Influencia de los revestimientos dentales en la adaptación marginal e interna de las cofias metálicas. Estudio in vitro / Influence of dental investments on the marginal and internal adaptation of metal copings. In vitro study

Objetivo. Evaluar la influencia de diferentes marcas de revestimientos dentales en la adaptación marginal e interna de las cofias metálicas. Método. La investigación fue in vitro, analítico, experimental y transversal; para ello, se confeccionaron 48 cofias metálicas, las cuales fueron cementadas en dientes humanos previamente tallados, luego las cofias fueron cortadas mesio-distalmente para evaluar su adaptación. La adaptación fue evaluada usando un estereomicroscopio Leica DM6000M. Para determinar si hay diferencia en la adaptación marginal e interna se empleó el análisis de varianza, la prueba de comparación múltiple y la prueba de Duncan. Adicionalmente, la prueba de Fisher, se utilizó para evaluar la adaptación total. Resultados. La mejor adaptación marginal e interna de las cofias metálicas lo presenta el revestimiento Fórmula 1 (Whipmix), seguido del Castorit súper C (Dentaurum) y Bellasun (Bego). Conclusión. Los revestimientos dentales no mostraron influencia en la adaptación marginal; sin embargo, si mostraron influencia en la adaptación interna.

Objective. To evaluate the influence of different brands of dental investments on the marginal and internal adaptation of metal copings. Method. The research was in vitro, analytical, experimental and transversal. For this, 48 metal copings were made, which were cemented on previously carved human teeth, then the copings were cut mesio-distally to evaluate their adaptation. The adaptation was evaluated using a Leica DM6000M stereomicroscope. To determine if there is a difference between marginal and internal adaptation; the analysis of variance, the multiple comparison test and the Duncan test were used. Furthermore, Fisher's exact test was used to evaluate the total adaptation. Results. The best marginal and internal adaptation of metal copings is presented by the Formula 1 coating (Whipmix), followed by Castorit super C (Dentaurum) and Bellasun (Bego). Conclusion. Dental investments did not show influence on marginal adaptation; however, they did show influence on internal adaptation.

Adaptación marginal e interna de cofias fabricadas por métodos convencionales, CAD/CAM de fresado y sinterizado por láser / Marginal and internal adaptation of copings manufactured by conventional methods, CAD/CAM milling and laser sintering

Introducción: la adaptación marginal e interna de nuestras restauraciones fabricadas por fundición sistemas de fresado y sinterización láser es uno de los factores clínicos más importantes para el éxito de las prótesis fijas, previniendo el riesgo de microfiltración y enfermedad periodontal. Objetivo: evaluar la adaptación marginal e interna de cofias metálicas en aleación Cr-Co confeccionadas por técnicas convencionales, CAD/ CAM de fresado y sinterizado por láser. Material y métodos: estudio de tipo experimental, comparativo e in vitro. Se imprimió un modelo maestro en Cr-Co, proveniente del escaneo de un premolar preparado para corona completa, sobre el cual se diseñaron 30 cofias divididas en tres grupos: el primero que corresponde al grupo cofias fundidas fresadas en disco de cera A (A = 10), el segundo grupo cofias fresadas en disco de metal presinterizado B (B = 10) y el tercer grupo cofias impresas por sinterización láser C (C = 10). Se empleó la réplica de silicona, colocando silicona al interior de cada cofia, sobre el modelo maestro, simulando al cemento, mediante una máquina de ensayo universal se realizó una compresión de 50 N. Luego de retirar cada cofia se rellenaron con silicona pesada de adición, obteniendo una réplica de silicona. Se efectuaron dos cortes transversales en sentido vestíbulolingual y mesiodistal. Se observó el espesor de silicona VPS (vinil poliéter silicona) mediante un estereomicroscopio (Nikon SMZ745T), obteniendo valores en micrómetros. Para el análisis estadístico se utilizó el software SPSS 25 con el fin de realizar la prueba de normalidad y ANOVA de dos vías bajo un nivel de confianza del 95%. Resultados: el menor gap lo obtuvo el grupo de fresadas, seguido de las impresas y por último las fundidas por métodos convencionales. ANOVA de dos vías reveló diferencias estadísticamente significativas entre los tres grupos (p < 0.0001). Conclusiones: se encontró que el gap varía con cada método de fabricación, la técnica convencional de fundido mostró un mayor gap, ninguna excediendo el rango clínicamente aceptable (AU)

