Development of nanobiosilicate, tricalcium phosphate and chlorhexidine materials for biomineralization with crystallographic similarity to hydroxyapatite and biomodified collagen.

OBJECTIVES: The aim of this work is to test experimental cements, doped with a silicate based bioactive nanoparticle (NanoBiosilicate). Methods, we synthesized a glass nanoparticle by Sol-Gel Stöber method, used to be incorporated in a dental material for endodontic uses. MATERIALS AND METHODS: We assess the mineralizing properties and biocompatibility. Besides the crystallography characterization of the resultant new crystals. Results, After analysis, and comparison with commercial materials, the material tested was similar in mechanical properties required by ISO, The ion release was effective after 2 hr. of setting and the novel material was cell compatible accepted by ISO. RESULTS: We found new formed Calcium Phosphate peaks in the spectroscopic analysis (FTIR), remarkably the crystals formed were comparable to hydroxyapatite when analyzed with a Selected Area Electron Diffractometer, with rings of 2.84 Å for 002, and the 2.77 Å is also visible for 210. The 6.83 Å and 6.88 Å, for respective 222 and 004. The incorporation of Chlorhexidine was not detrimental for this property, Significance, the features mentioned represented a progress in biomineralization field that was associated to an improved mineral structure formation with increased crystallographic similarity to natural hydroxyapatite. When chlorhexidine was added a favorable biomodification of the remaining collagen in dentinal walls and antimicrobial activity potential were also observed.

Effect of Tricalcium Silicate on Direct Pulp Capping: Experimental Study in Rats.

OBJECTIVES: Conduct a histological comparison of the pulp response to different materials, with a focus on the continuity and morphology of the mineralized barrier after direct pulp capping. MATERIALS AND METHODS: One hundred and eight maxillary first molars of 54 Wistar rats were subject to direct pulp capping and divided into three groups according to the materials used: calcium hydroxide (CH), mineral trioxide aggregate (MTA), and Biodentine. All cavities were sealed, and the animals were euthanized at 7, 14, and 21 days. Descriptive histological evaluation of the inflammation and formation of the mineralized barrier was performed. STATISTICAL ANALYSIS: Statistical analyses were performed using the Kruskal-Wallis test, which was complemented by the Dunn test; differences with p < 0.05 were considered statistically significant. RESULTS: The results showed that MTA and Biodentine elicited less intense inflammatory reactions than CH. With respect to the formation and quality of the dentin barrier formed, differences were observed at 21 days between the analyzed groups; the best results being obtained following treatment with MTA and Biodentine. CONCLUSION: MTA and Biodentine induced formation of a more continuous and uniform mineralized barrier with less intense pulp response than CH.

Bonding Strength of Luting Cement to Zirconia-Based Ceramic Under Different Surface Treatments.

OBJECTIVES: The aim of this study was to evaluate the bonding strength of self-adhesive luting cement to zirconia under different surface treatments. MATERIALS AND METHODS: Thirty-two zirconia samples were randomly divided into eight experimental groups based on the surface treatment employed (Control: no surface treatment; PMM: wear with diamond bur; JAT: blasting with glass beads; PMA: wear with a medium-roughness milling machine; Primer: primer application on the surface without treatment; PMM +Primer: PMM treatment plus primer application; JAT+Primer: JAT treatment plus primer application; and PMA+Primer: PMA treatment plus primer application). Cement cylinders were built on the ceramic surfaces, and the groups were subdivided according to the storage time employed (i.e., 24 hours or 60 days). After storage, the samples were subjected to microshear testing. STATISTICAL ANALYSIS: The Kruskal-Wallis test followed by the Dunn test was employed for comparison between the groups (p < 0.05). RESULTS: The PMM group yielded the optimal results and the mean values increased after both storage times following the primer application. The Control, PMA, and JAT groups gave similar results after 24 hours, while the JAT group gave superior results following primer application over this storage time. After 60 days of storage, all groups gave improved results following chemical treatment with a primer. CONCLUSION: It was concluded that mechanical preparation using the diamond bur followed by primer application significantly improved the bond strength between the ceramic and the luting cement.

