Effect of 830 nm Diode Laser Irradiation of Root Canal on Bond Strength of Metal and Fiber Post.

OBJECTIVE AND BACKGROUND: The correct selections of the cementing agent, the endodontic post material and placement protocol are critical to provide an increased longevity of the teeth that went through endodontic treatment. The irradiation with diode laser before post cementation, can promote an antimicrobial effect. However, there is a lack of information about the effect of 830 nm diode laser on the post bond strength. This study analyzed the effect of dentin root canal irradiation with high-intensity diode laser, at 830 nm, operating in continuous or pulsed mode, on the retention of metal or fiber posts, cemented with self-etching resinous composite (Panavia F) and zinc phosphate cement (ZnPO4). MATERIALS AND METHODS: Human roots were irradiated with diode laser (continuous and pulsed mode). The fiber posts were luted with Panavia F and the metal posts with Panavia F or ZnPO4 cement. Specimens were sectioned into three sections (cervical, middle, and apical). The bond strength was measured by a push-out mechanical analysis. For the statistical analysis, a three-way ANOVA test was applied following a Tukey's pairwise comparison with a significance level of p = 0.05. RESULTS: The irradiated groups presented higher bond strength compared with nonirradiated group (p < 0.05), and the cervical and middle thirds presented higher on bond strength than the apical. The association of metal post and Panavia F presented higher bond strength when irradiated on continuous mode (p < 0.05). Fiber post and Panavia F presented higher bond strength associated to pulsed mode. The mode seems not to make a significant difference. CONCLUSIONS: These results corroborate the importance of the post bond to dentin and root canal debris removal to increase the tooth longevity. It was shown that the dentin to post bond strength were enhanced by the diode laser irradiation either on continuous or pulsed modes.

Retrievability of implant-supported crowns when using three different cements: a controlled clinical trial.

PURPOSE: The purpose of this study was to analyze the removal of implant-supported crowns retained by three different cements using an air-accelerated crown remover and to evaluate the patients' response to the procedure. MATERIALS AND METHODS: This controlled clinical trial was conducted with 21 patients (10 women, 11 men; mean age: 51 ± 10.2 years) who had received a total of 74 implants (all placed in the posterior zone of the mandible). Four months after implant surgery, the crowns were cemented on standard titanium abutments of different heights. Three different cements (two temporary: Harvard TEMP and Improv; and one definitive: Durelon) were used and randomly assigned to the patients. Eight months later, one blinded investigator removed all crowns. The number of activations of the instrument (CORONAflex, KaVo) required for crown removal was recorded. The patients completed a questionnaire retrospectively to determine the impact of the procedure and to gauge their subjective perception. A linear regression model and descriptive statistics were used for data analysis. RESULTS: All crowns could be retrieved without any technical complications or damage. Both abutment height (P = .019) and cement type (P = .004) had a significant effect on the number of activations, but the type of cement was more important. An increased total number of activations had no or only a weak correlation to the patients' perception of concussion, noise, pain, and unwillingness to use the device. CONCLUSIONS: Cemented implant crowns can be removed, and the application of an air-accelerated device is a practicable method. A type of cement with appropriate retention force has to be selected. The impact on the patients' subjective perception should be taken into account.

Capacidad de sellado de tres agentes cementantes para restauraciones coronarias indirectas / Sealing ability of three luting agents used for cementation of indirect coronal restorations

