Micropuncture measurements of interstitial fluid pressure in normal and inflamed gingiva in rats

Mechanical Regulation of Oral Epithelial Barrier Function

Epithelial cell function is modulated by mechanical forces imparted by the extracellular environment. The transmission of forces onto the cytoskeleton by modalities such as mechanical stress and matrix stiffness is necessary to address by the development of new experimental models that permit finely tuned cell mechanical challenges. Herein, we developed an epithelial tissue culture model, named the 3D Oral Epi-mucosa platform, to investigate the role mechanical cues in the epithelial barrier. In this platform, low-level mechanical stress (0.1 kPa) is applied to oral keratinocytes, which lie on 3D fibrous collagen (Col) gels whose stiffness is modulated by different concentrations or the addition of other factors such as fibronectin (FN). Our results show that cells lying on intermediate Col (3 mg/mL; stiffness = 30 Pa) demonstrated lower epithelial leakiness compared with soft Col (1.5 mg/mL; stiffness = 10 Pa) and stiff Col (6 mg/mL; stiffness = 120 Pa) gels, indicating that stiffness modulates barrier function. In addition, the presence of FN reversed the barrier integrity by inhibiting the interepithelial interaction via E-cadherin and Zonula occludens-1. Overall, the 3D Oral Epi-mucosa platform, as a new in vitro system, will be utilized to identify new mechanisms and develop future targets involved in mucosal diseases.

Photoacoustic imaging of posterior periodontal pocket using a commercial hockey-stick transducer

SIGNIFICANCE

Photoacoustic imaging has shown advantages over the periodontal probing method in measuring the periodontal probing depth, but the large size of conventional photoacoustic transducers prevents imaging of the more posterior teeth.

AIM

Our aim is to develop a photoacoustic imaging system to image the more posterior periodontal pocket.

APPROACH

We report a clinical "hockey-stick"-style transducer integrated with fibers for periodontal photoacoustic imaging. Cuttlefish ink labeled the periodontal pocket as the photoacoustic contrast agent.

RESULTS

We characterized the imaging system and then measured the pocket depth of 35 swine teeth. Three raters evaluated the performance of the hockey-stick transducer. The measurements between the Williams probing (gold standard) and the photoacoustic methods were blinded but highly correlated. We showed a bias of ∼0.3  mm for the imaging-based technique versus Williams probing. The minimum inter-reliability was over 0.60 for three different raters of varying experience, suggesting that this approach to measure the periodontal pocket is reproducible. Finally, we imaged three pre-molars of a human subject. We could access more upper and posterior teeth than conventional linear transducers.

CONCLUSIONS

The unique angle shape of the hockey-stick transducer allows it to image more posterior teeth than regular linear transducers. This study demonstrated the ability of a hockey-stick transducer to measure the periodontal pocket via photoacoustic imaging.

Regulation of Epithelial Cell Functions by the Osmolality and Hydrostatic Pressure Gradients: A Possible Role of the Tight Junction as a Sensor

Epithelia act as a barrier to the external environment. The extracellular environment constantly changes, and the epithelia are required to regulate their function in accordance with the changes in the environment. It has been reported that a difference of the environment between the apical and basal sides of epithelia such as osmolality and hydrostatic pressure affects various epithelial functions including transepithelial transport, cytoskeleton, and cell proliferation. In this paper, we review the regulation of epithelial functions by the gradients of osmolality and hydrostatic pressure. We also examine the significance of this regulation in pathological conditions especially focusing on the role of the hydrostatic pressure gradient in the pathogenesis of carcinomas. Furthermore, we discuss the mechanism by which epithelia sense the osmotic and hydrostatic pressure gradients and the possible role of the tight junction as a sensor of the extracellular environment to regulate epithelial functions.

