New implant surgical guide

l?. J. R. O’Neilly, Eastman Columbus,

Dental Ohio

BDS,

Hospital,

LDSRCS, London,

England,

MS,a and

and E, A. McGlumphy, The

Ohio

State

University

DDS, College

MSb of Dentistry,

This article describes the process of making and using a surgical guide stent. It is intended to enable the surgeon to maintain the same horizontal and vertical axes of cylindrical endosseous implants during the surgical phase of implant placement as those determined at the treatment planning stage. Furthermore, the stent can be used with the entire series of surgical drills, thereby minimizing the chance of inadvertently enlarging the implant site as a result of freehand use of the handpiece. (J FROSTHET DENT 1993;70:506-10.)

c

ylindrical endosseous implants that are correctly located on the edentulous ridge may have an incorrect angdation. If an edentulous region is to be restored with a screw-retained prosthesis, it is desirable that the retaining screw emerges through the occlusal or palatalflingual sur-

Presented lumbus, aLecturer, “Assistant Dentistry,

at the Carl 0. Boucher Prosthodontics Conference, CoOhio Conservative Dentistry, Eastman Dental Hospital. Professor, Department of Restorative and Prosthetic The Ohio State University. 1993 by The Editorial Council of THE JOURNAL OF

Copyright PROSTHE'VICDENTISTRY. 0022-3913/93/$1.00

+ .lO.

10/l/50412

Fig. 1. Relationship of x (anterior-posterior), y (mediolateral) and z axes (superior-inferior) of implant to edentulous ridge and proposed restoration.

face of the restoration so that superior esthetics and function can be obtained.‘,* It is possible for the x (anteriorposterior) and y (medio-lateral) coordinates of the implant to be satisfactory with respect to the proposed restoration (Fig. 1). However, if the z (inferior-superior) coordinate is incorrect, prosthetic reconstruction with screw-retained prostheses is difficult if not impossible. It has been stated that when implants are placed in the anterior region of the maxilla, an error in angulation (2 coordinate) of the implant by as little as 10 degrees can render the implant unrestorable.3 Several surgical guide stents have been described in the literature.1,4-7 Balshi and Garver4 described a stent where 2 mm holes are made in an acrylic resin template to act as a guide for the 2 mm pilot drill. Because of its thickness and

Fig. 2. Stainless veyor.

steel template

mounted

in arm of sur-

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Fig. 3. A, Stainless steel template used to determine correct X, y, and z coordinates for proposed implants in relation to vacuum-formed matrix of diagnostic wax-up. B, Matrix is removed and coordinates are related to edentulous ridge. Difficulties in obtaining adequate accesswith head of handpiece can be anticipated at this stage.

Fig. 5. Additional acrylic resin has been added to stent for rigidity.

4. Vacuum-formed matrices are repositioned on cast and surveyor. The open side of stent is placed so that handpiece can be inserted when stent is placed. Fig.

spacing to allow irrigation, the stent cannot always guide the drill to the full depth of the hole. Once the 2 mm hole has been made, the stent is of little value and the remaining site preparation is done freehand. Furthermore, if an alternative implant location is preferred, the stent cannot be used. The stent described by Edge5 has drawbacks similar to those of Balshi and Garver.4 Pare1 and Sullivan6 and Hobo et a1.7 described a stent whereby the buccal contours of the proposed implant-supported restoration are created in the stent. The stent does not serve as a direct mechanical guide, and site preparation is done freehand. Engleman et a1.l also described a stent

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similar to that of Pare1 and Sullivan‘j; however, they suggest that the angulation of the implant site be verified by placing guide pins into the pilot holes with the stent in position. With this technique, the implant angulation (z axis) with respect to the proposed restorations can only be determined after the pilot hole has been prepared. This article describes a new method to make a surgical guide stent that would enable the operator to maintain the same r, y, and z coordinates of the implant throughout the course of the surgical phase.

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This technique includes the use of a stainless steel template that is of the same diameter as the head of the contra-angle handpiece used in the surgical stage (Fig. 2). One end is machined to a point and the opposite end is machined to fit in a surveyor. The diagnostic and preoperative evaluation procedures

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Fig. 6. Open side of stent is trimmed to receive head of handpiece.

Fig. 8. Bottom of guide channel has been removed and stent is used in later stages of implant site preparation.

Fig.

7. Guide stent used while pilot hole is drilled in bone.

described in other studies should be followed.‘, 3-i This evaluation would include appropriate radiologic examinations, (periapical, lateral cephalometric, tomographic, panoramic, and computerized tomography [CT]). A diagnostic wax-up or setup of the proposed prosthesis is also essential. When the intended artificial tooth position has been confirmed estheticahy and functionally, a stone cast is made of the wax-up and a vacuum-formed matrix is made over it for later use. A diagnostic cast is mounted on a surveyor. The cast is tilted to establish the most favorable coordinates (x, y, and z) for the implants by relating the position of the retaining screw(s) for the proposed prosthesis (formed by the matrix of the diagnostic wax-up) with the underlying edentulous