Degradation of Adhesive-Dentin Interfaces Created Using Different Bonding Strategies after Five-year Simulated Pulpal Pressure.

PURPOSE: To compare after five-year simulated pulpal pressure (SPP) the degradation of adhesive-dentin interfaces created using two simplified adhesives applied with different bonding strategies. MATERIALS AND METHODS: A two-step self-etch (CSE: Clearfil SE Bond) adhesive was used as a control multistep adhesive. The tested experimental materials were two simplified adhesives, a one-step self-etch (CS3: Clearfil S3 Bond) and a self-priming etch-and-rinse adhesive (SB2: Adper Single-Bond 2). Half of the bonded specimens were submitted to microtensile bond strength (µTBS) testing after 24 h. The other half submitted to SPP for five years before µTBS testing. Nonfractured sticks were evaluated using transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was used to evaluate silver-nitrate nanoleakage within the interface. Data were statistically analyzed by two-way ANOVA and Tukey's test (p < 0.05). RESULTS: Prolonged SPP induced bond-strength reduction for both SB2 and CS3. All bonding approaches showed increased nanoleakage after aging. The two simplified adhesives showed severe degradation at the resin-dentin interface. TEM revealed that the main degradation patterns for the etch-and-rinse adhesive SB2 was collagen breakdown, while polymer hydrolysis along with filler debonding was mainly observed in CS3. CONCLUSIONS: Simplified adhesives applied in etch-and-rinse mode are mainly characterized by hydrolysis and collagen degradation. In self-etch mode, simplified adhesives may principally show hydrolysis of the polymeric matrix and/or at the interface of fillers and coupling agent. The use of multistep self-etching adhesives may guarantee greater dentin bond durability compared to simplified adhesives.

A new arginine-based dental adhesive system: formulation, mechanical and anti-caries properties.

Secondary caries at the margins of composite restorations has been attributed to adhesive failure and consequent accumulation of cariogenic biofilms. OBJECTIVES: To develop and evaluate an etch-and-rinse adhesive system containing arginine for sustainable release and recharge without affecting its mechanical properties. Arginine metabolism by oral bacteria generates ammonia, which neutralizes glycolytic acids and creates a neutral environmental pH that is less favorable to the growth of caries pathogens, thus reducing the caries risk at the tooth-composite interface. METHODS: Experimental adhesives were formulated with methacrylate monomers and arginine at 5%, 7%, and 10% or no arginine (control). Adhesives were tested for: (i) mechanical properties of true stress (FS and UTS), modulus of elasticity (E), degree of conversion (DC), Knoop hardness number (KHN) and dentin microtensile bond strength (µ-TBS), (ii) arginine release and recharge, and (iii) antibacterial activities. Data was analyzed by t-test, one-way ANOVA and Tukey's tests. RESULTS: FS and UTS results showed no statistically significant differences between the 7% arginine-adhesive and control, while the results for E, DC, KHN and µ-TBS showed no difference among all groups. The 7% arginine-adhesive showed a high release rate of arginine (75.0µmol/cm2) at 2h, and a more sustainable, controlled release rate (up to 0.2µmol/cm2) at 30days. CONCLUSIONS: Incorporation of 7% arginine did not affect the physical and mechanical properties of the adhesive. Arginine was released from the adhesive at a rate and concentration that exhibited antibacterial effects, regardless of shifts in biofilm conditions such as sugar availability and pH. CLINICAL SIGNIFICANCE: Secondary caries is recognized as the main reason for failure of dental restorations. The development of an arginine-based adhesive system has the potential to dramatically reduce the incidence and severity of secondary caries in adhesive restorations in a very economical fashion.

