The original protocol of the Nobel Biocare Brånemark System (Gothenburg, Sweden) proposed that the prosthetic phase should begin after a healing period of three to six months after placement of an implant.¹ However, in the past five years, this approach has changed with the development of immediate provisionalization protocols (immediate loading), allowing loading of a single-implant crown or fixed prosthesis at the time of, or shortly after, implant placement. In certain clinical cases, provisionalization may be as effective as the conventional delayed approach.⁴ The long-term success of immediate-load implants depends on factors such as primary fixation of the implant, rigid fixation of the prosthesis (that is, minimal micromotion to the healing implant) and prevention of excessive lateral or torsional occlusal contacts on the prosthesis.^4–6

Although immediate loading has become popular clinically, situations such as poor primary fixation may compel the dentist to follow a more conventional delayed-loading protocol. In such instances, a one-stage approach, in which the head of the implant or healing abutment is left exposed to the oral cavity during healing, or a two-stage approach, in which the implant is allowed to heal while submerged below the gingiva, may be prudent. In most clinical situations, the one-stage approach allows the implant to remain in a relatively unloaded state but avoids the need for a second surgery to uncover it. Alternatively, depending on the implant system used, a two-stage surgical approach may be warranted, especially if the initial stability at placement is poor. Many dentists prefer to use a two-stage approach if extensive bone grafting is required at the time of implant placement or if the implant has minimal primary stability. Both the one- and two-stage approaches have been shown to provide equivalent results in identical clinical situations.⁷

Implant designs continue to evolve, with new thread designs and implant surface modifications (such as roughing via grit blasting and various forms of etching procedures) developed to enhance the predictability of implant survival in soft or poor bone situations. Some recent innovations in dental implant technology^8–10 are shown in Box 1. These implant surface modifications promote new bone growth (a process called "osteoconduction") and include enhanced hydrophilic surface properties of the titanium oxide surface, development of a three-dimensional oxide surface, sintered beads of titanium on the implant surface or modification of the titanium oxide to a titanium fluoroxide.¹¹ As an example of these surface modifications, the titanium fluoroxide surface results from an electrochemical etching process that modifies the oxide surface with a resulting low level of fluoride in the oxide surface (that is, 1–3 atomic percent).¹² This fluoridated oxide surface, which acts as a site for calcium and phosphate precipitation, increases bone contact and implant stability.^9,12 This surface also exerts specific effects that upregulate key genes involved in the promotion of human stem cell differentiation into bone (for example, growth factors such as bone morphogenetic protein-2 or runt-related transcription factor-2) and also activate key growth factor pathways in bone development.^13–15

	INITIAL PATIENT ASSESSMENT

TOP ABSTRACT INITIAL PATIENT ASSESSMENT IMPLANT TREATMENT PLANNING: THE... IMPLANT TREATMENT PLANNING FOR... CONCLUSION REFERENCES

 
The predictable esthetic and functional outcomes of implant treatment require comprehensive diagnostic and treatment planning.³ As a member of the implant team, the general dentist should collaborate with the oral and maxillofacial surgeon, the periodontist or endodontist, the prosthodontist and the laboratory technician, as well as with other team members such as radiologists and dental and surgical assistants. The dentist should conduct an initial assessment of the patient’s medical and dental history to determine the implant system and devices that will meet the patient’s therapeutic and esthetic requirements. The assessment should determine the patient’s history of bruxism, periodontal disease, tobacco use, uncontrolled diabetes mellitus and metabolic diseases of bone.¹⁷ In addition, in the process of carrying out the assessment, the dentist should educate the patient about the causes of tooth loss, determine the patient’s attitudes about treatment and his or her ability to tolerate it, and inform the patient of estimated treatment costs.¹

Throughout the surgical and prosthetic phases of the implant reconstruction, the dental practitioner should obtain comprehensive written and oral informed consent to the treatment from the patient. The consent form should document the risks, benefits and alternatives that have been discussed with the patient. Among those risks may be specific genetic risk factors that emerging evidence suggests may predict implant outcomes. For example, the expression of certain forms of alleles for the interleukin (IL)-1 cytokine (IL-1 genotype polymorphism) places some patients who use tobacco products at increased risk of experiencing both periodontal disease and increased loss of dental implants.^18,19

