Development, optimization and characterization of a full-thickness tissue engineered human oral mucosal model for biological assessment of dental biomaterials

Restorative dental materials and oral health care products come into direct contact with oral mucosa and can cause adverse reactions. In order to obtain an accurate risk assessment, the in vitro test model must reflect the clinical situation as closely as possible. The aim of this study was to develop and optimize a three-dimensional full-thickness engineered human oral mucosal model, which can be used for biological assessment of dental materials. In this study human oral fibroblasts and keratinocytes were isolated from patients and seeded onto a number of collagen-based and synthetic scaffolds using a variety of cell seeding techniques and grown at the air/liquid interface to construct human oral mucosa equivalents. Suitability of 10 different scaffolds for engineering human oral mucosa was evaluated in terms of biocompatibility, biostability, porosity, and the ability to mimic normal human oral mucosa morphology. Finally an optimized full-thickness engineered human oral mucosa was developed and characterized using transmission electron microscopy and immunostaining. The oral mucosa reconstruct resembled native human oral mucosa and it has the potential to be used as an accurate and reproducible test model in mucotoxicity and biocompatibility evaluation of dental materials.

Tissue-engineered oral mucosa: a review of the scientific literature

Tissue-engineered oral mucosal equivalents have been developed for clinical applications and also for in vitro studies of biocompatibility, mucosal irritation, disease, and other basic oral biology phenomena. This paper reviews different tissue-engineering strategies used for the production of human oral mucosal equivalents, their relative advantages and drawbacks, and their applications. Techniques used for skin tissue engineering that may possibly be used for in vitro reconstruction of human oral mucosa are also discussed.

HPLC analysis of components released from dental composites with different resin compositions using different extraction media

Components released from dental composite resins are essential factors in the assessment of biocompatibility of these materials. The effect of different extraction media on monomer release from composite resins based on different monomer types was evaluated. Three types of visible light cured composite resins were formulated based on the following monomers: triethylene glycol dimethacrylate (TEGDMA), bisphenol A glycerolate dimethacrylate (BisGMA), and urethane dimethacrylate (UDMA). Seventy-five composite resin discs were fabricated and light cured for 1 min in the absence of oxygen. Extraction media used were: distilled water, saline solution, artificial saliva, serum-free culture medium, and culture medium with 10% fetal calf serum. The analysis of extracts from the composite resins was carried out by High Performance Liquid Chromatography (HPLC). Quantifiable amounts of TEGDMA were released into the aqueous media. However, BisGMA and UDMA were not detectable in any of the extracts from the composite resins. Statistical analysis by one-way ANOVA followed by Tukey's test showed that there was a significant difference in TEGDMA release between culture media and other media (p < 0.05). From the results of this experiment it can be concluded that TEGDMA-based composite resins can release a high quantity of monomer into aqueous environments. The type of extraction medium may have a significant effect on monomer release from composite resins.

Osseointegration and osseoconductivity of hydroxyapatite of different microporosities

The aim of this study was to determine the relationship between changes in microporosity and the osseointegration and the osseoconductivity of hydroxyapatite (HAp). HAp cylinders were manufactured by a combination of uniaxial powder pressing and different sintering conditions, with different percentages of microporosity: HAp-I with 3.96+/-0.75% microporosity, HAp-II with 15.66+/-1.60% microporosity, and HAp-III with 29.72+/-0.69% microporosity. These HAp cylinders were surgically implanted in rabbit femurs. After 8 and 12 weeks, the femurs were removed, fixed, sectioned, ground, and stained by Stevenel's blue/Van Gieson for light microscopy and histomorphometry. Some ground sections were routinely processed for SEM. The osseointegration and the osseoconductivity were determined by means of image analysis and the data were submitted to ANOVA. In all cases the cortical bone was repaired and the HAp facing the medullary canal was lined with endosteum, which in some areas exhibited thin bone tissue formation. SEM observations showed no differences in the morphology of tissue-HAp interfaces for the three different porosities of HAp. There were no statistical differences between the groups related to either osseointegration or osseoconductivity. These results suggest that neither osseointegration nor osseoconductivity of HAp are influenced by changes in HAp microporosity.