Surface detail reproduction and dimensional accuracy of molds: influence of disinfectant solutions and elastomeric impression materials / Reprodução de detalhes da superfície e estabilidadedimensional de moldes: influência das soluçõesdesinfetantes e elastômeros

This study compared the surface detail reproduction anddimensional accuracy of molds after disinfection using 2% sodium hypochlorite, 2% chlorhexidine digluconate or 0.2% peracetic acid to those of molds that were not disinfected, forfour elastomeric impression materials: polysulfide (Light Bodied Permlastic), polyether (Impregum Soft), polydimethylsiloxane(Oranwash L) and polyvinylsiloxane (Aquasil Ultra LV). Themolds were prepared on a matrix by applying pressure, using aperforated metal tray. The molds were removed followingpolymerization and either disinfected (by soaking in one of thesolutions for 15 minutes) or not disinfected. The samples werethus divided into 16 groups (n=5). Surface detail reproductionand dimensional accuracy were evaluated using opticalmicroscopy to assess the 20 ­µm line over its entire 25 mm length. The dimensional accuracy results (%) were subjectedto analysis of variance (ANOVA) and the means were comparedby Tukey’s test (α=5%). The 20 ­µm line was completelyreproduced by all elastomeric impression materials, regardlessof disinfection procedure. There was no significant difference between the control group and molds disinfected with peraceticacid for the elastomeric materials Impregum Soft (polyether)and Aquasil Ultra LV (polyvinylsiloxane). The high­leveldisinfectant peracetic acid would be the choice material for disinfection.

Este estudo comparou a reprodução de detalhes da superfície e estabilidade dimensional de moldes obtidos após desinfecção utilizando hipoclorito de sódio 2%, digluconato de clorexidina 2%, ou ácido peracético 0,2% a moldes que não foram desinfetados com quatro elastômeros: polissulfeto (Light Bodied Permlastic), polieter (Impregum Soft), silicona reação porcondensação (Oranwash L) e silicona reação por adição (Aquasil Ultra LV). Os moldes foram preparados sobre matriz conten dolinhas de 20, 50 e 75 µm realizado sob pressão com moldeirade metal perfurada. Os moldes foram removidos após a polimerização e desinfetados (utilizando uma das soluções porimersão, armazenados em frascos fechados durante 15 minutos)ou não desinfetados. Assim, as amostras foram divididas em 16grupos (n=5). A reprodução detalhes da superfície e a precisão dimensional foram avaliadas usando microscopia óptica na linha 20 µm com 25 mm de comprimento, de acordo com a norma ISO 4823. Os resultados de precisão dimensional (%) foram submetidos à análise de variância (A NOVA) e as médias comparadas pelo teste de Tukey com 5% de nível de significância. A linha de 20 µm foi completamente reproduzida por todos os elastômeros, independentemente do processo de desinfecção. Não houve diferença estatisticamente significativa entre o grupo controle e moldes desinfetados com acido peracético para os elastômeros Impregum Soft (polieter) e Aquasil Ultra LV (siliconareação por adição). O desinfetante de alto nível ácido peracético seria o material de escolha para a desinfecção.

Influence of adding nanoparticles on the hardness, tear strength, and permanent deformation of facial silicone subjected to accelerated aging.

STATEMENT OF PROBLEM: The efficiency of adding nanoparticles to silicone protection has proven to prevent color degradation. However, reports of other physical property changes in facial silicone are scarce. PURPOSE: The purpose of this in vitro study was to evaluate the influence of adding nanoparticles on the hardness, tear strength, and permanent deformation of a facial silicone. MATERIAL AND METHODS: Specimens were made for each test, with 140 for the hardness test, 140 for the permanent deformation test, but 280 for the rupture test. This higher number was due to the fact that the first 140 specimens were ruptured and unusable after the initial reading. ZnO, BaSO4, and TiO2 nanoparticles at concentrations of 1% and 2% of silicone were used, as well as specimens without nanoparticles that consisted of only oil paint and of only silicone. Outcomes were measured before and after 1008 hours of accelerated aging. Data were analyzed by nested analysis of variance (ANOVA) and Tukey honest significant differences test (α=.05). RESULTS: Results showed that the presence of nanoparticles influenced the properties of the assessed groups. The nanoparticles decreased hardness values. The highest values of tear strength were observed for the groups with addition of BaSO4. The 1% ZnO group without oil paint showed the lowest values of permanent deformation. CONCLUSIONS: Based on the findings of this in vitro study, the use of ZnO nanoparticles is recommended, since they did not negatively affect the properties of the materials evaluated.

