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Crown Preparation with a Sonic Handpiece and Corresponding Finishing Tips
Crown placement can only be successful when a practitioner removes the correct amount of tooth structure on the prepared surface.
Domenico Massironi, DDS
As all clinicians know, an ill-prepared crown core may lead to problems, and the restoration material’s thickness might not correspond to functional loads. If a practitioner does not protect the core’s critical areas, then his/her technique could also injure or damage the corresponding pulp and periodontal tissue. Having the right instrument for crown preparation procedures is a critical element to completing a successful treatment. Sufficient professional knowledge and perfect control of a crown-preparation instrument are fundamental preconditions for achieving a desired result.
In this author’s opinion, special care must be taken during the positioning of the preparation margin. Esthetic demands and the need to disguise the restoration between natural dental elements, however, force this author to create suitable thicknesses and to position the prosthetic margin from the vestibular side to the intrasulcular region. This includes almost direct contact with the epithelial attachment.
Practitioners have used modified chamfer preparations to avoid injuries and changes to the periodontal tissue during intrasulcular positioning. This requires the practitioner to use a rotary diamond instrument for all anatomical preparations. The design of these instruments is more pronounced than a vertical chamfer, but less than a rounded shoulder, and is called a “modified chamfer” by the author. These diamonds provide enough space for the creation of stable prosthetic margins even during the firing of ceramics, and, therefore, are able to provide a highly precise, esthetically pleasing restoration. At the same time, this procedure is gentler on the tooth structure than conventional methods of manufacturing dentures, in areas where esthetics is of great importance.
Rotary instruments, however, can come in contact with gum tissue, causing tearing and bleeding. To prevent such issues and allow better instrument control during the positioning and finishing phases, using an oscillating instrument can be safer and more efficient. Oscillating instruments are easier to handle during these delicate phases because they are gentler on soft tissues, do not damage the gum tissue, and create an ideal finish of the dental surface in preparation for the subsequent cementing phase.
In the case presented, the author will demonstrate how he used an innovative sonic handpiece and corresponding tips to provide satisfactory results for preparing and finishing a crown core.
In this author’s opinion, Sonic Tips (KOMET USA, www.komet-usa.com) were designed for the exact positioning and finishing of crown margins, making crown preparation easier. Also, this author believes Sonic Tips are ideally suited for this indication, producing an exact marginal seal, site preparation, and clinical restoration.
A patient visited the office needing a ceramic crown on the lateral incisor (tooth No. 10). Using a rotary diamond instrument (2979.314.014, KOMET USA), the author prepared the supragingival area of the tooth (Figure 1). By taking an impression of the prepared tooth core, the material showed the parallel groves created by the rotary instrument and preparation step (Figure 2).
To complete the preparation and finishing of the crown core, the author used a modified chamfer Sonic Tip (SF979.000.014, KOMET USA) for the exact position of the crown core preparation (Figure 3). The Sonic Tip was used in a sonic handpiece (KOMET SF1LM, KOMET USA). To achieve the best synergy effects, this author recommends that a combination of rotary and sonic instruments be used.
Contrary to ultrasonic instruments, sonic instruments are not driven by an electrical power source allowing the sonic handpiece to be used like an ordinary handpiece. A sonic handpiece, like the SF1LM, attaches to the air tube of the dental turbine common in every dental office. The KOMET SF1LM comes with a MULTIflex® (KaVo Corporation, www.kavousa.com) connection. The oscillation generated by this type of power source expands in all directions. One of the benefits to this technique using a sonic instrument is that the practitioner does not need to hold onto the handpiece at a strenuous, fixed-tilt angle during use—making the tips easier to control. The lower frequency of vibration compared to ultrasonic devices does not limit the action of the instrument (excellent cutting through dentin at high settings and optimal finishing at low settings), but presents the further advantage of creating a roughness of a few microns while smoothing the surface of the dentin. This promotes the crown cement’s retentive properties which, in these conditions, flow perfectly, thus limiting the formation of undesirable and dangerous voids.
An impression of the crown core was taken after the author performed the finishing technique using the sonic instrument. The impression showed an irregular surface structure, which favors the correct impregnation and adhesion of the cement to be used in placing the crown (Figure 4).
For esthetic reasons, the preparation margin needs a larger support area for the subsequently applied crown. After the preparation, the finished crown core shows no damage to the soft tissue (Figure 5), and the case was completed with cementing the ceramic crown onto the crown core (Figure 6).
The success of prosthetic treatments is largely influenced by the performance of the instruments and the use of suitable materials, allowing standardization of the quality level and at least partly reducing the quality component that depends on the skills of the operator. The Sonic Tips and SF1LM sonic handpiece represent an enhancement in ultrasonic technology that has revolutionized the concept of lowering, positioning, and finishing the prosthetic margin—eliminating the disadvantages related to linear vibration of ultrasonic devices. Today, there is a range of versatile precision instruments on the market that allow preservation of the dental and gingival tissue during surgical interventions. In the author’s opinion, a sonically placed and finished crown margin is the best precondition of an exact impression and the successful creation of a durable restoration.
Dr. Massironi is a paid consultant for KOMET USA.
About the Author
DomeniCo massironi, DDs