RESUMEN
An important consideration in improving the longevity of dental resin composite restorations is how to minimize the stresses that develop between resin composites and the wall of the preparation as the resin shrinks during polymerization. If the stress is too great, failure of the bonded interface occurs and microleakage results, with possible margin failure, staining, and secondary caries. This present project was performed to validate a previously developed FEM approach for investigating polymerization shrinkage. Light-cured resin composite was condensed into a cylindrical cavity preparation, which contained a centrally located wire. A profilometer stylus was positioned on the end of the wire to detect the initial surface displacement as the wire moved with the superficial layer of composite resin. The plots of the experimentally derived data were compared to the data plot from the FEM. The initial segments of the experimental plots matched the calculated plot very closely in shape, thus validating the FEM approach.
Asunto(s)
Materiales Dentales/química , Resinas de Plantas/química , Luz , Ensayo de Materiales/instrumentación , Ensayo de Materiales/métodos , Polímeros , Reproducibilidad de los Resultados , Estrés MecánicoRESUMEN
PURPOSE: To compare the microleakage and bond strength exhibited by two light-cured, filled dentin bonding agents, a resin cement, and cavity varnish. MATERIALS AND METHODS: The four test groups of lining agents for amalgam restorations included (LF) Light-cured, Filled resin (Clearfil Liner Bond 2); (LCF) light- and chemical-cured, Filled resin (Clearfil Liner Bond + Protect Liner); (RC) Resin Cement (Panavia 21); and (V) Varnish (Copalite). For each group, 20 Class V cavity preparations were cut in human extracted molars. Tytin amalgam was condensed into the preparation. After storage for at least 24 hrs in distilled water at 37 degrees C, all restorations were subjected to 2500 thermal cycles (8 degrees C to 48 degrees C). After 1 wk, specimens were tested. For the leakage tests, teeth were immersed in 45Ca, sectioned, and radiographs of sections were evaluated and then evaluated by Ridit analysis. Retention samples were tested to failure in tension using an Instron machine and peak load (kg) was recorded. RESULTS: Compared to varnish, the two dentin bonding agents (LF and LCF) significantly decreased microleakage at the cementum margin but not at the enamel margin. The two dentin bonding agents also exhibited significantly greater retentive strength than either the resin cement or the varnish.
Asunto(s)
Amalgama Dental/química , Recubrimiento Dental Adhesivo , Filtración Dental/clasificación , Restauración Dental Permanente , Radioisótopos de Calcio , Aleaciones Dentales/química , Recubrimiento de la Cavidad Dental , Preparación de la Cavidad Dental/clasificación , Cemento Dental/ultraestructura , Esmalte Dental/ultraestructura , Materiales Dentales/química , Restauración Dental Permanente/clasificación , Restauración Dental Permanente/métodos , Análisis del Estrés Dental/instrumentación , Recubrimientos Dentinarios/química , Humanos , Procesamiento de Imagen Asistido por Computador , Metacrilatos/química , Microscopía Confocal , Diente Molar , Fosfatos/química , Radiofármacos , Cementos de Resina/química , Resinas de Plantas , Estrés Mecánico , Temperatura , Termodinámica , Factores de TiempoRESUMEN
