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Impression for Initial Crown on Tooth 36 -The Crown has Sub-gingival Margin. Illustrate your essay with Specific Examples.

1. Dental impression of 36th tooth and crowning procedure

Dental impressions have become fairly common procedures now-a-days. The process and different types of dental impressions, however, change with the type of the teeth, problems and pathophysiological conditions associated with them (Livaditisa, 1998). The procedure starts with numbing of the teeth and gums by local anesthesia. In most situations, dentists take impressions of teeth using a putty-like substance, known as 'Impression material". This impression will then be processed in the dental laboratory where a plaster cast will be generated. This cast will be used to make dental crowns which will be almost an accurate fit to the tooth in consideration since the cast fits snugly on the same tooth. The entire process takes about a week or so to complete. In some situations the dentist may choose to use a dental ceramic milling machine which results in the entire process being completed in a single visit.

During the two to three weeks waiting period, the tooth is covered with a temporary crown usually made of a thin sheet of plastic or even metal sometimes. This temporary crown is cemented in place until the new crown is ready. Subsequent to impression and crown preparation, the dentist will compare the color of the crown in the case of porcelain crown, so as to match the color with neighboring teeth. This process is called shade grade and involves comparison of pieces of porcelain of different colors with the teeth to select the appropriate color. Once a suitable match is found, the particular color of porcelain is used to generate the final crown. The final step is cementing the crown into place. This step involves numbing the teeth and gums and removal of the temporary crown if already placed on the tooth. Before the crown is cemented, the dentist follows certain steps to ensure proper placement. This involves inspection of proper fit by dental floss and usage of dental tools. The dentist usually asks the patient to bite down, and then removes and adjusts the crown until the patient is comfortable. Since the 36th tooth is not clearly visible in smiling or laughing, there is no need to determine the color match with neighboring teeth in these situations but dentists usually ask patients to self evaluate color match so as to make it as esthetically better as possible. The final step involves cementing the crown over the tooth. Once there is consensus between the dentist and the patient over crown and color and blending, cement is placed inside the crown and it will be subsequently seated on the tooth. Once the placement is complete the cement will be allowed to dry. The dentist then uses a dental tool to scrape of pieces of cement the overflow outside the edges of the crown. This completes the impression and crown placement procedure.

4. Discussion

Impression for crown of teeth with sub-gingival margins is difficult because in some cases there could be a defect that extends deep down into the sub-gingival region or the impression is indicated for generating a full coverage crown for solving esthetic issues (Kazuhiko et al, 2005). In the classical case it is always better for impression to be carried on teeth with supra-gingival margins because there are several studies that show that the gingival health in teeth with supragingival margins is almost same as the original teeth. However, there may be situations where the margins are sub-gingival and in these situations, the margins require retraction so that the impression material can penetrate and have access to the prepared margins (Livaditisa, 1998). A subgingival margin is only suitable when the attached gingival is free of inflammation on one hand and there is enough gingival tissue. In a case where the gingival tissue is not enough, a periodontal graft may be needed (Bassiouny and Yearwood, 1996). In most cases the appropriateness of the impression procedures should be evaluated based on the pros and cons of each procedure. Additional factors that should be taken into account are the extent of the sub-gingival margin present and the level of esthetic crown desired (Livaditisa, 1998). In most cases traditional fixed prosthodontic impression procedures are used. But with the advent of latest impression procedures which have the ability of better retraction , reduced sulcal bleeding and improved penetration of the impression material, these methods are more suitable for sub-gingival margins in the 36th tooth. One such system is the matrix impression system which combines the positive aspects of traditional methods with superior healing and esthetic appearance (Livatidisb, 1998). This method is suitable and indicated in situation were there are gingival recession and inflammations, two major processes that are a major hurdle for the impression procedure. The choice of the exact impression method however, rests in the hands of the dentist who considers the benefit of each method and customises is according to the situation.

5. Conclusion

Impression of the 36th tooth in the subgingival margin is very critical and requires the choice of correct impression methods. A careful selection of impression methods is necessary to promote efficient gingival retraction, reduce sulcus bleeding, assist in efficient impression material entry into the sulcus at proper pressure and prevention of air and fluid entrapment. In addition it must be kept in mind that there might be problems associated with gingival health such as gingival recession and gingival inflammation that require special treatment at the sub gingival margin. In these cases it is important to defer the procedure and promote oral hygiene and reinitiate the procedure once gingival health is regained. Thus it is vital to tailor or customise impression procedures based on the health status of each tooth and plan judiciously in such a way so as to achieve maximum prognosis and will prevent relapse in the future.

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