LYNDON F. COOPER, DDS, PHD
INGEBORG J. DE KOK, DDS, MS
LEE CULP, CDT
The widespread use of dental implants results in part from the high implant survival rates frequently reported in the literature. However, frustration with dental implants in clinical practice is often related to the frequency of restorative complications, some of which are associated with implant/abutment connections and interface design. The role of the dental implant abutment is critical to the biological responses of the peri-implant tissues and the mechanical responses of the component system. This article reviews the current state of dental implant abutment design and how abutments contribute to the control of dental implant success.
D ental implant therapy is an emerging part of any dental practice involved with replacing missing teeth. The widespread adoption of dental implants is due in part to the frequently reported high implant survival rates derived from well-controlled clinical investigations. For example, nearly a decade ago the analysis of data from many clinical studies of single-tooth implants indicated that implant survival rates approached 97% after five years. However, closer evaluation of this same study revealed that after two years, the prosthetic success rate was only 83%, with the majority of complications or failures being attributed to abutment screw loosening or failure.1
Frustration with dental implants in clinical practice is often related to the frequency of restorative complications. For example, for single-tooth implant restorations, Priest reported a 15% complication rate2 and Vermylen et al reported an 11% complication rate.3 Aside from mechanical complications, more recent measures suggest esthetic limitations, as evidenced by the observation that more than one half of single-tooth implant restorations fail to match the “ideal” contralateral tooth soft tissue contour and health.4 The goal of this article is to review the current state of dental implant abutment design and how abutments contribute to the control of dental implant success.
A dental implant abutment is formally defined as “that portion of a dental implant that serves to support and/or retain a prosthesis”.5 Implied is the obvious function of an abutment to physically connect the clinical crown (ie, prosthesis) to the implant. There are at least three ways this occurs among different implant systems (Table 1). One is a modular design in which the endosseous implant and the transmucosal abutment are separate components. Alternatively, the endosseous implant and transmucosal aspect of the system may be one component and, in such cases, the crown margin is part of this integrated implant system. The two key features that are critical to use and understanding of the modular vs integrated design systems are that the integrated design system lacks an implant/abutment interface approximating the implant/bone interface, and that the crown margin for integrated implant designs is established by implant placement and cannot be modified with preparation of the implant itself. Modular systems, while presenting an implant/abutment interface at the implant/bone interface, permits the crown margin location to be modified in relation to implant position. A third design has emerged that is unitary in which the endosseous, transmucosal, and restorative aspects of the implant system are a single component. While there is little information regarding the clinical performance of these implants, the direct presentation of the restorative platform at the time of implant placement implicates their use for immediate provisionalization scenarios.
When considering the many different modular design implant systems and ways that abutments and implants are connected using an abutment screw, one distinguishing characteristic invites further classification (Table 2). Conus or tapered interfaces present an interference fit of components that lack perceptible interfacial motion. Other external or internal connections have been referred to as close, sliding fits and will have some perceptible motion.6 The potential advantage of interference fit implant/abutment interfaces is the relative absence of interfacial micromotion.7
As suggested above, there are complications associated with some implant/abutment connections. Attempts to optimize the implant/abutment connection include various mechanical approaches8 and, more recently, modification of screws to achieve greater preload.9 It was also suggested that there existed a relationship between goodness of fit measured in axial rotational movement and long-term stability of the implant/abutment interface.8 Reduction of abutment screw friction has garnered repeated attention,10 and improved screw and associated torque control has improved abutment screw behavior. Improvement in implant screw loosening has been reported. However, there remain incidences of screw loosening at internal or external hex implant/abutment interfaces.
Other attempts to improve the behavior of the implant/abutment interface involved the re-engineering of the close, sliding interference fit represented by the original external hex abutment interface and consideration of conus interfaces that present an interference fit.6 Interference fit components are free of displacement upon function. More significantly, such interfaces are also geometrically locked against potential displacement that results from functionally imposed bending moments. The combined interference from rotational displacement, the high surface area, and the geometric constraint to displacement from lateral loads creates an implant/abutment interface that is largely free of micromotion and resistant to clinical prosthetic complication or failure. Norton suggested that this is a basis for complication-free single-tooth implant restoration.11 It must be a goal of clinical dental implant therapy to reduce or eliminate the potential for abutment screw loosening or failure.
