Effect of Sprue Design in Nickel-Chromium Cast Crown Margin

ABSTRACT Objective: To determine the effect of sprue design on the marginal accuracy of the casting. Material and Methods: It was an experimental in-vitro study. There are forty-four crowns of single sprue group with a forty-four double sprue group that was compared in 6 different locations of the margin. The sections were inspected under a microscope at 50X magnification and took a micrograph. The radius from an actual casting edge to a possibly excellent margin was then documented as marginal discrepancy (d), in µm. The marginal discrepancy was documented for each of the six sections per casting. Thus 264 sections were measured for each group. Data were analysed using (ANOVA) for analysis of variance. For bivariate analyses, Chi-square and Student t test were used. The significance level was set at < 0.05. Results: The marginal discrepancy was greater in the single sprue group of cast crown (43.1 ± 4.74 µm) and in double sprue group of cast crown was less (25.7 ± 4.25 µm). This difference is statistically significant (p<0.05). The correlation between single sprue group of casting with a double sprue group of casting by student's t-test where determination height was 95%. Conclusion: Double sprue design produces a higher accurate margin than single sprue design in the nickel-chromium alloy cast crown.

Fabrication of titanium restoration by means of calcium aluminate-bonded magnesia investment material and one-chamber arc casting apparatus.

Cast titanium restoration for molars has high biocompatibility and is covered by the Japanese national health insurance. Titanium casting requires specific investment material and casting apparatus. A cast restoration for the mandibular left second molar was fabricated using titanium in this study. A wax pattern fabricated on a definitive cast was invested in calcium aluminate-bonded magnesia investment material. Titanium was cast using an argon gas pressure one-chamber casting apparatus. No defects were observed on the surface and the hole was clearly reproduced. A smooth surface on the restoration was obtained by polishing at low speed. Reproductivity and polishing properties of the titanium restoration fabricated in this study were comparable to those of conventional dental metal restorations.

Irrigación del conducto radicular y tratamiento de superficie de pernos de fibra, previo a la cementación: revisión de tema / Root canal irrigation and fiber post treatments, before cementation: subject review

Introducción: el tratamiento endodóntico es muy solicitado para preservar las piezas dentales, así como la utilización de pernos de fibra cuando el remanente coronario no es el adecuado para recibir una prótesis coronaria, permitiendo de esta manera reconstruir el muñón dental para la posterior colocación de la restauración definitiva. Objetivo: identificar tanto el tratamiento de superficie de pernos de fibra como el irrigante radicular idóneos para conseguir una cementación adecuada; así como conocer cuál es el tratamiento de superficie que produce menos desintegración de las fibras del perno de fibra. Materiales y métodos: se incluyeron 47 artículos publicados en inglés, durante los últimos 20 años, teniendo en cuenta que los mismos se obtuvieron hasta octubre del 2018. Conclusiones: previa la cementación de pernos sean estos de fibra o de cuarzo es indispensable realizar tratamiento de superficie para así mejorar la adhesión, estos pueden ser químicos o físicos, los que ofrecen mejor resultado sin alterar de manera significativa la estructura del mismo es el enarenado con partículas de diamante sintéticas de 1-3 µm seguido de silanización y dentro de los químicos H2O2 al 10% por 1 min seguido de silano. Para obtener mejores resultados se debe accionar el silano a una temperatura de 80°C. En cuanto a protocolos de irrigación depende del sistema de cementación que se vaya a emplear EDTA 18% + Hipoclorito de sodio al 5,25% o EDTA 18% + clorhexidina al 2% cuando se va emplear un cemento autoadhesivo y NaOCl al 11% cuando se utilice el acondicionamiento ácido de lavado y secado.