Dentin bonding agents have been shown to enhance retention of amalgam restorations by mechanical means. Little research is available on which mode of curing may optimize amalgam bonding. This in vitro study compared the bond strengths exhibited by three variations of a bonding agent, each using a different curing mode, with two earlier versions of amalgam resin liners and cavity varnish. The six test groups of lining agents for amalgam restorations included [C] chemical-cured, [L] light-cured and [D] dual-cured versions of one filled adhesive resin (Clearfil Liner Bond 2V), [LF] Light-cured, Filled resin (Clearfil Liner Bond 2, Kuraray Co.); [LCF] Light- and Chemical-cured, Filled resin Clearfil Liner Bond + Protect Liner, Kuraray Co) and [V] Varnish (Copalite, Cooley & Cooley, Ltd). For each group, 20 Class V cavity preparations were cut in human molars. The preparations were 2.5 mm deep and 3 mm wide at the pulpal floor, with a slightly divergent taper. After treating the preparation with the bonding agent, a 3/4 inch, 18 gauge flat-headed wire nail was seated in the cavity with its head at the pulpal floor of the preparation, and Tytin amalgam (Kerr Corp, Romulus, MI) was condensed into the preparation around the nail. All restorations were stored for 24 hours in distilled water at 37 degrees C, then subjected to 2500 thermal cycles (8 degrees C to 58 degrees C). After one week the samples were tested to failure in tension using an Instron Universal Testing Machine (crosshead speed = 2 mm/min) and peak load (kg) was recorded. Significant differences in retention were found using ANOVA and the Games & Howell post hoc test (p = 0.05). The mean loads at failure (+/- SD) were C 13.1 (+/- 2.4), L 21.8 (+/- 6.1), D 26.8 (+/- 7.4), LCF 23.8 (+/- 7.4), LF 21.4 (+/- 3.3) and V 2.0 (+/- 1.8). All dentin-bonding agents exhibited significantly greater retention than the varnish. While the bond strengths of the dual cured (D) and the light-cured (L) liners were not significantly different from one another, both were significantly higher than the chemically-cured (C) resin liner in terms of retention.
Asunto(s)
Amalgama Dental/química , Recubrimiento Dental Adhesivo , Recubrimientos Dentinarios/química , Análisis de Varianza , Fenómenos Químicos , Química Física , Aleaciones Dentales/química , Recubrimiento de la Cavidad Dental , Preparación de la Cavidad Dental/clasificación , Materiales Dentales/química , Análisis del Estrés Dental/instrumentación , Humanos , Luz , Funciones de Verosimilitud , Ensayo de Materiales , Metacrilatos/química , Microscopía Confocal , Diente Molar , Pintura , Cementos de Resina/química , Resinas de Plantas , Estrés Mecánico , Propiedades de Superficie , Termodinámica , AguaRESUMEN
STATEMENT OF PROBLEM: Setting time of gypsum depends on the method of measurement. PURPOSE: In this study, four methods for ascertaining the setting time of gypsum were compared. MATERIAL AND METHODS: Gypsum setting was evaluated with Gillmore needles, setting expansion, scanning electron microscopy, and x-ray diffraction. Both die stone (Vel-Mix) and fast-setting dental stone (Snap-Stone) were investigated. By using Gillmore needles, both initial set and final set were recorded. Setting expansion was monitored until equilibrium was achieved. For scanning electron microscopy, samples of mixed stone were immersed into liquid nitrogen to stop the reaction. The water was subsequently removed by freeze-drying. Samples were then examined in a scanning electron microscope. For x-ray diffraction, the percentages of dihydrate and hemihydrate crystals were monitored every 1.5 minutes. RESULTS: Setting times for the fast-setting type III stone and for the regular-setting type IV stone were approximately 3 and 10 minutes, respectively, with the Gillmore needle indentation tests; 10 and 20 minutes with scanning electron microscopy; and 20 and 60 minutes with x-ray diffraction. CONCLUSION: Scanning electron microscopy, setting expansion, and x-ray diffraction indicated changes that occurred at times after a clinically relevant set was obtained in the gypsum setting reaction.
