Comparison of the linear dimensional accuracy of the maxillary denture teeth by three flask closure methods. An in vitro study.

PURPOSE: This laboratory study conducted to evaluate and compare the influence of different flask closure methods on linear dimensional changes of standardized simulated maxillary complete dentures. MATERIALS AND METHODS: Thirty casts were made from a silicone mold representing an edentulous maxillary arch. Thirty identical maxillary dentures were made and randomly assigned to 3 test groups (A, B, C). In Group A, flasks were placed directly in pressure clamp after trial closure. Group B: The final closure was done in a hydraulic press then transferred to pressure clamp. Group C: After trial closure flask was positioned between the two iron plates of the Restriction System flask closure (RSFC) method. Then linear distances were measured three times before and after polymerization: right incisor to left incisor (RI-LI), right premolar to left premolar (RPM-LPM), right molar to left molar (RM-LM) and left incisor- to- left molar (LI-LM) and right incisor- to- right molar (RI-RM) with the help of digital caliper with an accuracy of 0.01mm. ANOVA and Tuckey's test were used to compare the groups (p < 0.05). RESULTS: Inter molar (LM-RM) width showed the greatest dimensional change after processing and Linear dimensions were not significantly influenced by the packing procedure. CONCLUSION: Within the limitations of this study, Restriction System flask closure (RSFC) method demonstrated a similar performance in reducing the tooth movement when compared with other flask closure methods. The posterior region of the denture may present changes in the tooth position after processing, which need to be clinically adjusted.

[Tooth color matching systems and communication with dental laboratory in indirect restorations: 2011 update].

There has been many technological developments in the last decade. Today's shade-matching technologies have been developed in an effort to increase the success of color matching, communication, reproduction and verification in clinical dentistry and, ultimately, to increase the efficiency of esthetic restorative work within any practice. In general, the output of the color measurements can be classified and specified in several ways. The most common systems for describing color are Munsell's System and the international Commission on Illumination (CIE) L a b color system. Albert Munsell described color as a three-dimensional phenomenon. He described the three dimensions as hue, value (brightness), and chroma (saturation). Visual colour determination by comparison of teeth and shade guides is the most frequently applied method in dentistry. Vitapan Classical (Vita Zahnfabrik, Germany) and its derivations(evidence-based Vitapan 3D-Master shade guide and Linearguide) are the most commonly used shade guides. However, several factors can influence consistency of visual colour selection and specification: individual colour matching ability may vary, the colour perception of any individual may show temporal variation, the range of shades available is inadequate and does not cover the complete colour space of natural teeth, the shade guide tabs are not systematically distributed in their colour space, and changes in lighting conditions can cause alterations in perceived colour. instruments for clinical shade-matching encompass spectrophotometers, colorimeters and digital imaging systems. It can be concluded that different devices have different accuracy and precision. Colorimeters are significantly less reliable than spectrophotometers and digital cameras. Benefits and limitations exist, and the clinician must consider how the technology relates to expectations and needs. Combination of visual colour determination (Vitapan 3D-Master shade guide and Linearguide) with digital cameras and electronic devices (spectrophotometers) increase chances for successful shade matching.

Fit of single tooth zirconia copings: comparison between various manufacturing processes.

STATEMENT OF PROBLEM: Various CAD/CAM processes are commercially available to manufacture zirconia copings. Comparative data on their performance in terms of fit are needed. PURPOSE: The purpose of this in vitro study was to compare the internal and marginal fit of single tooth zirconia copings manufactured with a CAD/CAM process (Procera; Nobel Biocare) and a mechanized manufacturing process (Ceramill; Amann Girrbach). MATERIAL AND METHODS: Abutments (n=20) prepared in vivo for ceramic crowns served as a template for manufacturing both Procera and Ceramill zirconia copings. Copings were manufactured and cemented (Clearfil Esthetic Cement; Kuraray) on epoxy replicas of stone cast abutments. Specimens were sectioned. Nine measurements were performed for each coping. Over- and under-extended margins were evaluated. Comparisons between the 2 processes were performed with a generalized linear mixed model (α=.05). RESULTS: Internal gap values between Procera and Ceramill groups were not significantly different (P=.13). The mean marginal gap (SD) for Procera copings (51(50) µm) was significantly smaller than for Ceramill (81(66) µm) (P<.005). The percentages of over- and under-extended margins were 43% and 57% for Procera respectively, and 71% and 29% for Ceramill. CONCLUSIONS: Within the limitations of this in vitro study, the marginal fit of Procera copings was significantly better than that of Ceramill copings. Furthermore, Procera copings showed a smaller percentage of over-extended margins than did Ceramill copings.

