Development and Analysis of a Hydroxyapatite Supplemented Calcium Silicate Cement for Endodontic Treatment

Aim: To develop an endodontic cement using bovine bone-derived hydroxyapatite (BHA), Portland cement (PC), and a radiopacifier. Methods: BHA was manufactured from waste bovine bone and milled to form a powder. The cements were developed by the addition of BHA (10%/20%/30%/40% wt), 35% wt, zirconium oxide (radiopacifier) to Portland cement (PC). A 10% nanohydroxyapatite (NHA) cement containing PC and a radiopacifier, and a cement containing PC (PC65) and a radiopacifier were also manufactured as controls. The cements were characterised to evaluate their compressive strength, setting time, radiopacity, solubility, and pH. The biocompatibility was assessed using Saos-2 cells where ProRoot MTA acted as the control. Compressive strength, solubility and pH were evaluated over a 4-week curing period. Results: The compressive strength (CS) of all cements increased with the extended curing times, with a significant CS increase in all groups from day 1 to day 28. The BHA 10% exhibited significantly higher CS compared with the other cements at all time points investigated. The BHA 10% and 20% groups exhibited significantly longer setting times than BHA 30%, 40% and PC65. The addition of ZrO₂ in concentrations above 20% wt and Ta₂O₅ at 30% wt resulted in a radiopacity equal to, or exceeding that of, ProRoot MTA. The experimental cements exhibited relatively low cytotoxicity, solubility and an alkaline pH. Conclusions: The addition of 10% and 20% BHA to an experimental PC-based cement containing 35% ZrO₂ improved the material’s mechanical strength while enabling similar radiopacity and biocompatibility to ProRoot MTA. Although BHA is a cost-effective, biomimetic additive that can improve the properties of calcium silicate endodontic cements, further studies are now warranted to determine its clinical potential.

Silica-Based Bioactive Glasses and Their Applications in Hard Tissue Regeneration: A Review

Regenerative medicine is a field that aims to influence and improvise the processes of tissue repair and restoration and to assist the body to heal and recover. In the field of hard tissue regeneration, bio-inert materials are being predominantly used, and there is a necessity to use bioactive materials that can help in better tissue-implant interactions and facilitate the healing and regeneration process. One such bioactive material that is being focused upon and studied extensively in the past few decades is bioactive glass (BG). The original bioactive glass (45S5) is composed of silicon dioxide, sodium dioxide, calcium oxide, and phosphorus pentoxide and is mainly referred to by its commercial name Bioglass. BG is mainly used for bone tissue regeneration due to its osteoconductivity and osteostimulation properties. The bioactivity of BG, however, is highly dependent on the compositional ratio of certain glass-forming system content. The manipulation of content ratio and the element compositional flexibility of BG-forming network developed other types of bioactive glasses with controllable chemical durability and chemical affinity with bone and bioactivity. This review article mainly discusses the basic information about silica-based bioactive glasses, including their composition, processing, and properties, as well as their medical applications such as in bone regeneration, as bone grafts, and as dental implant coatings.

A Comparative Evaluation of Hydroxyapatite Crystals and Glutaraldehyde as Agents for Pulpotomy in Deciduous Molars

Purpose: To evaluate and compare clinically and radiographically use of hydroxyapatite crystals and 2% glutaraldehyde as a pulpotomy agent.

Method: Thirty deciduous molars were treated with pulpotomy using hydroxyapatite crystals and 2% glutaraldehyde.

Results: Clinical and radiographic findings were observed at three months and six months. The success rate was found to be 100% clinically and 80.33% radiographically in the hydroxyapatite crystals group and 100% clinically and radiographically in the glutaraldehyde group.

Clinical significance: The results of this study revealed that hydroxyapatite crystals is a potential pulpotomy agent for deciduous molars.

HRTEM study of biological crystal growth mechanisms in the vicinity of implanted synthetic hydroxyapatite crystals

Calcium phosphates are widely used as biomaterials. Ultrastructural assessments are of the utmost importance in our understanding of interfacial phenomena. The aim of this study was to learn more about the newly formed crystal growth mechanisms. The interfaces between implanted synthetic hydroxyapatite crystals (HAS) and newly formed crystallites were thoroughly examined on a molecular level. The bone-grafting material (HAS) was implanted into two adult patients, and small biopsies were recovered 6 months after implantation. The raw biomaterial was analyzed by x-ray diffraction and high-resolution transmission electron microscopy (HRTEM). Six months after their implantation, the HAS aggregates were surrounded by a mineralized bone matrix. Tiny crystallites also filled the spaces between the HAS crystals within the aggregates. These newly formed crystallites growing at the surfaces of the implanted HAS crystals appeared to be apatitic. The crystallographic investigations of the nucleation and growing mechanisms of the newly formed crystallites were performed by HRTEM in association with computer simulation and mathematical processing of digitized images. A relationship was noted between the orientation axes of crystallites growing nearby and the zone axes of the implanted HAS, thus strongly suggesting a guiding or substratum role of the HAS particles.