Objetivo: comparar ex vivo, por medio de un modelo de filtración bacteriana, la capacidad de sellado de un ionómero vítreo modificado con resinas, de un ionómero vítreo convencional y de un cemento de fosfato de cinc, utilizados para la cementación de coronas coladas (AU). Materiales y métodos: un total de 30 premolares humanos sanos, extraídos, fueron preparados de forma estandarizada para recibir una corona metálica con terminación en chamfer sobre dentina. Se realizaron impresiones, se vaciaron en densita tipo IV, se enceraron y se colaron en aleación de oro tipo III. Luego fueron separadas al azar en tres grupos de 10 (n=10) especímenes cada uno. Las coronas del grupo 1 fueron cementadas con Rely-X Luting Plus (3M/ESPE); y las del grupo 2, con Ketac-Cem (3m/ESPE); y las del grupo 3 (control), con el cemento de fosfato de cinc Harvard Cement (Harvard Debtal International GmbH, Hoppengarten, Alemania). Todos los especímenes fueron termociclados. Posteriormente, la superficie metálica oclusal fue reducida 1 mm hasta exponer la dentina, y las muestras se esterilizaron en autoclave. El proceso de filtración se realizó por medio de un sistema de doble cámara con medio de cultivo. El medio de la cámara superior se inoculó con E. faecalis y el sistema fue incubado durante 60 días. En la cámara inferior, la filtración bacteriana se controló diariamente. Los datos registrados fueron analizados por medio de las pruebas de Kaplan-Meyer y de Fischer, con un nivel de significación de P<0,05. Resultados: el tiempo de supervivencia para Rely-X Luting Plus no pudo ser estimado, ya que fue superior a los 60 días, tiempo máximo de duración de la experiencia. Para Ketac-Cem fue de 60 días, con un intervalo de confianza (95 por ciento) de 29,6-90,4. Y para Harvard Cement fue de 40 días, con un intervalo de confianza de 32,6-47,4. Las diferencias entre los grupos fueron estadísticamente significativas. Conclusión: Rely-X Plus demostró una capacidad de sellado superior.

In vitro comparisons of casting retention on implant abutments among commercially available and experimental castor oil-containing dental luting agents.

STATEMENT OF PROBLEM: Although cement-retained implant prostheses are widely used, the quantification of optimal retention remains controversial, and new dental luting agents should be evaluated. PURPOSE: The purpose of this study was to compare, in vitro, the casting retention on implant abutments after cementation with 3 commercially available luting agents and an experimental luting agent (castor oil polyurethane, COP) with variable weight percentages (wt%) of calcium carbonate (CaCO3). MATERIAL AND METHODS: Seventy-two palladium-silver cast copings were fabricated and divided into 6 groups: Temp Bond interim cement (TB); zinc phosphate cement (ZP); Rely X ARC resin cement (RX); pure COP (COP); COP + 10% wt% CaCO3 filler (COP 10); and COP + 50% wt% CaCO3 filler (COP 50). After cementation, the specimens were stored in distilled water at 37°C for 24 hours and subjected to removal force tests in a universal testing machine (5 kN; 0.5 mm/min). Statistical analyses were performed with the Kruskal-Wallis and Student-Newman-Keuls tests (α=.05). RESULTS: The median values of casting retention (N) were as follows: TB=57.20 ±10.4; ZP=343.56 ±50.3; RX=40.07 ±9.7; COP=258.98 ±41.4; COP 10=466.57 ±79.3; and COP 50=209.63 ±31.4. The Kruskal-Wallis test showed significant differences among the groups (P<.01). TB and RX had the lowest mean retention values; COP, COP 10, and COP 50 were equal to ZP, and COP 10 had the highest retention. CONCLUSIONS: The casting retention on implant-abutments provided by COP was similar to that of copings cemented with zinc phosphate and may be influenced by the addition of calcium carbonate.

Treatment of congenitally missing maxillary lateral incisors: an interdisciplinary approach.

Dentists have several treatment options when restoring patients with congenitally missing maxillary lateral incisors. Endosseous implant therapy combined with orthodontics can achieve predictable outcomes while meeting patient expectations. This case report exhibits an interdisciplinary approach involving orthodontics, implant surgery, and prosthodontics to resolve this common dental concern.

A 5-year prospective radiographic evaluation of marginal bone levels adjacent to parallel-screw cylinder machined-neck implants and rough-surfaced microthreaded implants using digitized panoramic radiographs.

OBJECTIVE: The purpose of this split-mouth study was to compare macro- and microstructure implant surfaces at the marginal bone level over five years of functional loading. MATERIALS AND METHODS: From January to February 2006, 133 implants (70 rough-surfaced microthreaded implants and 63 machined-neck implants) were inserted in the mandible of 34 patients with Kennedy Class I residual dentitions and followed until December 2011. Marginal bone level was radiographically determined at six time points: implant placement (baseline), after the healing period, after six months, and at two years, three years, and five years follow-up. RESULTS: Median follow-up time was 5.2 years (range: 5.1-5.4). The machined-neck group had a mean crestal bone loss of 0.5 mm (0.0-2.3) after the healing period, 1.1 mm (0.0-3.0) at two years follow-up, and 1.4 mm (0.0-2.9) at five years follow-up. The rough-surfaced microthreaded implant group had a mean bone loss of 0.1 mm (-0.4 to 2.0) after the healing period, 0.5 mm (0.0-2.1) at two years follow-up, and 0.7 mm (0.0-2.3) at five years follow-up. The two implant types showed significant differences in marginal bone levels. CONCLUSIONS: Rough-surfaced microthreaded design caused significantly less loss of crestal bone levels under long-term functional loading in the mandible when compared to machined-neck implants.

