Effect of dual cure composite as dentin substitute on the marginal integrity of Class II open-sandwich restorations.

This study compared the marginal adaptation of Class II open-sandwich restorations with an RMGIC versus a dual-cure composite as dentin substitute. Class II cavities were prepared on 50 extracted human third molars. The teeth were randomly assigned to two groups of 25 teeth to compare one dual cure composite (Multicore Flow) with one resin-modified glass-ionomer cement (Fuji II LC) in open-sandwich restorations covered with a light cure composite. The teeth were thermomechanically cycled (2000 cycles, 5 degrees C to 55 degrees C; 100,000 cycles, 50 N/cm2). The specimens were then sealed with a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for two hours and exposed to a photodeveloping solution for six hours. The specimens were sectioned longitudinally and silver penetration was directly measured using a light microscope. The results were expressed as a score ranging from 0 to 3. The data were analyzed with a non-parametric Kruskall and Wallis test. The degree of leakage significantly increased with Multicore Flow (median = 2) compared to Fuji II LC (median = 1). The resin-modified glassionomer cements remain the best intermediate materials when open-sandwich restorations are indicated. A comparison of the degradation of these materials over time remains a topic to be investigated by future studies.

Effect of dual cure composite as dentin substitute on marginal integrity of class II open-sandwich restorations.

The current study compared the marginal adaptation of Class II open-sandwich restorations with a RMGIC versus a dual-cure composite as dentin substitute. Class II cavities were prepared on 50 extracted human third molars. The teeth were randomly assigned to two groups of 25 teeth to compare one dual cure composite (MultiCore Flow) with one resin-modified glass-ionomer cement (Fuji II LC) in open-sandwich restorations recovered with a light cure composite. The teeth were thermomechanocycled (2000 cycles, 5 degrees C to 55 degrees C; 100,000 cycles, 50 N/cm2). The specimens were then sealed with a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for two hours and exposed to a photo-developing solution for six hours. The specimens were sectioned longitudinally and silver penetration was directly measured using a light microscope. The results were expressed as a score from 0 to 3. The data were analyzed with a non-parametric Kruskal and Wallis test. The degree of leakage significantly increased with MultiCore Flow (median 2) compared to Fuji II LC (median 1). Resin-modified glassionomer cements remain the best intermediate material when open-sandwich restorations are indicated. A comparison of the degradation of these materials over time remains a topic to be investigated by future studies.

Human biological reactions at the interface between bone tissue and polymethylmethacrylate cement.

This study investigated cytotoxicity of cement fragments harvested from two prosthesis revisions by the MTT test using L929 fibroblasts and human osteoblasts. The results did not show any toxicity of the extracts prepared after 48 and 78 months implantation. We consider that no MMA monomer has been released from the cement fragments. Histological studies on undecalcified samples harvested around revising prosthesis from 11 patients were used to evaluate tissue reactions at the bone-cement interface after 2-168 months implantation. Cement and prosthesis particles (5-35 microm) either dispersed or forming a layer were observed. A fibrous tissue layer, osteolysis, and osteonecrosis areas were observed at the interface. Besides, fibroblasts, macrophages, and multinucleated giant cells were also observed. New bone formation with osteoid, osteoblasts, and endochondral ossification with fibrocartilaginous tissue has been observed. The tissue reactions seemed to decrease with time. However, osseous trabeculae fractures were observed in the samples after 19 months. Although we consider that monomer toxicity, exothermic reaction, and particles formation may cause short-term prosthesis loosening; the trabeculae fractures may be due to prosthesis and bone cement micromovements. This fractures and particles formation may cause long-term prosthesis loosening.

Histological and biomechanical studies of two bone colonizable cements in rabbits.

We have developed two colonizable bone cements: the first is a partially resorbable bisphenol-alpha-glycidyl methacrylate (Bis-GMA)-based cement (PRC) and the second is a calcium phosphate cement (CPC). PRC is composed of aluminous silanized ceramic and particles of a bioresorbable polymer embedded in a matrix of Bis-GMA. CPC consisted of tricalcium phosphate, monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, and xanthane. Both cements were implanted into cavities drilled in rabbit femoral and tibial condyles. After 2, 4, 12, and 24 weeks of implantation, histological observations and biomechanical tests were performed. With CPC, a progressive osteointegration with a concomitant biodegradation in the presence of macrophages were observed. The mechanical study revealed a decrease of the compressive strength until the 4th week, followed by a slight increase. There was a general decrease in the elastic modulus with time. Moreover, by week 4, the histological study showed that the new bone was in direct contact with CPC margins. No inflammation was observed during the observation period. With PRC, the osteointegration as well as the biodegradation were slight, but its compressive strength was higher than that of cancellous bone and CPC (p < 0.05) at all observation periods. Its elastic modulus was greater than that of cancellous bone and CPC until the 4th week, then fell under the values of the cancellous bone.

Comparison of two implantation sites for testing intraosseous biocompatibility.