Influence of alginate impression materials and storage time on surface detail reproduction and dimensional accuracy of stone models.

This study compared the surface detail reproduction and dimensional accuracy of stone models obtained from molds prepared using different alginate impression materials (Cavex ColorChange, Hydrogum 5, or Jeltrate Plus) and with different storage times (1, 3, and 5 days) to models from molds that were filled immediately with no storage time. The molds were prepared over a matrix containing 50-µm line, (ISO 1563 standard) under pressure with a perforated metal tray. The molds were removed 2 minutes after loss of sticky consistency and either filled immediately or stored in closed jars at 100% relative humidity and 37°C for 1, 3, or 5 days. The molds were filled with dental plaster (Durone IV). Surface detail reproduction and dimensional accuracy were evaluated using optical microscopy on the 50-µm wide line, which was 25 mm in length, according to ISO 1563 standard. The dimensional accuracy results (%) were subjected to analysis of variance. The 50-µm wide line (ISO 1563 standard) was completely reproduced by all alginate impression materials regardless of the storage time. There was no statistically significant difference in the mean dimensional accuracy values of stone models made from molds composed of different alginate impression materials and with different storage times (p = 0.989). In conclusion, storing the mold for five days prior to filling did not change the surface detail reproduction or dimensional accuracy of the alginates examined in this study.

Pino anatômico com resina composta: relato de caso / Anatomic fiber post with composite resin: case report

O protocolo restaurador de dentes tratados endodonticamente é um desafio na odontologia adesiva atual, já que existem vários tipos de retentores intrarradiculares à disposição no mercado, com características ópticas e mecânicas que promovem um tratamento satisfatório. Dessa forma, a técnica de pino de fibra anatômico reembasado com resina composta direta torna-se eficiente para uso na clínica odontológica, especialmente em casos de condutos largos e tamanho reduzido de férula. Para tanto, o pino é limpo, aplica-se o silano e adesivo, além da resina composta não polimerizada para moldar o conduto radicular. Após, o pino é tratado novamente e cimentado com uma pequena espessura de linha de cimentação. Nesse artigo, o caso clinico abordará as etapas necessárias para a confecção do pino anatômico, além das estratégias de cimentação adesiva e a restauração com resina composta, trabalhando os conceitos da manutenção de uma delgada linha de cimentação para uma adequada reabilitação dental mantendo biomecânica e retenção do pino de fibra no interior do conduto radicular.

The restorative protocol for endodontically treated teeth is a challenge in adhesive dentistry, since there are several available types of intracanal posts with optical and mechanical characteristics that promotea satisfactory treatment. Thus, the anatomical fiber post technique is efficient for the use in dental practice, especially in cases of large root canals and small dental ferrules. So, the post is cleaned and then the silaneagent and adhesive system are applied, followed by the placement of the non-polymerized composite for root canal modeling. After this, the anatomical fiber post is treated again and followed by the luting procedure, showing a small cementation thickness. In this paper, the case report will address the necessary steps to realize the anatomical fiber post technique using strategies and adhesive cementation with composite resin restoration, working the concepts of maintaining a thin cement line and an adequate dental rehabilitation.

Effect of repeated microwave disinfections on bonding of different commercial teeth to resin denture base.

OBJECTIVE: To verify the influence of repeated microwave disinfections on the shear bond strength of two commercial types of teeth to acrylic resin, when the ridge lap surfaces were unmodified, bur abraded, bur grooved or etched by monomer. MATERIAL AND METHODS: Eighty specimens (n = 10) were adhered to the tooth ridge lap surface, polymerised in a water bath at 74°C for 9 h. Microwaved specimens were individually immersed in 150 ml of water and submitted to five simulated disinfections in a microwave oven calibrated at 650 W for 3 min. Control specimens were not microwave treated. Shear bond strength tests were performed in an Instron machine with a cross-speed of 1 mm/min. The fracture load values were transformed into shear bond strength as a function of the bonding area (0.28 cm(2)). Data were submitted to ANOVA and Tukey's test (α = 0.05). Fractured areas were classified as adhesive, cohesive (resin or tooth) or mixed failures. RESULTS: Repeated microwave disinfections increased the shear strength of the tooth/resin bond. Mechanical retention in microwaved and non-microwaved procedures improved the shear bond strength. CONCLUSIONS: The different commercial types of teeth influenced shear bond strength values, with Biotone teeth showing the lower values.

