Solving Complex Full-Arch Cases With Simple Solutions

INTRODUCTION
During the past decades, several researchers have explored the biological processes of osseointegration with the hopes of enhancing the possibility to obtain a better bone-implant contact than that described by Brånemark et al.¹ This has also led to improved knowledge about the possibility of early implant loading, without compromising the survival rate of implant-retained restorations and for faster bone healing.² Studies on implant macro design and surface topography have also contributed to gain a better insight into the process of rapid osseointegration.³ Immediate loading has become a predictable technique with specific indications in complete arch rehabilitation.⁴
The flat one protocol was developed to provide a simple solution to complete arch immediate load rehabilitation. The definitive prosthetic bridge was placed within 72 hours from surgery, and the entire protocol for both surgical and prosthetic phases is presented here together with clinical data collected during a 5-year follow-up.

CASE REPORT
Diagnosis and Treatment Planning
Our 32-year-old female patient (Figures 1 and 2) suffered from a severe form of juvenile periodontitis, as diagnosed by the criteria proposed by the American Academy of Periodontology.⁵ She was a moderate smoker in good overall medical conditions and, at the time, was not undergoing any pharmacologic treatment. She had no missing teeth, had Class I occlusal relationships, but presented with a wide diastema. No signs of marginal gingival inflammation were present, but the upper teeth were all suffering from grade 3 mobility and oral hygiene was poor, even though signs of spontaneous bleeding were absent and a rather wide attached gum was present. The lower arch was in a much better condition. No tooth clenching or grinding habit was diagnosed clinically.

Figure 1. Preoperative view.	Figure 2. Preoperative panoramic radiograph.

Probing depth was between 6 mm and 9 mm for all the maxillary teeth, and all molars showed Class 3 furcation involvement. All lower arch teeth showed a 3 mm to 5 mm probing depth with bleeding, but without furcation involvement. Bone density and morphology were normal. No cavities or signs of previous restorations or endodontic treatments were present.
In the treatment planning phase, attempts to perform surgical and nonsurgical periodontal treatments were excluded due to the severity of the clinical findings. The proposed treatment plan was to extract all the upper teeth and insert 12 postextractive implants. The implants were immediately loaded within 72 hours from their insertion using the “flat one bridge” protocol (Intra-lock System [Intra-Lock International).
Flat abutments may reduce interferences that may be generated by nonparallel implants and attempt to achieve a passive fit of the prosthetic metal framework. They also help to dissipate the occlusal forces transmitted over the bone-implant interface, which has been described as a potential risk factor for biological and biomechanical complications in implant-supported restorations.

Clinical Protocol
The surgical steps were performed after a complete diagnostic setup was mounted on the articulator and the custom trays were ready. An internal bevel incision was made on the buccal aspect of all maxillary teeth, while a paramarginal incision was made lingual. All the inflammatory tissue was removed, the teeth were extracted, and then 12 implants (Intra-Lock System) were immediately placed in the extraction sockets from the maxillary right first molar to the left first molar (Figure 3).
Single root teeth were replaced by implants of a slightly narrower diameter with respect to the extraction socket in order to avoid any possible damage to the thin buccal cortex; to this aim, a one-mm gap was left between the implants and the buccal cortex to avoid jeopardizing the implants’ survival. Drilling was performed toward a coronal-to-apical direction until obtaining a 3 mm more apical depth than the natural socket, thus achieving a good primary stability. The implant neck was placed 1.5 mm below the buccal cortical margin, thus predisposing a good position upon the peri-implant tissues having completed the healing processes^.6,7 In the first molar area, the implants were positioned in the palatal root socket with the use of an implant handpiece (AEU-7000 [Aseptico]) with an insertion torque of 50 Ncm.⁸

Figure 3. Intraoperative view after implant placement.	Figure 4. Postoperative view, after one month.
Figure 5. Occlusal view, after one month.	Figure 6. Panoramic radiograph, after 5 years.
Figure 7. Occlusal view during follow-up, after 5 years.	Figure 8. Lateral view showing interincisal papilla after 5 years.

Figure 9. Five-year follow-up.