Influence of core-finishing intervals on tensile strength of cast posts-and-cores luted with zinc phosphate cement

The core finishing of cast posts-and-cores after luting is routine in dental practice. However, the effects of the vibrations produced by the rotary cutting instruments over the luting cements are not well-documented. This study evaluated the influence of the time intervals that elapsed between the cementation and the core-finishing procedures on the tensile strength of cast posts-and-cores luted with zinc phosphate cement. Forty-eight bovine incisor roots were selected, endodontically treated, and divided into four groups (n = 12): GA, control (without finishing); GB, GC, and GD, subjected to finishing at 20 minutes, 60 minutes, and 24 hours after cementation, respectively. Root canals were molded, and the resin patterns were cast in copper-aluminum alloy. Cast posts-and-cores were luted with zinc phosphate cement, and the core-finishing procedures were applied according to the groups. The tensile tests were performed at a crosshead speed of 0.5 mm/min for all groups, 24 hours after the core-finishing procedures. The data were subjected to one-way analysis of variance (ANOVA) and Tukey's test (α = 0.05). No significant differences were observed in the tensile strengths between the control and experimental groups, regardless of the time interval that elapsed between the luting and finishing steps. Within the limitations of the present study, it was demonstrated that the core-finishing procedures and time intervals that elapsed after luting did not appear to affect the retention of cast posts-and-cores when zinc phosphate cement was used.

Comparison of different ultrasonic vibration modes for post removal

This in vitro study compared different ultrasonic vibration modes for intraradicular cast post removal. The crowns of 24 maxillary canines were removed, the roots were embedded in acrylic resin blocks, and the canals were treated endodontically. The post holes were prepared and root canal impressions were taken with self-cured resin acrylic. After casting, the posts were cemented with zinc phosphate cement. The samples were randomly distributed into 3 groups (n=8): G1: no ultrasonic vibration (control); G2: tip of the ultrasonic device positioned perpendicularly to core surface and close to the incisal edge; and G3: tip of the ultrasonic device positioned perpendicularly to core surface at cervical region, close to the line of cementation. An Enac OE-5 ultrasound unit with an ST-09 tip was used. All samples were submitted to the tensile test using an universal testing machine at a crosshead speed of 1 mm/min. Data were subjected to one-way ANOVA and Tukey's post-hoc tests (α=0.05). Mean values of the load to dislodge the posts (MPa) were: G1 = 4.6 (± 1.4) A; G2 = 2.8 (± 0.9) B, and G3= 0.9 (± 0.3) C. Therefore, the ultrasonic vibration applied with the tip of device close to the core's cervical area showed higher ability to reduce the retention of cast post to root canal.

Este estudo in vitro comparou diferentes modos de vibração ultra-sônica na remoção de pinos intra-radiculares fundidos. As coroas de 24 caninos superiores foram removidas, as raízes foram incluídas em blocos de resina acrílica e tratadas endodonticamente. Os espaços para os pinos intra-radiculares foram preparados e depois moldados com resina acrílica autopolimerizável. Após a fundição, os pinos intra-radiculares foram cimentados com cimento de fosfato de zinco. As amostras foram distribuídas aleatoriamente em três grupos (n=8): G1: sem vibração ultra-sônica (controle), G2: ponta do aparelho ultra-sônico posicionada perpendicularmente à superfície do núcleo e perto da borda incisal e G3: ponta do aparelho ultra-sônico posicionada perpendicularmente à superfície do núcleo na região cervical, perto da linha de cimentação. Uma unidade de ultra-som Enac OE-5 com uma ponta ST-09 foi usada. Todas as amostras foram submetidas ao teste de tração utilizando máquina universal de ensaios a uma velocidade de 1 mm/min. Os dados foram submetidos aos testes ANOVA e Tukey post-hoc (α = 0,05). Os valores médios de carga para deslocar os pinos (MPa) foram: G1 = 4,6 (± 1,4) A; G2 = 2,8 (± 0,9), B e G3 = 0,9 (± 0,3) C. Portanto, a vibração ultra-sônica aplicada com a ponta do dispositivo perto da zona cervical do núcleo apresentou maior capacidade de reduzir a retenção de pinos metálicos fundidos no canal radicular.

