Plate Implants (Blades)

Blades were the first endosteal dental implant to be used with reasonable success in a large number of patients. In all the original studies on blades, the researchers used one-stage systems, but the success rates were considerably lower than those of current root-form implants. It has been suggested⁶ that many of the problems of blade implants can be traced to the high temperature at which the bone sites were prepared and the routine immediate loading of this type of implant. Both these practices have been linked to the fibrous encapsulation that occurred with many of the original blade implants. Consequently, submersible titanium blades are now available, and in more recent blade studies,⁷ investigators have reported success rates above 80% for 5 years. However, the drawbacks to blade implants remain: difficulty of preparing precision slots for blade placement in comparison with placing holes accurately for root-form implants and the disastrously large circumferential area of the jaw that can be affected when a blade fails.

Root-Form Implants

Root-form endosteal dental implants are considered to be state-of-the-art implant dentistry. Advantages include adaptability to multiple intraoral locations, uniformly precise implant site preparation, and comparatively low adverse consequences similar to those experienced when a tooth is lost. Most root forms are made of titanium or titanium alloy with or without hydroxyapatite coating; these materials are perceived to have the highest biofunctionality. Both threaded and nonthreaded designs are available and are quite popular. Today many of the titanium implants are grit blasted or acid etched to roughen the surface and increase the area for bone contact. Even the theaded dental implants can be further subdivided into “straight” and “tapered” (see Fig. 13-4).

In the National Institutes of Health (NIH) Consensus Conference¹ in 1988, root-form implants were reported to have already constituted 78% of the dental implant market. This trend is credited to the Brånemark system, which set the precedent for surgical techniques and restorative procedures that result in predictably successful implants. Two of the most important additions from the Swedish research team, led by P. I. Brånemark, were atraumatic implant placement and delayed implant loading. These factors contributed to a remarkably increased degree of implant predictability. The original Brånemark success rate of 91% in the mandible over 15 years² has become the standard against which other implant systems are judged.⁸ Many of the other root-form implant systems are also believed to have reached or exceeded this high level of long-term success.

Clinical Evaluation

Evaluation of the planned implant site begins with a thorough clinical examination. This examination determines whether there is adequate bone and identifies anatomic structures that could interfere with ideal implant placement. Visual inspection and palpation allow the detection of flabby excess tissue, bony ridges, and sharp underlying osseous formations and undercuts that would limit implant insertion. However, clinical inspection alone may not be adequate if there is thick overlying soft tissue that is dense, immobile, and fibrous.

Radiographic Evaluation

Radiographic evaluation is also necessary. The best initial film is the panoramic view. However, there can be variations in magnification (5% to 35%); a small radiopaque reference object should therefore be placed near the proposed implant placement site during the exposure (Fig. 13-5). Measurement of this image on the actual radiograph enables the practitioner to correct for any magnification error (Fig. 13-6). A ball bearing placed in wax on a denture baseplate or in polyvinyl siloxane impression putty works well. Some new panoramic radiography machines have standardized enlargement ratios, which makes correction markers less necessary.

Fig. 13-5 Ball bearings (5-mm diameter) placed on the diagnostic cast at the proposed implant site.

Fig. 13-6 A panoramic radiograph exposed with the ball bearings positioned intraorally with a wax or resin baseplate.

The widths of the posterior mandible and maxilla are determined primarily by clinical examination. Bone width not revealed on a panoramic film can be evaluated in the anterior maxilla and mandible with a cephalometric film (Fig. 13-7). The location of the inferior alveolar canal and maxillary sinus can be determined by specialized computed tomography (CT) scans (Fig. 13-8), although high radiation exposure and considerable expense may limit their routine use. However, significant advances being made in this technology may change this trend.

Fig. 13-7 The lateral cephalometric radiograph can indicate bone width in the anterior midline.

Fig. 13-8 The computed tomography (CT) scan. A, CT scan with lines orienting the position of transverse mandibular cross-sections. B, reformatted CT cross-section of the posterior mandible. Arrows in A and B denote position of barium-impregnated resin in the surgical guide.