Análisis de las alteraciones de la posición de los dientes artificiales de prótesis totales maxilares en función del tamaño del arco / Analysis of position alterations in artificial teeth of maxillary complete dentures in function of the arch size

El propósito de este trabajo fue analizar en prótesis totales maxilares la influencia del tamaño de los arcos en el movimiento de dientes artificiales cuando los mismos se someten a las inclusiones con barrera de yeso tipo IV (especial), polimerizado en microondas y medidas gráficamente por computadora. Veinte y una réplicas de prótesis que se habían construido previamente, fueran divididos en tres grupos: grupo 1, constituido de 7 prótesis maxilares del tamaño pequeño; grupo 2, constituido de 7 prótesis de tamaño medio y, grupo 3, de gran tamaño. Las prótesis habían sido medidas en puntos demarcados previamente en los dientes, con un programa de computación gráfica, después del encerado y después de la polimerización y demuflado. La diferencia entre la medida, en las dos etapas, demostró la ocurrencia de pequeñas alteraciones. Fue concluido, del punto de vista estadístico, que no ha tenido diferencias significativas en las alteraciones de la posición de dientes, en los tres tamaños de modelos estudiados.

The purpose of this study was to evaluate the influence of maxillary arch size on the artificial teeth movement in complete dentures. The maxillary dentures were processed with a barrier-type IV gypsum molding technique, and polymerized by microwave energy. Twenty one dentures were fabricated and equally divided into 3 groups, according to maxillary residual ridge size: G1) small; G2) medium and G3) large size. Reference points were made on the incisal edges of the central incisors and the supporting cusps of the premolar and second molar teeth. Linear distances among reference points, in a horizontal plane, were measured with a computer program (Auto cad 2000) before and after processing denture. Although there were differences between measurements, indicating some movement degree among artificial teeth, the results showed no statistical significantly differences among three groups studied. It was concluded that the maxillary arch size has not influence on the artificial teeth position.

Dimensional stability of distances between posterior teeth in maxillary complete dentures / Estabilidade dimensional de distâncias entre dentes posteriores em prótese total superior

The aim of this study was to assess the displacement of posterior teeth in maxillary complete dentures stored in water at 37°C. Twenty acrylic resin-based maxillary complete dentures were constructed with the anterior teeth arranged in normal overlap and the posterior teeth in Angle class I. Metallic pins were placed on the labial cusp of the first premolars (PM), and on the mesiolabial cusp of the second molars (M). The final acrylic resin pressing was made in a metallic flask with aid of the RS tension system, and polymerized in a moist-hot cycle at 74°C for 9 hours. The dentures were deflasked after cooling in their own polymerizing water or after cooling in polymerizing water plus bench storage for 3 hours, and stored in water at 37°C for periods of 7, 30, and 90 days. Following deflasking and after each storage period tested, the PM-PM (premolar to premolar), M-M (molar to molar), LPM-LM (left premolar to left molar), and RPM-RM (right premolar to right molar) distances were measured with an STM Olympus microscope, with an accuracy of 0.0005 mm. Collected data were submitted to ANOVA and Tukey's test (5 percent). There was no statistically significant difference for the PM-PM, M-M, and LPM-LM distances after all storage periods when the flask cooling methods were considered. With exception of the RPM-RM distance after the 30-days water plus bench storage period, the other distances remained statistically stable.

