Hematopoietic Stem Cells as a Novel Source of Dental Tissue Cells.

While earlier studies have suggested that cells positive for hematopoietic markers can be found in dental tissues, it has yet to be confirmed. To conclusively demonstrate this, we utilized a unique transgenic model in which all hematopoietic cells are green fluorescent protein+ (GFP+). Pulp, periodontal ligament (PDL) and alveolar bone (AvB) cell culture analysis demonstrated numerous GFP+ cells, which were also CD45+ (indicating hematopoietic origin) and co-expressed markers of cellular populations in pulp (dentin matrix protein-1, dentin sialophosphoprotein, alpha smooth muscle actin [ASMA], osteocalcin), in PDL (periostin, ASMA, vimentin, osteocalcin) and in AvB (Runx-2, bone sialoprotein, alkaline phosphatase, osteocalcin). Transplantation of clonal population derived from a single GFP+ hematopoietic stem cell (HSC), into lethally irradiated recipient mice, demonstrated numerous GFP+ cells within dental tissues of recipient mice, which also stained for markers of cell populations in pulp, PDL and AvB (used above), indicating that transplanted HSCs can differentiate into cells in dental tissues. These hematopoietic-derived cells deposited collagen and can differentiate in osteogenic media, indicating that they are functional. Thus, our studies demonstrate, for the first time, that cells in pulp, PDL and AvB can have a hematopoietic origin, thereby opening new avenues of therapy for dental diseases and injuries.

Mechanical Stretching of Mouse Calvarial Osteoblasts In Vitro Models Changes in MMP-2 and MMP-9 Expression at the Bone-Implant Interface.

Bone to mechanical loading elicits a biological response that has clinical significance for several areas in dental medicine, including orthodontic tooth movement, tempromandibular joint disease, and endosseous dental implant osseointegration. Human orthopedic studies of failed hip implant sites have identified increased mRNA expression of several collagen-degrading matrix metalloproteinases (MMPs), while in vitro experiments have shown increases in MMP secretion after exposure to inflammatory mediators. This investigation evaluates the effects of mechanical deformation on in vitro osteoblasts by assessing changes in MMP gene expression and enzyme activity. We seeded mouse neonatal calvarial osteoblasts onto flexible 6-well plates and subjected to continuous cyclic mechanical stretching. The expression and activity of mRNA for several MMPs (2, 3, 9, and 10) was assessed. When subjected to mechanical stress in culture, only mRNA specific for MMP-9 was significantly increased compared to nonstretched controls (P < .005). Measurement of MMP activity by gelatin zymography demonstrated that none of the MMPs showed increased activity with stretching; however, MMP-2 activity decreased. Our results suggest that in response to stretch, MMP-2 responds rapidly by inhibiting conversion of a MMP-2 to the active form, while a slower up-regulation of MMP-9 may play a role in the long-term remodeling of extracellular matrix in response to continuous mechanical loading. This study suggests that the regulation of metalloproteinases at both the mRNA and protein level are important in the response of bone to mechanical stress.

A Model for Osteonecrosis of the Jaw with Zoledronate Treatment following Repeated Major Trauma.

This study aims to develop a reproducible rat model for post-traumatic bisphosphonate-related osteonecrosis of the jaw (BRONJ). In our previous studies using dental extraction as an inducing factor, only 30%-60% of zoledronate-treated animals fulfilled the definition of clinical BRONJ. We modified the zoledronate regimen and introduced repeated surgical extraction to illicit quantifiable BRONJ in all animals. Eighty retired-breeder female Sprague-Dawley rats were divided between the treatment (i.v. zoledronate; 80 µg/kg/week for 13 weeks) and control (saline) groups. On week 13, the left mandibular first molar was surgically extracted, followed by the second molar a week later. Animals were euthanized at 1-week, 2-weeks, and 8-weeks following extraction. The occurrence and severity of BRONJ were scored in each animal based on gross and MicroCT analysis. Parameters of bone formation and osteoclast functions at the extraction site were compared between groups. All zoledronate-treated animals developed a severe case of BRONJ that fulfilled the clinical definition of the condition in humans. Osteoclast attachment continued to be defective eight weeks after stopping the treatment. There were no signs of kidney or liver toxicity. Our data confirmed that repeated surgical extraction (major trauma) by itself consistently precipitated massive bone necrosis in ZA-treated animals, eliminating the need to induce pre-existing infection or comorbidity. These results will be the basis for further studies examining the in-vivo pathogenesis and prevention of BRONJ.