Adaptive crystal formation in normal and pathological calcifications in synthetic calcium phosphate and related biomaterials

Mineralization and crystal deposition are natural phenomena widely distributed in biological systems from protozoa to mammals. In mammals, normal and pathological calcifications are observed in bones, teeth, and soft tissues or cartilage. We review studies on the adaptive apatite crystal formation in enamel compared with those in other calcified tissues (e.g., dentin, bone, and fish enameloids) and in pathological calcifications, demonstrating the adaptation of these crystals (in terms of crystallinity and orientation) to specific tissues that vary in functions or vary in normal or diseased conditions. The roles of minor elements, such as carbonate, magnesium, fluoride, hydrogen phosphate, pyrophosphate, and strontium ions, on the formation and transformation of biologically relevant calcium phosphates are summarized. Another adaptative process of crystals in biology concerns the recent development of calcium phosphate ceramics and other related biomaterials for bone graft. Bone graft materials are available as alternatives to autogeneous bone for repair, substitution, or augmentation. This paper discusses the adaptive crystal formation in mineralized tissues induced by calcium phosphate and related bone graft biomaterials during bone repair.

Immunolocalization of fibronectin during reparative dentinogenesis in human teeth after pulp capping with calcium hydroxide

Exposed dental pulp is known to possess the ability to form a hard-tissue barrier (dentin bridge). The exact mechanisms by which pulp cells differentiate into odontoblasts in this process are unknown. Fibronectin has been demonstrated to play a crucial role in odontoblast differentiation during tooth development. This study tested the hypothesis that fibronectin is involved in the initial stages of replacement odontoblast differentiation and reparative dentin formation. We observed its immunohistochemical localization during dentin bridge formation in human teeth, after pulp was capped with calcium hydroxide [Ca(OH)2]. One day after the capping, precipitation of crystalline structures was observed at the TEM level in association with cell debris at the interface between the superficial necrotic zone and underlying pulp tissue. This layer of dystrophic calcification showed positive reaction for fibronectin, and pulp cells appeared to be closely associated with this layer, seven to ten days post-operatively. At 14 days, an alignment of cells, some of which were elongated and odontoblast-like, was observed adjacent to the fibronectin-positive irregular matrix. Between the cells, corkscrew fiber-like fluorescence was visible. At 28 days, the irregular fibrous matrix was followed by the formation of tubular dentin-like matrix lined with odontoblast-like cells. Therefore, it would seem that fibronectin associated with the initially formed calcified layer might play a mediating role in the differentiation of pulp cells into odontoblasts during reparative dentinogenesis, after pulp was capped with Ca(OH)2.

Response of odontoblast-like cells to hydroxyapatite ceramic granules

In this study the inductive influence of hydroxyapatite ceramic (HAC) granules on preodontoblast differentiation was investigated. Dental papilla cells harvested from upper molar tooth germs were implanted intramuscularly in a pouch created for this purpose. Six months after surgery tooth-root-like bodies had developed with pulp-like cavities in the specimens in which dental papilla cells had been implanted with and without HAC. These bodies consisted of regular tubular dentine in the central part, fibrodentine peripherally and sometimes osteodentine. HAC was haphazardly enclosed in these root-like bodies, whereas the implantation of HAC alone had no effect.

Comparative effect of calcium hydroxide and hydroxyapatite on the cellular activity of human pulp fibroblasts in vitro

When, in vivo, calcium hydroxide [Ca(OH)2] or hydroxyapatite are used as dental pulp-capping agents, a reparative dentine bridge is observed. New hard tissue is formed directly on the hydroxyapatite, whereas a characteristic necrotic area appears under Ca(OH)2. The differing pulpal reactions to these two capping agents suggest differing cell responses. After isolation and selection of human pulp fibroblasts in vitro, the cells were characterized by their morphology, their high alkaline phosphatase specific activity, and their synthesis of type I and III collagens and fibronectin. They were then incubated in the presence of either hydroxyapatite (1 mg/ml) or Ca(OH)2 (0.8 mg/ml). With Ca(OH)2, the cells exhibited dramatical alterations in morphology, DNA synthesis, alkaline phosphatase activity and protein synthesis, in accordance with the necrosis observed in vivo. With hydroxyapatite, phagocytic activity of pulpal fibroblasts toward hydroxyapatite particles (< 10 microns) was seen. As a consequence, DNA synthesis was affected. This inhibitory effect was not due to cell damage, as demonstrated by increased [3H]-proline and [3H]-leucine incorporation by the cells. There was also an inhibitory effect of hydroxyapatite on alkaline phosphatase activity, suggesting that the pulp fibroblasts were not in a differentiation stage. In conclusion, compared to the effects of Ca(OH)2 on human pulp fibroblasts, these data are consistent with the biocompatibility of hydroxyapatite previously described in vivo and testify to the occurrence of a biological response elicited by this synthetic biomaterial.