Asunto(s)
Sulfato de Calcio/química , Cristalización , Cristalografía por Rayos X , Pruebas de Dureza , Cinética , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Tecnología Odontológica/métodos , Agua/químicaRESUMEN
Previous studies on amalgam bonded restorations indicated that amalgam bonding agents increased the bond strength of amalgam to tooth structure. This in vitro study was designed to compare how the mode of curing and the presence of filler in the resin would affect the bond strength of amalgam. The five test groups of lining agents for amalgam restorations included Chemical-cured, Unfilled resin (CU-Clearfil New Bond); Light-cured, Unfilled resin with a delayed chemical-cure property (LU*-Clearfil Photo Bond); Light-cured, Filled resin with a delayed chemical-cure property (LF*-Clearfil Photo Bond + Protect Liner); Dual-cured, Unfilled resin (DU-All-Bond 2); and Varnish (V-Copalite). For each group, 20 class 5 cavity preparations were cut on the facial, lingual, or proximal surfaces of human molars, which were embedded in acrylic resin. The preparations were 2.5 mm deep and 3 mm wide at the pulpal floor with a slightly divergent taper. After treating the preparation with the bonding agent, a 3/4-inch, 18-gauge flat-headed wire nail was placed into the cavity with the head at the pulpal floor of the preparation, and Tytin amalgam was then condensed into the preparation around the nail. The restorations were stored for 24 hours in distilled water at 37 degrees C and then subjected to 2500 thermal cycles (8 degrees C to 48 degrees C). After 1 week, specimens were tested to failure in tension using an Instron Universal Testing Machine (crosshead speed = 2 mm/min) and peak load (kg) was recorded. The mean loads at failure (+/- SD) were LF* 26.4 (+/- 7.0), DU 23.9 (+/- 6.4), LU* 16.0 (+/- 3.1), CU 14.3 (+/- 8.0), and V 9.5 (+/- 5.6). Significant differences were found using a one-way ANOVA and the Games and Howell post hoc test at a significance level of alpha = 0.05. The LF* and DU groups were not significantly different from each other, but they were significantly higher in peak load than all other groups. LU* was significantly higher than the varnish (V) but not significantly higher than CU. CU was not significantly higher than the varnish (V). The adhesives forming a thicker resin interface (the light-cured resin with filled resin liner and the dual-cured unfilled resin) demonstrated significantly greater retention than the light-cured unfilled resin, chemical-cured unfilled resin, and the varnish control.
Asunto(s)
Amalgama Dental , Recubrimiento Dental Adhesivo/métodos , Recubrimiento de la Cavidad Dental , Recubrimientos Dentinarios , Adhesividad , Análisis de Varianza , Resinas Compuestas , Aleaciones Dentales , Materiales Dentales , Fracaso de la Restauración Dental , Ensayo de Materiales , Metacrilatos , Microscopía Electrónica de Rastreo , Cementos de Resina , Resinas de Plantas , Análisis de SupervivenciaRESUMEN
The authors compared the retention and clinical performance of a resin-modified glass ionomer, or RMGI, restorative and a light-cured resin sealant. The first permanent molars on one side of the dental arch in 50 children were sealed with an RMGI, and the same teeth on the other side were sealed with a resin sealant. At baseline, six months after placement and one year after placement, examiners documented sealant retention, secondary caries, marginal discrepancy and marginal staining. In general, the RMGI appeared to wear markedly. At one year, the retention of the RMGI was significantly less than the resin, but the RMGI had significantly fewer marginal discrepancies. There were no significant differences in caries development or marginal discoloration.
Asunto(s)
Cementos de Ionómero Vítreo , Selladores de Fosas y Fisuras , Cementos de Resina , Bisfenol A Glicidil Metacrilato , Niño , Alisadura de la Restauración Dental , Estudios de Seguimiento , HumanosRESUMEN
Linear (two-dimensional) and three-dimensional (3D) plating systems (Poly-Medics) composed of the resorbable copolymer of polyglycolic acid (PGA) and poly-l-lactic acid (PLLA) (Lactosorb) were studied in vitro. The plates were applied to osteotomized fresh frozen human cadaveric metacarpal bones that were then tested for torsional rigidity and three-point bending strength and rigidity. The results were compared to those from another study of two low-profile titanium plating systems (Leibinger and Synthes). Analysis of variance revealed that the linear-flat Lactosorb plate and screws had apex dorsal rigidity and force-to-displacement measurements equal to all but two of the titanium plates (3D). The 3D-flat Lactosorb plate had the highest torsional rigidity of the resorbable system, but it was only moderately rigid compared to the titanium plating systems. This in vitro biomechanical study of the copolymer PGA-PLLA plating system indicates that, in clinical applications, it may be better suited for metacarpal fractures rather than proximal phalangeal fractures due to the lower demands of torsional loading compared to apex bending.