Introduction: the marginal and internal adaptation of our restorations manufactured by casting, milling systems and laser sintering is one of the most important clinical factors for the success of fixed prostheses, preventing the risk of microleakage and periodontal disease. Objective: evaluate the marginal and internal adaptation of metal copings in Cr-Co alloy made by conventional techniques, CAD/CAM milling and laser sintering. Material and methods: an experimental, comparative and in vitro study, a Cr-Co master model was printed from the scan of a premolar prepared for a full crown. An experimental, comparative and in vitro study, a Cr-Co master model was printed from the scan of a premolar prepared for a full crown, on which 30 caps divided into three groups were designed; the first group corresponds to the cast copings milled on a wax disc A (A = 10), the second group milled copings on a presintered metal disc B (B = 10) and the third group printed by laser sintering copings C (C = 10). The silicone replica was used, placing silicone inside each coping, on the master model, simulating cement, using a universal testing machine, a 50 N compression was performed. After removing each coping, they were filled with heavy addition silicone, obtaining a silicone replica. Two cross-sections were made in the buccolingual and mesiodistal direction., observing the thickness of the VPS (vinyl polyeter silicone) silicone using a stereomicroscope (Nikon SMZ745T), obtaining values in micrometers. For the statistical analysis, the SPSS 25 software was used in order to perform the normality and two-way ANOVA tests under a 95% confidence level. Results: the smallest gap was obtained by the milled group, followed by the printed ones and finally those cast by conventional methods. Two-way ANOVA revealed statistically significant differences between the three groups (p < 0.0001). Conclusions: the gap was found to vary with each fabrication method, the conventional casting technique showed a larger gap, none exceeding the clinically acceptable range (AU)

Comparison between stone and digital cast measurements in mixed dentition : Validity, reliability, reproducibility, and objectivity.

PURPOSE: To assess the validity, reliability, reproducibility, and objectivity of measurements on stone casts of patients with mixed dentitions compared to measurements on three-dimensional (3D) digital models derived from surface scans of the stone casts. METHODS: Pairs of stone casts of 30 young patients in their mixed dentition stage were included and processed into 3D digital models using an intraoral scanner (iTero Element 2; Align Technology, San Jose, CA, USA). Then an experienced and an inexperienced examiner independently performed measurements of five defined parameters, each in triplicate, both on the digital models with analysis software (OnyxCeph3™; Image Instruments, Chemnitz, Germany) and on the original casts with a vernier calliper. Paired t-tests were used for validity and interexaminer objectivity, Pearson correlation coefficients for intermethod reliability, and intraclass correlation coefficients (ICCs) for reproducibility testing. RESULTS: Significant (p < 0.05) intermethod differences were identified for four parameters, but only the differences for overbite and intermolar distance exceeded the threshold of clinical relevance (≥ 0.5 mm). Intermethod reliability was high and method error invariably lower for the digital measurements and for the experienced examiner. Both examiners achieved ICCs > 0.907 with both methods. Interexaminer variation involved significant differences for all parameters but one (intermolar distance) on the stone casts and for three parameters on the digital models. CONCLUSION: Measurements performed on digital models of mixed dentitions can yield clinically acceptable outcomes with OnyxCeph3™ software. Both the digital and the analogue measurements were highly reproducible and reliable. Objectivity of the measurements could not be confirmed, as operator experience did make a difference.

Comparing Castability of Nickel-Chromium, Cobalt-Chromium, and Non-Precious Gold Color Alloys, Using two Different Casting Techniques.

Statement of the Problem: The castability of nonprecious gold color alloy using torch/ centrifugal and induction/vacuum-pressure casting techniques has not been studied yet. Purpose: This study was conducted to compare the castability of nickel chromium, cobalt-chromium and nonprecious gold color alloy using torch/centrifugal and induction/ vacuum-pressure casting techniques. Materials and Method: In this in vitro study, a total number of 54 identical acrylic wax meshes were prepared and divided into 6 different groups of 9 each. Group 1: nickel-chromium alloy, which was casted with induction technique. Group 2: nickel-chromium alloy was casted with centrifugal technique. Group 3: cobalt-chromium alloy was casted with induction technique. Group 4: cobalt-chromium alloy was casted with centrifugal technique. Group 5: nonprecious gold color alloy was casted with induction technique. Group 6: nonprecious gold color alloy was casted with centrifugal technique. Then castability of specimens was measured using modified Whitlock's method. The results were analyzed using two way ANOVA and post hoc tests. Results: ANOVA test revealed no statistically significant difference between different alloys with a p Value of 0.313. Moreover, it represented no significant differences within the groups regarding alloy types and casting techniques with a p Value of 0.511 and 0.682, respectively. Conclusion: No significant difference was found in the castability value of nickel-chromium, cobalt-chromium, and nonprecious gold color alloys. In addition, the castability value of three alloys tested in this study was not different by using torch/centrifugal or induction/vacuum-pressure casting machines.