Surface roughness of orthodontic band cements with different compositions

OBJECTIVES: The present study evaluated comparatively the surface roughness of four orthodontic band cements after storage in various solutions. MATERIAL AND METHODS: Eight standardized cylinders were made from 4 materials: zinc phosphate cement (ZP), compomer (C), resin-modified glass ionomer cement (RMGIC) and resin cement (RC). Specimens were stored for 24 h in deionized water and immersed in saline (pH 7.0) or 0.1 M lactic acid solution (pH 4.0) for 15 days. Surface roughness readings were taken with a profilometer (Surfcorder SE1200) before and after the storage period. Data were analyzed by two-way ANOVA and Tukey's test (comparison among cements and storage solutions) or paired t-test (comparison before and after the storage period) at 5 percent significance level. RESULTS: The values for average surface roughness were statistically different (p<0.001) among cements at both baseline and after storage. The roughness values of cements in a decreasing order were ZP>RMGIC>C>R (p<0.001). After 15 days, immersion in lactic acid solution resulted in the highest surface roughness for all cements (p<0.05), except for the RC group (p>0.05). Compared to the current threshold (0.2 µm) related to biofilm accumulation, both RC and C remained below the threshold, even after acidic challenge by immersion in lactic acid solution. CONCLUSIONS: Storage time and immersion in lactic acid solution increased the surface roughness of the majority of the tested cements. RC presented the smoothest surface and it was not influenced by storage conditions.

Microleakage of adhesive and nonadhesive luting cements for stainless steel crowns.

PURPOSE: This study's purpose was to compare the ability of 5 luting cements to reduce microleakage at stainless steel crown (SSC) margins on primary molar teeth. METHODS: Standard preparations were performed on 100 extracted primary molar teeth for SSC restoration. After fitting SSCs, samples were randomly divided into 5 groups of 20 teeth each, which were cemented with nonadhesive cement consisting of polycarboxylate (PC) or zinc phosphate (ZP), or with adhesive cement consisting of glass ionomer (GIC), resin-modified glass ionomer cement (RMGIC), or RMGIC with a bonding agent (RMGIC+DBA). After aging and thermocycling, the specimens were placed in 1% methylene blue, sectioned, and evaluated under a digital microscope. The data were compared between groups with the t test, analysis of variance, and the least significant difference test. RESULTS: Microleakage with adhesive cements was significantly lower than with nonadhesive cements (P<.05). Differences between cements were statistically significant at P<.001. RMGIC+DBA showed the lowest microleakage, followed in increasing order by RMGIC, GIC, and ZP. The PC cement showed the greatest microleakage. CONCLUSIONS: Adhesive cements were more effective in reducing microleakage in stainless steel crowns than nonadhesive cements. Use of a bonding agent with a resin-modified glass ionomer cement yielded better results than using the latter alone.

Effect of eugenol-based endodontic sealer on the adhesion of intraradicular posts cemented after different periods

OBJECTIVE: This study evaluated in vitro the influence of an eugenol-based sealer (EndoFill) on the retention of stainless steel prefabricated posts cemented with zinc phosphate and resin-based (Panavia F) cements after different periods of root canal obturation, using the pull-out test. MATERIAL AND METHODS: Sixty upper canines were decoronated and the roots were embedded in resin blocks. The specimens were distributed into 3 groups, according to the period elapsed between canal obturation and post cementation: Group I - immediately; Group II - 72 h and Group III - 4 months. The groups were subdivided according to the type of cement used for post cementation: A - zinc phosphate and B - Panavia F. Following the experimental periods, specimens were subjected to pullout test in an Instron machine with application of tensile force at a crosshead speed of 0.5 mm/min until post dislodgement. The maximum forces required for post removal were recorded (kN) and means were subjected to statistical analysis by 2-way ANOVA and Tukey-Kramer test (á=0.001) RESULTS: There were statistically significant differences (p<0.01) between the posts cemented with zinc phosphate cement (0.2112 kN) and Panavia F (0.0501 kN). However, no statistically significant differences (p>0.05) were found between the three post cementation periods, regardless of the cement. CONCLUSIONS: It was concluded that the eugenol-based sealer influenced the tensile strength of the posts cemented with the resin cement, but had no influence on the time waited between root canal obturation and post space preparation/post cementation.