The purpose of this study was to compare two implantation sites--the mandible and the femur of the rabbit--for testing in vivo intraosseous biocompatility. Twenty-two new Zealand rabbits were anesthetized, and the mandibular and femur bones were exposed. A hybrid glass ionomer cement or zinc oxide eugenol cement was loaded into silicone carriers and inserted into the two bones after drilling the two cortical plates. Eleven rabbits were killed 4 wk after implantation, and 11 rabbits were killed after 12 wk. The mandibles and femurs were prepared using standard histological procedures; tissue reactions were graded from none to severe. At 4 wk, no statistically significant difference was found between the two implantation sites. After 12 weeks, bone healing was statistically better in the mandible than in the femur. The mandible seems to be a better implantation site in the case of intraosseous implantation tests. The intraosseous biocompatibility of Vitremer was similar at 4 wk and superior at 12 wk to that of Super-EBA.

Expression of the transcription factors Otlx2, Barx1 and Sox9 during mouse odontogenesis.

The molecular mechanisms governing the decision between molariform and incisiform patterns of rodent dentition are not yet known. Transcription factors are regulators of regionally specific morphogenesis and key co-ordinators of gene activity during developmental processes. Here, we analysed the expression of several transcription factors during mouse tooth development. Otlx2/Rieg is a homeobox gene involved in Rieger syndrome, a human disorder characterized by dental hypoplasia. Otlx2/Rieg expression distinguishes stomatodeal epithelium well before tooth initiation, and thereafter its expression becomes restricted to the epithelia of both molar and incisor primordia. The recently identified homeodomain transcription factor Barx1 is first expressed in mesenchyme of the first branchial arch, but during advanced developmental stages the gene is exclusively expressed in the mesenchyme of molar primordia. Finally, the Sry-related transcription factor Sox9 is expressed in epithelial components and to a lesser degree in condensed mesenchyme of the developing teeth. These results suggest that Otlx2/Rieg, Barx1, and Sox9 participate in the hierarchical cascade of factors involved in the regulation of tooth morphogenesis.

Mouse Otlx2/RIEG expression in the odontogenic epithelium precedes tooth initiation and requires mesenchyme-derived signals for its maintenance.

The mouse Otlx2 gene is a new member of the paired-like family of homeobox genes whose human homologue, RIEG, is involved in Rieger syndrome, an autosomal-dominant disorder. One of the cardinal features of Rieger syndrome is dental hypoplasia, indicating that Otlx2/RIEG activity is essential for normal tooth development. Here, we analyzed the expression of Otlx2 during mouse tooth development and studied its regulation in dental explants. Otlx2 expression distinguishes stomatodeal from other ectoderm as early as Embryonic Day 8.5, well before tooth initiation. Thereafter, its craniofacial expression becomes restricted to the tooth-forming areas and to the epithelial components of molar and incisor primordia. Although Otlx2 induction precedes the specification of odontogenic mesenchyme, tissue recombination experiments show that the maintenance of its expression requires signals from the mesenchyme and that dental mesenchyme has the capacity to induce ectopic expression of Otlx2 in nondental epithelium. Finally, we compare Otlx2 expression with that of the recently identified homeodomain transcription factor Barx1 expressed in molar mesenchyme. Their strictly complementary expression patterns in the epithelial and mesenchymal components suggest that both genes participate in the reciprocal tissue interactions which are a hallmark of odontogenesis.

Comparison of the intraosseous biocompatibility of Dyract and Super EBA.

The purpose of this study was to compare the intraosseous biocompatibility of Dyract, a new hydrophilic glass-ionomer cement, to that of Super EBA. Twenty-four New Zealand rabbits were anesthetized, one leg was shaved, the femur exposed, and two holes were drilled through the cortical plate. The materials were loaded into silicone carriers and inserted into the femur. Half of the rabbits were killed 4 weeks after implantation and the other half at 12 weeks and the femurs were prepared using standard histological procedures. The tissue reactions were graded from none to severe. At 4 weeks both materials showed slight to moderate reactions, characterized by the presence of fibrous tissue interposition and inflammatory cells. At 12 weeks, bone healing had occurred, despite the persistence of some fibrous tissue interposition, and the reactions were classified as slight. At both observation periods, statistical analysis failed to show any difference between the two materials indicating that Dyract and Super EBA had similar intraosseous biocompatibility.

Model for quantitative immunohistochemical assessment of pulpal response to biomaterials.