Photoacoustic Imaging for Noninvasive Periodontal Probing Depth Measurements

The periodontal probe is the gold standard tool for periodontal examinations, including probing depth measurements, but is limited by systematic and random errors. Here, we used photoacoustic ultrasound for high-spatial resolution imaging of probing depths. Specific contrast from dental pockets was achieved with food-grade cuttlefish ink as a contrast medium. Here, 39 porcine teeth (12 teeth with artificially deeper pockets) were treated with the contrast agent, and the probing depths were measured with novel photoacoustic imaging and a Williams periodontal probe. There were statistically significant differences between the 2 measurement approaches for distal, lingual, and buccal sites but not mesial. Bland-Altman analysis revealed that all bias values were < ±0.25 mm, and the coefficients of variation for 5 replicates were <11%. The photoacoustic imaging approach also offered 0.01-mm precision and could cover the entire pocket, as opposed to the probe-based approach, which is limited to only a few sites. This report is the first to use photoacoustic imaging for probing depth measurements with potential implications to the dental field, including tools for automated dental examinations or noninvasive examinations.

Edema in Oral Mucosa after LPS or Cytokine Exposure

Lowering of interstitial fluid pressure (Pif) is an important factor that explains the rapid edema formation in acute inflammation in loose connective tissues. Lipopolysaccharide (LPS) and the pro-inflammatory cytokines interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) are pathogenetic in gingivitis. To test if these substances induce lowering of Pif in rat oral mucosa, we measured Pif with a micropuncture technique. IL-1β and TNF-α caused lowering of Pif, whereas LPS induced an immediate increase in Pif, followed by lowering after 40 min. Measurements of fluid volume distribution showed a significant change in interstitial fluid volume (Vi) 1.5 hr after LPS exposure as Vi changed from 0.41 ± 0.02 to 0.51 ± 0.03 mL/g wet weight ( p < 0.05), confirming edema. These findings show that LPS, IL-1β, and TNF-α induce lowering of Pif in the rat oral mucosa and contribute to edema formation in LPS-induced gingivitis.

Lymphangiogenesis and Lymphatic Function in Periodontal Disease

Lymphatic vessels return extravasated fluid, proteins, and cells back into the circulation and are important in immune cell trafficking. In the gingiva, lymphatic vessels are located in the lamina propria and travel over the external surface of the alveolar bone. The gingival lymphatics are important for fluid drainage, since lack of lymphatics has been shown to increase interstitial fluid pressure and fluid volume. Maintenance of gingival lymphatic vessels requires continuous signaling by the growth factors VEGF-C and -D via their receptor VEGFR-3. The growth factors are expressed in the gingival epithelium and also in immune cells in the lamina propria. VEGF-C seems to be crucial for lymphangiogenesis induced during periodontal disease development. The lymphatic vessels protect against periodontitis in mice, probably by clearing bacteria and bacterial products and by promoting humoral immune responses. Down-regulation of CCL21, a ligand important for dendritic cell migration, has been demonstrated in lymphatics from patients with periodontitis. High enzymatic activity in the gingiva of these patients may also contribute to impaired lymphatic function, due to the loss of structural components in the interstitium influencing lymphatic function. So far, knowledge is limited in this field because of the dearth of studies on the role of lymphatic vessels in periodontal disease.

Osmotic pressure of periimplant sulcular and gingival crevicular fluids: a split-mouth, randomized study of its measurement and clinical significance

OBJECTIVES

This study comparatively investigated periimplant sulcular fluid (PISF) and gingival crevicular fluid (GCF) by means of the osmotic pressure (OP) levels of PISF (PISFOP) and GCF (GCFOP). It was a preliminary research that aimed to quantify PISFOP and GCFOP as well as to evaluate their clinical significances around implants and teeth.

MATERIAL AND METHODS

Partially edentulous implant patients treated by the same clinicians and using the same implant system were randomized in a split-mouth trial design. Fifty-four implants and teeth from these patients were selected in the same mouth and jaw as matched pairs of samples, i.e. as symmetrical or corresponding implant and tooth. PISFOP/GCFOP measurement was performed by an osmometer following PISF/GCF sampling procedures. Clinical significance was evaluated by the correlations between PISFOP/GCFOP and some clinical examination parameters of periimplant/periodontal soft tissues. These parameters included Silness-Löe plaque index (PI), Löe-Silness gingival index (GI), bleeding on probing (BOP), probing pocket depth (PPD) and probing attachment level (PAL).