Materiales restauradores con desprendimiento de fluoruro y la reincidencia de caries: parte I: antecedentes / Fluoride releasing restorative materials and caries re-incidence: part I: background

El desarrollo de los materiales dentales restauradores con desprendimiento de fluoruro y la prevención de la reincidencia de caries, depende de muchos factores y no necesariamente sólo del efecto terapéutico del fluoruro sobre la estructura del diente. La relación de estos materiales con la presencia de caries secundaria es revisada en este artículo, así como también la evolución de la incorporación de fluoruro a distintos materiales dentales restauradores.

Correlation between margin fit and microleakage in complete crowns cemented with three luting agents

Microleakage can be related to margin misfit. Also, traditional microleakage techniques are time-consuming. This study evaluated the existence of correlation between in vitro margin fit and a new microleakage technique for complete crowns cemented with 3 different luting agents. Thirty human premolars were prepared for full-coverage crowns with a convergence angle of 6 degrees, chamfer margin of 1.2 mm circumferentially, and occlusal reduction of 1.5 mm. Ni-Cr cast crowns were cemented with either zinc phosphate (ZP) (S.S. White), resin-modified glass-ionomer (RMGI) (Rely X Luting Cement) or a resin-based luting agent (RC) (Enforce). Margin fit (seating discrepancy and margin gap) was evaluated according to criteria in the literature under microscope with 0.001 mm accuracy. After thermal cycling, crowns were longitudinally sectioned and microleakage scores at tooth-cement interface were obtained and recorded at ×100 magnification. Margin fit parameters were compared with the one-way ANOVA test and microleakage scores with Kruskal-Wallis and Dunn's tests (alpha=0.05). Correlation between margin fit and microleakage was analyzed with the Spearman's test (alpha=0.05). Seating discrepancy and marginal gap values ranged from 81.82 µm to 137.22 µm (p=0.117), and from 75.42 µm to 78.49 µm (p=0.940), respectively. Marginal microleakage scores were ZP=3.02, RMGI=0.35 and RC=0.12 (p<0.001), with no differences between RMGI and RC scores. The correlation coefficient values ranged from -0.27 to 0.30 (p>0.05). Conclusion: Margin fit parameters and microleakage showed no strong correlations; cast crowns cemented with RMGI and RC had lower microleakage scores than ZP cement.

Effect of ultrasonic instrumentation on the bond strength of crowns cemented with zinc phosphate cement to natural teeth: an in vitro study

Several studies have reported the benefits of sonic and/or ultrasonic instrumentation for root debridement, with most of them focusing on changes in periodontal clinical parameters. The present study investigated possible alterations in the tensile bond strength of crowns cemented with zinc phosphate cement to natural teeth after ultrasonic instrumentation. Forty recently extracted intact human third molars were selected, cleaned and stored in physiologic serum at 4°C. They received standard preparations, at a 16º convergence angle, and AgPd alloy crowns. The crowns were cemented with zinc phosphate cement and then divided into four groups of 10 teeth each. Each group was then subdivided into two subgroups, with one of the subgroups being submitted to 5,000 thermal cycles ranging from 55 ± 2 to 5 ± 2°C, while the other was not. Each group was submitted to ultrasonic instrumentation for different periods of time: group 1 - 0 min (control), group 2 - 5 min, group 3 - 10 min, and group 4 - 15 min. Tensile bond strength tests were performed with an Instron testing machine (model 4310). Statistical analysis was performed using ANOVA and Tukey's test at the 5 percent level of significance. A significant reduction in the tensile bond strength of crowns cemented with zinc phosphate and submitted to thermal cycles was observed at 15 min (196.75 N versus 0 min = 452.01 N, 5 min = 444.23 N and 10 min = 470.85 N). Thermal cycling and ultrasonic instrumentation for 15 min caused a significant reduction in tensile bond strength (p < .05).