For improved treatment outcomes, the dentist should design and compose the proposed prosthesis during the diagnostic phase. Planning will dictate the number of implants as well as their position and angulation. Based on this diagnostic information, a surgical guide or denture can indicate the desired implant position, angulation and need for hard- or soft-tissue augmentation before or during implant placement. During the clinical examination, the dentist should evaluate the residual ridge carefully for its shape and contour and other sites in the mouth for potential risks of recession (Box 2). A careful evaluation of the patient’s risk factors for soft- and hard-tissue changes, whatever final restoration is planned, should be made not only to comply with the informed consent process, but also to encourage realistic patient expectations.

	IMPLANT TREATMENT PLANNING: THE SINGLE TOOTH AND THE PARTIALLY EDENTULOUS ARCH

TOP ABSTRACT INITIAL PATIENT ASSESSMENT IMPLANT TREATMENT PLANNING: THE... IMPLANT TREATMENT PLANNING FOR... CONCLUSION REFERENCES

 
Preoperative planning helps to achieve esthetic goals by ensuring that the implant placement is restoratively driven. Implant-retained fixed partial dentures (FPDs) are an excellent alternative to long edentulous spans that conventionally would be restored with removable partial dentures.

As part of the informed consent process, treatment plan alternatives should include a discussion of the ability to control esthetics and function with the various methods of tooth replacement, including conventional FPDs, adhesive resin restorations (also called "Maryland bridges"), implants and removable partial dentures.

How many implants are necessary? In the diagnostic phase, the dentist should determine the number of endosseous-style implants to be placed. When replacing multiple adjacent teeth with dental implants, it often is clinically useful to replace three teeth with a short-span FPD on two implants, using the pontic to adjust for contours and final implant position. This approach is especially helpful in the anterior maxilla when multiple teeth are involved, where the smallest tooth to be replaced is planned as a pontic with implants placed in the canine and central incisor region.

Where should the implants be placed? The dentist’s preoperative planning should include an evaluation of the pattern of bone loss related to congenitally missing or traumatically lost teeth. In either instance, the dentition tends to be positioned more facially relative to the central axis of the alveolar ridge, which results in a thin facial plate of bone over the teeth. On tooth loss, this facial plate often is unevenly resorbed in a palatal and apical direction in the maxillae.²⁰ The dentist should consider the position and stability of the facial-buccal plate of bone for any evidence of bone loss, which often occurs in cases involving traumatic fracture or, potentially, during orthodontic therapy. In the mandible, the resorption pattern can occur at an uneven rate that may cause increased bone loss on the thin superior regions, producing a wider ridge with high muscle attachments.²¹

When determining the optimal tooth position for functional and esthetic purposes, the dentist should create a diagnostic setup with denture teeth on a trial base with soft- and hard-tissue contours waxed out to full contour. A vacuum-formed matrix of this diagnostic setup then can assist the surgeon in determining the position, placement and volume of site development—hard-and soft-tissue grafting—needed before implants can be placed. In planning the occlusion, one should consider tooth contacts in centric relation or maximum intercuspation that provide vertical loading down the long axis of the implant(s). Large lateral sliding contacts may create elevated bending or torsional loads, which situation leads to premature failure of abutments or the crown or bridge’s mechanical components.^22,23 Lastly, the patient should be able to open his or her mouth 35 millimeters or more at the implant site of interest to allow the surgeon access for drilling the osteotomy and placing the implant within the planned restoration. This may become an issue when the surgical dentist, unable to clear the opposing dentition with the handpiece, deviates to the facial aspect. This inadvertently places the implants at an increased angle to the occlusal plane, which can complicate the final design and biomechanics of the prosthesis.