Metal-ceramic bridges from commercial dental laboratories: alloy composition, cost and quality of fit

The quality of construction of fixed bridge prostheses directly affects their long-term survival. The cost, alloy composition and marginal fit of bridges made by 30 commercial dental laboratories is assessed. Duplicate models of a three unit bridge preparation were sent to 30 different laboratories, as if required for a patient receiving treatment under the General Dental Service. Material was sent via general dental practitioners, requesting metal-ceramic bridges made from 45% Au alloy, precious metal or non-precious metal. Proximal contacts were overbuilt at 65% of sites and pontic tissue contacts were excessive in all but one bridge. Eight laboratories did not use alloys corresponding to the request made. The mean marginal gaps of non-precious metal bridges (145 microns) were significantly greater than those for 45% gold alloy (106 microns). Marginal fit was poor and a number of factors have been observed, with other postulated, which may have contributed to this problem.

Variations in bridge construction in commercial laboratories

Identical working models for the construction of a porcelain bonded to metal three unit fixed bridge were sent to 30 different commercial dental laboratories in the United Kingdom. The material was sent from general dental practice addresses with the implication for treatment under the National Health Service. Each bridge on its return was examined for acceptability using subjective criteria based on clinical and technical factors. There was a wide variation between bridges which gave cause for concern. Lack of a satisfactory prescription for the laboratories to work to must have played a part in this variation. However, it is stressed that the prescription used in this work was deliberately chosen as representative of that which may be used by clinicians.

The effect of local interfacial geometry on the measurement of the tensile bond strength to dentin

The local detail of the geometry of the adhesive interface can have a significant effect on the measurement of dentin bond strengths and may be a contributory factor in the discrepancies among data in the published literature. The potential effect on the dentin bond strength due to modifications of the local stress distribution at the adhesive/dentin interface has been assessed. Tensile bond strength measurements for specimens with and without an adhesive flash were carried out and compared with the stress distribution at the adhesive interface determined by finite element stress analysis. The results showed that when the adhesive was constrained to the interface only, the tensile bond strength was 3.10 MPa, which increased to 6.90 MPa when a flash of adhesive was present. For a realistic measurement of dentin bond strength, the adhesive should be constrained to the interface only. Extension of the adhesive beyond the interface will result in an artificially high value for the dentin bond strength. A standardized method for the measurement of dentin bond strength is urgently needed, but must take these as well as all other known factors into account if results from different testing centers are to be directly comparable.

A critique of bond strength measurements

The lack of consistent values for dentine bond strengths in shear or in tension from what are superficially identical experimental procedures has led to ambiguities in the interpretation of the data. These variations in bond strength are usually considered to be related to different adhesive procedures. However so far little attention has been paid to the detail of the test procedures used. In this study the sensitivity of bond strengths to changes in testing conditions has been calculated using finite element stress analysis. It is shown that tensile and shear bond strengths are highly dependent on the geometry of the test arrangement and the materials involved. It is concluded that the concept of 'average stress' for the measurement of bond strength does not stand up to close examination. The measurement does not provide a material property as its value is dependent on local conditions and the actual stresses have little relationship to the average stress value. This demonstrates that there is a need for the standardization of test procedures for the measurement of bond strengths so that a universally valid comparison between different bonding agents can be performed.

Does obstructive jaundice adversely affect wound healing?

The effect of obstructive jaundice on wound healing has been investigated in an experimental study of abdominal wounds in rats following ligation and division of the common bile duct. Animals were jaundiced for 2 weeks before a second operation at which the abdominal wounds were made. The wounds in jaundiced and control animals showed no significant differences in mechanical strength during a 21-day period of study but there was a significant delay in the accumulation of collagen in the wounds of jaundiced animals. The findings suggest that the biochemical changes in the wounds of jaundiced animals did not interfere with wound repair and cast doubt on the thesis that jaundice has an adverse effect on wound healing.