Herramientas digitales para la obtención de registros, posicionamiento y articulación virtual de modelos / Digital tools for obtaining records, positioning and virtual articulation of casts

La siguiente revisión bibliográfica busca describir las alternativas digitales disponibles para la obtención de registros, posicionamiento y articulación virtual de modelos junto con ejemplificar algunos softwares que permitan la implementación de estas tecnologías en su trabajo diario. Se realizó una búsqueda de literatura en las bases de datos: Pubmed, LILACS, SciELO y Cochrane Library. Finalmente, luego de ser filtrados los resultados, se utilizaron un total de 36 publicaciones. Existen diversas herramientas disponibles actualmente para digitalizar una gran cantidad de técnicas que solo hasta hace algunos años eran realizadas manualmente por un operador. Algunas de ellas, facilitan una inmersión paulatina al mundo virtual del odontólogo novato ya que carecen de altos costos y recur-sos. Se sugiere que los odontólogos implementen estas tecnologías en su trabajo habitual según cada caso particular.

The following literature review seeks to bring together the digital alternatives available for obtaining records, positioning and virtual articulation of models together with exemplifying some softwares to allow the implementation of these technologies in their daily workflow. A literature search was carried out in the following databases: Pubmed, LILACS, SciELO and Cochrane Library. Finally, after the results were filtered, a total of 36 publications were used. There are various tools currently available to digitize a large number of techniques that were only performed manually by an operator until a few years ago. Some of them facilitate a gradual immersion into the virtual world of the novice dentist since they lack high costs and resources. It is suggested that dentists implement these technologies into daily dental practice according to each particular case.

Influence of manufacturing technique on marginal fit of cobalt chromium restorations: An in-vitro Study.

Background: For porcelain fused to metal restorations, computer-aided designing (CAD) / computer-aided manufacturing (CAM) systems claim to provide improved marginal fit than conventional casting systems. Aim: The present in-vitro study was conducted to compare the marginal fit of cobalt-chromium alloy copings fabricated with milled wax/lost wax, CAD/CAM milling/sintering and direct metal laser sintering (DMLS) techniques. Materials and Method: A metal die simulating a prepared tooth was fabricated and scanned using an optical scanner. A standardized coping design was used to manufacture 30 alloy copings divided into three groups of ten copings each i.e., milled wax/lost wax, milling/sintering and DMLS. A modified replica technique was used to measure the silicone film thickness at four pre-designated points on the margin under a digital stereo-microscope. Statistical Analysis: The mean values for marginal gap were compared using one-way Analysis of Variance (ANOVA) followed by Tukey-Kramer test for all pair-wise comparisons. Results: The mean marginal gap values obtained by using milled wax/lost wax technique, milling/sintering technique and DMLS technique were 88.44 µm, 61.135 µm and 55.39 µm, respectively. One-way ANOVA showed a significant difference for marginal fit between the lost wax group and the other two test groups (P < 0.05). Conclusion: The cobalt-chromium alloy copings fabricated using DMLS techniques displayed significantly better marginal fit than the milled wax/lost wax technique which may contribute to their improved clinical performance. DMLS technique produces restorations with an improved marginal fit and may be preferred by clinicians over milling and conventional casting techniques.

Assessment of the accuracy of laser-scanned models and 3-dimensional rendered cone-beam computed tomographic images compared to digital caliper measurements on plaster casts.

PURPOSE: This study investigated the accuracy of laser-scanned models and 3-dimensional (3D) rendered cone-beam computed tomography (CBCT) compared to the gold standard (plaster casts) for linear measurements on dental arches. MATERIALS AND METHODS: CBCT scans and plaster models from 30 patients were retrieved. Plaster models were scanned by an Emerald laser scanner (Planmeca, Helsinki, Finland). Sixteen different measurements, encompassing the mesiodistal width of teeth and both arches' length and width, were calculated using various landmarks. Linear measurements were made on laser-scanned models using Autodesk Meshmixer software v. 3.0 (Autodesk, Mill Valley, CA, USA), on 3D-rendered CBCT models using OnDemand 3D v. 1.0 (Cybermed, Seoul, Korea) and on plaster casts by a digital caliper. Descriptive statistics, the paired t-test, and intra- and inter-class correlation coefficients were used to analyze the data. RESULTS: There were statistically significant differences between some measurements on plaster casts and laser-scanned or 3D-rendered CBCT models (P<0.05). Molar mesiodistal width and mandibular anterior arch width deviated significantly different from the gold standard in both methods. The largest mean differences of laser-scanned and 3D-rendered CBCT models compared to the gold standard were 0.12±0.23 mm and 0.42±0.53 mm, respectively. Most of the mean differences were not clinically significant. The intra- and inter-class correlation results were acceptable for all measurements (>0.830) and between observers (>0.801). CONCLUSION: The 3D-rendered CBCT images and laser-scanned models were useful and accurate alternatives to conventional plaster models. They could be used for clinical purposes in orthodontics and prostheses.

