All-on-4^® Treatment Concept in a Severely Resorbed Jaw Using Narrow-Platform Implants: A Case Report

Naif Sinada, DMD

The use of osseointegrated dental implants to treat partially edentulous and fully edentulous patients is both a viable and mainstream procedure in modern-day dentistry. While use of these implants in the treatment of dentate and partially edentulous patients can present difficulties, their usage in the treatment of the severely atrophied jaw has been particularly challenging.¹

Many approaches to the restoration of severely resorbed edentulous maxillae and mandibles have been developed; these treatments, however, can be costly and time-consuming and involve extensive grafting of the edentulous ridges.^2-4 The All-on-4^® treatment concept (Nobel Biocare, www.nobelbiocare.com) has been shown to be a viable option, requiring limited grafting.^5-7 This approach has traditionally used a minimum of four regular-platform (4-mm) implants to support an acrylic, screw-retained provisional prosthesis, followed by fabrication of a definitive prosthesis.^6,8 The application of this technique to the severely resorbed edentulous jaw has been limited by the fact that implants wider than 4 mm traditionally have been recommended.^6,8 Limited data have been published regarding the use of narrow-platform (3.5-mm) dental implants using the All-on-4 treatment concept.^9,10 This case explains the use of 3.5-mm narrow-platform implants to provide a patient with a screw-retained acrylic provisional on the day of implant placement.

Clinical Case Overview

A 62-year-old Caucasian male patient presented to the postgraduate prosthodontic clinic requesting a solution to his terminal dentition. He had previously been seen by his periodontist for 15 years for periodontal maintenance. Although he demonstrated the ability to maintain excellent oral hygiene, he desired a fixed solution to replacing his periodontally compromised dentition. He presented with a removable appliance to close the diastema between teeth Nos. 23 and 26, which was in use for 10 years (Figure 1). A thorough patient history, full medical records, and full dental records were obtained for the treatment plan discussion and presentation.

Diagnosis

Thorough medical records revealed no significant medical history and no known drug allergies. No carious lesions were noted, and a full temporomandibular joint examination revealed normal range of motion, with asymptomatic and stable joints.

The periodontal diagnosis was chronic generalized severe periodontitis; however, records from the patient’s referring periodontist indicated that no significant progression of the disease was noted in the past 5 years. Although no bleeding on probing was noted, a determination was made that the patient’s periodontium was compromised, and that major prosthetic rehabilitation of a terminal dentition was needed (Figure 2 and Figure 3).

Treatment Plan

The patient was presented with four general treatment options:

• Option 1. Splinting of mobile teeth and 3-month maintenance intervals of the current dentition. Maintenance of his periodontium was presented as a viable treatment option because the main concern was mobility.

• Option 2. Extraction of all remaining teeth and fabrication of implant-retained maxillary and mandibular overdentures. This would require four to six maxillary implants for a palateless implant-retained maxillary overdenture and two to four mandibular implants for an implant-retained mandibular overdenture.

• Option 3. Extraction of all remaining teeth, immediate implant placement, and immediate loading of an all-acrylic, screw-retained, implant-supported provisional prosthesis. Because this treatment would require adequate prosthetic space, significant alveoplasty of the residual ridge would be indicated.¹¹

• Option 4. Extraction of all remaining teeth and delayed placement of six to eight implants for conventional implant-supported crown-and-bridge—allowing for the fabrication of separate anterior/posterior sectional fixed dental prostheses. Although this treatment would not require as much alveoplasty as Option 3, it would be costlier to the patient and potentially limited by the extent of the alveolar bone remaining.

The patient’s chief concern was the desire for a fixed solution to the replacement of his dentition, so he elected to proceed with Option 3. He chose not to pursue Option 4 because of the increased cost of that treatment and finances were a significant consideration for him. Although Option 3 would satisfy his dental needs and requirements, he was made aware that it would require a long surgical appointment, in which the teeth would first be extracted, followed by the reduction of the residual ridge for implant placement, and an immediate provisional delivered in one day. The patient was in excellent physical health with no significant medical history and was, therefore, deemed a good candidate for treatment to be completed in one appointment.

