August 1, 2003
by David M. Vassos, DDS
A continuing challenge in implant dentistry has been the placement of implant(s) in a manner that enables the creation of functionally and esthetically superior restorations. Over the years, a variety of surgical guides have been developed to optimize placement, but the fabrication of such guides remains costly and time-consuming, and inadequate posterior access all too often compromises their use. This article describes a system of implant-positioning rings that simplifies the task of accurate implant placement. Several case examples also are presented.
Accurate placement of dental implants is a crucial requirement for the achievement of an optimal restoration. Particularly in the anterior, incorrectly positioned implants may make it impossible to create a prosthesis with an esthetic emergence profile, compromising the patient’s ultimate appearance. Overangulation and/or overly lingual placement may also require restorative solutions that interfere with proper speech and oral maintenance.
In an effort to ensure that implants are placed optimally, various clinicians have advocated the use of a surgical guide.1,2 One common technique involves taking an alginate impression of both arches, then pouring up impressions to make models from which duplicate casts are created. The edentulous space on the casts is measured, appropriately sized implants are selected, and their desired positions are marked on the casts. Angulation is also surveyed at this time.
Individual denture teeth are inserted into the spaces on the cast and stabilized with wax. These teeth represent the appearance of the final restoration. Temporary splint material is warmed and vacuum-formed onto the cast while the denture teeth are in place. This creates a hard, thin plastic shell called a “vacuform.”
The vacuform and denture teeth are removed from the cast, and then the vacuform is replaced. On it holes are drilled through the center of each space where the denture teeth were positioned. Carried through into the cast model, the holes show where the implants will be placed. Metal sleeves approximately 3.5 mm tall are then placed into the holes; these are intended to guide the drilling during the surgical appointment.
A hard acrylic tray material is processed over the cast, incorporating the sleeves. The acrylic is then trimmed and polished, completing creation of the surgical stent.
Over the years, a variety of additional methods for creating stents have been described, including the labial outline stent made from a waxup,3 duplicates of the existing restoration,4 three-dimensional templates,5 and other methods.6-7 All these approaches share a number of drawbacks, however. Besides the cost (typically $125) and time required for fabrication, the stents also often prove to be unusable because of inadequate posterior access.
In an effort to overcome these problems, a system for optimizing implant placement by utilizing a standardized set of implant-positioning rings has been developed. This report describes the system and reports on its use in treating four patients.
MATERIALS AND METHODS
The positioning rings (V.I.P. Systems, Edmonton, AB) provide the clinician with a simple, immediate, and inexpensive means of establishing the proper interdental space for each implant to be placed.
The system consists of a set of 14 finely milled rings made out of polished, surgical-grade titanium. The rings range in diameter from 5mm to 11.5mm, increasing in half-millimeter increments. Each ring is 3mm high and contains a 2mm-wide hole.
Each ring also incorporates a radial groove that stops just short of the central hole. A standard hemostat, recommended for handling of the rings, fits into the groove and is held securely by it.
The implant-positioning rings are fully autoclavable and can be utilized in single- or multiple-implant indications, as well as when placing implants in the fully edentulous ridge.
When placing a single implant, the rings are employed as follows: First the biggest ring is selected that will fit into the edentulous space so that it touches the two adjoining natural teeth. If no natural teeth abut the space, a ring of the same diameter as the contralateral tooth is selected. Determination of the diameter can be made by measurement with a Boley gauge or comparison of the rings to the contralateral tooth.
Using a hemostat to hold the selected ring, the mucosa or bone is marked with a pilot drill placed through the ring’s central hole. The ring is then removed and the operator uses a tapered fissure bur or a spiral drill to penetrate the dense cortical bone.
After repositioning the ring, drilling with the pilot drill continues to a depth of roughly 7mm below the surface of the tissue. A parallel pin then replaces the drill, securing the ring in position, and the positioning is checked. Once the angulation is correct, osteotomy preparation proceeds according to the standard protocol.
If several implants are being placed, the ring sizes are selected by matching their diameter to either the contralateral teeth or the patient’s existing denture. The doctor begins with the most anterior implant, abutting each successive ring against the previously positioned one. Once all the rings and pins have been secured, the doctor reconfirms the parallelism of all the pins. Then the pins and rings are removed, and implant placement proceeds according to the standard protocol.