Introduction: nowadays the aim is to keep the dental organ in function as long as possible, in many cases the endodontic treatment is used to preserve the dental pieces; and the use of fiber post when the coronary remnant is not adequate to receive a crown prosthesis, allowing us in these cases rebuilt the thoot for the subsequent placement of the final restoration. Objective: to identify wich is the better surface treatment of fiber post and the root irrigator for adequate cementation; as well as know, which is the surface treatment that produces less fibers' disintegration of the fiber post. Materials and methods: it were included 47 articles published in English, during the last 20 years, considering that they were obtained until October 2018. Conclusions: Before posts cementation are these fiber or quartz it is indispensable to carry out the surface pretreatment to increase adhesion, the same ones that can be chemical or physical within these that offer the best result it is the sanded with particles of diamond synthetic of 1-3 µm followed by silanization and with 10% H2O2 for 1min followed by silane. For better results silane must be dryed at a temperature of 80 °C. And for irrigation protocols depends of the cementing system to be used EDTA 18% + sodium hypochlorite 5.25% or EDTA 18% + 2% chlorhexidine when a self-adhesive cement is to be used and 11% NaOCl when washing and drying acid conditioning is used.

Dental Arch Dimensions and Form in a Sudanese Sample.

The aim of this study is to determine the dental arch dimensions (width and length) and form in a group of a Sudanese sample population. BACKGROUND: The size and shape of dental arches have significant implication in orthodontic diagnosis and treatment planning as it affects the space available, dental esthetics and stability of the occlusion. MATERIALS AND METHODS: This study is a biometric analysis of dental casts of 50 adult Sudanese dental students (20 males, 30 females) aged between 19 to 22 years with normal occlusion. The study was conducted at the orthodontic clinics, Faculty of Dentistry, University of Khartoum. Each student was interviewed and written consent was given. The inclusion criteria were: complete permanent dentition fully erupted to the occlusal plane, no proximal caries or restorations, no attrition or dental anomalies, no extractions, no previous or ongoing orthodontic treatment and no fractures or jaw surgeries. Paired-test, ANOVA test, and Pearson's correlation were used for statistical analysis with a p-value set at 0.05. RESULTS: The result showed normal occlusion is higher in males than in females. Upper arch dimensions (width and length) found to be higher in males than females, inter canine width (ICW), males 36, and females 34.45; interpremolar width (IPmW) males 48.08, females 47.58; inter-molar width (IMW) males 53.04, females 52.4; the length for males 37.98 and for females was 37.09. Comparison of Lower arch dimensions between males and females showed ICW (27.08 and 26.86); IPmW (40.97 and 39.67); IMW (45.61 and 45.69); depth was (33.91 and 33.91) consequently. The ovoid-shaped arch form was more common in both genders. CONCLUSION: Length dimension showed the highest value with square arch form. The width dimensions increase with little change in the inter-canine region but appreciably more in the distal part of the arch. Men have a more massive arch form than females. The ovoid arch form dominates in the Sudanese population. CLINICAL SIGNIFICANCE: Knowledge of arch dimensions that are associated with normal occlusion is helpful in determining treatment goals and proper diagnosis and treatment plan by choosing the right arch form for each race.

Three-dimensional evaluation of extended pour alginate impression materials following variable storage time intervals and conditions.

PURPOSE: The purpose of this study was to assess and compare the dimensional accuracy of the stone casts made of three extended pour alginate impressions materials (Cavex Colorchange, Kromopan, and Neocolloid) following storage under different storage conditions and pouring at different time intervals. MATERIALS AND METHODS: A maxillary Frasaco (dentulous) model was selected as a standard model. Index holes of 1 mm depth and 1 mm diameter were made on the palatal cusp tips of right and left first premolars, mesiopalatal cusp tips of right and left third molars and in the midline of the palate, perpendicular to a line joining the index holes made on cusp tips of the first premolars as reference points for measurement. A single uniformly spaced custom tray was fabricated with heat-cure acrylic resin and used to make impressions for the entire study. A total of 210 impressions of the master model were made, seventy impressions were made from each of the alginate material brands and were subjected to three storage conditions (open air, uncontrolled humidity, and 100% controlled humidity) for three different storage time intervals (0, 1, 6 h). Since no storage was done in the immediate-pour group, it contained 10 specimens from each brand. Following the designated storage time interval, all impressions were poured in type IV gypsum. Measurements of stone casts were done in three dimensions, anteroposterior, lateral using Measuroscope and vertical by Dial Gauge. Data were organized in tables and statistical analyses were performed. Three-way ANOVAs were used to check if the material brands, storage time intervals, and conditions affect the measurements. Tukey HSD post hoc tests were used for the multiple comparisons if ANOVA is significant. One sample t-test was used to compare between the casts made of alginate brands and the master model. Significance level was set to α < 0.05 for all tests. RESULTS: Results showed that the material brands, storage time intervals, and conditions do affect the measurements in all three dimensions (all P < 0.05). In addition, all two-way and three-way interactions were significant for all measurements except the interaction of storage time intervals and conditions for B-C (lateral) measurements, and interaction of material brands and storage time intervals for C-D (anteroposteriorly) measurements. When stone casts were compared to the master model, immediate pour, and storage for 1 h in 100% controlled humidity resulted in statistically insignificant changes among all three alginate impression brands. In addition, the specimens made of Cavex Colorchange and Kromopan following storage in uncontrolled humidity condition for 1 h showed statistical insignificance when compared to the master model. CONCLUSION: Within the limitations of this study, it can be extrapolated that, although this class of alginate impression materials was manufactured for extended pour purposes, clinicians should avoid storage of the studied brands for 6 h. Whenever 1 h to pour is necessary, 100% controlled humidity is the ideal and standardized environment for all three alginate brands. Perhaps, Cavex Colorchange, and Kromopan can be safely stored in uncontrolled humidity condition while maintaining their optimal dimensional accuracy.