Asunto(s)
Fijadores Internos , Metacarpo/cirugía , Titanio , Fenómenos Biomecánicos , Humanos , Metacarpo/fisiopatologíaRESUMEN
Clinical problems associated with the polymerization shrinkage of dental composite restorations include tooth sensitivity, crown fracture, discoloration, recurrent decay, and loss of restoration. Our goal was to determine whether these complications could be attributed to the transient stresses developed during contraction. Thus, a finite element model was used to calculate the transitory deformations and composite-tooth interface stresses produced during the shrinkage of a chemical-cured ideal Class-V composite restoration. It was found that the interface stress peaks moved with the polymerization front, and that in some instances, their intermediate magnitudes were higher than the final, fully cured, values. Therefore, the results indicate that clinical failure may be related to these transitory changes during the polymerization process.
Asunto(s)
Materiales Dentales/normas , Estrés MecánicoRESUMEN
An important disadvantage of current dental resin composites is polymerization shrinkage. This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries. The objective of this study was to compare three filling techniques in terms of the transient stresses induced at the resin composite/tooth interface during polymerization. The techniques were: bulk filling (B), three horizontal increments (HI), and three wedge increments (WI). A simple Class V cavity preparation was modeled in finite element analysis. Polymerization shrinkage was simulated by a thermal stress analogy, thereby causing 1% shrinkage due to an arbitrary coefficient of thermal expansion. Interface normal and shear stresses were calculated at nine steps during polymerization, proceeding from 0% to 100% volume of cured resin. The importance of the interface transient stresses was revealed by the finding that, in most cases, their peak values exceeded the final or residual stress. Also, the WI and B techniques consistently exhibited the highest and lowest maximum transient stresses, respectively. These results from the simple model of a Class V restoration suggest that bulk filling of light-cured resin composites should be used in restorations which are sufficiently shallow to be cured to their full depth.
Asunto(s)
Resinas Compuestas/química , Restauración Dental Permanente/métodos , Análisis del Estrés Dental/métodos , Fenómenos Químicos , Química Física , Preparación de la Cavidad Dental , Análisis Diferencial Térmico , Calor , Humanos , Luz , Modelos Químicos , Polímeros , TermodinámicaRESUMEN
This study describes a relatively simple mechanical technique for measuring occlusal wear at the margin of dental restorations. The device was essentially a custom profilometer which consisted of a linear variable differential transformer with its core supported by double cantilever springs, a specially shaped stylus, a motor driven microscopic stage, custom computer software utilizing a colour coding to separate differences in slope, and a cross-hair-shaped mouse cursor to differentiate the boundary of wear. Two sets of visual standard stone casts were evaluated. The first set consisted of 17 stone replicas of machined steel dies and the second set consisted of five clinical casts, which have been used to measure the wear of composite restorations by direct vision. The reproducibility found when measuring the stone replicas of the machined steel dies was 2 microns, while, for the clinical standards, it was 16 microns.