At least three other abutment functions must be considered for every implant treatment scenario. The first is guiding the healing of peri-implant mucosa. Berglundh et al12 have described at the histological level the process of abutment tissue integration. At titanium implants, the formation of the peri-implant mucosal interface proceeds over a period of approximately six to eight weeks. A junctional epithelium and connective tissue contact form along the implant in a supracrestal manner (Figure 1). Previous investigations identified the formation of a biologic width composed of these histological elements.13,14 Other studies have confirmed the reproducible formation of a biologic width at various implants.15
The organization of the biologic width at abutments is associated with an adaptive immunological response. The establishment of an inflammatory cellular infiltrate in response to plaque accumulation at dental implants16 is similar to that which is observed at natural teeth. Recent studies suggest that the extent of this inflammatory cellular infiltrate (eg, a response to plaque) is related to the extent of crestal bone loss adjacent to the implant/abutment interface17 (Figure 1 View Figure). The resulting regulation by recruited cellular pro- and anti-inflammatory cytokines controls the tissue responses at the implant/abutment interface.
Inflammation in peri-implant tissues surrounding the implant/abutment interface may be influenced by a number of factors that may include plaque formation, restorative materials debris, residual cement, abutment material or design, and micromotion of the implant abutment interface. Although the abutment surface roughness was shown to have no influence on inflammation during an experimental four-week period in edentulous subjects,18 the implant/abutment interface and features of the abutment and abutment/crown interface are of clinical importance in controlling inflammation at peri-implant tissues. Every restorative and preventive clinical effort should be made to control inflammation at the abutment/tissue interface to ensure long-term clinical success.
Another dental implant abutment function is occlusal force transmission from the crown to the implant and the bone. Excessive forces have been considered detrimental to both the implant/bone interface and the implant/abutment interface. Suggested is the role of the implant/abutment interface in modulating the physical features of force transmission at the implant/bone interface and subsequent adaptation of crestal bone at the implant surface. In addition to maintaining the fidelity of the physical implant/abutment connection, when conus interfaces are compared with any horizontal interface (ie, perpendicular to the long axis of the implant), there is a noted advantage in the force distribution to surrounding bone.19 Irrespective of the design, clinicians are interested in knowing that occlusal forces will not overcome the strength of the implant, the abutment, or the integrity of the implant/abutment connection. There should be additional concern that force transmission to crestal bone is optimally controlled through this connection.
A third function of an abutment is to contribute to the esthetic merit of the implant-supported crown or prosthesis. Clearly, control of peri-implant mucosal inflammation is paramount to this goal. More pragmatic ways in which abutment design directly contributes to the esthetics include changes in the location of the crown, changes in the dimension and/or form of the restorative platform, and changes in the color of the abutment. Additionally, the features of abutment design that contribute to tissue health and dimensional stability are critical to the esthetic merit of the implant restoration. Current attempts to objectively define implant restoration esthetics have focused on peri-implant mucosal parameters.4, 20
The impact of the abutment on implant prosthesis esthetics is of increasing interest. Over two decades, abutment designs have been refined to include variations in transmucosal height, restorative platform diameter, angulation of the crown, and retention (ie, cement vs screw). A continual evolution of prefabricated abutments offered a continuous improvement in esthetic achievement with dental implant restorations and included the realization of more natural contours to improve esthetics. The introduction of the UCLA abutment provided a custom solution for implant restorations. This direct-to-implant restoration concept provided adaptability. Through waxing and casting, the height, diameter, and angulation could be addressed in order to provide a wide range of clinical solutions to problems associated with limited interocclusal distance, interproximal distance, implant angulation, and related soft tissue responses.21 A potential biological price paid for this adaptability is that the restorative margin is placed at the crest of bone, a situation not favorable to maintenance of crestal bone. Today, computer aided design/computer aided machining (CAD/CAM) offers the widest array of potential custom solutions for abutment design and manufacture using various materials.