Assessment of the tensile strength of hexagonal abutments using different cementing agents

The aim of this study was to assess the uniaxial tensile strength after thermal cycling in replicas of CeraOne®abutments (abutment and coping sets), using four types of cements (n = 10). A zinc phosphate cement (Fosfato de Zinco®/ SSW), a resin-modified glass ionomer cement (RelyX®luting / 3M-ESPE), a zinc oxide-eugenol cement (ZOE®/ SSW) and a zinc oxide cement without eugenol (TempBond NE®/ KERR) were used. After cementation, the samples were submitted to thermal cycles (1,000 cycles, 5ºC ± 2º to 55ºC ± 2º) for thirty seconds in each bath. Next, the samples were submitted to the tensile test in a universal test machine (0.5 mm/min). The data were submitted to ANOVA and the Tukey-Kramer test (p < 0.05), and statistically significant difference was found among the cements. The highest tensile strength mean value found was for zinc phosphate cement (33.6 kgf) followed by the resin-modified glass ionomer cement (20.5 kgf), zinc oxide-eugenol cement (8.4 kgf) and the temporary cement (3.1 kgf). Therefore, it was found that the permanent cements presented higher tensile strength, and the temporary cement could be used in situations requiring reversibility and the removal of cemented dental implant-supported prostheses.

Effect of eugenol-based endodontic cement on the adhesion of intraradicular posts

No presente estudo avaliou-se, in vitro, a influência do cimento endodôntico à base de óxido de zinco e eugenol (EndoFill) na adesão de pinos intra-radiculares cimentados com cimento resinoso (Enforce) ou cimento fosfato de zinco. Vinte e quatro caninos superiores uniradiculares foram distribuídos em dois grupos e obturados com cimento a base de oxido de zinco e eugenol + cones de guta-percha ou somente cones de guta-percha (sem cimento). Em metade dos espécimes em cada grupo (n=6), os pinos intra-radiculares foram cimentados com cimento resinoso Enforce e na outra metade com cimento de fosfato de zinco. Os espécimes foram submetidos a ensaios de resistência à tração numa máquina Instron 4444, sendo os valores de força máxima necessária ao desprendimento dos retentores registrados e submetidos à análise estatística pelo teste de Kruskal-Wallis (p<0,01). Os pinos cimentos com cimento fosfato de zinco apresentaram valor médio de resistência à tração superior (353,4 N) ao dos pinos cimentados com Enforce (134,9 N). Em relação à influência do cimento à base de eugenol na retenção dos pinos intra-radiculares, houve diferença significante (p<0,01) somente entre os grupos cimentados com Enforce, sendo que nos canais obturados com EndoFill + guta-percha houve menor resistência à tração que nos canais obturados apenas com guta-percha (respectivamente 101,5 e 168,2 N). Conclui-se que o cimento à base de fosfato de zinco apresentou maior retenção que o cimento resinoso Enforce e que o cimento obturador contendo eugenol (EndoFill) somente afetou as propriedades adesivas do cimento resinoso.

An ex vivo evaluation of resin-modified glass polyalkenoates and polyacid-modified composite resins as orthodontic band cements.

OBJECTIVES: The objective of this ex vivo study was to assess the use of resin-modified glass polyalkenoates and polyacid-modified composite resins, as orthodontic band cements. MATERIALS AND METHOD: Plain stainless steel bands were cemented to 350 human extracted third molar teeth using 1 of 7 different cements. Following complete cement cure, half of each sample group was exposed to mechanical stress in a ball mill. Stressed and unstressed samples were tested in tension and the stress at which initial cement failure recorded. The mode of failure was recorded using an adhesive remnant evaluation. RESULTS: The mean band retention stresses offered by the cements studied ranged from 0.96 to 1.56 MPa. Fuji Ortho provided the highest mean band retention stress in "stressed" (1.56 MPa) and "unstressed" (1.45 MPa) states. Exposure to mechanical stress did not appear to significantly influence band retention or mode of cement failure for most cements. Fuji Ortho cement recorded the highest Weibull modulus for all cements tested. Virtually all samples failed at either the cement/enamel or cement band interface. CONCLUSIONS: Significant differences in band displacement stress values and mode of failure were demonstrated between the cements studied. However, generic comparisons were difficult to make.