Treatment Sequence
Pretreatment Analyses

A full set of intraoral and extraoral photographs were made, along with a full-mouth series of radiographs and a full-volume cone-beam computed tomography (CBCT). CBCT provided invaluable information that could be used in conjunction with previously obtained dental records. The obtained 3-dimensional radiographic data helped determine the extent of alveolar bone loss, amount of residual bone available, and extent of sinus pneumatization. An evaluation of the patient’s CBCT data revealed no pathology noted and severe horizontal atrophy of the maxilla and mandible (Figure 4 and Figure 5). The classification of severe horizontal atrophy was based on the determination that the use of ≥ 4-mm-wide implants was not possible.

Maxillary and mandibular casts were mounted on a semi-adjustable articulator using a facebow registration. The maxillary incisal edges were deemed to be in an acceptable and desired position, so the incisal edge position was used as the primary reference to fabricate maxillary and mandibular immediate dentures. Conventional techniques were followed to fabricate heat-processed acrylic dentures for both arches.

Other important patient-relevant clinical parameters considered were:

• Lip support. Patients requiring lip support would be contraindicated for this type of prosthesis because the final implant-supported restorations would ideally have no flanges (or concavities of the intaglio surfaces). Therefore, an analysis of whether lip support would be needed is imperative before commencement.

• Analysis of maxillary and mandibular smile lines. High maxillary lip lines and low mandibular lip lines would require much greater reduction of the residual ridge so that the gingival-prosthetic “transition line” is not visible.

• Adequate prosthetic space. To minimize complications in the final restorations, adequate prosthetic space is required. Greater prosthetic space allows for thicker acrylic and metal framework to be used to help resist fracture and other complications such as debonding of teeth and loosening or fracture of prosthetic screws. The ideal required thickness of a metal-acrylic, implant-supported prosthesis has been reported as 15 mm.^12,13

Implant Planning

Because the posterior mandible displayed significant lingual concavities, implant planning on the mandible involved the placement of intraforaminal implants (Figure 6). With the All-on-4 treatment concept it is typically recommended that the posterior implants be tilted at 30 degrees to maximize anterior-posterior (A-P) spread. In this case, however, the existing topography of the alveolar ridges prevented the recommended 30-degree tilting of the two posterior mandibular implants; therefore, to maximize the surrounding bone around the planned implants, these two implants were tilted at 20 degrees to avoid the bilateral lingual concavities. Given that the planned implants provided less-than-ideal A-P spread, an additional implant was planned for the mandibular (five mandibular implants total), thereby allowing greater support for the planned distal cantilevers. The A-P spread of the planned maxillary implants, on the other hand, was amply adequate. Therefore, four implants were planned for the maxilla (Figure 7).

Maxillary Guide Fabrication

The maxillary CT planning was completed in conjunction with the planned prosthesis in mind, allowing prosthesis-driven planning. To achieve prosthesis-driven planning, two duplicates of the maxillary immediate dentures were made using clear orthodontic resin to fabricate two guides. The first was a reduction guide. The maxillary denture was duplicated in clear orthodontic resin, maintaining a minimum required thickness of the prosthesis (Figure 8). By using this guide during surgery, the surgeon could quickly identify whether the minimum reduction was completed to allow proper thickness of the prosthesis (Figure 9). If the bone interfered with the clear guide, then the bone was reduced until adequate clearance was achieved.

The second guide was an angulation guide. The maxillary denture was duplicated in clear orthodontic resin, with a window corresponding to the occlusal surfaces of the maxillary teeth. The window was made to ensure that the multi-unit abutments and the placed implants emerged from the occlusal surfaces of the proposed tooth positions, rather than from the facial surfaces (Figure 10).