Material choice is another aspect of abutment selection that affects implant esthetics. Transmucosal color display and light transmission affect the ultimate esthetic result of a restoration. For dental implants using metallic abutments, a gray tone is imparted to thin buccal mucosa (Figure 2 View Figure). The approach using titanium nitrite treated abutments of gold color has been introduced. The advantage of this approach is that the strength of titanium is preserved. The disadvantage is that there is no opportunity for light transmission through the metallic abutment.
A ceramic (ie, white) abutment (CerAdapt abutment, Nobel Biocare, Yorba Linda, CA) was introduced and heralded the beginning of an ongoing revolution in implant prosthodontics involving ceramic restorative systems and abutments. Today, ceramic abutments are more widely made from zirconia. The use of zirconia can be approached through prefabricated and modifiable components and rapid prototyping methods. The esthetic features of ceramic abutments are compelling, and the materials can be adapted to many prosthodontic restorative systems. More recent studies suggest that zirconia abutments can provide sufficient strength for predictable success.22,23 Concern for long-term mechanical integrity requires clinical evaluation.
Chee and Jivraj stated that the ideal abutment design should have a cement margin and follow the mucosal outline, and the material should be strong in thin sections and biocompatible.24 It is presently further suggested that an ideal abutment should provide integrity of the interface. Criteria for abutment success have not been universally accepted. Suggested is the evaluation of interface integrity (ie, loosening or fracture), related peri-implant tissue inflammation, and stability of the peri-implant tissue/abutment interface. Precise methods of measurement would be required and implemented. In this manner, it may be possible to further define clinical success of implant therapy with precise criteria and definitions of abutment complications.
Clinical decisions regarding implant restoration and abutment selection are often pragmatic and address issues of convenience and esthetics. Examples include choosing to use a stock abutment or custom abutment or whether or not a screw-retained or cement-retained crown should be used.While there is a major role for treatment planning in limiting the clinical decisions that must be made at the time of implant restoration, even after careful planning the challenges of implant position do emerge to confront the restorative team.
Stock abutments offer many solutions to implant placement. Dental implant manufacturers offer a wide range of stock abutments. The intent is typically one of restorative adaptability and simplicity. An appropriate array of stock abutments should permit selection between screw or cement retention, accommodation of transmuscosal height, selection of the restorative platform diameter, and selection of angled components. More recently, the introduction of alternative materials (eg, alumina oxide, zirconia) offers selection of stock abutments that provide additional esthetic advantages.
The decision to place a stock abutment directly after implant healing is a good one when restorative excellence can be envisioned. Placing the stock abutment permits peri-implant mucosal healing to occur against the titanium or zirconia material. In some instances where esthetics is of no concern or the crown margin is above the peri-implant mucosal crest, it is possible to place the abutment, make the impression, and provisionalize the abutment with a provisional crown or protective cap (Figure 3A View Figure, Figure 3B View Figure, Figure 3C View Figure, Figure 3D View Figure, Figure 3E View Figure, and Figure 3F View Figure). At the next subsequent appointment, the crown may be placed. This is the most direct method of implant restoration and facilitates many molar and premolar implant therapies.
Stock abutments may be used to create esthetic restorations. The placement of a stock abutment and its careful provisionalization is advocated for developing ideal peri-implant mucosal health and form. Again, placement of a titanium or zirconia abutment as a framework for peri-implant mucosal healing is known to result in a reproducible connective tissue contact and junctional epithelium.25 The careful adaptation of a provisional crown to a submucosal margin location without cement extravasation or retention further allows the clinical guidance of the peri-implant mucosal form. The concepts of transition contour should be applied to support the mucosal form and ensure the natural tooth-like appearance of the cervical crown form as it emerges from the mucosa.