Should implants be connected to natural teeth? Occasionally, implants are placed and connected to natural teeth using an FPD and a non-rigid connector.²⁴ Investigators have reported unpredictable incidences of movement (intrusion) of the natural retainer teeth in some cases.^24–27 Such incidences of intrusion may stem from "disuse atrophy" owing to a lack of normal mechanical loading. However, an exact cause remains unknown.²⁵ Therefore, to provide a prosthesis that is only supported or retained by implants often requires either placement of additional implants or use of augmentation (such as onlay bone, sinus lift grafting or distraction osteogenesis).^20,27–29

What should the dentist look for in planning? Implant position in the partially edentulous or single-tooth situation is critical for achieving a predictable esthetic outcome. As shown in Box 2, the initial evaluation should include factors associated with sufficient bone and soft-tissue volume. Additionally, the dentist should discuss these risk factors with the patient and members of the team performing the implant procedure.

When evaluating any proposed site in all three dimensions for hard- and soft-tissue contours, the dentist should rely on clinical observations and use mounted diagnostic casts and a diagnostic wax-up. When evaluating osseous contours, the dentist should use palpation and sounding with anesthesia (using an endodontic explorer and stopper probed to the periosteum measuring the gingival thickness every few millimeters) coupled with a radiographic examination using a radiographic guide with reference markers (such as gutta-percha). The markers should be positioned within a drilled channel parallel to the desired angulation of the implant. During the evaluation of the soft-tissue contours for shape, quantity, texture and color (Box 2), the dentist should note the parameters of the diagnostic wax-up for generation of radiographic and surgical guides. The periodontal tissues should be in optimal health before implant placement. A thick periodontal tissue biotype typically has thick, flattened osseous plates and offers a higher resistance to recession than does a thin tissue biotype. In contrast, a thin periodontal tissue biotype has a thin erythematous periodontium covering a thin or nonexistent alveolar crest that carries an increased risk of experiencing soft-tissue recession.^30,31

While evaluating the gingiva on the contralateral tooth or teeth, the dentist should consider the size, shape and color of the interdental papillae, the arcuate form of the free marginal gingiva and the relative root shape and size (that is, transition contour of the abutment and restorative emergence profile), along with the width of attached gingiva and the prominence of roots on the facial aspect.^30–32 In sites of thin tissue biotype, the dentist should consider using soft-tissue augmentation procedures (including submucosal grafts and/or free gingival grafting procedures) to increase the thickness of mucosal tissue over the implant or implant abutment. Papillae-saving incisions or flapless surgical approaches may improve the predictability of soft-tissue management. However, because the gingival response can be difficult to predict before surgery, it is important to conduct a careful evaluation and obtain informed consent from the patient or care-giver. In situations that pose a high risk of gingival recession, the dentist should consider a screw-retained crown or prosthesis instead of a cemented prosthesis. This approach allows contours to be retrieved and modified later without having to remake the entire prosthesis.

Can surgical guides aid in planning placement? A surgical guide fabricated and modified from a wax replica improves the accuracy of implant placement. Thus, surgical guides greatly facilitate predictable outcomes and may reduce the cost of treatment by reducing the need for expensive custom abutments. In some cases, such as those involving posterior single-tooth implants, a vacuum-formed matrix with the occlusal surface removed may be sufficient to indicate facial and lingual contours. In critical anatomical situations (for example, in the esthetic zone or adjacent to vital structures), the dentist can make a rigid guide of acrylic resin with the implant position and the desired restoration’s contours built into it. Removable sleeves in the guide will allow the surgeon to use it with drills of different sizes during osteotomy preparation. Because most implants are self-tapping and tend to find their own path on placement in soft bone, the dentist can use a vacuum-formed matrix during implant placement to help ensure that the implant is placed in the middle of the planned restoration. A surgical guide fabricated from a diagnostic wax-up can determine if augmentation (for instance, ramal onlay grafting) may prevent fenestration or dehiscence during implant placement.^28,33 Therefore, when fabricating a surgical guide, the dentist should consider tooth position, contours and angulation, along with the anticipated soft- and hard-tissue contours necessary to create an esthetic gingival profile.