Correlation of changes in the mandible and retina/choroid vasculature of a rat model of BRONJ.

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) causes bones of the mandible and maxilla to become necrotic and protrude into the oral cavity. Compromised blood supply to bone is also a feature of BRONJ. The design of this study was first to use our established technique of molar extraction and IV bisphosphonate injection to produce features of BRONJ in rats that mimic the human disease; second to confirm vascular changes in the mandible and eye using micro-CT of vascular casts, and image analysis of retina/choroid images; and third to show parallel bisphosphonate-induced changes in the structure and markers of the vasculature of the bone and eye. The results of this study show structural changes in the eye and mandible as well as biochemical changes including the up-regulation of VEGF in response to the bisphosphonate-associated ischemia. These changes are not associated with angiogenesis in either the eye or mandible as determined by reduced vascular complexity. These results suggest that observations of direct changes to the vasculature in the retina/choroid structures of the eye in patients taking bisphosphonates could serve as a window to the progression of debilitating changes occurring as a result of bisphosphonate therapy.

In vitro study of the adverse effect of nicotine and physical strain on human gingival fibroblasts as a model of the healing of wounds commonly found in the military.

BACKGROUND: Significant adverse effects on fibroblast growth and metabolism are observed with nicotine. We investigated the synergistic effects of nicotine and cyclical mechanical strain (CMS) on human gingival fibroblasts (HGFs) in a wound-healing model. METHODS: HGFs were isolated and grown in Dulbecco's modified Eagle's medium. Three-millimeter wounds were created on a confluent cell monolayer grown in a media containing 0, 1, 2, or 4 mM nicotine, with or without CMS. The applied deformation regimen remains constant for 6 days. On days 1, 2, 4, and 6, the cells were stained with hematoxylin and eosin Y for the evaluation of wound repopulation. RESULTS: The application of CMS alone demonstrates a biphasic response, with an initial stimulatory effect on wound repopulation (days 1-2) and less repopulation during the later phase (days 4-6). The addition of nicotine clearly demonstrated a time and inverse dose-dependent relationship on wound repopulation, with no effect during the early phase and reduced wound repopulation during the later phase. CONCLUSIONS: Initial treatment of HGF wounds with CMS resulted in faster wound repopulation regardless of nicotine presence. By day 6, wound healing of HGF exposed to both nicotine and CMS is delayed. These findings suggest that CMS and nicotine may affect fibroblasts and delay wound healing at other sites in the body as well.

Vascular alterations in the sprague-dawley rat mandible during intravenous bisphosphonate therapy.

Long-term use of intravenous bisphosphonates, such as zoledronic acid (zoledronate), has been linked to bisphosphonate-related osteonecrosis of the jaw (BRONJ). Invasive dental surgery seems to trigger the bone necrosis in most cases. To determine the effects of zoledronic acid on the vascular structure of the rat mandible. Extracted of the mandibular first molar in rats that received 2 IV injections of zoledronate (20 µg/kg), 4 weeks apart. Zoledronate-treated rats (n = 18) were then compared to a control group of untreated rats (n = 18). At the fourth, eighth, and 12th week after molar extraction, 8 rat mandibles from each group were perfused with 35% radiopaque triphenylbismuth in methyl methacrylate via carotid artery perfusion. Mandibles were harvested and examined by micro-CT to assess the spatial and dimensional changes of the vasculature as a result of zoledronate treatment. The micro-CT analysis showed that zoledronic acid-treated rats had blood vessels that were thicker, less connected, and less ordered than control rats that were not exposed to zoledronic acid. This study demonstrated that treatment with zoledronic acid in rats is associated with vascular changes in alveolar bone. Further studies are underway to explore whether these vascular changes contribute to the pathogenesis of BRONJ.

Effect of metformin on periimplant wound healing in a rat model of type 2 diabetes.