Stock abutments may be modified, and some are designed to encourage modification (Figure 4A View Figure, Figure 4B View Figure, Figure 4C View Figure, Figure 4D View Figure, Figure 4E View Figure, Figure 4F View Figure, Figure 4G View Figure, and Figure 4H View Figure). For esthetic purposes, a modifiable zirconia abutment may offer many of the same advantages as CAD/CAM approaches to custom abutment solutions. For example, while not infinitely modifiable, the adaptation of a zirconia abutment may permit changes in transmucosal height, customization of the restorative platform dimension and form (ie, from circular to triangular), and required changes in angulation. A stock zirconia abutment is selected to match the implant dimension and is first modified to provide proper submucosal dimension and form. This typically requires establishing concave interproximal contours and convex facial contours to support the established facial crown contour. The crown margin is then located in a shallow submucosal location circumferentially. This permits easy access for cement removal and allows tissue formation to occur largely on the zirconia substrate. At no point should the abutment/crown margin interface be closer than 2 mm to the implant/bone crest. Finally, the axial reduction should be performed in accordance with prosthodontic principles for retention and resistance form to support an all-ceramic restoration.
On the modified abutment, an ideal provisional crown may be fabricated and cemented using information provided by the diagnostic wax-up.While this procedure requires a significant investment of effort, there is no additional provisional component and few laboratory fees involved in creating this provisional restoration. After six to eight weeks of tissue healing and adaptation, a final impression may be made of the abutment using conventional prosthodontic techniques. The fabricated crown may be delivered at the next clinical visit, with good assurance that the tissue contour will support esthetics.
Custom abutments infer that the entire abutment be fabricated from an analog or virtual copy of the implant. The shape and position of the implant are reconciled to the planned location of the clinical crown and the existing peri-implant tissues. Manufacturer techniques involve waxing and casting to plastic or alloy cylinders and computer numerical control (CNC) milling of abutments from various materials. A wide range of possible morphologies exists, and custom abutments can ingeniously address many complex and challenging implant restorations.
The decision to place a custom abutment involves a commitment to make an impression at the fixture level or use an indexed healing abutment (Encode, Biomet 3i, Palm Beach Gardens, FL). This decision also makes provisional restoration a subsequent procedure involving either a delay for fabrication of the custom abutment or the investment in a provisional abutment to permit intervening temporization while the custom abutment is manufactured.At the present time, custom abutments involve work flows that are nonsequential; some interruption is required between impressing the implant and delivery of the custom abutment. A possible solution is impressing the implant at the time of implant surgery. Different work flow scenarios are possible based on implant restoration options (Figure 5).
If a custom abutment is prescribed following a two-stage surgical procedure, it may be imprudent to make a fixture-level impression at this time. Unpredictable alteration in peri-implant mucosal architecture during healing is complicated by the use of either healing abutments or provisional abutments. Changes in peri-implant tissue morphology require accommodation by healing against the healing abutment, or preferably by modification of the abutment form to represent tooth morphology. This may be less of an issue following one-stage surgical implant placement in which peri-implant mucosa has formed. Nonetheless, the tissue morphology is not adapted to the form of the permanent abutment (Figure 6A View Figure, Figure 6B View Figure, Figure 6C View Figure, Figure 6D View Figure, Figure 6E View Figure, Figure 6F View Figure, and Figure 6G View Figure). Despite this disadvantage, the custom solutions for abutments made of titanium or zirconium offer additional clinical avenues to restore dental implants. Both stock and custom abutments present some advantages and disadvantages (Table 3).
Custom abutments may be prepared from impressions made at the fixture level after a provisionalization phase using abutments and provisional crowns. Provided the abutments and provisional restorations fulfill the biologic requirements needed to maintain peri-implant health, this can represent a rigorous approach to restorative excellence. Preferred is the use of a titanium abutment that places the crown margin at least 2 mm from the implant /abutment interface.
This approach—using stock titanium abutments and Bis-acrylic provisional crowns (Direct abutments, Astra Tech, Inc,)—was undertaken to develop acceptable peri-coronal gingival and peri-implant mucosal form during a 12-week period of healing after immediate placement and provisionalization (Figure 7A View Figure, Figure 7B View Figure, Figure 7C View Figure, Figure 7D View Figure, Figure 7E View Figure, Figure 7F View Figure, Figure 7G View Figure, Figure 7H View Figure, Figure 7I View Figure, Figure 7J View Figure, Figure 7K View Figure, Figure 7L View Figure, Figure 7M View Figure, Figure 7N View Figure, Figure 7O View Figure, Figure 7P View Figure, Figure 7Q View Figure, Figure 7R View Figure, and Figure 7S View Figure). Although the work flow in this case required stepping back to the implant/abutment interface, the stability of the tissue/abutment interfaces permitted the laboratory to create the custom abutments and final crowns for try-in or delivery.
