridge of 10 mm were generated according to the anatomical data of the sinus area. They were either with fixed thickness of crestal cortical bone and variable thickness of sinus floor cortical bone or vice versa. Ten models were assumed to be under immediate loading or conventional loading. The standard implant model based on the Nobel Biocare implant system was created via computer-aided design software. All materials were assumed to be isotropic and linearly elastic. An inclined force of 129 N was applied.

RESULTS

Von Mises stress mainly concentrated on the surface of crestal cortical bone around the implant neck. For all the models, both the axial and buccolingual resonance frequencies of conventional loading were higher than those of immediate loading; however, the difference is less than 5%.

CONCLUSION

The results showed that bi-cortical implant in sinus area increased the stability of the implant, especially for immediately loading implantation. The thickness of both crestal cortical bone and sinus floor cortical bone influenced implant micromotion and stress distribution; however, crestal cortical bone may be more important than sinus floor cortical bone.

Information generation and processing systems that regulate periodontal structure and function

The periodontium is a very dynamic organ that responds rapidly to mechanical and chemical stimuli. It is very complex in that it is composed of two hard tissues (cementum and bone) and two soft connective tissues (periodontal ligament and gingiva). Together these tissues are defined by the molecules expressed by the resident periodontal cells in each compartment and this determines not only the structure and function of the periodontium but also how it responds to infection and inflammation. The biological activity of these molecules is tightly regulated in time and space to preserve tissue homeostasis, influence inflammatory responses and participate in tissue regeneration. In this issue of Periodontology 2000 we explore new experimental approaches and data sets which help to understand the molecules and cells that regulate tissue form and structure in health, disease and regeneration.

Alveolar bone dynamics in osteoporotic rats treated with raloxifene or alendronate: confocal microscopy analysis

In this study, the characteristics of the alveolar bone of rats with induced osteoporosis were examined. Thirty-two rats were divided into four groups according to the induction of osteoporosis and drugs administered: OG, osteoporotic rats without treatment (negative control); SG, rats which underwent sham surgery ovariectomy (SHAM); alendronate (AG), osteoporotic rats treated with alendronate; and RG, osteoporotic rats treated with raloxifene (RG). On the 8th day after ovariectomy and SHAM surgeries, drug therapy was started with AG or RG. On the 52nd day, 20 mg/kg calcein was administered to all of the rats, and on the 80th day, 20 mg/kg alizarin red was administered. Euthanasia was performed on the 98th day. The bone area marked by fluorochromes was calculated and data were subjected to two-way ANOVA test and Tukey's post-hoc test (p < 0.05). The comparison of the induced osteoporosis groups showed no statistically significant differences in bone turnover only between RG and SG (p = 0.074) and AG and OG (p = 0.138). All other comparisons showed significant differences (p < 0.001). The largest bone turnover was observed in RG and SG groups. RG was the medication that improved the dynamics of the alveolar bone of rats with induced osteoporosis, resembling that of healthy rats.

Evaluation of Platform Switching on Crestal Bone Stress in Tapered and Cylindrical Implants: A Finite Element Analysis

PURPOSE

To analyze and compare the stress distribution around tapered and cylindrical implants and investigate how different abutment diameters influence crestal bone stress levels.

MATERIALS AND METHODS

Six finite element models of an abutment (5 mm, 4.3 mm, and 3.5 mm in diameter) and supporting implants (tapered and cylindrical) were designed. A vertical force of 100 N and a 15-degree oblique force of 100 N were applied separately on the occlusal surface, and von Misses stresses were evaluated in the cortical and cancellous bone.

RESULTS

Higher stress was observed under oblique loading than under vertical loading of both tapered and cylindrical implants. Tapered implants demonstrated more stress under both vertical and oblique loading. Platform switching reduced peri-implant crestal bone stress in all models under vertical and oblique forces. The peri-implant crestal bone around tapered implants experienced 4.8% more stress under vertical loading and 35% more stress under oblique loading in comparison to bone around cylindrical implants (2.62 MPa with vertical loading, 8.11 MPa under oblique loading). Oblique loads resulted in much higher stress concentrations in the peri-implant crestal bone than vertical loads (238% in cylindrical and 308% in tapered implants). When the abutment diameter decreased, both models showed reductions of stress in the crestal bone under both types of loading.

