The Porcelain Jacket Crown / Its Usefulness in Removable Bridgework

Abstract

THE porcelain jacket crown has rendered wonderful service in raising the status of our profes­ sion. When indicated, it makes a restoration that is almost lifelike in ap­ pearance, comfort, durability and compatibility with the adjoining and underlying living tissues. In many of these respects, it affords a striking con­ trast to the old-fashioned gold shell crown. T o follow the first of the two pos­ sible methods of construction, the in­ direct, we first prepare the tooth in the mouth and reproduce with an amalgam die. Plaster models are made, and the crown is constructed to fit ex­ actly the amalgam die and to conform with the plaster models. T o follow the direct method, we would make the crown on the prepared tooth in the mouth without the aid of the amalgam die and plaster models. T he indirect technic is recommended because it offers uniformly better results. There are two types of the all-por­ celain jacket, one known as the shoulder crown, the other the shoulderless, or, as it is sometimes called, the overlap crown. W ith the shoulder crown, the shoulder is cut around the neck of the tooth just below the free gum-margin. This shoulder is made at right angles to the long axis of the tooth and of as little depth as possible. T he jacket is made to finish flush with the outer mar­ gin of the shoulder and at the same time to restore the proper enamel contour at the gum margin. T he shoulderless, or overlap, crown eliminates the cutting of a shoulder, the porcelain tapering down to a fine edge beneath the gum line. T he advantages of the shoulderless over the shoulder crown may be sum­ marized as follows: (1 ) conservation of tooth structure; (2 ) lessening of the danger of subsequent pulp involvement; (3 ) reduction of pain in the prepar­ ation. There are, however, some ac­ companying disadvantages: (1 ) the im­ possibility of getting a perfect fit at the gum margin; (2 ) the danger of frac­ ture of the porcelain; (3 ) the difficulty of getting the correct anatomic resto­ ration at the gingival third. Taking a common clinical case, that of a lower bicuspid with a gold shell crown, we frequently notice that the gum margin has receded. After the removal of the gold crown, we usually find that the enamel has been destroyed; the tooth is free of the bite, and there may be decay or sensitiveness around the neck of the tooth. From an esthetic