Compound Cavities - Part 2
Cavities which involve both approximal surfaces and the morsal edge of the incisors and cuspids- mesio-disto-morsal cavities- present the greatest difficulties from the mechanical stand-point in the whole range of operations for restoring lost portions of tooth-structure with gold, but when the operation is finished it becomes, by reason of its form, one of the most secure fillings that it is possible to make.
The filling may be started at the cervical border in the pits and grooves made for the purpose in either of the approximal cavities, preferably in that one which is farthest from the operator. Cohesive gold only is admis sible in this class of fillings.
The filling should be built up from the cervical border as squarely as possible until the morsal edge is reached. The same method is then employed in the approximal cavity nearest to the operator, and when the morsal edge is reached the fillings are united by carrying the gold across the morsal edge, and finally finished at the approximo-morsal angle nearest to the operator. The image represents the completed filling. If the approximal fillings have been securely anchored, the force applied upon their morsal extremities will have no tendency to dislodge them during the process of building the morsal edge, but if this preliminary step has not been properly taken, dislodgement is more than likely to occur before the operation is completed.
Cavities involving the mesial and morsal surfaces-mesio-morsal-of the bicuspids and molars offer no difficulties which are not readily overcome. The only preliminary necessary for the preparation and filling of the cavity is the obtaining of such an amount of space by some of the methods of temporary separation as will enable the operator to gain a clear view of the cavity in all of its parts, and permit of the original form being restored by the insertion of a contour filling.
Failures in this class of fillings are prone to occur at the cervical border, from secondary caries, and this is often due either to imperfect preparation of this portion of the cavity, to bruising of the enamel margin while condensing the gold against it, or to imperfect adaptation of the gold to the cervical wall". The greatest care should therefore be exercised in the preparation of the cavity and the introduction of the gold.
The cervical margin may be protected against bruising and perfect adaptation of the gold to the tooth secured by introducing a non-cohesive soft-rolled cylinder and condensing it against the cervical border. Many operators are in the habit of filling the cervical third of the cavity with non-cohesive cylinders and the balance, with cohesive foil. Others prefer to fill the entire cavity with cohesive foil, using crystal gold at the cervical border to form the foundation of the filling, as on account of its great soft ness it is easily placed and can be readily adapted to the walls of the cavity.
A safe rule in all contour work is to extend the gold a little beyond the desired line of contour, in order that there may be opportunity for final shaping and polishing without destroying the artistic contour of the finished filling. Thorough condensation of the gold is an important factor. in the stability of this class of fillings. Flow of gold fillings under stress, is much less, as shown by Dr. Black, in fillings that had been thoroughly condensed and hardened by malleting than in those which had not been malleted. These fillings are subject to great stress, and therefore need to be thoroughly anchored in the morsal. surface. First image shows a method of anchorage obtained by extending some portion of the niorsal cavity or by its natural form.
The last two images represent the method of " extension for prevention" suggested by Dr. Black for filling bicuspids and molars.
This method so exposes the margins of the fillings that they can be kept clean with the tooth-brush, and it effectually secures them against a recurrence of caries with ordinary care of the mouth, provided the operation has been properly performed.
Cavities situated upon the distal and morsal surfaces of the bicuspids and molars unite to form disto-morsal cavities.
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