PURPOSE: To investigate the effects of hyperglycemia and metformin (a popular biguanide antidiabetic) on periimplant healing. METHODS: Thirty-six male rats were assigned to 3 groups: (1) nondiabetic Wistar-Kyoto rats (controls), (2) Goto-Kakizaki (GK) spontaneously diabetic rats (GK group), and (3) GK rats were fed metformin (100 mg/kg body weight per day) in their water for 4 weeks (GK + Met group). The right maxillary first molars were extracted and sites were allowed 1 month to heal. Titanium implants (1 × 3 mm) were placed in healed extraction sites. Six rats from each group were analyzed at weeks 1 and 4 by micro computed tomography for bone/implant contact ratio, percent bone volume, trabecular number, and bone mineral density. Blood was also analyzed for glucose, HbA1c, and pyridinoline (PYD). RESULTS: At week 1, glucose levels in the GK-Met rats were high, and all bone parameters were similar to GK rats (lower bone parameters and higher PYD than controls). At week 4, glucose levels in the GK-Met rats and all parameters were similar to controls. CONCLUSIONS: Hyperglycemic GK type 2 diabetic rats showed improved blood glucose and wound healing around oral implants after metformin administration.

Development of a rat model of bisphosphonate-related osteonecrosis of the jaw (BRONJ).

The purpose of this study was to develop a rat model predictive of bisphosphonate-related osteonecrosis of the jaw (BRONJ) after exodontias. Thirty female rats were randomized into 2 groups, control and experimental. The experimental group received 2 intravenous injections of zoledronate (20 µg/kg). The mesial root of the right mandibular first molar was extracted. Rats were euthanized at 0, 4, and 8 weeks. Bone mineral density (BMD), collagen breakdown (pyridinium [PYD]), vascular regeneration (VEGF), and histology were examined. A trend toward higher PYD values was suggested in control vs experimental groups after wounding. Serum VEGF increased significantly after wounding for both control and experimental groups. After 8 weeks, VEGF continued to rise for the experimental group only. In the extraction socket area, BMD was significantly lower after wounding in control vs. zoledronate-treated rats. Histology sections from experimental groups showed bacteria and bone necrosis. Consistent findings of BRONJ features similar to those in humans were observed after zoledronate treatment.

Preparation, physical-chemical characterization, and cytocompatibility of polymeric calcium phosphate cements.

Aim. Physicochemical mechanical and in vitro biological properties of novel formulations of polymeric calcium phosphate cements (CPCs) were investigated. Methods. Monocalcium phosphate, calcium oxide, and synthetic hydroxyapatite were combined with either modified polyacrylic acid, light activated polyalkenoic acid, or polymethyl vinyl ether maleic acid to obtain Types I, II, and III CPCs. Setting time, compressive and diametral strength of CPCs was compared with zinc polycarboxylate cement (control). Specimens were characterized using X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. In vitro cytotoxicity of CPCs and control was assessed. Results. X-ray diffraction analysis showed hydroxyapatite, monetite, and brushite. Acid-base reaction was confirmed by the appearance of stretching peaks in IR spectra of set cements. SEM revealed rod-like crystals and platy crystals. Setting time of cements was 5-12 min. Type III showed significantly higher strength values compared to control. Type III yielded high biocompatibility. Conclusions. Type III CPCs show promise for dental applications.

Polymeric-calcium phosphate cement composites-material properties: in vitro and in vivo investigations.

New polymeric calcium phosphate cement composites (CPCs) were developed. Cement powder consisting of 60 wt% tetracalcium phosphate, 30 wt% dicalcium phosphate dihydrate, and 10 wt% tricalcium phosphate was combined with either 35% w/w poly methyl vinyl ether maleic acid or polyacrylic acid to obtain CPC-1 and CPC-2. The setting time and compressive and diametral tensile strength of the CPCs were evaluated and compared with that of a commercial hydroxyapatite cement. In vitro cytotoxicity and in vivo biocompatibility of the two CPCs and hydroxyapatite cement were assessed. The setting time of the cements was 5-15 min. CPC-1 and CPC-2 showed significantly higher compressive and diametral strength values compared to hydroxyapatite cement. CPC-1 and CPC-2 were equivalent to Teflon controls after 1 week. CPC-1, CPC-2, and hydroxyapatite cement elicited a moderate to intense inflammatory reaction at 7 days which decreased over time. CPC-1 and CPC-2 show promise for orthopedic applications.