CONCLUSION

In this finite element analysis, tapered implants increased crestal bone stress upon loading, and platform switching minimized the stress transmitted to the crestal bone in both tapered and parallel wall implants.

Dietary boron does not affect tooth strength, micro-hardness, and density, but affects tooth mineral composition and alveolar bone mineral density in rabbits fed a high-energy diet

The objective of this study was to determine whether dietary boron (B) affects the strength, density and mineral composition of teeth and mineral density of alveolar bone in rabbits with apparent obesity induced by a high-energy diet. Sixty female, 8-month-old, New Zealand rabbits were randomly assigned for 7 months into five groups as follows: (1) control 1, fed alfalfa hay only (5.91 MJ/kg and 57.5 mg B/kg); (2) control 2, high energy diet (11.76 MJ and 3.88 mg B/kg); (3) B10, high energy diet + 10 mg B gavage/kg body weight/96 h; (4) B30, high energy diet + 30 mg B gavage/kg body weight/96 h; (5) B50, high energy diet + 50 mg B gavage/kg body weight/96 h. Maxillary incisor teeth of the rabbits were evaluated for compression strength, mineral composition, and micro-hardness. Enamel, dentin, cementum and pulp tissue were examined histologically. Mineral densities of the incisor teeth and surrounding alveolar bone were determined by using micro-CT. When compared to controls, the different boron treatments did not significantly affect compression strength, and micro-hardness of the teeth, although the B content of teeth increased in a dose-dependent manner. Compared to control 1, B50 teeth had decreased phosphorus (P) concentrations. Histological examination revealed that teeth structure (shape and thickness of the enamel, dentin, cementum and pulp) was similar in the B-treated and control rabbits. Micro CT evaluation revealed greater alveolar bone mineral density in B10 and B30 groups than in controls. Alveolar bone density of the B50 group was not different than the controls. Although the B treatments did not affect teeth structure, strength, mineral density and micro-hardness, increasing B intake altered the mineral composition of teeth, and, in moderate amounts, had beneficial effects on surrounding alveolar bone.

Restorative aspects of periodontal disease: an update part 1

Today's dentistry is dominated by restorative procedures which are carried out to meet the demands of not only function but also aesthetics. Prosthetic and restorative therapies generally require a healthy periodontium as a prerequisite for successful treatment outcome. A mouth with a healthy periodontium may be affected by restorations of poor quality, and restorations of the highest quality may fail in a mouth with periodontal disease. This is the first of two articles that attempt to explain the concept of the complex question of biologic width and the problems that occur after improper margin placement in the periodontium. Initially, the dimensions of biologic width are considered and then margin placement and reasons for restorative procedures are discussed. This article also addresses the interactions between periodontal tissues and restorative procedures.

CLINICAL RELEVANCE

Understanding the impact of restorative procedures on periodontal health in regular dental examination by dentists can help in early diagnosis and treatment of periodontal diseases. This could prevent further progression of disease and reduce the frequency of tooth loss.

Eruptive and functional changes in periodontal ligament fibroblast orientation in CD44 wild-type vs. knockout mice

BACKGROUND AND OBJECTIVE

Periodontal ligament (PDL) fibroblasts establish principal fibers of the ligament during tooth eruption, and maintain these fibers during occlusion. PDL development and occlusal adaptation includes changes in the orientation of PDL fibroblasts; however, the mechanism for these changes in orientation is unclear. The objective of this study was to compare PDL fibroblast orientation in different stages corresponding with first molar eruption and occlusion in CD44 wild-type (WT) and knockout (KO) mice.

MATERIAL AND METHODS

CD44 WT and KO mice were raised to six postnatal stages corresponding with first molar (M1 ) eruption (postnatal day 8, 11, 14 and 18) and occlusion (postnatal day 26 and 41). Coronal sections of the first mandibular molar (M1 ) were prepared and the orientation of fibroblasts in the cervical root region was measured. Angle measurements were compared across developmental stages and between strains using Watson-Williams F-test (oriana software) and ANCOVA.

