Restoration of Severely Atrophic Jaws

Historically, the severely atrophic edentulous jaw has been a troublesome challenge for dentistry. Before implant dentistry arrived on the scene, there was only one option—the complete denture. However, implant dentistry now offers many more options, including the following: eposteal/subperiosteal, endosteal, mini and zygomatic implants, plus various regenerative grafting procedures (including autografts, allografts, alloplastic grafts), and various surface coatings and treatment to implant surfaces,¹ etc. The successes and problems with each have been reported extensively in the literature.^2-5

AN ALTERNATIVE TREATMENT METHOD FOR THE SEVERELY ATROPHIC JAW
A new method has arrived that solves the challenges usually found in treating the severely atrophic jaw. An existing implant modality with new innovations has become a technological and biological success. The custom dental implant (CDI) system includes both a custom-milled eposteal titanium implant and a custom-milled nanozirconia-ceramic fixed-removable restorative appliance. Both are produced using advanced CAD/CAM computer technology. This modern system has advanced to replace the older lost-wax (casting) methods. Twenty-five years of development from cast chrome-cobalt to CAD/CAM milled titanium has produced an implant with the ability to predictably support removable and fixed appliances.

The purpose of this article is to demonstrate a technique of producing an implant system for restoring the severely atrophic jaw. Previous publications, to be discussed later, demonstrated that this modality actually results in a union of the implant to underlying bone and intimate integration of the grafting material to the implant, validating the use of the CDI implant system in clinical practice.^6-9

A BREAKTHROUGH IN DENTAL MATERIALS
Nanozirconium ceramics represent a breakthrough in restorative materials. Brilliant aesthetics can be achieved with a lasting polish with very special milling equipment and software. Pre-shaded blocks can be easily milled and quickly polished with no packing or firing. Tooth-like properties are achieved due to this material having wear characteristics similar to natural teeth. Patients report that it feels like natural tooth structure. It has great serviceability in that easy chairside adjustments and repairs are possible. Its high flexural strength (200 MPa) adds durability to posterior restorations.¹⁰

Historical Evolution of the Subperiosteal Implant to the Present Day CDI
The historic eposteal/subperiosteal dental implant, since its conception 80-plus years ago, slowly evolved throughout the years to the present day, highly technical CDI. A complete version of this history can be found elsewhere.⁹ The authors, as well as a review of the history of the subperiosteal/eposteal CDI, indicate that success is dependent upon intimate contact of the implant to underlying bone and solidly stabilized and immobilized.^9,11-17

CASE 1
A Representative CDI Producing a Virtual Bone Model
A 73-year-old female presented with severely atrophic dental arches (Figure 1). The severely atrophic mandibular arch was treated in 2005 with a CDI manufactured from a direct bone impression with a hydroxyapatite (HA) coated cast titanium alloy and grafted with HA (Figure 2). The patient followed up with regular routine maintenance during the 9 interim years with no complications. With progressive loss of the stability of the upper denture, she requested the same successful CDI treatment for the upper arch. Consequently, it was decided to follow the new indirect, computer-generated, dual-scan CBCT design procedure to mill a titanium alloy CDI coated with HA and grafted with resorbable HA (OsteoGen Bioactive Resorbable Calcium Apatite Graft [Impladent]).

A dual CBCT protocol similar to Guided Surgery Protocol was performed, utilizing a previously constructed treatment denture that served as a radiographic guide (Figure 3). The treatment denture was constructed so that it satisfied the aesthetic requirements, and the patient approved it as being representative of the final appliance. The scans were used to produce a virtual model to orient the treatment denture to the bone base. The virtual models of the denture and basal bone were then matched up in the computer software to begin the implant design process (Figure 4).

Figure 1. The initial panoramic radiograph taken of this patient 9 years prior. Note the extremely atrophic mandible and maxilla both that could not be grafted without difficulty and, if attempted, it would have an extremely poor long-term prognosis.	Figure 2. A panoramic radiograph showing the very thin (all but invisible) bone of the mandibular restored by a mandibular custom dental implant (CDI), in service (at the time this radiograph was taken) for 9 years with no complications.
Figure 3. The “gutta-percha” radiopaque markers on the treatment denture were used in a dual CAT scan protocol.	Figure 4. The CBCT dual-scanned treatment denture superimposed over the virtual model of the maxilla. The dual-scan allows the biomedical engineer to design the final prosthesis within the aesthetic envelope. Notice how the precisely the abutment trajectory (oriented to specific teeth within the final prosthesis) was achieved.