Advanced glycation endproducts and rat dental implant osseointegration.

Advanced glycation endproducts (AGEs) are a diverse group of molecular adducts formed in environments high in reducing sugars that accumulate with aging and in diabetes. This study tests the hypothesis that AGEs inhibit the stabile osseointegration of dental implants through tissue interactions that interfere with bone turnover and compromise the biomechanical properties at the bone-implant interface. Maxillary first molars were extracted from 32 rats and allowed to heal for 4 weeks. Titanium implants (1 mm x 3 mm) were placed in the healed sockets of 2 groups of 16 rats consisting of 8 rats injected 3 times/wk for 1 month with AGE (prepared from glucose and lysine) and 8 rats injected with vehicle as a control. AGE injections continued for an additional 14 or 28 days before sacrifice. X-ray images, blood, and tissues were collected to examine bone/implant contact ratio, serum pyridinoline ([PYD] a collagen breakdown marker), osteocalcin ([OSC] a bone formation marker), and for immunohistochemistry with antibodies to AGE and the bone turnover-marker protein matrix metalloproteinase1. Compared with the AGE-treated groups, the controls showed significantly higher bone/implant contact at both 14- and 28-day time points. PYD (P < .05) and OSC (trend) levels from controls showed decreases at 28 days when compared with AGE-treated groups. Immunohistochemistry with AGE-specific and bone turnover marker antibodies showed stronger staining associated with the implant/tissue interface in AGE-treated rats. Our studies indicate an association between AGE and inhibition of bone turnover, suggesting that the formation of AGE in high glycemic conditions, such as diabetes, may contribute to a slower rate of osseointegration that negatively affects implant stability.

Cytotoxicity, calcium release, and pH changes generated by novel calcium phosphate cement formulations.

Few published studies describe the biological properties of calcium phosphate cements (CPCs) for dental applications. We measured several biologically relevant properties of 3 CPCs over an extended (8 wk) interval. Monocalcium phosphate, calcium oxide, and synthetic hydroxyapatite were combined with either modified polyacrylic acid, light-activated modified polyalkenoic acid, or 35% w/w polymethyl vinyl ether maleic acid to obtain Types I, II, and III CPCs, respectively. Set cements were placed in direct contact with L929 fibroblasts for up to 8 weeks. Media Ca(+2) and pH were determined by atomic absorption spectroscopy and pH electrode respectively. Cell mitochondrial function was measured by MTT assay. Type I cements suppressed mitochondrial activity > 90% (vs. Teflon controls), but significantly (p < 0.05) improved to control levels over 8 weeks. Type II cements suppressed mitochondrial activity > 90% at all times. Type III cements elevated mitochondrial activity significantly after 7 wks. The pH profiles approached neutrality by 24 h, and all cements released calcium into the storage medium at all periods (24 h - 8 wk). We concluded that several types of cements had long-term biological profiles that show promise for dental applications.

Effect of systemic parathyroid hormone (1-34) and a beta-tricalcium phosphate biomaterial on local bone formation in a critical-size rat calvarial defect model.