RESULTS

PISFOP was higher than GCFOP, and GI, BOP, PPD and PAL were higher in the implant group than in the tooth group (P<0.05). PISFOP positively correlated with the clinical parameters of implants (P<0.01 for PI, GI and BOP; P<0.05 for PPD and PAL), and GCFOP positively correlated with the clinical parameters of teeth (P<0.01 for PPD; P<0.05 for PI, GI, BOP and PAL).

CONCLUSIONS

The results reveal that PISFOP and GCFOP may be measured by osmometer, and their levels may be related with the clinical conditions of periimplant/periodontal soft tissues.

Integrated risk assessment of a hydroxyapatite-protein-composite for use in oral care products: a weight-of-evidence case study

Risk assessment of cosmetic ingredients represents a regulatory standard requirement in Europe and other regions. An integrated approach was designed to assess the safety of HPC, a particulate composite of hydroxyapatite and protein (gelatin) for use in oral care products, employing a weight-of-evidence assessment and considering specific physico-chemical properties and exposure conditions. An initial evaluation of the constituents suggested that their chemical nature does not represent a particular health hazard per se. Hydroxyapatite is the main component of teeth and bones in mammals; gelatin is used in food and assumed to be safe once a BSE/TSE risk has been excluded. In vitro screening tests were chosen to further evaluate the biocompatibility: Hen's egg test-chorioallantoic membrane (HET-CAM) to assess irritating effects towards mucous membranes; MTT cytotoxicity test with 3T3 fibroblasts; human corneal epithelial models to investigate inflammatory mediators and cytotoxicity; macrophage assays to measure cytotoxicity, inflammatory mediators and oxidative stress. Together with results from clinical studies, exposure estimates and analyses of kinetic properties, the presented information provides sound evidence to support the safe use of HPC. This is an example of a risk assessment for cosmetic use of small particles without the need for additional animal studies.

Importance of lymph vessels in the transcapillary fluid balance in the gingiva studied in a transgenic mouse model

The gingiva is frequently challenged by oral bacterial products leading to inflammatory responses such as increased fluid filtration and edema formation. The role of initial lymphatics for transcapillary fluid balance in the gingiva is unknown and was therefore investigated in genetically engineered K14-VEGF receptor 3-Ig (K14) lymphedema mice. The mutant mice demonstrated a total lack of lymphatics in the gingiva, whereas lymphatics were found in the submucosal parts of the alveolar mucosa, although they were almost completely absent in the mucosa. In wild-type (WT) mice, lymphatic vessels were detected in mucosal and submucosal parts of the alveolar mucosa. Interstitial fluid pressure (Pif) measured with micropipettes was increased in the gingiva of K14 mice in the normal situation ( P < 0.001) and after inflammation ( P < 0.01) induced by lipopolysaccharide from the oral bacteria Porphyromonas gingivalis compared with WT littermates. Fluid volume expansion caused a >75% increase in interstitial fluid volume followed by a drop in Pif after recovery in both strains. Continuous measurements during the expansion showed an increase in Pif followed by a decline, suggesting that compliance is increased after the disruption of the extracellular matrix during edema formation. In the alveolar mucosa, no strain differences were observed in Pif in the normal situation or after fluid volume expansion, suggesting that lymph vessels in the mucosa are not critical for tissue fluid regulation in any situation. Our study demonstrates an important role of gingival lymphatics in transcapillary fluid balance in the steady-state condition and during acute perturbations.

Fluid dynamics of gingiva in diabetic and systemically healthy periodontitis patients

OBJECTIVES

The influence of diabetes mellitus (DM) on the fluid dynamics of periodontium has not been reported in periodontal disease. The objectives of this study were (i) to investigate the alterations in the fluid dynamics of periodontium in diabetic periodontitis patients, and present the association of this phenomenon with the metabolic control of DM; (ii) to reveal any correlation between the fluid dynamics of periodontium and clinical signs of periodontal disease in DM and periodontitis.