The CDI was designed by the authors along with biomedical engineers (V2R Biomédical) in consultation with the contributing clinician, utilizing advanced CAD technology programming. The design incorporated maximal static bony landmarks: zygomatic buttresses, anterior nasal spine, superiorly on the anterior maxillary wall, hamular hutch, and palatine process. On the mandible, the surfaces include the mentum, lateral surface, external oblique ridge over the anterior border of the ramus, internal oblique ridge, mylohyoid ridge, genial tubercle, and joining right and left sections at the midline.

Parallel Abutment Posts With Emergence Profile Finish Line Stops
The abutments themselves were designed to create exactly parallel cylindrical titanium posts with a collar stop that would serve as finish lines 1.0 to 1.5 mm above the final bone level. The abutments were connected to cross-over struts, 1.25 mm in thickness. These cross-over connectors were designed to traverse a prepared counter-sunk osteotomy through the alveolar ridge, joining the buccal/labial to the palatal/lingual aspects of the framework (Figure 5). The framework was milled in ELI grade 5 titanium alloy on a 5-axis milling machine that precisely duplicated the computerized design (Elite48 Dental Studio) (Figure 6).

Figure 5. The virtual model with the crossover grooves cut through the alveolar ridge at the location of the transalveolar CDI struts.	Figure 6. The implant abutments with the parallel posts and the finish line stop collars. The final custom-milled titanium implant that has been grit-blasted, acid-etched, and coated with a molecular surface of plasma sprayed hydroxyapatite (HA). It is ready for delivery.

Titanium copings were then milled to be within 4 µm of the diameter of the titanium implant abutment posts. These copings would be incorporated into the final appliance for accurate friction fixed-removable retention (look ahead to Figure 16 to see the milled titanium copings incorporated into the final appliance).

The Surgical Procedure
Once the CDI is manufactured using CAD/CAM milling technology, it is delivered and grafted in a single surgery as has been described in more detail elsewhere.^10,18 Therefore, only a brief summary of these details will be discussed herein.

Figure 7 shows the extent of the original atrophic ridge. Figure 8 verified that the implant was fully seated with ideal approximation of the CDI struts to the bone. Figure 9 shows the extent of the HA grafting augmentation procedure. The implant was allowed to heal for 6 to 8 weeks using a milled friction fit acrylic interim appliance. The healed peri-implant tissue (Figure 10) was then sculptured to expose the CDI abutment finish line collars with a CO₂ laser (LightScalpel) (Figure 11), and the final laser-sculpted tissue was ready for the final impressions (Figure 12). The hygienic intaglio surface was designed to mirror the ridge, with no flanges. The patient was monitored carefully during the healing period.

Figure 7. The presurgical maxilla.	Figure 8. The precision fit of the CDI to the bone. Note that there are no gaps or space under the implant struts.
Figure 9. The HA grafting technique used to augment the implant partially covering the implant struts. This facilitates fully integrating the implant in bone once healing has occurred.	Figure 10. Complete healing 3 weeks subsequent to the CDI placement.
Figure 11. The finish line collar uncovering technique using a CO2 laser.	Figure 12. The collars clearly and ready for final impression.
Figure 13. The final impression trimmed and ready to be sent to the dental laboratory for duplication scanning and milling into the final nanoceramic appliance.	Figure 14. The front view of the appliance with the final impression.
Figure 15. The final milled appliance with the tissue simulated composite.	Figure 16. The underside of the appliance showing the milled copings.

The Restorative Procedure
The treatment denture, which was used in the CBCT dual-scan protocol, was used as an impression tray to pick up prefabricated milled copings that fit each abutment (Figures 13 and 14). The final prosthesis was then manufactured from the virtual digital records incorporating the copings without a connecting bar (Figures 15 and 16).