OBJECTIVE: The objective of this study was to evaluate local bone formation following systemic administration of parathyroid hormone (1-34) (PTH), a surgically implanted synthetic beta-tricalcium phosphate (beta-TCP) bone biomaterial serving as a matrix to support new bone formation. MATERIALS AND METHODS: Critical-size, 8 mm, calvarial through-and-through osteotomy defects were surgically created in 100 adult male Sprague-Dawley rats. The animals were randomized into five groups of 20 animals each to receive one of the following treatments: PTH (15 microg PTH/kg/day; subcutaneously), PTH/beta-TCP, beta-TCP, or particulate human demineralized freeze-dried bone (DFDB), and sham-surgery controls. Ten animals/group were euthanized at 4 and 8 weeks post-surgery for radiographic and histometric analysis. RESULTS: The histometric analysis showed that systemic PTH significantly enhanced local bone formation, bone fill averaging (+/-SE) 32.2+/-4.0% compared with PTH/beta-TCP (15.7+/-2.4%), beta-TCP (12.5+/-2.3%), DFDB (14.5+/-2.3%), and sham-surgery control (10.0+/-1.5%) at 4 weeks (p<0.014). Systemic PTH showed significantly enhanced bone formation (41.5+/-4.0%) compared with PTH/beta-TCP (22.4+/-3.0%), beta-TCP (21.3+/-4.4%), and with the sham-surgery control (23.8+/-4.2%) at 8 weeks (p<0.025). The DFDB group showed significantly increased bone formation from 4 (14.5+/-2.3%) to 8 weeks (32.0+/-3.2%) (p<0.006). The PTH/beta-TCP and beta-TCP groups both showed limited biomaterials resorption. The radiographic analysis was not diagnostic to distinguish local bone formation from the radiopaque beta-TCP biomaterial. CONCLUSIONS: Systemic administration of PTH significantly stimulates local bone formation. Bone formation was significantly limited by the beta-TCP biomaterial.

Rat model for studying tissue changes induced by the mechanical environment surrounding loaded titanium implants.

PURPOSE: This study presents a new rat oral implant model for assessing histologic changes in the mechanical environment surrounding loaded and unloaded dental implants. MATERIALS AND METHODS: The maxillary left first molar from retired breeder rats was extracted, and the site was allowed to heal for 1 month. A titanium miniscrew implant was then placed into the site and allowed to heal for 21 days. The mandibular left first molars in one group of rats were extracted to create an unloaded condition; in a second group of rats the mandibular left first molars were left in occlusion with the opposing screw head to simulate loading. Radiographs were taken on the day of placement and again at 7 days, 14 days, and 21 days after placement and were used to estimate the bone-implant contact ratio. The rats were sacrificed after 21 days. Peri-implant tissue samples from day 21 were processed for histology and immunohistochemistry with antibodies to osteocalcin and matrix metalloproteinase 13 (MMP-13). Two-dimensional finite element models were created from images of the histologic sections and immunohistochemical samples to observe tissue changes. RESULTS: Areas of high shear stress adjacent to the helical threads of loaded implants were associated with osteocalcin localization and bone formation but only minimal localization of MMP-13. Bone adjacent to unloaded implants showed fibrous tissue and extensive MMP-13 localization surrounding the apical two-thirds of each implant. These results agree with estimated bone-implant contact ratios, which showed a steady decrease in contact ratio for the unloaded implant group but a significantly higher contact ratio in the loaded group between 14 and 21 days. CONCLUSION: The rat oral implant model is useful for studies of the mechanical and physiologic environment affecting osseointegration in loaded and unloaded implants.

Tensile strain-induced Ets-2 phosphorylation by CaMKII and the homeostasis of cranial sutures.

BACKGROUND: Mechanotransduction underpins the homeostasis of musculoskeletal tissues, including cranial sutures. Intracellular calcium, [Ca 2+]ic, and protein phosphorylation are two intermediate variables in signal relay during mechanotransduction. This project establishes a chain of cause and effect, linking cellular strain to substrate phosphorylation, and identifies the agent and target sites of phosphorylation. METHODS: Cyclic tensile force (0.5 N at 1 Hz) was applied to 1-day-old rat sagittal sutures. [Ca 2+]ic was measured by FURA-2. Ets-2 phosphorylation by CaMKII was tested using Western blot autoradiography. Peptide array was constructed to determine the precise sites of phosphorylation. The results were confirmed with mass spectroscopy and Western blots using phospho-specific antibodies. RESULTS: [Ca 2+]ic increased rapidly in response to tensile stress. In the presence of Ca2+, CaMKII caused Ets-2 phosphorylation. Of the three possible sites for phosphorylation of Ets-2 by CaMKII, RVPS, FESF, RLSS, Serine 246, 310, and 313 were the targets. Furthermore, the contiguous sequence modified this effect. Mass spectroscopy showed 80 Da (molecular weight of phosphate group, -PO3) right shifts consistent with phosphorylation. There was cytosolic translocation of Ets-2 on tensile deformation of suture cells. CaMKII binding of Ets-2 occurred within 30 minutes after the onset of tensile strain. CONCLUSIONS: Cranial suture cells can respond to tensile forces by increasing [Ca 2+]ic, which causes CaMKII to phosphorylate Ets-2, thus altering Ets-2 binding to its downstream promoters. Of note, Ets-2 is at the intersection of three key pathways important in craniosynostosis: fibroblast growth factor-2, transforming growth factor-beta, and mechanotransduction.

