A Digitally Programmed Technique to Simplify Sequential Extraction Implant Treatment

The growing demand for implant treatment has created a need for simplified, streamlined treatment processes. Patients today have greater awareness of the possibilities of implant treatment than in the past. An evaluation of the dental needs of baby boomers demonstrates a large population of patients that would benefit from full-arch replacement implant treatment.^1,2 While "all-on-X" treatment has been popular due to its efficient protocols and one-visit therapy,^3,4 some limitations and compromises are associated with this treatment,⁵ and dentistry would benefit from more conventional, sequential extraction treatment protocols. The purpose of this article is to describe a technique for streamlining sequential extraction therapy to reduce patient chairtime and simplify the treatment provided by the clinician through the use of digital tools and techniques and new materials.

The sequential extraction technique for full-arch (or a large segment of an arch) rehabilitation has been successfully used for many years.⁶ This technique requires keeping patients in fixed provisional restorations while teeth are extracted and implants are placed and throughout the healing period. Typically, one to two appointments are needed to gather the requisite impressions, followed by an extensive, time-consuming appointment to prepare teeth, extract teeth, possibly place implants, perform bone grafting of extraction sites, and reline the provisional restoration at the correct vertical dimension and 3-dimensional orientation.^7,8 The procedure is challenging and requires a fair amount of expertise. Additionally, a combination of restorative doctors and surgical specialists may be needed, which usually requires a considerable amount of coordination.

The present authors propose a streamlined technique that includes data collection, diagnosis, laboratory planning, material consideration, and clinical implementation for a highly efficient digital process. The indications for this technique are patients requiring full-arch implant treatment (or a large segment of the arch); three to four teeth must be in appropriate positions to support a provisional restoration, and these teeth must not have associated active pathology or be painful. No minimum bone requirement is needed as long as the tooth has at least minimal bone support to create some stability. Lack of mobility is not a criterion, as a provisional restoration will be used to splint the tooth to other teeth in a cross-arch configuration. When possible, having a reasonable anterior-to-posterior spread of these abutment teeth is desirable.

The clinician needs to interview the patient to ascertain the patient's desires for esthetics and function. A comprehensive clinical evaluation will provide the data required to create a treatment plan, including which teeth are appropriate to be used as provisional abutments for the provisional restoration. Intraoral surface scans with a virtual centric record are performed to create virtual diagnostic models. (Alternatively, conventional impressions can be taken with the subsequent poured models scanned by the laboratory.) An appropriate radiographic assessment, including a cone-beam computed tomography (CBCT) scan, completes the evaluation.

The CBCT scan is meshed with the intraoral surface scan (or the laboratory scanned models) using available surgical planning software designed for the integration of intraoral surface scan STL data and CBCT scan DICOM data. A comprehensive treatment plan is then formulated using all the data collected, including the meshed CBCT scan and intraoral surface scan. The abutment teeth are selected. Consideration should be given such that implants may be placed in their ideal tooth positions for the final restoration. Ideally, a tooth should not be kept for provisional abutment support if that tooth position can be better utilized for an implant position. In this manner, just one implant surgical procedure will be needed.

The laboratory is then instructed regarding which teeth will be used for abutment support. The laboratory will produce shell crowns for those individual teeth to replicate their shape and form as they currently exist.

The first treatment appointment is used to prepare the three or four individual abutment teeth that will be utilized as provisional abutments. Simple tooth preparation is done ideally with a supra­gingival margin; such a margin will allow a simple, cord-free impression. If this is not possible due to decay, the presence of a previous restoration, or the need to create adequate retention and resistance form, then a subgingival margin may be used and will require a more time-consuming impression with retraction cord or paste. Preferably, a digital impression is taken along with a counter impression and centric record. If a conventional impression is taken, the subsequent model will be scanned with a laboratory scanner. The shell provisionals are then relined over the preparation and cemented into place. The provisionals should just replicate what existed before without any changes made to the appearance or function of the teeth. A virtual or conventional facebow should be taken if changes will be made to the current incisal plane.

The collected data, consisting of the CBCT scan and the new intraoral surface scan of the prepared teeth, is sent digitally to the laboratory (or the conventional impression of the prepared teeth). The laboratory begins the virtual wax-up by virtually extracting all the teeth that will be removed at the time of tooth extraction and full-arch provisionalization (ie, all teeth that have not been prepared). The laboratory will then complete the virtual wax-up for the provisional restoration by following all instructions and changes indicated by the clinician (eg, vertical dimension, arch form tooth shape, incisal edge position, etc). In defining parameters for the virtual wax-up, the die spacer thickness for the prepared teeth is set at the suggested parameters for the material to be used. The virtual wax-up is then merged with the CBCT scan. Surgical planning is then performed with the virtual wax-up demonstrating the desired tooth positions in conjunction with the locations of the available and significant anatomical structures.