Inflammatory Response to Cobalt-Chromium Alloys Fabricated With Different Techniques.

OBJECTIVES: To explore the in vitro cytokine expression of human peripheral blood mononuclear cells exposed to cobalt-chromium alloys, manufactured with different techniques, in comparison with commercially pure titanium grade 4 and titanium alloy grade 23. MATERIAL AND METHODS: Peripheral blood mononuclear cells (PBMC) were collected from 10 healthy blood donors and exposed to machine-ground coin-shaped: (a) cobalt-chromium (Co-Cr) specimens (n = 5) manufactured by four techniques, i.e. cast, milled, laser melted and presintered milled; (b) commercially pure titanium grade 4; and (c) titanium alloy grade 23. The cells were cultured for 4, 24 and 72 hours followed by investigations of pro- and anti-inflammatory cytokine release using Bio-Plex Pro™. RESULTS: In general, the PBMC produced significantly more cytokines when exposed to the cast and presintered milled Co-Cr materials compared to laser melted, milled Co-Cr and titanium materials. CONCLUSIONS: Within the limitation of the present study, it may be suggested that cast and presintered milled cobalt-chromium alloys provoke a stronger inflammatory response compared to milled and laser melted cobalt-chromium alloys and titanium materials.

In vitro investigations on retention force behavior of conventional and modern double crown systems.

OBJECTIVE: This study aimed to investigate the effects of long-term use on the retention force and wear behavior of double crown systems. METHODS: Based on a common double crown design sixty pairs of telescopic crowns were fabricated and divided into six groups, each consisting ten samples: "Gold standard" cast gold alloy primary and secondary crown (GG) and cast non-precious alloy (NN), computer-aided design (CAD)/computer-aided manufacturing (CAM)-milled zirconia primary crown and galvanoformed secondary crown (ZG), CAD/CAM-milled non-precious alloy primary and secondary crown (CC NN), CAD/CAM-milled zirconia primary crown and non-precious alloy secondary crown (CC ZN) and CAD/CAM-milled zirconia primary crown and polyetheretherketone (PEEK) secondary crown (CC ZP). In the constant presence of artificial saliva, all samples were subjected to 10,000 joining-separation cycles at a velocity of 120 mm/min. Wear was analyzed by reflected light microscopy and confocal microscopy before and after artificial aging. RESULTS: Retention force losses were observed in each group after long-term use, with significant losses in the groups ZG and CC ZP (pZG = 0.01, pCC ZP = 0.049). During artificial aging, no significant differences in pull-off force were recorded for groups GG, NN and CC ZN. Regarding wear, merely the Y-TZP primary crowns of the CC ZP group displayed no surface changes. SIGNIFICANCE: All tested production methods and material combinations seem to be suitable for clinical practice. CAD/CAM technology allows similarly predictable results to be achieved as the gold standard. Confocal microscopy is recommended for surface examinations of double crowns.

Adaptación de cofias Co-Cr fabricadas por colado por inducción y fusión selectiva láser en CAD/CAM con escaneo clínico / Adaptation of Co-Cr copings made by induction casting and selective laser melting in CAD/CAM with clinical scanning