Mandibular Guide Fabrication

The mandibular CT planning was also completed in conjunction with the planned prosthesis in mind, allowing prosthesis-driven planning. In the mandible, however, the distal-most molars (teeth Nos. 18, 31, and 32) were maintained bilaterally during the surgical and prosthetic conversion phases. Because the molars were not in the planned implant sites, it was decided that maintaining the molars would aid in preserving vertical dimension for the patient. Therefore, instead of fabricating an immediate denture, an immediate partial was fabricated (Figure 11). Thus, should the implants fail to achieve adequate primary stability, the patient would have an immediate partial instead of a complete denture. Conversely, if the implants achieved adequate primary stability, the teeth could be maintained until the conversion process was complete. At that point, the teeth could be extracted.

For the prosthesis-driven implant planning, an implant angulation guide was fabricated based on the proposed tooth position. The mandibular immediate partial denture was duplicated in clear orthodontic resin with a window corresponding to the occlusal surfaces of the mandibular teeth. As with the maxillary denture, the window was made to ensure that the multi-unit abutments and the implant placements emerged from the occlusal surfaces of the proposed tooth positions, rather than from the facial surfaces (Figure 12). On both the immediate partial denture and the angulation guide, a 0.80 orthodontic wire was fixated to the prostheses to aid the clinician in placement during conversion and surgery. When the conversion was complete, the orthodontic wire was easily removed using forceps and residual composite was removed using a high-speed acrylic bur.

Mandibular Treatment

The mandibular arch was planned to be completed first because teeth Nos. 18 and 31 would aid in maintaining the vertical dimension. The existing teeth (except Nos. 18, 31, and 32) were atraumatically extracted, and the residual alveolus was reduced based on dentoalveolar landmarks previously planned from the CBCT. When the reduction was complete, five intraforaminal implants were placed, with excellent primary stability. Angulation of the implants was checked and verified using the prefabricated implant angulation guide. Temporary cylinders were then placed onto the multi-unit abutments, and a rubber dam was placed around them to prevent contamination of the surgical sites with restorative materials. Multi-unit healing abutments were then placed until the conversion prosthesis was completed (Figure 13). After adjustment of occlusion and verification that the vertical dimension was maintained, the patient was sent home with postoperative surgical and hygiene instructions.

Maxillary Treatment

Four weeks after the mandibular arch was completed, the patient was seen to finish the maxillary arch. The existing teeth were atraumatically extracted, and the residual alveolus was reduced using the prefabricated reduction guide. When the reduction was complete, four maxillary implants were placed, with excellent primary stability. Angulation of the implants was checked and verified using the prefabricated implant angulation guide. Multi-unit temporary cylinders were first coated with acrylic to ensure even coating of acrylic on all cylinder surfaces. The prelined temporary cylinders were then placed onto the multi-unit abutments, and a rubber dam was placed around them to prevent contamination of the surgical sites with restorative materials (Figure 14). Multi-unit healing abutments were then placed until the conversion prosthesis was completed. As with the mandibular treatment, after adjustment of occlusion and verification that the vertical dimension was maintained, the patient was sent home with postoperative surgical and hygiene instructions.

Discussion

The success of the immediate acrylic implant-supported prostheses was based on several factors. First, all cantilevers in the interim prostheses were eliminated (Figure 15). Although the final mandibular prosthesis would incorporate a minimal cantilever bilaterally, it was deemed necessary to eliminate cantilevers in the interim prosthesis to minimize the forces on the implants during the healing stages.¹⁴

The elimination of concavities was another key factor. A cleansable surface of the interim prosthesis is important for adequate healing of the underlying soft tissues. A cleansable surface would require no concavities on the intaglio surfaces, allowing the patient to adequately clean the underlying surfaces and the keratinized tissue underneath the prosthesis to present with minimal inflammation (Figure 16).

A third factor in achieving successful immediate acrylic implant-supported prostheses is occlusion. For this patient, simultaneous bilateral contact with canine guidance was achieved. Currently, no consensus exists as to the desired occlusal scheme for interim acrylic implant-supported prostheses. Therefore, it was deemed that in this case a canine guidance was suitable because it matched the patient’s preoperative occlusal scheme.