Effect of ozonated water on the surface roughness of dental stone casts.

Infection control of dental stone cast is an important issue. Ozone is effective for disinfection against microorganisms and inactivation of viruses. However, there is little information regarding the use of ozone. We prepared 4 types of gypsum specimens and 3 types of disinfectants (4-5 ppm Ozonated water [OZW], 2% glutaraldehyde [GL], and 1% sodium hypochlorite [SH]). Gypsum specimens were immersed in each disinfectant for 5 and 10 min, and surface roughness was then examined using laser scanning microscopy. Surface microstructure was investigated using scanning electron microscopy. Immersion of gypsum specimens in SH, GL, and OZW increased the surface roughness to a maximum of 1.04, 0.37, and 0.30 µm, respectively, based on the difference between the average values of surface roughness before and after the disinfection procedure. The effects of OZW and GL were comparable. OZW is useful as a candidate for relatively safe disinfection of material for dental stone casts.

An Innovative Method to Determine the Width of Maxillary Anterior Teeth with the Help of Measurements Obtained from the Master Cast.

AIM: Analyse the correlation between the measurements made from the landmarks on the cast and the width of the anterior teeth in dentulous study subjects and assessed whether a similar correlation exists in edentulous condition. MATERIALS AND METHODS: Measurements were made on the cast of dentulous and edentulous subjects. The measurements made were, from incisive papilla to the right hamular notch, from incisiv e papilla to left hamular notch and distance between two hamular notches. After measuring these distances, the predicted value was calculated by taking mean of these three distances. The actual value in both the groups was measured with a flexible ruler. The mean and standard deviation of both groups were calculated. Results were analyzed with correlation and regression analysis. RESULTS: The analysis showed that there was a positive correlation between actual and predicted values in both dentulous and edentulous group of study subjects (p-value <0.01). As the actual value increased in both the groups, the predicted value also increased. So the actual value can be derived with the help of predicted value which will be useful in selecting the proper tooth mold size of the maxillary teeth for edentulous patients. CONCLUSION: A positive correlation exists between the width of the maxillary teeth (actual value) and mean of the distance (predicted value) between the right hamular notch and incisive papilla, left hamular notch and incisive papilla and interhamular distance in dentate subjects. CLINICAL SIGNIFICANCE: The results obtained from the present study will be helpful for selecting the proper teeth mold size along with other teeth selection methods. Further studies are required to derive a more scientific and reliable method for anterior teeth selection.

Effect of Type II Diabetes Mellitus, Candida Albicans and Streptococcus Mutans on the Biofilm Formation on Prosthetic Materials.