RESUMEN La técnica de cera perdida colada por centrifugación por inducción (CPCI) y fusión selectiva láser (SLM) en diseño y fabricación asistida por computador (CAD/CAM) con escaneo clínico, son técnicas para fabricar cofias de Cobalto-Cromo (Co-Cr), poseen diferentes procesos de elaboración. Objetivo: Evaluar in vitro la adaptación marginal e interna de cofias metálicas de Co-Cr confeccionadas sobre una línea de terminación chámfer con la técnica CPCI y SLM en CAD/CAM con escaneo clínico. Material y Métodos: Se confeccionó un modelo maestro de forma de premolar de Co-Cr en CAD/CAM con línea de terminación chamfer. Con un escáner clínico se escaneó el modelo maestro y se obtuvo 13 cofias Co-Cr fabricadas en SLM. Se tomaron impresiones para obtener modelos en yeso tipo IV donde se fabricaron 13 cofias de Co-Cr con técnica CPCI. La adaptación marginal e interna se evaluó usando la técnica de réplica de silicona, las muestras fueron divididas en segmentos: vestíbulo-palatino y mesio-distal y fueron evaluadas mediante estéreomicroscopio. Resultados: La discrepancia marginal e interna fueron menores para el grupo de CPCI en comparación a la técnica SLM en CAD/CAM con escaneo clínico. Además los resultados obtenidos para la adaptación marginal fueron menores a 120 μm y la adaptación interna menor a 350 μm para ambas técnicas. Conclusiones: La adaptación marginal e interna en la técnica CPCI en comparación con SLM en CAD/CAM con escaneo clínico fueron mejores con diferencia estadísticamente significativa (p<0.05). Además los resultados obtenidos se encontraban dentro de los parámetros clínicamente aceptables.

SUMMARY The technique of lost wax cast by induction centrifugation (CPCI) and selective laser fusion (SLM) in design and computer-aided manufacturing (CAD / CAM) with clinical scanning, are techniques for manufacturing cobalt-chromium copings (Co-Cr), have different production processes. Objective: To evaluate, in vitro, the marginal and internal adaptation of Co-Cr metal copings made on a chamfer termination line with the CPCI and SLM technique in CAD / CAM with clinical scanning. Material and Methods: A master model of Co-Cr premolar shape was made in CAD / CAM with chamfer termination line. With a clinical scanner, the master model was scanned and 13 Co-Cr copings manufactured in SLM were obtained. Impressions were taken to obtain models in type IV plaster where 13 Co-Cr copings with CPCI technique were manufactured. The marginal and internal adaptation was evaluated using the silicone replica technique, the samples were divided into segments: vestibulo-palatal and mesio-distal and were evaluated by stereo microscope. Results: The marginal and internal discrepancies were lower for the CPCI group compared to the SLM technique in CAD / CAM with clinical scanning. In addition, the results obtained for the marginal adaptation were less than 120 μm and the internal adaptation less than 350 μm for both techniques. Conclusions: The marginal and internal adaptation in the CPCI technique compared to SLM in CAD/CAM with clinical scan were better with statistically significant difference (p <0.05). In addition, the results obtained were within the clinically acceptable paramenters.

A new dental casting technique for production of void-free dental models.

PURPOSE: An essential of successful dental prosthesis is dental models. Voids present in dental models decreases accuracy and strength. This study investigates void formation in models fabricated by a new technique. The technique described in the study was based upon increasing soaking time of gypsum powder in water. MATERIALS AND METHODS: Voids in hand mixed, hand mixed after a soaking time of 1.5 minutes and vacuum mixed samples were examined. The voids were counted via a stereomicroscope and diameters of voids were recorded in 2 categories (0.01-0.05mm, 0.051-0.1mm). The amounts of voids were compared between the samples prepared with 3 methods. RESULTS: The samples prepared by conventional hand mixing method had the highest total number of voids and smaller voids. There was no significant difference between the amount of voids in the samples prepared by soaking powder in water and by mixing under vacuum. CONCLUSION: Soaking gypsum powder in water for 1.5 minutes before mixing may be an alternative to mixing gypsum under vacuum to avoid void formation in dental models.

Sex Identification Based on Tooth Crown Trait Analysis Among the Mongoloid Race

Abstract Objective: To determine whether anterior and posterior tooth crown traits exhibit sexual dimorphism and identify traits characteristic to the Mongoloid race, especially among the Indonesian population. Material and Methods: This study cross-sectional study analyzed 108 dental casts from 36 males and 72 females. The traits analyzed included winging, shoveling, double shoveling, canine mesial ridge, canine distal accessory ridge, hypocone, metaconule, Carabelli's cusp, protostylid, metaconulid, enteconulid, and hypoconulid. All tooth crown traits were scored based on the ASUDAS scoring system. Descriptive statistics were used to calculate the absolute and relative frequencies. The Chi-square tests was used to determine significant differences in anterior and posterior tooth crown traits between males and females. Level of significance was set at 5%. Results: None of the traits showed sexual dimorphism. Moreover, the most common traits among the Mongoloid race were hypocone (94.4%) and shoveling (86.1%). Conclusion: Although none of the traits exhibited sexual dimorphism, most of them had a higher incidence among females than males. Nonetheless, further research including adequate samples and a similar number of females and males, is needed, especially for population studies.

