Treatment Planning for Dental Implants: A Rationale for Decision Making, Part 2: Partial Edentulism

A previous review1 considered the factors involved in the decision of whether to extract all of the teeth in a jaw and place an implant-supported prosthesis, or save those teeth by performing extensive periodontal surgery and prosthetic reconstruction. The replacement of one or a few teeth by implants is determined by a different set of considerations than those affecting an entire dentition. It should also be noted that one long-term study of more than 10 years demonstrated 87% survival of maxillary and 99% survival of mandibular implant-supported prostheses in edentulous jaws.

Similar documentation for implant-supported fixed partial dentures or single-unit implant-supported crowns is also beginning to appear. One review of the survival for implant-supported fixed partial dentures functioning for 6 to 7 years revealed success in more than 93% of cases; single crowns demonstrated success in more than 97% of cases for the same time period. However, it is significant to note that tooth-supported fixed partial dentures have also demonstrated long-term success rates similar to implant-supported prostheses in edentulous jaws. Therefore, it is important to consider those factors that determine whether a dentist should treat one or a few compromised or healthy teeth, or extract the teeth and replace them with a fixed partial denture, an implant-supported restoration, or a removable prosthesis.

The replacement of one or a few missing teeth with implants is determined by specific considerations that include the status of the surrounding dentition, height of alveolar bone, possible implant distribution, and, very importantly in the anterior maxilla, aesthetic concerns. It must be recognized at the outset that periodontal therapy including osseous surgery, pocket reduction, hemisection, and/or root removal can compromise the teeth and supporting structures and may not improve the periodontal condition of those teeth. It is also important to note that restorative dentistry has recently shifted from a functionally driven to an aesthetically driven treatment approach. Patients

now demand the paradigm shift that was initiated by dentists. Single or multiple implants in the anterior “aesthetic zone” can present a challenge, and the ideal result may only be achievable with additional osseous grafting or soft-tissue surgical or regenerative procedures.

This review will not discuss the events that occur after implant placement and restoration, including factors leading to peri-implant bone loss and implant failure. These factors include biomechanical overload, parafunctional habits, environmental risk factors (smoking), peri-implant infection (peri-implantitis), or problems directly associated with implant materials, technique, or design. Considerations for decision making in treatment planning and the development of predictable treatment outcomes (the clinical skill of the clinician notwithstanding) will be based on the following criteria: (1) local oral pathology, (2) evaluation of the teeth and supporting alveolar bone, (3) financial considerations,

and (4) aesthetic challenges and patient comfort. These criteria will be incorporated into a decision tree (Chart).

Local oral pathology

Radiograph after tooth No. 36 was extracted. A radiopacity is present that complicates implant placement.

Systemic risk factors for implant failure were discussed in Part 1 of this series and they also apply to partial jaw edentulism. In terms of local oral pathology, periodontal and endodontic pathology are important and are discussed below. Of profound importance is the presence of soft tissue or intrabony lesions in or adjacent to a proposed implant site. Some of these lesions are listed in Table 1. These untreated lesions may represent contraindications to implant placement. Removal of cysts and other benign solitary jaw lesions,  identification of these lesions via histologic examination as local pathology, and then healing of the affected area may allow for subsequent placement of implants. Bone and/or soft-tissue augmentation may be required.

Table 1. Specific Local Contraindications to DentalImplant Placement.

cystsbenign tumorsmalignant tumorsresidual infection (PAP, osteomyelitis)cemento-osseous dysplasiacondensing osteitisidiopathic osteosclerosis (enostosis)jaw fracture

The presence of large areas of affected bone as seen in other disease processes such as osteomyelitis represents a distinct contraindication for dental implants. Paget’s disease, cemento-osseous dysplasia, and osteopetrosis are bone disorders associated with sclerotic bone and may predispose to osteomyelitis if surgically traumatized. Poor bone quality as a result of defective osteoblast or osteoclast function, enlarged marrow spaces and/or abnormally arranged trabeculae as seen in osteogenesis imperfecta, fibrous dysplasia, osteomalacia (vitamin D deficiency), and certain anemias also present severe challenges or contraindications for implant therapy and osseointegration.

Clinical signs and symptoms such as tooth mobility and pain, occurring separately or together, require an accurate diagnosis to determine if the underlying problems are treatable or are the result of a pathologic process that may necessitate extraction. Mobility and pain suggest traumatic occlusion, periodontal bone loss, root fracture, or endodontic involvement. Traumatic occlusion by itself is treatable. If it is combined with bone loss, then it may become a treatment dilemma and is discussed below. Vertical root fractures are generally untreatable, and either the affected root or tooth must be extracted. Some horizontally fractured teeth may be utilized to restore bone and tissue by means of orthodontic extrusion.