AIM: To investigate the biofilm formation on Prosthetic materials as affected by type II diabetes mellitus, Candida albicans and Streptococcus mutans. MATERIALS AND METHODS: Two types of saliva, natural saliva, and artificial saliva were collected and prepared respectively. The natural saliva was divided into diabetic and non-diabetic saliva. The artificial saliva was further divided into two groups, one inoculated with Streptococcus mutans and the second with Candida albicans. The 150 samples of various prosthetic materials were prepared using nickel-chromium alloy, ceramic, soft liner, tooth molding powder; heat cured the acrylic resin. The samples were then immersed in natural saliva and artificial saliva and studied for biofilm formation. RESULTS: Diabetic saliva formed more biofilm than non-diabetic saliva. Streptococcus mutans were able to form more biofilm than Candida albicans in artificial saliva on constitutive androstane receptor (hCAR) and spinal length (SL). In Diabetic saliva, there was a significant difference in the biofilm formation seen between MC and NCA (p < 0.05). No biofilm was formed on hCAR in natural saliva (diabetic or non-diabetic). In artificial saliva inoculated with Candida albicans and streptococcus mutans there is a significant difference in the biofilm formation in all the materials except NCA. CONCLUSION: Diabetic saliva has more potential to form biofilm than non-diabetic saliva. Also, Candida albicans and Streptococcus mutans both can form a biofilm on materials used with the maximum formation on hCAR. Smoother materials formed less biofilm than rougher surfaces like hCAR, PCM, SL. CLINICAL SIGNIFICANCE: It is desirable for dental restorative materials to have a low susceptibility for accumulation and formation of biofilm as it may lead to pathologies such as dental caries, periodontal disease, peri-implantitis, etc. which are plaque-related. The most commonly used materials in prosthodontics have been used in the study to establish a direct relationship with the formation of biofilm, this, in turn, helps us to take the right call in choosing a material for a patient with an already compromised systemic condition.

[Research on physical and mechanical properties, crown accuracy by using self- made FUS-invest dental investment].

PURPOSE: To evaluate the physical and mechanical properties of pure titanium castings cast by self- made FUS-invest dental investment, and evaluate casting accuracy. METHODS: Seven pure titanium castings were cast by self-made FUS-invest zirconium investment and analyzed using servo hydraulic dynamic experiment system (JJG139-83 standard), scanning electron microscope and energy spectrum analysis. Thirty-eight crowns of pure titanium were cast by two different methods. One cast by FUS-invest zirconium embedding material was used for experiment and the other cast by phosphate embedding material was used as control. Casting accuracy was assessed through measuring the difference value d at the marginal marker points and distance between casting pieces of wall and working modes of casting were examined under microscope. Scanning electron microscope with energy-dispersive spectrum (EDS) was used to analyze the status of composition of the casting surface. SPSS 17.0 software package was used to investigate the difference of two groups. RESULTS: ①Qualitative analysis of servo hydraulic dynamic experiment system showed various mechanical properties: elastic modulus (123.5±14.2) GPa, yield strength (569.3±16.5) MPa, tensile strength (668.4±16.1) MPa, elongation (4.5±0.2)%. EDS analysis of the fracture was observed at different depth (13, 25, 50, 350 µm) under the surface of pollution layer, a little Si and Fe with different atomic percentage was found but no Zr. ②No significant difference (P>0.05) was found between each group of four markers on the marginal fit, and internal fit, whereas significant difference (P<0.01) was found at different marker point. CONCLUSIONS: The mechanical properties of commercially pure titanium casting by self-made FUS-invest zirconium-based investment can meet the qualification of dental metal materials, although elongation was a little lower. Both the marginal adaptation and internal fit between the two groups had no significant difference. The mean marginal difference was 46 µm, the mean internal difference at axial angle was 56 µm and approximately 0 at axial wall.

A Direct Refractory Die Technique for Cast Gold Restorations.

Fabricating accurate cast gold restorations can be challenging for both clinicians and laboratory technicians. Removing the wax pattern from the master die often distorts the pattern, which, in turn, compromises the overall fit and marginal adaptation of the casting. This article demonstrates a laboratory technique in which the final restoration is cast directly on the refractory die without removing the wax pattern. Thus, distortion of the wax pattern is avoided, enabling the production of superbly fitting gold castings for both intracoronal and extracoronal restorations.