The laboratory then verifies both the surgical plan and restorative plan with the surgeon and restorative dentist, respectively. The manufacturing file created from the virtual wax-up can now be used to manufacture the provisional restoration. Polymethyl methacrylate (PMMA) is the conventional material used for a digitally milled provisional restoration. However, for long spans and possible cantilevers, material and design modifications may be considered. From a design standpoint, the restoration should be made thicker palatally or lingually. There are limitations to how thick the restoration may be when considering tongue space, speech, and comfort. In the digital age, zirconia is a relatively easy material to use; it has high flexural strength (900 MPa to 1400 MPa)⁹ and can be manufactured from the same design file as the PMMA.

The surgical guide is designed once there is confirmation of the implant position in the surgical plan. The laboratory designs the guide on the virtual model with the virtually extracted teeth and the retained prepared abutment teeth. The surgical guide, being held in place by the prepared abutment teeth, will therefore fit to a very precise position. The guide is then 3D printed.

With the two required items-the surgical guide and the provisional restoration-the clinical procedure may proceed, as follows:

The teeth planned for removal are extracted.

The provisional restorations on the individual abutment teeth are removed.

The surgical guide is seated with the aid of the prepared abutment teeth, and the implant procedure is performed.

Any adjunctive procedures before or after implant placement, such as bone grafting, are completed and all suturing is done.

The provisional restoration is seated on the prepared abutment teeth.

Occlusion is evaluated and any occlusal adjustment is performed.

The restoration is cemented with a fairly retentive provisional cement.

A 70-year-old woman presented requesting that her maxilla be restored with a fixed restoration. Her past medical history was noncontributory (American Society of Anesthesiologists [ASA] I). A comprehensive dental examination was performed, which included hard- and soft-tissue charting, periodontal charting with mobility of her remaining maxillary teeth, and a radiographic series. She was missing all maxillary molar and second premolar teeth (Figure 1 and Figure 2). Her remaining maxillary teeth had grade 1 to grade 2 mobility with probing depths of 2 mm to 8 mm.

She used a removable partial denture, which was stable and fit well, to replace her missing maxillary posterior teeth. A CBCT scan (Rayscan Alpha, Ray Co. Ltd., raymedical.com) (Figure 3) and intraoral surface scans (TRIOS 3, 3Shape, 3shape.com), including maxillary, mandibular, and centric record scans, were taken (Figure 4 and Figure 5). The prognosis of her remaining maxillary teeth was poor with a very low probability of any reasonable long-term success for a maxillary full-arch fixed restoration utilizing her maxillary teeth.

Treatment Plan

Treatment plans for fixed restoration of her maxilla included all-on-X treatment or sequential extraction treatment with bilateral sinus grafting. Both options were presented to the patient, with the benefits and disadvantages of each course of treatment being explained to her. She chose the sequential extraction treatment.

The treatment plan included bilateral sinus grafts with three maxillary teeth being retained to support a fixed maxillary provisional restoration and extraction of the remaining maxillary teeth with immediate implant placement (Figure 6 and Figure 7). After healing of the sinus grafts, additional implants were to be placed in the sinus grafts, for a total of eight maxillary implants supporting a full-arch, screw-retained zirconia restoration (crown-and-bridge style).

Sequence of Treatment

To begin the treatment, the following data was sent to the dental laboratory: the initial intraoral surface scans, which included a scan of the maxilla with the patient's removable partial denture in place (Figure 4 and Figure 5); a second intraoral surface scan of the maxilla without the maxillary removable partial denture; an intraoral surface scan of the mandible and a virtual centric record; and the treatment plan, which identified the teeth that would be kept to serve as provisional abutment teeth and the ideal implant positions. In this case, the teeth selected to serve as provisional abutment teeth were Nos. 6, 10, and 11. The laboratory made virtual crown preparations for these teeth and manufactured PMMA shell provisional crowns with a CAD/CAM process (3Shape Design software, 3Shape).

The first treatment appointment consisted of making crown preparations for teeth Nos. 6, 10, and 11 and relining the prepared shell crowns on them. A digital intraoral surface impression scan was made of the maxilla with these preparations (Figure 8).

The patient was interviewed regarding what changes she might like. The new digital intraoral surface impression scan (of the prepared teeth without the provisional crowns) was sent to the laboratory with the original digital impression scan and original CBCT scan. Instructions for the laboratory were to virtually extract all maxillary teeth except for tooth preparations Nos. 6, 10, and 11. The patient liked the way her original maxillary bridge looked, so the provisional design was to copy that.

The laboratory virtually extracted teeth Nos. 6, 10, and 11 and designed the provisional restoration (3Shape Design) copying the original bridge design (Figure 9 and Figure 10). The die spacer thickness parameter was set to cement gap 0.045 mm with an extra cement gap of 0.065 mm. This file was then imported into surgical planning and guide design software (3Shape Implant Studio, 3Shape), and final implant positions were planned for the area where implants could be placed (Figure 11 through Figure 13). This plan was verified by the clinicians, and the surgical guide was designed to sit on the prepared teeth (Figure 14).

The laboratory manufactured two provisional restorations, both from the same design file: one provisional was made from zirconia (1250 MPa) (ArgenZ HT+, Argen, argen.com) and the other from PMMA (Figure 15). The surgical guide was 3D printed, and guide sleeves compatible with the implant system (Paltop, Keystone Dental Group, keystonedental.com) and fully guided surgical guide system to be used (Paltop) were installed in the surgical guide (Figure 16).