Effect of ovariectomy and alendronate on implant osseointegration in rat maxillary bone.

Bisphosphonates such as alendronate (ALD), although controversial, are worthy of investigation for the enhancement of implant osseointegration in patients with low bone mass who are already taking bisphosphonates for osteoporosis. These patients may receive additional benefits and be acceptable candidates for dental implants without needing to change their medication regimen and possibly as a result of their medication regimen. The purpose of this study was to compare implant osseointegration in maxillary bone of normal rats with a rat model of postmenopausal estrogen deficiency (ovariectomized [OVX]), with and without ALD. An experimental group of 32 rats was divided in 4 groups: ALD-OVX (n=8 OVX with ALD), OVX (n=8 OVX without ALD), ALD (n=8 normal rats with ALD), and control (n=8 normal rats). All rats received one titanium microscrew implant in the left edentulous region of the maxillary arch. The ALD-OVX and ALD groups received subcutaneous injections of ALD 3 times a week. On the fourth week after ALD administration, an implant was placed in all 32 rats. The maxilla of each rat was radiographed 4 times: at 0, 7, 14, and 28 days. On day 28 after implant placement, all rats were killed, and the peri-implant tissue was embedded in plastic or paraffin for histological examination. The X rays were used for a chronologic calculation of the contact ratio between implant and bone surfaces. Radiographic bone density was determined at 3 points: mesial, apical, and distal. The results show that osseointegration of the implants was impaired in the estrogen-deficient OVX rats compared with the ALD-OVX rats. Fifty percent of the implants were lost at 2 weeks in the OVX group. Radiographic evidence suggested that none of the implants in the OVX group osseointegrated. In the histologic examination more bone was observed around implants from the ALD-OVX and ALD groups than around implants from the OVX group. The OVX group presented a dramatic reduction in implant bone contact at 2 weeks and a significant 13% reduction at 4 weeks vs day of implant (P = .006). The ALD-OVX group presented 50% more bone density than the OVX group (P = .0003). Both ALD groups (ALD and ALD-OVX) had significantly higher radiographic bone density than the other groups (P < .01 for each comparison). In conclusion, osseointegration of implants was enhanced by ALD. Radiographic bone density and contact ratio improved with ALD administration. Implant osseointegration was impaired by estrogen deficiency in the OVX group.

Effects of induced premaxillary suture fusion on the craniofacial morphology in growing rats.

OBJECTIVE: Due to premaxillary rapid development and fusion with the maxilla at the fetus stage, the functions of the premaxillary suture still remain unclear. This study was designed to explore the effect of artificial induced premaxillary suture fusion on craniofacial morphology. METHODS: Thirty Sprague Dawley rats were divided into control and experimental groups, with 3 week, 5 week and 8 week subgroups of five animals each. An incision was made in each rat along the premaxillary suture and cyanoacrylate was administered to immobilize the exposed premaxillary suture for experimental rats. No glue was applied to controls. Weights, dental impressions and radiographs were taken before and after surgery until sacrifice and used to determine the differences between groups using the one-way ANOVA test. RESULTS: After immobilizing the premaxillary suture, significant changes in the craniofacial morphology were measured at the different time points. In the experimental groups, local changes occurred at the 3rd week. A global alteration in craniofacial morphology was apparent at the 8th week in the experimental group compared to the control. At each successive time point, craniofacial morphological alterations increased in rats with fused premaxillary sutures. CONCLUSIONS: Induced premaxillary suture fusion can inhibit the growth of the premaxilla and cause extensive craniofacial morphological changes. These findings suggest that premaxillary suture fusion may be related to craniofacial malformation or malocclusion and to the formation of the flattened craniofacial profile in humans.

Infiltration/evaporation-induced shrinkage of demineralized dentin by solvated model adhesives.