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ridge (Fig. 3). The intended coordinates may be modified to accommodate radiographic or clinical findings. With this procedure, the proposed implant locations can be aligned with the intended prostheses and, most important, the underlying bone topography and relevant anatomic structures (Fig. l).l The template can also indicate possible difficulties in gaining correct access with the handpiece (Fig. 3, B). When the desired coordinates (x, y, and z) have been established, the diagnostic cast is carefully removed from the surveyor and the matrix of the diagnostic wax-up is set aside. A vacuum-formed matrix is made of the original diagnostic cast. The matrix is trimmed so that only the incisal edges, the occlusal surfaces of the supporting teeth, and the edentulous ridge are covered. A sufficient number of teeth should be present in the arch to adequately support and stabilize the stent. A matrix is then formed around the stainless steel template to provide a smooth internal surface of the stent against which the head of the handpiece can slide. The diagnostic cast is returned to the surveyor in its original position. The template is repositioned in the arm of the surveyor and placed so that the tip of the template is exactly over the proposed implant site on the edentulous ridge (Fig. 4). The x, y, and z axes can be verified if desired. The “open” side of the template is positioned to permit easy accessof the handpiece when the stent is placed clinically. Autopolymerizing acrylic resin is added incrementally to join the matrix on the diagnostic cast to the matrix around the template. Additional acrylic resin is added to give suf-

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Fig. 9. Implant angulation for first molar determined by described stent. Different stent was used for second molar. Differences in evaluation of occlusal access can be noted.

Fig.

ficient strength and rigidity (Fig. 5). If required, the template can be disconnected from the arm of the surveyor and the cast placed in a pressure pot. When the resin has polymerized, the template can be removed. The open side of the matrix is modified to enable the head of the handpiece to be fully inserted, thus forming the guide channel of the stent (Fig. 6). The bottom of the guide channel is in the form of an inverted cone where a hole for the pilot drill can be made through the stent at the apex of the inverted cone.

reducing the risk of inadvertent eccentric enlargement of the implant site as a result of freehand use of the handpiece. The stent is particularly indicated in situations where, because of prosthetic requirements, there is minimal latitude for alternative implant location and where radiographic examination indicates no adverse bone topography in the ideal sites. Fabrication is simple when it involves materials that are inexpensive and readily available. This stent can only be used along one specific path. Changing the angulation at the time of surgery is difficult. If the surgeon is unable to use the stent as described because of unfavorable bone topography, the stent can be modified. The guide channel of the stent should be reduced to the level of the occlusal surface or incisal edge of the intended restoration until it measures only 1 to 2 mm in height. Alternative coordinates (x, y, and z) for the implant can then be indicated, If the alternative z (superior-inferior) axis of the intended implant can be aligned so that it emerges through the approximate center of the modified guide channel, acceptable implant angulation can be anticipated. The coordinates of the new implant location can be verified by a paralleling pin placed in the pilot hole with the stent in position in a manner described Engleman et a1.l

SURGICAL

STAGE

When the pilot hole is made in the alveolar bone, the stent supports and guides the drill and the handpiece along the predetermined axes (x, y, and z) to the desired depth (Fig. 7). Once the pilot hole has been made, the inverted cone portion of the stent is removed with a bur. The operator can now continue to use the stent throughout site preparation and minimize the risk of accidentally enlarging the implant site because of the use of the handpiece freehand (Fig. 8). The use of this stent will establish reasonable x, y, and z axes of the implants, which result in ideal access for screw-retained prostheses (Figs. 9 and 10). DISCUSSION When the stent described in this article is used, the surgeon can maintain the predetermined x (anterior-posterior), y (medio-lateral) and z (superior-inferior) coordinates for the intended implants while the surgical site is actually being prepared. Use of this guide ensures that the implants are correctly oriented with respect to the proposed restorations, thus reducing the risk of difficult or complex prosthetic reconstruction1z3 In addition, the operator can use the entire series of surgical drills with the stent, thereby

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10. Distal implant placed with described stent. Different stent used for mesial implant. Angulation of mesial implant is shown. (Photograph courtesy of Dr. S. Porter, with permission.)

SUMMARY This article describes an implant surgical guide stent that is intended to minimize adverse implant position and angulation caused by operator error at the time of placement. REFERENCES 1. Engleman MJ, Sorensen JA, Moy P. Optimum placement of osseointegrated implants. J PROSTHET DENT 1988;59:467-73. 2. Sullivan R. Avoiding screw access problems. Nobelpharma News 1992;6(4):6.

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3. Wqtson RM, D&a DM, foreman GH, Coward T. Considerations in deeig~-,& h&&t&n of m&lIary implant supported prostheses. Int ~4 t2&&. I9&1;4:232-9. 4. Bale& Td, G&ver Do. Smgical guidestents for placement of implants. d&al %ixiiofac-Surg 198~45~463-5. 5. Edge J. Suqical placement guide for use with osseointegrated implants. J PFWIBE$ D&m 196~57:719-22. 6. Pare1 SM, Sullivan DY. Esthetics and osseointegration. OS1 publication 1989;24741. 7. Hobo S, Ichida E, Garcia LT. Osseointegration and occlusal rehabilitation. Tokyo: Quintessence Pub1 Co Ltd, 1989;120-1.

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