Delivery
With everything done meticulously, the final milled nanozirconium ceramic appliance could be delivered with no or minor occlusal adjustments (Figures 17 and 18), and the occlusion was checked to verify it could smoothly articulate in all masticatory excursions without any occlusal interferences.

Nine-Year Follow-Up of the Full Mandibular CDI
The CDI can be used in the most atrophic jaw applications. The authors have been using this modality routinely for more than 25 years in both the severely atrophic mandible and maxilla. The case reported here included a 9-year follow-up panoramic radiograph of the mandibular CDI (review Figure 2). CBCT screen shots taken of the mandibular implant show complete bone integration of the implant (Figures 19 and 20). The CBCT clearly shows that the implant struts were surrounded in bone generated by the described grafting technique.

No complications occurred in this case during the entire 9-year history. For this patient, there were no other options available as a consequence of her massive bone loss. This modality can be used with ease to solve almost any bone deficient condition.

Figure 17. The appliance delivered and fully seated in the patient’s mouth.	Figure 18. The aesthetics of the final appliance delivered.
Figure 19. A screenshot of a CBCT taken at a 7-year follow-up appointment. Note the fully integrated CDI struts.	Figure 20. A cross section demonstrating that the CDI struts are covered with solid bone.
Figure 21. A mandibular CDI was retrieved subsequent to the patient’s demise and sent for histology.	Figure 22. The histology of the bone formed over the implant.

Figure 23. The HA granules (used as the graft) and the implant strut are embedded in regenerated bone.

CASE 2
One Additional Application: The Posterior Mandibular Unilateral CDI
This case represents a posterior mandibular unilateral implant (Figure 21) that serviced the patient with no complications until his death of heart disease 9 years following its placement. The implant was harvested postmortem and acquired histology was completed. The macro-photograph of the histology shows the original level of the bone on the inferior lateral surface of the implant (Figure 22). Notice that both the HA granules used as the graft and the implant strut are embedded in regenerated bone (Figure 23).

This case is the fifth and final case in the following study (Table).

Sequential Statistical Analysis of Retrieved CDIs
To confirm the long-term survivability and utility of the CDI, Baker et al6 commenced a randomized retrieval study of these CDI implants mentioned to statistically demonstrate, with accepted sequential analysis, the validity of this implant modality. This type of analysis required 5 implants sequentially retrieved in a random manner from patients who had volunteered for the study. That goal has been met with the recovery of 5 cases from deceased patients.^6,10 These implants are summarized in Table.

Histologic studies were performed on tissues (the 9-year unilateral mandibular case reported above) from the bone-implant interface of these types of implants, and features of the relevant tissues were found to exhibit the exact histologic features as those of the osseous integrated implants reported by Brånemark.¹⁹

DISCUSSION
There is evidence that there is osseous integration with these implants. One of the authors (Dr. Nicholson) has noted throughout the years that when revisiting previously fixated sites (to remove screws or plates that would interfere with the placement of dental implants), integration occurs spontaneously over fracture reduction fixation plates and screws as well as fixation apparatus for orthognathic surgical procedures without any grafting processes.

This integration concept has been purported to solve the fibrous encapsulation problem reported by James et al.²⁰ When the implant was constructed from inadequate/poor impressions and placed on transient alveolar bone, and not placed on static bony landmarks, fibrous connective tissue would infiltrate under and around the implant struts where bone had resorbed. This process can cause long-term problems, such as: sinking into the resorbed areas, loss of prosthetic alignment, and flange impingement with resulting infections. The accurate CAD/CAM technique permits optimal design of the implant. The new hygienically designed restorative scheme minimizes tissue impingement over the struts.

For many years, one of the authors (Dr. Nicholson) worked with developing fixed appliances that fit onto and over parallel cylindrical abutments that were retained with no cement. However, the task of attaining the necessary accuracy to achieve successful fixation was difficult since the laboratory wax-up was all done by hand. New milling techniques have now made it possible to achieve exact parallel abutments with coping that can be milled with precision. The abutments themselves are now designed to create exactly parallel cylindrical posts with a collar stop. This collar serves as a finish line 1.0 to 1.5 mm above the bone for ideal finish lines located just at the level of the healed soft tissue. This creates a conventional emergence profile to achieve cleanability and a smooth transition from the implant to the appliance.