Implant Insertion, Placement of Provisional

The patient presented for her appointment, and the procedure proceeded according to the following sequence: Bilateral maxillary sinus grafts were performed. The provisional restorations were removed from teeth Nos. 6, 10, and 11, and the preparations were cleaned of all residual cement. The maxillary teeth were extracted leaving teeth Nos. 6, 10, and 11 in place (Figure 17). The extraction sockets were fully debrided and thoroughly irrigated.

Next, the surgical guide was inserted, and complete seating was confirmed by examining the seating windows in the guide. Flapless, fully guided osteotomy preparations were performed in the extraction sockets (Figure 18). The implants were inserted through the surgical guide. Intrabony defects between extraction sockets and implants were grafted with xenograft bone graft material (Bio-Oss^®, Geistlich Biomaterials, geistlich-na.com). The implant sites with graft material were obturated with collagen plugs (Collaplug, Zimmer Biomet, zimmerbiometdental.com) and fixed in place with sutures.

The zirconia provisional was then inserted and evaluated for complete seating, appropriate occlusal contacts, and guidance (Figure 19). No adjustments were needed. A PMMA replica of the zirconia provisional was available as a backup in case adjustment was required.

Lastly, the zirconia provisional was cemented with a polycarboxylate cement (Durelon^™, 3M Oral Care, 3m.com), and the patient was reappointed for 1 week to evaluate the occlusion and for follow-up to the surgical procedure (Figure 20 through Figure 23).

Digital technology has enabled the streamlining of full-arch implant treatment, such as all-on-X techniques.^10,11 Digital collection of data such as CBCT scans and intraoral surface scanning has facilitated comprehensive 3D data compilation in a highly efficient, clinically practical manner. Software for diagnostic analysis, surgical and restorative planning, surgical tools, surgical guide design, restorative tools, and provisional and final restoration design is commonly used in dental laboratories. 3D printing as well as computer numerical control (CNC) machining are readily available, and materials for these technologies are ever improving. Numerous commercially available products utilize these technologies to aid in the all-on-X technique.¹² Although an effective technique, there are factors to consider regarding all-on-X procedures such as the frequent need for extensive bone reduction and its subsequent limitations.¹³ Therefore, the sequential extraction protocol used to produce a crown-and-bridge style restoration may be a viable treatment option. The concepts of streamlined treatment, including data collection, diagnosis, treatment planning, surgical and restorative clinical protocols, new materials, laboratory technology, and clinical treatment tools, as described herein, should be utilized for sequential extraction patients. The protocol and process described can have many variations depending on available technology and the clinical factors with which the patient presents.

The virtual models made with intraoral surface scanning can be produced by using conventional models that are scanned in the laboratory. There may be fixed crown-and-bridge segments that do not allow for abutment preparation and impression-making prior to the surgical procedure. In such a scenario, whichever teeth can be prepared should have this done, as they will enable accurate positioning of the provisional restoration, and the teeth prepared at the surgical procedure can have a simple, quick reline. This would require a PMMA provisional.

Zirconia would usually be the material of choice due to its considerable strength (900 MPa to 1400 MPa)⁹ and ease of use for digital design and manufacturing. The material cost is relatively low, which should be reflected in the laboratory fee when using zirconia for a provisional restoration. In some instances, it may be necessary at the time of the procedure to alter the plan regarding which teeth to use as provisional abutments. Because of this possibility, it is advisable not to rely solely on a zirconia provisional, which would be difficult, if not impossible, to modify. A backup PMMA provisional restoration should be available if deviation from the original plan is needed that cannot be easily resolved with a zirconia provisional. The same manufacturing file for the zirconia provisional restoration can be used for the backup PMMA provisional restoration, thereby alleviating the design work for the laboratory. Also, if a replacement provisional is required due to fracture or staining, the same manufacturing file may be used to produce another provisional restoration.

Full-arch implant treatment is a burgeoning procedure due to predictability of dental implants and the baby boomer generation seeking oral care with a need for full-arch tooth replacement, a desire for improved quality of life, a relatively high dental IQ, expendable income, and an expanding public awareness of dental implant treatment and possibilities. There are multiple approaches to full-arch treatment. However, both patients and clinicians prefer methods that lessen the number of dental appointments, limit the number of surgical interventions, and reduce the overall treatment time. This article has presented a protocol that takes advantage of currently available tools, technologies, and materials to simplify procedures for the sequential extraction protocol for full-arch treatment.

Michael Klein, DDS
Chief Technology Officer, Keystone Dental Group, Burlington, Massachusetts; Former Clinical Associate Professor, Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, New York; Private Practice, Cedarhurst, New York

Allon Waltuch, DDS
Private Practice, Cedarhurst, New York

Lauren Lehrfield, BSc, RDH
Senior Quality Assurance/Regulatory Affairs (QA/RA) Project Manager, Keystone Dental Group, Burlington, Massachusetts