Successful Implant Planning and Surgery: An Eight-Step Digital Protocol
Scott MacLean, DDS
If dental implant placement is executed poorly, the final implant position can have detrimental effects on the long-term success of a prosthesis. Cooper reported that dental implant malposition is the primary cause of delayed implant failure and implant- and implant prosthesis-related complications.1 The positioning of dental implants has improved with the aid of 3-dimensional (3D) planning.1,2 The development of 3D implant planning software applications has enabled the fusion of cone-beam computed tomography (CBCT) digital imaging and communications in medicine (DICOM) files with intraoral scan stereolithography (STL) files.2 DICOM data can be aligned with a digital cast-like surface scan (ie, STL) to allow visualization of surgical planning for guided and nonguided surgery.
To further enhance dental implant planning and surgery success, this article proposes an eight-step digital protocol. Focusing on the single platform-shifted/switched implant, the protocol creates a checklist for clinicians when planning implant platform depth (IPD).
Implant Platform Depth
IPD represents the most coronal implant platform position for a restorative prosthesis. Researchers have discussed final implant position in efforts to idealize the long-term success of single-tooth replacements.3-5 In the past, many surgical plans focused on placing a bone-level implant using non-digital planning. While available bone is a factor when planning implants, the ideal IPD should be evaluated with a complete etiological approach to comprehensive care in mind. Underlying etiological factors include airway, occlusion, temporomandibular joint (TMJ) conditions, periodontal class, genetics, muscles, and biomechanical issues. Etiological issues can influence the final IPD. Once a comprehensive treatment plan is apparent to the dental team, they can inform the patient of the available options as related to the plan.
Tarnow and Chu reported that 50% of implant placements are single-implant cases.4 If placement of the implant is to be immediate, this will have an additional influence on the final implant position. Immediate placement of dental implants requires the surgical and restorative team to have a detailed understanding of the ideal final IPD based on anatomical markers of an unhealed site. The success rate of immediate implants has been shown to be equal to or higher than that of implants placed with a delayed approach.5 Thus, the implant position must be understood from a 3D standpoint relative to the remaining teeth, soft tissue, bone, and anatomical structures.
The IPD establishes the restorative requirements of the definitive restoration. Many clinicians use both analog and digital "wax-ups" in planning the implant position. The IPD then helps determine the implant position within the bone as related to the local anatomy. Once the IPD is planned, the clinician can determine the implant type, length, and width. In most implant systems, the implant platform is the connection for the restorative prosthesis. Robbins and Rouse's "global diagnosis" planning module focuses on the use of the final incisal position to establish the plan within a restorative case.6 A step-by-step protocol is beneficial for guiding both the restorative and surgical approaches to the final implant platform position.
Information should be collected regarding patients' medical history, radiographs, periodontal records, and all existing restorations. The goal is to uncover pre-existing conditions that may alter planning. Designed to help minimize suboptimal implant placement, the eight-step protocol focuses on the prosthodontic steps to plan an implant within a comprehensive treatment plan.
Eight-Step Protocol for Placing a Dental Implant
Step 1: Restorative Classification
First, a CBCT scan and mounted articulated models are obtained. With digital record acquisition, intraoral scanning allows for quick and easy models. The patient's esthetic and restorative requirements are evaluated. The restorative classification can influence the final position of the implant platform. The restorative case classifications, proposed by Coachman, are as follows7: (1) restorative only (no surgical changes required); (2) crown-lengthening restorative (occlusion/esthetic); (3) fully seated condylar position (FSCP), vertical dimension of occlusion (VDO), and occlusal plane restorative (airway, occlusion, and TMJ); (4) implant restorative (airway, occlusion, and TMJ); (5) orthodontic restorative (airway, occlusion, and TMJ); (6) orthognathic restorative (airway, occlusion, and TMJ).
These six restorative classifications all influence the final IPD and, therefore, should be reviewed prior to digital planning. Doing so will prompt the dental team to investigate the issues that may cause the IPD to be in a new or altered position. For example, orthodontics can change the implant position after teeth have been bodily moved. Even FSCP and VDO improvements can alter the final IPD position. By using systematic classifications of mounted models, an evaluation of the proposed outcome can be made using digital or analog diagnostic wax-ups. In many cases, a referral to a dental specialist may be necessary to evaluate airway, occlusion, and TMJ.