Is a screw-retained or a cemented restoration preferable? The type of final restoration, whether screw-retained or cemented, may alter the position and placement angle of an implant.

A screw-retained restoration (one in which a prosthetic crown or FPD is secured to the implant or abutment with a prosthetic connecting screw) often requires a vertical implant orientation relative to the occlusal plane. The orientation increases both the palatal position of the head of the implant and the facial position of the apex of the implant (Figure 1). For example, to create screw access in the cingulum area of a central incisor, the dentist places the implant in a location more vertical than what would be appropriate if a cemented crown were planned. Because the apex of the implant may perforate the facial plate, the site may need osseous grafting before or at the time of implant placement. However, an implant placed too much to the palatal aspect in a facial-lingual dimension may require an anterior cantilever in the porcelain contours. This placement introduces a risk of poor oral hygiene and recession.^28,32

View larger version (50K): [in this window] [in a new window]   Figure 1. Screw-retained crowns in the anterior area. Screw access needs to come through the cingulum area, which necessitates a more facial position of the apex of the implant. Therefore, bone grafting or other site development often is required.

View larger version (49K): [in this window] [in a new window]   Figure 2. Cement-retained crowns in the anterior area. A cement-retained crown on either a prefabricated or a custom abutment allows the long axis of the implant to be positioned through the incisal edge of the planned restoration. Bone grafting or other site development may be needed, depending on the osseous width and soft-tissue thickness.

How much bone is necessary? Single-tooth applications require adequate interproximal bone. For example, a 4-mm–diameter implant requires 8 mm of space, including 2 mm of bone between the alveolar crest and the root apexes on each side. Because 1 mm of peri-implant bone continuously models or remodels, at least 1 mm of facial and lingual cortical bone is needed on each side of the implant.^5,34,35

Implant position relative to the adjacent teeth. For proper development of the emergence profile (the contour of the restoration from the margin though the gingival tissues), the dentist should position the implant so that it is apical to the adjacent teeth. First, the dentist should consider the soft-tissue thickness and the position of the inter-dental alveolar bone morphology adjacent to the teeth on either side of the proposed site. For a central incisor with a normal gingival attachment, the head of the implant should be placed 2 to 3 mm apical to the planned cementoenamel junction (CEJ) of the restoration (to create a transition from the cylindrical implant to the triangular crown).^{28–30,32,36} This depth allows the connective tissue and junctional epithelial biological width to form on the transmucosal portion of the implant body or on the abutment’s mucosal transition zone.³⁷ The dentist should avoid excessive countersinking of the implant, as this can lead to bone loss, diminish soft-tissue support and increase the risk of long-term gingival recession.³² If the head of the implant cannot be placed 2 to 3 mm below the planned CEJ—owing to, for example, the proximity of a sinus or vital structure—then a phased treatment may be indicated, with bone augmentation followed later by implant placement or use of an alternative prosthetic intervention.

Special situations in single-tooth implant placement. If the tooth that is lost was maloccluded or periodontally involved, the tooth’s position may not be the optimal position for an implant. Immediate placement planning should consider sites that have teeth with short roots, thick tissue bio-types and/or teeth planned for extraction owing to unrestorable caries. In each case, the facial plate must be intact. An intact facial plate allows for primary stability of the implant and support for the gingival tissues.

Immediate placement in the extraction socket. In immediate implant placement, it often is advantageous to position the implant slightly to the palatal aspect of the socket so the cutting threads of the implant do not cut away or otherwise disrupt the thin facial plate of bone. This will leave up to 1 mm of space between the implant and the internal surface of the facial bony plate, which will fill with the clot and, subsequently, bone and connective tissue. Traumatically avulsed teeth often are poor candidates for immediate placement, because the facial plate of bone typically is fractured or absent. To establish primary stability with an immediate placement, the dentist should place one-third to one-half of the implant body in sound bone that extends beyond the apex of the socket. As a result, the head of the implant may be excessively countersunk (with the associated risk of unpredictable gingival recession).