O propósito deste trabalho foi verificar a movimentação de dentes posteriores em prótese total superior armazenada em água a 37°C. Vinte próteses totais superiores foram confeccionadas com resina acrílica, com os dentes anteriores em transpasse normal e os posteriores em Classe I de Angle. Pinos metálicos foram colocados na cúspide vestibular dos primeiros pré-molares (PM) e cúspide mésio-vestibular dos segundos molares (M). A prensagem final da resina acrílica foi feita em mufla metálica com auxílio do dispositivo RS de contensão e a polimerização em ciclo de água a 74°C durante 9 horas. As próteses foram demufladas após esfriamento em água de polimerização ou em água de polimerização mais armazenagem em bancada por 3 horas e armazenadas em água a 37°C pelos períodos de 7, 30 e 90 dias. Após demuflagem e após cada período de armazenagem em água, as distâncias PM-PM (pré-molar a pré-molar), M-M (molar a molar), PMD-MD (pré-molar direito a molar direito) e PME-ME (pré-molar esquerdo a molar esquerdo) foram medidas com microscópio Olympus STM, com precisão de 0,0005 mm. Os dados coletados foram submetidos à análise de variância e ao teste de Tukey com significância de 5 por cento. Em todos os períodos de armazenagem, as distâncias PM-PM, M-M e PME-ME não apresentaram diferenças estatisticamente significativas quando as muflas foram esfriadas pelos dois métodos. Com exceção da distância PMD-MD no período de 30 dias de armazenagem em água mais bancada, as demais distâncias permaneceram sem diferença estatística significativa.

Finite element analysis of the effect of the bucco-lingual position of artificial posterior teeth under occlusal force on the denture supporting bone of the edentulous patient.

To improve the quality of the complete denture prosthesis, the bucco-lingual position of the artificial posterior teeth must be determined with consideration of the shape of the maxillary and mandibular residual ridge and the relationship between them. The arrangement of posterior artificial teeth should be considered not only for the denture stability but also for the avoidance of high pressure on the supporting structures. A two-dimensional finite element method program to investigate the statics for the contour of the complete denture and the residual ridge was developed. With this program, the effect of the bucco-lingual position of the artificial posterior teeth under occlusal force on the denture supporting bone could be investigated.

A new technique for determining the denture tooth bond.

Defective bonds between resin teeth and denture base material remain a continuing source of failure. Findings from the limited number of studies on this topic are diminished by the numerous experimental approaches adopted. National and international standard specifications also adopt different methods of specimen preparation and physical straining. A critical appraisal of the various standards is carried out and a new procedure for determining the denture tooth to acrylic resin bond is described. A study using this technique found that physical modification and alginate contamination of the tooth had no significant effect on the bond strength. Ineffectual wax elimination was the main cause of failure.

[The use of standard plastic teeth to replace single missing teeth in incorporated defects]. / Ispol'zovanie standartnykh plastmassovykh zubov v tseliakh zameshcheniia edinichnykh otsutstvuiushchikh zubov pri vkliuchennykh defektov.

A method for prosthetic repair of dentition defects due to loss of one tooth is proposed. A standard plastic tooth is fixed to the tooth limiting the dentition defect by means of composite filling material. A cavity similar to Black's class-III cavity is formed in the artificial tooth.

Estudo da inclinaçäo das vertentes das cúspides de suporte, em relaçäo ao plano áxio-orbital, em dentes naturais e duas marcas de dentes artificiais utilizados em prótese parcial removível / A study of the inclination of supporting cusp slopes, in relation to the axio-orbital plan, on natural teeth and two brands of artificial teeth utilized in removable partial prosthodontics

