Franklin Garcia-Godoy

Sorption and solubility of resin-based restorative dental materials

OBJECTIVES To measure the water sorption and solubility of different resin-based restorative dental materials. METHODS Eight commercial restorative materials were selected: two resin composites (Z100 and Prodigy), four polyacid-modified resin composites (Compoglass, Compoglass F, Dyract and Dyract AP), and two light-cured glass ionomers (Vitremer and Fuji II LC). Five disc specimens were prepared of each material, following the manufacturers instructions, and were grounded wet with silicon carbide paper. Water sorption and solubility of the different materials were calculated by means of weighting the samples before and after water immersion and desiccation. Data were analyzed by one-way ANOVA and Student-Newman-Keuls tests (P<0.05). RESULTS Compoglass and Compoglass F showed the lowest values of water sorption and solubility, while Vitremer and Fuji II LC displayed the highest values. Solubility values of Prodigy, Z100, Dyract and Dyract AP did not show significant differences among them, while their water sorption values attained some differences and were lower for Prodigy followed by Dyract and Z100. CONCLUSIONS The attained water sorption and solubility values are mainly influenced by the generic type of material and variations occurring between materials of the same type may result from differences in resin matrix compositions.

Plasticity of stem cells derived from adult periodontal ligament

BACKGROUND The neural crest contains pluripotent cells that can give rise to neurons and glial cells of the peripheral nervous system, endocrine cells, connective tissue cells, muscle cells and pigment cells during embryonic development. Stem cells derived from the neural crest may still reside in neural crest derivatives including the periodontal ligament (PDL). However, the pluripotency of PDL-derived stem cells has not been investigated. AIM To identify subpopulations of stem cells from the adult PDL and study their pluripotency. Human PDLs were harvested from impacted wisdom teeth (patients aged 19-22 years). RESULTS This study demonstrated that subpopulations of PDL cells expressed embryonic stem cell markers (Oct4, Sox2, Nanog and Klf4) and a subset of neural crest markers (Nestin, Slug, p75 and Sox10). Such PDL cell subpopulations exhibited the potential to differentiate into neurogenic, cardiomyogenic, chondrogenic and osteogenic lineages. Furthermore, preliminary evidence suggesting insulin production of PDL cells might be indicative of the generation of cells of the endodermal lineage. CONCLUSION These findings suggest that the PDL may contain pluripotent stem cells that originate from the neural crest. Our observations open the door to prospective autologous therapeutic applications for a variety of conditions.

In vitro cytotoxicity of five glass-ionomer cements.

To evaluate the cytotoxic effects of five glass-ionomer cements (GICs) on an odontoblast cell line (MDPC-23), disks of every material were prepared and divided into Group 1: Vitrebond, Group 2: Vitremer, Group 3: Fuji II LC, Group 4: Fuji IX GP, Group 5: Ketac-Molar, Group 6: Z-100 (positive control). In Group 7, phosphate-buffered saline solution (negative control) was applied on filter paper. After placing the samples in the bottom of wells, the cells (30,000cells/cm(2)) were plated and incubated for 72h. The cell number was counted, the cell morphology was assessed by scanning electron microscopy and the cell metabolism was evaluated using methyltetrazolium assay. The statistical analysis of Kruskal-Wallis was used to determine if the scores obtained for the cell metabolism and number of cells were different at the 95% confidence level. In groups 1, 2, 3, 4, 5, and 6 the materials decreased the cell number by 74.5%, 75.5%, 45.5%, 29.5%, 32.5%, and 88.5%, respectively. In groups 1, 2, 3, 4, and 5, the experimental GICs reduced the cell metabolism by 79%, 84%, 54%, 40%, and 42.5%, respectively. Despite the fact that all experimental materials were cytotoxic to the MDPC-23 cells, the GICs were the least cytotoxic. On the other hand, the RMGICs caused the highest cytophatic effects.