Asunto(s)
Resinas Compuestas/química , Alisadura de la Restauración Dental , Sulfato de Calcio , Humanos , Procesamiento de Imagen Asistido por Computador/instrumentación , Procesamiento de Imagen Asistido por Computador/métodos , Microscopía/instrumentación , Modelos Dentales , Reproducibilidad de los Resultados , Programas Informáticos , AceroRESUMEN
This study compares a visual method for measuring composite wear with a relatively inexpensive mechanical technique. The visual measurements used a set of 17 graduated stone standards as the reference. Two sets of 10 unknown casts were evaluated. The first was a set of 10 stone replicas selected from the reference set in the range of 25-250 microns. The second set was composed of 10 casts of clinical restorations. The mechanical test employed a computer-controlled custom profilometer. Depth was recorded at 50 equidistant positions around the margin. A significant correlation was found (r > 0.98) between the visual and mechanical means for both measurement techniques. Mean values were equivalent for the standard casts. However, visual estimation of the clinical casts were significantly lower (61% of mechanical values) and thus not accurate for clinical use.
Asunto(s)
Resinas Compuestas/química , Alisadura de la Restauración Dental , Análisis de Varianza , Sulfato de Calcio , Odontólogos , Humanos , Procesamiento de Imagen Asistido por Computador/instrumentación , Procesamiento de Imagen Asistido por Computador/métodos , Análisis de los Mínimos Cuadrados , Modelos Dentales , Estándares de Referencia , Acero , Propiedades de SuperficieRESUMEN
OBJECTIVES: The initial and final forms of reactive gypsum products have been photomicrographed previously. However, the purpose of this project was to document the microscopic morphology of setting dental stone at various stages during the reaction. METHODS: Two dental products, a conventional (Type IV) die stone and a fast-setting (Type III) stone, were investigated. At selected times ranging from 1 min to 24 h after mechanically mixing the stone under vacuum, the conversion of calcium sulfate hemihydrate to a dihydrate was suspended by immersion into liquid nitrogen. Water was immediately removed by freeze-drying the specimen to prevent any further reaction so that the specimen could be returned to room temperature for examination in a scanning electron microscope (SEM). RESULTS: Crystal formation appeared to be nearly complete at the 20 min interval for the die stone and at the 10 min interval for the fast-setting dental stone. Transitions noted during these times include the nucleation and growth of small needle-like crystals on and near the larger prismatic-shaped hemihydrate crystals, the concurrent decrease in size and number of the hemihydrate crystals, and the progressive entanglement of the growing dihydrate crystals. SIGNIFICANCE: The two-step process of suspending the reaction, then freeze-drying the specimen made it possible to observe and document the intermediate stages during crystal growth of dental stone. These observations should be helpful in understanding the structural dynamics of crystal growth during the setting of gypsum dental products. This procedure should be applicable to the study of other water-based dental materials.
Asunto(s)
Sulfato de Calcio/química , Materiales Dentales/química , Cristalografía , Materiales de Impresión Dental , Liofilización , Microscopía Electrónica de Rastreo , Modelos Dentales , Tamaño de la Partícula , Factores de TiempoRESUMEN
PURPOSE: This investigation introduces percent adherent area and 10-minute and 8-hour peel-strength values as an in vivo evaluation of three popular maxillofacial prosthetic adhesives when used with three extraoral prosthetic polymers. MATERIALS AND METHODS: Specimens of Silastic MDX 4-4210, Silastic Medical Adhesive A (Dow Corning Corporation, Midland, MI), and Silicone A-2186 (Factor II, Inc, Lakeside, AZ) were adhered to 25 subjects' arms using Secure Medical Adhesive (Factor II, Inc), Pros-Aide Adhesive (ADM Tronics Inc, Northvale, NJ), and Hollister Colostomy Adhesive (Hollister Inc, Libertyville, IL). After 10 minutes, the peel strength required to remove the specimens was measured. Additional specimens were then adhered to the subjects and worn for 8 hours. The nonadherent areas of the specimens were then marked, the peel strength was measured again, and then the percent adherent area was calculated. RESULTS: Hollister Colostomy Adhesive showed greater 10-minute peel-strength values when used with Silastic Medical Adhesive A. The peel-strength values of the Hollister Colostomy Adhesive when used with Silastic MDX 4-4210 increased with time. The greatest percent adherent area was obtained with Silastic MDX 4-4210 using Pros-Aide Adhesive, and the lowest was obtained with Pros-Aide Adhesive using Silicone A-2186 and Silastic Medical Adhesive A. CONCLUSIONS: There was no clearly superior adhesive/prosthetic material combination based on the tests used in this study; however, individual skin variations between patients affect the adhesive properties.