Treatment is similar in full-arch cases. The midline is determined using the nose, the philtrum of the lips, and the frenum and marked extraorally with a black felt-tip pen. Intraorally the midline is marked with a bur mark on the ridge. The central incisor ring size is determined by comparison with the denture central incisor. This ring is then placed immediately adjacent to the marked midline, and the positioning sequence described above follows. (If both arches are being treated, placement should begin in the maxilla.)
The same procedure is followed for the lateral incisor and so on, until all parallel pins and rings have been positioned as desired on one side of the arch. The other side is then treated in the same manner.
Once all parallel pins have been positioned as desired, osteotomy preparation is completed. It is recommended to have at least two sets of rings available for full-arch cases.
The following examples illustrate the use of the VIP System.
After radiographic evaluation and ridge-mapping established that an adequate foundation of bone existed at the healed site of the patient’s lower right first molar, a 10.5mm implant-positioning ring was selected and assessed within the edentulous space. A pilot drill positioned through the hole of the ring was utilized to mark the mucosa (Fig. 1). The ring was then removed, and penetration of the cortex was achieved with a spiral drill. After replacing the ring, drilling with the pilot drill continued to a depth of about 7mm.
A parallel pin was then inserted, and the patient was instructed to close down, confirming the position and angulation of the sulcus (Fig. 2). Drilling and placement of the implant then proceeded according to the standard protocol.
This patient was missing all the teeth from the upper left central incisor on back. After creation of a mucoperiosteal flap, a 9mm ring was selected to match the upper right central incisor (Fig. 3). The ring was then butted up against the existing incisor (Fig. 4), and a spiral drill and pilot drill were utilized to create the sulcus. Insertion of the parallel pin confirmed the correct positioning (Fig. 5), and the steps were then repeated for all the remaining implants to be placed (Figs. 6a-c).
A significant amount of ridge resorption was evident in this patient, who was missing all four upper incisors. A flap was created, and augmentation was accomplished using a titanium-mesh framework filled with a collagen membrane, irradiated bone, and platelet-rich plasma.
After the mesh was screwed into place (Fig. 7), it was covered again with a guided-bone-regeneratio
n (GBR) membrane. The tissue was released, positioned over the grafted ridge, and approximated.
The tissue was allowed to heal for six months, after which the titanium-mesh framework was removed. Using the patient’s partial denture as a gauge, four implant-positioning rings were selected, drilling was accomplished, and the parallel pins were inserted to confirm the positioning (Fig. 8). The radiograph in Figure 9 illustrates the ideal spacing of the implants after placement.
In this case, implant-positioning rings facilitated placement of implants in a patient with an edentulous maxilla. First a ring was selected corresponding to the size of the left central incisor on the patient’s denture (Fig. 10).
After creation of a flap, the patient’s midline was marked on the lip and ridge, then the ring was positioned to adjoin the midline mark (Fig. 11). Figure 12 shows the parallel pin in position. Placement of the additional rings and parallel pins continued for the remaining upper left teeth (Fig. 13). Figure 14 shows the radiographic results after placement of the implants, and Figure 15 demonstrates the final restoration.
The V.I.P. System rings help the implant practitioner to determine the precise distance needed between each implant being placed. Moreover, the height of the rings guides the pilot drill, ensuring that it is parallel to the long axis of any adjoining teeth. This helps to avoid off-axis loading, an important condition for long-term implant survival.
If bone at the implant site is deficient, grafting should be employed to build up the ridge, to create an ideal emergence profile and esthetics.
Adequate stability of the rings during drilling is easy to achieve, but adjustment of the angulation can be achieved, if necessary. If placement of the parallel pin reveals the angulation to be unsatisfactory, the clinician can immediately drill again to improve the positioning. Since the diameter of the pilot drill is only 2mm and typical implant diameters range from 4.3 to 6mm, the ultimate osteotomy should still prove acceptable.
The implant-positioning system described in this article offers a number of advantages over traditional surgical templates. Because a customized device need not be fabricated, implants can be placed as soon as the patient elects to proceed with treatment.
The fact that the rings are reusable means that the cost-per-patient when using this system is a fraction of that incurred when surgical templates are employed. Moreover, the rings’ low profile (3mm tall) ensures that they can be utilized even in areas of the mouth where access is extremely limited.
Despite its simplicity, the system allows clinicians to place implants with a high degree of accuracy and thus to achieve an optimal emergence profile.
Dr. Vassos is Diplomate, American Board of Oral Implantology/Implant Dentistry, Fellow and Diplomate, International Congress of Oral Implantology and Honored Fellow, American Academy of Implant Dentistry.
Oral Health welcomes this original article.
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