The advantages of this approach are many. Primary among them is the opportunity to refine peri-implant mucosal contours directly and iteratively if required. Maintaining these contours is assured by using stone working casts, as illustrated. The main disadvantage is the need for additional abutments and implant analogs to achieve the provisional and final restoration. While this clinical scenario illustrates a custom abutment solution using modification of stock components, this work could be achieved using CAD/CAM solutions. The stock component approach is rapid, does not involve sourcing of materials to a third party, and provides assurances of implant/abutment fit based on the quality of these manufactured components.
CAD/CAM manufacture of abutments is gaining interest in the dental marketplace. The promise of a “custom” solution for every clinical situation is conceptually aligned with the rapid prototyping methodology. The initial offering (Procera Abutment, Nobel Biocare) included milled titanium abutments, and another (Atlantis, Zimmer Dental Inc, Carlsbad, CA) reinforced the concept of individual or custom manufacture of abutments using milled titanium. More recent innovations include the introduction of milled zirconia abutments, and several options are available to clinicians. The advantages of a milled abutment include: range of anatomic shapes and position correction opportunities; homogeneity and integrity of the material milled; ability to control parallelism of axial walls for retention and among implants for simplicity; possibility to create complex contours, including submucosal form; and adaptability to most, if not all, dental implants. In all cases, an accurate fixture-level impression is required, a digital model is constructed, and CAD is used to design the abutment (Figure 8 View Figure). This model is then used to guide CNC milling of an abutment using the material of choice.
CAD/CAM manufacture offers expanded opportunities for design, a promise of quality based on the integrity of the bulk material chosen for milling, and accuracy of fit based on the milling process and design parameters. A disadvantage is that the work flow requires that some interim abutment (eg, healing or provisional) be placed until the final abutment is returned. This time period may involve unintended changes in soft tissue morphology associated with the healing or provisional abutment. Such changes in buccal tissue contour are well-defined following abutment placement, and the risk of clinical crown margin/mucosal contour discrepancies must be considered in the context of each situation.
The ultimate success of a dental implant restoration may require multifactorial assessment that includes the measurement of implant success and survival, patient-centered outcomes (eg, satisfaction and function), and objective esthetic evaluation. The role of the dental implant abutment is critical in contributing to the biological responses of peri-implant tissues and the mechanical responses of the component system. The selection of implant/abutment interface design, the procedural decisions (eg, fixture- vs. abutment-level impressions), the integrated use of provisional crowns to develop peri-implant tissue morphology, and the peri-implant tissue responses affected by these decisions must be carefully considered. Decisions regarding dental implant abutments are essential aspects of clinical dental implant excellence.
Lyndon F. Cooper, DDS, PhD, received an honorarium from Astra Tech, Inc. Lee Culp,CDT, received an honorarium from TDS/U-Best Dental Technology.
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| 1. Modular dental implant design | separate endosseous and transmucosal components |
| 2. Integrated dental implant design | endosseous and transmucosal components connected |
| 3. Unitary dental implant design | the endosseous, transmucosal, and restorative features of the system are one component |
| Close/sliding fits | external hex screw-retained | high torque required
|
| | internal hex screw-retained | relatively frequent loosening |
| | | simple abutment removal |
| Interference fits | screw-retained conical designs | low torque required |
| | Press-fit tapered designs | difficulty removing abutment |
| | | infrequent loosening |
| | | little peri-implant inflammation |
Stock abutments
Screw vs. cement retention
Transmucosal height
Restorative platform diameter
Axial angulation |
Customized abutments
Adopt to most anatomic or geometric circumstances
Manufactured using:
Casting
Modification (ie, addition or subtraction) of stock abutments
CAD/CAM |
FIGURE 1 Illustration of the implant/abutment interface, which approximates the implant/bone interface and can influence the biology that affects crestal bone maintenance. The biological management of this complex is derived from the junctional epithelium that is attached to the titanium or zirconia abutment and the connective tissue contact that intervenes between the crestal bone and epithelium.Within this connective tissue is an inflammatory cellular infiltrate that mediates both acute and chronic responses to sulcular bacteria, debris, and the implant and abutment materials. Micromotion between the implant and abutment is implicated in the inflammatory status of this important tissue. Together the structural and functional elements of the complex establish the health and contribute to the morphology of peri-implant tissues.