Histological observations of hard tissue barrier formation in amputated dental pulp capped with alpha-tricalcium phosphate containing calcium hydroxide

This study was performed to evaluate the pulpal response to alpha-tricalcium phosphate (alpha TCP) containing calcium hydroxide (Ca(OH)2). The dental pulps of monkeys were amputated and dressed with four agents: alpha TCP, alpha TCP containing 1% Ca(OH)2, alpha TCP containing 5% Ca(OH)2, and Ca(OH)2 being used as a control. The pulpal responses were histologically evaluated after 4 and 8 weeks. The pulp tissue treated with alpha TCP proliferated above the level of the original wound surface, and a thin layer of hard tissue barrier was formed directly against the capping agent. The barrier demonstrated atubular matrix lined with flattened or cuboidal cells, but occasionally appeared irregular in form. Ca(OH)2 dressing resulted in destruction of pulp tissue, with a thick hard tissue barrier being formed below the level of the exposure site. The barrier consisted coronally of osteodentin and pulpally of tubular dentin lined with odontoblast-like cells. By contrast, 1% Ca(OH)2 added to alpha TCP produced a slight proliferation of pulp tissue. An atubular matrix barrier, pulpally lined with cuboidal cells, formed above the exposure site. It was later followed by the formation of tubular matrix lined with columnar cells. Teeth treated with 5% Ca(OH)2 showed a thin necrotic layer and a thick barrier formation. The barrier was composed of tubular dentin-like tissue lined with odontoblast-like cells. It would appear that alpha TCP containing a small amount of Ca(OH)2 may be clinically useful as a capping agent, as it induced consistent hard tissue formation, without excessive destruction of underlying pulp tissue.

Apatite formation on three kinds of bioactive material at an early stage in vivo: a comparative study by transmission electron microscopy

Apatite formation on the surface of three kinds of bioactive material at an early stage after implantation in bone was studied using transmission electron microscopy (TEM). The materials were apatite- and wollastonite-containing glass-ceramic (A-W GC) as a surface-active glass-ceramic, dense sintered hydroxyapatite (HA) as a surface-active ceramic, and dense sintered beta-tricalcium phosphate (beta-TCP) as a resorbable ceramic. Particles of these materials, ranging from 100-300 microns in diameter, were implanted into rat tibiae, and specimens were prepared at 3, 7, 10, and 14 days after implantation. For A-W GC, dissolution of the glassy and probably wollastonite phase was observed in the surface region on and after the third day, and a collagen-free thin apatite layer on the surface of the material was evident on and after the seventh day. This apatite layer was observed before the mineralization of the surrounding bone matrix and was sometimes evident even where the material bordered on the bone marrow. On and after the tenth day, the surrounding bone matrix calcified and A-W GC-bone bonding through an apatite layer was completed. For HA, a mineralized collagen-free layer was observed on the surface of the ceramic on and after the tenth day. This layer was always present near calcifying bone and it was difficult to distinguish from immature bone. For beta-TCP, such a surface mineralized layer was rarely evident, even just before bone-ceramic contact, and finally the bone bonded to beta-TCP directly. Cell-mediated degradation of beta-TCP was frequently observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulp capping with Bioglass and autologous demineralized dentin in miniature swine

The purpose of this study was to compare the responses of mechanically exposed dental pulps which had been capped with three dissimilar materials: a bioactive ceramic (Bioglass), autologous demineralized dentin matrix (DDM), and a calcium hydroxide product (Life), with Teflon discs as controls. Mechanical dental pulp exposures were made after preparation of deep buccal Class V cavities in 48 teeth in four miniature swine. The exposures were capped and the cavity preparations restored with zinc oxide-eugenol (IRM) cement. The animals were killed after 90 days, the coronal 2/3 of the teeth removed, and sections prepared for either histological or microradiographic examination. The pulpal inflammatory reactions and the degree of reparative dentin formation were assessed from demineralized serial sections. A qualitative assessment of the degree of mineralization of the reparative dentin was made from microradiographs of undecalcified sections. The observations suggest that reparative dentin formation occurs under a variety of pulp-capping materials, but the structure of the reparative dentin varies with the material and the condition of the underlying pulp.