Analysis of the Mechanical Behavior and Surface Rugosity of Different Dental Die Materials.

AIM: This work evaluated the mechanical and surface behavior of different die materials. The studied materials are polyurethane resin Exakto-Form (Bredent), Gypsum type IV, Fuji Rock EP (Gc), and Durone (Dentsply). MATERIALS AND METHODS: Two metallic matrices molded in polyvinyl siloxane provided 30 cylindrical test specimens for the diametral compression test and 30 hemispherical test specimens for the surface rugosity test. The cylindrical test specimens were submitted to tests of diametral compression strength using a DL2000 universal assay machine, with a load cell of 2000 Kgf and constant speed of 1 mm/min connected to the software. Kruskal-Wallis and Dunn's nonparametric tests were used to analyze the results. The hemispheres were submitted to the surface rugosity assay using a SJ201-P rugosimeter with a sensitivity of 300 µm, speed of 0.5 mm/s, and cut-off of 0.8 mm, and the readings were taken on the convex surface of the test specimens and metallic matrix. Results were analyzed using with Fisher's least significant differences test (LSD) and Dunnett's test. RESULTS: Kruskal-Wallis test showed significant difference between die materials for diametral compression strength (P = 0.002). Dunn's test showed significantly higher values for modified polyurethane resin (Exakto-Form). The gypsum type IV, which did not significantly differ regarding diametral compression strength, showed 34.0% (Durone) and 42.7% (Fuji Rock) lower values in comparison to Exakto-Form. CONCLUSION: Within the parameters adopted in this study, it is possible to conclude that Exakto-Form polyurethane resin showed higher resistance to compression and was closer to the metallic matrix rugosity, and, along with the gypsum type IV Durone, showed better reproducibility of details relative to the Fuji Rock.

Reinforcement of provisional restoration with cast metal framework: A case report / 대한치과보철학회지

Provisional restoration plays an important role in the process of restoration with fixed partial denture by providing protection and restoring function and esthetics of abutment tooth. This is especially true in patients requiring use of provisional prosthesis for a long term. However, such situations may lead to higher possibility of provisional prosthesis fracture, and if expected so, reinforcement of provisional prosthesis should be considered. In this article, a patient requiring prosthetic treatment with increase of vertical dimension of occlusion was introduced. Due to increased vertical dimension of occlusion, the provisional restoration was expected to withstand relatively larger amount of load during a relatively long observation period. In order to minimize possible occurrence of fracture, reinforcement of the provisional restoration was sought by insertion of cast-metal framework and by using bis-acryl resin. The reinforced provisional restoration showed satisfactory results during the observation period of 4 months.

Comparison of digital models generated from three-dimensional optical scanner and cone beam computed tomography

PURPOSE: The objective of this study was to compare the accuracy of digital models from 3 dimentional (3D) optical scanner and cone beam computed tomography (CBCT). MATERIALS AND METHODS: We obtained digital models from 11 pairs of stone casts using a 3D optical scanner and a CBCT, and compared the accuracy of the models. RESULTS: The error range of average positive distance was 0.059 - 0.117 mm and negative distance was 0.066 - 0.146 mm. Statistically (P < 0.05), average positive distance was larger than 70 µm and shorter than 100 µm, and that of negative distance was larger than 100 µm and shorter than 120 µm. CONCLUSION: We concluded that the accuracy of digital models generated from CBCT is not appropriate to make final prostheses. However, it may be acceptable for provisional restorations and orthodontic diagnoses with respect to the accuracy of the digitalization.

Stress on external hexagon and Morse taper implants submitted to immediate loading.

BACKGROUND/AIMS: This study aimed to evaluate the stress distribution around external hexagon (EH) and Morse taper (MT) implants with different prosthetic systems of immediate loading (distal bar (DB), casting technique (CT), and laser welding (LW)) by using photoelastic method. METHODS: Three infrastructures were manufactured on a model simulating an edentulous lower jaw. All models were composed by five implants (4.1 mm × 13.0 mm) simulating a conventional lower protocol. The samples were divided into six groups. G1: EH implants with DB and acrylic resin; G2: EH implants with titanium infrastructure CT; G3: EH implants with titanium infrastructure attached using LW; G4: MT implants with DB and acrylic resin; G5: MT implants with titanium infrastructure CT; G6: MT implants with titanium infrastructure attached using LW. After the infrastructures construction, the photoelastic models were manufactured and a loading of 4.9 N was applied in the cantilever. Five pre-determined points were analyzed by Fringes software. RESULTS: Data showed significant differences between the connection types (p < 0.0001), and there was no significant difference among the techniques used for infrastructure. CONCLUSION: The reduction of the stress levels was more influenced by MT connection (except for CT). Different bar types submitted to immediate loading not influenced stress concentration.

