ABSTRACT
Introduction: It is important to construct the sprue in a way that ensures that the mold gets an appropriate supply of metal at the right speed. Many manufacturers now offer sprue designs that have not been advocated in textbooks or publications for their normal use. Aim: The goal of this research was to compare the sprue design's marginal fit to that of the other designs. Methods: During this investigation, we attempted to see whether the fabrication of metal copings could be improved. Three sprue designs were used in this research for the assessment of casting accuracy: normal cylindrical, funnel-shaped, and cuboidal or flattened sprue forms. Results: The mean marginal disparity of nickel-chromium (Ni-Cr) alloy copings made by three distinct brands was determined to be statistically insignificant. Conclusion: Within the limitation of the study, it was concluded that the marginal accuracy of metal copings fabricated with three different brands of Ni-Cr alloy did not reveal a statistically significant result. However, out of the three different sprue designs, that is, cylindrical, cuboidal, and funnel shape, the marginal accuracy of cylindrical and cuboidal sprue designs was found to be better than that of the funnel shape sprue design because the funnel shape sprue design is narrow at the point of attachment, thereby increasing the flow pressure and decreasing the turbulence of the molten metal.
ABSTRACT
BACKGROUND: The present study determined the effect of implant angulation and implant number on the dimensional precision of implant definitive casts. MATERIALS AND METHODS: Three definitive casts with implant analogs placed in a triangular pattern were made from dental stone. Group I was control group, Group II in which implant numbers 1 and 3 were at 5° convergence to the implant number 2. Group III in which implant numbers 1 and 3 are at 5° divergence to the implant number 2. Group IV in which implant numbers 1 and 3 are at 10° convergence to the implant number 2. Implant analogs were secured in all the definitive casts with cyanoacrylate. Three open tray impressions of the definitive cast were obtained and poured in Type IV dental stone. Coordinates in the three planes were measured at implant analog top surface and base of the cast using a fine tip measuring stylus. The data were aligned and angular differences between implant analog vectors from definitive and duplicate casts were measured. RESULTS: There was a significant correlation between dental implant number and dental implant angulation (P < 0.05). There was a significant result when comparing the effect of the parallel group from 5° divergence and 10° convergence groups. A significant results while comparing the parallel group with 5° divergence and 10° convergence was obtained whereas while comparing 5° divergence, 5° divergence, and 10° convergence a nonsignificant difference was obtained (P > 0.05). CONCLUSION: Close proximity of implant angulation toward right-angled direction results in higher precision of implant.
ABSTRACT
INTRODUCTION: Single crowns or fixed partial dentures retainers usually get dislodged due to inadequate resistance form. Hence, it is prudent to evaluate features of a tooth preparation, which can prevent these failures. AIM: To evaluate the effect of auxiliary features, occlusal surface modifications, and total occlusal convergence (TOC) on the resistance of a full veneer crown. MATERIALS AND METHODS: An ivorine mandibular molar tooth was prepared with features of inadequate resistance form, i.e., 2.5 mm axial wall height and TOC of 20°. Seven auxiliary preparation features were subsequently added one by one to it. They were mesiodistal grooves, buccolingual and mesiodistal grooves, buccolingual grooves, mesiodistal boxes, occlusal inclined planes, 8° reduced TOC in the cervical aspect, and mesiodistal grooves added to 8° reduced TOC in the cervical aspect. Ten dies with their respective crowns were prepared for each group. Resistance testing of all the samples was performed on the INSTRON testing machine. RESULTS: Modification of the overtapered die preparation by reducing the TOC to 8° in the cervical 1.5 mm of the axial wall and then subsequently adding mesiodistal grooves to the reduced TOC cervically offered the greatest resistance to dislodgment statistically. CONCLUSION: For an overtapered preparation, reducing the TOC to 8° in the cervical aspect and subsequently adding proximal grooves can provide maximum resistance form.