Effect of polymerization techniques on vertical dimension and tooth position in complete dentures.

Due to the changes in the composition and processing of acrylic resins, it seems appropriate to evaluate the influence of polymerization methods about the alteration of occlusal vertical dimension and the horizontal positioning of artificial teeth of total dentures. For this, 64 specimens were made, simulating a maxillary total denture waxed from a standard maxillary denture. The experimental samples were divided into two groups: Group 1 - The resins were submitted to polymerization in a hot water bath, Group 2 - The same resins were submitted to poly-merization by microwave energy. The samples were measured horizontally and vertically before and after the polymerization process. Based on the results, it can be concluded that there was no statistically significant difference between the conventional polymerization method and the polymerization method by microwave, related to the stability of occlusal vertical dimension and horizontal positioning of artificial teeth on the specimens evaluated.

Influence of opacifiers on dimensional stability and detail reproduction of maxillofacial silicone elastomer.

BACKGROUND: We evaluated the influence of chemical disinfection and accelerated aging on the dimensional stability and detail reproduction of a silicone elastomer containing one of two opacifiers. METHODS: A total of 90 samples were fabricated from Silastic MDX 4-4210 silicone and divided into groups (n = 10) according to opacifier content (barium sulfate or titanium dioxide) and disinfectant solution (neutral soap, Efferdent, or 4% chlorhexidine). The specimens were disinfected 3 times per week during 60 days and then subjected to accelerated aging for 1008 hours. Dimensional stability and detail reproduction tests were performed after specimens' fabrication (baseline), chemical disinfection and periodically during accelerated aging (252, 504, and 1008 hours). The results were analyzed using 3-way repeated-measures ANOVA and the Tukey HSD test (α = 0.05). RESULTS: All groups exhibited dimensional changes over time. The opacifier (p = .314), period (p < .0001) and their interactions (p = .0041) affected the dimensional stability of the silicone. Statistical significant dimensional differences occurred between groups with (0.071) and without opacifiers (0.053). Accelerated aging influenced the dimensional stability of the samples. All groups scored 2 in the detail reproduction tests, which represents the fully reproducing of three test grooves with accurate angles. CONCLUSIONS: Incorporation of opacifiers alters the dimensional stability of silicones used in facial prosthetics, but seems to have no influence on detail reproduction. Accelerated aging is responsible for most of the dimensional changes in Silastic MDX4 4210, but all dimensional changes measured in this study remained within the limits of stability necessary for this application.

Luting glass ceramic restorations using a self-adhesive resin cement under different dentin conditions.

OBJECTIVES: The aim of this study was to investigate the bond strength of ceramic restorations luted using a self-adhesive resin cement (RelyX Unicem, 3M ESPE) under different dentin conditions. MATERIAL AND METHODS: In the experimental groups, ceramic restorations were luted to bovine incisors with RelyX Unicem under the following conditions: [Dry dentin]: surface was dried using air stream for 15 s; [Moist dentin]: excess dentin moisture was removed with absorbent paper; [Bonding agent]: Clearfil SE Bond (Kuraray) self-etching adhesive system was previously applied to dentin. In the Control group, cementation was done using an etch-and-rinse adhesive (Excite DSC) and Variolink II resin cement (Ivoclar Vivadent). Photoactivation of the resin cements was performed with UltraLume LED 5 unit (Ultradent). The restorations (n=5 per group) were sectioned into beams and microtensile testing was carried out. Data were subjected to ANOVA and Tukey's test (p<0.05). Failure modes were classified under Scanning Electron Microscopic (SEM) (x120 magnification). RESULTS: The bond strength was dependent on the moisture status of the dentin. Bond strength in the "dry dentin group" was significantly lower than that of all other groups, which showed similar results. A predominance of mixed failures was detected for the control group, while a predominance of adhesive failures was observed for the "bonding agent" and "dry dentin" groups. The "moist dentin" group presented predominantly cohesive failures within the luting material. The previous application of a self-etching adhesive showed no significant effect. CONCLUSIONS: Only excess dentin moisture should be removed for the cementation of ceramic restorations with self-adhesive resin cements.