Evaluation of the laboratorial processes' quality applied to titanium prostheses: plasma casting and laser welding - metallographic analysis / Avaliação da qualidade de processos laboratoriais aplicados nas próteses em titânio: fundição a plasma e soldagem a laser - análises metalográficas

Objective: The aim of this study was to evaluate the quality of laboratory processes in titanium alloys. Methods: Eight bars were cast using the voltaic arch technique. Three bars after casting were cut at three points and received, in total, nine laser welding points. All samples were analyzed under naked eye; 50X; 100X and 200X lens with electronic microscopy. Results: All samples showed a perfect casting, without continuity solution or defects such as emptiness, bubbles, cracks, porosity or inclusions. The nine welding points didn?t present any union failures, cracks or empty spaces and comparing this result with previous studies, there was improvement in the processes' quality. Conclusion: The good quality observed in these laboratorial processes were due to the improvement of the technician?s learning curve, observation of thelaboratorial protocols, the correction of possible defects in the equipment used and the application of statistical process control (SPC).

Objetivo: Avaliar a qualidade de processos laboratoriais aplicados em ligas de titânio. Métodos: Oito padrões em cera foram fundidos com o uso da técnica de arco voltaico. Três barras, após fundidas, foram cortadas em três pontos gerando nove pontos de solda com a técnica a laser. Todas as amostras foram analisados a olho nú e em aumento de 50x, 100x e 200x usando microscopia eletrônica - análise metalográfica.Resultados: Todas as amostras apresentaram boa fundição, sem soluções de continuidade, sem falhas como vazios, bolhas, trincas, porosidades e inclusões. Os nove pontos de soldas a laser não apresentaram falhas de união, trincas ou vazios e comparando estes resultados com achados anteriores, houve melhora na qualidade dos processos. Conclusão: Conclui-se que a boa qualidade observada nesta investigação dos processos laboratoriais do titânio se deve tanto a melhora na curva de aprendizagem dos técnicos, observação dos protocolos laboratoriais como também correção dos possíveis defeitos nos equipamentos utilizados como também ao controle estatístico do processo (CEP).

Stability of surgically assisted rapid palatal expansion: a randomized trial.

The aim of this study was to evaluate the orthodontic retention of maxillary skeletal stability after surgically assisted rapid palatal expansion (SARPE). Ninety digitized plaster casts from 30 adult patients who underwent SARPE were assessed. Thirty patients were divided equally into two groups: the No Retention Group (n = 15) and the Retention Group (n = 15) with a Transpalatal Arch [TPA]). After the end of expansion, the expander appliance was stabilized and remained in place for 4 months. The additional retention period began in the Retention Group as soon as the expander was removed and replaced by a TPA. During the same period, the No Retention Group remained without retention. The casts were created pre-operatively, at 4 months and 10 months post-expansion. The models were digitized by means of a 3D Vivid 9i laser scanner. The palatal area and volume were assessed. Both variables increased after 4 months compared with pre-operative values (p < .05). At 10 months, patients' palatal areas and volumes were stable in both groups (p > .05). In conclusion, no retention other than the expander appliance is needed after SARPE.

Mini-implant and Nance button for initial retraction of maxillary canines: a prospective study in cast models / Mini-implante e botão de Nance para retração inicial de caninos superiores: estudo prospectivo em modelos

OBJECTIVE: Bone anchorage is a key factor for the successful management of some malocclusions for it allows the application of continuous forces, decreases treatment time and is independent from patient compliance. METHODS: The goal of this work was to establish a dental model comparison in order to measure the anchorage loss after the initial retraction of upper canines between the two groups. Group A used mini-implants and Group B used Nance button. All patients had two models cast (M1 and M2). The first models were taken on baseline (M1) and the other models were taken after canine retraction (M2). RESULTS: All measurements were pooled and submitted to statistical analysis. In order to verify the inter-examiner systematic error a paired t-test was performed. Dahlberg's formula was used to estimate the casual error. For comparison purposes between Before and After stages, a paired t-test was done. For the comparison between mini-implant and Nance button groups, a Student t-test was applied. All tests adopted a 5% (p<0.05) significance level. CONCLUSION: No statistically significant difference was observed between the two groups when measurements and comparisons to assess molar anchorage loss after canine initial retraction were performed. Two different anchorage systems were applied on dental models (mini-implants and Nance's button) for each group.