During dentin bonding, solvated adhesive comonomers are applied to water-saturated decalcified dentin matrices. When alcohol-solvated hydrophilic or hydrophobic methacrylate monomers are applied, they chemically remove water and cause matrix shrinkage during comonomer infiltration. Evaporation of solvent induces further shrinkage. The purpose of this work was to compare the shrinkage of water-saturated dentin matrices infiltrated with ethanol- or methanol-solvated 2-hydroxyethyl methacrylate (HEMA), 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane (BisGMA), or triethyleneglycol dimethacrylate (TEGDMA) at 90/10, 70/30, 50/50, and 30/70 mass fraction % alcohol/monomer before and after evaporation of alcohol. Thin (ca 0.2 mm) disks of human mid-coronal dentin were demineralized and placed in a well beneath the contact probe of a linear variable differential transformer (LVDT). The height of the matrix was measured before and after random application of one of the twelve alcohol/monomer mixtures. Matrix height was measured during infiltration and during solvent evaporation. Between trials, residual monomer was extracted using ethanol. These studies were repeated on specimens in which 100% alcohol was used to substitute for water in the matrix. Both studies revealed that matrices shrink 30-50% but that pretreatment of matrices with alcohol prevents BisGMA phase separations from occurring. Wet bonding with ethanol instead of water permits infiltration of relatively hydrophobic alcohol/monomers.

Net expansion of dried demineralized dentin matrix produced by monomer/alcohol saturation and solvent evaporation.

The purpose of this work was to determine if nonaqueous methacrylate monomer/alcohol mixtures could expand dried collapsed demineralized dentin matrix. Thin disks (ca. 200 microm) of human dentin were demineralized and placed in wells beneath contact probes of linear variable differential transformers. The probes were placed on water-saturated expanded matrices to record the shrinkage associated with drying. Monomer mixtures containing hydroxyethyl methacrylate, 2,2-bis[4-(2-hydroxy-3 methacryloyloxy)propoxyphenyl] propane, or triethyleneglycol dimethacrylate were mixed with methanol or ethanol at alcohol/monomer mass fraction % of 90/10, 70/30, 50/50, or 30/70. They were randomly applied to the dried matrices to determine the rate and magnitude of expansion; then shrinkage was recorded during evaporation of the alcohols. The results indicated that matrix expansion was positively correlated with the Hoy's solubility parameters for hydrogen bonding forces (delta(h)) of the monomer/solvent mixtures (p < 0.001). Expansions were more rapid with methanol-containing than with ethanol-containing monomer mixtures. For the test solutions, triethyleneglycol dimethacrylate-containing mixtures produced the slowest rate of matrix expansion and hydroxyethyl methacrylate-containing mixtures the most rapid expansion. When the solvents were evaporated, the matrix shrank in proportion to the solvent content and the delta(h) of the monomer-solvent mixtures. The results indicate that expansion of dried, collapsed dentin matrices requires that the delta(h) of the mixtures be larger than 17 (J/cm(3))(1/2). The greater the delta(h) of the monomer solutions, the greater the rate and extent of expansion.

Fractal analysis of the PDL-bone interface and implications for orthodontic tooth movement.

BACKGROUND: The periodontal ligament (PDL) is a soft tissue interposed between the tooth and the alveolar bone. It is responsible for transmission of forces in vivo; this promotes bone remodeling. The purpose our study was to use fractal analysis to quantify the complex morphology of the PDL-bone interface. METHODS: We used Scion Image (Scion Corp, Frederick, Md) and Benoit fractal analysis (Tru Soft International, St. Petersburg, Fla) programs to calculate the fractal dimension of the PDL-bone interface in rats via the box-counting method. Rats in the experimental groups received an initial force of 0.1N or 0.5N with customized springs for 6 hours. RESULTS: Our studies showed an increase in normal fractal dimension at the root apices of the rats' maxillary molars. We also found evidence that the fractal dimension varies along the entire root length from the apex to the cementoenamel junction. CONCLUSIONS: Mechanical loading might lead to an increase in fractal dimension at the PDL-bone interface apart from mechanisms of bone cell directed remodeling. These changes in fractal dimension are proportional to loading and could provide a new parameter for force determination in orthodontic tooth movement.