RESULTS

PDL fibroblast orientation increased significantly in CD44 WT (9-87°) and KO mice (14-93°; p ≤ 0.05) between intraosseous eruption (day 11), mucosal penetration (day 14) and preocclusal eruption (day 18); however, the PDL fibroblast orientation did not change significantly with the onset of occlusion (day 26) or continued function (day 41). Within each strain, the variance in fibroblast orientation during preocclusal eruption (day 18) was significantly higher than the variance of all other time points (p < 0.0005). CD44 WT and KO mice showed a similar pattern of PDL development and eruption with a significant difference in CD44 WT vs. KO fibroblast orientations only during early function (day 26, 92° vs 116°; p = 0.05).

CONCLUSIONS

The development of PDL fibroblast orientation is highly similar between CD44 WT and KO mice. Between early (day 11) and late (day 18) eruptive stages PDL fibroblast orientation increases, corresponding with the upward movement of M1 . The PDL fibroblast orientation established in preocclusal eruption (day 18) is maintained during early (day 26) and late (day 41) stages of occlusal function, suggesting that PDL cells adapt to mechanical loads in the oral cavity before M1 occlusion.

Photofunctionalized dental implants: a case series in compromised bone

PURPOSE

Ultraviolet (UV) light treatment of titanium, or photofunctionalization, has been shown to enhance its osteoconductivity in animal and in vitro studies, but its clinical performance has yet to be reported. This clinical case series sought to examine the effect of photofunctionalization on implant success, healing time, osseointegration speed, and peri-implant marginal bone level changes at 1 year after restoration.

MATERIALS AND METHODS

Four partially edentulous patients were included in the study. Seven implants with identical microroughened surfaces were photofunctionalized with UV light for 15 minutes. Osseointegration speed was calculated by measuring the increase in implant stability quotient (ISQ) per month. Marginal bone levels were evaluated radiographically at crown placement and at 1 year.

RESULTS

All implants placed into fresh extraction sockets, vertically augmented bone, simultaneously augmented sinuses, or the site of a failing implant remained functional and healthy at 1 year, even with an earlier loading protocol (2.1 to 4.5 months). ISQs of 48 to 75 at implant placement had increased to 68 to 81 at loading. In particular, implants with low primary stability (initial ISQ < 70) showed large increases in ISQ. The speed of osseointegration of photofunctionalized implants was considerably greater than that of as-received implants documented in the literature. Mean marginal bone levels were -0.35 ± 0.71 mm at crown placement and had significantly increased to 0.16 ± 0.53 mm at 1 year, with coronal gains in marginal bone level that surpassed the implant platform. No implants showed marginal bone loss.

CONCLUSIONS

Within the limits of this study, photofunctionalization expedited and enhanced osseointegration of commercial dental implants in various clinically challenging/compromised bone conditions. Photofunctionalization resulted in preservation--and often a gain--of marginal bone level, and long-term large-scale clinical validation is warranted.

Primary human alveolar bone cells isolated from tissue samples acquired at periodontal surgeries exhibit sustained proliferation and retain osteogenic phenotype during in vitro expansion

OBJECTIVES

Bone tissue regeneration requires a source of viable, proliferative cells with osteogenic differentiation capacity. Periodontal surgeries represent an opportunity to procure small amounts of autologous tissues for primary cell isolation. Our objective was to assess the potential of human alveolar bone as a source of autologous osteogenic cells for tissue engineering and biomaterials and drug testing studies.

MATERIALS AND METHODS

Alveolar bone tissue was obtained from 37 patients undergoing routine periodontal surgery. Tissue harvesting and cell isolation procedures were optimized to isolate viable cells. Primary cells were subcultured and characterized with respect to their growth characteristics, gene expression of osteogenic markers, alkaline phosphatase activity and matrix mineralization, under osteogenic stimulation.