Luting glass ceramic restorations using a self-adhesive resin cement under different dentin conditions

OBJECTIVES: The aim of this study was to investigate the bond strength of ceramic restorations luted using a self-adhesive resin cement (RelyX Unicem, 3M ESPE) under different dentin conditions. MATERIAL AND METHODS: In the experimental groups, ceramic restorations were luted to bovine incisors with RelyX Unicem under the following conditions: [Dry dentin]: surface was dried using air stream for 15 s; [Moist dentin]: excess dentin moisture was removed with absorbent paper; [Bonding agent]: Clearfil SE Bond (Kuraray) self-etching adhesive system was previously applied to dentin. In the Control group, cementation was done using an etch-and-rinse adhesive (Excite DSC) and Variolink II resin cement (Ivoclar Vivadent). Photoactivation of the resin cements was performed with UltraLume LED 5 unit (Ultradent). The restorations (n=5 per group) were sectioned into beams and microtensile testing was carried out. Data were subjected to ANOVA and Tukey's test (p<0.05). Failure modes were classifed under Scanning Electron Microscopic (SEM) (x120 magnifcation). RESULTS: The bond strength was dependent on the moisture status of the dentin. Bond strength in the "dry dentin group" was signifcantly lower than that of all other groups, which showed similar results. A predominance of mixed failures was detected for the control group, while a predominance of adhesive failures was observed for the "bonding agent" and "dry dentin" groups. The "moist dentin" group presented predominantly cohesive failures within the luting material. The previous application of a self-etching adhesive showed no signifcant effect. CONCLUSIONS: Only excess dentin moisture should be removed for the cementation of ceramic restorations with self-adhesive resin cements.

Preparation and evaluation of dental resin luting agents with increasing content of bisphenol-A ethoxylated dimethacrylate.

Resin luting agents in which bisphenol-A glycidyl dimethacrylate (Bis-GMA) and/or triethylene glycol dimethacrylate (TEGDMA) are replaced with increasing amounts of bisphenol-A ethoxylated dimethacrylate are prepared. Degree of conversion (DC), diametral tensile strength (DTS), Young's modulus (YM), Knoop hardness (KHN), film thickness (FT), water sorption (W(sp) ), and solubility are evaluated. Regression analyses investigate the substitution of each monomer. The most appreciable differences are detected when TEGDMA is replaced: decreased DC, DTS, and W(sp), and increased YM, KHN, and FT. For substitution of Bis-GMA, the only significant differences are reduced W(sp) and increased YM. An ideal formulation of resin cement would make use of the three monomers.

Effect of flask closure method and post-pressing time on the upper denture base adaptation.

OBJECTIVES: The purpose of this study was to evaluate the effect of flask-closure methods, post-pressing times and acrylic resins on denture base adaptation. MATERIALS AND METHODS: The resins were flasked using a hydraulic press and closed with the traditional clamp or RS system. Conventional heat-cure resin was polymerised immediately or at 6 h post-pressing at 74 degrees C for 9 h. Rapid cycle heat-cure resin was polymerised in boiling water for 20 min. After cooling, the bases were deflasked and the sets of cast-base transversally sectioned in the regions distal to the canine, mesial to the first molar and in the posterior palatal zone. The adaptation was measured with an optical microscope (0.0005 mm) at five reference points for each section. Data were analysed using anova and Tukey's test (alpha = 0.05). RESULTS: Traditional clamp and immediate post-pressing time improved base adaptation for conventional heat-cure resin. Both post-pressing times showed most accurate base adaptation for conventional heat-cure resin when the traditional clamp was used. Immediate post-pressing time improved base adaptation for conventional heat-cure resin and the 6-h delay in time was significant for the rapid cycle heat-cure resin. CONCLUSIONS: Traditional clamp and immediate post-pressing time improved base adaptation for conventional heat-cure resin.