Desajuste vertical entre implante de hexágono interno e pilares Ucla totalmente calcináveis e com base de CoCr após a fundição pelo processo convencional / Vertical misfit between internal hexagon implants and Ucla burnout and CoCr prefabricated base abutments after conventional casting procedures

Objetivo: avaliar, por meio de um microdurômetro, o grau de desajuste na adaptação de pilares Ucla em implantes. Material e métodos: foram utilizados dez implantes de hexágono interno de plataforma regular, e seus respectivos componentes protéticos do tipo Ucla com antirrotacional, como seguem: dez pilares Ucla totalmente calcináveis e dez pilares Ucla com base de CoCr. Todos os pilares Ucla foram fundidos pelo mesmo laboratório de prótese e pelo mesmo processo laboratorial. Cada implante recebeu apenas dois pilares, que foram anexados por meio de um parafuso de titânio quadrado utilizando-se torque de 30 Ncm com torquímetro manual. Cada conjunto implante/pilar recebeu quatro marcações aleatórias em torno da circunferência, na qual foram feitas as medições do espaço existente entre as peças utilizando uma lupa estereoscópica de 100 vezes de aumento. Resultados: os resultados obtidos mostraram diferenças significativas entre os grupos submetidos ao teste Mann-Whitney (p < 0,05). Conclusão: o pilar Ucla com base de CoCr apresentou menor desajuste marginal vertical, quando comparado ao pilar Ucla totalmente calcinável, após o processo de fundição nos implantes de hexágono interno.

Objective: to evaluate, using a microhardness device, the misfit between Ucla abutments and internal hex implants. Material and methods: 10 internal hex implants received 10 Ucla burnout and 10 Ucla abutments with CoCr collar. All the abutments were cast in the same laboratory and under the same protocol. A square-head titanium screw was tightened to a 30 Ncm using a manual wrench. Each abutment/implant set receive four random markings around its perimeter. A stereoscopic lens was used to investigate the misfi t at 100 magnification. Results: there was a statistically significant difference between tested abutments (Mann-Whitney p < 0.05). Conclusion: the Ucla abutment with the CoCr collar presented less vertica misfit values after casting for internal hex dental implants.

Effect of production method on surface roughness, marginal and internal fit, and retention of cobalt-chromium single crowns.

STATEMENT OF PROBLEM: New production methods have been developed for metal-ceramic restorations. Different production methods may show different surface roughness and fit, which may affect retention and long-term success. PURPOSE: The purpose of this in vitro study was to examine 3 different production methods with regard to surface roughness, marginal and internal fit, and retention of cobalt-chromium alloy single-crown copings. MATERIAL AND METHODS: A master abutment of a premolar mandibular tooth preparation with 4-mm height and a 0.6-mm deep 120-degree chamfer finish line with a 12-degree angle of convergence was replicated in die stone and scanned. Thirty-six cobalt-chromium alloy copings were produced using 3 different production techniques. Twelve copings were produced by laser-sintering, 12 by milling, and 12 by milled wax/lost wax. The surface microstructure of 2 copings in each group was analyzed using interferometry. The remaining 10 copings in each group were used to evaluate marginal and internal fit by using an impression material replica method, and retention was evaluated by using a uniaxial tensile force pull-off test. The copings from each test group were cemented with zinc phosphate cement onto resin abutments. Statistical analyses of differences in marginal and internal fit were performed using 1-way ANOVA and the Mann-Whitney U test. Differences in surface topography were analyzed with the Kruskal-Wallis and Mann-Whitney U tests for nonparametric data. Differences in retentive values were analyzed using the Mann-Whitney U test for nonparametric data (all α=.05). RESULTS: Differences in surface microstructure were seen. The laser-sintered copings showed increased surface roughness compared with milled and milled wax/lost wax copings. Differences in marginal and internal fit were noted. Laser-sintered showed significantly smaller spaces between coping and abutment than milled wax/lost wax copings (P=.003). At the margins, laser-sintered copings showed significantly smaller spaces than either the milled wax/lost wax group (P=.002) or the milled group (P=.002). At the chamfer, laser-sintered copings showed significantly smaller spaces than milled wax/lost wax copings (P=.005). At the center of the axial walls, laser-sintered copings showed significantly smaller spaces than those in the milled wax/lost wax (P=.004) and milled copings (P=.005). No significant differences were noted between milled and milled wax/lost wax copings (P>.05). No significant differences were detected regarding retentive forces in the pull-off tests (P>.05). CONCLUSIONS: Laser-sintered Co-Cr crown copings showed increased surface roughness and better internal and marginal fit than copings produced by milling or milled wax/lost wax technique. However, the crown pull-off tests did not reveal any significant differences.

