The Effect of Die Spacer Thickness on Retentive Strength of all Zirconium Crowns (An In vitro Study)

Aim: The purpose of this study was to evaluate the effect of different die-spacer thicknesses on the retentive strength of all zirconium crowns using self-adhesive resin cement (Relyx Unicem). Materials and method: A total of 24 freshly extracted sound human maxillary first premolar teeth were mounted and then received a standardized preparation for full contour zirconia crown restorations with a deep chamfer finishing line, planner occlusal reduction, 6° overall taper. The teeth were scanned directly using Sirona Omnicam digital intra-oral scanner. Preparations surface areas were measured using Auto CAD architecture software. Teeth were then randomly assigned into 3 main groups according to the die spacer thickness selected during the designing phase by inLab SW 16.1 designing program (n=8): Group A: 80 μm; Group B: 100 μm and Group C: 120 μm. Monolithic zirconia crowns were constructed using Sirona In-Lab MC X5 milling unit. Each group was cemented with Relyx Unicem self-adhesive luting cement. Statistical analyses: The data were statistically analyzed using 1-way ANOVA and Post-hoc Bonferroni test at 0.05 level of significance. Results: The statistical analysis showed that die spacer thickness had a significant effect on the crown retentive stress and the highest mean of retentive stresses was recorded for Group A (7.4 ± 0.7 SD) while Group C recorded the lowest mean of retentive stresses (5.5 ± 0.8 SD). In addition, the predominant mode of failure was type 3 (cement principally on ceramic). Conclusion: Within the limitations of this study, the use of 80 μm spacer thickness resulted in significally higher retention values than 100 μm and 120 μm spacer. In contrast, there was no significant difference in retention between 100 μm and 120 μm.

An Evaluation of the Effects of Marginal Design, Die Spacer, and Seating Force on the Marginal Fit of Cast Metal Crowns after Luting – An Invitro.

The marginal adaptation of cast metal crowns is essential for the success of cast restoration. The marginal design, die spacer and the seating force are considered as important factors effecting the marginal fit of cast metal crowns. Aims and Objectives; The aim and objectives of the present study is to evaluate the marginal fit of cast metal crowns 1.With three different marginal designs that are shoulder, shoulder with bevel and chamfer 2.With and without die spacer 3.Under seating forces 100N and 300N. METHODOLOGY: The study was done using 3 brass dies of 6mm height 10o taper with three different marginal designs shoulder, shoulder with 45o bevel and chamfer . 20 impressions of each metal die were made and casts were poured. 10 specimens of each group were coated with die spacer while the other 10 specimens were to serve as control group. Cementation done with GIC under two different seating forces (100N and 300N). The marginal discrepancy is determined by measuring the crown height before and after cementation. From this study it was concluded that specimen with combination of chamfer marginal design with die spacer under 300N seating force exhibited superior marginal adaptation.

An in vitro study to evaluate the effect of storage time and application of subsequent layers on the variation in thickness of three commercially available die spacers.

Aims : The application of a paint-on die spacer onto the dies prior to the fabrication of cast crowns is an acceptable procedure to improve the fit of the restoration. The primary purpose of this study was to evaluate the variation in thickness of different brands of die spacer based on the effect of storage time and application of additional layers. Materials and Methods: Dies were duplicated from a master model of ivorine teeth, with a full ceramic preparation. Dies obtained were then painted with one, two, and three coats of each brand of die-spacers separately. These dies were embedded in die stone and sectioned bucco-lingually. The same procedure was done after three and six months. The thickness of the paint on die spacer was measured at five points on the die using an optical microscope, and the data were statistically analyzed. Results and Conclusion : There was a definite variation in the thickness of the die spacer with all the three brands and at various points on the die. Two coat thicknesses were found to be in the range of tolerance of 20-40 microns. Thickness at occlusal groove was noted to be the maximum with least at occlusoaxial line angles. Thickness also showed a very significant increase when bottles were stored for a period of three to six months and then applied.

Effect of the use of die spacer on the marginal fit of copings cast in NiCr, NiCrBe and commercially pure titanium

The goal of this study was to evaluate the effect of using die spacers on the marginal fit of NiCr (M1) and NiCrBe (M2) alloys and commercially pure titanium (cpTi) (M3) copings cast by the lost wax technique. Using a metal matrix, 45 resin added extra hard type IV stone models were obtained for the fabrication of wax patterns under the following conditions: no die spacer (A), with one die spacer layer (B) and with two die spacer layers (C), with five repetitions for each condition (alloy x die). Each die was waxed and the wax patterns were invested as per manufacturer's instructions. Three wax patterns were embedded in each casting ring, each corresponding to one of the conditions. Each coping, seated to the metal matrix by a seating pressure standardizing device (SPSD), was taken to an optical microscope for measurement of marginal discrepancy. The obtained data (µm) were analyzed statistically by ANOVA and Tukey' test (a=5 percent). There was statistically significant difference (p<0.05) among the materials (M1=110.67; M2=130.33 and M3=148.33). Regarding the use of the die spacer, there was a statistically significant difference (p<0.05) among the three conditions (A=162.00; B=131.06 and C=96.67). It was concluded that there is less marginal discrepancy with two die spacer layers.

O objetivo deste trabalho foi avaliar o efeito do uso de espaçadores na adaptação marginal de "copings" de ligas de NiCr (M1) e NiCrBe (M2) e titânio (M3) fundidos pela técnica de cera perdida. A partir de uma matriz metálica, foram obtidos 45 troquéis de gesso resinado tipo IV para confecção dos padrões de cera nas seguintes condições: sem a presença de espaçador (A), com uma camada de espaçador (B) e com duas camadas de espaçador (C), com cinco repetições para cada condição (liga x espaçador). Foi realizado o enceramento de cada troquel e os padrões de cera foram incluídos no revestimento indicado pelo fabricante. Em cada anel de fundição foram incluídos 3 padrões de cera, sendo cada um correspondente a cada condição. Cada "coping", adaptado à matriz metálica por meio de um dispositivo padronizador da pressão de assentamento, foi levado ao microscópio óptico para aferição das medidas da desadaptação marginal. Os dados obtidos (µm) foram submetidos à análise estatística por ANOVA e teste de Tukey (a=5 por cento). Entre os materiais houve diferença estatisticamente significante (M1=110,67, M2=130,33 e M3=148,33). Em relação ao fator espaçador, houve diferença estatisticamente significante entre as três condições (A=162,00; B=131,06 e C=96,67). Conclui-se que a presença de duas camadas de espaçador propicia menor desadaptação marginal.