Effect of cement types on the tensile strength of metallic crowns submitted to thermocycling

O objetivo deste estudo foi verificar a resistência à tração de coroas metálicas fixadas com diferentes cimentos e submetidas à termociclagem. Setenta e duas coroas foram fundidas com liga de Ni-Cr Verabond II e cimentadas em preparos padronizados com 8º de paredes laterais e acabamento cervical com ombro reto, ombro biseldo 20º e ombro chanfrado 45º. As coroas foram separadas em três grupos de oito elementos de acordo com os cimentos: fosfato de zinco (SS White), ionômero de vidro modificado por resina Vitremer (3M ) e resinoso Rely X (3M), e submetidas a 500 ciclos térmicos em banhos de 5ºC e 55ºC. A retenção foi avaliada de acordo com a carga de tração (kgf) necessária para separar a coroa do preparo, numa máquina Instron com velocidade de 0,5 mm/minuto. Os resultados submetidos à análise de variância e ao teste de Tukey (5 por cento) mostraram que a retenção mais eficiente foi obtida com o cimento resinoso, independentemente do tipo de acabamento cervical.

In vitro evaluation of the retention of composite fiber and stainless steel posts.

PURPOSE: This study compared the tensile retentive strength of composite fiber-reinforced dowels luted with a resin cement to stainless steel dowels luted with zinc phosphate cement. MATERIALS AND METHODS: The crowns of 40 extracted human mandibular premolars were removed with a separating disc 1-mm coronal to the cementoenamel junction. The teeth were randomly divided into 4 groups (n = 10). A post space was prepared in each specimen to a depth of 9 mm, using the drill supplied by the respective manufacturer. For the stainless steel post group, 1.25-mm-diameter posts were cemented with zinc phosphate cement. For the composite fiber reinforced groups, posts with diameters of 1.00, 1.25, and 1.50 mm were luted with a Bisphenol A-Glycidyl Methacrylate (BIS-GMA) resin bonding system (Jeneric/Pentron, Wallingford, CT) according to manufacturer specifications. The specimens were stored in a sealed container with a moist environment for 24 hours, placed in a fixture in an 801 Materials Test Systems (MTS) machine (MTS Systems Corp, Minneapolis, MN), and loaded in tension at a rate of 5.0 mm/min until failure. Differences among the 4 groups were determined using a one-way analysis of variance and Tukey-B post-hoc tests (alpha = 0.05). RESULTS: The mean loads to failure ranged from 43.9 +/- 10.4 kg for the stainless steel dowel group to 19.9 +/- 5.7 kg for the composite fiber-reinforced 1.00-mm-diameter group. The stainless steel post luted with zinc phosphate cement provided significantly greater tensile resistance than all composite fiber dowel groups. The retention of the 1.00-mm composite fiber-reinforced post was significantly less than the remaining groups. CONCLUSIONS: Under the conditions of this study, the stainless steel dowel luted with zinc phosphate cement provided significantly greater retention.

Fracturas radiculares por fuerzas compresivas de premolares con núcleos prefabricados / Root fractures of premolars with prefabricated posts due to compressive forces

En este estudio descriptivo comparativo de diseño no experimental, se evaluó la relación fuerza por área y volumen en las fracturas radiculares, aplicando fuerzas compresivas a dos tipos de núcleos prefabricados. Se seleccionaron 30 primeros premolares inferiores recién extraídos e hidratados. Se realizaron tratamientos endodóntico y obturaciones hasta el tercio apical. Se calcularon el área del conducto y el volumen del diente. Se clasificaron 15 dientes para Fill-Post (Filhol Dental) y 15 para Flexi-Post (Essencial Dental System). Se cementaron con fosfato de zinc y se sometieron a fuerzas compresivas con el Instron, hasta producir fractura radicular. Se hizo análisis clínico y radiográfico. Con la ayuda de la prueba de Chi se concluyó que las fracturas radiculares de los dientes con Fill-Post y Flexi-Post dependieron de la fuerza compresiva; igualmente, la resistencia a la fractura radicular dependió del tipo de poste; no se registró fractura de los postes radiculares