Asunto(s)
Adhesivos , Prótesis Maxilofacial , Adhesividad , Adulto , Análisis de Varianza , Estudios de Evaluación como Asunto , Femenino , Humanos , Masculino , Elastómeros de Silicona , Piel , Factores de TiempoRESUMEN
We have constructed a family of novel in vitro transcription vectors in which functional T3, T7 and SP6 RNA polymerase promoters are arranged in tandem and directed towards a multiple cloning site. This prototype vector, named pTRIPLEscript, permits the transcription of one strand of a DNA insert by any of the three commonly used bacteriophage RNA polymerases with no apparent cross talk, i.e., use of the wrong promoter sequence. The vector has two main uses: (i) to clone probe sequences that will be distributed to many laboratories, allowing the use of the most convenient RNA polymerase; and (ii) to circumvent the problem of RNA polymerase-dependent premature termination.
Asunto(s)
ARN Polimerasas Dirigidas por ADN/genética , Vectores Genéticos , Regiones Promotoras Genéticas , Transcripción Genética , Secuencia de Bases , Clonación Molecular , Datos de Secuencia Molecular , Proteínas ViralesRESUMEN
Clinical failures are often associated with the polymerization shrinkage of resin composite restorative materials. These problems include tooth sensitivity and fracture, marginal leakage, loss of the restoration, and recurrent decay. Our goal was to examine transient composite distortions and interface stresses as a bulk-filled light-cured composite polymerized in a Class V restoration. The analysis was based on a finite element model. The curing of the restoration was divided into 4 steps: approximately 1/30, 1/4, 1/2, and full depth (1/1) of cure. Since the actual curing pattern is not known, calculations were performed for three hypothetical (flat, convex, and concave) polymerization front shapes. The calculations showed that the assumed shape was a critical factor in determining cured surface deformations. For example, the initial cure depth (1/30) resulted in a surface bulge if the polymerization front was presumed convex, while the concave front resulted in a large intrusion. By the time that about 1/2 the depth of the restoration was cured, the differences were essentially gone. The final surface outline was intruded. Interface stresses in the curing restoration were qualitatively similar regardless of the assumed polymerization shape. As with surface distortions, the stresses changed with curing depth. It was concluded that (1) transient events during polymerization are possible contributors to clinical complications, and (2) more must be known about the polymerization pattern.
Asunto(s)
Resinas Compuestas/química , Restauración Dental Permanente , Análisis del Estrés Dental , Fenómenos Químicos , Química Física , Preparación de la Cavidad Dental , Elasticidad , Dureza , Humanos , Luz , Modelos Estructurales , Propiedades de SuperficieRESUMEN
OBJECTIVES: The correlation between shear bond strength and surface roughness was investigated using new surface measurement methods. METHODS: Bonding agents and associated resin composites were applied to set amalgam after mechanically roughening its surface. Surface treatments were noe (as set against glass), 80 grit, and 600 grit abrasive paper. Surface roughness (R(a) as measured parallel and perpendicular (+) to the direction of the polishing scratches and true profile length were measured. A knife-edge was applied (rate = 2.54 mm/min) at the bonding agent/amalgam interface of each sample until failure. RESULTS: Coefficients of determination for mean bond strength vs either roughness (R(a), of profile length were significantly higher for measurements in parallel directions than for those measurements in (+) directions. The shear bond strength to set amalgam for a PENTA-containing adhesives system (L.D. Caulk Division) was not significantly different from that of a PENTA-free adhesive (3M Dental Products Division), even though PENTA has been reported to increase bond strength to nonprecious metals. SIGNIFICANCE: The shear bond strength of resin composite to amalgam is correlated to surface roughness when it is measured parallel to the polishing scratches. This correlation is significantly lower when surface roughness is measured in the typical manner, perpendicular to the polishing scratches.