RESULTS

Alveolar bone cells were successfully isolated from 28 of the 30 samples harvested with bone forceps, and from 2 of the 5 samples obtained by bone drilling. The yield of cells in primary cultures was variable between the individual samples, but was not related to the site of tissue harvesting and the patient age. In 80% of samples (n = 5), the primary cells proliferated steadily for eight subsequent passages, reaching cumulative numbers over 10(10) cells. Analyses confirmed stable gene expression of alkaline phosphatase, osteopontin and osteocalcin in early and late cell passages. In osteogenic medium, the cells from late passages increased alkaline phosphatase activity and accumulated mineralized matrix, indicating a mature osteoblastic phenotype.

CONCLUSIONS

Primary alveolar bone cells exhibited robust proliferation and retained osteogenic phenotype during in vitro expansion, suggesting that they can be used as an autologous cell source for bone regenerative therapies and various in vitro studies.

Three-dimensional analysis using finite element method of anterior teeth inclination and center of resistance location

OBJECTIVE

To locate the centre of resistance of consolidated units of four and six anterior teeth during retraction.

METHODS

Twelve three-dimensional (3D) models were designed in SolidWorks of the anterior segment with four and six teeth and their supporting structure. A proper force system was applied in each model to retract the teeth bodily. The exact location of the centre of resistances (CRes) was determined. It was found that the path of CRes change in four-tooth and six-tooth units according to the anterior teeth torque.

RESULTS

A posterior shift of the CRes by increasing the inclination of teeth was shown. However, vertical position has a fluctuant behaviour. First it moves apically, then it moves incisally. Furthermore, results suggest that in en masse retraction, translation can be achieved with a smaller amount of moment-to-force ratio than in four-incisor retraction. In other words, for bodily retraction of anterior incisor segments, we should apply force in a more apical position.

CONCLUSION

Different anterior torques between 7 and 35 degrees, cannot affect the CRes position dramatically. The area of CRes shifting is 0.92 mm (anterioposteriorly) x 0.74 mm (superior-inferiorly) in the six-tooth unit in the teeth model and 0.85 mm (anterioposteriorly) x 0.82 mm (superior-inferiorly) in the teeth and bone model. In the four-tooth model, the area of CRes shifting is 0.97 mm (anterioposteriorly) x 0.93 mm (superior-inferiorly) in tooth model and 0.77 mm (anterioposteriorly) x 0.87 mm (superior-inferiorly) in the teeth and bone model.

[Clinical and radiological study on tissue regeneration after alveolar bone augmentation with various osteoplastic materials and membranes]

The aim of the study was to compare the efficiency of alveolar bone augmentation using a variety of osteoplastic materials and collagen membrane and healing under a clot. The study included patients undergoing the extraction of symmetric teeth. After extraction one of the sockets were filled with osteoplastic materials while symmetrically located socket with no bone grafting served as a control. In group 1 augmentation was performed using Bio-Oss Collagen Bio-Gide membrane, in group 2 - Osteodent-M and Collost membranes, in group 3 - BIOPLAST-dent and BIOPLAST-dent-MK membranes. Clinical and radiological evaluation revealed positive impact of bioplastic materials on the bone tissue healing and recovery rates. The best results showed Bio-Oss Collagen with barrier bioresorbable membrane Bio-Gide allowing the creation of the most favorable conditions for delayed implantation.

A radiographic assessment of the regeneration process in post-operative alveolar bone defects in patients with different IL-1B-511 genotypes

BACKGROUND

IL-1 is the main regulator of inflammatory reactions. This cytokine also plays an important role in bone tissue remodeling processes. The IL-1α-coding gene and the IL-1β-coding gene are located on the long arm of chromosome 2. These genes contain polymorphic sites. Polymorphic modifications in IL-1-coding genes determine the level of IL-1 release, which can affect bone tissue regeneration.

OBJECTIVES

The objective of the present study was to assess the correlation between IL-1B-511 genetic polymorphism and the regeneration of the alveolar ridge bone.