DESIGN

Fifteen well-controlled diabetic chronic periodontitis patients (Group 1), 14 systemically healthy chronic periodontitis patients (Group 2), and 14 systemically and periodontally healthy individuals were included in the study. Gingival crevicular fluid volume (GCF-V) and gingival tissue osmotic pressure (GOP) were used as the parameters of periodontal fluid dynamics. GCF-V was measured by a Periotron device, while GOP was measured by a digital osmometer. Silness-Löe plaque index (PI), Löe-Silness gingival index (GI) and clinical attachment loss (AL) levels were recorded to determine the periodontal health status.

RESULTS

PI, GI and AL were higher in Groups 1 and 2 than in Group 3 (P<0.05), but similar between Groups 1 and 2 (P>0.05). Increased GCF-V and GOP were observed in Groups 1 and 2 compared with Group 3 (P<0.01), and the increase in Group 1 was greater than that in Group 2 (P<0.01). There were strong positive correlations between GCF-V and GOP in all three groups: between GI and GCF-V and GI and GOP in Groups 1 and 2; and between AL and GCF-V and AL and GOP in Groups 2 and 3.

CONCLUSION

The results suggest that (i) DM may have an additive influence on the fluid dynamics of periodontium in the presence of periodontal disease; (ii) this phenomenon may not be prevented by the metabolic control of DM; (iii) the clinical signs of periodontal disease may be affected by the fluid dynamics of periodontium in both DM and periodontitis.

Fluid dynamics of gingiva and gingival health in children with end stage renal failure

OBJECTIVES

Impaired homeostasis and fluid balance are important physiopathological alterations in patients with chronic renal failure which may adversely affect the fluid dynamics and health status of tissues and organs. There are insufficient data about this phenomenon in periodontal tissues. The aim of this study was to evaluate the fluid dynamics of gingiva in children with end stage renal failure (ESRF), correlating this entity with gingival health in the same patient group.

DESIGN

Fifteen paediatric ESRF patients undergoing peritoneal dialysis (test group) and 15 systemically healthy children (control group) who were without periodontitis participated in the study. Fluid dynamics of gingiva were assessed via the gingival crevicular fluid (GCF) volume and tissue osmotic pressure (GOP) levels in the groups. GCF volume was measured using a Periotron 8000, whereas GOP was measured using a digital osmometer. Silness and Löe Plaque index (PI) and, Löe and Silness gingival index (GI) scores were utilized to determine the gingival health status in the study population.

RESULTS

There were increases in the GCF volume and GOP of the test group compared to those of the control group (p<0.01). The PI and GI scores were higher in the test group than in the control group (p<0.01). Strong and positive correlations were found between GI and GCF volume, GI and GOP and, GCF volume and GOP in both groups (p<0.01).

CONCLUSIONS

Our findings suggest that the fluid dynamics of gingiva may alter in children with ESRF, and this phenomenon may consequently affect the gingival health of these patients.

Osmotic pressure and vasculature of gingiva in experimental diabetes mellitus

BACKGROUND

Alterations in tissue osmotic pressure (OP) and vasculature are considered to be the inevitable aspects of an inflammatory process that subsequently alter the fluid dynamics of the tissues involved. The aim of this study was to reveal a profile of OP and vascular changes in periodontally healthy gingival tissues and analyze the relationship between them in diabetes mellitus (DM) to evaluate the possible effects of DM on the fluid dynamics of the periodontium.

METHODS

Experimental DM was created by intraperitoneal streptozotocin injection in 10 periodontally healthy rats. These rats were used as the test group, and 10 systemically and periodontally healthy rats served as the control group. Gingival tissue samples obtained from the groups were used for the test procedures. OP was measured in the supernatants of these samples by a semimicrodigital osmometer. Vasculature was assessed as the alterations in vascularization (vessel number [VN]) and vasodilatation (vessel diameter [VD]) by histomorphometric means.