Comparison of margin discrepancy of complete gold crowns fabricated using printed, milled, and conventional hand-waxed patterns.

STATEMENT OF PROBLEM: The recent application of printing for the fabrication of dental restorations has not been compared and evaluated for margin discrepancy (margin fit) with restorations fabricated using milling and conventional hand-waxing techniques. PURPOSE: The purpose of this in vitro study was to evaluate and compare margin discrepancy of complete gold crowns (CGCs) fabricated from printed, milled, and conventional hand-waxed patterns. MATERIAL AND METHODS: Thirty crown patterns were produced by each of 3 different methods: printed by ProJet DP 3000, milled by LAVA CNC 500, and hand waxed, then invested and cast into CGCs. Each crown was evaluated at 10 positions around the margin on the corresponding epoxy die under ×50 light microscopy to determine the mean and maximum margin discrepancy. Measurements were made using a micrometer positioning stage. The results were compared by ANOVA (α=.05). RESULTS: Milled and hand-waxed patterns were not statistically different from each other (P>.05), while printed patterns produced significantly higher mean and maximum margin discrepancy than milled and hand-waxed patterns (P<.05). CONCLUSIONS: Relative to margin discrepancy, the LAVA CNC 500 milled and hand-waxed patterns were not significantly different from each other. The ProJet DP 3000 printed patterns were significantly different from LAVA CNC 500 milled and hand-waxed patterns, with an overall poorer result. Fabricating CGCs from printed patterns produced a significantly higher number of crowns with unacceptable margin discrepancy (>120 µm).

Effect of casting atmosphere on the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium.

STATEMENT OF PROBLEM: The marginal adaptation of prosthetic crowns is still a significant clinical problem. PURPOSE: The purpose of this in vitro study was to evaluate the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium under different casting conditions. MATERIAL AND METHODS: Four casting conditions were selected: flame-torch, induction/argon, induction/vacuum, and induction/air; and 2 alloys were used, Ni-Cr-Be and Ni-Cr. For each group, 10 metal specimens were prepared. Silicone indirect impressions and analysis of the degree of rounding were used to evaluate the marginal deficiencies of metal copings, and a standardized device for the setting pressure associated with optical microscopy was used to analyze the marginal misfit. Results were evaluated with 2-way ANOVA (α=.05), followed by the Tukey honest significant difference post hoc test, and the Pearson correlation test (α=.05). RESULTS: Alloy (P<.001) and casting technique (P<.001) were shown to affect marginal deficiencies. The Ni-Cr cast using the torch technique showed the highest marginal deficiency, and the Ni-Cr-Be cast in a controlled argon atmosphere showed the lowest (P<.001). Alloy (P=.472) and casting techniques (P=.206) did not affect the marginal misfit, but significant differences were found in the interaction (P=.001); the lowest misfit was achieved using the Ni-Cr-Be, and the highest misfit occurred with the molten Ni-Cr, using the cast torch technique. No correlation was found between deficiency and marginal misfit (r=.04, P=.69). CONCLUSIONS: The interactions demonstrated that the alloy containing beryllium that was cast in an argon atmosphere led to reduced marginal deficiency. Improved marginal adaptation can be achieved for the same alloy by using the torch technique.

A Proposed Methodology to Assess the Accuracy of 3D Scanners and Casts and Monitor Tooth Wear Progression in Patients.