FIGURE 2 Buccal photograph of the implant-supported restoration of a maxillary canine tooth. This image reveals the multifaceted nature of dental implant esthetics. An acceptable clinical crown was placed onto a titanium abutment circa 1995. At the time, alternative materials were not widely available, so the resulting color of the buccal tissue is gray. Despite this, there is reasonable maintenance of the buccal contour, filling of the interproximal embrasures, and absence of inflammation.
FIGURE 3A A single implant replacing the lower left first molar was placed using a two-stage procedure. At the time of second stage surgery, this radiograph was made. From this point, it was possible to place a definitive abutment and proceed directly to restoration.
FIGURE 3B Through a linear incision, this conical designed abutment was inserted in the dental implant and placed using finger pressure. The abutment chosen completely traverses the periimplant mucosa and presents a 5-mm restorative platform at a crestal position for restoration.
FIGURE 3C Immediately before a final impression, all dental implant abutments should be properly seated using a torque controlling device. This implant design mandates 25 Ncm of seating torque, which will assure integrity of the assembly in function.
FIGURE 3D A closed tray impression was facilitated by the abutment design and the associated impression coping. Some dental implant systems offer abutments that provide a simple impression system for a stock abutment that is not modified. After making this impression, the abutment was protected using a stock abutment cap provided by the implant manufacturer. No provisional crown was fabricated.
FIGURE 3E From the impression, a working cast was fabricated and a porcelain-fused-to-metal (PFM) crown was made for the first molar
FIGURE 3F After seating the PFM crown on the abutment and checking interproximal, occlusal, and excursive contacts, the crown was cemented on the abutment using permanent cement. Note that the crown margin was at the tissue level. This scenario represents a situation where the morphology of the peri-implant mucosa was not critical to the esthetic perceptions of the patient.
FIGURE 4A Preoperative radiograph of the left maxillary central incisor that was not restorable. The decision to replace the tooth with a dental implant was made by the patient, periodontist, and prosthodontist. An immediate provisionalization protocol was offered and preferred
FIGURE 4B A stock zirconia abutment (Zir Ceramic, Astra Tech, Inc,Waltham, MA) was placed on the implant at the time of implant installation for immediate provisionalization. This photograph reveals the shape of the abutment prior to modification in the prosthodontist’s in-office dental laboratory (ie, chairside).
FIGURE 4C Postsurgical radiograph of the dental implant and conus interface zirconia abutment. Note the morphology of the prepared abutment following its modification before the immediate provisionalization appointment.
FIGURE 4D Twelve-week postoperative buccal photograph of implant and abutment at No. 9 following removal of the provisional crown. The peri-implant tissues were pink, stippled, and knife edged. There was no sulcular bleeding. The abutment was intact and must be seated with a torque controlling device before the final impression was made directly using retraction cord and vinylpolysiloxane material.
FIGURE 4E Occlusal view of the abutment for the implant crown. Note that epitheilization of the suclus was visible. This tissue formed against the provisional crown and was well healed. This region of the sulcus does not contribute to the biological attachment to the abutment. The health of this tissue is attributable to the absence of inflammation at the implant/abutment interface.
FIGURE 4F Buccal view of the final crown. An all-ceramic crown (Procera, Nobel Biocare, Yorba Linda, CA) was cemented onto the abutment using glass ionomer cement. Note that the peri-implant tissues remained free of inflammation and the contour did not change appreciably
FIGURE 4G Buccal view of the implant crown replacing the maxillary left central incisor five years after implant placement. When compared to the postoperative photograph, there was little evidence of changes to the buccal tissue contour. There was no history of the abutment loosening, and the peri-implant mucosa remained inflammation free.