RESULTS

There was a gross increase in the OP level of the test group (172.7 +/- 59.7 mOsm/kg) compared to the control group (11.4 +/- 4.2 mOsm/kg; P <0.001). VN was found to be significantly larger in the test group (12.7 +/- 2.8) than in the control group (6.8 +/- 1.1; P <0.001). VD was found to be smaller in the test group (10.1 +/- 2.8 microm) than in the control group (15.5 +/- 2.4 microm), and this difference was statistically significant (P <0.001). A positive correlation between OP and VN (r = 0.77; P <0.001) and a negative correlation between OP and VD (r = 0.1; P >0.05) were observed in the test group.

CONCLUSION

Our results reveal that the fluid dynamics of periodontal soft tissues may be affected by the diabetic conditions in this diabetic model because of the increased OP and VN during the pathogenesis of the disease.

Osmotic pressure and vasculature of gingiva in periodontal disease: An experimental study in rats

Alterations in vascularisation, vasodilatation and tissue osmotic pressure (OP) are inevitable aspects of the inflammatory process that have an adverse effect on the fluid dynamics of the tissue involved. The aim of this study was to investigate tissue OP and its relationship with the vasculature in inflammed gingival tissues, in order to reveal the possible effects of vascular changes on OP in the fluid dynamics of periodontal soft tissues during periodontal disease. The parameters of fluid dynamics assessed in this study were OP, vascularisation and vasodilatation. Ligature-induced periodontitis was performed in 10 rats (test group), and gingival biopsies taken from the diseased teeth were utilised for the test procedures. These biopsies were compared with biopsies of the same teeth from 10 periodontally healthy rats (control group). OP was measured in mosmol/kg using a semi-micro digital osmometer. Vascularisation and vasodilatation were examined histopathologically; the number of vessels (VN) was quantified and the micrometric changes in vessel diameters (VD) were calculated as the alterations in the vasculature. OP, VN and VD were found to be higher in the test group (84.3+/-37.1 mosmol/kg, 13.2+/-3.2 and 19.5+/-1.3 microm, respectively) than the control group (11.6+/-3.8 mosmol/kg, 6.8+/-1.1 and 15.5+/-2.4 microm, respectively) (P<0.000). There was a strong, positive correlation between OP and VN (r=0.55, P<0.000) and a weak, negative correlation between OP and VD (r=0.1, P>0.05) in the test group. These results confirm that the OP of periodontal soft tissues does change during inflammatory conditions. The increase in OP during this process may be affected by increased vascularisation in the inflammed tissue.

Fluid dynamics of gingival tissues in transition from physiological condition to inflammation

BACKGROUND

An increase in gingival sulcular fluid filtration is a common clinical sign of early gingivitis. The aim of this study was to describe the fluid dynamics of the gingival interstitial tissues at the level of the sulcus in the transition towards inflammation.

METHODS

In 13 anesthetized rabbits, a silk ligature was placed around incisors close to the gingival margin, in order to prevent mechanical cleaning of plaque deposition. After 2 to 7 days, animals were anesthetized and interstitial fluid pressure measured using glass micropipettes connected to a servonull pressure system at the level of the free and attached gingiva.

RESULTS

Interstitial pressure was 3.8 +/- 2.9 cmH2O, significantly higher than the normal physiological value (about -1 cmH2O). Colloid osmotic pressure of interstitial fluid samples collected using the wick technique was measured using an osmometer whose membrane had a molecular cut-off of 30 kD and averaged 12.8 +/- 2.8 cmH2O (unchanged relative to control). Mean gingival sulcular fluid flow, measured by placing a PE tube (0.5 mm OD, 0.28 mm ID) in the sulcus, was 0.16 +/- 0.12 microl/h; the mean colloid osmotic pressure was 13.6 +/- 6.6 cmH2O, corresponding to a protein concentration of approximately 2.8 g/dl. Proteins of gingival fluid may leak from inflamed gingival interstitium or derive from bacteria of dental plaque. Histological analysis of gingival biopsies showed neutrophilic polymorphonuclear leukocyte infiltrates in both the dermis and epidermis layer.