Periapical pathosis (PAP) is generally a consequence of pulp pathology that sometimes presents with the clinical symptoms of mobility, pain, and swelling, and may require endodontic therapy or extraction. Vitality testing of the pulp usually differentiates the problem from a more generalized process such as cemento-osseous dysplasia. Accurate evaluation regarding the cause of apical pathology is essential for proper treatment planning. Endodontic failure is suggested by the appearance of PAP, increase in size of an existing PAP, and signs of root resorption. In such cases, retreatment with or without apical surgery is needed, and healing is then determined by regeneration of alveolar bone and re-establishment of a functional periodontal ligament. It is suggested that the resolution of PAP be accomplished prior to implant surgery in an adjacent site. Another option is surgical removal of the tooth, with or without a bone graft, and subsequent placement of a fixture at that site.

It is also suggested that there be a “sufficient” distance between an implant and the apex of an endodontically treated tooth. Although considered endodontic failure by some, the presence of a small, non-expanding periapical radiolucency of several years duration in a properly filled, nonvital tooth without periodontal pathology, if adjacent to an implant site, is not a contraindication to placement of a fixture. The immediate placement of a dental implant into an extraction site with radiographic PAP has been contraindicated by some. However, in the absence of a symptomatic, localized acute infection, this concept has been challenged if proper treatment, including surgical debridement of the socket and apical area, is provided.

Table 2. Accepted Treatment Modalities for the FurcatedMolar Tooth.*

chemotherapeutic maintenanceroot planingmodified Widman flapopen flap debridementbone grafting ± guided tissue regenerationosseous resection ± root removaltunnelinghemisectionextraction

*Modified from References 16 and 48.

Local inflammatory conditions including gingivitis and periodontitis must be resolved prior to implant placement. Vertical bone loss may be successfully treated; however, circumferential bone loss may also jeopardize the adjacent teeth, and if they are intended to serve as a prosthetic abutment, reconsideration for extraction is warranted. The retention of a molar with class 2 or 3 furcation involvement presents a formidable challenge for the clinician. Retention of this tooth may require periodontal, endodontic, and restorative treatment, and perhaps even surgical root resection or grafting procedures. An extensive literature review outlined the many treatment modalities (Table 2) as well as prognostic factors, including root anatomy, tooth mobility, endodontic and restorative complexities, patient cooperation, and very significantly, a high level of expertise of the clinicians involved in treatment. This review suggested that long-term retention of compromised teeth with or without root resection is questionable if any of the above factors are not optimal.

In summary, systemic medical challenges for implants remain the same for the totally and partially edentulous patient. Additional complications result from oral pathologic conditions. Periodontal and endodontic pathology affecting adjacent teeth must be evaluated for treatment so these conditions do not jeopardize implant success.

Evaluation of teeth and supporting alveolar bone

Radiograph of a horizontal fracture of tooth No. 41.

Clinical photograph after removal of the coronal portion of No. 41

Clinical photograph of the coronal portion of No. 41.

The coronal portion of No. 41 is reshaped, bonded to the adjacent teeth, and used as a temporary restoration during osseointegration of the implant.

Radiograph of the restored implant.

Fistula distal to tooth No. 16

Placement of gutta-percha point for diagnostic radiograph.

Radiograph demonstrating periodontal-endodontic communication that condemns this tooth.

The most important consideration that favors an implant-supported single restoration is the desire to preserve tooth structure. If the teeth adjacent to an edentulous space are not restored and are free of caries, periodontal pathology, or endodontic pathology, then the choice of an implant is best. Conventional endodontic, periodontal, and prosthetic procedures can help maintain teeth and have a high success rate. However, certain clinical, periodontal, and endodontic conditions are not associated with long-term tooth retention. The subsequent function and aesthetics required of a particular segment of the dentition will also help determine the reality of when to halt conventional treatment and/or retreatment and proceed in a new direction. The choice of some traditional prosthetic approaches may need to be re-evaluated in favor of implant-supported restorations. These include long-span fixed partial dentures, cantilevered fixed restorations when there is reduced interarch space, and a compromised abutment used to support a removable partial denture.

There are many important questions to consider when attempting to decide whether to retain a tooth or extract the tooth and place an implant. Is the tooth in the maxillary anterior region? Is the tooth to be an abutment for a fixed or removable partial denture and meant to bear significant occlusal load? Is there mobility? What is the extent, severity, and course of bone and tissue loss? Patient compliance also influences treatment decisions. What is the patient’s level of plaque control and attitude toward oral hy-giene? If oral hygiene is poor, is it due to neglect or a physical or psychological incapacity? Is the home care situation correctable, or will sophisticated surgical procedures be in vain? In addition, one must not overlook the occasional need to sacrifice ap-parently healthy teeth for aesthetic considerations. This paradoxical situation may arise in the anterior maxilla where adjacent natural tooth and implant restorations cannot conform to optimum aesthetics due to bone and subsequent tissue loss around the natural teeth. This situation may result in the absence of interdental papillae.