FIGURE 4H Five-year postoperative radiograph shows that the integrity of the implant/abutment interface remains intact. Note the approximation of the interproximal crestal bone adjacent to the implant/abutment interface. It is possible that a more concave interproximal contour of the transmucosal aspect of the abutment would have offered greater tissue volume for interproximal tissue formation.
FIGURE 5 Possible work flow scenarios for implant restoration using different abutments.
1. Stock abutment placement allows direct provisionalization at abutment placement. Prudent delay in impression making at the abutment level permits
tissue adaptation to a properly contoured crown. Subsequent abutment-level impression procedures are easily accomplished, and the dental laboratory typically can fabricate a crown with excellent guidance of tissue contours from the impression.
2. When esthetics is not of concern, an abutment may be placed and the abutment-level impression accomplished at the same clinical visit. A provisional cap may be used instead of a provisional crown to facilitate treatment. The dental laboratory will manufacture the crown without anticipation of tissue changes. When the crown is seated, excessive peri-implant tissues may require removal to permit full seating of the crown.
3. If a fixture-level impression is made after implant healing, a healing abutment may be placed or replaced. Alternatively, a provisional abutment may be used to create a provisional crown. This may require time and cost for dental laboratory assistance. From the fixture analog, the laboratory fabricates an abutment and crown. Subsequent delivery of the abutment is challenged by intervening changes in peri-implant tissue contours related to healing and the form of the healing abutment relative to the final abutment. Little change is possible to the abutment if the crown has been made simultaneously. If the abutment is modified, the crown is then manufactured or modified by the laboratory and delivery is performed at a subsequent visit.
4. If a fixture-level impression is made, a provisional crown may be prepared and delivered with intensions of permitting tissue adaptation. A subsequent fixture-level impression must be made and should capture the details of the peri-implant tissues. The laboratory then has adequate information to fabricate both the abutment and crown for delivery at the subsequent visit.
FIGURE 6A An implant was placed using a one-stage procedure. The healing abutment was removed and a fixture-level impression was made.
FIGURE 6B A custom abutment was fabricated in the laboratory from the fixture-level impression. The abutment analog was incorporated in the model and the abutment was milled from a stock titanium abutment (e Ti Design, Astra Tech, Inc.,Waltham, MA).
FIGURE 6C Closer looks reveal how the abutment was modified to support the soft tissue and provide support for the all-ceramic crown. The interproximal finishing lines were scalloped to facilitate cement removal.
FIGURE 6D Lingual view of the abutment at the time of delivery. The tissue had not been adapted to receive the restoration, as noted by the blanching of the periimplant mucosa.
FIGURE 6E Buccal view of the crown at the time of delivery. Tissue adaptation had not been developed prior to delivery.
FIGURE 6F Buccal view of the crown at the three-year follow-up. Tissue health had been maintained by the abutment contours and crown design.
FIGURE 6G Three-year follow-up radiograph. The bone was maintained by the implant fixture and abutment interface design.
FIGURE 7A Initial presentation of a 50-year-old female patient with existing and failing maxillary single crowns and fixed partial dentures. A co-morbid condition of mandibular edentulism required a fixed partial denture. Tooth No. 11 was replaced with an implant and a provisional crown at this time.
FIGURE 7B Preoperative panoramic radiograph reveals mandibular edentulism and status of existing maxillary teeth. The treatment plan included four mandibular implants, an immediately loaded implant-supported fixed denture, and other immediately placed and provisionalized implants.
FIGURE 7C After removal of several clinical crowns, the existing condition of the alveolar ridges and teeth was revealed. The alveolar ridges exhibited minimal resorption.
FIGURE 7D Postsurgical radiographic survey of the implants revealed the implants and provisional fixed partial denture. The mandibular implants had integrated, and a provisional fixed denture with a non-precious alloy framework was attached to stock abutments (UniAbutments, Astra Tech, Inc) throughout the maxillary therapy.
FIGURE 7E At 12 weeks after maxillary implant placement, note the symmetry of the maxillary buccal tissues following the initial healing period. The maxillary provisionals were removed, and the implants at Nos. 3, 5, 7, 8, and 11 were impressed at the fixture level using open tray fixture impression copings for the selected dental implants (Astra Tech, Inc).