The parallel cylindrical posts each have a mated milled titanium coping that is precisely fabricated to a 4-µm tolerance. When these copings are incorporated in the final appliance, the restoration is fixed and secure. However, the milled tolerance built into the system allows the appliance to be removed by the patient proper for cleaning. In other words, this is the “ideal” clinicians have tried to achieve for years. A fixed appliance that a patient can easily remove for daily cleansing! This greatly reduces the possibility for future failure due to the inability of a patient to clean under a fixed appliance.

Finally, the underlying cause of the patients’ tooth loss must be briefly discussed. Tooth loss due to periodontal disease and abscessed teeth are related to systemic disease.21,22 It is imperative that clinicians become aware of the mechanism behind this oral-systemic connection. It should go without saying that implants fail due to ignoring this disease connection. Therefore, clinicians need to take periodontal disease seriously and treat it prior to placement of any dental implants.

IN SUMMARY
For many patients, there is no other option. The CDI is an eposteal implant that becomes firmly attached to underlying bone. More than 25 years of experience with the implant have shown that the implant is capable of supporting both removable and fixed appliances. Once the many constituent factors of this process are understood and taken into account, the CDI becomes a powerful device in the armamentarium of the implant dentist. Furthermore, it often represents the only tool that can be employed to successfully correct cases involving severely atrophic jaws.

Acknowledgment
Special thanks to Michel Poirier, DDS, president of V2R Biomédical, and Dr. Éric Wagnac, for their contribution to the development of this technique and planning aspect of these cases, and to Jay Watson and Ron Tsai of Elite48 Dental Studio for the manufacturing of the CDI and prostheses.

References

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3. Clementini M, Morlupi A, Agrestini C, et al. Success rate of dental implants inserted in autologous bone graft regenerated areas: a systematic review. Oral Implantol (Rome). 2011;4(3-4):3-10.
4. Hämmerle CH, Jung RE, Feloutzis A. A systemic review of the survival of implants in bone sites augmented with barrier membranes (guided bone regeneration) in partially edentulous patients. J Clin Periodontol. 2002;29(suppl 3):226-233.
5. Chrcanovic BR, Abreu MH. Survival and complications of zygomatic implants: a systematic review. Oral Maxillofac Surg. 2013;17:81-93.
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8. Carlson JT Jr, Wang D, Anabtawi MZ, et al. Histomorphometric observations of bone integration from cadaveric subperiosteal mandibular implants. Presented at: AADR 37th Annual Meeting and Exhibition; April 3, 2008; Dallas, TX. Abstract 267.
9. 3M ESPE Lava Plus High Translucency Zirconia. precisodental.com/digital-dental-materials/full-contour-dental-zirconia/lava-ultimate-dental-restorative. Accessed October 28, 2014.
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18. Nordquist WD, Naisbitt D. A maxillary subperiosteal implant design that maximizes bone support and accommodates a cemented, low-profile, parallel guiding planes Hader bar. J Oral Implantol. 1995;21:304-308.
19. Jaarda MJ, Lang BR, Kaigler D, et al. Early detection of osseointegration using scanning electron microscopy and the interfacial biopsy chamber: a pilot study. Implant Dent. 1992;1:84-87.
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22. New reports confirm perio-systemic connection and outline clinical recommendations [news release]. Chicago, IL: American Academy of Periodontology. perio.org/perio.org/consumer/EFP_AAP_Workshop_Proceedings. Accessed October 28, 2014.

Dr. Nicholson is an oral and maxillofacial surgeon with 40 years experience designing and placing custom dental implants. He is an innovator in the field of implant dentistry and has lectured internationally on the subject. He can be reached at (760) 274-5279 or at charlesnicholsondds.oms@hotmail.com.

Dr. Nordquist is a Diplomate in the American Board of Oral Implantology/Implant Dentistry. He is an oral biologist and has published books concerning the oral-systemic disease connection and has written numerous professional articles regarding implant dentistry. He can be reached at (619) 236-7959 or via email at the address wnordquist@yahoo.com.

Disclosure: Drs. Nicholson and Nordquist report no disclosures.