Written by Timothy F. Kosinski, DDS Friday, 28 February 2003 19:00
Providing highly accurate, simple, and consistent final crown and bridge impressions is a critical step in the fabrication of aesthetic, properly fitting restorations. Because many different materials on the market today make highly speculative claims as to their chemistry, it is imperative that you find materials of uniformly high quality for this procedure. In particular, look for a mixing unit that provides a smooth, well-mixed, heavy-body material that is easily placed into an impression tray, eliminating voids and poor mixes.
The patient, a 41-year-old white male, presented via an emergency visit with a fractured cemented post within the maxillary right central incisor. The maxillary anterior teeth had been previously restored with Diamond (Jelenko) and Ceramco II (Ceramco) PFM crowns. Albacast (Jelenko) cast posts and cores supported the maxillary right and left lateral incisors. The crowns originally were placed for aesthetic purposes, including positioning and shade, and the mandibular anteriors had been lightened by using the Nite White (Discus) system. The following technique was used to replace the fractured post.
|Figure 1. The tooth was fractured to the gingival level.||Figure 2. The root was prepared and the gingival tissue was retracted.||Figure 3. The whiteness of the gingival tissue indicates the blood flow is controlled.|
The fractured post was removed by using a Cavitron Jet (DENTSPLY) ultrasonic scaler, which allows for removal without damage to the root structure. The tooth was fractured to the gingival level (Figure 1). Root canal therapy was performed on the maxillary right central incisor. The original crown was relined and seated as a transitional treatment.
The root was prepared and the gingiva retracted by using Oa Ginga Braid (Van R) and No. 2 Twist Ginga Plain (Ginga Pak) cords (Figure 2). These cords pull the tissue away from the prepared tooth, serving as a retraction as well as providing homeostasis. After the assistant inserted the loaded Imprint II Penta Heavy-Body Impression Material (3M ESPE) cartridge into the Pentamix Mixing Unit (3M ESPE), the plunger was depressed to ascertain the appropriate pressure against the foil bag. A small amount of material was extruded by pressing the button and then discarding it. After waiting for a uniform mix, the tray was filled with Imprint II Penta Heavy-Body Impression Material. Because of its viscosity, heavy-body impression material can be extruded most easily by using the Pentamix mixing unit.
A prefabricated plastic ParaPost (Coltene Whaledent) was positioned in the root canal, and Imprint II Garant Light-Body Impression Material (3M ESPE) was syringed around the preparation. Note the whiteness of the tissue where the blood flow has been controlled (Figure 3). Meanwhile, the assistant filled a Bosworth tray with Imprint II Penta Heavy-Body Impression Material dispensed from the Pentamix mixing unit (Figure 4). Dentist and assistant should both aim to finish at the same time, to ensure both the light-body and heavy-body impression materials are in their most fluid states and not beginning to harden.
|Figure 4. A tray is filled with heavy-body impression material dispensed from the Pentamix unit.||Figure 5. The ParaPost is easily picked up in the final impression.||Figure 6. The stone model was poured.|
The tray was slowly seated in the mouth and immobilized by using passive pressure. Oral set time was 4 minutes. The impression was removed, making sure the plastic ParaPost was engaged. The impression was rinsed, dried, and disinfected. Imprint II Penta Heavy-Body Impression Material is hydrophilic and accurately captures detail reproduction. Note that the ParaPost was easily picked up in the final impression, which will be used to fabricate the custom cast post and core (Figure 5). After waiting 30 minutes, the stone model was poured (Figure 6).
To provide adequate coronal support, the new crown was fabricated by using an Albacast cast post and core.
After adjusting occlusion and cleaning the site with Hemaseal and Cide (Advantage Dental), the cast post and core and the final crown were simultaneously cemented by using KetacCem Glass Ionomer Cement (3M ESPE) (Figures 7 and 8).
|Figures 7 and 8. The cast post and core and the final crown were simultaneously cemented.|
This case report describes the technique and materials used to replace a fractured cemented post. Of particular importance is the selection of impression materials and an appropriate delivery system. Extruding heavy-body impression materials via a syringe, or hand-mixing materials, can result in ergonomic pressure that can prove painful to your assistant while also potentially creating voids within the tray. The delivery system used in this procedure eliminates the need for hand-mixing any impression material while still helping achieve uniformity in set time.
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