Effect of flask closure method and post-pressing time on the displacement of maxillary denture teeth.

The purpose of this study was to verify the influence of flask closure methods and post-pressing times on tooth displacement in maxillary dentures. Twenty similar maxillary dentures were made using a heat-polymerized acrylic resin, and randomly assigned to 4 experimental groups (n=5) according to the protocol: 1-conventional flask closure and immediate polymerization; 2- conventional flask closure and polymerization after 6-hour post-pressing time; 3- RS flask closure system and immediate polymerization; and 4- RS flask closure system and polymerization after 6-hour post-pressing time. Three transverse and 2 anteroposterior linear distances between teeth were measured before and after the denture processing with an optical microscope with accuracy of 0.0005mm. Analysis of variance (ANOVA) and Tukey's test were performed to compare the results. The 6-hour post-pressing time (conventional = 0.44mm and RS = 0.33mm) showed no statistically significant difference in tooth movement, in relation to the flask closure methods, when compared to the immediate time (conventional = 0.40mm and RS = 0.28mm). The RS system standardized the tooth displacement, independently of the post-pressing times. Dimensional changes were more uniform when the dentures were submitted to the 6-hour post-pressing time and RS flask closure method, suggesting that these factors may reduce the magnitude of tooth movement.

Comparative study of tubular diameter and quantity for human and bovine dentin at different depths.

This study compared the tubular dimensions and distribution of human and bovine dentin. Ten human molars and 10 bovine incisors were ground with a high-speed handpiece to obtain 3 sections at different dentin depths (superficial, middle and deep). The specimens were sputter-coated with gold to be examined under scanning electron microscopy (SEM). Three SEM micrographs were recorded randomly for each dentin depth. The number of tubules was counted and the diameter of 5 tubules selected at random was measured in each SEM micrograph. Data were analyzed statistically by ANOVA and Tukey's test (alpha=0.05). In bovine teeth, superficial dentin (4.21 microm) and middle dentin (3.98 microm) had a significantly greater (p<0.05) diameter than deep dentin (3.14 microm) tubules. In human teeth, superficial dentin tubule diameter (2.42 microm) was significantly smaller (p<0.05) than deep dentin (2.99 microm) and middle dentin (2.94 microm) tubule diameters, which did not differ significantly from each other (p>0.05). The number of tubules per square millimeter, regardless of the region, was significantly greater in human dentin (22,329) than in bovine dentin (15,964). There was a clear difference in tubule structure and morphology between human and bovine dentin.

SEM evaluation of marginal sealing on composite restorations using different photoactivation and composite insertion methods.

AIM: This in vitro study evaluates the influence of marginal sealing methods in composite restorations with different adhesive systems submitted to mechanical load. MATERIALS AND METHODS: Eighty bovine incisor crowns were embedded in Polyvinyl chloride (PVC) molds with the buccal surface exposed, where cavities (4mm x 4mm x 3mm) were made. Samples had the adhesive systems, Single Bond or Clearfil SE Bond, applied according to the manufacturer's recommendations. The cavities were filled with a Z-250 composite according to the restoration technique (bulk filling or three increments) and photoactivation (conventional, soft start, pulsatile light or light-emitting diode [LED]). The samples were duplicated with epoxy resin for scanning electron microscopy observations. Samples were also submitted to mechanical load (200,000 cycles; 2 Hz) and new replicas were made. RESULTS: The results, in percentages, were submitted to ANOVA followed by Tukey's test (P < 0.05). There was statistical difference between the cycle group (23.84%) and the non cycle group (18.63%). Comparing the restoration technique, there was no statistical difference between bulk filling (19.62%) and three increments (22.84%). There was no statistical difference among the groups: Pulsatile light (24.38%), soft start (22.75%), LED (21.47%) or conventional (16.34%). Furthermore, there were no statistical differences between the adhesive systems: Clearfil SE Bond (21.32%) and Single Bond (20.83%). CONCLUSIONS: The photoactivation methods, the restorative techniques and the adhesive systems did not influence gap formation.