OBJETIVO: a ancoragem óssea é fundamental para o sucesso do tratamento de algumas más oclusões, pois permite a aplicação de forças contínuas, diminui o tempo de tratamento e independe da colaboração do paciente. MÉTODOS: o propósito desse trabalho foi comparar, por meio de modelos dentários, a perda de ancoragem após a retração inicial de caninos superiores entre dois grupos. O grupo A utilizou o mini-implante enquanto o grupo B utilizou o Botão de Nance. Para todos os pacientes foram realizados dois modelos (M1 e M2). Os primeiros modelos foram realizados ao início (M1), e os outros ao final da retração inicial de canino (M2). RESULTADOS: todas as medidas foram tabuladas e submetidas à análise estatística. Para verificar o erro sistemático intraexaminador foi utilizado o teste t pareado. Na determinação do erro casual utilizou-se o cálculo de erro proposto por Dahlberg. Para comparação entre as fases Início e Após, foi utilizado o teste t pareado. Para a comparação entre os grupos de mini-implante e Botão de Nance, foi utilizado o teste t de Student para medidas independentes. Em todos os testes foi adotado nível de significância de 5% (p<0,05). CONCLUSÃO: ao se medir e comparar em modelos dentários a perda de ancoragem dos molares após a retração inicial de canino utilizando-se dois sistemas de ancoragem distintos (Mini-implante e Botão de Nance), pôde-se observar a inexistência de diferença estatisticamente significativa entre os dois grupos.

Influência do processo de fabricação de reconstruções metalocerâmicas na microestrutura de liga níquel-cromo / Manufacture process of metal-ceramic reconstructions influence on the nickel-chromium alloy microestructure

Introdução: Durante a fabricação de reconstruções dentárias, que utilizam sistemas metalocerâmicos, é utilizado um tratamento térmico para promover a adesão da porcelana ao metal. Entretanto, sabe-se que tratamentos térmicos podem alterar a microestrutura do material metálico, modificando suas propriedades. Objetivo: Este trabalho objetivou avaliar as possíveis modificações causadas na microestrutura de liga à base de níquel-cromo utilizada para reconstruções metalocerâmicas, quando a mesma é submetida ao tratamento térmico para adesão da porcelana.Material e método: O material pesquisado foi dividido nos grupos CR, F e TT, que representam, respectivamente, o material como recebido do fabricante, o material apenas submetido ao processo de fundição e o material após fundição e tratamento térmico. Os grupos CR e F foram submetidos à análise química quantitativa. A caracterizaçãomicroestrutural dos três grupos foi realizada através da técnica de microscopia eletrônica de varredura, com um sistema de Energy Dispersive Spectroscopy. Técnicas de análise e processamento digital de imagens foram aplicadas às micrografias dos grupos F e TT, para determinação de possíveis modificações quantitativas nas fases presentes. Resultado: A microestrutura da liga era formada por uma matriz de estrutura dendrítica de coloração cinza, rica em níquel; uma segunda fase interdendrítica de coloração branca e aspecto rendilhado, rica em molibidênio, e precipitados de coloração preta, podendo ser ricos em silício ou titânio. Também foram identificadas porosidades.Conclusão: A microestrutura após o processo de fundição apresentou um tamanho da fase interdendrítica menor. Não foram identificadas mudanças na microestrutura e na composição química das fases após o tratamento térmico.

Introduction: Manufacturing process of metal-ceramic dental reconstructions systems includes heat treatment to promote adhesion of the porcelain in the metal. However, it is known that heat treatment can promote changes in the microstructure of metallic materials, thereby affecting their properties. Objective: This work evaluated themicrostructure stability of dental quality nickel base alloy submitted to the heat treatment aiming at achieving porcelain adhesion. Material and method: The samples divided into three sets, CR, F and TT, representing,respectively, the material received from the manufacturer, the material just before the casting process and the material after casting end heat treatment. The CR and F sample sets were submitted to quantitative chemical analysis. The samples of CR, F and TT sets was submitted to the microstructural characterization by scanning electron microscopy and energy dispersive spectroscopy. Digital images processing techniques were applied to micrographics of F and TT sets to determine the changes in the material microstructure before and after heat treatment. Result: The alloy microstructure exhibits a gray dendritic structure in a clear matrix, rich in nickel, and a white inter-dendritic second phase, rich in molybdenum, with scattered precipitates, rich in titanium or silicon,and porosity. Conclusion: The microstructure has an average size of the interdendritic phase less than the alloy after casting. Changes in the microestructure and in the chemical composition of each phase were not identified, whether before nor after thermal treatment.