The anatomy of an edentulous area is critical for implant success. In the absence of teeth to stimulate load-related bone formation the width of the alveolar ridge  may be insufficient to support an implant. This situation is usually time-related and often seen in

Table 3. Clinical Situations That Are Unfavorable toTooth Retention.Clinical/Radiographic Periodontal Endodonticvertical root fracture furcation periodontal- involvement endodontic w/ poor communication prognosis for regenerationenlarging periapical >50% bone loss wide post in anradiolucency with mobility; severe abutment tooth attachment loss

areas of congenitally missing teeth and long-term non -replacement of previously extracted teeth. While neither situation precludes the placement of implants, bone augmentation and/or edentulous ridge expansion procedures may be necessary. This requires additional expertise by the clinician,  increases the cost of treatment, and must be factored into the treatment plan.

It is also possible to correct narrow alveolar ridge width due to congenital absence of teeth through orthodontic site development. When it is known that the maxillary permanent lateral incisors are congenitally missing, the canines can be allowed to erupt mesially, adjacent to the central incisors. Subsequently, the canines are orthodontically moved distally to their normal position. This will allow for adequate alveolar ridge development for future implant placement. Orthodontic site development procedures are associated with less than 1% bone loss over 4 years. This compares very favorably to the 34% narrowing of the alveolar ridge observed over a 5-year period when anterior teeth are extracted.

It is also critically important to realize that when teeth are congenitally or traumatically missing, bone growth must be completed before fixture placement to avoid infraocclusion, maxillary palatal displacement, or mandibular lingual displacement of the restored implant. In addition, passive eruption of the dentition that continues until 18 to 19 years of age, and possibly until the early 20s in males, should be complete for optimum aesthetics. It has also been reported that in some adults there is a very subtle, slow (20 or more years) growth change in the dental arches that will become evident only after decades of observation. For patients with restored single-tooth implants, such growth may result in a vertical disocclusion or malposition of adjacent teeth. It is suggested that patients be initially informed of this possibility and that crown replacement may eventually be required.

Radiograph of extensive bone loss around tooth No. 11

Clinical photograph of No.11 with orthodontic appliance in place. A restoration was bonded to the crown to engage the labial spring of the removable appliance.

Clinical photograph demonstrating extrusion of tooth and shortening of clinical crown.

Radiograph of osseointegrated implant.

Clinical photograph of completed case with porcelain-fused-to-metal restorations on Nos.11 and 21.

For certain situations that anticipate a difficult implant placement or a poor aesthetic result for a single implant, there are alternative treatments to bone augmentation. This may occur when teeth considered to be hopeless are in the anterior aesthetic zone. If considerable bone loss is present around a single tooth, or if there is a horizontal fracture (without apical infection), then orthodontic forced eruption (extrusion) may be considered. Orthodontic extrusion after endodontic treatment stimulates bone deposition at the alveolar crest and increases the area of attached gingivae. When sufficient bone and soft-tissue volume have been created, the tooth is extracted and an immediate implant placed. This procedure may also be utilized prior to extraction of the tooth and placement of a fixed partial denture with a hygienic or unaesthetic long pontic.

Another complication for implant placement that may result from extensive bone resorption or an anatomic abnormality is the

presence of a large nerve in a proposed implant site. This is most often due to extensive resorption of the mandibular alveolar ridge posterior to the mental foramen. Two procedures to correct this situation are bone augmentation and transposition (lateralization) of the nerve. While success rates for osseointegration after transposition of the nerve are high, potential significant side effects are associated with this procedure.

The decision to retain or remove teeth also requires careful consideration of the eventual prosthetic situation. It is not desirable to preserve a tooth with a poor or even guarded prognosis to support a fixed or removable prosthesis. If all considerations are favorable (Chart), then the restorative suggestions (from most to least desirable) are as follows: implant-supported fixed partial denture, tooth-supported fixed partial denture, implant abutment support for a removable partial denture, or natural tooth abutment support for a removable partial denture. While clinical studies suggest similar predictability of tooth-to-implant and implant-supported fixed prostheses, the latter may be more desirable due to the advantages of retrievability of the restoration and elimination of the risk for intrusion of the tooth abutment. An implant abutment with a precision or semiprecision attachment  joined to a natural tooth crown should be avoided due to the possibility of intrusion of the natural tooth.

In summary, it is far simpler to maintain the alveolar bone and soft-tissue architecture of a healthy tooth than to try to recreate it. Thorough evaluation of potentially pathologic situations and immediate intervention (extraction of a hopeless tooth and placement of an implant) will avoid further loss of supporting tissues that might result from indecision. In addition, use of orthodontic techniques to create an implant site is a viable treatment modality.