PURPOSE: The aim of this study was to detail and assess the capability of a novel methodology to 3D-quantify tooth wear progression in a patient over a period of 12 months. MATERIALS AND METHODS: A calibrated stainless steel model was used to identify the accuracy of the scanning system by assessing the accuracy and precision of the contact scanner and the dimensional accuracy and stability of casts fabricated from three different types of impression materials. Thereafter, the overall accuracy of the 3D scanning system (scanner and casts) was ascertained. Clinically, polyether impressions were made of the patient's dentition at the initial examination and at the 12-month review, then poured in type IV dental stone to assess the tooth wear. The anterior teeth on the resultant casts were scanned, and images were analyzed using 3D matching software to detect dimensional variations between the patient's impressions. RESULTS: The accuracy of the 3D scanning system was established to be 33 µm. 3D clinical analysis demonstrated localized wear on the incisal and palatal surfaces of the patient's maxillary central incisors. The identified wear extended to a depth of 500 µm with a distribution of 4% to 7% of affected tooth surfaces. CONCLUSION: The newly developed 3D scanning methodology was found to be capable of assessing and accounting for the various factors affecting tooth wear scanning. Initial clinical evaluation of the methodology demonstrates successful monitoring of tooth wear progression. However, further clinical assessment is needed.

Evaluation of effect of recasting of nickel-chromium alloy on its castability using different investment materials: An in vitro study.

CONTEXT: Castability has been found to be affected by many aspects of the entire casting system. Very few references in dental literature are available regarding recasting of the base metal alloys. AIMS: To evaluate and compare the castability of fresh and reused nickel-chromium alloy and to evaluate the effect of two brands of investment materials on castability of nickel-chromium alloy. SUBJECTS AND METHODS: For the experimental purpose of evaluation of the effect of recasting of nickel-chromium alloy on its castability, different percentages of new and casted alloy (Nickel-chromium alloy-(Wirolloy NB, Type 4 (Ni-67%; Cr-25%; Mo-5%; Si-1.5%; Mn, Nb, B, C each <1%) and two commercial brands of investment materials namely, Deguvest Impact (Degudent; Dentsply Germany) and Bellavest SH (Degudent; Dentsply Germany) was used to obtain 30 samples. Castability value was obtained using Whitlock's formula. Student t-test and one way ANOVA using SPSS 20.0 software was done. RESULTS: The results of this study confirm earlier works that demonstrate that there is no significant difference in castability values of new and recast alloys. In addition, it also demonstrated, there was no difference in castability using Deguvest Impact and Bellavest SH investment materials. CONCLUSIONS: Within the limitations of the study, it was concluded that there was no significant difference found in castability of different percentage combinations of new and once casted alloy using two investment materials. The addition of new alloy during recasting to maintain the castability of nickel-chromium alloy may therefore not be required.

Marginal Accuracy of Castings Fabricated with Ringless Casting Investment System and Metal Ring Casting Investment System: A Comparative Study.

BACKGROUND: The thermal expansion of the investment can be restricted by the metal casting ring because the thermal expansion of the ring is less than that of the investment. The ringless casting procedure is in use in clinical dentistry, though there is little scientific data to support its use in fixed partial dentures. In this study, marginal discrepancy of castings produced with the ringless casting technique and the conventional technique using the metal rings were compared. MATERIALS AND METHODS: A total of 30 wax patterns were fabricated directly on a metal die. Optical stereomicroscope was used to measure the marginal discrepancy between the metal die and wax patterns. A total of 15 castings were invested using Bellavest T phosphate-bonded investment with the ringless technique and 15 were invested with the same investment with a metal ring; 30 castings were produced using a nickel-chromium ceramo-metal alloy. The internal surface of the castings was not modified and seated with finger pressure. The vertical marginal discrepancy was measured using an optical stereomicroscope at a magnification of 100x. The data obtained were statistically analyzed using students t-test (paired t-test and unpaired t-test). RESULTS: The castings of the ringless technique provided less vertical marginal discrepancy (240.56 ± 45.81 µ) than the castings produced with the conventional metal ring technique (281.98± 53.05 µ). The difference was statistically significant. CONCLUSION: The ringless casting technique had produced better marginal accuracy compared with conventional casting technique. Ringless casting system can be used routinely for clinical purpose.

Characterization of the interface between cast-to Co-Cr implant cylinders and cast Co-Cr alloys.