Pela técnica da estereometria, foram analisadas, em relaçäo ao plano áxio-orbital, as inclinaçöes das vertentes triturantes distais superiores e mesiais inferiores das cúspides de suporte. Essas vertentes säo as superfícies onde podem ocorrer interferências em balanceio, consideradas entre as mais danosas ao sistema estomatognático. O estudo foi realizado em 5 pacientes com dentes íntegros e oclusäo ideal sem disfunçäo do sistema estomatognático. Foram analisadas 3 situaçöes de dentiçäo para cada paciente, ou seja, a primeira na condiçäo de dentes naturais, a segunda com dentes artificiais Trubyte Biotone 33º, e a terceira, com dentes artificiais Orthosit PE. Dentro das condiçöes experimentais desta pesquisa, chegamos à conclusäo de que, em dentes naturais, as vertentes analisadas apresentam uma semelhança estatística entre si, ou seja, parece existir um paralelismo relativo entre elas. Observou-se, também que näo há correspondência entre as inclinaçöes das vertentes analisadas dos dentes superiores com as suas respectivas vertentes antagônicas inferiores. A inclinaçäo cuspídica dos dentes inferiores foi sempre maior em relaçäo aos superiores, e esse fato ocorreu com maior amplitude nos dentes artificiais. Os dois tipos de dentes artificiais testados näo apresentaram as inclinaçöes das vertentes analisadas, perfeitamente compatíveis com as dos dentes naturais. Entretanto, os dentes Trubyte Biotone com 33º de inclinaçäo cuspídica foram os que mais se aproximaram das inclinaçöes médias dos dentes naturais. Estes, sob aspecto da anatomia oclusal, parecem ser os mais indicados para se utilizar em próteses parciais removíveis

[Bonding strength and fracture resistance of artificial teeth in dental prostheses]. / Protézismüfogak szakítószilárdsága.

Debonding of plastic teeth from its denture base has been frequently experienced in our prosthetic practice. Three of nine products investigated have fulfilled the requirements for bonding according to ISO test 3336. Loading forces necessary to produce fractures varied between 170-810 N within the tooth and 80-230 N at the tooth-denture base interface. Comparative significances were noted for the mean breaking force against fracture and debonding when comparing the resistance of "Acry Rock" to the other eight materials tested. Maximizing the extension of the polymerization surface through a larger surface area of individual teeth seemed to be a significant factor in the determination of the debonding force necessary to produce fracturing.

[Selection error of upper anterior artificial teeth].

Seventy two cases of selection error of upper anterior artificial teeth due to the esthetic factors were investigated out of the 1,507 cases of removable dentures, which were made at the Prosthodontics department of Nihon University school of dentistry at Matsudo for 17 years from November, 1971 to November, 1988. The following were the results of the investigation. 1. Frequency of the selection errors amounted to 4.8% of the total selected cases as broken down in 1.6% by Shade and 4.0% by Mould, the rate of selection errors of the Mould being significantly high. 2. By Mould, selection errors in Ovoid type occupied a significantly high rate. 3. Regarding frequency of Mould after re-selection ST and TO occupied a high rate of 45.9%. 4. Mould of re-selection were almost uniformly small, showing a trend of intumescence becoming emphatically.

A new method for matching tooth colors with color standards.

A new method for quantitative intra-oral tooth color determination is presented. Basically, the tooth color is assessed by visual comparison with opaque color standards, which are logically arranged according to three visual color dimensions. The standards were analyzed spectrophotometrically, and the C.I.E. color coordinates were computed. Illumination and observation were standardized during the matching procedure. Two distinct situations, method 1 and method 2, were investigated. The situation in method 1 is to be considered as large window illumination and small window collection of the reflected light. For method 2, the same small window was used for both illumination and observation. Using both methods, the color of a tooth could be quantified into three separate color dimensions. Using method 1, the consistency among 25 examiners was high in determining the color of ten teeth; using method 2, the inter-examiner agreement was low. For the same tooth, different color standards were selected with method 1 or method 2. The standard selected with method 2 often appeared to be in disagreement within clinical expectations. The differences in results between method 1 and method 2 are explained by the optical properties of the translucent dental enamel (e.g., volume reflection). Method 1 allows for reproducible quantification of clinical tooth discoloration according to C.I.E. color specifications and can possibly be applied in prosthetic dentistry.