CONCLUSIONS

Based on hydraulic and colloid osmotic data, the Starling pressure gradient favored filtration from gingival interstitium to the sulcular space, a condition opposite to that observed in healthy gingiva where fluid filtration is absent.

Effect of the sensory neuropeptide antagonists h-CGRP((8-37)) and SR 140.33 on pulpal and gingival blood flow in ferrets

In a previous study, it was concluded that the neuropeptides calcitonin gene-related peptide (CGRP) and substance P are released during resting conditions in the (exposed) ferret dental pulp, contributing to a basal vasodilator tone in the pulpal vessels. In order to exclude the possibility that the method used elicited axon reflexes, which might be responsible for neuropeptide release, the present study was designed without pulp exposure. Non-invasive laser-Doppler flowmetry was used to measure the effects of intra-arterial infusions of the antagonists h-CGRP((8-37)) and SR 140.33 (neurokinin 1-receptor antagonist) on pulpal and gingival blood flow before, during and after electrical tooth stimulation. Infusions of h-CGRP((8-37)) reduced the basal blood flow in the pulp by 31.4+/-5.2% (p<0.001) and in the gingiva by 22.6+/-4.8% (p<0.05). A further significant decrease in basal blood flow was measured in both pulp and gingiva following SR 140.33 administration. The reduction in blood flow was 16.9+/-1.9% (p<0.005) in the pulp and 19. 3+/-5.6% (p<0.05) in the gingiva. The systemic arterial pressure remained unchanged both during and after the periods of infusion. Tooth stimulation before the antagonist infusion significantly increased the pulpal blood flow by 71.9+/-15.3% (p<0.005). Infusion of h-CGRP((8-37)) greatly reduced this electrically induced vasodilatation, indicating that CGRP is the principal factor responsible for the vasodilatation observed after tooth stimulation. This study confirms the previous finding that a resting vasodilator tone due to the release of CGRP and SP exists in the ferret dental pulp. It is concluded that spontaneous, basal release of the neuropeptides CGRP and substance P exists both in dental pulp and gingiva in the ferret.

Effect of venous stasis and hypoproteinemia in gingival fluid formation in rats

Experiments were performed to provide information on the mechanisms of the formation of gingival fluid in rats and on the determinants of its flow and composition. For this purpose we studied the effect of increasing net capillary filtration by venous stasis induced by multiple ligations of the jugular vein or by hypoproteinemia induced through puromycine nephrosis. A 1 microliter glass capillary was placed in the sulcus of the first maxillary molar for collection of gingival fluid (GF). Colloid osmotic pressure (COP) was determined in GF, in wick fluid from attached gingiva and buccal mucosa, and in plasma. Interstitial fluid hydrostatic pressure (Pi) was measured by micropuncture technique and the fractional removal rate of radio-labelled human serum albumin (kAlb) was recorded in attached gingiva and buccal mucosa. During venous stasis the gingival fluid flow increased from 1.7 microliters/h to 3.8 microliters/h, whereas COPGF fell from 14.1 mmHg to 8.8 mmHg. COP in wick fluid from gingiva was reduced from 10.3 to 4.3 mmHg. Pi increased from 6.8 to 13.1 mmHg, and kAlb in sham-operated controls increased from 0.068 to 0.189 h-1. In buccal mucosa COPi was significantly decreased to 7.1 mmHg in rats with venous stasis, whereas Pi and kAlb remained unchanged compared to the sham-operated controls. In hypoproteinemic rats COPGF was 5.0 mmHg and COPp was reduced from 18.9 to 8.0 mmHg. COPi declined from 8.9 mmHg to 2.4 mmHg in gingiva and from 8.1 mmHg to 2.7 mmHg in buccal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)