Diagnostic Casts

Accurately mounted diagnostic casts (see Chapter 2) are essential for treatment planning. They are used to study the remaining dentition, evaluate the residual bone, and analyze maxillomandibular relationships. They can be helpful to the surgeon for fixture placement. A diagnostic waxing is performed on the cast or on a duplicate. Proposed fixture installation sites are checked for proper alignment, direction, location, and relation to the remaining dentition. The waxing helps determine the most esthetic placement of the teeth to be restored and the potential for functional speech disturbances. After adjustments and the diagnostic waxing are completed, a resin template can be made from the cast to guide the surgeon during implant placement (Fig. 13-9). Diagnostic waxings and surgical templates are essential when implants are planned as part of a full-mouth reconstruction or when the anterior esthetic zone is restored (Fig. 13-10).

Fig. 13-9 A, Patient with bilateral missing posterior teeth planned for posterior implant-supported restorations. B, Diagnostic cast. C, Diagnostic denture tooth arrangement to simulate three-unit fixed prostheses on each side of the mandible. D, Vacuumed matrix formed over the cast with 1.5-mm (0.060-inch) thermoplastic sheet. E, The matrix is marked with the most appropriate implant locations and alignments and then removed from the cast. F, The completed surgical guide with holes drilled to guide the surgeon during implant site preparation.

Fig. 13-10 A, Diagnostic cast with missing maxillary left lateral incisor. B, The denture tooth is positioned for optimum esthetics. C, The denture tooth is trimmed from the lingual side until it is 2 mm thick. D, If the tooth is held in position with light-cured composite, a vacuum matrix can be performed directly without duplicating the cast. E, The matrix can be trimmed to the height of contour with a stiff bristle brush. F, The denture tooth can be glued back into the matrix. G and H, The surgeon can use this template to guide both horizontal and vertical positioning.

Bone Sounding

When the results of clinical and radiographic examinations are equivocal and additional information is needed, sounding of the bone with a probe may be attempted. Under local anesthesia, a needle or sharp caliper is pushed through the tissue until it contacts bone. This can help the examiner judge soft tissue thickness at the planned implant sites.

Anatomic Limitations

To maximize the chance of success, the implant should be placed entirely within bone and away from significant anatomic structures (e.g., the inferior alveolar canal). Ideally, 10 mm of vertical bone dimension and 6 mm of horizontal should be available for implant placement. Placement at these dimensions prevents encroachment on anatomic structures and allows 1.0 mm of bone on both the lingual and the facial aspects of the implant. There should also be adequate space between adjacent implants. The minimum recommended distance varies slightly among implant systems but is generally accepted as 3.0 mm (Fig. 13-11). This space is needed to ensure bone viability between the implants and to allow adequate oral hygiene once the restorative dentistry is complete. Specific limitations resulting from anatomic variations among different areas of the jaws also must be considered. These include implant length, diameter, proximity to adjacent structures, and time required for integration.

Fig. 13-11 Recommended minimum distances (in millimeters) between implants and between implants and natural teeth.

The anterior maxilla, posterior maxilla, anterior mandible, and posterior mandible each require special considerations in placing implants. Some common guidelines include staying 2.0 mm above the superior aspect of the inferior alveolar canal, 5.0 mm anterior to the mental foramen, and 1.0 mm from the periodontal ligament of adjacent natural teeth.

After tooth loss, resorption of the ridge follows a pattern that results in crestal bone thinning and a change in angulation of the residual ridge. These sequelae most often cause problems in the anterior mandible and maxilla. The irregular anatomy of the residual ridge may lead to problems with achieving ideal implant angulation or adequate bone thickness along the labial aspect of the implant. Techniques for the management of these problems during surgery are discussed in this chapter, but they must be anticipated in the preoperative phase.

Posterior maxilla

Implant placement in the posterior maxilla poses two specific concerns. First, the bone of the posterior maxilla is less dense than that of the posterior mandible. It has larger marrow spaces and a thinner cortex, which can affect treatment planning, inasmuch as increased time must be allowed for integration of the implants and additional implants may be needed. A minimum of 6 months is usually needed for adequate integration of implants placed in the maxilla. In addition, one implant for every tooth that is being replaced is normally recommended, especially in the posterior maxilla.