The Comparison of the Effect of Endodontic Irrigation on Cell Adherence to Root Canal Dentin

The purpose of this study was to compare the effect of 10 different endodontic irrigation and chelating treatments on dental pulp stem cell (DPSC) attachment to root canal surfaces. Thirty-eight extracted human nondiseased single-canal teeth were cleaned and shaped using ProTaper and ProFile rotary instrumentation (Tulsa Dentsply, Tulsa, OK). The irrigation treatments investigated were 6% sodium hypochlorite, 2% chlorhexidine gluconate, Aquatine Endodontic Cleanser, and Morinda citrifolia juice. The irrigation treatments were used in conjunction with EDTA or MTAD. The instrumented teeth were immediately placed in cell culture with confluent DPSCs for 1 week. The number of attached DPSCs appeared to be correlated with the cytotoxicity of the root canal irrigating solution (analysis of variance, p < 0.0001). The presence or absence of the smear layer had little influence on DPSC activity (chi-square, p > 0.05). The results suggest that biocompatible irrigants are needed to promote DPSC attachment to root canal dentin, which is essential to accomplish some regenerative endodontic therapies.

Antagonist Enamel Wears More Than Ceramic Inlays

Wear phenomena of ceramic inlays are not fully understood. The aim of the present study was to evaluate ceramic wear, antagonist enamel wear, and luting cement wear over 8 years. The two-fold null hypothesis was that there would be (1) no difference in wear behavior between ceramic and enamel, and (2) no influence of filler content of luting composites on composite wear. From 96 restorations, 36 Class II inlays from 16 participants were selected. For inlays with opposing enamel cusps (n = 17), replicas of inlays and enamel were scanned with a 3-D laser scanner. Luting gaps of inlays (n = 36) were analyzed with a profilometer, including 3-D data analysis. Ceramic and enamel wear increased between 4 and 8 years, with significantly higher values for enamel after 6 years (p < 0.05). Luting gap wear increased continuously up to 8 years (p < 0.05), with no influence of luting composites (p > 0.05) and location of teeth (p > 0.05).

Bracket bonding with 15- or 60-second etching and adhesive remaining on enamel after debonding.

The purposes of this study were to (1) evaluate the shear bond strength of brackets fixed to enamel that has been etched for 15 or 60 seconds, (2) correlate etch time with amount of resin remaining on the enamel after debonding; and (3) evaluate enamel morphology after acid etching. Sixty recently extracted human premolars were randomly divided into two groups. Group 1 was etched for 15 seconds, and group 2 for 60 seconds. A 37% phosphoric acid solution was used for etching. The brackets were Mini-Taurus, and the bonding system was Mono-Lok2. After bonding, the teeth were held at 37 degrees C and 100% humidity for at least 48 hours. To debond, a blade was placed at the ligature groove of the bracket. The force in Newtons required to dislodge the bracket was measured, employing a crosshead speed of 1 mm/min. Bond strength was calculated on the basis of bracket area. Immediately after removal of the bracket, the teeth were rinsed and dried using an air-water syringe, and the adhesive remnant index (ARI) was assessed. Enamel surfaces were analyzed using a scanning electron microscope (SEM). The results showed that shear bond strength was greater (p=0.016) when the enamel was etched for 60 seconds, and the amount of adhesive remaining on the teeth was also greater (p=0.001). There was no significant correlation between shear bond strength and the ARI calculated in the total sample (n=60, r=0.017; p>0.05). SEM evaluation revealed that the shorter etching time created a less retentive enamel surface. Absolute enamel loss also decreased.

Cell Survival within Pulp and Periodontal Constructs

The purpose of this study was to measure cell survival and degradation within tissue-engineered dental constructs. Dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PLSCs) were seeded on three types of tissue engineering scaffolds: a synthetic open-cell D,D-L,L-polylactic acid (polymer) scaffold, a bovine collagen scaffold (collagen), and a calcium phosphate bioceramic (calcium phosphate) scaffold. The dental pulp and periodontal constructs (n = 144) were maintained in cell culture for between 3 and 14 days. The cell survival and degradation within the constructs were measured using histologic criteria. The DPSC and PLSC survival was optimal in the polymer and collagen constructs but not the calcium phosphate constructs, especially over longer time periods. These in vitro results suggest that both the polymer and collagen scaffolds and the DPSCs and PLSCs can be combined to create pulp and periodontal constructs for use in future regenerative dental treatments.