STATEMENT OF PROBLEM: The affordable Co-Cr cast alloy should provide an ideal interface with prefabricated cast-to cylinders from the same alloy family. The alloy microstructures should be maintained up to the interface, and porosities and reaction regions should be absent, and sufficient bond strength between alloys should be provided. PURPOSE: The purpose of this in vitro study was to evaluate the metallurgical interfacial compatibility between Co-Cr dental casting alloys and a prefabricated Co-Cr dental implant cast-to-cylinder. MATERIAL AND METHODS: A Co-Cr alloy was cast to Co-Cr implant cylinders. Specimens were cross-sectioned longitudinally and divided into as-cast and heat-treated groups. The microstructures of specimens were evaluated by optical and scanning electron microscopy. The elemental composition of as-received prefabricated implant cylinders and diffusion characteristics of cast interfacial regions were determined by energy dispersive x-ray spectroscopy. Vickers hardness values were defined across the interface on cast specimens and for the as-received implant cylinders. ANOVA and Tukey honest significant differences tests were used for the statistical evaluation of hardness values. RESULTS: No significant reaction regions or porosity were present in the interface. Microstructural aspect and interdiffusion indicated a metal-metal bond between the Co-Cr implant cylinder and cast alloy. Mean hardness values demonstrated a significant rise across the interface (373.5 ±12.8; 363.8 ±12.6, respectively) from the wrought cylinder (338.6 ±10.5; 329 ±9.7, respectively) to the cast alloy (399.8 ±7.4; 392.3 ±10.3, respectively) for the as-cast and heat-treated conditions, respectively. CONCLUSIONS: Co-Cr casting alloy cast on to prefabricated Co-Cr implant cylinders provided interfaces which appear to fulfill the requirements of the established criteria.

Digital assessment of preliminary impression accuracy for edentulous jaws: Comparisons of 3-dimensional surfaces between study and working casts.

PURPOSE: The aim of this study was to compare 3-dimensional surfaces of study and working casts for edentulous jaws and to evaluate the accuracy of preliminary impressions with a view to the future application of digital dentistry for edentulous jaws. METHODS: Forty edentulous volunteers were serially recruited. Nine dentists took preliminary and final impressions in a routine clinical work-up. The study and working casts were digitized using a dental 3-dimensional scanner. The two surface images were superimposed through a least-square algorithm using imaging software and compared qualitatively. Furthermore, the surface of each jaw was divided into 6 sections, and the difference between the 2 images was quantitatively evaluated. RESULTS: Overall inspection showed that the difference around residual ridges was small and that around borders were large. The mean differences in the upper and lower jaws were 0.26mm and 0.45mm, respectively. The maximum values of the differences showed that the upward change mainly occurred in the anterior residual ridge, and the downward change mainly in the posterior border seal, and the labial and buccal vestibules, whereas every border of final impression was shortened in the lower jaw. The accuracy in all areas except the border, which forms the foundation, was estimated to be less than 0.25mm. CONCLUSION: Using digital technology, we here showed the overall and sectional accuracy of the preliminary impression for edentulous jaws. In our clinic, preliminary impressions have been made using an alginate material while ensuring that the requisite impression area was covered.

Stress Over Implants of One-Piece Cast Frameworks Made With Different Materials.

This study aims to compare stress transmitted to implants and passive fit of one-piece cast frameworks fabricated with 3 different materials: commercially pure titanium (G1-CP Ti), cobalt-chromium alloy (G2-Co-Cr), and nickel-chromium-titanium alloy (G3-Ni-Cr-Ti). In total, 12 frameworks simulating bars for fixed prosthesis in a model with 5 implants were fabricated. The passive fit of the framework interface was measured using an optical microscope and the stresses transmitted to implants were measured using quantitative photoelastic analysis. Data were statistically analyzed by analysis of variance (ANOVA) and least significant difference (LSD) tests (α = 0.05). Mean and standard deviation values of passive fit and stress over implants are presented, respectively: G1 [472.49 (109.88) µm and 11.38 (9.23) KPa], G2 [584.84 (120.20) µm and 15.83 (9.30) KPa], and G3 [462.70 (179.18) µm and 16.39 (9.51) KPa]. For stress over implants, there were significant differences between G1, G2, and G3 (P = 0.035), being the lowest values for the G1. There were no significant differences for passive fit between G1 and G3 (P = 0.844), but both were statistically different from G2 (P = 0.028 and P = 0.035, respectively), which showed the worse results. It may be concluded that the stress over implants was affected by the tested materials. The CP Ti presented the best values for the evaluated items.