The second concern is that the maxillary sinus is close to the edentulous ridge in the posterior maxilla. Frequently, because of the resorption of bone and increased pneumatization of the sinus, only a few millimeters of bone remain between the ridge and the sinus (Fig. 13-12A). In treatment planning for implants in the posterior maxilla, the surgeon should leave 1.0 mm of bone between the floor of the sinus and the implant so the implant can be anchored apically into cortical bone of the sinus floor. Adequate bone height for implant stability can usually be found between the nasal cavity and the maxillary sinus. If there is not adequate bone for implant placement and support, bony augmentation through the sinus should be considered (see Fig. 13-12).

Fig. 13-12 A, The arrow denotes thin maxillary bone inferior to the sinus, which would be inadequate for implant placement without additional grafting procedures. B, Radiograph showing successful treatment with dental implants after graft placement.

Anterior mandible

With regard to anatomic limitations, the anterior mandible is usually the most straightforward area for treatment planning. It usually has adequate height and width for implant placement, and the bone quality is normally excellent; therefore, it requires the least amount of time for integration. Success with immediate loading of implants in the anterior mandible has been reported. This seems to be possible because the implants can have good initial stability.

When possible, an implant in the anterior mandible should be placed through the entire cancellous bone so that the apex of the implant engages the cortex of the inferior mandibular border (Fig. 13-13). In the premolar area, care must be taken that the implant does not impinge on the inferior dental nerve. Because this nerve courses as much as 3.0 mm anterior to the mental foramen before turning posteriorly and superiorly to exit at the foramen, an implant should be at least 5.0 mm anterior to the foramen.

Fig. 13-13 Whenever possible, implants should engage two cortical plates of bone.

Posterior mandible

The posterior mandible poses some limitations on implant placement. The inferior alveolar nerve traverses the mandibular body in this region, and treatment planning must allow for a 2.0-mm margin from the apex of the implant to the superior aspect of the inferior alveolar canal. This is an important guideline: Disregarding it can cause damage to the nerve and numbness of the lower lip. If ade-quate length is not present for even the shortest implant, nerve repositioning, onlay grafting, or a conventional nonimplant-supported prosthesis must be considered.

Implants placed in the posterior mandible are usually shorter, do not engage cortical bone inferiorly, and must support increased biomechanical occlusal forces once they are loaded, because of their location in the posterior area. Consequently, allowing slightly more time for integration may be beneficial. In addition, if short implants (8 to 10 mm) are used, “overengineering” and placing more implants than usual to withstand the occlusal load is recommended. Short implants are often necessary because of bone resorption, which thus increase the crown/implant ratio when the normal plane of occlusion is reestablished (Fig. 13-14).

Fig. 13-14 Shorter implants usually have two problems: (1) less bone contact and (2) longer crowns, which increase the forces acting on the implant. More favorable crown-to-implant ratios (A) have a better prognosis than less favorable ratios (B).

The width of the residual ridge must be carefully evaluated in the posterior mandible. Attachments of the mylohyoid muscle maintain it along the superior aspect of the ridge, and a deep (lingual) depression exists immediately below it. This area should be palpated at the time of evaluation and examined at the time of surgery.

Restorative Considerations

Implant placement

Implant placement is crucial in the design of the restoration. Thus, the treatment-planning aspects of implant placement must begin with a restorative dentistry consultation. Implant placement dictates the appearance, contour, and long-term function of the prosthesis. To prevent damage, staying at least 1.0 mm away from the adjacent natural tooth is essential, but staying as close to the natural tooth as possible is also important; therefore, acceptable contours can be created by the restorative dentist. For proper access during oral hygiene procedures, a minimum of 3.0 mm should be left between implants. In addition, implants must not encroach on the embrasure spaces or be angled so that screw access is necessary through the facial surfaces of the completed restoration (Fig. 13-15).

Fig. 13-15 Implant placement and angulation dictate the screw emergence position and crown contours. Esthetics and access for hygiene can be greatly affected. A, A restored tooth. B, Ideal implant location with acceptable crown contours and lingual screw emergence., C, Acceptable implant location for a cement retained crown. D, If the implant is more facially inclined, an angled abutment for a cement retained crown may be necessary. E, If the implant is too lingual and too shallow, inadequate crown contours for hygiene will result. F, If the implant is angled too far facially and too shallow, the implant and/or abutment may become an esthetic failure.

To minimize harmful lateral forces, the long axis of the implant should be positioned in the central fossa of the restoration. This dictates placing the implant accurately in all three planes of space. Superoinferior placement is important to ensure the optimal emergence profile of the restoration. Ideally, the superior surface of the implant should be 2.5 to 3.0 mm directly inferior to the emergence position of the planned restoration, particularly when the restoration is to be located in the anterior esthetic zone (Fig. 13-16).