An alternative to immediate extraction is tissue expansion by decorticalization of the crown of the tooth, followed by advancement of a facial flap, with or without a submucosal connective tissue graft and primary closure. At a later time, the dentist re-enters the site and places an implant in the optimal location.^38,39 Alternatively, the use of fixed orthodontic extrusion can create either simple orthodontic luxation of the remaining root or development of additional soft and/or hard tissue, depending on the rate of extrusion.⁴⁰

Healing abutments and provisional restorations. Surgical management of the implant site and prosthetic abutment choices affect the preservation, development and maintenance of the interproximal papillae. In the anterior esthetic zone, a narrow-diameter healing abutment allows the provisional crown to reposition the soft tissue at the time of abutment placement. A restoration fabricated at the time of implant placement (immediate provisionalization) can guide the healing of adjacent soft tissues, although the provisional crown should be left out of occlusion (maximum intercuspation and all eccentric positions) during the healing phase. When performing an immediate provisionalization protocol, the dentist should monitor the occlusion, because the mobility of the adjacent natural teeth increases during the inflammation and healing of the implant site.^4,41,42 The dentist can make final impressions and place the definitive restoration after a healing period of six to 12 weeks. As hard and soft tissues heal, interproximal contacts and gingival embrasure form allow the maturing tissue to adapt to the provisional restoration. The dentist can complete the final restoration when the gingival tissues have matured, typically six weeks or more after implant placement.

	IMPLANT TREATMENT PLANNING FOR THE EDENTULOUS ARCH

TOP ABSTRACT INITIAL PATIENT ASSESSMENT IMPLANT TREATMENT PLANNING: THE... IMPLANT TREATMENT PLANNING FOR... CONCLUSION REFERENCES

 
What type of prosthesis design should be considered? Mandibular arch. The dentist can restore the mandibular arch using a fixed complete denture (FCD), FPD or overdenture. The FCD has either a gold casting or computer-aided design/computer-aided manufacturing (CAD/CAM) milled titanium framework, with either prosthetic acrylic resin teeth or teeth veneered with porcelain.¹ An overdenture with attachment to the implant can be supported and retained fully by the implant or by a combination mucosaborne/implant-borne prosthesis.^43–45

Maxillary arch. If minimal bone resorption exists, restoring the edentulous maxilla with a porcelain-fused-to-metal restoration is a possibility.³⁶ A diagnostic work-up should include impressions, jaw relationship records and an esthetic try-in using prosthetic denture teeth on a trial denture base. To determine the degree of lip support, the dentist should evaluate the smile line (that is, the anterior and posterior occlusal planes) of a diagnostic denture set-up in the mouth. In addition, the dentist should evaluate the patient’s lip support with and without the anterior facial denture flange.^32,46 The anterior smile line, both relaxed and exaggerated, not only demonstrates the degree of tooth exposure anticipated, but also provides clues about the expected crown length, gingival display and potential need to use gingival tone porcelain for appropriate tooth length and esthetics.

Discussing the treatment plan with the dental laboratory technician, before it is finalized, is helpful. A fixed maxillary prosthesis has greater incidences of esthetic, phonetic and oral hygiene problems than does an overdenture prosthesis; this is associated in part with excessively long anterior teeth, excessive facial cantilever pontics and mesial-distal complications with embrasure forms.⁴⁶ Given the clinical and laboratory complexity and costs of these types of prostheses, a maxillary over-denture on four to six implants, typically connected with a rigid bar-and-clip attachment system, may be an alternative. The overdenture often provides predictable esthetics and lip support and prevents air escape (for example, superior to the prosthesis or through exaggerated gingival embrasures). An overdenture often is considered the treatment of choice for patients with moderate-to-severe resorption, problems with dexterity and problems with phonetic palatal contours.^43,44,47