FIGURE 7F The impressions were poured without a soft tissue matrix for the implants. The hard tissue model, with modified implant site, was sculpted to mimic the natural root contours. The minimal sculpting was guided by clinically establishing the buccal contours with provisionalization and then refined using knowledge of the cervical contours of teeth and roots to establish proper interproximal form.
FIGURE 7G Lateral view showing the modified contour of the hard tissue model with custom zirconia implant abutments. The abutments were modified from stock abutments (Zir Design Abutments, Astra Tech, Inc) using water-cooled high-speed diamond bur instrumentation. The submucosal contours were refined using a blue polishing wheel (Dialite, Brasseler USA, Savannah, GA).
FIGURE 7H Facial view of the completed crowns (IPS Empress®, Ivoclar Vivadent, Amherst, NY) showing correct emergence profiles on custom implant abutments and natural teeth. The form of the abutments was established to support the soft tissue contours without displacement and blanching, as well as to permit proper emergence of the clinical crown from a shallow region of the peri-implant sulcus.
FIGURE 7I Posterior teeth require consideration of additional mechanical loading.Here, titanium abutments were also adapted to the contours of the tissues established by the provisional crowns cemented onto direct abutments (Direct Abutments, Astra Tech, Inc). Custom titanium abutments (Bi-abutments, Astra Tech, Inc) were modified for shape, and the axial walls and chamfer region were modified with titanium compatible ceramics to enhance the color.
FIGURE 7J Lingual view of the completed restorationsl as planned for placement on natural teeth and custom titanium implant abutment (molar) and zirconia abutment (premolar).
FIGURE 7K View of the custom implant abutments showing proper contours and shade in relation to the natural tooth preparation. Note the symmetry of the central incisor soft tissue contours and the attempt to maintain the interproximal tissues created clinically between the lateral incisor and central incisor implant.
FIGURE 7L Lingual view of the completed restorationsl showing the correct emergence profile. This reflects ideal implant positioning and the anatomic replication of tooth-like form using the zirconia abutments.
FIGURE 7M A properly refined zirconia abutment possesses mechanical integrity (ie, appropriate reduction), subgingival form (ie, transition contour), peri-coronal form (ie, finishing line), and color to aid in predictably defining tooth-like esthetic attributes for the implant crown and peri-implant mucosa.
FIGURE 7N At implant and crown delivery, note the absence of blanching of the tissues following abutment placement. This reflects the care taken in modifying the hard tissue working cast and the careful adaptation of the zirconia abutment to the prepared tissue site. The crown margins were 0.5 mm to 1.0 mm beneath the mucosal crest to facilitate cement removal.
FIGURE 7O One-year postoperative facial photograph of the maxillary tooth, implant-supported crowns, and the implant-supported fixed denture. Note the maintenance of soft tissue contours during this one-year period and the preservation of peri-implant and peri-coronal health.
FIGURE 7P The mandibular implant-supported fixed denture was made using a proprietary CAD program (TDS, TurboDentSytems, U-Best Dental Technology, Anaheim, CA) to design a titanium framework that optimally supported the acrylic denture teeth (image courtesy of TurboDentSystems).
FIGURE 7Q The CNC milled framework was veneered using acrylic resin and denture teeth (BlueLine, Ivoclar Vivadent, Amherst, NY) and characterized to match the maxillary anterior rehabilitation.
FIGURE 7R View showing the adaptation of the peri-implant mucosa to the zirconia abutments and ceramic crowns. Note the preservation of architecture and the coral pink color indicating a relative absence of inflammation at the implants and teeth.
FIGURE 7S The peri-implant mucosa at No. 11 is fully contoured on the facial and interproximal aspects of the restoration. The form and color are well integrated with the surrounding teeth.
FIGURE 8 This illustration of a computer aided design implant abutment reveals the details available to the designer. All aspects of the abutment morphology can be controlled in the context of available information. The subsequent manufacture is performed using CNC milling techniques to provide an abutment fabricated from a variety of materials.