MATERIAL AND METHODS

The study was carried out at the Department of Oral Surgery in Bytom, Poland, which is part of the Silesian Medical University of Katowice. The study population comprised 92 patients with mandibular or maxillary alveolar bone defects which had developed following the surgical removal of tooth roots or the enucleation of impacted teeth or cysts. Genetic material was obtained from the epithelial cells of the inner buccal surface. The IL-1B-511 genotype was determined in each patient by means of the phenol-chloroform technique, in order to enable DNA isolation, as well as by the PCR-RFLP method. Once this had been achieved the patients could be classified into 3 groups according to the following genotypes: IL-1B-511 1/1, IL-1B-511 1/2 and IL-1B-511 2/2. Bone regeneration was assessed radiographically using Digora 2.5 software. A comparison was made over a 6-month follow-up period of post-operative bone loss regeneration observed in patients with different types of the IL-1B-511 gene (alleles 1/1, 1/2, 2/2).

RESULTS

A careful analysis of the X-ray images showed that the average increase in the optical density of post-operative bone defects was statistically lower in patients with the IL-1B-511 2/2 genotype than in those possessing the IL-1B-511 1/1 or IL-1B-511 1/2 genotypes. The results indicate that alveolar bone regeneration proceeds more slowly in patients with the IL-1B-511 2/2 genotype compared to those with alleles 1/1 and 1/2.

Extracellular matrix mineralization in periodontal tissues: Noncollagenous matrix proteins, enzymes, and relationship to hypophosphatasia and X-linked hypophosphatemia

As broadly demonstrated for the formation of a functional skeleton, proper mineralization of periodontal alveolar bone and teeth - where calcium phosphate crystals are deposited and grow within an extracellular matrix - is essential for dental function. Mineralization defects in tooth dentin and cementum of the periodontium invariably lead to a weak (soft or brittle) dentition in which teeth become loose and prone to infection and are lost prematurely. Mineralization of the extremities of periodontal ligament fibers (Sharpey's fibers) where they insert into tooth cementum and alveolar bone is also essential for the function of the tooth-suspensory apparatus in occlusion and mastication. Molecular determinants of mineralization in these tissues include mineral ion concentrations (phosphate and calcium), pyrophosphate, small integrin-binding ligand N-linked glycoproteins and matrix vesicles. Amongst the enzymes important in regulating these mineralization determinants, two are discussed at length here, with clinical examples given, namely tissue-nonspecific alkaline phosphatase and phosphate-regulating gene with homologies to endopeptidases on the X chromosome. Inactivating mutations in these enzymes in humans and in mouse models lead to the soft bones and teeth characteristic of hypophosphatasia and X-linked hypophosphatemia, respectively, where the levels of local and systemic circulating mineralization determinants are perturbed. In X-linked hypophosphatemia, in addition to renal phosphate wasting causing low circulating phosphate levels, phosphorylated mineralization-regulating small integrin-binding ligand N-linked glycoproteins, such as matrix extracellular phosphoglycoprotein and osteopontin, and the phosphorylated peptides proteolytically released from them, such as the acidic serine- and aspartate-rich-motif peptide, may accumulate locally to impair mineralization in this disease.

[Three-dimensional finite element analysis of removable partial denture with periodontally compromised abutments]

OBJECTIVE

To evaluate three-dimensional (3D) finite element (FE) modeling of different periodontally compromised unilateral distal extension removable partial denture (RPD) abutments using the data of a 3D non-contact digitizing scanner.

METHODS

FE models were established, and the following structures were simulated in the models: alveolar bone, mucosa, abutments, periodontal ligaments, framework and artificial teeth. The alveolar bone and periodontal ligaments around the distal abutment in the three models were designed as normal, with bone defect and with periodontal ligaments defect respectively.Vertical or buccally inclined forces of 50, 100, 100 N were applied on the artificial teeth of the RPD and the stress distributions on the supporting tissues were calculated.

RESULTS

Under vertical loading, the maximal stress on the alveolar bone of the abutment were as follows: periodontal ligaments defect model (3.57 MPa) > bone defect model (3.21 MPa) > normal model (2.63 MPa). Under buccally inclined loading, the maximal stress on the alveolar bone of the abutment were as follows: periodontal ligaments defect model (2.50 MPa) > bone defect model (2.41 MPa) > normal model (1.79 MPa). Under buccally inclined loading, the stresses on distal aspects of the residual alveolar ridge were higher than that of the vertical loading model.

CONCLUSIONS

3D non-contact digitalizing scanner was useful for the finite element modeling process of removable partial denture.