Effect of Two Dentin Desensitizing Agents on the Retention of Cast Copings on Compromised Preparations Using Three Cements

Abstract

This study was designed to evaluate the effects of two dentin desensitizing agents on the retention of cast copings on compromised preparations using three cements. A total of 45 extracted intact human molars of approximately similar crown sizes were selected and mounted in epoxy resin blocks. They were designed to simulate all metal full coverage compromised crown preparation for a molar tooth, with occlusal convergence of 20o. An occlusalnotch was prepared for exact repositioning of the copings during measurements. The Impressionsof the prepared teeth were made with a vinyl polysiloxane impression material using plastic tubes and tray adhesive. The impressions poured using type IV dental stone. Wax patterns were made on stone dies with casting wax with flat occlusal surfaces and a consistent thickness. A round sprue wax shaped as a loop was attached to the center of the occlusal surface of each wax pattern parallel to the long axis of the prepared tooth to facilitate connection of the coping to the Universal testing machine. The test copings were cast with Ni-Cr base-metal alloyusing an induction casting machine. Copings were recovered using airborne-particle abrasion. Each coping were then gently checked on its relevant working dies and prepared teeth for seating and marginal fit. Minor adjustments necessary to seat castings on dies were completed by using a disclosing medium and a small round bur under magnification. Before cementation, it was also verified that all copings were not self-retentive by ensuring that all castings separated from the dies without any resistance when the specimens were held upside down. The fitting surfaces of all castings were cleaned with an ultrasonic cleaner and stored in paper envelope until cementation. Temporary crowns were fabricated with tooth-colored self-curing acrylic resin over the dies using equal sizes of molar ready- made celluloid crowns. Fifteen of the prepared teeth were treated with Gluma desensitizer, another fifteen were treated with i-Flor desensitizer, and the remaining fifteen were left without treatment to be used as a control group. The desensitizing agents were used to seal the dentin after crown preparation and again just before the final coping cementation. Temporary cementation of the acrylic crowns were simulated for all specimens. Zinc oxide eugenol temporary cement for teeth on which copings were to be cemented with zinc phosphate and glass ionomer cements.Non-eugenol temporary cement for teeth on which copings were to be cemented with the resin cement.Specimens were stored in water for 3 days was done, then the temporary crowns were removed and the cement was cleaned. The desensitizers were again applied to the same previously sealed teeth as mentioned before.Three different cements were used Zinc phosphate, glass ionomer, Self-adhesive resin cement. The copings were initially seated, during cementation, utilizing static finger pressure, using the indexing occlusalnotch in the preparation as an orientation guide,then axially loaded with a 5 kg load using a specially designed device for 10 minutes to ensure cement setting.All samples were stored in distilled water at room temperature for 24 hours before being tested.