The flat abutments were then placed on implants with a torque of 35 Ncm, and impressions were taken at the same appointment by placing impression copings on the abutments before suturing. The impression copings were splinted with a rigid material and an open custom tray was seated full of impression material (Take 1 [Kerr]). Once impression setting time was over the impression copings were unscrewed and the tray removed. The next step was to use a thermoformed tray made over the final wax-up, filled with impression material. The patient was instructed to gently close to find the correct maxillomandibular relationship thanks to the guide of the inclined planes reproduced in the custom tray. This kind of impression allows accurate gathering of interarch relationships, vertical dimension, and all the data needed by the dental laboratory team for the fabrication of the final prosthetic restoration. Flat abutments were then covered with a cover screw and the patient was sent home.
On day 2, the cast framework was delivered from the dental laboratory and its passive fit was checked intraorally. In addition, a first check of aesthetics was made as well as another interarch record with hard wax to minimize deformations. The prosthetic casting should be made of molybdenum-free chrome-cobalt alloy, the use of which is indicated due to its favorable properties. It is chemically very similar to titanium, therefore reducing the risks for galvanic shock. It also has a low specific weight and is non-flexible. Such mechanical strength is extremely important to provide an effective splint and to prevent any transverse micromovements that could compromise osseointegration.
The size of the cast framework should be ideally about 2 mm (apical-to-coronal) x 3 mm (buccal-to-palatal), thus being strong enough to splint rigidly the implants between each other and to avoid risk of prosthetic fractures and being not so wide to prevent from achieving a good aesthetic result. An opaque layer was applied before indirectly fabricated composite resin teeth (Sinfony [3M ESPE]) were inserted. The complete bridge was then screwed onto the flat abutments through access holes on the occlusal surfaces of the prosthetic teeth and aesthetic and functional considerations were made before the final delivery of the prosthesis.
On day 3, the final prosthesis was delivered and the retaining screws were secured with a 25 Ncm torque (Figures 4 and 5); all the necessary final occlusal adjustments were made directly at chairside.
The choice occlusal design was based on literature suggestions, and in the absence of evidence that any particular occlusal scheme may be superior.⁹ A simplified design was chosen to avoid any forced interarch relations.¹⁰ The maximum number of bilateral centric stops during closing in maximum intercuspation was achieved as well as multidimensional freedom of occlusal contact movements. Occlusal contacts ideally should be located in the middle of the occlusal surfaces of all posterior teeth, while cuspids and incisors ideally should only have a light contact in maximum intercuspation. They should not be able to tear a 40-m shim stock articulating paper.
Finally, the patient was given oral hygiene instructions and follow-up procedures, with the aim to provide the needed supportive therapy for implants maintenance over time.

Follow-up Care
In order to evaluate the clinical predictability of the procedure, the patient underwent scheduled standardized assessments. The patient was recalled for follow-up at 6, 12, 24, 36, 48, and 60 months after the insertion of the prosthesis.
The clinical outcome was successful for this patient, with positive results that were kept stable over time. After 5 years of service, the only complication observed was the loosening of one of the retaining screws, which needed to be replaced. From time to time, the fixed denture should be removed and cleaned, and the screws have to be retightened to 25 Ncm torque. Probing was negative on all the implants, there were no signs of bleeding, no pathologic findings were detected from radiographs, a good quantity of keratinized gum and a good creeping of the papillae in the incisors’ area were present (Figures 6 to 9).

DISCUSSION
The achievement of a good clinical success, in terms of both the survival rate and aesthetic result, has always been considered a difficult target for immediately loaded complete arch implant-retained rehabilitations. Several techniques based on peculiar implants and prosthetic design have been proposed throughout the years by different manufactures, but very little data exists on their success rate, mainly coming from few prospective studies. Moreover, none of them seem to have addressed the issue of postextraction complete arch rehabilitations.
The protocol described in this clinical case appears to be a rather simple procedure. The use of the flat abutments, which have been designed to reduce the forces that counteract a passive implant-to-casting fit, may allow decreasing the risk for biomechanical complications and may help dissipating the forces acting on each single implant during cyclic loads. The 12 implants were positioned in the postextraction sockets, and during the 5-year follow-up span only a single screw needed to be replaced and retightened.
The flat abutment protocol can be provided also with a lower number of supporting implants, and ongoing cases have been encouragingly performed with a minimum of 6 and 8 implants in the lower and upper arch respectively, even if only future studies will be helpful to ascertain the minimum number of implants to be required for prosthetic support. In that case, such protocol may also present some favorable ethical and social implications due to the accomplishment of a good cost-to-benefit ratio with a minimally invasive procedure. It enables the clinician to try achieving a passive reciprocal relationship between implants. It may also give excellent aesthetic results, good function with a reduced trauma, lower costs, reduced chairside time, and considerably less stress for the patient with respect to other complete-arch implant retained fixed dentures.

IN SUMMARY
This case report described a new technique for immediately loading an implant-supported fixed screw-retained bridge that has flat abutments to achieve a superior passive fit. The definitive prosthetic bridge was placed within 72 hours from surgery and follow-up data over a 5-year period are presented. Good aesthetic results were achieved, and at the end of the follow-up period neither biological nor biomechanical complications were observed.

References

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Dr. Bucci Sabattini received his MD from the University of Milan, Italy, in 1980. He has focused his research and clinical practice on dental implants, and is a visiting professor at the department of oral surgery of the University of Pavia, Italy. He is also the director of the Centro Diagnostico Chirugico Magentino in Magenta, Italy. He has authored more than 150 publications in international journals, including 4 books on implantology. He can be reached at vbs@cdcmagentino.it.

Disclosure: Dr. Bucci Sabbatini reports no disclosures.

Dr. Mascolo has a master’s degree in oral surgery and qualified for Implantology at the Brånemark Dental Health Care Clinic Gothenburg 2003. He is in private practice in Novi Ligure (AL) Italy and focuses his practice on implantology in compromised patients. He can be reached at andrea@studiomascolo.eu.

Disclosure: Dr. Mascolo reports no disclosures.

Dr. Patel is a graduate of University of North Carolina at Chapel Hill School of Dentistry and the Medical College of Georgia/American Academy of Implant Dentistry Maxi Course. He is the cofounder of the American Academy of Small-Diameter Implants and is a clinical instructor at the Reconstructive Dentistry Institute. Dr. Patel has placed more than 2,500 mini-implants and has worked as a lecturer and clinical consultant on mini-implants for various companies. He can be reached at pareshpateldds2@gmail.com or at dentalminiimplant.com.

Disclosure: Dr. Patel reports no disclosures.