Another critical factor is A-P spread, defined as the distance between a line measured from the center of the anterior-most implant(s) and a line measured from the distal of the distal-most implant(s). A favorable A-P spread can influence not only the distal extent of the provisional prostheses but also the limit of the distal cantilevers in the definitive prostheses. The favorable A-P spread in this patient’s maxilla, for example, eliminated the need for a distal extension in the maxillary interim prosthesis. The mandibular A-P spread, on the other hand, limited the opportunity to place mandibular first molars in the provisional prosthesis. In addition, a bilateral one-tooth cantilever would be indicated in the definitive prosthesis to achieve first-molar occlusion. Because of the prosthesis-driven treatment planning employed in this case, this limitation was not only anticipated before any surgical appointments, but also discussed with the patient beforehand. The limited A-P spread was also the reason that the mandibular treatment needed five implants placed instead of four. Addressing the patient’s treatment based on these factors enabled a more predictable approach and increased the ability of the practitioner to manage the patient’s expectations and desires.

After 4 months of healing (Figure 17), the following factors were assessed:

• Primary stability of the implants (and implant components). At 4 months, the implants had adequate time to achieve osseointegration. Therefore, this was a good time to assess primary stability of the implants. If any implants were not integrated, planning would commence for placement of rescue implants (or alternative treatment plans). Prosthetic components were also checked to ensure that recommended torque values were maintained and components retightened accordingly.

• Healing of the residual ridges. The residual ridges were assessed for adequate keratinized tissue. If keratinized tissue was not obtained, this would be an appropriate time to plan for adjunctive surgical procedures to enhance the amount and quality of attached tissue around the osseointegrated dental implants.

• Oral hygiene. The prosthesis was removed to assess the patient’s ability to clean around the implants and/or abutments. Residual debris is an indication that either the patient is noncompliant, the prosthesis is not cleansable due to concavities in the intaglio surface, or the ridge topography is not conducive to cleaning. Any of these issues would require intervention at this stage, which could range from providing oral hygiene instructions to modifying the prosthesis.

The interim prostheses would then be used as the primary guide to fabricate the final prostheses. First, they are used to fabricate maxillary and mandibular master casts. These casts will then be used to mount the master casts at the existing occlusal vertical dimension. When these final master casts are fabricated and mounted, teeth can be set and tried in to verify esthetics and phonetics. The final prostheses can then be made with a metal bar reinforced in acrylic. In the present case, all the preoperative assessments have thus far allowed the prostheses to be made without concern regarding adequate space.

Conclusion

Numerous clinical studies and case reports in the current literature discuss the efficacy of the All-on-4 treatment concept as a viable option.^5,6 However, few reports exist applying this treatment protocol to a severely resorbed jaw.⁷ As shown in this case report, the use of narrow-diameter (3.5-mm) implants is a feasible treatment protocol for patients either who are unwilling to go through extensive grafting procedures or for whom such procedures cannot be performed. For the author’s patient in particular, this treatment approach was a successful option that not only met his desire to achieve a fixed final prosthesis, but also enabled him to avoid a removable interim phase. Although the treatment consisted of two long surgical/prosthetic visits, condensing traditionally prolonged treatment phases of multiple surgical visits into two visits allowed the patient to maintain his busy lifestyle and budget his time away from work and daily activities appropriately. Ultimately, the treatment enabled the replacement of a terminal, periodontally compromised dentition with fixed interim full-arch implant-supported prostheses on both arches (Figure 18). The patient was referred to the restoring doctor for final prostheses (Figure 19 through Figure 21).

Acknowledgments

The author wishes to thank the University of Maryland postgraduate prosthodontic residency program residents, staff, assistants, and students for their continued guidance and support, with particular appreciation to Andrey Doroshenko, DDS, for completion of all prosthetic phases of this case. Appreciation is also extended to Rose Morgan, office manager of the postgraduate prosthodontic residency program, for assistance in completion of this case. Additionally, sincere appreciation is extended to Carl Driscoll, DMD, and Elias Rivera, DDS, MS, for their continued mentorship and guidance throughout.

Disclosure

The author had no disclosures to report.

About the Author

Naif Sinada, DMD Third-year postgraduate prosthodontics resident, University of Maryland School of Dentistry, Baltimore, Maryland

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