Step 2: FSCP, VDO, and Occlusal Plane
After the case has been evaluated at the current centric occlusion position, it may need to be mounted in a FSCP/neuromuscular position for the proposed treatment plan. Changes in mandibular and occlusal positions may influence the IPD. New digital smile design simulations can be proposed using analog and digital models.8 Outcome plans help the team determine the position of the final implant platform in all dimensions. Bone resorption can occur in multiple dimensions, making it difficult to evaluate without simulations and/or wax-ups.9 This position can be evaluated using splint therapy before placing implants to ensure an appropriate position of the implant platform post-insertion. A digital smile design should be performed in the new occlusion/joint/muscle-based position to evaluate the positional requirements of single and multiple implants.8
Step 3: Restorative Design
The restorative design is based on esthetics, function, and biomechanical factors. A width/height ratio of 75% to 80% has been proposed as ideal for an anterior central incisor.10 The replacement of a maxillary central incisor should be influenced by the dimensions of the contralateral incisor. The planning could be modified if the patient experienced altered passive eruption, which, if correction was required, should be factored into the final position of the IPD at implant placement.
Step 4: Implant/Abutment Design
The available bone in height and width is an important factor in the final prosthesis design. Misch described the classifications of FP1, regular tooth width/height; FP2, longer tooth/width ratios; and FP3, a prosthesis in which pink material must be added to compensate for missing soft tissue and bone volume.9 It is critical to understand the final design of the restoration prior to choosing the IPD. Once the final diagnosis is determined, the plan should incorporate the soft-tissue requirements.
Step 5: Depth, Angle, and Position
The requirements for an ideal IPD control the final depth, angle, and position of the implant. With the use of 3D implant planning, the implant platform can be positioned ideally in relation to the surrounding bone and teeth. The position of the implant platform has been proposed to be 3 mm to 3.5 mm below the CEJ.11 This measurement represents the connective tissue (1.5 mm) and junctional epithelium (2 mm).11 However, the CEJ is a position that is influenced by altered passive eruption. If the adjacent teeth have not erupted fully, then the CEJ may not be in an appropriate position.
Chu et al showed that the "zenith" is the high point of the gingival architecture,12 and it has been suggested that a clearly defined reference position, ie, "zenith reference," be considered. This point can be used to position the IPD based on the restorative needs of the patient case. The team can then evaluate and finalize the restoration in an anterior-posterior and medial-lateral position. Linkivicius suggested that the ideal position of an implant is 1.8 mm from the buccal plate, 2 mm from adjacent teeth, and 3 mm from other implants.3 Many times bone augmentation is required at this stage. The planning from steps 4 and 5 allow the clinician to determine if the prosthesis is classified as FP1, FP2, or FP3.9
Step 6: Confirmation of 360-degree Mucosal Seal
Planning for the mucosal seal is critical for the long-term success of the IPD. Many 3D planning software applications enable the IPD to be planned by examining the soft and hard tissues. Software applications allow for the import and superimposition of STL model data from intraoral scans.
Abrahamsson et al investigated the mucosal seal around implants using a dog model.11 The implants tested were external platform with non-platform-switched abutments. The researchers repeated this study with platform-switched implants and abutments and found the results more favorable. The seal was 1 mm to 1.5 mm of connective tissue and 2 mm of junctional epithelium in height. The total healthy mucosal seal was 3 mm to 3.5 mm.
In a 10-study meta-analysis, Atieh et al reported that non-platform-switched implants/abutments demonstrated more bone loss than platform-switched implants/abutments.13 Other studies have reported that the thickness of the soft tissue around implants can preserve crestal bone.11,13-15
Step 7: Anatomical - Bone, Nerve, and Sinus
Once the implant platform position has been established, the anatomical structures in the site may be evaluated. If the site has a deficiency of bone volume, bone augmentation may be necessary. Occasionally, bone reduction may be needed. Associated vital anatomical structures (eg, nerves, sinuses, teeth, implants, as well as bone contours, density, and volume, etc) are identified.
Step 8: Implant Width and Length
Based on the evaluation of the anatomical structures, the last step is to choose the final implant width and length. The use of 3D planning applications facilitates the virtual positioning of the implant into an ideal position, with consideration given to all of the prosthodontic steps and the patient's anatomy. A minimum distance of 1.8 mm from the buccal plate has been proposed to accommodate buccal bone and soft-tissue support.3 Placement of an implant 1.5 mm from natural teeth and 3 mm from other implants has been suggested.3
Conclusion
This eight-step protocol for planning the placement of a dental implant provides a checklist to assist the dental team in detecting problems prior to surgery. This can allow clinicians to inform patients about any limitations that may be involved in their specific case, and it can ensure that the implant platform depth is positioned ideally for esthetics, function, occlusion, and longevity.
About thte Author
Scott MacLean, DDS
Director, Seattle Study Club, Kirkland, Washington; Private Practice, Halifax, Nova Scotia, Canada
References
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