Asunto(s)
Amalgama Dental , Recubrimiento Dental Adhesivo , Pulido Dental , Recubrimientos Dentinarios , Ensayo de Materiales/métodos , Cementos de Resina , Aleaciones Dentales/química , Amalgama Dental/química , Microscopía Electrónica de Rastreo , Propiedades de Superficie , Resistencia a la TracciónRESUMEN
Aluminum oxide particles are commonly used as a sandblasting media, particularly in dentistry, for multiple purposes including divesting the casting investment materials and increasing effective surface area for enhancing the mechanical retention strengths of succeedingly applied fired porcelain or luting cements. Usually fine aluminum oxide particles are recycled within the sandblasting machine. Ceramics such as aluminum oxides are brittle, therefore, some portions of recycling aluminum oxide particles might be brittle fractured. If fractured sandblasting particles are involved in the recycling media, it might result in irregularity metallic materials surface as well as the recycling sandblasting media itself be contaminated. Hence, it is necessary from both clinical and practical reasons to monitor the particle conditions in terms of size/shape and effectiveness of sandblasting, so that sandblasting dental prostheses can be fabricated in optimum and acceptable conditions. In the present study, the effect of recycling aluminum oxide particles on the surface texture of metallic materials was evaluated by Fractal Dimension Analysis (FDA). Every week the alumina powder was sampled and analyzed for weight fraction and contaminants. Surface texture of sandblasted standard samples was also characterized by FDA. Results indicate very little change in particle size, while the fractal dimension increased. Fractal dimension analysis showed that the aluminum oxide particle as a sandblasting media should be replaced after 30 or 40 min of total accumulated operation time.
Asunto(s)
Óxido de Aluminio/química , Aleaciones Dentales , Recubrimiento Dental Adhesivo , Pulido Dental , Fractales , Presión del Aire , Microanálisis por Sonda Electrónica , Equipo Reutilizado , Análisis de Fourier , Ensayo de Materiales , Tamaño de la Partícula , Propiedades de Superficie , Tecnología Odontológica , Resistencia a la Tracción , Factores de TiempoRESUMEN
Previous studies of newly synthesized proteins during early development in sea urchins have revealed several different patterns of synthesis that can be used to predict the existence of mRNA classes with distinct regulatory controls. We have identified clones for abundant maternal mRNAs that are actively translated during early development by screening a cDNA library prepared from polysomal poly(A)+RNA isolated from 2-cell stage (2-hour) Strongylocentrotus purpuratus embryos. Probes prepared from these cDNA clones and several previously characterized maternal mRNA cDNAs were used to compare relative levels of individual mRNAs in eggs and embryos and their translational status at various developmental stages. These abundant mRNAs can be classified into two major groups which we have termed cleavage stage-specific (CSS) and post cleavage stage (PCS) mRNAs. The relative levels of the CSS mRNAs are highest during the rapid cleavage stage and decrease dramatically at the blastula stage (12-hours). In contrast, PCS mRNAs are present at relatively low levels during the rapid cleavage stage and then increase at the blastula stage. Polysome partition profiles reveal that CSS mRNAs are translated more efficiently than PCS mRNAs in the unfertilized egg, at fertilization, and during the cleavage stages. Following the blastula stage, some CSS transcripts move out of polysomes and accumulate as untranslated RNAs, while newly transcribed PCS mRNAs are recruited into polysomes. These data suggest that the rapid cell cycles following fertilization require high levels of specific cleavage stage proteins, and the synthesis of these proteins occurs preferentially over PCS mRNAs.