Fig. 13-16 Superior or inferior positioning may affect crown contours and pocket depth. A, The implant is not placed deep enough. This creates a short, overcontoured crown. B, Placement 2 to 3 mm apical to the tooth emergence position is ideal. C, Placing the implant 4 mm apical to the crown contours may create an excessively deep gingival sulcus. D to H, Clinical example of a properly positioned implant, both facially and apically, which results in good esthetics.

Implant and restoration size

The choice of implant and its superoinferior placement location are modified by the diameter of the intended restoration and can be adjusted for different sizes of teeth. For example, the typical root diameter of a maxillary central incisor is 8.0 mm; the average implant diameter is 4.0 mm. Therefore, a distance of 2.5 to 3.0 mm is needed to make the transition gradually from 4.0 to 8.0 mm. If this is done over too short a distance, the restoration will be overcontoured or look unnatural. In contrast, many mandibular central and lateral incisors are smaller than 4.0 mm at the cementoenamel junction. Therefore, an esthetic restoration on a 4.0-mm implant is impossible. Smaller-diameter implants (about 3.0 mm) are available to allow esthetic restoration in these areas. It is also possible to use a larger implant (5.0 to 6.0 mm) for molar restorations in patients with adequate bone (Fig. 13-17).

Fig. 13-17 A, Small-diameter implant and abutment positioned to restore a mandibular lateral incisor. The fixed abutment can be custom prepared and narrowed to allow restoration of a small-diameter tooth. B, Completed implant restoration of the mandibular lateral incisor. C, Wide-diameter (5.0 mm) implant in position to replace maxillary first molar. D, Completed implant restoration of the maxillary first molar. E, The minimum bone dimension for a small diameter implant is 5 mm. Ideally, at least 1 mm of bone is still left on either side of the implant site after the osteotomy has been prepared. F, The minimum bone dimension for a wider (5 mm) implant is approximately 7 mm. At least 1 mm of bone should still remain laterally after the site has been prepared.

Restoration size must always be considered during the treatment planning stage so that a properly sized implant is placed in the ideal location.

Single tooth implant

Treatment planning for the single tooth restoration, particularly in the anterior esthetic zone, is one of the most challenging problems faced by the implant restorative dentist. Placement of the implant for both esthetics and biomechanical loading (to minimize screw loosening) is especially crucial. In addition, at the treatment planning stage, the decision to place an implant with an antirotational feature built into the system (e.g., a spline or a hexagon) is essential (Fig. 13-18).

Fig. 13-18 A, Standard external hexagon in use. B, Internal hexagon connection implant.

Soft tissue contours

For implant treatment planning in the anterior esthetic zone, it is important to look closely at the soft tissues that will frame the restoration. It can be challenging to achieve a completely formed papilla between the implant restoration and the adjacent teeth in the final outcome. If the interdental tissue and underlying bone have already been lost before implant placement, it may not be possible to achieve ideal papillary contours. The literature contains guidelines that help in predicting whether adequate soft tissue contour can be maintained. As diagrammed (Fig. 13-19), the relationship of interdental bone to the interproximal contact seems to predict whether an interdental papilla will be present or not. If the distances between the bone and the contact is short (∼5 mm), a papilla is usually present. If the distance is long ∼8 mm), a papilla would not normally be present without additional soft tissue grafting.^9,10

Fig. 13-19 Relationship of interdental bone to position of interproximal contacts seems to predict whether interdental papilla will be present or not. If the distance between the bone and the contact is <5 mm (A), a papilla if usually present; if the distance is >8 mm (B), there is usually no interdental papilla present.

Surgical Access

Several types of incision can be used to gain access to the residual ridge for implant placement. The incision chosen should allow retraction of the soft tissue for unimpeded implant placement and should preserve attached tissue esthetics and quantity.