The purpose of this study was to propose a new method for quantitative evaluation of the pulpal inflammation to restorative materials using immunohistochemistry and image analysis. Class V cavities were prepared and filled with different restorative materials in 20 healthy premolars to be extracted for orthodontic reasons. Teeth were extracted at different time intervals, fixed, demineralized, and embedded in paraffin. Six-micrometer-thick sections were cut serially and mounted on slides and every fifth section was stained using hematoxylin and eosin or Masson's trichrome, and served to localize the inflammatory reaction. The slides corresponding to the bulk of the inflammatory reaction were then used for immunohistochemical detection of the inflammatory cells using monoclonal antibodies: CD15 (granulocytes and histiocytes), CD45RO (T lymphocytes and monocytes), Pan-B cell (B lymphocytes, macrophages, and a subpopulation of T lymphocytes), CD45RA (B lymphocytes and monocytes), and EMA (plasma cells). The slides were observed and submitted to computerized image analysis using a SAMBA 2000 system for counting of the cells. The CD15, CD45RO, Pan-B-cell, and CD45RA antibodies positively stained the target cells, which could be counted with the computer. The EMA antibody did not permit staining of cells. These results indicate that polymorphonuclears, T lymphocytes, and B lymphocytes are present in inflamed human dental pulp. The immunologic detection of inflammatory cells followed by computerized image analysis allows an accurate characterization of pulpal pathology, and could be useful for the study of pulp reactions to restorative biomaterials.

In vivo comparison of the biocompatibility of two root canal sealers implanted into the mandibular bone of rabbits.

The purpose of this study was to evaluate the in vivo biocompatibility of two zinc oxide-eugenol-based sealers, Sealite and Pulp Canal Sealer, after implantation into the mandibular bone of rabbits. Thirty female New-Zealand rabbits were randomly divided into three groups on the basis of the material to be implanted in each side of the mandible: six rabbits received a positive control implant (silicone tubes filled with asbestos) in both sides of the mandible; 12 rabbits received a Sealite implant in the left side and a negative control implant (silicone tubes filled with silicone adhesive) in the right side of the mandible; and 12 rabbits received a silicone tube filled with Pulp Canal Sealer in the left side and a negative control implant in the right side of the mandible. The sealers were implanted in a freshly mixed, unset state. The rabbits were killed 4 or 12 weeks after implantation and the implants and surrounding bone were sectioned and treated in accord with standard histologic procedures. The tissue reactions were scored and rated as none, very slight, slight, moderate, severe, and very severe. The statistical analysis of the data showed that the two sealers had similar, good biocompatibility, and that the reactions observed at the 12-week period were better than those observed at the 4-week period. Both sealers may be used indifferently in routine endodontic practice.

Ex vivo evaluation of side-perforated needles by injection of anesthetic solutions into the mandibular bone and the periodontal ligament of pigs.

New 27-gauge side-perforated needles were compared with conventional needles during injection in dense tissues on the basis of (a) the force to be applied on the syringe plunger and (b) the frequency of complete needle clogging. A miniaturized force transducer was used to measure the forces applied to the syringe plunger. One hundred intraosseous injections and one hundred intraligamentary injections were performed in fresh pig mandibles, using both types of needles. Results showed that (a) less force was required when performing injections with the side-perforated needles and (b) side-perforated needles got clogged less frequently than conventional ones. This result is of special interest for routine dental practice.

[Physico-chemical properties of 4 endodontic sealing cements]. / Etude des propriétés physico-chimiques de quatre ciments de scellement endodontique.

Four endodontic sealers were compared with two series of tests, in thin layer and in 10 mm long and 5 mm diameter rods. Under these conditions, the Pulp Canal Sealer showed the best ability to present a thin layer and the same flow than the Cortisomol. Its setting time was 15 minutes. Forty-eight hours later, the Sealite showed a very good tightness compared to the other sealers. At 30 days, the Pulp Canal Sealer and the OZn-Eugénol were the tightest ones. Less water was absorbed with the Cortisomal and the Sealite. Is there, for these sealers, any correlation between water-absorbtion and tightness?

[Dye penetration of 3 temporary ready-to-use cements]. / Pénétration d'un colorant au niveau de trois ciments temporaires prêts à l'emploi.

Dye penetration following obturation of standardized access cavities with three different ready to use temporary cements was compared (Cavit G, Dentorit and Ciprospad). Leakage and dye penetration of the materials were simultaneously evaluated. Ciprospad appears to be the most adapted material.

[Biomechanical behavior of the pulpectomized tooth]. / Comportement biomécanique de la dent dépulpée.

No accurate information is in fact available regarding the biomechanical properties of devitalized teeth. The time frame seems to be a more significant factor than nature of the pulpectomy itself, as far as the risk of fracture is concerned. The use of a pivot or other form of root anchorage does not seem to play a determining role in the long-term reliability of restorations. Partial restorations can be substituted for full coronoperipheral reconstruction insofar as they protect the cusps. Each clinical situation must be matched with the appropriate reconstruction.

Injection pressure of anesthetics using 30-gauge needles with or without side perforation.

A testing bench was designed and constructed to simulate resistance by living tissues to the injection of dental anesthetics. A full series of pressure measurements were made on that bench using 30-gauge dental needles: (a) without side perforation; (b) with side perforation; and (c) with side perforation, the axial perforation being clogged at the tip of the needle. The results obtained in this physical model suggest that (a) the injection pressure at the tip of the needles is essentially the same whether there exists a side perforation on the needle wall or not and (b) when the axial perforation is clogged, the anesthetic solution can flow into the tissues through the side perforation under approximately the same pressure as that measured with unclogged needles. The latter result may be of special interest for intraosseous and intraligamentary (periodontal ligament) injections.