Financial considerations

While the cost of a simple extraction of one tooth, replacement with an implant, and subsequent crown restoration may be slightly more expensive than attempting to save the tooth with endodontic therapy and a post/crown, this approach is definitely less expensive than an extraction and subsequent construction of a 3-unit fixed partial denture. Thus, the long-term prognosis of a re-tained tooth must also be a consideration in treatment planning. Additional procedures may also have to be factored into the treatment plan. Surgical procedures that may include root amputation, apicoectomy, bone augmentation, or crown lengthening will add significantly to the cost of maintaining a tooth or a few teeth. Likewise, prosthetic procedures that include additional splinting for stabilization or to support a molar  tooth with an amputated root may be necessary.

In summary, considerations involving the location of the implant and the surrounding hard and soft tissues will increase costs substantially.

Aesthetic challenges and patient comfort

Patient concerns regarding restorative treatment in the maxillary anterior region usually relate to color, clinical crown length and shape of teeth, lip support, gingival contours, and length of time needed for a provisional restoration. Dentist concerns for this area mainly relate to the presence of labial bone support at the site and the presence of the interdental papilla. Some of the confounding factors for achieving optimum aesthetics and comfort have been discussed earlier. It remains, however, that some patients are willing to endure significant discomfort and cost. The treating dentist(s) must be absolutely certain that a patient understands the limitations of each treatment option. It is also important that the patient understands how he or she arrived at the present situation and that different procedures are available to treat the existing problems. Furthermore, many of the treatment approaches are relatively recent, and long-term studies to determine outcomes have not been published.

Implant exposed due to inadequate labial bone around tooth No21

The emergence profile of the implant restoration, the length of time elapsed between extraction and implant placement, the maintenance of proper interdental form, and the presence of active infection involving the labial bony plate are just some of the important concerns regarding management of hard and soft tissues in the anterior region of the mouth, which is referred to as the aesthetic zone. Ideally, site preparation involves the atraumatic extraction of a noninfected tooth, with hard and soft tissues remaining in-tact, and immediate placement of an implant. This is not always the case. Implant sites can be termed mature (missing tooth with hard-tissue healing), delayed (extracted tooth, hard-tissue healing incomplete), or recent (extracted tooth with soft-tissue healing).35 If a considerable loss of tissue is present at a projected implant site, delayed implant placement becomes a reasonable choice. Nevertheless, augmentation and regenerative procedures will most likely be required.

Preservation of the interdental papillae and labial bony plate become essential to aesthetic success of a restored implant. Interdental papilla preservation surgery as well as prosthetic principles involved in maintaining the papilla have improved the clinical outcome. If there has been loss of the interdental papilla due to trauma, several (adjacent) teeth are missing, or there has been an extended time since extraction, then local gingival “plastic” reconstructive techniques may be required. However, if the loss of the papilla is due to periodontitis or acute infection, then the situation is more complex and repair involves both soft-tissue and bone replacement. One approach to recreate both gingival tissue and alveolar bone is orthodontic forced eruption

(discussed previously in this article). The placement of bone grafts such as onlay grafts for the facial aspect of potential implant sites; tissue and bone regeneration techniques based on the use of barrier membranes for guided tissue regeneration (GTR), guided bone regeneration (GBR), and edentulous ridge expansion techniques; and the use of platelet-rich plasma to enhance maturation of bone and periodontal soft-tissue grafts8 have all been reported to improve clinical outcomes (but increase the cost) of implant treatment.

Another important concern for the patient is the duration of treatment, especially in the aesthetic zone. Immediate loading of implants attempts to satisfy patient concerns regarding temporary restoration of an edentulous space. The original Brånemark protocol called for undisturbed healing of the site for 6 to 12 months after tooth extraction to ensure ossification of the socket. An atraumatic ex-traction followed by flapless, immediate implant insertion was designed to maintain buccal alveolar bone and the interdental papillae, thereby obviating additional reconstructive procedures. Limited data suggests that this technique may stabilize gingival architecture as opposed to the 2-stage approach. However, it should also be noted that a recent review of the literature suggested that while there is evidence to support immediate loading of full-arch implant-supported restorations, this view is not universally accepted. The same results cannot be extrapolated to single-tooth or partial-arch applications.

In summary, implant placement and restoration in the maxillary anterior region may necessitate additional surgical procedures to enhance aesthetics. However, this also generates considerable additional expense for the patient. Immediate loading of implants to eliminate the undesirable aspects of removable temporary restorations has not yet been evaluated in a controlled clinical trial.

Conclusion

The replacement of one or a few teeth by implant-supported restorations presents different challenges than the restoration of

an edentulous jaw with implants. Aesthetics and the nature of the interim restoration are important considerations, and while clinical procedures have been developed to replace alveolar bone, restoration of normal tissue architecture cannot now be predictably achieved.