When the quantity of attached tissue is adequate and the underlying bone is expected to be of sufficient width, a simple crestal incision is recommended. However, closure must be performed carefully, because the implant lies directly beneath. In the posterior mandible, an incision may be placed toward the buccal aspect of the ridge to allow the flap to be retracted by a suture. This may be a disadvantage, however, because the incision line is thus immediately over the area where the bone may be thinnest, and a dehiscence can occur during surgery. An incision slightly to the palatal side is particularly effective in the maxillary anterior zone. After the bone is exposed, the surgical template is positioned, and a periodontal probe is used to make a preliminary assessment of the potential implant site. The residual ridge may have areas that are uneven or with sharp ridges. These areas should be smoothed before implant placement.

Implant Placement

Placement procedures for all implant systems require atraumatic preparation of the recipient site. Thermal injury to bone is minimized by using a low-speed, high-torque handpiece, along with copious irrigation. The irrigation is either externally or internally applied and directed through channels in the drill. Manufacturer recommendations relating to the type of irrigation and speed of the drilling equipment should be followed. Threaded implants often require final thread preparation in the bone at very low speeds.

The implant recipient site is prepared with a series of gradually enlarged burs. All implant systems have an initial small-diameter drill used to mark the implant site. The implant site is located through use of the surgical template, which may also assist in directing angulation of the implant. The center of the implant recipient site is marked with the initial drill, and a pilot hole is prepared. A paralleling pin is then placed in the preparation to check alignment and angulation.

At this point, a final determination is made regarding the adequacy of the recipient site for implant placement. Although implant placement is a surgical procedure, it is influenced by critical restorative parameters. The template communicates the range of acceptable implant positions and angulations. At this step, if it is apparent that supporting bone will not allow proper positioning of the implant, further osseous augmentation may be necessary, either simultaneously with implant placement or as a separate procedure with implant placement delayed until proper osseous support is available.

After the desired depth and diameter of the recipient site are achieved, the implant is placed. For titanium implants, an uncontaminated surface oxide layer is required for osseous integration. Hydroxyapatite-coated implants are also sensitive to contamination.

Nonthreaded implants are positioned in the recipient site and gently tapped into place with a mallet and seating instrument. Threaded implants are screwed into place, which also requires cutting the screw threads in the recipient site. Self-tapping implants are available for use in the maxilla, where the bone is soft enough to make prethreading unnecessary. After all implants are placed, tension-free closure prevents wound dehiscence.

Postoperative Evaluation

A radiograph should be taken postoperatively to evaluate the position of the implant in relation to adjacent structures (e.g., the sinus and the inferior alveolar canal) and other implants. Any significant problems noticed at this time should be corrected.

Patients are given mild analgesics and 0.12% chlorhexidine gluconate rinses for 2 weeks after surgery to keep bacterial populations to a minimum during healing. Weekly evaluations are recommended until soft tissue healing is complete (2 to 3 weeks). If possible, complete or partial removable dental prostheses should not be worn for 1 week after surgery. The resin over the implant can then be reduced by 2.0 or 3.0 mm and replaced with a soft liner, so that the denture can be worn without injuring the healing implant site.

Implant Uncovering

If a two-stage system is used, implant uncovering is performed after complete implant fixture integration has been achieved. The time interval for integration to occur varies and depends on the particular site and patient. Longer times may be required if the bone quality and surgery were less than ideal or if the bone-implant interface was questionable at the time of placement. In general, recommended integration times are 6 months in the maxilla, 3 months in the anterior mandible, and 4 months in the posterior mandible.

The goals of surgical uncovering are to accurately attach the abutment to the implant, to preserve attached tissue, and to recontour tissue as necessary. These goals may be accomplished with any of these three techniques: the tissue punch, crestal incision, or flap repositioning.

After the implant is exposed, the implant abutment is placed. There are two approaches for this procedure. The first approach is to place the same abutment as will be used in the restoration. The second approach is to place an interim healing cap that will remain until the tissue heals and will then be replaced by the abutment during the restorative treatment procedures.

When the abutment is placed, the superstructure must be completely seated on the implant body without gaps or intervening tissue. In systems with antirotational facets in the implant (see Fig. 13-18), these features must be aligned to allow complete seating of the abutment. Thesuperstructure–implant body interface should be evaluated radiographically immediately after the uncovering. If a gap is present, the superstructure must be repositioned.

Clinical Implant Components

Terms used to describe similar implant components vary widely among manufacturing companies. A list of terms used in this book and a partial list of alternative terms are provided in Table 13-1.

Table 13-1 IMPLANT TERMINOLOGY