Is a fixed complete denture appropriate? An FCD provides excellent function and patient acceptance.^46,47 During the diagnostic phases, the dentist should discuss with the patient the advantages and disadvantages of the FCD compared with those of an overdenture. If using a ceramometal full-arch fixed reconstruction, the dentist should consider replacing every three teeth with a three-unit FPD on two implants (for instance, teeth nos. 6–8) using the pontic contours to adjust for implant alignment and esthetic demands.³² A fixed maxillary reconstruction entails between six and eight implants (first molar, first premolar, canine and central incisor) with four independent FPDs (molar to premolar, canine to central incisor, bilaterally). Using care to limit loading, the dentist may use six implants with distal cantilevers on two FPDs (cantilever pontics limited to one premolar-sized tooth). An overdenture should use a sufficient number of implants for long-term stability, typically four in the maxilla (canine and second premolar region) and two in the lower canine or first premolar region.⁴⁸ Using the denture setup, the dentist fabricates a radiographic guide with radiopaque markers (such as gutta-percha or bur shanks) within the denture at the sites of interest. An alternative approach involves duplicating the denture setup with teeth made using 5 percent medical-grade barium sulfate mixed with clear autopolymerizing resin. This approach allows easy visualization of tooth size, angle and position on conventional and/or computerized tomography–aided treatment planning. In the mandible, the trial setup helps the dentist evaluate the height and position of the prosthetic teeth relative to the symphyseal cross-sectional anatomy.^49,50 A conventional FCD with acrylic teeth requires a minimum of 15 mm from the alveolar crest to the planned incisal edge.²⁰ If the vertical dimension of occlusion and jaw anatomy is insufficient, the dentist could perform an aggressive alveolectomy or rehabilitate the affected teeth with ceramometal restorations (along with treatment planning for the additional cost).

The dentist should use radiographic information and a diagnostic setup to help determine the type of definitive prosthesis design. Skeletal Class I and II relationships with minimal resorption may allow normal contours and lip support with an FCD. A prognathic Class III relationship can increase prosthetic problems, especially if implants cannot be placed distal to the mental foramens. In such cases, an overdenture approach yields a more predictable result.⁴³

Is an overdenture appropriate? The overdenture approach provides the patient with significant treatment flexibility. In a 2002 report, the panelists at a consensus conference on overdentures held at McGill University in Montreal recommended that the standard of care in the treatment of the edentulous lower jaw be two implants and an over-denture.⁵¹ This minimally invasive approach significantly improves the patient’s physiological bone mass, quality of life and, possibly, nutritional status.⁵¹ Two implants spaced between 12 and 16 mm apart (edge to edge) in the mandibular canine region can be restored with freestanding attachments such as ball attachments, Locator (Zest Anchors, Escondido, Calif.) or ERA (Sterngold, Attleboro, Mass.) style attachments or an overdenture bar system (for example, a Hader bar [Attachments International, San Mateo, Calif.]) and a plastic clip attachment in the denture. Bar reconstructions are appropriate for nonparallel implants in which the connecting bar is designed to parallel the retromolar pads (fulcrum of rotation), allowing the overdenture to gain retention from the bar and support from the mucosal tissue.²⁹ For patients who are sensitive to pressure on the mandibular mucosal tissues, the dentist should consider placing four implants that are connected with a rigid bar and an overdenture that rests solely on the bar. In the maxillary arch, an overdenture typically requires four to six implants rigidly connected with a bar-and-clip attachment system.⁴⁸

	CONCLUSION

TOP ABSTRACT INITIAL PATIENT ASSESSMENT IMPLANT TREATMENT PLANNING: THE... IMPLANT TREATMENT PLANNING FOR... CONCLUSION REFERENCES

 
The use of dental implant–supported restorations has given dentists an expanded ability to provide predictable replacements for missing teeth. New designs and implant surface treatments will expand the use of this treatment modality further, especially in the areas of immediate loading and use in areas of poor bone quality through application of tissue-engineering technologies. However, the ultimate outcome—the satisfied patient—is a result of careful assessment and teamwork among the dentist and his or her surgical colleagues.