Stem cell responses in tooth regeneration

Scientific advances in the creation of restorative biomaterials, in vitro cell culture technology, tissue grafting, tissue engineering, molecular biology, and the human genome project provide the basis for the introduction of new technologies into dentistry. This review is intended to facilitate the development of stem cell therapy for use with established therapeutic modalities to restore and regenerate oral tissues. Teeth have been shown to mineralize in response to injury for many decades, but only in recent years has the position of the stem cells been localized around blood vessels. The cells have been identified as myofibroblastoid pericytes. The ability to control the differentiation and proliferation of these cells is being examined to create stem cell therapies that can solve dental problems more effectively than current treatment regimes. Although the problems of introducing these technologies are substantial, the potential benefits to patients and the profession are equally promising - a cure for caries and diseases, a cure for oral cancer, correction of congenital defects, and the regeneration of teeth and tissues to restore oral functions. The purpose of this review is to describe how these new technologies can most usefully be employed in dentistry to enable clinicians to satisfy patient demand for a nondefective dentition.

Nonlinear visco-elastic finite element analysis of different porcelain veneers configuration.

This study is aimed at evaluating the biomechanical behavior of feldspathic versus alumina porcelain veneers. A 3D numerical model of a maxillary central incisor, with the periodontal ligament (PDL) and the alveolar bone was generated. Such model was made up of four main volumes: dentin, enamel, cement layer and veneer. Incisors restored with alumina and feldspathic porcelain veneers were compared with a natural sound tooth (control). Enamel, cementum, cancellous and cortical bone were considered as isotropic elastic materials; on the contrary, the tubular structure of dentin was designed as elastic orthotropic. The nonlinear visco-elatic behavior of the PDL was considered. The veneer volumes were coupled with alumina and feldspathic porcelain mechanical properties. The adhesive layers were modeled in the FE environment using spring elements. A 50N load applied at 60 degrees angle with tooth longitudinal axis was applied and validated. Compressive stresses were concentrated on the external surface of the buccal side of the veneer close to the incisal margin; such phenomenon was more evident in the presence of alumina. Tensile stresses were negligible when compared to compressive ones. Alumina and feldspathic ceramic were characterized by a different biomechanical behavior in terms of elastic deformations and stress distributions. The ultimate strength of both materials was not overcome in the performed analysis.

Effect of pH on compressive strength of some modification of mineral trioxide aggregate

Objectives: Recently, it was shown that NanoMTA improved the setting time and promoted a better hydration process which prevents washout and the dislodgment of this novel biomaterial in comparison with WTMA. This study analyzed the compressive strength of ProRoot WMTA (Dentsply), a NanoWMTA (Kamal Asgar Research Center), and Bioaggregate (Innovative Bioceramix) after its exposure to a range of environmental pH conditions during hydration. Study Design: After mixing the cements under aseptic condition and based on the manufacturers` recommendations, the cements were condensed with moderate force using plugger into 9 × 6 mm split molds. Each type of cement was then randomly divided into three groups (n=10). Specimens were exposed to environments with pH values of 4.4, 7.4, or 10.4 for 3 days. Cement pellets were compressed by using an Instron testing machine. Values were recorded and compared. Data were analyzed by using one-way analysis of variance and a post hoc Tukey’s test. Results: After 3 days, the samples were solid when probed with an explorer before removing them from the molds. The greatest mean compressive strength 133.19±11.14 MPa was observed after exposure to a pH value of 10.4 for NanoWMTA. The values decreased to 111.41±8.26 MPa after exposure to a pH value of 4.4. Increasing of pH had a significant effect on the compressive strength of the groups (p<0.001). The mean compressive strength for the NanoWMTA was statistically higher than for ProRoot WMTA and Bioaggregate (p<0.001). Moreover, increasing of pH values had a significant effect on compressive strength of the experimental groups (p<0.001). Conclusion: The compressive strength of NanoWMTA was significantly higher than WMTA and Bioaggregate; the more acidic the environmental pH, the lower was the compressive strength. Key words:Compressive strength, mineral trioxide aggregate, Nano.